United States
Environmental Protection
Agency
Office of Solid Waste
and Emergency Response
Washington, D.C. 20460
EPA/530-SW-89-049
August 1989
Solid Waste
v/EPA
Waste Minimization
in Metals Parts Cleaning
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Waste Minimization
in
Metal Parts Cleaning
United States
Environmental Protection
Agency
Office of Solid Waste
August 1989
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This booklet provides information on ways to reduce wastes associated with
metal parts cleaning operations. It was published by EPA's Office of Solid
Waste and Emergency Response and is part of EPA's waste minimization
program under the 1984 RCRA amendments.
Other EPA Waste Minimization Publications
Waste Minimization Benefits Manual
Manual for Waste Minimization Opportunity Assessments
Guide to Waste Minimization for the Paint Manufacturing Industry
Guide to Waste Minimization for the Pesticide Formulating Industry
Guide to Waste Minimization for the Commercial Printing Industry
(The latter three publications were developed jointly by EPA's Risk Reduction
Engineering Laboratory and the California Department of Health Services.)
Disclaimer
This guide is advisory only. It is intended to be used by industrial personnel
responsible for metal parts cleaning operations in order to help them develop
approaches for minimizing wastes. Compliance with environmental and oc-
cupational safety and health laws is the responsibility of each individual
business and is not the focus of this document. Mention of any product,
service, or process in this document is for educational purposes only and
should not be considered an endorsement by the U.S. Environmental Protec-
tion Agency.
Acknowledgments
This document was prepared under contract 68-01 -7053 by Jacobs Engineering
Group Inc. The project team included Michael Callahan, Deborah Hanlon,
Sally Lawrence, and Michael Meltzer under the direction of Carl Fromm. The
design and layout was done by Vincent P. Medina of Jacobs Engineering
Group Inc.
The following people provided valuable reviews of this document. EPA ap-
preciates their assistance in this important effort: Stephen Evanoff, General
Dynamics Corporation; Brad Gruss, Vice President, Fremont Industries; Jerry
Kohl, North Carolina State University; Richard Randolph, Dow Chemical
Corporation; Ed Rodzewicz, Parker-Anchem Corporation; Marvin Weast,
Retired Director of R & D, Turco Purex, Pennwalt Corporation; and Kathleen
Wolf, Rand Corporation/Source Reduction Research Partnership.
In addition, we would like to thank E.I. du Pont de Nemours and Company for
granting permission to reprint an illustration which appears as Figure 7 of this
document.
u
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Waste Minimization in Metal Parts Cleaning Operations
TABLE OF CONTENTS I
Acknowledgments ii
1. Introduction 1
1.1 What is Waste Minimization? 2
1.2 Incentives for Minimizing Waste 3
1.3 Waste Minimization Assessments 4
2. Waste Minimization in Parts Cleaning Operations 6
2.1 Overview of Parts Cleaning 6
2.2 Waste Minimization Strategy for Parts Cleaning 8
Can Cleaning Be Avoided? 8
Select the Least Hazardous Medium 9
Maximize Cleaning Efficiency 11
Recycle and Reuse Waste 11
3. Waste Minimization Approaches
for Specific Classes of Cleaning Media 12
Solvents 12
3.1 Eliminate Need for Solvents 12
3.2 Substitution Alternatives for Solvents 13
Use Less Toxic Solvents 13
Aqueous Cleaners 14
Emulsion Cleaners 15
Mechanical/Thermal Methods 16
3.3 Minimize Solvent Losses 17
General Options 17
Cold Cleaning 20
Vapor Degreasing 23
3.4 Solvent Segregation and Recycle/Reuse 26
Keep Solvents Segregated 26
Recycling 27
ill
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Waste Minimization i n M e t a I Parts Cleaning Operations
TABLE OF CONTENTS!
