EPA-600/R-94-131
August 1944
«yEPA Research and
Development
REPLACING SOLVENT
CLEANING WITH
AQUEOUS CLEANING
United States
Environmental Protection
Agency
Prepared for
Office of Environmental Engineering
and Technology Demonstration
Prepared by
Air and Energy Engineering Research
Laboratory
Research Triangle Park NC 27711
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EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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E PA- 600 /R- 94-131
August 1S94
REPLACING SOLVENT CLEANING WITH AQUEOUS CLEANING
By
Kenneth R. Monroe
The Center for Aerosol Technology
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
EPA Cooperative Agreement CR 819541-01-0
EPA Project Officer: Charles H. Darvin
Air and Energy Engineering Research Laboratory
Research Triangle Park, North Carolina 27711
Prepared for:
U.S. Environmental Protection Agency
Office of Research and Development
Washington, D.C. 20460
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ABSTRACT
This report documents actions taken by Robert Bosch Corporation,
Charleston, SC, in replacing the cleaning solvents CFC-113 and trichloroethylene
(TCE) with aqueous solutions. Bosch has succeeded in eliminating all CFC-113 use
and so far has eliminated two thirds of their TCE usage. Their goal is to be
completely free of chlorinated cleaning solvents by the end of 1995.
These changes in cleaning have not only responded to the environmental goals
of the Montreal Protocol and EPA's 33/50 program but have also resulted in improved
cleaning at dramatically reduced costs. An early key decision was to replace their
aging, large central degreasing stations with a multitude of small cleaning units, each
designed and dedicated for cleaning just one part at one step in the product assembly
process. This strategy demanded reassessment of each cleaning step and the
identification of apparatus and chemistry for optimizing each aqueous replacement.
This report summarizes the actions taken to achieve aqueous cleaning of four typical
component parts, previously cleaned with chlorinated solvents. The report provides
quantitative comparisons of cleaning performance and costs of the old chlorinated
(1988) and the new aqueous (1992) cleaning methods. For each of these
components, the new aqueous cleaning step matched or exceeded the cleanliness
levels of the old, chlorinated cleaning methods and did so at similar or lower costs.
ii
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CONTENTS
Abstract ii
Figures v
Tables vi
Acknowledgment vii
Units viii
1. Introduction 1
2. Site/Organization Description 4
3. Cleaning Operations at Bosch, Charleston 7
Parts being cleaned 7
Previous solvent cleaning technology 7
Costs of previous technology 9
Options for replacing chlorinated solvents 10
Cleaning process selection 11
Cleanliness criteria 11
Hardware selection 12
Chemistry selection 13
4. Conversion Plans and Performance of Four Cleaning Steps 15
Part A 15
The 1988 cleaning sequence 15
The 1992 cleaning sequence 18
Performance comparisons 20
Cost comparisons 23
Part B, 304 stainless steel subassembly 23
The 1988 cleaning sequence 26
The 1992 cleaning sequence 26
Performance comparison: chlorinated solvents
vs. high-pressure aqueous spray 27
Cost comparison: chlorinated solvents vs.
high-pressure aqueous spray 27
iii
\
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CONTENTS (Continued)
Part C, induction coil 29
The 1988 cleaning sequence for coils 29
The 1992 cleaning sequence for coils 29
Performance comparisons between coil cleaning
sequences 31
Cost comparisons between coil cleaning sequences . . 31
Part D, Viton B O-ring 33
1988 cleaning sequence for O-rings 33
1992 cleaning sequence for O-rings 33
Performance comparisons between O-ring
cleaning sequences 35
Cost comparisons between O-ring cleaning
sequences 35
5. Summary 37
6. Postscript Reflections 39
iv
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FIGURES
Number Page
1. Reduction in CFC usage and costs 2
2. TCE vapor degreaser 8
3. Cleaning sequences for Part A 17
4. Reduced rejection rate before Part A heat treatment (soft stage)
brought about by the switch to the 1992 cleaning process 21
5. Reduced rejection rate at Part A visual inspection (hard stage)
brought about by the switch to 1992 cleaning process 22
6. Comparison of cleaning costs in Part A 24
7. Cleaning sequences for Part B 25
8. Cleaning cost comparisons for Part B 28
9. Cleaning sequences for Part C, a purchased induction coil 30
10. Comparisons of coil cleaning costs 32
11. Cleaning sequences for Part D, Viton B O-rings 34
12. Comparisons of O-ring cleaning costs 36
v
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TABLES
Number Page
1. Nonlabor annual operating costs, all cleaning steps 3
2. The Bosch solvent replacement team 6
3. Representative components for cleaning 16
vi
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ACKNOWLEDGMENT
The author wishes to acknowledge the cooperation and support of the
Robert Bosch Corporation, Charleston, South Carolina, in the preparation of this
report. The initial and primary contact person at Bosch was Roland K. De'ssaure, a
manufacturing engineer in the Automotive Group. He arranged the initial project
presentation at Bosch and fielded many questions and requests over the following
months. Wolfgang A. Hasper, Unit Manager, Industrial Engineering, contributed
valuable cost and performance data. Steve Bledsoe, Manager, Engineering Services,
provided guidance with respect to the corporate outlook on the company's
environmental responsibilities and goals.
vii
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UNITS
The majority of the data reported here are in English units, the primary units
used by both the vendors in rating equipment and Bosch in their process descriptions.
These English units have been retained to simplify communication with most of the
intended readership. For those few readers preferring metric units, multiplying factors
for converting from the English units used in this report to their metric equivalents are
given in the table below.
METRIC CONVERSION FACTORS (Approximate)
Symbol
When You
Know Number
of
Multiply By
To Find
Number of
Symbol
LENGTH
in
inches
2.54
centimeters
cm
ft
feet
30.5
centimeters
cm
MASS
lb
pounds
0.454
kilograms
kg
VOLUME
gal
gallons
3.79
liters
L
PRESSURE
atm
atmospheres
98.1
kilopascals
kPa
psi
pounds per
square inch
6.89
kilopascals
kPa
TEMPERATURE (Exact)
°F
degrees
Fahrenheit
5/9 (after
subtracting 32)
degrees
Celsius
°C
viii
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SECTION 1
INTRODUCTION
Several factors now strongly favor industrial cleaning of metal surfaces based
on chemicals other than chlorinated solvents:
1. The Copenhagen amendments to the Montreal Protocol have established
January 1,1996 as the deadline for the phaseout of production of Class
I substances*. These include the solvents 1,1,2-trichloro-
1,2,2-trifluoroethane (CFC-113), methyl chloroform (1,1,1-trichloroethane,
abbreviated TCA), and carbon tetrachloride.
2. The CAA also requires all products manufactured after May 15,1993
with TCA or other Class I substances to display a label announcing that
fact along with the warning that these solvents are destructive to the
ozone layer [Federal Register, Vol. 58, No. 27, p. 8162, Thurs., Feb. 11,
1993].
3. The costs of these chemicals have skyrocketed, and the costs of most
other chlorinated solvents may follow the same pattern.
What are the options available to a manufacturer now using chlorinated
cleaning solvents and facing these realities? Many industrial leaders have already
responded to this crisis and found acceptable answers. This report describes one
such set of solutions carried out by Robert Bosch Corporation in Charleston, SC.
