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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. In an effort to assist these manufacturers Waste Minimization Assessment Centers (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). That document has been superseded by the Facility Pollution Prevention

Guide (EPA/600/R-92/088, May 1992). The WMAC team at

the University of Tennessee performed an assessment at a

plant that manufactures electrical load centers. Raw materials,

including coiled sheet steel and coiled copper strips, polystyrene pellets, and miscellaneous fasteners, are used in metalworking, injection molding, painting, and assembly operations.

The team’s report, detailing findings and recommendations,

indicated that a large quantity of waste overflow rinse water is

generated and that significant cost savings could be achieved

by installing valves that will allow operators to turn off the flow

during periods of nonuse.

This Research Brief was developed by the principal investigators and EPA’s National Risk Management Research 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 become an increasingly costly problem for manufacturers and an

additional stress on the environment. One solution to the

problem of waste generation 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 generation of waste but who lack

the in-house expertise to do so. Under agreement with EPA’s

National Risk Management Research 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 manufacturing plants and also have the knowledge and skills needed

to minimize waste generation.

The pollution prevention opportunity 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 in-house expertise in pollution

prevention.

The potential benefits of the pilot project include minimization

of the amount of waste generated by manufacturers, and

reduction of 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 pollution prevention opportunity assessments require several site visits to each client served. In general, the WMACs

Pollution Prevention Assessment

for a Manufacturer of Electrical Load Centers

ENVIRONMENTAL

RESEARCH BRIEF

Richard J. Jendrucko*, Todd M. Thomas*, and

Gwen P. Looby**

* University of Tennessee, Department of Engineering Science and Mechanics

** University City Science Center, Philadelphia, PA

United States

Environmental Protection

Agency

National Risk Management

Research Laboratory

Cincinnati, OH 45268

Research and Development EPA/600/S-95/029 September 1995
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follow the procedures outlined in the EPA Waste Minimization

Opportunity Assessment Manual (EPA/625/7-88/003, July 1988).

The WMAC staff locate the sources of waste in the plant and

identify 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 technological and economic information is developed. Finally, a confidential report that details the WMAC’s findings

and recommendations (including cost savings, implementation

costs, and payback times) is prepared for each client.

Plant Background

This plant manufactures electrical load center housings for use

in residential and commercial buildings. It operates 6,000 hr/yr

to produce over one-million units annually.

Manufacturing Process

Electrical load center housings are manufactured by this plant

from raw materials including coiled sheet steel stock and coiled

copper strips, polystyrene pellets, and miscellaneous fasteners. The major operations performed by the plant are metal

working, injection molding, painting, and assembly.

Metal Working

Metal housing boxes are fabricated from either cold-rolled steel

or galvanized steel received at the plant in coils. After inspection, coils are transferred to impact cutting operations in which

the steel is sheared into flat patterns and then sent to boxforming operations.

Next, the cut patterns are loaded into the die of a large press

that punches hole patterns which provide inlets or outlets for

electrical wiring into the metal sheets. Then the metal pieces

are formed into a box shape using another press. Box corners

are spot-welded for reinforcement. Finished boxes undergo

inspection, and those that pass are transported to the

electrocoating painting operation. Defective boxes are shipped

offsite for recycling.

Copper electrical contacts used in the internal components of

the finished product are also manufactured onsite. Copper

strip rolls are inspected and transferred to cutting operations.

Appropriately cut copper pieces are dropped onto a chain

conveyor and transported through a gas-fired heat-treatment

oven. After heat treatment, about 20% of the parts are sent

offsite to be nickel plated. Parts that have been plated are

fastened to plastic parts manufactured onsite to form subassemblies. Unplated copper parts are stored until needed in

final assembly.

Injection Molding

Various plastic structural pieces that are used to hold electrical

contacts and switches in place are manufactured onsite using

injection molding machines. Polystyrene pellets are vacuumconveyed to a feed hopper above the injection molding machine. The pellets are metered into the machine’s heated

barrel in the appropriate quantity.

