&EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S-92/016 May 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Manufacturer of
Permanent-Magnet DC Electric Motors
F. William Kirsch and Gwen P. Looby*
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 Cen-
ters (WMACs) were established 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 permanent-magnet DC
electric motors—approximately 12 million motors and repair
parts per yr. The armatures and stators are manufactured
separately and then assembled into complete motor units.
After assembly, the motors are appropriately masked and
painted according to customer specifications. The team's re-
port, detailing findings 'and recommendations, indicated that
the majority of waste was generated in the armature assembly
line but that the greatest savings could be obtained by install-
ing an electrostatic powder coating system to reduce the gen-
eration of waste paint solids (93%) and to eliminate the gen-
eration of waste paint liquids.
This Research Brief was developed by the principal investiga-
tors and EPA's Risk Reduction Engineering Laboratory, Cincin-
nati, OH, to announce key findings of an ongoing research
project that is fully documented in a separate report of the
same title, which is available from the authors.
Introduction
The amount of waste generated by industrial plants has be-
come an increasingly costly problem for manufacturers and an
'University City Science Center, Philadelphia, PA 19104.
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
in-house 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
engineering faculty and students at the University of
Tennessee's (Knoxville) WMAC. The assessment teams have
considerable direct experience With process operations in manu-
facturing 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 $50 million, employ no more than
500 persons, and lack in-house expertise in waste minimiza-
tion.
The potential benefits of the pilot project include minimization
of the amount of waste generated by manufacturers, reduced
waste treatment and disposal costs for participating plants,
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
Assessment Manual (EPA/625/7-88/003, July 1988). The WMAC
ug> Printed on Recycled Paper
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staff locates 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 detailing the WMAC's findings and recom-
mendations (including cost savings,' implementation costs, and
payback times) is prepared for each client.
Plant Background
The plant produces permanent-magnet DC electric motors for
general use. The plant operates 6,860 hr/yr to produce ap-
proximately 13 million motors and parts.
Manufacturing Process
Raw materials for the manufacture of the motors and parts
Include Iron and aluminum castings, steel tubing and shafting,
copper wire, copper commutators, steel laminations, purchased
fans, poles, epoxy coating, varnish, adhesive, and cleaning
chemicals. The two separate parts of the product (the armature
and the stator) are manufactured separately and then as-
sembled into complete motor units. An abbreviated process
flow diagram is illustrated in Figure 1.
The following steps are involved in making the motors:
Armature Assembly
Assembly of the armatures begins with the cutting and machin-
ing of steel shafts. A semi-synthetic metal working fluid or
coolant is used in the machining area to cool the grinders and
lathes; spent coolant is disposed of offsite as hazardous waste.
Metal scrap is hauled offsite by a metal reclaimer.
Approximately 2% of the shafts are then taken to the painting
area to be coated with a "black oxide" paint while the remaining
98% receive no coating. The painting process is described in
detail. Next, all shafts are transported to a subassembly area
where steel laminations are stacked (the height will vary ac-
cording to motor design) and pressed onto a shaft. Assembled
armatures are then preheated in a laminating oven. After pre-
heating, each part Is manually dipped into a 200-gal epoxy
powder dip tank and allowed to cool. An exhaust hood collects
released epoxy dust that is ducted to a collection bag filter for
periodic disposal offsite as hazardous waste. This powder
becomes waste after collecting moisture from the atmosphere.
Next, the epoxied shafts with lamination are put onto a coil-
winding machine on which copper wire is manually wound onto
the epoxy-coatod unit and fitted between the "fins" of the
lamination. Wood or paper insulators are manually tapped
between each "fin" and then copper commutators are applied
to the end of each shaft and wire terminators are connected to
the copper commutators. The armatures are then manually
loaded into an oven in which varnish is applied over wires at
both ends of the lamination and drying occurs. Surface varnish
and epoxy along with some lamination metal is then ground off
to meet specifications. Small amounts of this waste varnish/
epoxy powder are disposed of in the municipal trash. In addi-
tion, varnish that becomes too thick for proper application is
shipped offsite as a hazardous waste.
Finally, pre-purchased fan components are preheated in an
eloctrfc oven and manually dropped down onto shafts. The part
is allowed to air cool to produce a tight fit. From the sub-
assembly area, finished armatures are transported to the fin-
ished goods stock room to await final assembly.