Aqueous 31
3.5 Substitution Alternatives for Aqueous Cleaners 31
3.6 Use of Less Hazardous Compounds 31
3.7 Maintain Solution Quality 31
Precleaning Inspection 31
Avoid Unnecessary Loading 32
Provide Continuous Heating 32
Proper Solution Make-Up 32
Remove Sludge and Soils Promptly 33
Monitor Cleaning Solution Strength 33
Equipment Maintenance 33
Reduce Drag-Out 34
Increase Rinsing Efficiency 34
Employ Closed Loop Systems 36
Proper Parts Drying 36
Abrasives 38
Use of Greaseless or Water-Based Binders 38
Use of Liquid Spray Compositions 38
Control Water Level in Mass Finishing Equipment 38
4. Implementation 39
5. Conclusions 39
6. Selected Bibliography 41
7. Sources of Information on Waste Minimization 48
IV
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Waste Minimization in Metal Parts Cleaning Operation
"The Congress hereby declares it to be the national policy of the United States that, whenever feasible,
the generation of hazardous waste is to be reduced or eliminated as expeditiously as possible." HSWA 1984.
1. INTRODUCTION
SOLVENTS
AQUEOUS
ABRASIVES
The Hazardous and Solid Waste Amendments of 1984 to the Resource Conser-
vation and Recovery Act (RCRA) establish as a national policy that hazardous
wastes are to be reduced or eliminated as expeditiously as possible. To help
accomplish this goal, the U.S. Environmental Protection Agency (EPA) will
provide technical materials and guidance to companies through its waste
minimization technology transfer program. As part of EPA's program, this
booklet was prepared to provide waste minimization options to companies
with parts cleaning operations.
Parts cleaning is an important process for a large variety of organizations
involved in the manufacture, repair, and maintenance of parts and equipment.
From large metal fabrication plants to captive maintenance shops of industrial
facilities, parts cleaning operations are essential to doing business.
The reason for focusing attention on minimizing waste in parts cleaning
operations is because the solvents and other chemicals used in parts cleaning
often result in significant air emissions, wastewater discharges, and the gen-
eration of hazardous wastes. Waste minimization offers a significant and often
cost effective opportunity to reduce the emissions and discharges of toxic pol-
lutants into the environment.
This booklet is organized as follows. This introduction covers basic definitions
and concepts of waste minimization, and it outlines incentives for minimizing
waste. A general strategy for minimizing waste is presented. An approach for
applying this waste minimization strategy to parts cleaning operations is
provided in Section Two, which begins with an overview of parts cleaning
operations. Section Three presents waste minimization options in solvent
cleaning, agueous-based cleaning, and abrasive cleaning applications. A
discussion of options implementation follows; then conclusions, waste mini-
mization information sources, and a bibliography close the document.
This booklet is intended to provide the reader with key concepts and establish
a good point of departure in the search for viable waste minimization tech-
niques. Examples are provided throughout the text to help the reader obtain
more detail or specifics for an option being discussed. However, this booklet
is not intended to replace in-depth references or provide detailed information
that may be needed to fully evaluate the feasibility of a specific option.
Where this information is available, the examples provided in this booklet
include the economics of implementing a waste minimization option. How-
ever, the economics of making changes in an operation are often facility-
specific; the scale of an operation may have a great deal to do with whether new
capital outlays can be justified, for example. Because of differences between
facilities, generalizations are difficult and the reader is advised to consider site
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Waste Minimization in Metal Parts Cleaning Operations
specifics in determining whether a waste minimization option is economically
feasible. In addition to the conventional capital and operating costs that are
part of profitability analysis, waste minimization projects should; be consid-
ered for their less tangible but beneficial consequences, such as avoided
regulatory compliance costs, liability avoidance, improved health and envi-
ronment and resulting improved public image. The reader is referred to EPA's
Waste Minimization Benefits Manual for additional information (USEPA,
1988C).
1.1 What is Waste Minimization?
Waste minimization can be accomplished either through source reduction or
recycling of hazardous wastes that are generated or subsequently treated, dis-
posed of, or stored (Figure 1). Although much of the current focus of waste
minimization is on hazardous waste, EPA encourages and promotes the mini-
mization of all wastes released into air, water, and land.
