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POLLUTION PREVENTION
AT AN AGING MIDWESTERN MANUFACTURING FACILITY
This report describes the results of an Industrial Pollution Prevention Project (IP3)
demonstration project in Nebraska. The goal of the project was to demonstrate the adoption of
pollution prevention (P2) practices by a rural and aging manufacturing facility.
INTRODUCTION
The manufacturing facility is located in a predominantly agricultural area. The plant site is
a 100 acre area on which several buildings are located -- the largest of which is the manufacturing
facility (805,000 square feet). The facility produces fabricated metal products for farm and industrial
uses including structural steel members and plates, farm gates, fencing, and livestock watering tanks,
in addition to a wide variety of structural bolts, fasteners, etc. Because of the nature of its
manufacturing, the facility is licensed as a hazardous waste generator and is permitted under the
RCRA and NPDES systems.
In its various manufacturing processes, the facility performs many operations including
electroplating, conversion coating, cleaning, machining, grinding, impact deformation, shearing,
welding, sand blasting, hot-dip coating, painting, assembly and testing. Many of these processes
result in the production of a variety of pollutants that have to be disposed of in some fashion
depending on their nature. For example, the electroplating line results in the production of acids and
rinse water containing zinc and chromium, and the hot-dip galvanizing process results in the
production of acids and rinse water containing zinc, lead, and iron, which must be treated as a
hazardous substance containing heavy metals. The painting processes result in the production of
used industrial cleaners, acids, solvents, and chemicals used in the cleaning and degreasing of metal
components.
All process wastewaters produced at this facility are treated in accordance with stipulations
of the discharge permit. The wastewater is treated by lime and polymer addition and pH adjustment
before discharge. In the past, waste disposal at this facility has resulted in potential problems to both
surface and ground water resources in the area. The waste disposal systems at the facility constitute
a major expense. The management at the facility recognized that the economic viability of the
facility depended on reducing pollution control expenses and lowering or eliminating the burden of
regulation the company must endure.
P2 OPPORTUNITY ASSESSMENT
A work plan for the P2 assessment program was developed identifying several tasks,
including:
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1. Development of a detailed assessment and evaluation of current practices and
characterization of all wastes produced by the facility.
2. Identification and delineation of all possible P2 opportunities.
3. Economic and technical evaluation of all waste prevention and minimization alternatives
including short-term as well as long-term impacts of these alternatives.
4. Development of recommendations to be made to the management of the manufacturing
facility for P2 implementation that would be based on economic priority in terms of greatest
benefit and shortest pay-back periods.
5. Providing technical assistance, where appropriate, during the process of implementation
of the recommended alternatives.
6. Review of the results and impacts after implementation of the recommendations.
In developing the work plan, a multi-media approach was emphasized in developing
pollution prevention and minimization strategies affecting all operations and processes.
The waste stream evaluation process conducted at the facility followed procedures outlined by the
U.S. Environmental Protection Agency (see References section at the end of this report: U.S. EPA,
1990; 1992; 1993).
In conducting the P2 opportunity assessment, emphasis became focused on finding those
areas where the impact on reducing the total pollutant load produced by this facility could be the
greatest. Those areas were the electroplating, hot-dip galvanizing and the painting lines as well as
the tube-mill production area. Because these areas produced the bulk of the wastes with the greatest
toxicity and hazard, it was judged that improvements in these areas would produce the greatest
impacts.
The Electroplating Systems
The manufacturing facility operates both an automated line and a manual electroplating line.
These lines are used to deposit a thin zinc film onto small items such as bolts, fasteners and nuts,
which are then used in the construction of larger plant products such as farm buildings. The
automatic electroplating line is a barrel system which plates about 65 kgs (145 Ibs) of work per load.
The barrels are moved by a conveyor chain.
The automated electroplating line processes an average of 65 kgs (145 Ibs) of work pieces
per barrel. There are 36 stations on the line, with an approximate cycle time of 3.5 minutes at each
station (about two hours per barrel). The work is first cleaned in a soak cleaner and an
electrocleaning solution. It is then rinsed, pickled in a hydrochloric acid bath, and rinsed again
before going into a chloride-zinc electroplating bath. After residing in the plating bath for about an
hour and ten minutes (20 stations), the work is rinsed. A light yellow chromate finish is added. A
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short rinse (20 seconds) follows the chromating process after which the work is dried at 65 °C
(150°F). The electroplating solution is circulated through a filter to remove impurities. Particles
removed by the filter are rinsed into the treatment system. The total rinse water use in the automatic
electroplating line at this facility was estimated at 166 liters per minute (20 gpm) during 8 hours of
operation daily.
The manual process is more operator intensive, which requires hand moving of barrels from
station to station. The barrels are bigger, but the average load of work per barrel is also 65 kgs (145
Ibs). This line is used more often than the automated line, especially when small quantities need to
be plated. The work is cleaned in a soak cleaning bath (no electrocleaning) for about 15 minutes.
It is then rinsed, pickled in hydrochloric acid, and rinsed again before being placed in the chloride-
zinc electroplating tank (stainless steel pieces are dipped in nitric acid, instead of hydrochloric acid).
The work pieces are plated for an average of 1 to 1.5 hours before being removed from the tank. A
short rinse precedes the chromate coating; which can be clear or yellow, depending on customer
preference. After a final short rinse, the pieces are placed on a table to air dry. A more detailed
analysis of these electroplating lines is given by Parr (1994).
Pollution Prevention Opportunities in the Electroplating Systems
House Keeping Practices. To obtain better product quality and assure that the lower flow
rates will not compromise rinsing efficiency, it was recommended that housekeeping practices be
changed. There needed to be a thorough cleaning of the electroplating area including all tanks
(inside and out), floor, and all equipment related to the electroplating process. A system needed to
be established for recording when maintenance is done, tanks are emptied, chemicals are added, and
testing on tank parameters is performed (e.g. pH, temperature, chemical concentration).
Rinse Water Use. The suggested process changes were designed to reduce waste of both
rinse water and electroplating chemicals. To achieve these reductions, improved cleanliness and
more careful chemistry control were required. It was recommended that the rinse rates be reduced
to decrease the amount of wastewater being discharged to the treatment plant. For both the
automated and manual electroplating lines, reactive rinsing was recommended in order to decrease
water use from the rinses following the acid dip (pickling) and alkali cleaning processes (Tsai and
Nixon, 1989; Hunt, 1988). Water from the rinse after pickling would no longer go down the drain,
but would instead flow to the rinse tanks following alkali cleaning. Rinse water flow calculations
showed that for these two processes, the required flow on each line could be as low as 8 liters per
minute (2 gpm) (Durney, 1984).
At this plant, it was found that the effluent from the rinsing step after the acid dip could be
directed to the rinse tanks after the cleaning process. This change would save a total of about 76 m3
(20,000 gal.) of water per day resulting in a cost savings of about $150 per day in waste treatment,
sludge disposal, and water costs. Counter-current tanks similar to those on the automated line (after
the cleaning and acid dip processes) would be needed on the manual line to incorporate this change.
The cost of these counter-current tanks was estimated at $1,000.
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It was recommended that the rinse processes after the electroplating tanks on both the
automatic and manual lines be changed to counter-current with a rinse flow rate of 20 liters per
minute (5.3 gpm) each. About 24 m3 (6,400 gal.) of water per day can be saved, resulting in a cost
reduction of $50 per day. The cost associated with these changes was estimated at $1,000 for the
counter-current tank system.
Electroplating Chemistry. The testing of chemical and operating parameters in the tanks
needed to be done on a daily basis for several variables. Electroplating tank variables included pH
and temperature in addition to the concentrations of cleaners, acid dips, zinc metal, boric acid, total
chlorides, and the wetting agent. Chromating tank variables included pH, temperature, and chromate
concentration.
Other Changes. Other recommended changes that were needed to improve the process
included increasing the temperature of the cleaning tanks on the automatic line from 71 °C to 93 °C
(160°F to 200°F). It was noted that a certain amount of grease originating at the machining steps
of bolt production was accumulating in the automatic electroplating line's cleaning tanks. Grease
skimming from the top of the cleaning tanks needed to be improved to remove more of the grease
and oil before it carries over into the downstream processes. The filtering system on the
electroplating tanks needed to be repaired, as it was inoperative. Once the filtering system is repaired
(on both lines), it should be possible to determine if these systems are adequate to maintain
contaminants at proper low levels. In fact, it was recommended that a new filtering system be
installed.
It was noted that anode bags should be used to keep contaminants and dirt from the zinc balls
out of the electroplating solution. Also, a drain board needed to be installed over the drip tank after
the chromate rinse (on the auto line) to direct all dragout back into the rinse tank.
By using a trivalent chrome conversion coating process instead of the hexavalent chrome
process that was being used, the facility should reduce the toxicity of the waste produced. Lower
treatment costs would be realized since hexavalent chrome must be chemically reduced to its
trivalent form, which is less expensive to treat, before sending it to waste treatment plant. The
potential disadvantages of these changes would be: a slight reduction in corrosion protection, the
need for closer monitoring and testing of the process, and that trivalent chrome coats are only
available in a bright blue color instead of the customary light yellow.
To recapture some of the chemical dragout from the electroplating and chromating, it was
recommended that still rinse tanks be used after these processes. It is estimated that about 50% of
the chemical lost to dragout can be recaptured by this method (Hunt, 1988). It was also
recommended that air agitation be used in the tanks to increase rinsing efficiency.
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The electroplating process should be supplied with as clean a water as possible. It was noted
that the facility had a reverse osmosis (RO) purification unit which was not in use, so it was
recommended that the RO unit be used to supply water to the electroplating, chromating, and still
rinse tanks. This change would remove potential contaminants in tap water including total dissolved
solids (TDS) and hardness, thereby increasing process efficiency.
The barrel withdrawal rates were measured at 5.2 m/min (17 ft/min) in the automated line
and 8.2 m/min (27 ft/min) in the manual line. According to Foecke (1993), the maximum rate of
withdrawal should be about 2.4 m/min (8 ft/min). This change would help decrease the amount of
dragout from each tank resulting in decreased chemical usage.
It was also recommended that the hang time of the barrels over the tanks be increased by
pausing longer before moving to next station. The barrel hang time on the auto line was 23 seconds.
There was still significant dripping from the barrels after this time period. The hang time over tanks
on the manual line varied according to operator discretion. For the most part, hang time was
observed to be minimal, and dragout was consequently significant.
Results of Implemented Changes in The Electroplating Systems
Recommended changes to the automatic electroplating line were presented to the facility. To
date, four recommendations have been implemented, the results of which are summarized in this
section.
The first recommendation to be implemented was to clean the outside and inside of all the
tanks on the plating line and remove bottom sludge that had developed. In particular, the bath
contents of the electroplating tank were pumped into a temporary holding tank and the bottom sludge
was shoveled into eight 55-gallon drums for disposal (this sludge is not listed as hazardous under
RCRA regulations). The liquid portion of the plating bath was then pumped back into the plating
tank and additional chemicals and water were added to restore them to normal levels.
Another recommendation that was implemented was regular testing of the cleaning, acid dip,
electroplating, and chromating processes to maintain chemical concentrations at their optimum
levels.
The third implemented recommendation was the hiring of an employee with suitable
chemistry background to perform operational control testing (among other duties including the
galvanizing system chemistry, as discussed below) and report results back to the plating operator so
that any required chemical additions can be made. The results of this testing are being documented,
and chemical additions are now being made on a regular basis.
The fourth implemented recommendation was the reducing of all rinse flows. Flow control
devices have been installed on the rinses after the alkaline cleaning and acid dip processes to
maintain flow rates at the recommended levels. The two systems have not been connected together
as was recommended. The flow rate for the two rinses after electroplating also have been reduced,
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although neither a countercurrent system nor flow control devices have been installed. The new rates
have not been measured, and it has also not been determined if they are being maintained at a
consistent level. According to the plating operator, the valves controlling flow are not turned on as
far as in the past. The flows still appear to be above recommended levels (as judged by visual
observation), but until flow control valves are installed or some other way of producing a consistent
flow is devised, the current method will be continued.
The implemented changes also have resulted in significant product quality increases as
evidenced by the results of the 5% neutral salt spray testing (as per ASTM B-l 17) done on bolts
plated on the automated line before and after the changes were initiated. These results are presented
in Table 1 below, and show a 1,000% increase in white rust protection and a 550% increase in red
rust protection.
Table 1. Results of 5% neutral salt spray tests
Parameter
Hours to White Rust
Hours to Red Rust
Pre-Change
Results
16
48
Post-Change
Results
168
264
Typical
Values
96 - 250
200 - 350
In conclusion, the facility has been very encouraged by these positive results. Also,
from a waste prevention and minimization perspective, the implemented changes have been
effective. The reduction in rinse flows will no doubt lead to less wastewater needing to be treated
at the waste treatment plant. The cleaning of tanks, removal of sludge, and use of oil absorbent pads
on the cleaning baths should help reduce the drag-out of dirt, grease, and other contaminants to
downstream processes. This will help to increase bath life which will result in fewer bath dumps and
reduced chemical use. The costs associated with these implemented changes have been modest.
The Galvanizing System
The galvanizing process at the facility is a five-step procedure consisting of pickling, rinsing,
prefluxing, galvanizing, and final rinsing. The pickling step prepares work for galvanizing by
removing oxides from the steel surface using a 10% sulfuric acid solution at a temperature of 70 °C
(158°F). The work pieces are dipped in the pickling acid for varying lengths of time, and then taken
away to be rinsed.
After pickling, work pieces are rinsed to remove the acid. The preferred rinsing method is
to dip work pieces in the rinse tank, which is filled with unheated municipal water. The rinse water
is agitated by moving the work pieces back and forth in the rinse tank.
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After the first rinsing, work pieces are placed in the preflux tank, which is a crucial step in
the "dry kettle" galvanizing process. The work is coated with flux chemicals (ZnCl2 and NH3C1)
prior to entering the zinc kettle. The preflux tank is kept at 70°C. Normally, the preflux solution
should be allowed to dry thoroughly before proceeding with galvanizing.
Galvanizing is accomplished by immersing steel in a tank filled with molten zinc for 2 to 3
minutes. Livestock fencing, the majority of the steel galvanized at this plant, uses the wet kettle
galvanizing method. This means that a flux layer is floated on top of the galvanizing kettle. A flux
layer covers the kettle, and work pieces pass through it as they enter and leave the kettle. For
galvanizing other materials such as building components, the kettle flux layer is skimmed to the side
and not used.
The work pieces are cooled by rinsing them in a second rinse booth located next to the
galvanizing kettle. This final rinse is needed to cool the work to below 200°C (390°F), which stops
the possible growth of a brittle zinc-steel alloy layer. Cooling also makes it easier for operators to
handle the work pieces. A detailed analysis of the galvanizing system at this facility is given by
Montag(1993).
Pollution Prevention Opportunities in the Galvanizing Process
Pollution prevention efforts in the galvanizing area were concentrated on reducing the
volume and metal content of rinse water since this is the principal medium through which metal is
lost. Volume reductions can be accomplished by installing additional galvanizing equipment. Metal
content reductions are possible by either discontinuing use of the kettle flux, or switching to a
different kettle flux.
Rinse Water Use. The galvanizing system at this plant initially used about 265 m3 of rinse
water per day. Flow through the first rinse booth was measured during the waste stream assessment
period at 1,200 liters per minute. Freshly galvanized pieces are cooled in the second rinse booth.
Flow through this booth nowadays is estimated at approximately 1,200 liters per minute, a reduction
in flow which is due to recent modifications after the assessment was completed. The rinse booths
operate only when there are materials to be rinsed being carried through them.
Rinsing in a rinse tank, instead of a rinse booth, after galvanizing is the most important step
in decreasing galvanizing water use. Use of rinse tanks after pickling is also important. The rinse
booths could be replaced by rinse tanks linked in a counter-current flow arrangement. The benefit
of such a system is that it allows water to be reused several times before it is discharged to the drain,
in addition to the fact that work pieces are always rinsed using the cleanest water as they leave the
process line.
A rinse test was conducted to verify the usefulness of the rinse tank concept. This test
successfully demonstrated the feasibility of continuous-flow rinsing. Based on the results of the
rinse test, a continuous rinse water flow rate of 24 liters per minute (6.3 gal/min) will remove
pickling acid adequately for two rinse tanks in series. This flow rate will adequately cool the work,
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preventing the water temperature from rising high enough as to pose a worker safety problem. The
proposed system would use about 35 m3 of water (or less) per day. This represents a savings of
about 83%. One of the changes resulting from the study was the replacement of the spray orifices
(nozzles) in the rinse booths by water-saving (low-flow) ones. This ch'ange resulted in an immediate
reduction in the water use by 60% and resulted in savings in water use and waste treatment costs of
about $250 per day.
The cost of the proposed galvanizing equipment changes is estimated at about $70,000, and
ventilation system improvements required to remove pickling solution vapors from the proposed
pickling tank location would cost $25,000. Due to the expense of the suggested galvanizing changes,
phased installation was recommended. The estimated payback period on the suggested
modifications is about 10 months.
Galvanizing Chemistry. Fencing currently is being fluxed twice: once in the preflux tank,
and a second time as it enters the kettle. For galvanizing of objects other than fence panels (such as
building parts), the kettle flux is skimmed to the side and is not used. The kettle flux is 98% ZnCl2
and contains a small amount of KC1. Kettle flux adds significantly to the metal content of
galvanizing rinse water, so discontinuing the use of kettle flux would enhance pollution prevention.
Prefluxing is crucial in dry kettle galvanizing. To obtain good fluxing, proper concentrations
of ZnCl2 and NH4C1 must be maintained, and iron and sulfate concentrations must be minimized.
Frequent sampling is required.
In the preflux chemistry, two terms (i.e., degrees Baume (°Be), and Ammonium Chloride
Number (ACN)) are important to the operation of the system. The °Be is a unit of density which is
directly related to the ZnCl2 concentration. Optimum density ranges from 12 to 15 °Be (1.09 g/mL
to 1.12 g/mL), measured at 20°C. The ACN of a preflux is the ratio of the NH4C1 concentration
divided by the concentration of all other components in solution. An optimum ACN value is
difficult to ascertain. In U.S. practice, recommended values range from 1.17, used by most
galvanizers, to 1.8 recommended by Cook (1982). Sjoukes (1990), a galvanizing expert from the
Netherlands, recommends ACN values of 1.75 to 2.5.
The plant currently collects samples of the preflux solution for detailed analysis, including
ACN, three or four times a year. More frequent ACN determinations (at least monthly) are needed
for galvanizing strictly by the "dry kettle" method. This becomes more important if the kettle flux
continues to be used after installing the recommended counter-current flow rinse system. This is
because zinc chloride will be dragged into the preflux from the post-pickling rinse.
In-house testing was recommended for faster data acquisition. It was also recommended that
a chemist be hired to perform chemical testing on a continuous basis. The same chemist would
conduct tests associated with the electroplating lines, as pointed out above.
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Additionally, a recommendation was made to the facility to switch from the zinc chloride
preflux to a mixture of mostly ammonium chloride and some zinc chloride, or ammonium chloride
alone. This recommendation was based on the work of Sjoukes (1990). This would probably
produce better results by enhancing product quality, since the proposed counter-current flow system
(with fresh water being added at the final rinse tank) would not complicate preflux chemistry.
Another problem associated the galvanizing operation was a layer of oil floating on the
surface of the acid bath. This was not surprising since there was no cleaning stage prior to pickling.
The oil problem could be minimized by installing a skimmer system to remove the oil layer
periodically. A better alternative is to reduce the amount of oil being left on the work pieces during
fabricating by careful monitoring of oil usage during that step.
The Painting System
The painting operation at the facility is a sequential system consisting of washing, etching,
oven drying, spray painting, and oven curing. The paints used at the facility are of the traditional
solvent-based variety which contain volatile organic compounds (VOC's). In 1992, the painting
operation was estimated to have emitted about 37,500 kg (82,500 Ibs) of xylene, and 11,000 kg
(24,200 Ibs) of toluene. Xylene and toluene are defined as hazardous under the 1990 Clean Air Act
(CAA), and will be regulated strictly in the near future. Reducing emissions of these VOC's should
receive a high priority.