Stator Assembly ',
Stator assembly begins with machining of steel tubing. After
machining, parts are transferred to the cleaning area where
they are manually conveyed and dipped in a series of five
tanks to prepare the surface for adhesive fastening of magnetic
poles. The first tank is a caustic-solution bath. Secondly, the
parts are dipped in a rinse tank after which they are immersed
in a phpsphating tank. Another rinse tank follows the
phosphating tank and finally the parts are dipped in a sealing
tank that contains sodium nitrate. Solutions from tanks #1 and
#3 are dumped every 6 wk. Sludge from those tanks is shov-
eled out of the tank bottoms and shipped offsite as hazardous
waste; wastewater from the tanks flows to the septic tank
where the acidic water from tank #3 neutralizes the caustic
water from tank #1. The water streams from rinse tanks #2 and
#4 are combined for neutralization and pumped to the sewer.
From the septic tank, the wastewater is pumped to the sewer.
i
The machined and cleaned tubing lengths are then transported
to the adjacent pole area where they are manually wiped clean
with an acetone-wetted cloth. On an annual basis, 75% of
these cloths are shipped offsite, washed, and brought back to
the plant for reuse. The remaining 25% of the rags are too torn
or thin for reuse and are shipped offsite for incineration. Next,
the pole pieces with adhesive applied are manually applied to
the inside surface of each unit and held in place with clamps.
The adhesive is cured by baking the stator units in one of four
curing ovens. Next, the stator units are taken to another subas-
sembly area where the poles are magnetized and then the
units are transferred to final assembly.
In final assembly, armatures are placed inside the stators and
iron castings with bearings are positioned on the end of the
stators to form the complete motors. Upits may then be trans-
ported to the painting area, if required.
Painting
About 2% of this plant's products arei painted black for cos-
metic purposes. Parts to be painted are manually removed
from final assembly and placed on a conveyor system. These
parts are conveyed through a water curtain spray paint booth
and are manually spray-painted with solvent-based flat black
paint. Paint overspray is captured in the water curtain and is
precipitated out with the use of a chelating agent. Waste paint
sludge from this operation is periodically removed from the
booth and shipped offsite as hazardous waste. In addition,
some paint is skimmed off the top of the water and added to
the paint sludge. Water from the water curtain sump that has
become too contaminated with paint is shipped offsite as waste
paint liquids.
Approximately 3% of the painted products are conveyed through
an "air-dry" spray paint booth to which gloss black painHs
added. Used air filters are removed from this booth and added
to the paint solids waste barrels.
Each paint booth has one spray gun; in use. The guns are
cleaned periodically with solvent; spent solvent is shipped
offsite as a hazardous waste.
Finally the product pieces are air-dried, packaged, and shipped.
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Armature Assembly
Machining
Sub-Assembly
Laminating
Epoxy Coating
Sub-Assembly
Varnish Coating
Tolerancing
Fan Addition
Waste Epoxy
Waste Varnish
Stator Assembly
Machining
5-Stage Surface Prep
Acetone Cleaning
Poles Glued in
Curing
Pole Magnetization
Spent Coolant
Scrap Metal
Final Assembly
- castings added
Acetone Contaminated Rags
Surface Prep Liquid
Water and Sludge
Paint Line
Waste Paint Liquids
Waste Paint Solids
Waste Solvent
Packaged and
Shipped
Figure 1. Abbreviated Process Flow Diagram.
Existing Waste Management Practices
• A coolant recovery system recovers almost all of the
coolant for reuse in the machining tools.
Waste Minimization Opportunities
The waste currently generated by the plant, the source of the
waste, the quantity of the waste, and the annual treatment and
disposal costs are given in Table 1.
Table 2 shows the opportunities for waste minimization that the
WMAC recommended for the plant. The minimization opportu-
nity, the waste in question, the possible waste reduction and
associated savings, and the implementation cost along with
the payback time are also shown in Table 2. The quantities of
waste currently generated by the plant and possible waste
reduction depend upon the production level of the plant. All
values should be considered in that context.
It should be noted that the economic savings of the WMOs
usually address only the raw material cost avoidance and
reduction of 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 WMO
reflect the savings achievable when implementing each WMO
independently and do not reflect duplication of savings that will
result when WMOs are implemented in a package.
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Additional Recommendations
In addition to the opportunities recommended and analyzed by
the WMAC team, five additional measures were considered.