They eliminated their use of CFC-113 (544,000 lbs. in 1988) and reduced their
consumption of trichloroethylene (TCE) from 133,000 lbs. in 1988 to 43,000 lbs. in
1992. As graphed in Figure 1, the reduced use of chlorofluorocarbon (CFC) alone has
returned a major dollar savings in chemical costs. Table 1 compares the annual
operating costs for all chemicals and electric power used in cleaning for the years
1988 and 1993. The 1988 values represent the usages before the introduction of any
*A Class I substance is a substance listed in Section 602(a) of the Clean Air Act
(CAA) Amendments of 1990 plus any subsequent additions. Typically it includes
substances having ozone depletion potentials of 0.2 or greater.
1
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T3
C
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o
OT
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a>
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CO
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o
IL
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600
500
400
300
200
100
2 "
1988 1989
1990
1991
1992
1993
m CFC Usage
u (1000s of lbs.)
544
510
160
86
45
0
# Price/pound ($)
1.1
1.35
2.71
3.08
3.86
Annual Cost
(1000s of $)
(Usage x Price/pound)
598
689
434
265
174
0
Figure 1. Reduction in CFC usage and costs.
2
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SECTION 1
INTRODUCTION
Several factors now strongly favor industrial cleaning of metal surfaces based
on chemicals other than chlorinated solvents:
1. The Copenhagen amendments to the Montreal Protocol have established
January 1,1996 as the deadline for the phaseout of production of Class
I substances*. These include the solvents 1,1,2-trichloro-
1,2,2-trifluoroethane (CFC-113), methyl chloroform (1,1,1-trichloroethane,
abbreviated TCA), and carbon tetrachloride.
2. The CAA also requires all products manufactured after May 15, 1993
with TCA or other Class I substances to display a label announcing that
fact along with the warning that these solvents are destructive to the
ozone layer [Federal Register, Vol. 58, No. 27, p. 8162, Thurs., Feb. 11,
1993].
3. The costs of these chemicals have skyrocketed, and the costs of most
other chlorinated solvents may follow the same pattern.
What are the options available to a manufacturer now using chlorinated
cleaning solvents and facing these realities? Many industrial leaders have already
responded to this crisis and found acceptable answers. This report describes one
such set of solutions carried out by Robert Bosch Corporation in Charleston, SC.
They eliminated their use of CFC-113 (544,000 lbs. in 1988) and reduced their
consumption of trichloroethylene (TCE) from 133,000 lbs. in 1988 to 43,000 lbs. in
1992. As graphed in Figure 1, the reduced use of chlorofluorocarbon (CFC) alone has
returned a major dollar savings in chemical costs. Table 1 compares the annual
operating costs for all chemicals and electric power used in cleaning for the years
1988 and 1993. The 1988 values represent the usages before the introduction of any
*A Class I substance is a substance listed in Section 602(a) of the Clean Air Act
(CAA) Amendments of 1990 plus any subsequent additions. Typically it includes
substances having ozone depletion potentials of 0.2 or greater.
1
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¦O
c
=J
&
o
V)
"D
c
CO
CO
3
O
u_
O
600
500
400
300
200
100
2 «
Q.
iS
1988
1989
1990
1991
1992
1993
m CFC Usage
123 (1000s of lbs.)
544
510
160
86
45
0
# Price/pound ($)
1.1
1.35
2.71
3.08
3.86
Annual Cost
(1000s of $)
(Usage x Price/pound)
598
689
434
265
174
0
Figure 1. Reduction in CFC usage and costs.
2
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TABLE 1. NONLABOR ANNUAL OPERATING COSTS, ALL CLEANING STEPS
19 8 8
19 9 3
TCE
CFC
Total
TCE
HMD/Additive
Total
Solvent Loss, ($)
50,000
600,000
650,000
16,000
6,000
22,000
Electric Power, ($)
53,000
47,000
100,000
33,000
8,000
41,000
aqueous replacement technology. The low solvent costs estimated for 1993 ($22,000)
reflect primarily the elimination of all CFC solvent cleaning. Also, TCE costs were
reduced from $50,000 to $16,000. Not only have the chemical costs been
dramatically reduced, but electric power costs have also gone down. Reduced power
costs were realized because of the switch from a few large central cleaning stations to
many small, dedicated cleaning units, each customized for cleaning just one
component type.
Bosch's goal now is to eliminate all TCE-based operations by the end of 1995
and thus achieve a chlorinated-solvent-free operation. The objective of this report is
to provide the details of how these goals and cost savings have been achieved so that
others can learn from these experiences. What has proven successful at Bosch may
transfer directly to other sites in the same industrial category and to other industries
with similar cleaning problems.
The report begins in Section 2 with a brief corporate profile of Robert Bosch
GMBH and, in particular, the manufacturing plant in Charleston, SC. Section 3
contains a discussion of general cleaning problems at Bosch, Charleston, and
describes their philosophical approach in finding suitable replacement technology for
CFC-113 and TCE cleaning. Section 4 reviews the details of converting the cleaning
of four typical parts from chlorinated solvents to aqueous cleaning. The steps of both
the 1988 cleaning process (chlorinated solvents) and the 1992 cleaning process (the
aqueous replacement process) for each component type are listed. The performance
(cleaning adequacy as assessed by visual inspection and extraction tests) and relative
costs of the 1988 and 1992 processes are compared.
3
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SECTION 2
SITE/ORGANIZATION DESCRIPTION
The Robert Bosch Corporation, with corporate offices in Broadview, IL, is a US
subsidiary of Robert Bosch GMBH, Stuttgart, Germany. The parent company is a
large, worldwide conglomerate with annual sales of about 20 billion dollars and
employees numbering about 160,000. Sales of the US subsidiary are a little over one
billion dollars per year. It employs over 5,000 people spread among eight business
segments. Robert Bosch, Charleston is a manufacturing plant in the Automotive
Group, which is the largest subdivision of the Robert Bosch Corporation.
The Charleston plant has been operating since 1973. It currently operates with
about 600,000 ft2 of manufacturing space and employs approximately 1,700 people,
350 of whom are support personnel and engineers. The plant has a heavy
engineering emphasis in support of its assembly and test functions.
The primary products produced at Robert Bosch, Charleston, are gasoline fuel
injectors, antilock brake systems, and diesel fuel pumps. They are sold to
manufacturers such as Ford and General Motors. This activity is listed under
Standard Industrial Code (SIC) 3714, motor vehicle parts. Nationwide, this SIC is
one of the top three in terms of total TCA (1,1,1 -trichloroethane) emissions and is
probably number one in terms of the number of facilities emitting TCA. Robert Bosch,
Charleston, however, does not and has not used TCA. Their metal parts have been
cleaned with CFC-113 and trichloroethylene (TCE). Since all CFC-113 use has now
been eliminated, its parts do not require a Class I substance label. Nonetheless, the
organization has made the decision to phase out the use of all chlorinated solvents by
the end of 1995, including TCE. This decision is partly based on being a good
4
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community citizen and supporting the U. S. Environmental Protection Agency's (EPA's)
33/50 program,* but also on the improved cleaning efficiency and product performance
spawned by the replacement cleaning technologies. Eliminating chlorinated solvents
has been good for both Charleston's environment and product quality.
The primary Robert Bosch contacts in the preparation of this report were
Roland De'ssaure, Manufacturing Engineer [(803) 760-7637] and Wolfgang Hasper,
Unit Manager, Industrial Engineering [(803) 760-7659] who contributed most of the
information reported here. The details and data summaries originated with them and
their coworkers. They are justifiably proud of their success in solving their cleaning
problems and are willing to share their experiences with others facing similar
problems.