Inside the molding machine, plastic is melted and injected

under high pressure into a separable cavity-mold. Once the

cavity is filled with molten plastic, the mold is allowed to cool,

thus hardening the plastic into the desired shape. After plastic

solidification, the mold opens allowing the formed parts to drop

onto a conveyor belt. After storing 95% of the parts until

needed in final assembly, the remaining parts are shipped

offsite for the production of subassemblies used in the final

products.

Electrocoating

Metal boxes are painted using a cathodic electrocoating system in which resinous materials containing pigments in a water

suspension are deposited on the part’s surface using an electric potential difference. Because this paint system is a form of

electrocoating, boxes must be thoroughly washed and rinsed

to remove contaminants prior to coating.

The metal boxes are conveyed through the following tanks in

sequential order:

• heated dilute potassium hydroxide solution spray-wash for

removal of surface particulates and oils

• clean water rinse

• heated dilute phosphorous solution spray-wash for etching of

the metal

• clean water rinse

• deionized water wash

• paint solution

• deionized water rinse to remove residual paint solution

• surfactant solution rinse to facilitate water drainage

Painted boxes are conveyed through a gas-fired oven for

curing. After the boxes exit the oven, they are cooled and

inspected. Those boxes that pass inspection are transferred

into storage to await final assembly.

Final Assembly

Final assembly of the electrical load centers consists of installation of component parts, such as breakers and switches, into

painted steel housings on an automated-robotic assembly line

and manual installation of internal and external components

that require part manipulation not suitable for robots.

An abbreviated process flow diagram for the production of

electrical load centers is shown in Figure 1.

Existing Waste Management Practices

This plant already has implemented the following techniques to

manage and minimize its wastes.

• Waste computer paper is collected and recycled.

• The use of chlorinated cleaning solvents has been eliminated.

• Wooden pallets are repaired and reused.

• Copper and steel scrap are recycled.

• Self-adhering labels are used on the load centers in order to

eliminate the use of glue.

Pollution Prevention Opportunities

The type of waste currently generated by the plant, the source

of the waste, the waste management method, the quantity of
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the waste, and the waste management cost for each waste

stream identified are given in Table 1.

Table 2 shows the opportunities for pollution prevention that

the WMAC team recommended for the plant. The opportunity,

the type of waste, the possible waste reduction and associated

savings, and the implementation cost along with the simple

payback time are given in the table. The quantities of waste

currently generated by the plant and possible waste reduction

depend on the production level of the plant. All values should

be considered in that context.

It should be noted that the economic savings of the opportunities, in most cases, results 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 also should be noted that the savings given

for each opportunity reflect the savings achievable when implementing each pollution prevention opportunity independently

and do not reflect duplication of savings that may result when

the opportunities are implemented in a package.

This research brief summarizes a part of the work done under

Cooperative Agreement No. CR-819557 by the University City

Science Center under the sponsorship of the U. S. Environmental Protection Agency. The EPA Project Officer was Emma

Lou George.
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Figure 1. Abbreviated process flow diagram for electrical load center manufacture.

E l e c t r o c o a t i n g

Cold-Rolled

or

Galvanized Steel

Inspection

Impact Metal

Cutting

Operations

Metal

Forming

Potassium

Hydroxide

Spray

Wash

Spray

Rinse

Spray

Rinse

Deoxidized

Water

Spray

Wash

Phosphate

Solution

Spray

Wash

Electrocoat

Painting

Deionized

Water

Spray

Rinse

Dionized

Water

Surfactant

Wash

Oven

Curing

Storage

Automated

Assembly

Manual

Assembly

Injection

Molding

Cutting

Operations

Heat

Treating

Storage

Offsite

Fabrication of

Subassemblies

Offsite

Plating

Storage

Polystyrene

Pellets

Copper Strip

Rolls

95%

of Parts

5%

of Parts

20%

of Parts

80%

of Parts

Finished

Product
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Table 1. Summary of Current Waste Generation

Annual Quantity Annual Waste

Waste Stream Generated Source of Waste Waste Management Method Generated (lb/yr) Management Cost