Two major types of paint are in use at the plant. One is a solvent-based paint, which is used
for painting gates, and the other is a silicone polyester paint used for painting building panels. In
1992, 74% of paint used by the automatic paint line was used in painting farm gates. In addition,
large quantities of a mixture of several aromatic solvents are used for purposes such as cleaning paint
supply piping. About 2,200 liters (580 gallons) of this solvent are consumed each month. A detailed
analysis of the painting system at this facility is given by Montag (1993).
Painting Alternatives. The only practical way to significantly reduce VOC emissions is to
change paint materials. There are several possible materials and alternative painting methods to
consider. One choice is to use water-based paint for gates, which accounts for over 74% of the
plant's paint use. If water-based paints are applied electrostatically, a high transfer efficiency can be
obtained. Installation of new spray equipment is the only facility change that will be required, and
therefore, the investment should be relatively small. Consequently, testing of water-based painting
alternatives was recommended for immediate consideration.
Another method to reduce VOC emissions from painting gates, and also to eliminate chromic
acid etching of galvanized building panels, is to switch to an autophoretic painting process. This
process involves dipping metal to be painted into tanks filled with paint. Immersion is required
because the coating is deposited by a chemical reaction between the paint and the metal which takes
several minutes to occur. The autophoretic process resembles electrocoating, except that no electric
current is required. Metal painted by this process reportedly has withstood salt spray tests of up to
3,000 hours without coating failure (Anonymous, 1992). The paint reportedly exhibits a high degree
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of hardness and good resistance to chalking from ultraviolet light exposure. An autophoretic system
to coat gates was estimated to cost about $300,000. A detailed analysis of this painting method
would be required. A serious drawback of this painting method is that color varies with the
dissolved iron concentration in the paint, which increases slowly due to contact of the paint with the
steel being painted. Another drawback is the fact that a separate paint tank is needed for each desired
color.
A third alternative for painting is to consider the use of powder coating. Agricultural gates
are ideally suited for powder coating because they are made in only two colors. Transfer efficiency
is not an issue in this method because overspray is captured and blended with fresh powder for reuse.
Powder coating would entirely eliminate volatile organics from the paints used for farm gates. An
industrial supply contractor estimated that powder coating could be added to the existing paint line
at this plant for as little as about $40,000. However, installation costs were estimated to be much
higher than this estimate because the automatic paint line is quite old, and therefore must be replaced
entirely. A new paint line was estimated to cost about $200,000.
Pollution prevention in the painting area at this plant will not be offset by significant savings
in terms of reduced waste disposal costs at the present time. However, the Clean Air Act
requirements will soon demand that action be taken. Estimates of the installation costs for various
painting alternatives are shown in Table 2. As a result of this study, the plant has experimented with
water-based paints as well as a powder coating system. The facility has requested bids to construct
a powder coating system.
Table 2. Summary of costs of painting alternatives at the plant
OPTION COST
Water-based Spray Painting $25,000
Autophoretic Coating $300,000
Powder coating $200,000
The Tubing Manufacture System
A tube mill is used at the manufacturing facility to form metal pipe from coils of sheet steel.
The plant makes the tubing for all its gates, and for sale to other companies. The major tube mill
components include the coil unwinder, the feeder, the initial cold rolls, the welder, the re-galvanizer,
the final cold rolls, the metering cutter, and the coolant distribution system.
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A water-based fluid coolant is used by plant for lubrication and cooling of the tube mill.
About 800 liters (210 gallons) of coolant per month are consumed at a cost of about $800. The
coolant flows from its application points into sumps below the components. The sumps, in turn,
drain by gravity to a large collection tank. The collection tank contains an oil removal system,
consisting of a plastic tube pulled through the liquid coolant. Floating oil adheres to the polyethylene
tube, and is removed by a scraper. The oil removal system is not able to remove oil fast enough.
The oil in the coolant originates from grease leaking out of the tube mill gearboxes. Over
the years, oil and grease leaks have covered the tube mill and the surrounding area. Grease combines
with the metal filings created when excess metal is scraped off the fresh welds, and together they
make a black substance that fills the bottom of the sumps in about a month. The mill is occasionally
shut down while operators scoop out all the grease. About two-thirds of the coolant is lost each time
the sumps are cleaned, and this is the only time coolant is discharged from the system. A detailed
analysis of the tube mill system at this facility is given by Montag (1993).
Recommended Tube Mill Changes. Recommendations for the tube mill area at this plant are
mostly concerned with changes which would minimize grease contamination of the coolant. The old
oil removal system needs to be replaced and an efficient oil removal system, which should allow the
coolant to be used for several times its current life. A suitable new oil removal unit was estimated
to cost less than $2,500. The payback period was estimated at less than six months assuming that
the coolant's useable life is only doubled. Beyond that, the actual payback period could be even
shorter.
There is also a problem with the coolant turning rancid. Coolant rancidity usually is
controlled by adding one of several possible biocides. If rancidity problems continue after an
improved oil removal system is installed, a new biocide may be needed.
It should be possible to prevent gearbox leakage, or at least reduce leakage from falling into
the sumps through regular maintenance. Also, preventing metal filings from falling into the sump
below the weld scraper would keep them from combining with the grease. It was strongly
recommend that the entire area be shutdown for a short period of time for a thorough cleaning. This
would vastly improve the operation of the system. The cleaning should include all equipment, floor
grates, and the return trough.
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SUMMARY AND CONCLUSIONS
In this report, the preliminary results of an extensive pollution prevention program at a metals
fabricating and finishing facility are reported. The plant is a large, fairly aged, facility located in the
midwestern United States. The principal operations involved at this facility include electroplating,
conversion coating, cleaning, machining, grinding, impact deformation, shearing, welding, sand
blasting, hot-dip galvanizing, painting, assembly and testing of various metallic components that are
being made. The discussion in this report has centered on the principal operations that produce the
bulk of the wastes at this facility including electroplating, galvanizing, painting, and tube
manufacturing. Additional information regarding the manufacturing facility and its processes can
be found in Dahab and Montag (1993), Dahab et al. (1994), Montag (1993) and Parr (1994). (See
the references at the end of this report.)
This project has entailed an extensive and systematic waste stream assessment and
evaluation. The operations and processes at this facility result in the production of large quantities
of wastewater with significant concentrations of metals that require expensive treatment. One of the
major constraints in making recommendations was the fact that the facility was fairly old and not
very profitable. Consequently, all of the recommendations for process and operational modifications
resulting from the P2 opportunity assessment had to meet critical economic payback periods.
The pollution prevention recommendations in the electroplating system, to date, have
contributed to significant reductions in the amount of wastewater that needs to treated as well as a
significant increase in the product quality. The product quality increase is clearly demonstrated by
the 550 % and 1000 % increase in the level of protection against white and red rust, respectively, in
the neutral salt spray tests conducted on the products before and after project implementation. The
plant management has been quite pleased by these results since numerous claims have been made
against the facility because of corroded fasteners.
The principal modification to the galvanizing process centered on dramatic reductions in the
amount of wastewater produced in this process while improving product quality. As indicated, it
was apparent that rinse water use could be reduced by as much as 83 percent of what the process was
using prior to the waste stream assessment. One of the changes resulting from the study was the
replacement of the spray nozzles in the rinse booths by water-saving (low-flow) ones. This change
resulted in an immediate reduction in the water use by 60% and resulted in savings in water use and
waste treatment costs of about $250 per day. The process modifications were estimated to have a
payback period of about 10 months. Product quality should improve with the suggested
improvements in process chemistry.
Pollution prevention in the painting line was concentrated on reducing VOC emissions which
soon will be regulated under the Clean Air Act of 1990. The costs of proposed modifications
probably could not be justified in terms of savings due simply to reduced waste. Installation
expenses will have to be recovered through adjustments in the pricing of products. However, the
modifications are well justified in terms of expected regulatory requirements.
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The tube mill system was associated with excessive coolant loss as well as rancidity. The
proposed changes were expected to significantly reduce coolant loss with an estimated payback of
less than six months by installing a better oil and grease removal system. As it turned out, the
facility was able to install a suitable oil removal system for a fraction of the estimate made during
waste stream assessment.
EPILOGUE
The P2 Opportunity Assessment for the facility conducted in this project also produced
longer-term recommendations in addition to the recommendations reported here (see the
Recommendations Reports in the Appendices to this report). The facility will continue over the
coming months and years to adopt additional recommendations from the assessment.
For example, subsequent to the implemented changes described above, the company has also:
(1) added a new sludge containment area, which conforms to modern RCRA standards
(compared to the past when they simply piled up sludge outside until it was hauled
away);
(2) revised their wastewater treatment plant system by installing a new sludge filter press
to produce much drier sludge than before;
(3) with the hiring of the new chemist (as recommended), the facility continues to
optimize the process lines in both the electroplating and galvanizing lines; and
(4) as of May 1995, the company indicated that they were well on their way in
revamping the painting lines including the possible purchase of a new power coating
system.
In conclusion, implementing pollution prevention and improving facility performance and
profitability will be an ongoing work at this manufacturing site in Nebraska.
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REFERENCES
Anonymous. (1992). Steelcase Inc. replaces zinc plating lines, Finishers Management, March, pp.
17-20.
Cook, T. H., Mergen, D.E., and Clark, D.L. (1986). Increasing profits in hot dip galvanizing, Metal
Finishing 84(23):23-27.
Cook T.H. and Horton, W.S. (1982). Ammonium chloride control in galvanizing preflux, Metal
Finishing 80(19): 19-23.
Dahab, M.F. and D. Montag. (1993). Waste minimization in a metal-finishing industry: a pilot
project, Presented at the Third International Conference on Waste Management in the
Chemical and Petrochemical Industries, Salvador-Bahia, Brazil, October 20-23.
Dahab, M.F., D. Montag and J. Parr, 1994, "Pollution prevention and waste minimization at a
galvanizing and electroplating facility," Water Science and Technology, (In Press).
Durney, L.J. (1984). Electroplating Engineering Handbook, Lewis Publishers, Inc. Chelsea,
Michigan.
Foecke, T. (1992). Lecture Notes, Training in pollution prevention through rinsing process
modifications, Waste Reduction Institute for Training and Applications Research,
Minneapolis, MN. USA.
Hunt, G.E. (1988). Waste Reduction in the Metal Finishing Industry, Journal of the Air Pollution
Control Association 38(5):672-680.
Montag, D. (1993). Pollution prevention in the metal finishing industry, Master of Science Thesis,
University of Nebraska-Lincoln Libraries, December.
Sjoukes, F. (1990). Chemical reactions in fluxes for hot dip galvanizing, Anti-Corrosion Methods
and Materials 37(4): 12-14.
Parr, J. (1994). Waste Minimization opportunities for the electroplating industry: a case study,
Master of Science Thesis, University of Nebraska-Lincoln Libraries, February.
Tsai, E.G. and Nixon, R. (1989). Simple Techniques for Source Reduction of Wastes from Metal
Plating Operations, Hazardous Waste & Hazardous Materials 6(l):67-78.
U.S. Environmental Protection Agency. (1990). Guides to Pollution Prevention - The Fabricated
Metal Products Industry, EPA Report No. EPA/625/7-90/006, July.
U.S. Environmental Protection Agency. (1992). Facility Pollution Prevention Guide, EPA Report
No. EPA/600/R-92/088, May.
U.S. Environmental Protection Agency. (1993). A Primer for Financial Analysis of Pollution
Prevention Projects, EPA Report No. EPA/600/R-93/059, April.
University of Tennessee Center for Industrial Services. (1990). Waste Reduction Assessment and
Technology Transfer. Second edition, 9/22-9.
Wentz, C.A. (1989). Hazardous waste management, McGraw-Hill Book Company, New York.
14
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APPENDICES
15
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The Appendices include the following:
The interim and final reports on recommendations for implementing
P2, which were submitted to Behlen Manufacturing Company
officials.
Abstracts and tables of contents of two lengthy and highly technical
reports on the project and the technologies considered in the project.
(These two reports are referenced at the end of the above report as
Montag, D. (1993) and Parr, J. (1994) and are available in their
entirety as Masters of Science Theses from the University of
Nebraska-Lincoln libraries.)
An article from the November 1994 issue of Environmental Solutions.
(Reprinted by permission of Advanstar Communications Inc.)
16
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INDUSTRIAL POLLUTION PREVENTION PILOT PROJECT
An Interim Report
Submitted to the
Behlen Manufacturing
Columbus, Nebraska
Submitted by
M.F. Dahab, Ph.D., P.E.
Principal Investigator
Department of Civil Engineering
University of Nebraska-Lincoln
Lincoln, NE 68588-0531
This Project is funded by the
U.S. Environmental Protection Agency
Office of Water
Washington, D.C.
Steve Wurtz, EPA Region VII, and
James Lund, EPA Washington, Project Managers
February 8, 1993
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INTRODUCTION
Work began in early 1992 on an industrial pollution prevention pilot project for
Behlen Manufacturing Company of Columbus, Nebraska. The project, which is
partially funded by the U.S. EPA, is part of an effort by the University of Nebraska-
Lincoln to establish a pollution prevention and waste minimization program throughout
Nebraska.
Behlen Mfg. Co. produces fabricated metal parts for farm and industrial uses.
The areas of electroplating, galvanizing, painting, tubing manufacture, and water use
are being studied for ways to prevent pollution.
This report begins with a section on electroplating, and then covers galvanizing,
painting, tubing manufacture, water use, and the waste treatment plant. Each of the
sections describes the process and then gives preliminary recommendations for
minimizing waste production and/or improving product quality.
SECTION 1 - ELECTROPLATING
Behlen currently operates both automated and manual electro- plating lines.
These lines electroplate zinc onto small items such as nuts and bolts which are then
used in the construction of larger products such as fabricated metal farm buildings.
A diagram of each line is included in the appendix section of this document.
Automated Electroplating Process Description
The automated electroplating line processes an average of 140 pounds of work
per barrel. There are 40 stations on the line, with an approximate cycle time of 3.5
minutes per station (about 2 hours and twenty minutes total run time per barrel). This
includes a 23 second hang time over the tank to allow solution to drip off the barrel
before going to the next station. The barrels rotate while in the tank to help keep the
work and solution well mixed.
Stations 1 and 2 (tanks 1 and 2 -- 200 gallons each) are filled with a soak
cleaner called Metex S 1651 (8 to 12 ounces per gallon of water) and are maintained
at a temperature of 150 to 170°F. According to the product information sheet, Metex
S 1651 has a biodegradable surfactant which aids in the removal of dirt and oils from
the surface of the work, and it works in hard water. The cleaner contains 12% sodium
hydroxide, which acts to remove oil from work pieces through a saponification
1
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reaction. The sodium hydroxide also breaks down organic compounds and dissolves
amphoteric metals.
Stations 3 and 4 (tank 3 -- 400 gallons) involve a cleaning process known as
electrocleaning. Electrocleaning works by applying a positive charge to the work and
a negative charge to plates hung at the edge of the tank. Rust, burrs, and smut are
repelled from the parts, and are attracted to the negatively charged plates. The
chemical used in this tank is Metex E 1726 (8 to 12 ounces per gallon of water). The
tank temperature is maintained at 150 to 170°F. Metex E 1726 is 50% sodium
hydroxide, and helps to removes oils missed by the soak cleaner tanks.
The contents of the cleaning tanks (soak cleaner and electrocleaner) are
discharged to the waste treatment system about every one to four months. The tanks
are dumped if either the chemical addition indicated by daily testing equals the
chemicals needed to mix a new batch, or if the operator judges that the tank is dirty
and should be changed.
NOTE: The first eight tanks of the plating line (this includes cleaning, rinsing, and
hydrochloric acid pickling) are all emptied at the same time.
Stations 5 and 6 (tanks 4 and 5 -- 200 gallons each) involve rinsing the work
with ambient temperature water to remove loosened dirt and oils, and cleaning
solution dragout. Flow through the rinse tanks is counter-current (fresh water flows
into tank 5 overflows into tank 4, and then overflows out to waste treatment system)
and about 15 gallons per minute is used. The rinse tanks are cleaned when they are
emptied, and any accumulation of metal sludge is rinsed into the waste treatment
system.
After rinsing, the barrels continue through the process to stations 7 and 8 (tank
6 -- 400 gallons) where the work is pickled in hydrochloric acid. HCI acts to remove
alkalinity and the thin film of oxide or tarnish that develops on pieces due to the
previous cleaning processes. The tank contains about 12% hydrochloric acid at room
temperature. Vapor rising from the tank due to the pickling process enters a hood and
is exhausted outdoors.
Stations 9 and 10 (tanks 7 and 8 -- 200 gallons each) involve rinsing the pieces
with ambient temperature water to remove all remaining contaminants prior to the
electroplating process. Flow through the two rinse tanks is counter-current at a rate
of about 12 gallons per minute.
The ninth tank (stations 11 through 30) is the electroplating tank, which holds
5,500 gallons of solution. Work stays in the tank for 20 stations (about 70 minutes).
The electroplating solution contains zinc, potassium chloride, sodium chloride, boric
acid, a leveling agent, a wetting agent, and a brightener at a pH of about 5. A
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monthly check of the solution is done (by the John Schneider Company) to see if any
chemical additions are needed. Balls of zinc are held in titanium baskets along the side
of the tank. A potential difference of 8 volts is applied between the zinc balls and the
work pieces (the zinc being positively charged and the work negative). About 1,000
amps of current is drawn by this process. The current acts to dissolve and then
deposit zinc from the balls onto the work in the barrel.
The electroplating solution is circulated through a filter to remove impurities,
and a heat exchanger helps to cool tank contents to room temperature. The filter is
cleaned in the hydrochloric acid tank on the manual electroplating line and rinsed in
the rinse tank following the HCI tank (also on the manual line).
Stations 31 and 32 (tanks 10 and 11-- 200 gallons each) involve rinsing the
pieces with water to remove chemicals and loose zinc particles incurred during the
electroplating process.
Rinse water flow in each tank is approximately 9 gallons per minute. The waste water
drains to the waste treatment plant.
Tank 12 (station 33) is a drip tank where the barrel hangs above the tank to
allow dragout from the rinse tanks to drip off. The waste water drains to the
treatment plant.
Station 34 (tank 13 - 200 gallons) involves a yellow chromate conversion
coating process. Tank contents include chromic acid, formic acid, carboxylic acid, anc
nitric acid at a temperature of 80 F. The barrel is dipped into the tank for only 40
seconds during which time a yellow chromate coating of about one half micron
thickness is deposited on the work. The barrel rotates about 20% of the time while
in the tank compared to continuous rotation at the other stations (this is to prevent
the chromate coating from being knocked off). The chromate tank is disposed of every
three days, and prior to entering the waste treatment system, the chromium VI is
reduced to chromium III with sodium bisulfite and sulfuric acid. Fumes from the
chromate tank and the chromate rinse tank are collected by exhaust hoods and
directed outdoors.
Station 35 (tank 14 -- 200 gallons) is a static rinse tank in which the barrel i;>
dipped to remove excess chromic acid solution. This rinse tank is emptied daily. Prior
to emptying, the rinse tank's contents must be treated with sodium bisulfite and
sulfuric acid.
Station 36 (tank 15 -- 200 gallons) is a drip tank to allow dragout from the rinse
tank to drip off (tank contents must be neutralized with sodium bisulfite and sulfuric
acid before emptying to waste treatment plant).
Following the drip tank, tanks 16 and 17 (stations 37 and 38) are drying areas.
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150°F air is blown through the barrels to speed drying of the work inside.
At stations 39 and 40, the pieces are allowed to cool before being removed
from the barrel. At this point, the empty barrels have come full circle and are ready
to be filled with a new load of work to be electroplated.
Automatic Electroplating Recommendations
Operation of the soak cleaner tanks can be improved in several ways:
Temperature should be increased from the current 150 to 170°F to the
temperature recommended by the soak cleaner manufacturer (200 to 205°F).