Source reduction is the in-plant reduction of waste, usually and preferably
within the process that generates it. Recycling is the use, reuse, or reclamation
of waste material. Treatment of hazardous waste is not considered by EPA to
be waste minimization, unless it is performed as a necessary step to render the
waste recyclable. The reduction of waste toxicity by dilution, or of waste
volume by dewatering (or more generally, by the removal of an inert innocu-
ous component) are not considered alone and by themselves to be viable waste
minimization options.
One approach to waste minimization is source reduction. The in-plant source
reduction approach relies on changes to input materials, to the physical plant
(or technology), or to the operating practices component of the manufacturing
process. Of all three methods of source reduction, the improvement of oper-
ating practices is often the easiest, least costly, and most effective waste mini-
mization approach, especially in the initial stages of a waste minimization
effort.
Source reduction is generally preferable to recycling because waste generation
is directly curtailed or avoided in the first place. Recycling should be
conducted wherever possible, for wastes that cannot be eliminated or reduced
by making changes in the process.
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Waste Minimization in Metal Parts Cleaning Operations
Figure 1. WASTE MINIMIZATION DEFINITIONS
WASTE MINIMIZATION
The elimination or reduction, to the extent feasible, of hazardous waste that is generated and would
otherwise be subsequently treated, stored or disposed of. It includes any source reduction or recycling
activity undertaken by a generator that results in either (1) the reduction of total volume or quantity of
hazardous waste or (2) the reduction of toxicity of the hazardous waste, or both, so long as such reduction
is consistent with the goal of minimizing present and future threats to human health and the environment
(USEPA 1986).
SOURCE REDUCTION
Any activity that reduces or eliminates the generation of hazardous waste at the source, usually
within a process (USEPA 1986).
RECYCLING
A material is "recycled" if it is used, reused, or reclaimed (40 CFR 261.1(c)(7). A material is "used
or reused" if it is either (1) employed as an ingredient (including its use as an intermediate) to make
a product; however a material will not satisfy this condition if distinct components of the material
are recovered as separate end products (as when metals are recovered from metal containing
secondary materials) or (2) employed in a particular function as an effective substitute for a
commercial product (40 CFR 261.1(c)(5). A material is "reclaimed" if it is processed to recover a
useful product or if it is regenerated. Examples include the recovery of lead values from spent
batteries and the regeneration of spent solvents (40 CFR 261.1(C)(4).
1.2 Incentives For Minimizing Waste
There are numerous economic, regulatory, legal, and other incentives for mini-
mizing waste. A summary of these incentives is provided in Table 1.
It is worth noting that, unlike traditional end-of-pipe treatment approaches,
waste minimization offers real potential for reducing manufacturing cost and
thus can successfully compete with other plant improvement projects for
funding.
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Waste Minimization in Metal Parts Cleaning Operations
1.3 Waste Minimization Assessments
Specific waste minimization options can be identified and developed by
conducting a waste minimization assessment. The assessment process (Figure
2) is a set of procedures for investigating waste streams, generating waste mini-
mization options, evaluating their feasibility and implementing those that are
found to be feasible. The reader is referred to the EPA's Waste Minimization
Opportunity Assessment Manual (USEPA 1988B) for details on how to execute
the assessments and other components of the overall waste minimization
program. The most successful programs in industry include a strong manage-
ment and employee commitment to reduce waste and save money.
Table 1. Incentives for Waste Minimization
Economics
Increased land disposal costs.
Savings in raw material and manufacturing costs.
Avoidance of costly alternative treatment technologies.
Regulations
Certification of a waste minimization program on the hazardous waste manifest.
Biennial waste minimization program reporting.
Land disposal restrictions and bans.
Increasing permitting requirements for waste handling and treatment.
Liability
Potential reduction in generator liability for environmental problems at both onsite and offsite
treatment, storage, and disposal facilities.
Potential reduction in liability for worker safety.