Eliminating chlorinated solvents on the production floor required a large team
effort. Table 2 lists those playing primary roles. The team begins with' the Vice
President/Plant Manager, a necessary team member. From the start, Bosch
management supported the solvent replacement team. Equally important,
management recognized that set-backs would occur. All management asked was that
the team do its best. The team included both planners and users of the solvent
replacement strategies, and other support personnel as shown by the variety of skills
represented in Table 2. In-house plating personnel contributed their specialized skills
for the chemical selection.
Changeovers to nonchlorinated solvents began in earnest early in 1990, and
continue today. By the end of 1992, all CFC use had been eliminated by adopting
one of the process changes reported in Section 4. The 1992 processes described in
Section 4 are themselves continually being reevaluated and improved. Certain steps
in the replacement processes described in Section 4 are no longer current, having
been superseded by newer steps. Additional upgrades will continue to be introduced.
*The EPA's 33/50 program is a voluntary pollution prevention initiative to reduce the
1988 national pollution releases and off-site transfers of 17 toxic chemicals by 33%
by the end of 1992 and by 50% by the end of 1995. TCE is one of the 17 target
chemicals on the 33/50 list. Bosch, Charleston, has already met its 1995 TCE goal.
5
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TABLE 2. THE BOSCH SOLVENT REPLACEMENT TEAM
J. Moulton
VP/Plant Manager
T. Smith
Production Manager
F. Skibba
Production Manager, Heat Treatment
R. Dessaure
Process Engineer
M. Carpenter
Process Engineer
P. Amarendran
Process Engineer
W. Hasper
Process Engineer
S. Bledsoe
Process Engineer
G. Boatright
Environmental Officer
C. McNeely
Quality Gauging
J. Evans
Quality Gauging
H. Marano
Purchasing, Capital and Chemicals
D. Root
Solvent Recovery
T. Walker
Facility
J. Bays
Production Supervisor, Heat Treatment
C. Nunnally
Plant Chemist
J. Kochanowski
Metallurgist
S. Grant
Assistant Plant Chemist
B. Adkins
Production Setup
C. Cyran
Production Setup
C. Branch
Production Operator
T. Langley
Setup
T. Fontenot
Supervisor, Contamination Test
A. Gadson
Operator, Contamination Test (3 shifts)
B. Garderson
Operator, Contamination Test (3 shifts)
M. Davis
Operator, Contamination Test (3 shifts)
J. Mingoia
Sp. Equip. Mechanic
S. Bugarin
Sp. Equip. Mechanic
M. Adair
Sp. Equip. Mechanic
6
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SECTION 3
CLEANING OPERATIONS AT BOSCH, CHARLESTON
PARTS BEING CLEANED
Most of the parts cleaned at Bosch, Charleston are for two assemblies, a fuel
injector and an antilock brake system. The cleaning processes associated with these
products are typical of all Bosch cleaning processes and will be discussed here.
The fuel injector assembly, for example, consists of several component parts.
Some parts are cleaned more than once during the assembly process, resulting in
over 30 separate cleaning operations. The parts to be cleaned consist of mild steel,
stainless steel, plastic, and rubber. Contamination to be removed typically includes
metal chips and fibers, grinding coolants, shop dirt, chemical residues, fingerprints,
etc.
Cleaning operations at Bosch include both gross cleaning and precision
cleaning. Gross cleaning is carried out on the open production floor, and precision
cleaning is done in the Class 10,000 cleanroom where final assembly takes place.
Inadequate cleaning can compromise product performance and cause failure. Part
cleanliness is thus more than just a cosmetic consideration. While the cleaning
requirements are less than those of the semiconductor or disk drive industries who
worry about submicrometer-size particles, part cleanliness at Bosch means more than
simple washing or scrubbing in soap and water. Particles larger than about 25
micrometers (jim) are of concern and are targets for removal by the cleaning process.
PREVIOUS SOLVENT CLEANING TECHNOLOGY
in 1988, all cleaning operations for manufacturing were performed using either
CFC-113 or trichloroethylene (TCE). Typically these cleaning steps were carried out
in large centrally located degreasers (Figure 2). Eight units used TCE; seven used
CFC-113. These degreasers were off-the-shelf, commercially available units, and all
7
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Figure 2. TCE vapor degreaser.
8
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included some form of solvent recovery. The units used combinations of sprays and
ultrasonic agitation to dislodge the contaminants, in addition to vapor degreasing.
Both the TCE and the CFC units acted as general purpose cleaning stations for
the various cleaning steps required in manufacturing. Parts passed through the
cleaning stations in their order of arrival. Throughput time for baskets containing a
total of 60-100 lbs. of parts was typically about 40 minutes.
In this operating mode, solvent consumption in 1988 was 544,000 lbs. of
CFC-113 and 133,000 lbs. of TCE.
COSTS OF PREVIOUS TECHNOLOGY
Costs of cleaning using CFC-113 and TCE fall into five categories: capital,
solvent, operating expenses, maintenance, and waste disposal. Waste disposal
depends on site location, as do labor and energy costs. Capital equipment and
chemicals, while less site-specific, change with time-quite rapidly over the last few
years (Figure 1).
The capital costs of centrally located vapor degreasers of the size pictured in
Figure 2 averaged $250,000. When replacing these units, Bosch chose not to resell
them as operating used equipment but to scrap them.
At $1.10/lb., the 1988 cost for CFC-113 solvent was $600,000. The cost for
TCE was $50,000. By prorating plant power costs, the cost of power for operating all
the cleaners was estimated to be $100,000/yr. Operating labor requirements in the
three-shift operation averaged one man/cleaner/shift or $75,000 per year per cleaner
per shift.
Maintenance costs were minor on the central cleaners. The equipment had
little time down for either scheduled or unscheduled maintenance. Waste disposal
costs were also small for the CFC-113 central cleaners, most of the losses being
dragout and vapor losses to the atmosphere. The TCE degreasers also had some
atmospheric losses, but about 92% of the vapor was recovered for reuse.
9
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OPTIONS FOR REPLACING CHLORINATED SOLVENTS
Options considered for replacing the chlorinated solvents included "no clean,"
using other organic solvents, aqueous (water-based) cleaning and supercritical carbon
dioxide. The most desirable option considered by Bosch, Charleston, in replacing
chlorinated solvent cleaning, was the "no clean" option. For the "no clean" option, the
cleaning step is examined to decide if it is absolutely necessary. Sometimes the
cleaning step can be eliminated with only minor changes, or no changes, in the rest of
the manufacturing process. The cleaning step is simply omitted. Successful
replacement of a chlorinated solvent clean with a "no clean" is a fairly rare event, but
has large benefits in reduced costs and cycle time.
An example of this type of process change at Bosch involved the replacement
of solvent cleaning of a part between two machining steps. In the "no clean"
replacement process, the oil-based lubricant is centrifuged off the parts, eliminating
the wash and rinse cycles formerly used. This eliminated a waste stream, reduced
the cycle time, chemical usage, and floor space needed. This "no clean" replacement
resulted from a suggestion by shop-floor manufacturing personnel.
For all those operations for which "no clean" was not feasible, Bosch,
Charleston, decided to bypass interim alternatives, such as the
hydrochlorofluorocarbon solvents. They also decided not to revert to the hydrocarbon
cleaners of earlier years (although the cleaning of the polyamide coil discussed in
Section 4 remains a temporary exception). The Bosch decision was to immediately
address the long-term environmental issues associated with cleaning and develop
cleaning methods that would be as permanent as could be conceived under present
knowledge and regulations. The interim solutions were abandoned as "not buying
time but wasting time."