Tank temperature and concentration should be monitored daily. This will
improve the effectiveness of the cleaner.
Fresh water use can be decreased by using water from rinse tank #4 as
makeup for the soak cleaner and electrocleaner tanks.
Filtration could prevent sludge build-up in the bottom of the soak cleaner tanks.
Raising the temperature and filtering tank contents should improve product
cleanliness and increase tank life.
A grease skimmer and trap should be used to remove grease and oil from the
surface of the tank solution to minimize carryover to downstream tanks.
2. Electrocleaning recommendations are similar to those for the soak cleaners and
include:
Increasing temperature to 200°F, using a grease skimmer and trap, monitoring
temperature and concentration daily, filtering solution, and using water from
tank #4 as makeup.
3. Recommendations for the rinsing process after both cleaning and pickling are
as follows:
The flow of rinse water through rinse tanks 4, 5, 7, and 8 can be reduced. As
before, fresh water should enter tank #8, but at a reduced rate of about 0.6
gallons per minute (gpm) (flow control valves to maintain specific flow rates are
about 35 dollars -- not installed). The flow is directed counter current into tank
#7. Water overflowing from tank #7 would be directed to tank #5, and then
countercurrentto tank #4. Rinse water flow can be cut from a total of 27 gpm
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to about 0.6 gpm, a savings of 26.4 gpm. Since it costs about 0.275 cents
to treat a gallon of waste (based on Behlen estimates), 35 dollars per day could
be saved. Also, the acid rinsed from the pieces in tank 7 will help to neutralize
alkalinity from the cleaning tanks (stations 1 through 4) thus increasing the
effectiveness of rinse tanks 5 and 4.
NOTE: All rinse water flow estimates are based on the use of deionized water
and standard conditions. Flow estimates will increase if tap water is used and
current housekeeping conditions prevail.
A 50 gallon tank could be used to store water overflowing from rinse tank #4.
This water could be used as makeup for tanks #1, #2, and #3.
4. The hydrochloric acid tank pH should be checked daily to increase tank
effectiveness.
5. Operation of the electroplating process can be improved in the following ways:
Electroplating tank chemistry should be checked daily. Chlorides, zinc,
temperature, and pH should be tested.
The electroplating solution should be filtered more rapidly to aid in the removal
of impurities. A typical plating tank filtration system filters 2 bath volumes per
hour.
Air agitation would facilitate better mixing of electroplating tank contents. This
will improve plating results.
The use of anode bags would decrease bath contamination from insoluble
anode material.
Perform regular maintenance on rectifiers, filter system, and barrel and tank
anodes to optimize plating performance.
6. The following changes are recommended for the rinsing and chromating
following the electroplating process:
Eliminate the drip tank prior to chromating (tank 12). By eliminating the drip
tank, tanks #11 and #12 can be used as counter-current rinses with a flow rate
of about 0.3 gallons per minute (gpm). Tank #10 could then be used as a static
rinse (no flow), and the water from this tank could be used as make-up for the
electroplating tank. Air agitation of this still rinse tank would improve rinsing
efficiency if the plating solution is highly contaminated. This set of changes
should decrease rinse water use from the current level of 17 gpm (combined
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flow rate for tanks 10 and 11 now) to 0.3 gpm. This would result in a water
savings of about 8,016 gallons per day, or $22 per day in waste treatment cost
savings. As previously stated, flow control valves for specific flow rates are
available for about 35 dollars.
NOTE - There is adequate space on the line to move the chromate tank down
one space (to tank 14) if a drip tank is desired prior to chromating.
Substituting trivalent chromium for hexavalent chromium should be considered.
This could help remove a hazardous waste from the process. Chromate tank
concentration and temperature should be monitored daily.
7. Changes to the process after chromating are as follows:
A static rinse tank should be used after chromating. A float and pump system
can be used to withdraw water from the rinse tank to use as makeup for the
chromate tank.
A drain board should be installed over the drip tank so that solution falling over
the tank is directed back to the rinse tank.
Manual Electroplating Process Description
The manual electroplating line is more labor intensive than the automated line.
The barrels are hooked onto a chain conveyor system and the operator physically
moves the barrels from station to station using the conveyor system. The barrels are
bigger than those used on the automated line, but the average load of work is still
about 140 pounds. The barrels rotate while in the tanks to promote mixing.
There is no electrocleaning process on this line. Also, a nitric acid tank is
available for pickling stainless steel pieces (this doesn't occur often), and a yellow or
clear chromate finish may be added after the zinc electroplating process (depending
on customer preference).
Station 1 (tank 1 -- 600 gallons) is the soak cleaning station. The tank can
accommodate three barrels at one time. The barrels are left in the soak cleaner
solution (Metex S 1651) for about 15 minutes. The process is heated to about 200
F and as stated in the automated section, acts to remove dirt and oil from the work
in the barrel.
Stations 2 and 3 (tanks 2 and 3-100 gallons) are fresh water rinse stations.
The barrels are dipped into either tank 2 or tank 3 for a period of about 30 seconds
to remove dragout from the soak cleaning tank. The flow rate through the tanks is 2
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gallons per minute for tank 2, and 7 gallons per minute for tank 3. The barrels hang
over the tank for about 5 seconds and then move to the next station (HCI pickling).
Station 4 (tank 4 -- 200 gallons) is hydrochloric Acid pickling. The barrel is
dipped into this tank for about 10 minutes to remove oxides, tarnish, and alkalinity.
This tank is also used to clean the filter from the electroplating tank pump on the
automated line. Tanks 1, 2, 3, and 4 are emptied at the same time, usually about
once every 3 months.
Station 5 is a rinse tank (tank 5 -- 100 gallons) used to capture dragout from
the hydrochloric acid tank. The flow rate through this tank is about 7.5 gallons per
minute. The barrel is dipped into this tank for one complete rotation and then removed
(about 10 seconds). This tank is also used to rinse off barrels after being dipped in the
nitric acid tank (station 6), and to rinse the filter from the automated electroplating
tank.
Station 6 (tank 6 -- 100 gallons) is the nitric acid tank
which is used to pickle stainless steel parts. This tank is not used very often and is
covered with a heavy piece of plastic between uses.
Station 7 (tank 7 -- 900 gallons) is the electroplating tank. The chemicals used
are the same as for the automated electroplating tank. There is no filtering system on
this tank, and the tank solution is checked monthly to determine if chemical additions
are needed. Barrels are dipped into the tank for a period of between 45 minutes to 1.5
hours (depends on customer specifications). The electroplating of zinc onto the work
pieces is similar to that described for the automated line.
Station 8 (Tank 9 -- 100 gallons) is a rinse tank with a flow rate of about 6
gallons per minute. The barrel must be lifted over tank 8 (clear chromate tank) to get
to this rinse tank (the chromate tank is covered with a heavy plastic sheet during this
time). This rinse tank is only used to rinse barrels coming from the electroplating tank.
Station 9 (tank 8 -- 100 gallons) is the clear chromate tank. This solution is
similar to the yellow chromate finish described on the automated line except that it
leaves a clear finish on the pieces instead of a yellow finish. This clear finish is used
if preferred by the customer. The barrel is dipped into the tank for a period of about
3/4 to 1 full rotation (about 10 seconds. It is then allowed to hang over the tank until
most of the dragout has dripped back into the tank. The barrel is then rinsed in tank
11 for about 20 seconds and then taken to the drying tables (station 12) where the
work is removed and allowed to dry.
The chromate tank is emptied about once every 6 months. The hexavalent
chromium (Cr VI) is neutralized to trivalent chromium (Cr III) with sodium bisulfite and
sulfuric acid before emptying to the waste treatment system.
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Station 10 (tank 10 -- 100 gallons) is the yellow chromate station. It is similar
to the yellow chromate tank described on the automated line (including temperature
of about 80 F). The barrel is dipped into the tank for about 1 full rotation (about 10
seconds) and then allowed to hang over the tank until most of the solution dragout
has dripped back into the tank. This yellow chromate finish is used as per customer
preference. The contents are treated as previously described before being emptied to
the waste treatment system (tank is emptied about once every 4 months).
Station 11 (tank 11 -- 100 gallons) is a rinse station used after a barrel has
been dipped into the yellow or clear chromate tanks. The barrel is dipped into the tank
for about 20 seconds (2 full rotations) and then allowed to hang above until most of
dragout has dripped off. This is a still rinse tank (flow is not continuous) and is
emptied about once a month (chromates are neutralized before emptying to the waste
treatment plant.
Station 12 is a drying area where finished pieces are taken out of the barrel and
allowed to air dry.
Manual Electroplating Recommendations
1. All recommendations for the soak cleaning tank are similar to those made for
the auto line including:
installation of a grease skimmer and trap, daily monitoring of solution
temperature (already at 200 degrees Fahrenheit) and concentration, solution
filtration to remove sludge build-up, and use of rinse water from tank #2 to
make up for evaporation and dragout losses.
2. Changes recommended for the process after cleaning and before electroplating
(tanks 2, 3, 4, 5, and 6) are as follows:
By moving the nitric acid tank next to the hydrochloric acid tank (tank 5) and
using one of the empty tanks at the end of this side of the line (tank 7) (see
figure in appendix for the manual line), it is possible to create two counter
current systems that would be similar to those on the automated line. The fresh
water flow would originate in tank #7 at 0.6 gpm (using flow control valves)
and then be allowed to gravity flow to tanks #6, #3, and finally #2 where it
could be collected in a 50 gallon tank and used for make-up in the soak cleaner
tank. This would result in a savings of about 16 gpm (the current 16.5 gpm
versus 0.6 for the proposed method) and a waste treatment savings of about
21 dollars per day.
Daily testing of the hydrochloric acid tank concentration and pH would optimize
8
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pickling results.
NOTE: The use of disposable filters on all filtration systems (especially the Auto
electroplating tank) will eliminate the use of the hydrochloric acid tank for filter
cleaning as is currently done. This will result in extending the bath life and
better results in the plating process that follows.
3. Recommendations for the electroplating tank are similar to those made for the
auto electroplating tank:
Daily monitoring of solution pH, temperature, total chloride and zinc levels,
installation of an efficient filtering system to remove impurities and dirt (no filter
currently on this tank), air agitation, use of anode bags, and regular
maintenance of the rectifiers, filters, and anodes.
4. Changes proposed for rinsing after electroplating include:
A system similar to that proposed for the auto line should be considered with
a still rinse immediately after the electroplating tank and 2 counter current
tanks following with a flow of 0.3 gpm (using flow control nozzles). The still
rinse could be used for make-up into the electroplating tank and the rinse tank
following the still rinse could be used for make-up into the still rinse (as
needed).
NOTE: This change would entail moving the clear and yellow chromate tanks
next to each other. Secure lids would prevent contamination of one tank while
the other was being used.
5. Changes to the chromating process and rinsing after are as follows:
The use of trivalent chrome instead of hexavalent chrome must be considered.
As stated above, secure lids on each of the chromate tanks (clear and yellow)
would prevent contamination when barrels pass over the tanks.
The use of one static rinse tank (no flow) followed by a drip area consisting of
a drain board (to drain rinse dragout back into the rinse tank) would be the
desirable method.
Recommendations for both Auto and Manual Electroplating Lines
1. Housekeeping:
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Conduct a thorough clean-up of the electroplating area, including tanks and
floor. The dirt, grease and grime that has built up around and in the tanks has
a detrimental effect on product quality. The placement of lids over the tanks
when not in use might be beneficial.
All tanks should be checked for leaks and other potential hazards.
Establish strict routines for:
1) regular maintenance of the electroplating area including the equipment used
(e.g. rectifiers, pumps, heaters, barrels, and barrel anodes)
2) tank emptying and cleaning
3) chemical additions to tanks (in between emptying)
4) regular testing of tank contents (in the case of the soak cleaner,
electrocleaner, electroplating, and chromate tanks) to make sure they are
operating at optimum conditions
NOTE: All of the above should be incorporated into a written procedures
manual for each line.
2. Hire a chemist to monitor and direct the operation of each line:
The current operator can run the line but he has no knowledge of the chemistry
involved in the electroplating process. A person with a thorough understanding
of how cleaning, rinsing, and plating work would help create a more efficient
and cost effective electroplating operation.
3. Use of deionized water in all process and rinse tanks:
The current water used (from the Columbus Municipal supply) has extremely
high values for hardness (300 mg/l as CaC03), alkalinity (304 mg/l as CaC03),
and TDS (total dissolved solids) (440 mg/l). Deionized water would make
chemical processes (e.g. cleaning and electroplating) more effective and would
help in the rinsing process as well. It would also extend the life of the baths
which would result in less chemical use. This should lead to a higher quality
product while decreasing water usage.
4. Slower withdrawal rates for barrels from the tank solution:
Current rates are 17 ft/min. for the automated line and 27 ft/min. for the
manual line. According to the literature, the maximum rate for withdrawal
10
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should be about 8 ft/min. This change would help decrease the amount of
dragout from each tank resulting in decreased chemical usage.
5. Increase barrel hang time over the tank to decrease-dragout into the next tank:
The current hang time on the auto line is 23 seconds. There is still significant
dripping from the barrels after this time period. The hang time over tanks on the
manual line varies with operator discretion. For the most part it is minimal or
non-existent, and dragout is visually significant. A study must be done to see
how increasing the hang time affects the dragout rate from the barrels.
NOTE: It will be necessary to see how increased hang time affects the amount
of water used per barrel in the rinsing process (since rinse tanks are continuous
flow).
6. Decrease flow rates used in the rinse tanks:
Combined rinse tank flow rates for both the auto and manual lines are 64.5
gallons per minute (gpm). This adds up to a rinse water usage of about 31,000
gallons per day (based on an 8 hour work day) which must be treated at the
waste treatment plant at an average cost of 0.275 cents per gallon (85 dollars
per day or 22,150 dollars per year).
Average rinse water rates seen in the literature are 10 gpm for single
continuous flow tanks and 0.3 gpm for counter current flow rinses using 2
tanks (e.g. rinse tanks after electrocleaning and acid tanks on the auto line).
Counter current flow using 2 tanks can contribute significantly to a reduction
in water use. Currently the rinse system uses between 2 and 15 gallons per
minute per tank, with the two counter current systems (after the soak and
electrocleaner tanks, and the acid tank) using 15 and 12 gpm respectively.
Note: It may be necessary to delay implementation of this recommendation
until after deionized water is used which will improve the effectiveness
of the rinsing process.
Section 2 - Galvanizing
Galvanizing is a five step process consisting of pickling, rinsing, prefluxing,
galvanizing, and final rinsing. The next few paragraphs describe galvanizing in greater
detail.
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Pickling
Pickling prepares work for galvanizing by removing oxides from the steel
surface. The pickling tank is maintained at a temperature of 155 to 160 degrees
fahrenheit. It holds a 10% (by weight) sulfuric acid bath, which is inhibited with
Rodine 85. The work pieces are dipped in the pickling acid for varying lengths of
time, and then taken away to be rinsed.
Pickling time is very important because, while the time must be sufficiently long
to remove oxides, excessive pickling can dissolve the base steel. The "proper" time
depends on how much mill-scale is present, and is chosen based on operator
experience. Fencing is pickled for 5 to 10 minutes.
Pickling consumes 17,000 pounds of 66 degree Baume sulfuric acid each
month. Some of the acid is lost by evaporation and drag-out, but most of the acid
used is hauled away as hazardous waste. The pickling tank is emptied once every five
weeks, due to the slow rate of pickling when the acid becomes spent. Envirite
Corporation of Harvey, Illinois hauls away the used pickling acid, and recycles it.
Envirite charges Behlen $5,500 each time the pickling tank is emptied.
Behlen has purchased a sulfuric acid recovery system to recycle the acid bath
contents. The acid recovery system is installed and operating. It precipitates iron
sulfate and zinc sulfate by cooling the pickling solution. Operating principles of the
system are explained in an attached summary, which was published by the
manufacturer.
The pickling tank contains a small amount of Rodine 85, an inhibitor. Inhibitors
are chemicals which minimize acid attack on the base metal during pickling. Page 9
of Pickling of Steels (Mulcahy, 1973) explains inhibitor action.
Rodine 85 is composed of 40-50% substituted triazine, 1-5% thiourea, -1
10% hydrochloric acid, < 1 % formaldehyde and < 1 % ortho toluidine. 1.5 gallons of
Rodine 85 are added to each fresh tank of acid, and a total 60 gallons of Rodine 85
are used each year. The recovery system does not remove inhibitor, so less inhibitor
will be used in the future.
Rinsing
After pickling, the work is rinsed with city water to remove all pickling acid.
The preferred rinsing method is to dip work pieces in the rinse tank, which is filled
with unheated city water. The rinse water is agitated by moving the crane back and
forth while the work is submerged. When pickling is finished, the work is withdrawn,
and held over the rinse tank to allow excess water to drip off before going to the
12
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preflux tank. The steel surface must not be allowed to dry completely, or oxidation
will result.
As could be expected, contaminants build up in the rinse tank. A recent
analysis of rinse tank water indicated that it contains 297 mg/l total iron and 473 mg/l
total zinc. In order to prevent excessive buildup of chemicals in the rinse water, 2000
gallons from the rinse tank are emptied to the waste treatment plant each week.
Alternate rinse
The rinse booth located between the pickling tank and the rinse tank can be
used as a substitute for the rinse bath. Operators say the rinse tank water is too
dirty, so the rinse booth is almost always used (fencing is rinsed for about 17
seconds). The booth drains directly to the treatment plant without storing water for
further use. Flow rate through the rinse booth was recently measured by David
Montag at 300 gallons per minute.
Prefluxing
After the first rinsing comes prefluxing, which is a crucial step in the dry kettle
galvanizing process. The work is coated with flux chemicals prior to entering the zinc
kettle. The preflux tank is kept at 160 degrees fahrenheit, and is filled with water
containing zinc chloride and ammonium chloride. Work pieces are dipped in the
preflux tank and withdrawn. The preflux solution should be allowed to dry thoroughly
before proceeding with galvanizing.
Behlen uses 1,006 pounds per month of zinc ammonium chloride mixture
(ZnCI2-2NH4CI with 56 wt% ZnCI2 and 44 wt% NH4CI), and about 482 pounds per
month of additional ammonium chloride is used.
To obtain good fluxing, proper concentrations of zinc chloride and ammonium
chloride must be maintained, and iron and sulfate concentrations must be minimized.
Frequent sampling is required for good chemistry control. Preflux sampling and
sample frequencies are described below.
Two of the terms used in preflux chemistry may be unfamiliar to the reader.
These terms are degrees Baume (°Be), and Ammonium Chloride Number (ACM). °Be
is a unit of density, and any density expressed in °Be can be converted to other, more
familiar, units. A density conversion table is included in the appendix.
The preflux density depends almost entirely on ZnCI2 concentration. The
desired density range is about 1 2 to 1 5 °Be (1.09 g/ml to 1.12 g/ml) measured at 70
13
-------
to 75°F.
The ACN of a preflux is a ratio of the NH4CI concentration divided by the
concentration of all other components in the solution. Opinions about the best ACN
differ: Mineral Research Corporation recommends 1.17, Dr. T.H. Cook recommends
1.4 to 1.8, and Sjoukes recommends 1.75 to 2.5.
Mr. Richard Robak, the galvanizing team leader, draws all preflux samples.
Density is checked daily, and iron and sulfate samples are drawn every 3 to 4 days.
Behlen's maximum specification for iron is 1 %, and the max for sulfate is 1.5 to 2%.
Every three or four months, Mr. Robak sends a preflux sample to Mineral Research
Development Corp. of Charlotte, N.C.. Mineral Research performs a detailed analysis,
including ACN determination.
A detailed preflux analysis was performed on a sample drawn on 6/16/92. The
density was 15.99 degrees Baume, and the ACN was 0.92. This means that Behlen's
flux has more zinc chloride than necessary and too little ammonium chloride. A low
concentration of ammonium chloride in the preflux causes poor fluxing for dry
galvanizing (Cook, 1982; Sjoukes, 1990). The low ACN indicated by Behlen's most
recent preflux sample analysis should be corrected immediately. A letter from Mr.