Public Image and Environmental Concern
Improved image in the community and among employees.
Reduced impact on the environment.
Source: USEPA, 1988B.
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Waste Minimization in Metal Parts Cleaning Operations
Figure 2. The Waste Minimization Assessment Procedure
The Recognized Need to Minimize Waste
'*
T
PLANNING AND ORGANIZATION
Get management commitment
Set overall assessment program goals
Organize assessment team
Assessment Organization &
Commitment to Proceed
T
ASSESSMENT PHASE
Collect process and facility data
Set priorities for assessment targets
Review data and inspect site
Develop options
Screen & select options for detailed analysis
Assessment Report of
Selected^ Options
FEASIBILITY ANALYSIS PHASE
Technical evaluation
Economic evaluation
Select options for implementation
«
Final Report, including
Recommenced Options
T
IMPLEMENTATION
Justify projects and obtain funding
Installation (equipment)
Implementation (procedure)
Evaluate performance
a
Successfully Implemented
Waste Minimization Projects
Select New Assessment
Targets and Reevaluate
<- Previous Options
H
"»,
fe
g
I
1
jj
5
ft
M
k
u
s
5
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^ Repeat the Process
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Waste Minimization in Metal Parts Cleaning Operations
2. WASTE MINIMIZATION IN PARTS CLEANING OPERATIONS
2.1 Overview of Parts Cleaning.
SOLVENTS
AQUEOUS
ABRASIVES
Parts cleaning is an integral process operation for industries that repair,
maintain, or manufacture parts and equipment. Examples of such industries
are automobile repair, equipment repair, and transportation maintenance
industries (trucks, trains, ships, and aircraft). Manufacturing groups include
furniture manufacturers, metal fabricators, machinery manufacturers, elec-
tric and electronic equipment manufacturers, and instrument manufacturers,
among many others.
While the science of parts cleaning is very complex, the aim of cleaning is
relatively simple to avoid the generation of rejects during subsequent use
or processing steps by removing contamination (i.e. soil) from the surface of
the parts being cleaned. Removal of soils can be achieved by way of
detergency, solvency, chemical reaction, or mechanical action. Each of these
actions, or a combination of actions, can be employed in a cleaning operation.
Organic solvents, the most widely used class of cleaners, are used primarily
for removing organic or oil-based contaminants. The types of solvents
commonly used for commercial cleaning applications are shown in Table 2
along with other cleaning media, listed by their cleaning action. Table 3
provides a summary of cleaning methods or means of applying a particular
cleaning medium.
Aqueous cleaners can contain acids, alkalies or chelating agents. Acid
cleaners such as sulfuric, nitric, and hydrochloric acids are used to remove
oxidation scale and rust from metal surfaces. Alkaline cleaners are solutions
of inorganic salts often used in heated soak tanks to remove heavy oily soils
and some solid soils. Caustic solution is often employed as a paint stripping
agent. For both acid and alkaline aqueous cleaners, rinse water plays an
important part in the cleaning operation.
Abrasives are designed to remove rust, oxides, and burrs to create a smooth
surface. Common abrasives are sand, aluminum oxide, or silicon carbide
mixed with an oil- or water-based binder.
Detailed review and discussion of parts cleaning can be found in several
references in the bibliography, including Spring, 1963 and 1974; Durney,
1984, and the American Society for Metals' Metals Handbook, 1988.
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Waste Minimization in Metal Parts Cleaning Operations
Table 2. Cleaning Media, Listed by Action
Detergency
(1) Alkaline salts and caustics
(2) Surfactants (soaps and synthetic soaps)
(3) Alkaline cleaners (1 and 2 combined)
(4) Emulsion cleaners (solvents and surfactants)
Solvency
(1) Aliphatic hydrocarbons: naphtha, kerosene, diesel fuel
(2) Aromatic hydrocarbons: benzene, toluene, xylene
(3) Non-flammable solvents (halogenated hydrocarbons: TCA, TCE,
PCE, methylene chloride, chlorofluorocarbons)
(4) Polar solvents (ketones, alcohols, esters, ethers, terpenes, amines)
(5) Emulsifiable solvents (flushed away with water)
(6) Diphase cleaners (solvent and aqueous layered media)
Chemical Reaction
(1) Acidic baths (pickling) yield soluble salts by reaction with oxides,
sulfides, etc.
