v>EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S-92/034 Sept. 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a
Manufacturer of Custom Molded Plastic Products
Richard J. Jendrucko* and Phylissa S. Miller**
Abstract
The U.S. Environmental Protection Agency (EPA) has funded a pilot
project to assist small- and medium-size manufacturers who want to
minimize their generation of waste but who lack the expertise to do
so. Waste Minimization Assessment Centers (WMACs) were es-
tablished at selected universities and procedures were adapted from
the EPA Waste Minimization Opportunity Assessment Manual'(EPA/
625/7-88/003, July 1988). The WMAC team at the University of
Tennessee performed an assessment at a plant manufacturing
custom-molded structural foam plastic products — approximately
840,000 parts per year. Resin pellets are blended with colorant
pellets and regrind, then processed through a mold and press
machine. Unfinished products are degated to remove seams, have
attachments inserted, and are drilled, if necessary. Next, parts are
patched and sanded. Finally, the part undergoes finishing operations
including nickel coating, spray fill application, and top coat application.
The team's report, detailing findings and recommendations, indicated
that the majority of waste was generated in the mold and press
machines but that the greatest savings could be obtained by utilizing
electrostatic spray equipment in the finishing department to reduce
(by 28%) the amount of paint solids waste generated.
This Research Brief was developed by the principal investigators
and EPA's Risk Reduction Engineering Laboratory, Cincinnati, OH,
to announce key findings of an ongoing research project that is fully
documented in a separate report of the same title available from
University City Science Center.
Introduction
The amount of waste generated by industrial plants has be-
come an increasingly costly problem for manufacturers and an
' University of Tennessee, Department of Engineering Science and Mechanics
" University City Science Center, Philadelphia, PA
additional stress on the environment. One solution to the prob-
lem of waste is to reduce or eliminate the waste at its source.
University City Science Center (Philadelphia, PA) has begun a
pilot project to assist small- and medium-size manufacturers
who want to minimize their formation of waste but who lack the
inhouse expertise to do so. Under agreement with EPA's Risk
Reduction Engineering Laboratory, the Science Center has
established three WMACs. This assessment was done by en-
gineering faculty and students at the University of Tennessee's
(Knoxville) WMAC. The assessment teams have considerable
direct experience with process operations in manufacturing
plants and also have the knowledge and skills needed to
minimize waste generation.
The waste minimization assessments are done for small- and
medium-size manufacturers at no out-of-pocket cost to the
client. To qualify for the assessment, each client must fall within
Standard Industrial Classification Code 20-39, have gross annual
sales not exceeding $75 million, employ no more than 500
persons, and lack inhouse expertise in waste minimization.
The potential benefits of the pilot project include minimization of
the amount of waste generated by manufacturers, and reduced
waste treatment and disposal costs for participating plants. In
addition, the project provides valuable experience for graduate
and undergraduate students who participate in the program,
and a cleaner environment without more regulations and higher-
costs for manufacturers.
Methodology of Assessments
The waste minimization assessments require several site visits
to each client served. In general, the WMACs follow the proce-
dures outlined in the EPA Waste Minimization Opportunity As-
Printed on Recycled Paper
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sessment Manual (EPA/625/7-88/003, July 1988). The WMAC
staff locate the sources of waste in the plant and identifies the
current disposal or treatment methods and their associated
costs. They then identify and analyze a variety of ways to
reduce or eliminate the waste. Specific measures to achieve
that goal are recommended and the essential supporting tech-
nological and economic information is developed. Finally, a
confidential report that details the WMAC's findings and rec-
ommendations (including cost savings, implementation costs,
and payback times) is prepared for each client.
Plant Background
The plant manufactures custom-molded plastic products in-
cluding dashboards, door seals, and fan shrouds for automo-
biles, television cabinets, postage meter housings, and computer
disk storage organizers. The plant operates 6,240 hr/yr to
produce approximately 840,000 parts.
Manufacturing Process
This plant manufactures its various finished products from
structural foam. Primary raw materials consist of seven types
of resin pellets and colorants. Other raw materials necessary
for the production processes are various solvents, paints and
finishing materials.
The following unit operations are involved in manufacturing the
products:
Structural Foam Production
• Resin pellets are blended with colorant pellets and "regrind"
from material recycling in a batch mixing process, and are then
vacuum fed into hoppers on each of the ten mold and press
machines.