Mark Keffer of Mineral Research to Mr. Dick Robak of Behlen recommends adding
more ammonium chloride to Behlen's preflux. Mr. Keffer's letter is included in the
appendix. Other suggested chemistry changes are given at the end of the galvanizing
section.
Galvanizing
Galvanizing is accomplished by immersing steel in a tank filled with molten zinc
for 2 to 3 minutes. Livestock fencing, the majority of the steel being galvanized, uses
the wet kettle galvanizing method. This means that a flux layer floats on top of the
galvanizing kettle. A flux layer covers the kettle, and work pieces pass through the
layer when entering and leaving the kettle. For galvanizing other than fence panels,
such as building parts, the kettle flux layer is skimmed to the side and not used.
The flux used by Behlen is called Preact, and is supplied by Mineral Research
Corporation. Preact is 98% zinc chloride, and contains a small amount of potassium
chloride. Behlen uses 16,300 pounds of Preact flux per month. Fencing galvanized
without using the kettle flux always comes out covered with sharp zinc "icicles".
Since the icicles could cut farm animals, the smoother finish obtained by using a kettle
flux is considered necessary.
14
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POLLUTION PREVENTION
AT AN AGING MIDWESTERN MANUFACTURING FACILITY
This report describes the results of an Industrial Pollution Prevention Project (IP3)
demonstration project in Nebraska. The goal of the project was to demonstrate the adoption of
pollution prevention (P2) practices by a rural and aging manufacturing facility.
INTRODUCTION
The manufacturing facility is located in a predominantly agricultural area. The plant site is
a 100 acre area on which several buildings are located -- the largest of which is the manufacturing
facility (805,000 square feet). The facility produces fabricated metal products for farm and industrial
uses including structural steel members and plates, farm gates, fencing, and livestock watering tanks,
in addition to a wide variety of structural bolts, fasteners, etc. Because of the nature of its
manufacturing, the facility is licensed as a hazardous waste generator and is permitted under the
RCRA and NPDES systems.
In its various manufacturing processes, the facility performs many operations including
electroplating, conversion coating, cleaning, machining, grinding, impact deformation, shearing,
welding, sand blasting, hot-dip coating, painting, assembly and testing. Many of these processes
result in the production of a variety of pollutants that have to be disposed of in some fashion
depending on their nature. For example, the electroplating line results in the production of acids and
rinse water containing zinc and chromium, and the hot-dip galvanizing process results in the
production of acids and rinse water containing zinc, lead, and iron, which must be treated as a
hazardous substance containing heavy metals. The painting processes result in the production of
used industrial cleaners, acids, solvents, and chemicals used in the cleaning and degreasing of metal
components.
All process wastewaters produced at this facility are treated in accordance with stipulations
of the discharge permit. The wastewater is treated by lime and polymer addition and pH adjustment
before discharge. In the past, waste disposal at this facility has resulted in potential problems to both
surface and ground water resources in the area. The waste disposal systems at the facility constitute
a major expense. The management at the facility recognized that the economic viability of the
facility depended on reducing pollution control expenses and lowering or eliminating the burden of
regulation the company must endure.
P2 OPPORTUNITY ASSESSMENT
A work plan for the P2 assessment program was developed identifying several tasks,
including:
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1. Development of a detailed assessment and evaluation of current practices and
characterization of all wastes produced by the facility.
2. Identification and delineation of all possible P2 opportunities.
3. Economic and technical evaluation of all waste prevention and minimization alternatives
including short-term as well as long-term impacts of these alternatives.
4. Development of recommendations to be made to the management of the manufacturing
facility for P2 implementation that would be based on economic priority in terms of greatest
benefit and shortest pay-back periods.
5. Providing technical assistance, where appropriate, during the process of implementation
of the recommended alternatives.
6. Review of the results and impacts after implementation of the recommendations.
In developing the work plan, a multi-media approach was emphasized in developing
pollution prevention and minimization strategies affecting all operations and processes.
The waste stream evaluation process conducted at the facility followed procedures outlined by the
U.S. Environmental Protection Agency (see References section at the end of this report: U.S. EPA,
1990; 1992; 1993).
In conducting the P2 opportunity assessment, emphasis became focused on finding those
areas where the impact on reducing the total pollutant load produced by this facility could be the
greatest. Those areas were the electroplating, hot-dip galvanizing and the painting lines as well as
the tube-mill production area. Because these areas produced the bulk of the wastes with the greatest
toxicity and hazard, it was judged that improvements in these areas would produce the greatest
impacts.
The Electroplating Systems
The manufacturing facility operates both an automated line and a manual electroplating line.
These lines are used to deposit a thin zinc film onto small items such as bolts, fasteners and nuts,
which are then used in the construction of larger plant products such as farm buildings. The
automatic electroplating line is a barrel system which plates about 65 kgs (145 Ibs) of work per load.
The barrels are moved by a conveyor chain.
The automated electroplating line processes an average of 65 kgs (145 Ibs) of work pieces
per barrel. There are 36 stations on the line, with an approximate cycle time of 3.5 minutes at each
station (about two hours per barrel). The work is first cleaned in a soak cleaner and an
electrocleaning solution. It is then rinsed, pickled in a hydrochloric acid bath, and rinsed again
before going into a chloride-zinc electroplating bath. After residing in the plating bath for about an
hour and ten minutes (20 stations), the work is rinsed. A light yellow chromate finish is added. A
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short rinse (20 seconds) follows the chromating process after which the work is dried at 65°C
(150°F). The electroplating solution is circulated through a filter to remove impurities. Particles
removed by the filter are rinsed into the treatment system. The total rinse water use in the automatic
electroplating line at this facility was estimated at 166 liters per minute (20 gpm) during 8 hours of
operation daily.
The manual process is more operator intensive, which requires hand moving of barrels from
station to station. The barrels are bigger, but the average load of work per barrel is also 65 kgs (145
Ibs). This line is used more often than the automated line, especially when small quantities need to
be plated. The work is cleaned in a soak cleaning bath (no electrocleaning) for about 15 minutes.
It is then rinsed, pickled in hydrochloric acid, and rinsed again before being placed in the chloride-
zinc electroplating tank (stainless steel pieces are dipped in nitric acid, instead of hydrochloric acid).
The work pieces are plated for an average of 1 to 1.5 hours before being removed from the tank. A
short rinse precedes the chromate coating; which can be clear or yellow, depending on customer
preference. After a final short rinse, the pieces are placed on a table to air dry. A more detailed
analysis of these electroplating lines is given by Parr (1994).
Pollution Prevention Opportunities in the Electroplating Systems
House Keeping Practices. To obtain better product quality and assure that the lower flow
rates will not compromise rinsing efficiency, it was recommended that housekeeping practices be
changed. There needed to be a thorough cleaning of the electroplating area including all tanks
(inside and out), floor, and all equipment related to the electroplating process. A system needed to
be established for recording when maintenance is done, tanks are emptied, chemicals are added, and
testing on tank parameters is performed (e.g. pH, temperature, chemical concentration).
Rinse Water Use. The suggested process changes were designed to reduce waste of both
rinse water and electroplating chemicals. To achieve these reductions, improved cleanliness and
more careful chemistry control were required. It was recommended that the rinse rates be reduced
to decrease the amount of wastewater being discharged to the treatment plant. For both the
automated and manual electroplating lines, reactive rinsing was recommended in order to decrease
water use from the rinses following the acid dip (pickling) and alkali cleaning processes (Tsai and
Nixon, 1989; Hunt, 1988). Water from the rinse after pickling would no longer go down the drain,
but would instead flow to the rinse tanks following alkali cleaning. Rinse water flow calculations
showed that for these two processes, the required flow on each line could be as low as 8 liters per
minute (2 gpm) (Durney, 1984).
At this plant, it was found that the effluent from the rinsing step after the acid dip could be
directed to the rinse tanks after the cleaning process. This change would save a total of about 76 m3
(20,000 gal.) of water per day resulting in a cost savings of about $150 per day in waste treatment,
sludge disposal, and water costs. Counter-current tanks similar to those on the automated line (after
the cleaning and acid dip processes) would be needed on the manual line to incorporate this change.
The cost of these counter-current tanks was estimated at $ 1,000.
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It was recommended that the rinse processes after the electroplating tanks on both the
automatic and manual lines be changed to counter-current with a rinse flow rate of 20 liters per
minute (5.3 gpm) each. About 24 m3 (6,400 gal.) of water per day can be saved, resulting in a cost
reduction of $50 per day. The cost associated with these changes was estimated at $1,000 for the
counter-current tank system.
Electroplating Chemistry. The testing of chemical and operating parameters in the tanks
needed to be done on a daily basis for several variables. Electroplating tank variables included pH
and temperature in addition to the concentrations of cleaners, acid dips, zinc metal, boric acid, total
chlorides, and the wetting agent. Chromating tank variables included pH, temperature, and chromate
concentration.
Other Changes. Other recommended changes that were needed to improve the process
included increasing the temperature of the cleaning tanks on the automatic line from 71 °C to 93 °C
(160°F to 200°F). It was noted that a certain amount of grease originating at the machining steps
of bolt production was accumulating in the automatic electroplating line's cleaning tanks. Grease
skimming from the top of the cleaning tanks needed to be improved to remove more of the grease
and oil before it carries over into the downstream processes. The filtering system on the
electroplating tanks needed to be repaired, as it was inoperative. Once the filtering system is repaired
(on both lines), it should be possible to determine if these systems are adequate to maintain
contaminants at proper low levels. In fact, it was recommended that a new filtering system be
installed.
It was noted that anode bags should be used to keep contaminants and dirt from the zinc balls
out of the electroplating solution. Also, a drain board needed to be installed over the drip tank after
the chromate rinse (on the auto line) to direct all dragout back into the rinse tank.
By using a trivalent chrome conversion coating process instead of the hexavalent chrome
process that was being used, the facility should reduce the toxicity of the waste produced. Lower
treatment costs would be realized since hexavalent chrome must be chemically reduced to its
trivalent form, which is less expensive to treat, before sending it to waste treatment plant. The
potential disadvantages of these changes would be: a slight reduction in corrosion protection, the
need for closer monitoring and testing of the process, and that trivalent chrome coats are only
available in a bright blue color instead of the customary light yellow.
To recapture some of the chemical dragout from the electroplating and chromating, it was
recommended that still rinse tanks be used after these processes. It is estimated that about 50% of
the chemical lost to dragout can be recaptured by this method (Hunt, 1988). It was also
recommended that air agitation be used in the tanks to increase rinsing efficiency.
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The electroplating process should be supplied with as clean a water as possible. It was noted
that the facility had a reverse osmosis (RO) purification unit which was not in use, so it was
recommended that the RO unit be used to supply water to the electroplating, chromating, and still
rinse tanks. This change would remove potential contaminants in tap water including total dissolved
solids (TDS) and hardness, thereby increasing process efficiency.
The barrel withdrawal rates were measured at 5.2 m/min (17 ft/min) in the automated line
and 8.2 m/min (27 ft/min) in the manual line. According to Foecke (1993), the maximum rate of
withdrawal should be about 2.4 m/min (8 ft/min). This change would help decrease the amount of
dragout from each tank resulting in decreased chemical usage.
It was also recommended that the hang time of the barrels over the tanks be increased by
pausing longer before moving to next station. The barrel hang time on the auto line was 23 seconds.
There was still significant dripping from the barrels after this time period. The hang time over tanks
on the manual line varied according to operator discretion. For the most part, hang time was
observed to be minimal, and dragout was consequently significant.
Results of Implemented Changes in The Electroplating Systems
Recommended changes to the automatic electroplating line were presented to the facility. To
date, four recommendations have been implemented, the results of which are summarized in this
section.
The first recommendation to be implemented was to clean the outside and inside of all the
tanks on the plating line and remove bottom sludge that had developed. In particular, the bath
contents of the electroplating tank were pumped into a temporary holding tank and the bottom sludge
was shoveled into eight 55-gallon drums for disposal (this sludge is not listed as hazardous under
RCRA regulations). The liquid portion of the plating bath was then pumped back into the plating
tank and additional chemicals and water were added to restore them to normal levels.
Another recommendation that was implemented was regular testing of the cleaning, acid dip,
electroplating, and chromating processes to maintain chemical concentrations at their optimum
levels.
The third implemented recommendation was the hiring of an employee with suitable
chemistry background to perform operational control testing (among other duties including the
galvanizing system chemistry, as discussed below) and report results back to the plating operator so
that any required chemical additions can be made. The results of this testing are being documented,
and chemical additions are now being made on a regular basis.
The fourth implemented recommendation was the reducing of all rinse flows. Flow control
devices have been installed on the rinses after the alkaline cleaning and acid dip processes to
maintain flow rates at the recommended levels. The two systems have not been connected together
as was recommended. The flow rate for the two rinses after electroplating also have been reduced,
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although neither a countercurrent system nor flow control devices have been installed. The new rates
have not been measured, and it has also not been determined if they are being maintained at a
consistent level. According to the plating operator, the valves controlling flow are not turned on as
far as in the past. The flows still appear to be above recommended levels (as judged by visual
observation), but until flow control valves are installed or some other way of producing a consistent
flow is devised, the current method will be continued.
The implemented changes also have resulted in significant product quality increases as
evidenced by the results of the 5% neutral salt spray testing (as per ASTM B-l 17) done on bolts
plated on the automated line before and after the changes were initiated. These results are presented
in Table 1 below, and show a 1,000% increase in white rust protection and a 550% increase in red
rust protection.
Table 1. Results of 5% neutral salt spray tests
Parameter
Hours to White Rust
Hours to Red Rust
Pre-Change
Results
16
48
Post-Change
Results
168
264
Typical
Values
96 - 250
200 - 350
In conclusion, the facility has been very encouraged by these positive results. Also,
from a waste prevention and minimization perspective, the implemented changes have been
effective. The reduction in rinse flows will no doubt lead to less wastewater needing to be treated
at the waste treatment plant. The cleaning of tanks, removal of sludge, and use of oil absorbent pads
on the cleaning baths should help reduce the drag-out of dirt, grease, and other contaminants to
downstream processes. This will help to increase bath life which will result in fewer bath dumps and
reduced chemical use. The costs associated with these implemented changes have been modest.
The Galvanizing System
The galvanizing process at the facility is a five-step procedure consisting of pickling, rinsing,
prefluxing, galvanizing, and final rinsing. The pickling step prepares work for galvanizing by
removing oxides from the steel surface using a 10% sulfuric acid solution at a temperature of 70°C
(158°F). The work pieces are dipped in the pickling acid for varying lengths of time, and then taken
away to be rinsed.
After pickling, work pieces are rinsed to remove the acid. The preferred rinsing method is
to dip work pieces in the rinse tank, which is filled with unheated municipal water. The rinse water
is agitated by moving the work pieces back and forth in the rinse tank.
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After the first rinsing, work pieces are placed in the preflux tank, which is a crucial step in
the "dry kettle" galvanizing process. The work is coated with flux chemicals (ZnCl2 and NH3C1)
prior to entering the zinc kettle. The preflux tank is kept at 70°C. Normally, the preflux solution
should be allowed to dry thoroughly before proceeding with galvanizing.
Galvanizing is accomplished by immersing steel in a tank filled with molten zinc for 2 to 3
minutes. Livestock fencing, the majority of the steel galvanized at this plant, uses the wet kettle
galvanizing method. This means that a flux layer is floated on top of the galvanizing kettle. A flux
layer covers the kettle, and work pieces pass through it as they enter and leave the kettle. For
galvanizing other materials such as building components, the kettle flux layer is skimmed to the side
and not used.
The work pieces are cooled by rinsing them in a second rinse booth located next to the
galvanizing kettle. This final rinse is needed to cool the work to below 200°C (390°F), which stops
the possible growth of a brittle zinc-steel alloy layer. Cooling also makes it easier for operators to
handle the work pieces. A detailed analysis of the galvanizing system at this facility is given by
Montag(1993).
Pollution Prevention Opportunities in the Galvanizing Process
Pollution prevention efforts in the galvanizing area were concentrated on reducing the
volume and metal content of rinse water since this is the principal medium through which metal is
lost. Volume reductions can be accomplished by installing additional galvanizing equipment. Metal
content reductions are possible by either discontinuing use of the kettle flux, or switching to a
different kettle flux.
Rinse Water Use. The galvanizing system at this plant initially used about 265 m3 of rinse
water per day. Flow through the first rinse booth was measured during the waste stream assessment
period at 1,200 liters per minute. Freshly galvanized pieces are cooled in the second rinse booth.
Flow through this booth nowadays is estimated at approximately 1,200 liters per minute, a reduction
in flow which is due to recent modifications after the assessment was completed. The rinse booths
operate only when there are materials to be rinsed being carried through them.
Rinsing in a rinse tank, instead of a rinse booth, after galvanizing is the most important step
in decreasing galvanizing water use. Use of rinse tanks after pickling is also important. The rinse
booths could be replaced by rinse tanks linked in a counter-current flow arrangement. The benefit
of such a system is that it allows water to be reused several times before it is discharged to the drain,
in addition to the fact that work pieces are always rinsed using the cleanest water as they leave the
process line.
A rinse test was conducted to verify the usefulness of the rinse tank concept. This test
successfully demonstrated the feasibility of continuous-flow rinsing. Based on the results of the
rinse test, a continuous rinse water flow rate of 24 liters per minute (6.3 gal/min) will remove
pickling acid adequately for two rinse tanks in series. This flow rate will adequately cool the work,
-------
preventing the water temperature from rising high enough as to pose a worker safety problem. The
proposed system would use about 35 m3 of water (or less) per day. This represents a savings of
about 83%. One of the changes resulting from the study was the replacement of the spray orifices
(nozzles) in the rinse booths by water-saving (low-flow) ones. This ch'ange resulted in an immediate
reduction in the water use by 60% and resulted in savings in water use and waste treatment costs of
about $250 per day.
The cost of the proposed galvanizing equipment changes is estimated at about $70,000, and
ventilation system improvements required to remove pickling solution vapors from the proposed
pickling tank location would cost $25,000. Due to the expense of the suggested galvanizing changes,
phased installation was recommended. The estimated payback period on the suggested
modifications is about 10 months.
Galvanizing Chemistry. Fencing currently is being fluxed twice: once in the preflux tank,
and a second time as it enters the kettle. For galvanizing of objects other than fence panels (such as
building parts), the kettle flux is skimmed to the side and is not used. The kettle flux is 98% ZnCl2
and contains a small amount of KC1. Kettle flux adds significantly to the metal content of
galvanizing rinse water, so discontinuing the use of kettle flux would enhance pollution prevention.
Prefluxing is crucial in dry kettle galvanizing. To obtain good fluxing, proper concentrations
of ZnCU and NH4C1 must be maintained, and iron and sulfate concentrations must be minimized.
Frequent sampling is required.
In the preflux chemistry, two terms (i.e., degrees Baume (°Be), and Ammonium Chloride
Number (ACN)) are important to the operation of the system. The °Be is a unit of density which is
directly related to the ZnCl2 concentration. Optimum density ranges from 12 to 15 °Be (1.09 g/mL
to 1.12 g/mL), measured at 20°C. The ACN of a preflux is the ratio of the NH4C1 concentration
divided by the concentration of all other components in solution. An optimum ACN value is
difficult to ascertain. In U.S. practice, recommended values range from 1.17, used by most
galvanizers, to 1.8 recommended by Cook (1982). Sjoukes (1990), a galvanizing expert from the
Netherlands, recommends ACN values of 1.75 to 2.5.
The plant currently collects samples of the preflux solution for detailed analysis, including
ACN, three or four times a year. More frequent ACN determinations (at least monthly) are needed
for galvanizing strictly by the "dry kettle" method. This becomes more important if the kettle flux
continues to be used after installing the recommended counter-current flow rinse system. This is
because zinc chloride will be dragged into the preflux from the post-pickling rinse.