The next option considered was aqueous cleaning. Aqueous cleaning with
deionized water has proven very effective, especially when customized for one specific
cleaning step on a specific part. The costs of deionized water cleaning become
affordable when used in the limited quantities required by small, dedicated cleaning
10
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stations that incorporate multiple reuses before discharge. Bosch team members
decided that parts cleaning could best be done with small custom cleaners dedicated
to one or a few cleaning steps, which is a major switch from the large central cleaners
of 1988. This switch eliminated any possibility of cross contamination, shortened cycle
times, and allowed better matching of each cleaning process to the specific part and
contaminants. The switch from large central cleaners to small custom units has
improved part cleaning efficiency and reduced solvent losses. This fresh approach of
introducing single function washers for critical cleaning tasks was made easier by the
fact that much of the existing cleaning equipment was 10 years old and in need of
replacement. Particles larger than 500 (xm were being generated in some of these
units. Retrofitting or modifying this existing equipment would be both expensive and
short-sighted. Selecting new, customized equipment, however, required careful
analyses of many cleaning steps. While this process was lengthy and demanding and
continues even today, improvements in product yield and quality that accompanied the
early efforts have convinced Bosch that this approach is best for them.
The team reviewed other options for replacing chlorinated solvents, but did not
choose them for testing. Some, like supercritical carbon dioxide cleaning, sounded
exotic and expensive and not production-ready. The primary reason for dismissing
other options, however, was that aqueous replacement technology had more
advantages and fewer potential problems.
CLEANING PROCESS SELECTION
Cleanliness Criteria
Bosch, Charleston uses two tests to judge the cleanliness of the parts and the
effectiveness of the cleaning techniques. The first is a visual inspection.
Contaminants inspected for include fibers, dust, and machining debris. In the second
test, lots are periodically audited by a five-minute ultrasonic extraction of one basket of
parts from the lot in petroleum distillate. The particles released during the extraction
are collected on a 2" filter with a 5 jxm pore rating and weighed to assess cleanliness.
11
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Control charts plotting reject rates from both the visual inspection and the extraction
test monitor the efficiency of the cleaning process. (Figure 4, p. 21, shows a typical
chart of part rejection based on visual inspection.)
Supporting tests may be carried out in a vendor's facility, but vendor data have
generally played a minor role in the replacement team's decisions. Time lapses
between vendor cleaning and evaluation at Bosch hinder this approach. New process
evaluation at Bosch is typically done on production equipment made available for tests
during off hours. Either an existing production unit is modified or adopted to a new
process, or a prototype production unit is ordered from a vendor. Modifications and
fine tuning are then carried out on the production scale units before the new process
is incorporated into an ongoing production line.
Hardware Selection
Solvent replacement selection at Bosch has always started with the selection of
the cleaning process and associated hardware, such as ultrasonics, high-pressure
spray, or turbo washing, rather than the selection of a cleaning solvent or fluid. The
argument for this approach is that there are hundreds of chemicals to choose from but
only a handful of cleaning processes.
To rapidly identify suitable aqueous cleaning hardware, Bosch first investigated
off-the-shelf washing stations. If off-the-shelf units proved ineffective or were not
available, Bosch retrofitted existing equipment or engineered custom units of their own
design. In one application, they converted a low-pressure spray washer to high
pressure; in another, a high-pressure unit was modified to use water instead of CFC-
113. A turbo washer has also proved very successful in aqueous cleaning of certain
parts, but no single piece of hardware solved all cleaning problems.
Drying following wash and rinse was a particularly sensitive issue for Bosch.
Functional requirements typically require that all water be removed before the next
operation. Removal of water by heating the parts often produced unacceptable
spotting. Centrifuging at room temperature after aqueous cleaning has now become
the part drying technique almost universally adopted by Bosch. The centrifuges used
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provide the option of warm air circulation during the spinning, but this drying
assistance has not often been necessary.
Chemistry Selection
Compatibility of a chemistry with a part is determined by Bosch's chemical and
metallurgical laboratories. These tests for chemical compatibility and absence of part
degradation take 24 to 96 hours and are conducted before introducing any chemical
into production. Safety considerations (flammability or toxicity) cause some solvents
to be eliminated from consideration. The production floor itself then becomes the
laboratory for final acceptance tests. Causes of rejection include poor cleaning in
production and objections from production personnel regarding solvent odor or part
appearance after cleaning.
All but one replacement solution adapted to date has consisted of deionized
water alone or deionized water containing an alkaline cleaner. The specific additives
and surfactants used in the cleaning steps were selected to be compatible with the
part being cleaned, the soil being removed, and the cleaning equipment used. These
decisions involved experimenting with various proprietary products to confirm rust
protection and satisfactory soil removal.
For instance, oil-based lubricants are used for machining the parts. The parts
are cleaned in aqueous systems with chemistries that allow the removed oil to
separate from the water. Oil is removed from the tanks in most operations by
skimming or gravity separation in holding tanks, and is subsequently shipped off-site in
sealed containers for disposal.
Parts cleaned by an aqueous replacement method typically had a different feel
and appearance than when cleaned with a chlorinated solvent. They looked duller
and often had a different color, and some visible water spots. These obvious
differences worried production personnel who were slow to accept the new cleaning
process until they adjusted to the new acceptance tests and received assurances from
the Quality Gauging Department that the new cleaning process was adequate. Only
after a transition period, which varied from part to part and was as long as six months,
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did production personnel accept ownership of the new cleaning apparatus. Until this
confidence built, all breakdowns, equipment, and performance problems were
immediately passed back to the replacement team. Once transfer of ownership was
completed on one part, acceptance for other parts developed more easily and quickly
14
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SECTION 4
CONVERSION PLANS AND PERFORMANCE OF FOUR CLEANING STEPS
This section reviews the details of the conversion of four parts from TCE- or
CFC-113-based cleaning steps to aqueous cleaning. The four parts selected are
described in Table 3 and typify Bosch cleaning operations that have been switched out
of CFC or TCE cleaning. These four cleaning steps were chosen because they show
the wide variety of options available and results possible when ingenuity is applied to
solvent replacement. Each part is discussed separately in the following sections,
which summarize the steps taken to select a specific aqueous replacement process,
and compare before and after cleaning performance and operating costs.
PART A
Figure 3 shows two process flows for cleaning Part A. The one in the left
column is the 1988 process based on TCE and CFC-113. The other is the 1992
aqueous process developed to replace the 1988 chlorinated solvent process.
The process flow consists of two stages, one before an annealing heat
treatment-the "soft" stage of the process flow-and a "hard" stage following the heat
treatment. This machine and anneal sequence typifies many Bosch-processed parts.
The 1988 Cleaning Sequence
The 1988 cleaning sequence following the soft machining consisted of three
separate operations, labeled with a solid square in Figure 3. The initial step was a
cycle through a central degreaser (Figure 2). Four other parts were also cleaned in
this degreaser. From the TCE degreaser, Part A received a low-pressure
15
-------
TABLE 3. REPRESENTATIVE COMPONENTS FOR CLEANING
1. Part A
Composition: 440C steel.
Size and shape: Approximately 1/2" diameter, cylindrical, 1" long.
Special cleaning challenge: Internal recess (see circle). rztm
Contamination to be removed: Metal chips, grinding media, shop dirt, -h(~~
cleaning chemical residues, fibers.
Measurement of cleaning effectiveness: Visual inspection (100%),
extraction testing for particles, statistical process control (SPC)
charts.
2. Part B (Subassembly)
Composition: 304 steel.
Size and shape: 3/4" pin, 1/16" diameter.
Special cleaning challenge: Internal bore (see arrows).
Contamination to be removed: Grinding media, shop dirt, cleaning
chemical residues, fibers.