• Pellets proceed through an electrically heated zone and to a
zone where a blowing agent, hydrocerol or nitrogen gas, is
added. Next, molten plastic is injected into a mold. Nitrogen gas
is sometimes used during this process to pressurize the mold.
Chilled water is continuously circulated through the press molds
for cooling.
• From the mold and press machines, the product may be sold to
the customer unfinished or may be directed to one of four work
areas: inserting, degating, and drilling (considered as one op-
eration), finishing department, secondary department, or defective
product recycling.
Inserting, Degating, or Drilling
• The majority of molded parts are manually "degated"to remove
seams formed in the presses. Following degating most parts
have brass or aluminum fastener attachment inserts applied
which are ultrasonically bonded to the piece. Inserting may also
include an ultrasonically-induced bonding process (between
molded pieces) in the production of shelving.
• A smaller portion of formed molds is drilled as needed along
with the remaining product from degating not transferred to
inserting. All molds from drilling proceed to inserting and then
are transferred to either the secondary department or the
finishing department.
Secondary Department
• Products from inserting, degating, and drilling abng with products
directly from the mold and presses enter a patching process
where a filler is applied to improve surface smoothness.
• A very small product fraction may proceed to binding where
toluene is applied for the mating of two surfaces.
• Products from bonding and patching are manually power-finish-
sanded and either transferred to the finishing department or
shipped directly to the customer.
Finishing Department
• Products brought to the finishing department begin at nickel
coating, "spray-fill", or top-coat. Items that are nickel-coated
proceed to "spray-fill" and to top-coat. Those beginning at
spray-fill continue to top-coat.
• At nickel coating, a conductive paint and methyl ethyl ketone
(MEK) thinner are mixed and then air-sprayed onto the product
in spray booths. Next, the items are positioned on an overhead
conveyor for an 11-12 minute passage through an infrared
oven followed by transfer to a "spray-fill" booth.
• At a "spray-fill" booth, "spray-fill", reducers, and catalyst are
mixed and applied. Products are passed through the same
infrared oven for drying followed by finish-sanding.
• Products proceed to a top-coat paint booth where paint, solvent
reducers, and a catalyst are mixed and applied by hand-held
spray guns. Painted parts proceed through the infrared oven
described above. Next, some product pieces are textured with
a catalyzed polyurethane paint. These items are dried in a
propane gas-fired oven and then boxed for shipment to the
customer.
• A mixture of several solvents including acetone, MEK, and
recovered solvent is used to spray clean equipment and wipe
down walls. Overspray in each paint booth collects in a water
bath from which paint solids are skimmed once per shift.
Additional overspray coats the paint booth walls from which
residue must be scraped periodically.
An abbreviated process flow diagram is shown in Figure 1.
Existing Waste Management Practices
This plant already has implemented the following techniques to
manage and minimize its wastes:
• The plant has purchased approximately 13 new paint guns to
improve paint application efficiency to result in some reduction
of overspray occurring during the painting process.
• Approximately four years ago, water baths were installed in
each booth to collect overspray and reduce airborne emissions.
• Plant personnel installed a distillation unit to recover waste
solvent used for cleaning paint guns and paint booth walls.
• Inhouse waste surveys have been conducted sporadically for
approximately 7-8 years in order to reduce the amount of waste
produced.
Waste Minimization Opportunities
The type of waste currently generated by the plant, the source
of the waste, the quantity of the waste, and the annual man-
agement costs are given in Table 1.
Table 2 shows the opportunities for waste minimization that the
WMAC team recommended for the plant. The type of waste,
the minimization opportunity, the possible waste reduction and
associated savings, and the implementation cost along with the
payback times are given in the table. The quantities of waste
currently generated by the plant and possible waste reduction
depend on the production level o* the plant. All values should
be considered in that context.
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Resin Mixing, Melting,
Extruding, and Molding
V
V
Inserting, Degating,
and Drilling
Finishing
- Texture Coating
- Nickel Coating
- Spray-Fill
- Top-Coat
Spent Rags,
Rejects,
Water/Oil
Solvent Evaporation,
Spent Solvent,
Paint So]ids
Figure 1. Abbreviated process flow diagram.