In-house testing was recommended for faster data acquisition. It was also recommended that
a chemist be hired to perform chemical testing on a continuous basis. The same chemist would
conduct tests associated with the electroplating lines, as pointed out above.
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Pilot project adds polish
to metal finisher's
pollution prevention efforts
BY M.F. DAHAB AND JIM LUND
AN AGING MIDWESTERN MANUFAC-
turing facility that produces fabricated
metal products for farm and indus-
trial uses was chosen as the site for an
industrial pollution prevention and
waste minimization pilot project The project
goal was to demonstrate that using appropri-
%ate management and operating procedures
can reduce the total pollution produced by an
industrial operation. The facility is a licensed
hazardous waste generator.
The plant engages in a variety of pollu-
tion-generating activities, including electro-
plating, conversion coating, cleaning,
machining, grinding, impact deformation,
shearing, welding, sand blasting, hot-dip
coating, painting, assembly and testing. The
hot-dip galvanizing process results in pro-
duction of rinsewater containing such heavy
metals as zinc and iron. Painting processes
generate used industrial cleaners, acids, sol-
vents, and chemicals used in cleaning and
degreasing metal components.
Process wastewaters are treated by adding tion and minimization opportunities;
lime and polymer, and adjusting pH before • Evaluating economic and technical
discharge. Past disposal practices at the facil- aspects of waste prevention and rninimiza-
ity had threatened area
surface and groundwater.
Waste disposal is a major
operating expense.
Procedures and
methods. The waste-
stream evaluation fol-
lowed Environmental
Protection Agency guid-
ance. A pollution pre-
vention assessment work
plan identified several
tasks, including:
• Developing a
detailed assessment and
evaluation of current
practices, and characteri-
zation of all wastes pro-
duced by the facility,
• Identifying possible pollution preven-
Past disposal
practices at he tacity
bad threatened area
surface and ground-
water. Waste fcposal
is a major operating
expense.
tion alternatives, and
their short- and long-
term impacts;
• Developing rec-
ommendations to man-
agement for
implementation based
on greatest benefit and
shortest payback peri-
ods;
• Providing techni-
cal assistance during
implementation of rec-
ommended alternatives;
and
• Reviewing the
results and impacts on
waste prevention after
implementing the alternatives.
In developing the pilot project:, empha-
Reprinted with permission from the November 1994 issue of Environmental Solutions.
Copyright 6 1994 Advanstar Communications Inc.
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sis was placed on areas in which the impact
on reducing total pollutant load would be
greatest — the electroplating, hot-dip gal-
vanizing and painting lines, and tube-mill
production areas. Strategy development
stressed a multimedia approach to prevent-
ing and minimizing pollution.
Electroplating systems. The facility
operates an automated and a manual elec-
troplating line to deposit a thin zinc film onto
such items as bolts, fasteners and nuts, which
are used to construct larger plant products.
The automatic line is a barrel system that
plates about 145 pounds of work per load.
Barrels are moved by a conveyor chain. An
average of 145 pounds of pieces per barrel
are processed by 36 stations on the line. The
cycle takes about 3.5 minutes per station, or
about two hours per barrel.
The work first is soaked in cleaner and
an electrocleaning solution. It then is rinsed,
pickled in a hydrochloric acid bath, and
rinsed again before entering a chloride-zinc
electroplating bath. After about an 70 min-
utes in the plating bath (20 stations), the
work is rinsed, and a light yellow chromate
finish is added. A short rinse (20 seconds)
follows the chromating process, after which
work is dried at 65 degrees Celsius.
The electroplating solution is circulated
through a filter to remove impurities, which
are rinsed into the treatment system. Total
rinsewater use in the automatic electroplat-
ing line, which operates eight hours a day,
was estimated at 166 liters per minute.
The manual process requires operators
to move barrels from station to station. The
barrels are bigger, but the average load of
work per barrel is the same as in the auto-
mated process. The manual line is used more
than the automated line, especially when
plating small quantities. The work is cleaned
in a soak cleaning bath (no electrocleaning)
for about 15 minutes. It then is rinsed, pick-
led and re-rinsed before entering the chlo-
ride-zinc electroplating tank (Stainless steel
pieces are dipped in nitric acid instead of
hydrochloric acid.) Pieces are plated 60 to
90 minutes before being removed. A short
rinse precedes the chromate coating, which
can be clear or yellow. After a final short
rinse, pieces are placed on a table to dry.
To obtain better product quality and
ensure that the lower flow rates would not
compromise rinsing efficiency, housekeep-
ing changes were recommended. These
included a thorough cleaning of the elec-
troplating area (tanks, floor and electro-
plating process equipment), and a
maintenance recordkeeping system.
The suggestions, designed to reduce nn-
sewater and electroplating chemical waste,
called for improved cleanliness and better
chemistry control. Also recommended was
reducing rinse rates to decrease the amount
of wastewater discharged to the treatment
plant. Reactive rinsing was recommended
for both electroplating lines to decrease water
Use of still rinse tanks
(olio wing electroplating
and chromating was
recommended to
recapture some of the
chemical dragout from
these processes.
use from the rinses following pickling and
alkali cleaning. Pickling rinsewater no longer
would go down the drain, but instead flow
to rinse tanks following alkali cleaning.
Effluent from the rinsing step after the
acid dip could be directed to the rinse tanks
after the cleaning process, saving about 76
cubic meters of water and $150 per day in
waste treatment, sludge disposal and water
costs. Countercurrent tanks similar to diose
on the automated line would be needed on
the manual line to incorporate this change, at
a cost of about $ 1,000. It was recommended
mat rinse processes following electroplating
on both lines be changed to countercurrent
widi a rinse flow rate of 20 liters per minute
each. About 24 cubic meters of water a day
can be saved, saving $50 per day.
Daily testing of chemical and operating
parameters in the tanks needed to be per-
formed for several variables. Electroplating
tank variables included pH and temperature
in addition to concentrations of cleaners, acid
dips, zinc metal, boric acid, total chlorides
and the wetting agent Chromating tank vari-
ables included pH, temperature and chro-
mate concentration.
Other recommended changes included
increasing the temperature of automatic line
cleaning tanks from 71 degrees Celsius to
93 degrees Celsius. Grease skimming needed
improvement, because grease originating
from the machining steps of bolt production
accumulated in the automatic electroplating
line's cleaning tanks. An inoperative filter
system on the electroplating tanks also
needed repairs. Once the repairs are made
on both lines, it should be possible to deter-
mine whether the systems are adequate to
maintain contaminants at low levels;.
Installing a new filtering system was recom-
mended.
Anode bags were recommended to keep
contaminants and dirt from the zinc balls
out of the electroplating solution. Addition-
ally, a drain board was needed over the dri p
tank following the chromate rinse on the
automatic line to direct dragout back to the
rinse tank. By changing to a trivalent-
chrome-conversion coating process instead
of the hexavalent chrome process, the facil-
ity should decrease the toxicity of the waste
it produces. This would save on treatment
costs, because hexavalent chrome must be
reduced chemically to its trivalent form —
which is less toxic and less expensive to treat
— before it is sent to a treatment plant.
Some potential disadvantages of these
changes are a slight reduction in corrosion
protection, the necessity of closer process
monitoring and testing, and the fact that triva-
lent chrome coats are available only in bright
blue instead of the customary light yellow.
Use of still rinse tanks following elec-
troplating and chromating was recom-
mended to recapture some of die chemical
dragout from these processes. This
method should recapture about half of the
chemical lost to dragout. It was also rec-
ommended that air agitation be used in the
tanks to increase rinsing efficiency.
The water supplied to the electroplating
process should be as clean as possible. It was
recommended that the facility's reverse
osmosis purification unit be used to supply
water to the electroplating, chromating and
still rinse tanks. This would remove poten -
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tial contaminants in tap water, including
total dissolved solids and hardness, before
its use in the electroplating line, increasing
process efficiency.
The barrel withdrawal rates were mea-
sured at 5.2 meters per minute in the auto-
mated line and 8.2 meters per minute in the
manual line. The maximum withdrawal rate
should be about 2.4 meters per minute.
Changing this would decrease die amount
of dragout from each tank, resulting in
decreased chemical use.
It was also recommended that the hang
time of barrels over the tanks be increased
by pausing longer before moving to the next
station. Although hang time on the auto-
mated line was 23 seconds, significant drip-
ping from barrels occurred after this time.
Hang time over tanks on the manual line
varied. Generally, hang time was observed
to be minimal, and dragout was significant.
Results of system changes. Several
recommended changes to the automatic
electroplating line were implemented. All
tanks were cleaned, inside and outside, on
the plating line, and accumulated bottom
sludge was removed. The bath contents of
the electroplating tank were pumped into
a temporary holding tank, and nonhaz-
ardous bottom sludge was shoveled into
eight 55-gallon drums for disposal. The liq-
uid portion of me plating bath was pumped
back into the plating tank, and additional
chemicals and water were added to restore
them to normal levels.
Other changes included:
• Regular testing of cleaning, acid dip,
electroplating and chromating processes to
maintain optimal-level chemical concen-
trations;
• Hiring a qualified individual to per-
form operational control testing and work
with the plating operator to make required
chemical additions; and
• Reducing rinse flows, and installing
flow measurement and countercurrent
rinsing.
Flow control devices have been installed
on the rinses following the alkaline clean-
ing and acid-dip processes to maintain flow
rates at recommended levels. The two sys-
tems have not been connected as recom-
mended. Flow rates for the two rinses
following electroplating also have been
reduced* The new rates have not been mea-
sured, so it has not been determined
whether diey are being maintained consis-
tently. The plating operator reports the
valves that control flow are not opened as
far as in the past. Besides decreasing the rin-
sewater flow rate, adding the countercur-
rent system to the manual line should
increase the rinsewater's utility.
Product quality has been increased sig-
nificantly, as evidenced by results of the 5
percent neutral salt spray testing performed
on bolts plated on the automated line before
and after die changes occurred. The results
Tank clearing, sludge
removal and use of oi
absorbent pads on the
cleaning baths should
reduce the dragout of
dft, grease and other
contaminants to down-
stream processes.
show a 1,000 percent increase in white rust
protection and a 550 percent increase in red
rust protection.
From a waste prevention and minimiza-
tion perspective, the changes have been
effective. Reduction in rinse flows should
lead to less wastewater for treatment at an
onsite facility. Tank cleaning, sludge removal
and use of oil absorbent pads on the clean-
ing baths should reduce the dragout of dirt,
grease and other contaminants to down-
stream processes. This will increase bath life,
resulting in fewer bath dumps and reduced
chemical use. Costs of implementing these
changes have been modest.
The galvanizing system. The facili-
ty's galvanizing process consists of pickling,
rinsing, prefluxing, galvanizing and final
rinsing. The pickling step prepares work
for galvanizing by removing oxides from
the steel surface using a 10 percent sulfuric
acid solution at 70 degrees Celsius.
Work pieces are rinsed after pickling.
The preferred method is to dip them in the
rinse tank, which is filled with unheated
municipal water. The rinsewater is agitated
by moving the pieces back and forth in die
tank. After the first rinsing, work pieces are
placed in the preflux tank, a crucial step in
the dry-kettle galvanizing process. Work is
coated with flux chemicals before entering
the zinc kettle. The preflux tank is main-
tained at 70 degrees Celsius. The preflux
solution generally is allowed to dry thor-
oughly before galvanizing.
Galvanizing is accomplished by immers-
ing steel in a tank rilled with molten zinc for
two to three minutes. Most steel galvanized
at this plant uses the wet-kettle method. A
flux layer is floated on top of the galvanizing
kettle, and work pieces pass through it as they
enter and leave the kettle. For galvanizing
materials, such as building components, the
kettle flux layer is skimmed to the side and
not used. Work pieces are cooled by rinsing
them in a second rinse booth next to the gal-
vanizing kettle. This final rinse is needed to
cool the work to below 200 degrees Celsius,
which prevents growth of a brittle ;dnc-steel
alloy layer. Cooling also allows operators to
handle the pieces.
Galvanizing operations. Pollution
prevention efforts in galvanizing were con-
centrated on reducing the volume imd metal
content of rinsewater, as this is the princi-
pal medium through which metal is lost.
Volume reductions can be accomplished by
installing additional galvanizing equipment.
Metal content reductions are possible by
discontinuing use of the kettle flux or
switching to a different kettle flax.
The galvanizing system initially used
about 265 cubic meters of rinsewater per
day. Flow through the first rinse booth was
measured during wastestream assessment
at 1,200 liters per minute. Freshly galva-
nized pieces are cooled in the second rinse
booth. Flow through this booth was esti-
mated at about 1,200 liters per minute. The
rinse booths operate only while materials
to be rinsed are carried through diem.
Rinsing in a tank instead of a booth is
die most important step in decreasing gal-
vanizing water use. Using rinse tanks after
pickling also is important. It was recom-
-------
mended that rinse booths be replaced by
rinse tanks linked in a countercurrent flow
arrangement. This allows water to be reused
several times before being discharged and
ensures that work pieces are rinsed with clean
water as they leave the process line.
A rinse test conducted to verity' die use-
fulness of the rinse tank concept successfully
demonstrated the feasibility of continuous-
flow rinsing. Based on die results, a contin-
uous rinsewater flow rate ot 24 liters per
minute removes pickling acid adequately for
two rinse tanks in series. This flow rate cools
the work, preventing the water temperature
from rising high enough to pose a safety
problem. The proposed system would use
no more than 3 5 cubic meters of water per
day, representing a savings ot about 83 per-
cent. As a result of the study, water-saving
(low-flow) nozzles were installed in the rinse
booths. This immediately reduced water use
by 60 percent, yielding water and waste treat-
ment savings of about $250 per day.
The proposed galvanizing equipment
changes cost about $70,000. Ventilation sys-
tem improvements to remove pickling solu-
tion vapors from the proposed pickling tank
location would cost $25,000. Due to the
expense, phased installation of suggested gal-
vanizing changes was recommended. The
payback period is estimated at about 10
months.
Livestock fencing is being fluxed twice
— once in the preflux tank and again as it
enters the kettle. For galvanizing objects
other than fence panels, kettle flux is not
used. The kettle flux is 98 percent zinc chlo-
ride and contains a small amount of potas-
sium chloride. Kettle flux adds significandy
to the metal content of galvanizing rinse-
water, so that discontinuing its use would aid
pollution prevention.
Prerluxing is crucial in dry-ketde galva-
nizing. To obtain good fluxing, proper con-
centrations of zinc chloride and ammonium
chloride must be maintained, and iron and
sulfate concentrations minimized. Frequent
sampling is required.
Switching from zinc chloride preflux to a
mixture of mosdy ammonium chloride and
some zinc chloride or ammonium chloride
alone was recommended. This probably would
enhance product quality, because the proposed
countercurrent flow system (with fresh water
being added at the final rinse tank) would not
complicate preflux chemistry.
Another problem with the galvanizing
operation was a layer of oil floating on the
surface of the acid bath. The oil could be
minimized by iastalling a skimmer to remove
it periodically or to reduce oil use in the fab-
ricating step.
The painting system. The painting
operation at the facility consists ot washing,
etching, oven drying, spray painting and
oven curing. The plant's painting operation
in 1992 was estimated to have emitted about
37,500 kilograms of xylene and 11,000 kilo-
grams of toluene. Reducing emissions of
these volatile organic compounds should be
was to switch to an
process to reduce
VOC emissions and
eliminate chromic-
a top priority.
Two types of paint are used at the plant.
A solvent-based paint is used for painting
gates, and a silicone polyester paint is used
for coating building panels. Seventy-four per-
cent of die paint used in the automatic paint
line in 1992 was used to paint farm gates.
About 2,200 liters per month of a mixture of
aromatic solvents are used for such purposes
as cleaning paint-supply piping.
The only practical way to reduce VOC
emissions significantly is to change paint
materials. One alternative is to use water-
based paint for the gates. If water-based
paints are applied electrostatically, a high
transfer efficiency can be obtained. The
investment should be relatively small,
because the only facility change required is
installing new spray equipment. Immediate
testing of water-based paints was recom-
mended.
Another suggestion was to switch to an
autophoretic painting process to reduce
VOC emissions and eliminate chromic-acid
etching. This involves dipping metal to be
painted into tanks filled with paint The coat-
ing is deposited via a chemical reaction
between the paint and metal which requires
several minutes of immersion. The auto-
phoretic process resembles electrocoating
but requires no electric current. Metal
painted using this process reportedly has
withstood salt spray tests up to 3,000 hours
without coating failure. The paint report-
edly exhibits a high degree of hardness and
good resistance to chalking from ultraviolet
light exposure.
The estimated cost of an autophoretic sys-
tem to coat gates was $300,000. A serious
drawback of diis method is that color varies
with the dissolved iron concentration in die
paint, which increases slowly due to contact
ot the paint with the steel being painted.
Another drawback is the tact that a separate
paint tank is needed for each color.
Another alternative is powder coating.
Agricultural gates are ideally suited for pow-
der coating, because they are made in only
two colors. Transfer efficiency is not an issue,
because overspray is captured and blended
with fresh powder for reuse, and VOCs are
not emitted. An industrial supply contractor
estimated that powder coating could be
added to the existing paint line for about
$40,000. However, installation costs prob-
ably would be higher, because the automatic
paint line is old and should be replaced. A
new paint line was estimated to cost about
$200,000.
Pollution prevention in die painting area
at this plant will not be offset by significant
savings in disposal costs.However, the Cleim
Air Act will require that action be taken soon.
As a result ot this study, the plant has exper-
imented with water-based paints and
requested bids to construct a powder coat-
ing system.
Tubing manufacture system. A tube
mill at the facility forms metal pipe from
coils of sheet steel. The plant makes tubing
for all its gates and also sells tubing to other
companies. The major tube mill compo-
nents include a coil unwinder, feeder, ini-
tial cold rolls, welder, re-galvanizer, final
cold rolls, metering cutter and coolant dis-
tribution system. A water-based fluid ax)lant
is used to lubricate and cool the tube mill.
-------
About 800 liters of coolant per month are
consumed at a cost of" about $800. The
coolant flows from application points into
sumps below the components. The sumps
drain by gravity to a large collection tank,
which contains an oil removal system con-
sisting of a plastic tube pulled through the liq-
uid coolant. Floating oil adheres to the
polyethylene tube and is removed by a scraper.
However, the oil removal system is unable to
remove oil quickly enough.
Oil in the coolant originates from grease
leaking out of the tube mill gearboxes. Over
the years, oil and grease leaks have covered
the tube mill and the surrounding area.
Grease combines with metal filings created
when excess metal is scraped from fresh
welds. Together, the grease and filings form
a black substance that fills the bottom of the
sumps in about a month. The mill occa-
sionally is shut down while operators scoop
out the grease. About two-thirds of the
coolant is lost each time the sumps are
cleaned, and this is the only time coolant is
discharged from the system.
Recommendations for the tube mill focus
on minimizing grease contamination of the
coolant. The old oil-removal system should
be replaced with a system that would allow
coolant reuse. A suitable unit was estimated
to cost less than S2,500. The payback period
was estimated at less than six months, assum-
ing the coolant's usable life is doubled. If
coolant could be used longer, the payback
period would be shorter.
The coolant also turns rancid. Coolant
rancidity usually is controlled by adding a bio-
cide. If rancidity problems continue after an
improved oil removal system is installed, a dif-
ferent biocide may be needed. Gearbox leak-
age should be prevented or kept from falling
into the sumps through regular maintenance.
In addition, preventing metal filings from
falling into the sump below the weld scraper
would keep them from combining with the
grease. It was recommend that the entire area
be shut down for thorough cleaning, as this
would vastly improve system operation.
Cleaning should include equipment, floor
grates and the return trough. ^]
M.F. Dahab is an associate professor of civil
engineering and biological systems engineering
at the University of Nebraska-Lincoln. Jim Limd
is director of the Industrial Pollution Prevention
Project in the Environmental Protection Agen-
cy's Office of Water.