(a) Mineral acids: sulfuric, hydrochloric, phosphoric acids
(b) Passivating acids: nitric, chromic
(c) Organic acids
(d) Specialty acids containing surfactants for wetting-out action or a foam blanket or pickling
inhibitors to prevent excessive attack on the metal
(2) Alkaline baths
(a) Alkaline de-rusters containing organic sequestrants which solubilize metal oxides and also
remove soils
(b) Molten alkali with or without hydride (reductant) or nitrate (oxidant) or electric current; also
removes soils
(3) Chelating agents react with soils to form soluble complexes
(4) Electropolishing (reverse current cleaning), electrodissolution of
metal substrate at the anode
(5) Oxidizing or reducing agents to chemically render the soil soluble
Mechanical Action
(1) Turbulence/agitation
(2) Abrasives
(3) Deformation
(4) Ultrasonic cleaning
(5) Heat
(6) Electrocleaning (direct current hydrogen scrubbing at the cathode)
Source: Adapted from Spring, 1963.
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Waste Minimization in Metal Parts Cleaning Operations
Table 3. Cleaning Methods
Wiping
Wire brushing
Grinding or machining
Sandblasting or abrasive
blasting
Shot blasting
Liquid blasting
(hydroblast)
Hydroblast with abrasives
Blasting with softer
material, e.g. plastic
bead blasting
Cryogenic paint stripping
Physical distortion
Molten salt bath
Wipe on, wipe off
Immersion
Circulation of cleaner
Air sparging (aqueous
cleaners only)
Spray cleaning
Tumbling in barrels
Ultrasonic cleaning
Steam cleaning or stripping
Vapor degreasing
(solvents only)
Electrocleaning (aqueous
cleaners only)
Flame or hot air
impingement
Centrifugal wheel
2.2 Waste Minimization Strategy for Parts Cleaning
Can cleaning be avoided?
The recommended strategy for developing effective waste minimization
options for parts cleaning operations relies on systematic exploration of the
following sequence of steps:
1. Avoid the need to clean.
2. Select the least hazardous medium for cleaning.
3. Maximize cleaning efficiency.
4. Segregate cleaning wastes.
5. Maximize recycling and reuse.
This strategy is consistent with the multi-media approach and general
emphasis of reducing the waste at the source. Each step is discussed in the
following sections.
In many instances, by controlling the factors that contribute to surface
contamination of the parts, the need for cleaning can be reduced or eliminated
altogether. Control of part contamination starts with a study of contamina-
tion sources. Sources can be incoming soils applied by metal vendors or soils
applied in house (i.e., coolants, stamping fluids, drawing compounds, rust
inhibitor, etc.). Some frequently encountered sources and types of contami-
nation are shown in Table 4.
8
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Waste Minimization in Metal Parts Cleaning Operations
Upon identifying the type and origin of the contamination, it is worthwhile
to examine whether cleaning can be avoided or its extent reduced. For
example, protective coatings of grease or paint (which require solvents for
removal) can be replaced with peel coatings or shrink-wrapping of items with
polymeric sheeting. Moisture which can lead to rust can often be reduced or
eliminated by allowing the parts to dry more thoroughly between operations
or by storing them indoors to avoid condensation and/or rain.
Also of importance is the location of cleaning operations in manufacturing
sequence. Articles to be cleaned prior to finishing should only be cleaned at
the point in time when they are ready for coating. Parts should not be cleaned
and conversion-coated and then warehoused or staged for subsequent batch
coating. During storage, the parts can become contaminated by air-borne oils
or by handling. These contaminants will interfere with ultimate finish quality
and increase the rate of rejects.