These measures were not completely analyzed because of
Insufficient data or minimal savings as indicated below. They
were brought to the plant's attention for future reference,' how-
ever, since these approaches to waste reduction may increase
In attractiveness with changing plant conditions.
• Install drag-out boards on the tanks in the five-step clean-
ing operation to drain tank solutions back into the tanks.
* Collect the solvent used for cleaning the paint spray guns
for reuse. Currently, the solvent becomes part of the liquid
paint wastes.
• Use a detergent or a water-based solvent rather than the
currently used solvent to clean dirty metallic raw material
to reduce the costs associated with handling and removing
the waste currently associated with this cleaning process.
• Convert the current varnish spray system to a more effi-
cient robotic dip system.
• Install an automatic metering system to reduce the amount
of excess adhesive used in attaching the poles to the
inside surface of the stators.
This research brief summarizes a part of the work done under
Cooperative Agreement No. CR-814903 by the University City
Science Center under the sponsorship of the U.S. Environmen-
tal Protection Agency. The EPA Project Officer is Emma Lou
George. '
Tablt 1. Summary of Current Waste Generation
Waste Generated
Source of Waste
Annual Quantity
Generated
Annual Waste
Management Cost, $
Afe?a/scrap
Waste coolant
Thickened varnish
Waste epoxy powder
Znc phosphate/caustic
stodge
Waste sealant
Waste adbasiva
Spent solvent
Paint solids (Including plastic
shoots, filters, and precipi-
tated pa/nt from the paint
booth water curtain)
Westa paint liquids
(water from the paint
booth water curtain that is
too contaminated to be
mused)
Cutting and machining of steel shafts 1-1/2 truck loads
Metal scrap is hauled offsite by a metal reclaimer
Cooling of the grinders and lathes in the machining area 17,600 Ib
Application of varnish to armature assemblies 920 Ib
Application of epoxy powder to armature assemblies 5,175 Ib
Five-stage washer in stator assembly line 3,520 Ib
Five-stage washer in stator assembly line *
Adhesive application to the poles in the stator assembly line 30 Ib
Cleaning of paint spray guns 2,640 Ib
Spray paint booth 7,920 Ib
Water curtain in the spray paint booth 8,840 Ib
658
5,504
524
3,948
1,813
*
20
719
6,151
3,463
'Quantity and cost unknown.
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Table 2. Summary of Recommended Waste Minimization Opportunities
Waste Generated
Minimization Opportunity
Annual Waste Reduction
Quantity
Percent
Net Annual Implementation Payback
Savings Cost Years
Paint solids
Paint liquids
Paint solids
Paint liquids
Paint solids
Paint liquids
Waste epoxy
powder
Zinc phosphate/
caustic sludge
Waste sealant
Waste adhesive
Install an electrostatic powder 7,392 Ib
coating system to replace the 8,840 Ib
water curtain spray paint booth.
Retain the gloss paint booth;
because of its limited use, a change
is not recommended.
Replace the compressed air paint 3,960 Ib
spray guns with air-assisted airless 4,420 Ib
paint spray guns. Paint overspray will
be reduced as a result of increased
paint adhesion to the product
Use the currently inactive electro- 3,696 Ib
static spray paint booth to replace 4,420 Ib
the water curtain spray paint booth.
Reduced raw material costs and
waste generation will result from using
the system. Retrain plant personnel in
proper operating techniques.
Recycle spent epoxy powder. Install 4,658 Ib
an air-tight collection system to permit
recycling.
Discontinue the use of the pole 3,520 Ib
adhesive and utilize a mechanical
means of attaching the poles to the *
inside surfaces of the stators. Imple- 30 Ib
mentation of this WMO would
eliminate the need for the five-stage
washer in the stator assembly line.
93
100
50
50
47
50
$10,2301* $78,440
7.7
5,850' 15,440
9,970' 7,000
2.6
0.7
90
100
100
100
14,470' 6,480
31,760'* 110,880
0.5
3.5
'Includes raw material cost savings.
'Total cost savings have been reduced by the cost of new material required.
•&U.S. GOVERNMENT PRINTING OFFICE! I99Z - 648-080/40Z58
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feULK RATE
United States Center for Environmental POSTAGE & FEES PAID
Environmental Protection Research Information : EPA
Agency Cincinnati, OH 45268 PERMIT NO. G-35
Official Business :
Penalty for Private Use $300 ;
EPA/600/S-92/016
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