Measurement of cleaning effectiveness: Visual inspection (100%),; 51
extraction testing for particles; SPC ^
3. Part C (Coil)
Composition: Polyamide 66
Size and shape: 1-1/4" high, 3/4" diameter
Contamination to be removed: Fibers, soldering splatter, contamination
generated from shipping
Measurement of cleaning effectiveness: Visual inspection (audit only);
extraction testing for particles; SPC
4. Part D (O-Ring)
Composition: Viton B
Size and shape: 1/2" ring made of 1/32" stock
Contamination to be removed: Metal fibers, filler material, plastic
contamination, contamination generated from shipping
Measurement of cleaning effectiveness: Extraction testing for particles;
SPC
16
-------
1988
1992
Soft
~ Soft machine
~ Soft machine
4
4
¦ Immersion ultrasonic cleaning TCE
¦ Turbo wash aqueous (wash time:
4
15 min; drain time: 2 min); (5%
¦ Solvent low pressure spray
detergent: 150 °F)
4
4
¦ Vibratory Immersion CFC
¦ Turbo rinse deionized water (130 °F);
4
rinse time: 15 min; drain time: 2 min
~ Heat treat
4
¦ Spray rinse/air blow-off (0.2%
detergent)
4
~ Heat treat
Qty/day: 42,000
Cycle time, 2 baskets (1,300 pes):
18 min (same for wash and rinse)
Hard
¦ Immersion ultrasonic cleaning TCE
¦ Immersion ultrasonic cleaning TCE*
4
4
~ Auto deburr
~ Auto deburr
4
4
¦ Ultrasonic immersion CFC
¦ High-pressure spray wash aqueous
4
(deionized water; 2,000 psi; 4
~ Visual inspect/extraction
min/tray)
4
O Centrifugal dry (6 min, 2 trays)
4
~ Visual inspect/extraction
Qty/Day: 42,000
~ = Noncleaning
¦ = Wash
O = Dry
*Turbo washer (aqueous) introduced 10/93.
Figure 3. Cleaning sequences for Part A.
17
-------
(8-10 atmospheres) solvent spray with a petroleum distillate (flash point of 104 °F).
This spraying unit was dedicated to processing Part A ; no other parts were cleaned in
this sprayer. The final cleaning step before annealing was immersion in CFC-113.
The parts fed into the bath through a spiral chute and were lifted from the bath on a
track that was mechanically vibrated to provide agitation and complete cleaning.
After each of the heat treatment and deburring steps, the parts again passed
through the central degreaser. They then were subjected to 100% microscopic
inspection for contamination. Lots were also audited by the ultrasonic extraction test.
The cleaning effectiveness of the 1988 process was not satisfactory. Reject rates
ranged from 4 to 6.3 percent. Therefore, the motivation to change stemmed from both
performance and environmental issues.
The 1992 Cleaning Sequence
To begin the replacement of the chlorinated solvents, the team sent samples of
dirty parts to six vendors of aqueous cleaning equipment. These parts were evaluated
by the visual inspection and ultrasonic extraction tests when they were returned. By
these tests, a turbo washer with a proprietary detergent proved most successful for
this processing step. Turbo washing implies turbulent washing in a vigorously stirred
solution, the agitation being supplied by a high-speed impeller. This high-energy
feature is physically and economically feasible in a small, dedicated unit.
The decision was made to further evaluate aqueous cleaning in a turbo
washer. A series of in-house metallurgical and chemical laboratory tests confirmed
that the turbo washed parts exhibited no dimensional or chemical changes. The
component surfaces appeared to have retained the properties needed for operation in
the final assembly. No residue or altered texture could be detected.
With manufacturing compatibility established and rough cost estimates favoring
the aqueous process, the decision was made to switch the cleaning to the turbo
washer. Prototype units were ordered and introduced into production. Primary fine
tuning on the production floor consisted of trial and error adjustment of the detergent
concentration. Reducing the formation of foam is typically an important factor in
-------
selecting detergent concentration. Five percent was the optimum detergent
concentration to produce a balance between effective cleaning and water spotting,
foam formation, or residues.
The new 1992 process consisted of two cycles, a wash cycle in the aqueous
detergent solution and a rinse cycle in deionized water alone (Figure 3). In the initial
manufacturing version, two units, each with 160 gallons capacity, were used for the
wash and rinse cycles. The initial process also included an insurance rinse, called the
"spray rinse/air blow-off" in Figure 3. This additional step was carried out in a
machine already available at Bosch and became part of the initial replacement
sequence. Subsequent plans assume that all three "wash" steps in the soft portion of
the 1992 process can be compressed into one step in one apparatus. However, the
wash cycle fluid is currently filtered to only 25 pm while a 3 fim pore size is used for
the rinse water filter.
The cleaning steps in the "hard" portion, previously ultrasonic TCE and CFC
baths, were replaced with aqueous turbo washing (effective 10/93) and a high-
pressure (2,000 psi) wash followed by a centrifugal drying step. The custom
modification of the washer was performed in-house by Bosch personnel and included
the incorporation of a redesigned manifold with five high-pressure pumps. Adding
point-of-use filters immediately upstream of the spray nozzles was also important.
This modified washer proved more effective in eliminating debris from the deburring
operation than the CFC ultrasonic immersion step it replaced. An alkaline aqueous
cleaning solution is used in the turbo washer. The high-pressure washer now uses
just deionized water, although the initial protocol called for an additive.
A rotary disk skimmer is incorporated in the design adopted to separate oils
from the wash solution. This feature, in addition to filtration of the wash solution,
means cleaning solution replacement occurs only once a week. The oils are collected
in a container and sent out as waste for disposal; the wash water is treated and
discharged to the city sewer system.
19
-------
Performance Comparisons
Visual inspection has been the primary criterion for assessing cleanliness. All
components are 100% visually inspected for residue, rust, fibers, dirt, in addition to
machining defects and burrs. By this criterion, the aqueous process clearly
outperforms the 1988 chlorinated solvent process. Figure 4 shows that rejection rates
from visual inspections before the heat treat step have dropped to almost zero from
the nearly 40 percent rate that was characteristic of the 1988 process. Previously, the
high humidity months from June to August always correlated with high rejection rates
at visual inspection because of rust. This high incidence of rust would disappear
during the winter months. The 1992 process has eliminated the phenomenon. Bosch
chemists believe that water vapor condensed under surface particles at high humidity
and formed hydrochloric acid (HCI) with residual chlorinated solvent. The HCI
corroded the metal, producing rust spots. Eliminating the chlorinated solvent stopped
the acid formation.
Rejects from the visual inspection after the cleaning steps of the hard
processing sequence were also significantly reduced with the 1992 process (Figure 5).
Two types of rejects are plotted in Figure 5, those attributed to metal chips and those
attributed to other particulate contamination. Rejects from both sources are detected
by microscopic inspection. The first five months of the 1992 process (months eight to
twelve in Figure 5) included a manually operated crank for moving parts under the
high-pressure spray. Automating this motion (1/93 in Figure 5) further reduced the
reject rate.
At the end of the hard processing sequence, extraction tests were also done on
an audit basis. By 1992, the filter used to collect extracted particles had been
changed to a 2" diameter with a 3 jim pore rating. Particles on the filter are now
counted optically on an optical imaging system (rather than by weighing). Thus, direct
quantitative comparisons between the 1988 and 1992 processing sequences are not
appropriate. Reject rates because of extraction audits have not changed between the
two processes; however, extraction tests continue to be secondary criteria,
20
-------
Month, 1992
Figure 4. Reduced rejection rate before Part A heat treatment (soft
stage) brought about by the switch to the 1992 cleaning process.