The project on vchich this report is based iras
funded jointly by EPA and the University of
Nebraska-Lincoln Center for Infrastructure
Research.
More reading
Anonymous, "Steelcase Inc. replaces zinc
plating lines," Finishers Management, March
1992, pp. 17-20.
Cook, T.H., D.E. Mergen and D.L.
Clark, "Increasing profits in hot dip galva-
nizing," .MetalFinishing, Vol. 84, No. 23,
1986, pp. 23-27.
Cook, T.H. and W.S. Horton, "Ammo-
nium chloride control in galvanizing pre-
flux," Metal Finishing, Vol. 80, No. 19, 1982,
pp. 19-23.
Dahab, M.F. and D. Montag, "Waste
minimization in a metal-finishing industry:
A pilot project," Third International Confer-
ence on Waste \Ianagement in the Chemical and
Petrochemical Industries, Salvador-Bahia, Brazil,
Oct. 20-23, 1993.
Dahab, ME, D. Montag and J. Parr, "Pol-
lution prevention and waste minimization at
a galvanizing and electroplating facility," Water
Science and Technology, in press, 1994.
Durney, L.J., Electroplating Engineering
Handbook. Chelsea, Mich.: Lewis Publishers
Inc., 1984.
Hunt, G.E., "Waste reduction in the
metal finishing industry," Journal of the Air
Pollution Control Association, Vol. 38, No. 5,
1988, pp. 672-680.
Montag, D., Pollution Prevention in the
Metal Finishing Industry (master's thesis). Lin-
coln, Neb.: University of Nebraska-Lincoln
Libraries, December 1993.
Sjoukes, F., "Chemical reactions in fluxes
for hot dip galvanizing," Anti-Corrosion Meth-
ods and Materials, Vol. 37, No. 4, 1990, pp.
12-14.
Parr,J., Waste Minimization Opportuni-
ties for the electroplating industry: A Case Study
(M.S. thesis). Lincoln, Neb.: University of
Nebraska-Lincoln Libraries, February 1994.
Tsai, E.C. and R. Nixon, "Simple tech-
niques for source reduction of wastes from
metal plating operations," Hazardous Waste
& Hazardous Materials, Vol. 6, No. 1, 1989,
pp. 67-78.
U.S. Environmental Protection Agency,
Guides to Pollution Prevention-The Fabricated
Metal Products Industry. Washington, D.C.,
EPA Report No. EPA/625/7-90/006, July
1990.
Facility Pollution Prevention Guide.
Washington, D.C., EPA Report No.
EPA/600/R-92/088, May 1992.
.-I Primer for Financial Analysis of
Pollution Prevention Projects. Washington,
D.C., EPA Report No. EPA/600/R-93/059,
April 1993.
University of Tennessee Center for
Industrial Services. Waste. Reduction Assess-
ment and Technology Transfer, 2nd edition,
9/22-9.
Wentz, CA Hazardous Waste blanagement
New York: McGraw-Hill Book Go., 1989.
©Reprinted from ENVIRONMENTAL SOLUTIONS, November 1994
AN ADVANSTAR PUBLICATION Printed in U.S.A.
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INDUSTRIAL POLLUTION PREVENTION PILOT PROJECT
A Summary Report
Introduction
This project is intended to develop an industrial pollution prevention and minimization
pilot project in Nebraska. The goal of the project is to demonstrate that through proper
management and operating practices, the total pollution produced by an industrial operation can
effectively be reduced significantly. The net effect of this pollution prevention program is to
improve the economic net-worth of the industry by lowering expenditures on pollution control
measures as well as minimizing the burden of regulation imposed by the government. Behlen
Manufacturing Company of Columbus, Nebraska, has agreed to be the demonstration site for
this project.
Behlen Manufacturing is an employee-owned facility engaged largely in the production
of fabricated metal products for farm and industrial uses. The facility is located in Columbus,
NE in a predominantly rural area. The plant site is a 97 acre area on which several buildings
are located. The largest of these buildings is a 805,000 square foot manufacturing facility and
a 42,000 square foot office complex. Because of the nature of its manufacturing, Behlen is
permitted under the RCRA and the NPDES systems.
In its various manufacturing processes, Behlen performs many operations including
electroplating, conversion coating, cleaning, machining, grinding, impact deformation, shearing,
welding, sand blasting, hot-dip coating, painting, assembly and testing. Many of these processes
result in the production of a variety of pollutants (gaseous, solid, and liquid) that have to be
disposed of in some fashion depending on their nature. For example, the hot-dip galvanizing
process results in the production of rinse water which must be treated as a hazardous substance
containing heavy metals (e.g. zinc and iron) in addition to being highly corrosive. The painting
processes result in the production of used industrial cleaners, acids, hexavalent chromium,
solvents, and chemicals used in the cleaning and de-greasing of metal components.
All process wastewaters produced at this facility are treated in accordance to stipulations
under the NPDES permit. The wastewater is treated by lime and polymer addition and pH
adjustment before discharge to the Loup Power Canal. In the past, waste disposal at this facility
resulted in potential problems to both surface and ground water resources in the area. The waste
disposal systems at Behlen undoubtedly constitute a major expense to this facility. The
management at Behlen welcomes any improvement in its economic picture by reducing its
pollution control expenses and lowering or eliminating the burden of regulation the company
must endure.
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Project Tasks
In developing the demonstration pilot project at Behlen, emphasis was placed on areas
where the impact on reducing the total pollutant load produced by this facility was greatest.
These areas are electroplating, hot-dip galvanizing, the painting line, and the tube-mill area. As
pointed out above, these areas produce the bulk of the wastes with the greatest toxicity and
hazard, and consequently any improvements in these areas should result in the greatest impacts.
In developing a work plan, a multi-media approach was emphasized in developing pollution
prevention and minimization strategies affecting all operations and processes at Behlen. The
work plan consisted of several tasks. These tasks are summarized as follows:
1. A detailed assessment and evaluation of the current practices in the areas identified above
along with a detailed characterization of all wastes (gaseous, liquid, and solid) produced
at this facility.
2. Identification and delineation of all possible pollution prevention and minimization
opportunities.
3. Economic and technical evaluation of all waste prevention and minimization alternatives
including short as well as long term impacts of these alternatives.
4. Recommendation to Behlen Manufacturing for implementation based on economic
priority in terms of greatest benefit and shortest pay-back periods.
5. Providing technical assistance, where appropriate, to Behlen during the process of
implementation of the recommended alternatives.
6. Review of the results and impacts on waste prevention after the implementation of the
alternatives.
7. Development of a demonstration program involving technical workshops, if appropriate,
and informational materials such as capsule and summary reports for use by interested
individuals and corporations.
8. Reporting of the study results to the U.S. EPA in generic terms for use by other
industries with similar processes and operations.
This report provides a summary of all activities completed to date and essentially covers
Tasks 1 through 4, as identified above. A detailed summary report will be provided to Behlen
Manufacturing at the conclusion of this study.
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Project Recommendations
The initial phases of this study were begun in early 1992 with a detailed waste stream
assessment of all operations at Behlen Manufacturing. In this report, the recommendations
presented to Behlen for consideration are discussed sequentially by process category, as indicated
above.
Galvanizing
The galvanizing process at Behlen is a five step process consisting of pickling, rinsing,
prefluxing, galvanizing, and final rinsing. Pollution prevention efforts in the galvanizing area
should concentrate on reducing the volume and metal content of rinse water since this is the
principal medium through which metal is lost. Volume reductions can be accomplished by
installing additional galvanizing equipment. Metal content reductions are possible by either
discontinuing use of the kettle flux, or switching to a different kettle flux.
Rinse Water Use
The galvanizer uses about 55,000 gallons of rinse water per day. The rinse booth located
between the acid tank and the rinse tank is used for spray rinsing after pickling. Flow through
the booth was measured during the waste stream assessment period at 300 gallons per minute.
Freshly galvanized pieces are cooled in the booth next to the galvanizing kettle. Flow through
this booth these days is estimated at approximately 300 gallons per minute. The flow rate
estimate for the second rinse booth has been reduced to reflect recent modifications after the
assessment was completed.
Rinsing in a rinse tank (instead of a rinse booth) after galvanizing is the most important
step in decreasing galvanizing water use. Use of rinse tanks after pickling is also important.
As discussed at the March 19th meeting at Behlen, the rinse booths could be replaced by rinse
tanks linked in a counter-current flow arrangement as shown in Figure 1. The benefit of such
a system is that it allows water to be reused several times before it goes down the drain, in
addition to the fact that work pieces are always rinsed using the cleanest water as they leave the
process line.
A rinse test was conducted on April 1, 1993 which successfully demonstrated the
feasibility of continuous-flow rinsing. Based on the results of the rinse test, a continuous rinse
water flow rate of 7 gallons per minute will remove pickling acid adequately for two rinse tanks
in series. A flow rate of 7 gpm flow will cool the work, preventing the water temperature from
rising high enough as to pose a worker safety problem.
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The proposed system would use about 10,000 gallons per day. This represents a savings
of about 45,000 gallons of water per day. The cost of these proposed galvanizing equipment
changes is estimated at about $70,000, and ventilation system improvements required to
remove pickling solution vapors from the proposed pickling tank location would cost $25,000.
Due to the expense of the suggested galvanizing changes, phased installation is recommended.
The final cooling tank could be added first and linked to the existing system as shown in Figure
2.; entitled Interim Solution. For a cost of about $17,000, the rinse tank at the West end of
the line could be installed in a pit on the East end where the second rinse booth is now located.
The costs and payback periods for the recommended galvanizing system and for the
recommended interim solution are summarized in Table 1.
Table 1. Costs and pay-back periods for the recommended changes to the galvanizing line.
OPTION
Adding 3 rinse tanks as in
Figure 1 - Proposed System
Using the existing rinse
tank in place of the second
rinse booth as in Fig. 2
COST
$95,000
$17,000
PAYBACK
10 months
3 months
Galvanizing Chemistry
Fencing currently is being fluxed twice: once in the preflux tank, and a second time as
it enters the kettle. For galvanizing of objects other than fence panels (such as building parts),
the kettle flux is skimmed to the side and is not used. The kettle flux is called Preact, and is
supplied by Mineral Research Corporation. Preact is 98% zinc chloride, and contains a small
amount of potassium chloride. Behlen uses 16,300 pounds of Preact each month, at a cost of
about $8,500. Kettle flux adds significantly to the metal content of galvanizing rinse water, so
discontinuing the use of kettle flux would enhance pollution prevention.
Prefluxing is crucial in dry kettle galvanizing. The preflux tank holds a solution of zinc
chloride (ZnCl2) and ammonium chloride (NH4C1). To obtain good fluxing, proper
concentrations of ZnCl2 and NH4C1 must be maintained, and iron and sulfate concentrations
must be minimized. Frequent sampling is required.
Two preflux chemistry terms which may be unfamiliar are degrees Baume (°Be), and
Ammonium Chloride Number (ACN). The °Be is a unit of density. Preflux density is directly
related to the ZnCl2 concentration. Optimum density ranges from 12 to 15 °Be (1.09 g/ml to
1.12 g/ml) as measured at 70 to 75°F. The ACN of a preflux is the ratio of the NH4C1
concentration divided by the concentration of all other components in the solution. Opinions
-------
about the best ACN differ. For example, Mineral Research Corporation recommends 1.17 while
Dr. T.H. Cook (America's most prominent galvanizing researcher) recommends 1.4 to 1.8, and
F. Sjoukes (European galvanizing expert) recommends 1.75 to 2.5. Every three or four months,
Mr. Dick Robak (of Behlen) sends a preflux sample to Mineral Research Development Corp.
of Charlotte, N.C. Mineral Research performs a detailed analysis, including ACN. More
frequent ACN determinations (about every 2 weeks) would be helpful in attempting to galvanize
strictly by the "dry kettle" method.
If the kettle flux continues to be used after installing a counter flow rinse system,
frequent preflux sampling will be needed in order to maintain a proper ACN. This is because
zinc chloride will be dragged into the preflux from the post-pickling rinse. The magnitude of
zinc chloride drag-in will be established when samples taken at Behlen during a June 16th rinse
test are fully analyzed. Tony Raimondo Jr. (of Behlen) indicated that Mineral Research
Development would probably be willing to analyze samples more frequently, and that they would
still provide the service for free. Also, in-house preflux testing is possible. In his article:
"Ammonium Chloride Control in Galvanizing Preflux," Cook (1982), Dr. T.H. Cook described
a procedure for determining ammonium chloride concentration. The procedure is relatively
simple, but it utilizes strong a strong acid and a strong base, and therefore, an experienced
chemist should perform the test. It should be possible for either Mr. Will or Mr. Zobel (of
Behlen) to conduct such a test.
In addition, if a kettle flux must be maintained, it would be helpful to switch to one that
is a mixture of zinc chloride and ammonium chloride, or even to pure ammonium chloride. Use
of pure ammonium chloride kettle flux is described by F. Sjoukes in an article entitled:
"Chemical Reactions in Fluxes for Hot Dip Galvanizing" (Sjoukes, 1990). A different kettle
flux would probably give better results, and with different flux, the proposed counter flow
system with fresh water being added to the final rinse tank would not complicate preflux
chemistry.
Another problem associated the galvanizing operation is the oil floating on the surface
of the acid bath. This is not surprising since there is no caustic cleaning stage prior to pickling.
The oil problem could be minimized by installing a trough into which oil can be skimmed
periodically. An attempt should be made to minimize oil on steel to be galvanized.
Painting
Painting is a sequential process consisting of washing, etching, oven drying, spray
painting, and oven curing. The paints used at Behlen are of the traditional solvent based variety,
and contain volatile organic compounds (VOC's). Last year the painting operation was estimated
to have emitted about 82,000 pounds of xylene, and 23,000 pounds of toluene. Xylene and
toluene are defined as hazardous by the 1990 Clean Air Act, and will be regulated strictly in the
near future, so reducing emissions of these VOC's should receive a high priority.
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The two major types of paint in use at Behlen are Farmmaster paint, which is used for
painting gates, and Pratt and Lambert silicone polyester paint, which is used for painting
building panels. Last year (1992), 34,567 of the 47,312 gallons of paint consumed by the
automatic paint line were used in painting gates. Additionally, large quantities of a solvent
named "Vanblend 99" are used. This is a mixture of several aromatic solvents, and is used with
Farmmaster paint for such purposes as line cleaning between colors. Approximately, 570
gallons of Vanblend 99 are consumed each month.
Painting Alternatives
The only practical way to significantly reduce VOC emissions is to change paint
materials. There are several possible materials from which to choose.
One choice is to use water based paint for gates, which accounts for over 70% of
Behlen's paint use. If water based paints are applied electrostatically, a high transfer efficiency
can be obtained. New spraying equipment is all that would be required to make this change,
and therefore, the investment should be minimal. George Werner has reservations about water
based spray painting systems, so there are no plans to test such equipment.
With regard to painting, it is necessary that everyone concerned be kept aware of the
importance of making progress toward reducing VOC emissions. Something really needs to be
done about VOC's, and since using water based paint is the lowest cost solution, testing of water
based painting alternatives should be conducted.
Another way to reduce VOC emissions from painting gates; and possibly to eliminate
chromic acid etching of galvanized building panels; is to switch to an autophoretic painting
process; an example of which is manufactured by Parker Amchem. This process involves
dipping metal to be painted into tanks filled with paint. Immersion is required because the
coating is deposited by a chemical reaction between the paint and the metal which takes several
minutes to occur. The autophoretic process resembles electrocoating, except that no electric
current is required. Metal painted by this process reportedly has withstood salt spray tests of
up to 3,000 hours without coating failure. The paint exhibits a high degree of hardness, and
good resistance to chalking from ultraviolet light exposure. An autophoretic system to coat gates
would cost about $300,000. Parker Amchem has never built an autophoretic coating system
large enough to coat building panels, so detailed analysis would be required to ensure that it is
possible. Another difficulty is that the red and green vary somewhat in color. The variation
is due to the changing iron content of the paint as corrosion products enter the paint and as
makeup chemicals are added. Since each color requires a separate tank, and building panels
come in several colors, the only color which would be practical for building panels probably is
a clear coating which could be used as a base coat for pigmented paints. Since an autophoretic
coating is a good primer, the top coat can be an inexpensive paint. Companies using this system
have reported the cost of applying autophoretic paint to be about 3 cents per square foot. Parker
8
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Amchem is willing to assist Behlen in planning an autophoretic coating system.
Agricultural gates are ideally suited to powder coating because they come in only two
colors. Transfer efficiency is not an issue in powder coating because overspray is captured and
blended with fresh powder for reuse. Powder coating gates would eliminate VOC's from about
70% of the current production. Industrial Finishing Systems, which is one of Behlen's long-time
painting equipment suppliers, indicated that powder coating could be added to the existing paint
line for as little as $40,000. Unfortunately, the real cost of a powder coating system would be
much higher. This is because the automatic paint line is quite old, so powder coating should
be installed on a new line. A new line would cost about $200,000. The pollution prevention
measures in the painting area probably will not pay for themselves in terms of reduced current
waste disposal costs, but Clean Air Act requirements will soon mandate that action be taken.
Estimates of the installation costs for various painting alternatives are shown in Table 2.
Table 2. Estimated costs of painting alternatives.
OPTION
Water Based Spray Painting
Autophoretic Coating
Powder coating
COST
$25,000a
$300,000
$200,000
Approximate; industrial rimsning Systems is preparing a detailed estimate.
Tubing Manufacture
A water-based fluid coolant (Metkool 711) is used by Behlen for lubrication and cooling
of the tube mill. About 195 gallons per month are consumed at a cost of about $800. The
coolant flows from its application points into sumps below the components, and the sumps, in
turn, drain by gravity to a large collection tank. The collection tank contains an oil removal
system, consisting of a plastic (tygon) tube pulled through the liquid coolant. Floating oil
adheres to the polyethylene tube, and is removed by a scraper. The oil removal system is not
able to remove oil fast enough.
The oil in the coolant comes from grease leaking out of the gearboxes. In addition, oil
and grease cover the tube mill and the surrounding area. Grease and metal filings from the;
scarfer combine to make a black substance that fills the bottom of the sumps in about a month.
The mill is occasionally shut down while operators scoop out all the grease. About two-thirds;
of the coolant is lost each time the sumps are cleaned, and this is the only time coolant is
discharged from the system.
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Recommended Tube Mill Changes
Recommendations for the tube mill are mostly concerned with changes which would
minimize grease contamination of the coolant:
The old oil removal system needs to be replaced. A suitable oil removal system can be
furnished by Production Supplies Inc. An efficient oil removal system should allow the coolant
to be used for several times its current life. The new oil removal unit only costs $2,500.
Doubling the coolant's useable life would pay for a new oil removal system in 6 months.
Beyond that, the actual pay-off period could be even shorter.
There is a problem with the coolant turning rancid. Coolant rancidity is usually
controlled by adding one of several possible biocides. If rancidity problems continue after an
improved oil removal system is installed, a new biocide may be needed.
It should be possible to prevent gearbox leakage, or at least reduce leakage from falling
into the sumps through regular maintenance. Also, preventing metal filings from falling into the
sump below the scraper which removes excess metal from the fresh weld, and thus keep them
from combining with the grease.
We strongly recommend shutting down the entire area for a short period of time for a
thorough cleaning. This would vastly the improve operation of the system. The cleaning should
include all equipment, floor grates, and the return trough.
Automated and Manual Electroplating
Behlen Manufacturing currently operates both an automated and a manual electroplating
line. The processes are shown in Figures 3 and 4. These lines are used to deposit (electroplate)
a thin zinc film onto small items such as nuts and bolts, which are then used in the construction
of larger plant products such as farm buildings.
The automated electroplating line processes an average of 140 pounds of work per barrel.
There are 36 stations on the line, with an approximate cycle time of 3.5 minutes at each station
(about two hours per barrel). The work is first cleaned in a soak cleaner and an electrocleaning
solution. It is then rinsed, pickled in a hydrochloric acid bath, and rinsed again before going
into a chloride-zinc electroplating bath. After being in the plating bath for about an hour and
ten minutes (20 stations), the work is rinsed. A light yellow chromate finish is added. A short
rinse (20 seconds) follows the chromating process after which the work is dried at 150 F.