Miscellaneous solid waste Metalworking, injection molding, final assembly Shipped offsite to municipal landfill 1,080,000 $28,950

Scrap steel Metal cutting Sold to recycler 301,220 -6,5501

Spent hydraulic oil Metalworking and injection molding machines Shipped offsite to be blended into fuel 16,660 12,065

Absorbent and oil Leaks from metalworking and injection molding Shipped offsite to controlled landfilled 4,325 7,530

machines

Scrap copper Metal cutting Sold to recycler 9,990 -2,7901

Plastic scrap Injection molding Shipped offsite to municipal landfill 2,4002 6,3003

Potassium hydroxide cleaning solution Cleaning of boxes prior to painting Treated in onsite wastewater treatment system 1,525,125 1,340

Evaporated water Potassium hydroxide and sodium phosphate tanks Evaporates to plant air 3,423,750 0

Rinse water Rinse following potassium hydroxide cleaning Treated in onsite wastewater treatment system 1,029,200 900

Sodium phosphate solution Etching of metal prior to painting Treated in onsite wastewater treatment system 127,960 110

Rinse water Rinse following sodium phosphate treatment Treated in onsite wastewater treatment system 971,100 850

Overflow rinse water Rinse following potassium hydroxide cleaning and Treated in onsite wastewater treatment system 83,000,000 72,890

sodium phosphate treatment

Deionized wash water Wash prior to painting Treated in onsite wastewater treatment system 439,900 390

Paint tank sludge Cleaning of paint tank Shipped offsite to controlled landfill 2,600 5,710

Waste permeate Ultrafiltration of paint solution Treated in onsite wastewater treatment system 2,116,500 1,860

Waste filter paper Filtration of paint solution Shipped offsite to municipal landfill 1,2502 04

Deionized water rinse Post-painting rinsing Treated in onsite wastewater treatment system 1,037,500 910

Wastewater from deionized water Post-painting rinsing Treated in onsite wastewater treatment system 332,000 290

and surfactant rinse

Spent HCl Ion exchange regeneration Treated in onsite wastewater treatment system 19,780 20

Spent caustic Ion exchange regeneration Treated in onsite wastewater treatment system 24,720 20

1Net revenue received

2Also included in total amount of miscellaneous solid waste generated (1,080,000 lb/yr) 3Cost represents raw material cost only. Other waste management costs are included in $28,950 cost associated with miscellaneous solid waste 4Included in $28,950 cost associated with miscellaneous solid waste
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Table 2. Summary of Recommended Pollution Prevention Opportunities

Annual Waste Reduction

Net Annual Implementation Simple

Pollution Prevention Opportunity Waste Stream Reduced Quantity (lb/yr) Per Cent Savings Cost Payback (yr)

Install electrically-activated flow valves that will Overflow rinse water 14,940,000 18 $ 15,800 $ 1,000 0.1

allow operators to turn off the continuous rinse

water overflow during periods when painting

does not occur.

Filter and reuse hydraulic oil used in the metal- Spent hydraulic oil 8,330 50 10,200 5,000 0.5

working and injection molding machines in

order to extend its useful life. The filtered oil

should be tested periodically to ensure that it is

suitable for reuse.

Utilize reusable cloth rags provided by a rental Miscellaneous solid waste 4,500 negligible 13,800 625 0.1

service to replace paper towels used for

clean-up.

Collect and store waste hydrochloric acid and Spent HCl 19,780 100 8,000 18,200 2.3

sodium hydroxide produced from the regener- Spent caustic 24,720 100

ation of the deionized water ion exchange

unit and use to neutralize the effluent wastewater stream.

Implement an improved maintenance pro- Absorbent and oil 3,240 75 7,170 14,880 2.1

gram for the injection molding and metal

working machines to ensure that all hydraulic oil leaks are repaired in a timely

fashion.

Collect scrap plastic from the older injection Plastic scrap 1,800 75 4,730 0 immediate

molding machines used in the plant and

reuse it as feedstock in the newer injection

molding machines.
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BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/S-95/029