21
-------
3/92 4
10 11 12 1/93
Figure 5. Reduced rejection rate at Part A visual inspection (hard stage)
brought about by the switch to 1992 cleaning process.
22
-------
depending as they do on variables such as part orientation and the condition of the
extraction fluid.
Cost Comparisons
A comparison of two types of costs for cleaning is in Figure 6~prorated
nondepreciated capital costs and annual labor costs of operation. The prorated
nondepreciated capital costs represent the initial capital cost of the cleaning equipment
divided among the different part types cleaned by that equipment. In 1988, many
different parts were cleaned in the same equipment. The capital costs in Figure 6
represent the fractional use of the equipment. Similarly, labor costs represent the
costs of operator labor for cleaning just Part A. All of the cleaning equipment used in
the 1992 process of Figure 3 is dedicated to cleaning one component. No other parts
are cleaned in this equipment. Cost comparisons for solvent/chemical use and utility
power have not been broken down according to part but were presented in Figure 1
as total annual costs for site cleaning operations.
The data in Figure 6 show the 1992 aqueous process to be less expensive in
terms of both capital and operating labor costs. The combination of the cost savings
and the reduced reject rates of the 1992 aqueous process confirms that chlorinated
solvent replacement has been a smart business move for Bosch besides being an
environmentally responsible action.
PART B, 304 STAINLESS STEEL SUBASSEMBLY
The subassembly is also a stainless steel component machined at Bosch. Only
the post annealing cleaning sequence is depicted in Figure 7. The description of the
cleaning steps associated with the soft machining steps has been omitted (they are
similar to those for Part A). The 1988 cleaning sequence following annealing
consisted of four steps and used both TCE and CFC-113. This cleaning sequence
resulted in virtually reject-free parts. The 1992 aqueous replacement process has
matched the cleaning performance of the 1988 process and has done so at lower
capital and operating costs.
-------
Prorated, Nondepreclated Capital Costs, No Price Index Adjustment
1988 1992
Soft
Footprint*
Footprint
(ftxft)
(ftxft)
TCE ultrasonic
$ 50,000
17x21
Turbo wash "j
4x5
Low pressure solvent spray
140,000
8x7
Turbo rinse >
$70,000 4x5
Vibratory CFC
38,000
8x10
Spray rinse J
3x4
Hard
Footprint
Footprint
(ftxft)
(ftxft)
TCE ultrasonic
$ 50,000
17x21
Turbo wash
$35,000
4x5
CFC ultrasonic
$50,000
15x22
High-pressure spray
50,000
5x4
Centrifugal dry
6,000
2.5x2.5
Total $328,000
Total $161,000
Prorated, Operating Labor Costs - 1992 dollars
TCE ultrasonic
Low pressure solvent spray
Vibratory CFC
TCE ultrasonic
CFC ultrasonic
0.2 man year
0.5 man year
0.5 man year
0.2 man year
0.5 man year
Turbo wash
Turbo rinse
Spray rinse
High-pressure spray
Centrifugal dry
}
0.5 man year
0.5 man year
Total
1.9 man years/shift
($143,000)
Total
1 man year/shift
($75,000)
'Footprint: the dimensions of the floor space occupied by the equipment.
Figure 6. Comparison of cleaning costs in Part A.
-------
1988 1992
~ Auto deburr
~ Auto deburr
4
4
¦ Immersion/agitation in petroleum
¦ High-pressure spray aqueous
distillate
(4 min/tray)
i
1
¦ Immersion ultrasonic aqueous
O Centrifugal dry
4
I
¦ Immersion ultrasonic TCE
1
~ Visual inspection
¦ High-pressure spray CFC
Qty/day: 42,000
i
Parts/tray: 300
~ Visual inspection
~ = Noncleaning
¦ = Wash
O = Dry
Figure 7. Cleaning sequences for Part B.
25
-------
The 1988 Cleaning Sequence
The first of four wash steps in the 1988 cleaning sequence was immersion with
agitation in a tank of in-house design. The cleaning solvent for this step was a
petroleum distillate. An aqueous ultrasonic bath was next, followed by ultrasonic
cleaning in TCE in one of the central degreasing units. The fourth step was a high-
pressure spray wash with CFC-113. This high-pressure cleaning step appeared to be
critical to the success of the cleaning operation, and high pressure became the focus
of the replacement search. Ultrasonics alone did not clean the part adequately; the
large mechanical forces that are characteristic of high-pressure spraying seemed
necessary for satisfactory cleaning.
The 1992 Cleaning Sequence
Solutions other than water were considered for the high-pressure spray. The
group of candidates included many commercially available semiaqueous solvents such
as terpenes, and some petroleum distillates. The fire and explosion hazards
associated with high-pressure spraying of these flammable solvents discouraged
further development. Certain semiaqueous solvents were declared objectionable
because of odors or greasy residues left on parts. Water became the fluid of choice
for replacing CFC-113 in high-pressure spraying, having both safety and flexibility in its
favor.
The 1992 cleaning sequence chosen is a one-step exposure to high-pressure
water containing a wetting agent and a rust inhibitor. Bosch engineers converted one
high-pressure CFC unit to a high-pressure water sprayer and initiated a series of
exploratory cleaning trials. Variables in the test matrix included type of cleaning
agent, pressure, temperature, nozzle-to-part distance, and exposure time. From these
test results, an acceptable cleaning recipe and sprayer design were developed for the
in-house modified unit. The single nozzle of the original hand-held spray equipment
was replaced by five manifolds, positioned for maximum part coverage and sized to
match the total fluid flow of the original single-nozzle design.
26
-------
Bosch then contracted with an equipment supplier to build a custom, automated
production unit meeting the design specifications determined by Bosch's in-house
work. This arrangement proved highly successful as the equipment supplier could use
both the clean part specifications, in terms of visual inspection and extraction tests,
and the technical guidance provided by the Bosch prototype experiments.
Preacceptance tests at the equipment supplier's site led to initial minor modifications.
Additional changes in chemical additives and cycle times were made on the production
floor at Bosch. The nozzle material was also changed to tungsten carbide to reduce
particle generation due to erosion of the nozzle by the high-pressure water. Two
months separated initial introduction into production and full production acceptance.
Performance Comparison: Chlorinated Solvents vs. High-pressure Aqueous
Spray
The cleaning performance of the 1992 high-pressure aqueous cleaning
sequence has matched that of the 1988 chlorinated solvent cleaning sequence. The
1988 cleaning sequence worked very well with virtually no cleaning-related rejects by
visual inspection. The 1992 process performs similarly.
Cost Comparison: Chlorinated Solvents vs. Hiah-pressure Aaueous Spray
Figure 8 contains prorated nondepreciated costs of capital equipment for both
the 1988 and the 1992 cleaning sequences. It also includes estimates of prorated
annual labor costs for both sequences. Labor costs for the automated 1992 process
are dramatically lower than those of the 1988 process, which was primarily a manual
process. As before, no breakdown of power and chemical solvent costs by part has
been made. Table 1 contains these costs for all cleaning operations.