The manual process is more operator intensive, which requires hand moving of barrels
from station to station. The barrels are bigger but the average load of work per barrel is still
140 pounds. This line is used more often than the automated line, especially when small
quantities need to be plated. The work is cleaned in a soak cleaning bath (no electrocleaning)
10
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for about 15 minutes. It is then rinsed, pickled in hydrochloric acid, and rinsed again before
being placed in the chloride-zinc electroplating tank (stainless steel pieces are dipped in nitric
acid, instead of hydrochloric acid -- this does not occur often). The work is plated for an
average of 1 to 1.5 hours before being removed from the tank. A short rinse precedes the
chromate coating; which can be clear or yellow, depending on customer preference. After a
final short rinse the pieces are placed on a table to air dry.
Recommended Changes to the Electroplating Process:
Rinse rates should be reduced to decrease the amount of wastewater being discharged to
the treatment plant. We believe that the rinse flow rate after the cleaning and acid dip processes
on both, the automated and manual electroplating lines, can be reduced to as low as 2 gallons
per minute (gpm). This value needs to be confirmed by actual rinse testing (as should the other
rinse changes recommended). The effluent from rinsing after the acid dip should be directed
to the rinse tanks after the cleaning process. This change would save a total of about 19,000
gallons of water per day resulting in a cost savings of about $150.00 per day for waste
treatment, sludge disposal, and water costs. Counter-current tanks similar to those on the
automated line (after the cleaning and acid dip processes) will be needed on the manual line to
incorporate this change. The cost of these counter-current tanks is estimated at $1,000.00. The
estimated cost of flow control nozzles to maintain the 2 gpm flow rate is about $45.00. A
summary of costs associated with changes in the electroplating line are shown in Table 3.
The rinse process after the electroplating tank on both the automatic and manual lines
should be changed to counter-current with a rinse flow of 5 gpm. About 6000 gallons of water
per day can be saved resulting in a cost reduction of $50.00 per day. The costs associated with
these changes are estimated at $1,000 for the counter-current tanks system and $45 for the flow
control nozzle.
To obtain better product quality and assure that the lower flow rates will not compromise
rinsing efficiency it is recommended that housekeeping practices be changed. There needs to
be a thorough clean-up of the electroplating area including the tanks (inside and out), floor, and
all equipment related to the electroplating process. Records should be kept to show when
maintenance is done, tanks are emptied, chemicals are added, and testing on tank parameters is
done (e.g. pH, temperature, chemical concentration). The testing of tank parameters should be
done on a daily basis for such variables as temperature and concentration of the cleaners,
concentration of the acid dips, zinc metal, boric acid, total chlorides, pH, and the wetting
solution in the electroplating tanks as well as pH, temperature, and concentration of the chromate
in the chromating tanks.
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Other recommended housekeeping changes needed to improve the process include
increasing the temperature of the cleaning tanks on the automatic line from 160°F to 180°F.
Grease skimming from the top of the cleaning tanks must be improved to remove more of the
grease and oil before it carries over into the downstream processes. The filtering system on the
electroplating tanks needs to be repaired or improved. Once the current filtering system is
repaired (on both lines), it will be possible to determine if this system is enough to maintain
contaminants at proper levels. It is recommended that a new filtering system be installed if this
is not the case. Anode bags should be used to keep contaminants and dirt in the titanium baskets
(used to hold zinc balls) and out of the electroplating solution. Also, a drain board should be
installed over the drip tank after the chromate rinse (on the auto line) to direct all dragout back
into the rinse tank.
By using a trivalent chrome conversion coat process instead of the current hexavalent
chrome process, Behlen could reduce the toxicity of a hazardous waste, lower treatment costs
(hexavalent chrome must be chemically reduced to trivalent before sending it to waste treatment
plant), and maintain overall costs at current levels. The disadvantages of these change would
be a reduction in corrosion protection, the operator must monitor the process closely, and
trivalent chrome coats are only available in a "bright blue" color.
To recapture some of the chemical dragout from the electroplating and chromating, it is
recommended that still rinse tanks be used after these processes. It is estimated that about 50%
of the chemical lost to dragout can be recaptured by this method. It is also recommended that
air agitation be used in the tanks to increase rinsing efficiency.
Since Behlen has a reverse osmosis (RO) purification unit which is currently not in use,
it is recommended that RO water be used to supply water to the electroplating, chromating, and
still rinse tanks. This change would remove contaminants in tap water including total dissolved
solids (TDS) and hardness thereby increasing process efficiency.
Current barrel withdrawal rates are 17 ft/min. for the automated line and 27 ft/min. for
the manual line. According to information received from WRITAR (Waste Reduction Institute
for Training and Applications Research), the maximum rate of withdrawal should be about 8
ft/min. This change would help decrease the amount of dragout from each tank resulting in
decreased chemical usage.
It is also recommended that the hang time of the barrels over the tank (before moving
to next station) be increased. The current barrel hang time on the auto line is 23 seconds.
There is still significant dripping from the barrels after this time period. The hang time over
tanks on the manual line varies with operator discretion. For the most part it is minimal or non-
existent, and dragout is visually significant.
14
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Acknowledgements
The project team acknowledges the valuable assistance received from all Behlen
Manufacturing employees during this study. In particular, we would like to acknowledge Mr.
Dick Goc, Mr. Tony Raimondo, Jr. and Rod Gering for their constant cooperation ami
assistance. This project is funded, in part, by the U.S. Environmental Protection Agency, and
in part by the University of Nebraska-Lincoln Center for Infrastructure Research (CIR) under
the Nebraska Research Initiative. The Project Officers for the U.S. EPA are Mr. James Lund,
of the Office of Water, Washington, D.C., and Mr. Carl Blomgren, of EPA Region VII in
Kansas City.
15
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Table 3. Summary of costs and advantages of recommended changes in the electroplating lines.
CHANGE
COST
SAVINGS
Est. Payback
Period
1) Lower Rinse Flow Rates
a) auto line - after cleaning and acid pickling,
and after electroplating
c) manual line — after cleaning and acid pickling,
and after electroplating
$90 (two flow control valves)
$50 (to hook up acid and cleaner rinses)
$3,000 (three counter current tank) see(3)
$135 (three flow control valves)
24,760 gpd see(l)
$138/day in WTX (2), sludge disposal,
and water costs
7,680 gpd
$59/day in WTX, sludge disposal,
and water costs
5 weeks
2 months
2) Soak Cleaners and Electrocleaners
a) increase temperature from 160°F to 180°F
(auto line only)
b) more efficient grease skimmer
c) testing concentration of cleaning solution (daily)
d) filtering solution (to remove dirt and metals)
$0.08/day + heat loss from tank and
solution surface see(4)
$140 (not installed) for float valve system
(also considering a squeegee system) see(4)
test kit free from ISA (5)
see (4)
less chemical dragout, cleaner work
less organic contamination, cleaner work
more efficient process, cleaner work
longer tank life
see (6)
3) HC1 Acid Pickling
a) testing concentration of acid (daily)
b) testing iron contamination
$20 (Baume) density hydrometer) or
$0.54/test (test kit from JSA)
see (4)
more efficient process
see (6)
4) Electroplating
a) testing:
1) iron contamination, pH and temperature,
total chlorides, zinc, boric acid, and wetter
b) filtering tank solution
1) auto line
2) manual line
c) peroxide addition (daily)
d) anode bags over titanium baskets
a total of only $7.30/week
$7,212 for 2 filtering units - one on each end
of tank (Serfilco Inc.)
$3,607 one filter unit (Surfilco Inc.)
minimal, see (4)
< $100, see (4)
more efficient process, better plating
cleaner tank solution, better plating
removal of iron contamination
capture contaminant metals and dirt
see (6)
see (7)
see (6)
see (6)
5) Chromating
a) testing:
1) pH, temp, and chromate concentration
b) replace hex-chrome with tri-chrome process
no cost (time only)
see (4)
more efficient process, better conversion
coating
less toxic process, less WTX and
disposal costs
see (4)
(1) gpd = gallons per day
(2) WTX = waste treatment system
(3) estimate from Imperial Co., in process of obtaining other estimates
(4) In process of obtaining estimate
(5) JSA = John Schneider Company
(6) difficult to estimate, will result in a better product and more efficient process
(7) difficult to estimate, will result in better plating and less chemical use.
16
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POLLUTION PREVENTION IN THE METAL FINISHING INDUSTRY
Mohamed F. Dahab
David L. Montag
ABSTRACT
The concept of pollution prevention has recently received
much attention in the media. Minimizing harm to the
environment by reducing the generation of pollution at its
source is a logical approach to pollution problems. The
University of Nebraska Lincoln (UNL) is encouraging Nebraska
businesses to adopt pollution prevention.
One part of this effort has been a research project
focused on industrial pollution prevention. During 1992 and
1993, a pollution prevention project was conducted at a large
metal finishing company in Nebraska. The manufacturing
processes studied were electroplating, galvanizing, painting,
and tubing fabrication.
By examining the available literature and interviewing
experts in the metal finishing industry, UNL researchers were
able to identify several promising pollution prevention
options. Tubing manufacture used a water based metalworking
fluid that was susceptible to decomposition by anaerobic
bacteria. The bacterial growth was encouraged by oil
contamination from leaking gearboxes. This problem was
minimized by replacing grease seals on the gearboxes and by
installing an improved oil removal system to purify the
coolant.
The paint used by the company contained volatile
solvents, which evaporate as the paint dries and eventually
contribute to smog (ozone pollution). Volatile organic
compound emissions can be avoided by using coating materials
other than traditional solvent based paint. Alternative
materials studied were water based paint, autophoretic
coatings, and powder coating. At the time of this writing,
the company was seriously considering installing a powder
coating line.
The galvanizing process produced large volumes of rinse
water which was contaminated with sulfuric acid, and zinc, and
which required expensive treatment prior to disposal. A test
was conducted that successfully demonstrated that a counter
current continuous flow rinse could reduce water use. Tests
were also conducted to prove the feasibility of using a
11
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continuous flow rinse to remove flux chemicals from the
surface of freshly galvanized parts. These tests were
unsuccessful. Testing was also conducted to change the
process chemistry to avoid depositing a flux chemical film on
the finished work. In this way, the need to rinse could be
avoided. Unfortunately the chemistry changes resulted in
unacceptable product quality, and the proposed rinsing system
was not considered feasible. A rinse water flow reduction of
about 21 percent was achieved, however, by installing new
spray nozzles in the existing spray booths.
in
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS i
ABSTRACT '.'.'. ii
TABLE OF CONTENTS '. iv
LIST OF FIGURES vi
LIST OF TABLES vi
LIST OF SYMBOLS AND ABBREVIATIONS vii
CHAPTER 1
INTRODUCTION 1
1.1 Objectives. 3
1.2 Literature Review 4
1.2.1 General Pollution Prevention 4
1.2.2 Barriers to Pollution Prevention 7
1.2.3 Metal Finishing Pollution Prevention .... 8
1.2.4 Metalworking Fluid Pollution Prevention . . 10
1.2.5 Paint Application Pollution Prevention ... 12
1.2.6 Galvanizing Pollution Prevention 15
1.2.7 Waste Minimization Assessment Methods ... 19
1.2.8 Measuring the Success of Pollution
Prevention Programs 21
CHAPTER 2
CASE STUDY 23
CHAPTER 3
TUBING MANUFACTURE 25
3.1 Recommended Tube Mill Changes 28
Chapter 4
PAINTING 30
4.1 Washing 31
4.2 Rinsing 31
4.3 Etching 32
4.4 Rinsing 33
4.5 Drying 33
4.6 Painting 33
4.7 Flow Coating 36
4.8 Oven Curing 36
4.9 Painting Changes 37
4.10 Water Based Paint 37
4.11 Autophoretic Coating 39
4.12 Powder Coating 40
CHAPTER 5
GALVANIZING 43
5.1 Galvanizing Proposals 45
5.2 Rinse Tank System 46
5.3 Post Pickling Rinse Test 48
iv
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5.4 Interim Galvanizing System 52
5.5 Initial Cooling Rinse Test 53
5.6 Dry Kettle Galvanizing 57
5.7 Preflux Chemistry Adjustments 60
5.8 Second Cooling Rinse Test 61
CHAPTER 6
DISCUSSION AND CONCLUSIONS 65
REFERENCES 68
APPENDIX 76
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11
Waste Minimization Opportunities For the
Electroplating Industry: A Case Study
Mohamed F. Dahab
Gary Keefer
John Parr, M.S.
ABSTRACT
Standard waste minimization and assessment
methodologies were applied to an aging electroplating
(manual and automated lines) facility that produced zinc
plated nuts and bolts. The recommendations made and the
results of implemented changes are reported in this thesis.
In addition, an extensive literature review was performed
concerning waste minimization opportunities for the
electroplating process and includes sections on improving
rinsing efficiency, housekeeping, drag-out reduction and/or
return, material substitution, and recovery and recycling
techniques.
The waste assessment involved documenting the
electroplating processes and recommending changes that would
reduce waste and increase product quality. The most
profound change recommended dealt with the rinsing processes
after the alkaline cleaning, acid dip, and zinc
electroplating processes. The use of countercurrent rinses
and reduced rinse flows were estimated to result in a
savings of $209.00 per day in process wastewater treatment,
sludge disposal, and water costs. Total cost for these
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recommended changes is about $4,600.00 with an overall
payback period of about 22 days.
Some of the recommended changes have been implemented
and include: a thorough clean-up of the electroplating area
including inside and outside the tanks; regularly testing
chemical concentrations in the process tanks and making
additions as needed; the hiring of a chemist to perform the
testing and oversee all chemical processes on the lines; and
reducing rinse flow rates. Since these changes have been in
effect, product quality has improved, as documented by a
1000% increase in white rust protection, and a 550% increase
in red rust protection.
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IV
TABLE OF CONTENTS
TOPIC PAGE
ACKNOWLEDGEMENTS 1
ABSTRACT ii
TABLE OF CONTENTS iv
LIST OF TABLES vil
LIST OF FIGURES ix
Chapter 1. Introduction and Objectives 1
1.1 Introduction JL
1.2 Objectives 4
Chapter 2. Literature Review 5
2.1 Electroplating 5
2.1.1 Electroplating Theory 5
2.1.2 Other Types of Metal Finishes 6
2.1.3 Types of Metals Plated 8
2.1.4 Processes involved in Electroplating 9
2.2 Rinsing in the Electroplating Process 1].
2.2.1 Rinsing Theory 12
2.2.2 Requirements for Efficient Rinsing 15
2.2.3 Calculating Contaminant Concentration 16
2.2.4 Calculating Adequate Rinse Water Volumes 19
2.2.5 Countercurrent Rinsing 20
2.3 Wastes Produced From the Electroplating Process 21
2.3.1 Make-up of Generated Wastes 22
2.3.2 Identifying Hazardous Wastes 23
2.3.3 Effluent Discharge Limits 25
2.4 Waste Minimization Opportunities 28
2.4.1 Opportunities for Improving Housekeeping 28
2.4.2 Opportunities for Increasing Bath Life 31
2.4.3 Opportunities for Improving Rinse Efficiency 33
2.4.4 Opportunities for Drag-out Reduction 35
2.4.5 Opportunities for Material Substitution 39
2.4.6 Opportunities for Recovery and Recycling 41
Chapter 3. Overview and Application of Waste
Assessment Procedure 46
Chapter 4. Case Study Introduction and Electroplating
Process Description 51
4.1 Case Study Introduction 51
4.2 Electroplating Process Description 52
4.2.1 Overview of Electroplating Operations 52
4.2.2 Description of Chemical Processes 54
4.2.3 Description of Rinsing Processes 62
4.2.4 Description of Other Processes Involved 64
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TABLE OF CONTENTS (Continued)
TOPIC
PAGE
Chapter 5. Methods and Materials
Chapter 6. Results of Preliminary Testing
6.1 Testing Results
6.2 Calculating Recommended Rinse Flows From
Drag-Out Testing Results
Chapter 7. Recommended Changes to the Automated and
Manual Electroplating Processes
7.1 Housekeeping Recommendations
7.2 Rinsing Process Recommendations
7.2.1 Changes to Automated Line Rinsing Processes
7.2.2 Changes to Manual Line Rinsing Processes
7.2.3 Summary of Rinse Water and Cost Savings
7.2.4 General Rinse Process Changes
7.3 Other Recommendations to the Automated and
Manual Electroplating Lines
7.3.1 Changes to Process Bath Operations
7.3.2 Changes to Reduce or Contain Drag-out
Contaminants
7.3.3 Change to Improve Process Efficiency
Chapter 8. Results of Implemented Changes to the
Automated and Manual Electroplating Lines
Chapter 9. Conclusions
REFERENCES
APPENDICES
Appendix A;
Appendix B
Appendix C
Appendix D
Testing Procedures Used to Determine
Chemical Concentrations of Undiluted
Process Tank Samples
Data From Drag-Out Testing
Calculating Recommended Rinse
Flow rates
Data from Lowered Rinse Flow
Testing
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Pilot project adds polish
to metal finisher's
pollution prevention efforts
BY M.F. DAHAB AND JIM LUND
AN AGING MIDWESTERN MANUFAC-
turing facility that produces fabricated
metal products for farm and indus-
trial uses was chosen as the site for an
industrial pollution prevention and
waste minimization pilot project The project
goal was to demonstrate that using appropri-
%ate management and operating procedures
can reduce the total pollution produced by an
industrial operation. The facility is a licensed
hazardous waste generator.
The plant engages in a variety of pollu-
tion-generating activities, including electro-
plating, conversion coating, cleaning,
machining, grinding, impact deformation,
shearing, welding, sand blasting, hot-dip
coating, painting, assembly and testing. The
hot-dip galvanizing process results in pro-
duction of rinsewater containing such heavy
metals as zinc and iron. Painting processes
generate used industrial cleaners, acids, sol-
vents, and chemicals used in cleaning and
degreasing metal components.
Process wastewaters are treated by adding tion and minimization opportunities;
lime and polymer, and adjusting pH before • Evaluating economic and technical
discharge. Past disposal practices at the facil- aspects of waste prevention and mimmiza-
ity had threatened area
surface and groundwater.
Waste disposal is a major
operating expense.
Procedures and
methods. The waste-
stream evaluation fol-
lowed Environmental
Protection Agency guid-
ance. A pollution pre-
vention assessment work
plan identified several
tasks, including:
• Developing a
detailed assessment and
evaluation of current
practices, and characteri-
zation of all wastes pro-
duced by the facility,
Past disposal
(i^fcesatBiefacity
had threatened area
surface and ground-
water. Waste dfeposal
expense.
tion alternatives, and
their short- and long-
term impacts;
• Developing rec-
ommendations to man-
agfiment for
implementation based
on greatest benefit and
shortest payback peri-
ods;
• Providing techni-
cal assistance during
implementation of rec-
ommended alternatives;
and
• Reviewing the
results and impacts on
waste prevention after
implementing the alternatives.
Identifying possible pollution preven- In developing the pilot project, empha-
Reprinted with permission from the November 1994 issue of Environmental Solutions.
Copyright © 1994 Advanstar Communications Inc.
-------
sis was placed on areas in which the impact
on reducing total pollutant load would be
greatest — the electroplating, hot-dip gal-
vanizing and painting lines, and tube-mill
production areas. Strategy- development
stressed a multimedia approach to prevent-
ing and minimizing pollution.
Electroplating systems. The facility
operates an automated and a manual elec-
troplating line to deposit a thin zinc film onto
such items as bolts, fasteners and nuts, which
are used to construct larger plant products.
The automatic line is a barrel system that
plates about 145 pounds of work per load.
Barrels are moved by a conveyor chain. An
average of 145 pounds of pieces per barrel
are processed by 36 stations on the line. The
cycle takes about 3.5 minutes per station, or
about two hours per barrel.