It should be noted that, in most cases, the economic savings of the
minimization opportunities result from the need for less raw material
and from reduced present and future costs associated with waste
treatment and disposal. Other savings not quantifiable by this study
include a wide variety of possible future costs related to changing
emissions standards, liability, and employee health. It should also be
noted that the savings given for each opportunity reflect the savings
achievable when implementing each waste minimization opportunity
independently and do not reflect duplication of savings that would
result when the opportunities are implemented in a package.
Additional Recommendations
In addition to the opportunities recommended and analyzed by the
WMAC team, three additional measures were considered. These
measures were not completely analyzed because of insufficient
data, implementation difficulty, or a projected lengthy payback. Since
one or more of these approaches to waste reduction may, however,
increase in attractiveness with changing conditions in the plant, they
were brought to the plant's attention for future consideration.
• Wash clean-up rags used during painting and on the mold and
press machines inhouse.
• Send molds to a vendor for application of Teflon coatings to
eliminate the need for the use of the mold release agent. Teflon
can operate continuously at temperatures up to 550 °F. Thus, it
would be suitable for use in these molds since their operating
temperature is 300 to 400 °F.
• Install a carbon adsorption solvent recovery system for the
paint booths to recover finishing solvents.
This research brief summarizes a part of the work done under
Cooperative Agreement No. CR-814903 by the University City Sci-
ence Center under the sponsorship of the U.S. Environmental
Protection Agency. The EPA Project Officer was Emma Lou George.
Table 1. Summary of Current Waste Generation
Waste Generated Source of Waste
Decanted water from oil separator Hydraulic oil leaks and seepage from molds and presses. Water
leakage during changing of press and mold cooling water manifolds.
Annual Quantity Annual Waste
Generated Management Cost
Waste solvents (still bottoms)
Paint solids
Landfilled materials
(e.g., dust, sanding belts and
disks, etc.)
MEK evaporation1
Toluene evaporation
Acetone evaporation
Xylene evaporation
Catalyst evaporation
Recovered solvent evaporation
Rejected forms
Spent hydraulic oil
23,737 gal
nanifolds.
Spray gun cleaning and periodic paint booth wall cleaning. 4,620 gal
Painting booth water baths. 16,280 gal
Grinding of recycled parts. Sanding operations in the Secondary 79,412 Ib
Department.
Cleaning, painting, and mixing operations in the finishing department. 4,426 gal
Cleaning, painting, and mixing operations in the finishing department. 1,100 gal
Cleaning, painting, and mixing operations in the finishing department. 2,204 gal
Cleaning, painting, and mixing operations in the finishing department. 771 gal
Cleaning, painting, and mixing operations in the finishing department. 3,012 gal
Cleaning, painting, and mixing operations in the finishing department. 1,714 gal
Rejects from molding, degating and finishing department. 853,531 Ib
Items returned by the customer for unacceptable finish,
dimensioning, cracking, and paint quality.
Hydraulic oil leaks and seepage from molds and presses. 2,250 gal
$12,003
35,082
92,079
1,994
17,261
2,310
6,546
2,776
7,681
O2
O3
6,1884
1 Figures provided under Annual Waste Management Cost for all solvents reflect raw materials cost only as there is currently no additional waste
management cost associated with evaporation.
2Recovered solvent, according to plant personnel, has no raw material cost component.
3Plant personnel report no raw material costs or waste management costs associated with recycling rejected forms.
4Figure provided is the raw material cost only as plant personnel report no incremental cost associated with recycling spent oil through a reclaimer.
•&V.S. GOVERNMENT PRINTING OFFICE: 19*4 - 550-4X7/801*8
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Table 2. Summary of Recommended Waste Minimization Opportunities
Annual Waste Reduction
Waste Generated
Minimization Opportunity
Paint solids/Solvents
Paint solids/Solvents
Water
Paint solids
(water fraction)
Utilize electrostatic spray
equipment in the finishing
department.
Re-train paint personnel to
improve paint spraying
techniques.
Modify molding press cooling
water manifolds.
Install a vacuum dryer
system to reduce the amount
of water in paint solids
shipped offsite.
Quantity
Percent
Net
Annual Savings
Implementation
Costs
Payback
Years
81,385lb
4,831 Ib
98,513 Ib
44,929 Ib
28
50
50
$203,923
20,392
3,011
33,269
$48,200
3,500
2,320
30,800
0.2
0.2
0.8
0.9
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/S-92/034
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