27
-------
Prorated, Nondepreclated Capital Costs, No Price Index Adjustment
1988 1992
Footprint*
Footprint
(ftxft)
(ftxft)
Agitation in petroleum distillate
$0
3x3
High-pressure aqueous $160,000
10x7
(in-house dip tank)
spray
Ultrasonic immersion, aqueous
50,000
17x21
Centrifugal dry 6,000
2.5x2.5
Ultrasonic immersion, TCE
50,000
4.5x4.5
High-pressure spray, CFC-113
100,000
Total $200,000
5x5
Total $166,000
Prorated, Operating Labor Costs - 1992 Dollars
Dip tank
Ultrasonic immersion, aqueous
Ultrasonic immersion, TCE
High-pressure spray, CFC-113
Total
(manual)
0.25 man year
0.25 man year
0.20 man year
0.75 man year
1.45 man years/shift
($109,000)
High-pressure aqueous ]
spray >
Centrifugal dry J
Total
(automated)
0.25 man year
0.25 man year/shift
($19,000)
'Footprint: the dimensions of the floor space occupied by the equipment.
Figure 8. Cleaning cost comparisons for Part B.
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PART C, INDUCTION COIL
The induction coil is an assembly containing several materials, including
polyamide 66. This part differs from Parts A and B discussed earlier not only in
composition but also in that it is a part fabricated outside the Bosch, Charleston plant.
The part is received ready for assembly without additional machining or other
processing except cleaning. Cleaning of the coil is essential. Otherwise,
contaminants from the coil will interfere with the operation of the product.
The 1988 Cleaning Sequence for Coils
Figure 9 shows the outside origin of the coil by the label "warehouse" before
cleaning for assembly. The 1988 cleaning step was ultrasonic cleaning in CFC-113.
The 1992 Cleaning Sequence for Colls
The 1992 process differs from the 1988 process in the substitution of the
ultrasonic cleaning fluid and the apparatus in which the cleaning is carried out. The
ultrasonic cleaning fluid in the 1992 process is a petroleum distillate, and the
apparatus used is a dedicated ultrasonic bath modified to be compatible with the
petroleum distillate operation (the commercial unit was designed as an aqueous bath).
The key modifications needed to make the ultrasonic unit compatible with the
petroleum distillate operation were: (1) the addition of cooling coils, (2) an exhaust
line for improved ventilation, and (3) improved bath filtration. A centrifugal drying step
has also been added in the 1992 process. The centrifugal drying apparatus includes a
pump and filters for reusing the removed cleaning fluid.
The decision to use a petroleum distillate in an ultrasonic bath was based
primarily on expediency and represents the only instance in which Bosch used an
interim replacement solution before developing the long-term replacement. The
reason for this action was to achieve the corporate goal of CFC-free operation by the
end of 1992. Replacement of the CFC used for cleaning the coil was the final step in
achieving that goal. The petroleum distillate was known to be compatible with the coil
and was an easy action to implement in order to achieve a CFC-free plant.
-------
1988
~ Warehouse
4
¦ Immersion ultrasonic cleaning (CFC)
4
~ Assembly
1992
~ Warehouse
i
¦ Immersion ultrasonic cleaning
(petroleum distillate)
I
O Centrifugal dry
4
~ Assembly
~ = Noncleaning
¦ = Wash
O = Dry
Figure 9. Cleaning sequences for Part C, a purchased induction coil.
30
-------
Developing an aqueous cleaning process, while thought to be feasible and the likely
long-term solution, was perceived as a more difficult, longer task because of drying
and spotting problems.
Ultrasonic cleaning with the petroleum distillate did allow Bosch, Charleston to
meet their deadline for CFC-free operation. Developing a suitable cleaning process
for the coil that is not based on a volatile organic compound (VOC) is now underway.
However, the cost justification for this next replacement task is not nearly so
compelling as with CFC-113 replacement. With CFC replacement, some payback
times (time required for the savings in cleaning costs to exceed the cost of the new
equipment) were about one month. No such dramatic results will accompany the
replacement of petroleum distillates.
Performance Comparisons Between Coil Cleaning Sequences
Coil cleanliness is checked by visual inspection audits (one tray out of 10-20
trays is visually inspected). The visual inspector looks for fibers, dirt, and other foreign
matter. However, the primary measure of part cleanliness is the extraction test with a
petroleum distillate. Based on the extraction tests, the performance of the 1992
process is superior to that of the 1988 process. Virtually no rejects occur after the
1992 cleaning sequence. The same was not true for the 1988 cleaning sequence,
which occasionally did have cleaned parts rejected and returned for recleaning before
assembly.
Cost Comparisons Between Coil Cleaning Sequences
Figure 10 summarizes costs for the two cleaning sequences. Labor costs are
estimated to be similar, but the capital costs associated with half-time use of the
original ultrasonic apparatus exceed those of full-time use of the modified newer unit.
$6,000 of the capital costs represent modifications to the off-the-shelf unit.
31
-------
Prorated, Nondepreclated Capital Costs, No Price Index Adjustment
1988 1992
Footprint*
Footprint
(ftxft)
(ftxft)
Ultrasonic CFC bath
$100,000
24x7
Ultrasonic petroleum distillate bath
$26,000
6x4
Centrifugal dry (including a safety
10,000
2.5x2.5
modification)
Total $100,000
Total
$36,000
CO
ro
Prorated, Operating Labor Costs -1992 Dollars
Ultrasonic CFC bath
0.5 man year/shift
($38,000)
Ultrasonic petroleum distillate bath
Centrifugal dry
0.5 man year/shift
($38,000)
Footprint: the dimensions of the floor space occupied by the equipment.
Figure 10. Comparisons of coll cleaning costs.
-------
PART D, VITON B O-RING
Bosch's fully assembled fuel injector has five O-rings, all of which are
purchased. The only Bosch processing of the O-rings is cleaning before assembly.
Just one O-ring is in a sensitive location, and only this O-ring is audited for
cleanliness.
1988 Cleaning Sequence for O-Rinas
The 1988 cleaning sequence for the O-rings (Figure 11) was identical to the
1988 cleaning sequence for the coils, Part C (Figure 9). These parts shared the same
cleaning equipment in 1988, splitting the use of the ultrasonic apparatus between
them. CFC-113 was the solvent used during ultrasonic cleaning of both parts.
1992 Cleaning Sequence for O-Rinas
Early concern over ultrasonic CFC cleaning of O-rings arose because of
suspected part degradation caused by the ultrasonic action. This fear of damage
directed Bosch's replacement selection away from ultrasonics and high-pressure
sprays and toward the lower intensity mechanical actions of the turbo washer. The
cleaning sequence labeled 1992 in Figure 11, depicts a three-step wash operation
consisting of a turbo wash (140 °F), a turbo rinse (60 °F), and a centrifugal drying
step. In practice, the 1992 cleaning sequence has been found to work better without
any detergent or cleaning agent in the wash solution. The wash step and the rinse
step are, in effect, a rinse-rinse sequence. Both use the same cleaning solution
(deionized water) although carried out in sequence in separate units at different
temperatures.
These turbo washers are small, 15 gallon units dedicated to O-ring cleaning.
The centrifugal drying step is done in a spin dryer. These low cost units easily
maintain an adequate throughput.
33
-------
1988 1992
~ Warehouse
~ Warehouse
4
4
¦ Immersion ultrasonic cleaning CFC
¦ Turbo wash deionized water (140 °F;
4
2 min)
~ Assembly
4
O Turbo rinse deionized water (60 °F;
2 min)
4
O Centrifuge dry (room temperature;
1 min)
~ Assembly
Qty/day: 42,000 each of 5 types of
O-rings (210,000 total)
O-rings/basket: 1500
~ = Noncleaning
¦ = Wash
O = Dry
Figure 11. Cleaning sequences for Part D, Viton B O-rlngs.
34
-------
Performance Comparisons Between O-Rina Cleaning Sequences
The primary measure of cleaning effectiveness comes from the visual
inspection audits. Plastic or metal fibers are the most common cause of lot rejection.