The work first is soaked in cleaner and
an electrocleaning solution. It then is rinsed,
pickled in a hydrochloric acid bath, and
rinsed again before entering a chloride-zinc
electroplating bath. After about an 70 min-
utes in the plating bath (20 stations), the
work is rinsed, and a light yellow chromate
finish is added. A short rinse (20 seconds)
follows the chromating process, after which
work is dried at 65 degrees Celsius.
The electroplating solution is circulated
through a filter to remove impurities, which
are rinsed into the treatment system. Total
rinsewater use in the automatic electroplat-
ing line, which operates eight hours a day,
was estimated at 166 liters per minute.
The manual process requires operators
to move barrels from station to station. The
barrels are bigger, but the average load of
work per barrel is the same as in the auto-
mated process. The manual line is used more
than the automated line, especially when
plating small quantities. The work is cleaned
in a soak cleaning bath (no electrocleaning)
for about 15 minutes. It then is rinsed, pick-
led and re-rinsed before entering the chlo-
ride-zinc electroplating tank (Stainless steel
pieces are dipped in nitric acid instead of
hydrochloric acid.) Pieces are plated 60 to
90 minutes before being removed. A short
rinse precedes the chromate coating, which
can be clear or yellow. After a final short
rinse, pieces are placed on a table to dry.
To obtain better product quality and
ensure that the lower flow rates would not
compromise rinsing efficiency, housekeep-
ing changes were recommended. These
included a thorough cleaning of the elec-
troplating area (tanks, floor and electro-
plating process equipment), and a
maintenance recordkeeping system.
The suggestions, designed to reduce rin-
sewater and electroplating chemical waste,
called for improved cleanliness and better
chemistry control. Also recommended was
reducing rinse rates to decrease the amount
of wastewater discharged to the treatment
plant. Reactive rinsing was recommended
for both electroplating lines to decrease water
Use of still rinse tanks
folio wing electroplating
and chromating was
recommended to
recapture some of the
chemical dragout from
these processes.
use from the rinses following pickling and
alkali cleaning. Pickling rinsewater no longer
would aro down the drain, but instead flow
w
to rinse tanks following alkali cleaning.
Effluent from the rinsing step after the
acid dip could be directed to the rinse tanks
after the cleaning process, saving about 76
cubic meters of water and $150 per day in
waste treatment, sludge disposal and water
costs. Countercurrent tanks similar to those
on the automated line would be needed on
the manual line to incorporate this change, at
a cost of about SI,000. It was recommended
that rinse processes following electroplating
on both lines be changed to countercurrent
with a rinse flow rate of 20 liters per minute
each. About 24 cubic meters of water a day
can be saved, saving $50 per day.
Daily testing of chemical and operating
parameters in the tanks needed to be per-
formed for several variables. Electroplating
tank variables included pH and temperature
in addition to concentrations of cleaners, acid
dips, zinc metal, boric acid, total chlorides
and the wetting agent. Chromating tank vari-
ables included pH, temperature and chro-
mate concentration.
Other recommended changes included
increasing the temperature of automatic line
cleaning tanks from 71 degrees Celsius to
93 degrees Celsius. Grease skimming needed
improvement, because grease originating
from the machining steps of bolt produc tion
accumulated in the automatic electroplating
line's cleaning tanks. An inoperative filter
system on the electroplating tanks also
needed repairs. Once the repairs are made
on both lines, it should be possible to deter-
mine whether the systems are adequate to
maintain contaminants at low levels.
Installing a new filtering system was recom-
mended.
Anode bags were recommended to keep
contaminants and dirt from the zinc balls
out of the electroplating solution. Addition-
ally, a drain board was needed over the drip
tank following the chromate rinse or the
automatic line to direct dragout back to the
rinse tank. By changing to a trivalent-
chrome-conversion coa'ting process instead
of the hexavalent chrome process, the facil-
ity should decrease the toxicity of the waste
it produces. This would save on treatment
costs, because hexavalent chrome must be
reduced chemically to its trivalent form —
which is less toxic and less expensive to treat
— before it is sent to a treatment plant.
Some potential disadvantages of these
changes are a slight reduction in corrosion
protection, the necessity of closer process
monitoring and testing, and the tact that iiiva-
lent chrome coats are available only in bright
blue instead of the customary light yellow.
Use of still rinse tanks following elec-
troplating and chromating was recom-
mended to recapture some of the chemical
dragout from these processes. This
method should recapture about half of the
chemical lost to dragout. It was also rec-
ommended that air agitation be used in the
tanks to increase rinsing efficiency.
The water supplied to the electroplating
process should be as clean as possible. It was
recommended that the facility's reverse
osmosis purification unit be used to supply
water to the electroplating, chromating and
still rinse tanks. This would remove poten-
-------
tial contaminants in tap water, including
total dissolved solids and hardness, before
its use in the electroplating line, increasing
process efficiency.
The barrel withdrawal rates were mea-
sured at 5.2 meters per minute in the auto-
mated line and 8.2 meters per minute in the
manual line. The maximum withdrawal rate
should be about 2.4 meters per minute.
Changing this would decrease the amount
of dragout from each tank, resulting in
decreased chemical use.
It was also recommended that the hang
time of barrels over the tanks be increased
by pausing longer before moving to the next
station. Although hang time on the auto-
mated line was 23 seconds, significant drip-
ping from barrels occurred after this time.
Hang time over tanks on the manual line
varied. Generally, hang time was observed
to be minimal, and dragout was significant.
Results of system changes. Several
recommended changes to the automatic
electroplating line were implemented. All
tanks were cleaned, inside and outside, on
the plating line, and accumulated bottom
sludge was removed. The bath contents of
the electroplating tank were pumped into
a temporary holding tank, and nonhaz-
ardous bottom sludge was shoveled into
eight 55-gallon drums for disposal. The liq-
uid portion of the plating bath was pumped
back into the plating tank, and additional
chemicals and water were added to restore
them to normal levels.
Other changes included:
• Regular testing of cleaning, acid dip,
electroplating and chromating processes to
maintain optimal-level chemical concen-
trations;
• Hiring a qualified individual to per-
form operational control testing and work
with the plating operator to make required
chemical additions; and
• Reducing rinse flows, and installing
flow measurement and countercurrent
rinsing.
Flow control devices have been installed
on the rinses following the alkaline clean-
ing and acid-dip processes to maintain flow
rates at recommended levels. The two sys-
tems have not been connected as recom-
mended. Flow rates for the two rinses
following electroplating also have been
reduced* The new rates have not been mea-
sured, so it has not been determined
whether they are being maintained consis-
tently. The plating operator reports the
valves that control flow are not opened as
tar as in the past. Besides decreasing the rin-
sewater flow rate, adding the countercur-
rent system to the manual line should
increase the rinsewater's utility.
Product quality has been increased sig-
nificantly, as evidenced by results of the 5
percent neutral salt spray testing performed
on bolts plated on the automated line before
and after the changes occurred. The results
Tank cleaning, stadge
removal and use of oi
absorbent pads on Hie
cleaning baths should
reduce the dragout of
drt, grease and other
stream processes.
show a 1,000 percent increase in white rust
protection and a 550 percent increase in red
rust protection.
From a waste prevention and minimiza-
tion perspective, the changes have been
effective. Reduction in rinse flows should
lead to less wastewater for treatment at an
onsite facility. Tank cleaning, sludge removal
and use of oil absorbent pads on the clean-
ing baths should reduce the dragout of dirt,
grease and other contaminants to down-
stream processes. This will increase bath life,
resulting in fewer bath dumps and reduced
chemical use. Costs of implementing these
changes have been modest.
The galvanizing system. The facili-
ty's galvanizing process consists of pickling,
rinsing, prefluxing, galvanizing and final
rinsing. The pickling step prepares work
for galvanizing by removing oxides from
the steel surface using a 10 percent sulfuric
acid solution at 70 degrees Celsius.
Work pieces are rinsed after pickling.
The preferred method is to dip them in the
rinse tank, which is filled with unheated
municipal water. The rinsewater is a^tated
by moving the pieces back and forth in the
tank. After the first rinsing, work pieces are
placed in the preflux tank, a crucial step in
the dry-kettle galvanizing process. Work is
coated with flux chemicals before entering
the zinc kettle. The preflux tank is main-
tained at 70 degrees Celsius. The preflux
solution generally is allowed to dry thor-
oughly before galvanizing.
Galvanizing is accomplished by immers-
ing steel in a tank filled with molten zinc for
two to three minutes. Most steel galvanized
at this plant uses the wret-kettle method. A
flux layer is floated on top of the galvanizing
kettle, and work pieces pass through it as they
enter and leave the kettle. For galvanizing
materials, such as building components, the
kettle flux layer is skimmed to the side and
not used. Work pieces are cooled by rinsing
them in a second rinse booth next to the gal-
vanizing kettle. This final rinse is needed to
cool the work to below 200 degrees Celsius,
which prevents growth of a brittle zinc-steel
alloy layer. Cooling also allows operators to
handle the pieces.
Galvanizing operations. Pollution
prevention efforts in galvanizing were con-
centrated on reducing the volume and metal
content of rinsewater, as this is the princi-
pal medium through which metal is lost.
Volume reductions can be accomplished by
installing additional galvanizing equipment.
Metal content reductions are possible by
discontinuing use of the kettle flux or
switching to a different kettle flux.
The galvanizing system initially used
about 265 cubic meters of rinsewarer per
day. Flow through the first rinse booth was
measured during wastestream assessment
at 1,200 liters per minute. Freshly galva-
nized pieces are cooled in the second rinse
booth. Flow through this booth was esti-
mated at about 1,200 liters per minute. The
rinse booths operate only while materials
to be rinsed are carried through them.
Rinsing in a tank instead of a booth is
the most important step in decreasing gal-
vanizing water use. Using rinse tanks after
pickling also is important. It was recom-
-------
mended that rinse booths he replaced by
rinse tanks linked in a countercurrent flow
arrangement. This allows water to he reused
several times before being discharged and
ensures that work pieces are rinsed with clean
water as they leave the process line.
A rinse test conducted to verity the use-
fulness of the rinse tank concept successfully
demonstrated the feasibility of continuous-
flow rinsing. Based on the results, a contin-
uous rinsewater flow rate of 24 liters per
minute removes pickling acid adequately tor
two rinse tanks in series. This flow rate cools
the work, preventing the water temperature
from rising high enough to pose a satety
problem. The proposed system would use
no more than 35 cubic meters of water per
day, representing a savings ot about S3 per-
cent. As a result of the study, water-saving
(low-flow) nozzles were installed in the rinse
booths. This immediately reduced water use
by 60 percent, yielding water and waste treat-
ment savings of about $250 per day.
The proposed galvanizing equipment
changes cost about $70,000. Ventilation sys-
tem improvements to remove pickling solu-
tion vapors from the proposed pickling tank
location would cost $25,000. Due to the
expense, phased installation ot suggested gal-
vanizing changes was recommended. The
payback period is estimated at about 10
months.
Livestock fencing is being fluxed twice
— once in the preflux tank and again as it
enters the kettle. For galvanizing objects
other than fence panels, kettle flux is not
used. The kettle flax is 98 percent zinc chlo-
ride and contains a small amount of potas-
sium chloride. Kettle flux adds sigruficandy
to the metal content of galvanizing rinse-
water, so that discontinuing its use would aid
pollution prevention.
Pre'fluxing is crucial in dry-kettle galva-
nizing. To obtain good fluxing, proper con-
centrations of zinc chloride and ammonium
chloride must be maintained, and iron and
sulfate concentrations minimized. Frequent
sampling is required.
Switching from zinc chloride preflux to a
mixture of mosdy ammonium chloride and
some zinc chloride or ammonium chloride
alone was recommended. This probably would
enhance product quality, because the proposed
countercurrent flow system (with fresh water
being added at the final rinse tank) would not
complicate preflux chemistry.
Another problem with the galvanizing
operation was a layer of oil floating on the
surface of the acid bath. The oil could be
minimized by installing a skimmer to remove
it periodically or to reduce oil use in the fab-
ricating step.
The painting system. The painting
operation at the tacility consists of washing,
etching, oven drying, spray painting and
oven curing. The plant's painting operation
in 1992 was estimated to have emitted about
37,500 kilograms of xylene and 11,000 kilo-
grams of toluene. Reducing emissions of
these volatile organic compounds should be
Another suggestion
was to switch to an
autophoretic painting
eliminate chromic
acid etching.
a top priority.
Two types of paint are used at the plant.
A solvent-based paint is used for painting
gates, and a silicone polyester paint is used
for coating building panels. Seventy-tour per-
cent of the paint used in the automatic paint
line in 1992 was used to paint farm gates.
About 2,200 liters per month of a mixture of
aromatic solvents are used for such purposes
as cleaning paint-supply piping.
The only practical way to reduce VOC
emissions significantly is to change paint
materials. One alternative is to use water-
based paint for the gates. If water-based
paints are applied electrostatically, a high
transfer efficiency can be obtained. The
investment should be relatively small,
because the only facility change required is
installing new spray equipment. Immediate
testing of water-based paints was recom-
mended.
Another suggestion was to switch to an
autophoretic painting process to reduce
VOC emissions and eliminate chromic-acid
etching. This involves dipping metal to be
painted into tanks filled with paint The coat-
ing is deposited via a chemical reaction
between the paint and metal which requires
several minutes of immersion. The auto-
phoretic process resembles electrocoating
but requires no electric current. Metal
painted using this process reportedly has
withstood salt spray tests up to 3,000 hours
without coating failure. The paint report-
edly exhibits a high degree of hardness and
good resistance to chalking from ultraviolet
light exposure.
The estimated cost of an autophoretic: sys-
tem to coat gates was $300,000. A serious
drawback of this method is that color varies
with the dissolved iron concentration in the
paint, which increases slowly due to contact
of the paint with the steel being painted.
Another drawback is the fact that a separate
paint tank is needed for each color.
Another alternative is powder coating.
Agricultural gates are ideally suited for JK»W-
der coating, because they are made in only
two colors. Transfer efficiency is not an issue,
because overspray is captured and blended
with fresh powder for reuse, and VOCs are
not emitted. An industrial supply contractor
estimated that powder coating could be
added to the existing paint line for about
$40,000. However, installation costs prob-
ably would be higher, because the automatic
paint line is old and should be replaced. A
new paint line was estimated to cost about
$200,000.
Pollution prevention in the painting area
at this plant will not be offset by significant
savings in disposal costs.However, the Clean
Air Act will require that action be taken soon.
As a result of this study, the plant has exper-
imented with water-based paints and
requested bids to construct a powder coat-
ing system.
Tubing manufacture system. A tube
mill at the facility forms metal pipe trom
coils of sheet steel. The plant makes tubing
for all its gates and also sells tubing to other
companies. The major tube mill compo-
nents include a coil unwinder, feeder, ini-
tial cold rolls, welder, re-galvanizer, final
cold rolls, metering cutter and coolant dis-
tribution system. A water-based fluid coolant
is used to lubricate and cool the tube mill.
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About 800 liters of coolant per month are
consumed at a cost of about S800. The
coolant flows from application points into
sumps below the components. The sumps
drain by gravity to a large collection tank,
which contains an oil removal system con-
sisting of a plastic tube pulled through the liq-
uid coolant. Floating oil adheres to the
polyethylene tube and is removed by a scraper.
However, the oil removal system is unable to
remove oil quickly enough.
Oil in the coolant originates from grease
leaking out of the tube mill gearboxes. Over
the years, oil and grease leaks have covered
the tube mill and the surrounding area.
Grease combines with metal filings created
when excess metal is scraped from fresh
welds. Together, the grease and filings form
a black substance that fills the bottom of the
sumps in about a month. The mill occa-
sionally is shut down while operators scoop
out the grease. About two-thirds of the
coolant is lost each time the sumps are
cleaned, and this is the only time coolant is
discharged from the system.
Recommendations for the tube mill focus
on minimizing grease contamination of the
coolant. The old oil-removal system should
be replaced with a system that would allow
coolant reuse. A suitable unit was estimated
to cost less than $2,500. The payback period
was estimated at less than six months, assum-
ing the coolant's usable life is doubled. If
coolant could be used longer, the payback
period would be shorter.
The coolant also turns rancid. Coolant
rancidity usually is controlled by adding a bio-
cide. If rancidity problems continue after an
improved oil removal system is installed, a dif-
ferent biocide may be needed. Gearbox leak-
age should be prevented or kept from falling
into the sumps through regular maintenance.
In addition, preventing metal filings from
falling into the sump below the weld scraper
would keep them from combining with the
grease. It was recommend that the entire area
be shut down for thorough cleaning, as this
would vastly improve system operation.
Cleaning should include equipment, floor
grates and the return trough. IT
M.F. Dahab is an associate professor of civil
engineering and biological systems engineering
at the University of Nebraska-Lincoln. Jim Lund
is director of the Industrial Pollution Prevention
Project in the Environmental Protection Agen-
cy's Office of Water.
The project on ivhich this report is hosed icas
funded jointly by EPA and the University of
Nebraska-Lincoln Center for Infrastructure
Research.
More reading
Anonymous, "Steelcase Inc. replaces zinc
plating lines," Finishers Management, March
1992, pp. 17-20.
Cook, T.H., D.E. Mergen and D.L.
Clark, "Increasing profits in hot dip galva-
nizing," Metal Finishing, Vol. 84, No. 23,
1986, pp. 23-27.
Cook, T.H. and W.S. Horton, "Ammo-
nium chloride control in galvanizing pre-
flux," Metal Finishing, Vol. 80, No. 19, 1982,
pp. 19-23.
Dahab, M.F. and D. Montag, "Waste
minimization in a metal-finishing industry:
A pilot project," Third International Confer-
ence on Waste Management in the Chemical and
Petrochemical Industries, Salvador-Bahia, Brazil,
Oct. 20-23, 1993.
Dahab, ME, D. Montag and J. Parr, "Pol-
lution prevention and waste minimization at
a galvanizing and electroplating facility," Water
Science and Technology, in press, 1994.
Durney, L.J., Electroplating Engineering
Handbook. Chelsea, Mich.: Lewis Publishers
Inc., 1984.
Hunt, G.E., "Waste reduction in the
metal finishing industry, "Journal of the Air
Pollution Control Association, Vol. 38, No. 5,
1988, pp. 672-680.
Montag, D., Pollution Prevention in the
Metal Finishing Industty (master's thesis). Lin-
coln, Neb.: University of Nebraska-Lincoln
Libraries, December 1993.
Sjoukes, F., "Chemical reaction*; in fluxes
for hot dip galvanizing," Anti-Corrosnon Meth-
ods and Materials, Vol. 37, No. 4, 1990, pp.
12-14.
Parr, J., Waste Minimization Opportuni-
ties for the electroplating industry: A Case Study
(M.S. thesis). Lincoln, Neb.: University of
Nebraska-Lincoln Libraries, Febrairy 1994.
Tsai, E.C. and R. Nixon, "Simple tech-
niques for source reduction of was tes from
metal plating operations," Hazardous Waste
6-Hazardous Materials, Vol. 6, No. 1, 1989,
pp. 67-78.
U.S. Environmental Protection Agency,
Guides to Pollution Prevention-The Fabricated
Metal Products Industry. Washington, D.C.,
EPA Report No. EPA/625/7-90/006, July
1990.
Facility Pollution Preventivn Guide.
Washington, D.C., EPA Report No.
EPA/600/R-92/088, May 1992.
A Primer for Financial Analysis of
Pollution Prevention Projects. Washington,
D.C., EPA Report No. EPA/600/R-93/059,
April 1993.
University of Tennessee Center for
Industrial Services. Waste Reduction Assess-
ment and Technology Transfer, 2nd edition,
9/22-9.
Wentz, CA Hazardous Waste MaiiagenKnt
New York: McGraw-Hill Book Co., 1989.
©Reprinted from ENVIRONMENTAL SOLUTIONS, November 1994
AN AOVANSTAR <£p PUBLICATION Printed in U.S.A.
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