By this measure, the 1992 cleaning sequence outperforms the 1988 cleaning
sequence. Lot rejection runs about 1 % now compared with 1988 lot rejections of
approximately 5%. The obvious improvement caused by the 1992 process led to only
10 days elapsing between the initial production trial and full production acceptance.
Extraction tests yield nondiscriminating poor results for both cleaning
sequences. Neither cleaning sequence performs well by this test. This observation
supports the suspicion of part damage by ultrasonics. Indeed, prolonged exposure to
ultrasonic agitation in the petroleum distillate results in O-ring disintegration and
disappearance. The O-ring evidently is eroded away. Even the five minute exposure
to ultrasonic petroleum distillate produces eroded Viton B particles in addition to
foreign particles extracted off the surface. The extraction test is therefore of dubious
value as a measure of cleaning sequence efficiency for these Viton O-rings.
Cost Comparisons Between O-Rina Cleaning Sequences
Costs of the 1988 O-ring cleaning sequence are identical to those of the
induction coil. The 1992 cleaning sequence, on the other hand, is carried out in small
units that reduce capital costs significantly (Figure 12). Even these modest capital
costs could be reduced by eliminating the rinse step that is a repeat of the wash step.
Labor costs are estimated to be the same for the two cleaning sequences.
35
-------
Prorated, Nondepreciated Capital Costs, No Price Index Adjustment
1988 1992
Footprint*
Footprint
(ftxft)
(ftxft)
Ultrasonic CFC bath
$100,000
24x7
Turbo wash "J
2x3
Turbo rinse >
$11,000
2x3
Centrifuge j
1x1
Total
$100,000
Total $11,000
Prorated, Operating Labor Costs - 1992 Dollars
Ultrasonic CFC bath 0.5 man year/shift Turbo wash "J
($38,000) Turbo rinse V 0.5 man year/shift
Centrifuge J ($38,000)
"Footprint: the dimensions of the floor space occupied by the equipment.
Figure 12. Comparisons of O-ring cleaning costs.
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SECTION 5
SUMMARY
The examples reviewed in Section 4 show that Bosch, Charleston has
succeeded in every instance in replacing a CFC-113 or TCE cleaning sequence with a
sequence based on a nonchlorinated solvent. Furthermore, these replacement
sequences have all cleaned as well as or better than the chlorinated sequence and
have done so with reduced capital costs and the same or reduced labor costs.
Costs of replacement solvents and operating power were not broken down by
part cleaning sequence. For the entire Charleston site, however, the 1988 costs,
based on the CFC/TCE cleaning sequences of that year, greatly exceed those of the
1993 cleaning sequences (Table 1). The primary reason for the dramatic reduction in
nonlabor operating costs over this 5-year period has been the elimination of CFC
solvent losses, as plotted in Figure 1. Although the price per pound of CFC-113 has
more than tripled over that period, Bosch's CFC costs have been eliminated. Cost
reductions in the future will not be as impressive now that all CFCs have been
replaced. The dominant nonlabor operating cost factor in Table 1 is now electric
power, but even this cost has been cut in half because of the new cleaning
sequences.
Comparative costs between 1988 and 1993 cleaning sequences (Table 1) do
not include the engineering and other labor expended in developing and carrying out
the replacement strategies and tactics. These costs are substantial and continue to
be incurred today as Bosch continues to upgrade and improve its parts cleaning
operations. Many 1992 cleaning sequences described in this report will differ from the
sequences actually in use in the future. Some have already changed. Clearly, Bosch
is convinced that the time and resources already spent in converting from chlorinated
solvents have been a good investment. This activity will continue until all TCE and
hydrocarbon solvents have been replaced.
37
-------
None of the aqueous cleaning systems employed or designed by Bosch,
Charleston, have been "closed loop" in the sense of having zero discharge. However,
the replacement washers typically recirculate the wash solution through filters
(ultrafiltration is planned on some units) which has lengthened bath replacement times
to one to two weeks. The need for bath changes between scheduled periods of
preventive maintenance is determined by the particle count in the bath. Parts with
less critical cleanliness requirements may not require as frequent replacement of the
bath solution.
Complete regeneration of the wash solution in the Charleston plant is a future
project. Bosch GMBH has several sites in Germany that have been operating with a
closed-loop aqueous system since 1989. During 1994, Bosch, Charleston plans to set
up some closed-loop systems based on vacuum drying and distillation.
38
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SECTION 6
POSTSCRIPT REFLECTIONS
While carrying out Bosch's plan for eliminating chlorinated solvents, the
replacement team contacted many equipment vendors in the United States. Support
for the team's efforts was not always uniform, with many promises made and then
disregarded by the vendors. More surprising and troubling was the lack of basic
product information. For example, power densities of ultrasonic cleaners and energy
distribution in the bath were generally not known. Worse yet, methods for measuring
this characteristic seemed not to exist.
Chemical suppliers, on the other hand, were able to provide detailed information
regarding product composition and residues. However, particle concentration in many
delivered chemicals seemed unnecessarily high.
The conclusion is that successful replacement of chlorinated cleaning solvents
is unlikely to be a simple, routine task. Outside suppliers will not provide all needed
answers. The right answer for a given site will ultimately have to be made by that
site, and the quality of the replacement selection will reflect the time and effort
invested in making the selection. The encouraging message of the Bosch experience
is that a determined program, with total support from management, more than justifies
itself both economically and environmentally.
39
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Publication No. EPA- 60 0 / r- 94-131
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TECHNICAL REPORT DATA
(Please read Inuructions on the reverse before com/-
1 . REPORT NO. 2
EPA-600 /R-94-131
4. TITLE AND SUBTITLE
Replacing Solvent Cleaning with Aqueous Cleaning
5. REPORT DATE
August 1994
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Kenneth R. Monroe
8. PERFORMING ORGANIZATION REPORT NO.
94U-5396-006
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR819541-01-0
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory-
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final report; 3/93-1/94
14. SPONSORING AGENCY CODE
EPA/600/13
15.supplementary notes ^EERL project officer is Charles H. Darvin, Mail Drop 91, 919/
541-7633.
16. abstract repGrt documents actions taken by Robert Bosch Corp. , Charleston,
SC, in replacing the cleaning solvents 1,1, 2~ trichloro-1, 2, 2-trifluoroethane (CFC-
113) and trichloroethylene (TCE) with aqueous solutions. Bosch has succeeded in
eliminating all their CFC-113 use and so far has eliminated two-thirds of their TCE
use. Their goal is to be completely free of chlorinated cleaning solvents by the end
of 1995. These cleaning changes have not only responded to the environmental goals
of the Montreal Protocol and EPA's 33/50 program but have also resulted in impro-
ved cleaning at dramatically reduced costs. An early key decision was to replace
their aging, large central degreasing stations with several small cleaning units, each
designed and dedicated for cleaning just one part at one step in the product assembly
process. This strategy demanded reassessment of each cleaning step and identifica-
tion of apparatus and chemistry for optimizing each aqueous replacement. The re-
port summarizes the actions taken to achieve aqueous cleaning of four typical com-
ponents, previously cleaned with chlorinated solvents. The report provides quanti-
tative comparisons of cleaning performance and costs of the old chlorinated (1988)
and the new aqueous (1992) cleaning methods. For each component, the new method
matched or exceeded the old method at similar or lower costs.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Solvents
Cleaning
Degreasing
Pollution Prevention
Stationary Sources
Chlorinated Solvents
Aqueous Cleaning
13 B
11K
13 H
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
. 48
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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