Examination and subsequent control of contamination sources may lead to
reduction or elimination of cleaning requirements, as illustrated above.
However, it is also important to note that an unwarranted relaxation of
cleaning requirements may have an opposite effect of increasing waste
generation associated with rework of the rejects, e.g. due to poor coating
quality. Any proposed changes to the cleaning process require careful
evaluation of potential waste generation in downstream operations.
Select the least The choice of cleaning medium for a given parts cleaning operation is
hazardous medium determined by a number of factors:
physical and chemical properties of contaminants, substrate surface,
and cleaning media.
the amount of contaminant to be removed
the required degree of cleanliness and product quality
size, shape, and complexity of part to be cleaned
volume or number of parts to be cleaned per unit time
costs of raw materials, equipment, and labor
worker protection
environmental protection
Shrink-wrapping
Oil is often used to coat metal parts before shipment in order to prevent rust, which forms on exposure to air
and moisture. Similar protection can be achieved by a removable plastic coating, such as polyethylene shrink-
wrapping. At the receiving facility, the use of vapor degreasing to remove the oil is no longer necessary.
Removal of oil contaminants prior to welding
The welding of metal parts which have residual oils present on or near the weld leads to the formation of
carbonaceous deposits due to pyrolysis of organics at high temperatures. Such deposits are extremely difficult
to remove. Cleaning the parts prior to welding greatly reduces the subsequent cleaning requirements.
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Waste Minimization in Metal Parts Cleaning Operations
Table 4. Types and Sources of Surface Contamination
Contaminant
Pigmented metal
drawing compounds
Non-pigmented
metal drawing
compounds
Polishing and
buffing compounds
Cutting and
grinding
fluids
Oxidation and
scale
Quenching oils
Rust protection oils
Lube oils and hydraulic
fluids
Paint and inks
Moisture
Fingerprints
Particulate
matter
Fluxes
Composition
Oil with friction
reducing pigments
(talc, chalk,
lithopone, sulfur,
graphite or lime)
Mineral oils and
highly chlorinated
synthetic oils,
mineral oils and
greases, vegetable or
animal oil and/or
fats, aliphatic esters,
and emulsifiable
synthetic oils
Greases, metallic
soaps, abrasives
and waxes
Plain and sulfonated
mineral and fatty oils,
chlorinated mineral
oil soaps, salts and
saturated fatty alcohols
Rust (metal oxides),
heavy metal salts,
water scale'
Pigment with binder
Water
Body oils,
particulates
Metal chips, dust,
carbonaceous deposits
Rosin, terpenic
compounds
Origin/Use
Press and punch
operations
Press forming,
bending (tubes)
Polishing and
buffing
Machining
operations
Corrosion
oxidation
deposition
welding
Heat treatment
Storage
Surface protection,
identification
Exposure to water,
condensation
Manual handling
Dusty environment,
coking
Soldering
10
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Waste Minimization in Metal Parts Cleaning Operations
The relative importance of these factors can change considerably over time.
For example, both benzene and carbon tetrachloride (former standards in
industry) have been found to be carcinogenic and were regulated out of use
as metal cleaners because of heightened concern over worker exposure. This
same concern, and increased disposal costs, have caused some major automo-
tive manufacturers to phase out solvent cleaners in favor of aqueous cleaners.
In looking for a new cleaning medium or procedure, a company should
consider the least toxic or most environmentally acceptable medium, then, if
this is not satisfactory, progress to more toxic or less environmentally desir-
able alternatives. This pattern dictates that cleaning media be evaluated in
the following order:
water or air
abrasive media with water or air as carrier
aqueous detergent solutions
alkaline solutions
acids
solvents
Ideally, the cleaning method of choice would involve the shortest cleaning
sequences, employing the least toxic cleaning medium, generating the least
amount of wastes, and still providing the necessary minimum level of
cleaning to the part at minimum cost. For facilities attempting to change from
one cleaning medium to another, the impact on subsequent operations must
be considered. Any proposed changes to the cleaning process requires
careful evaluation of potential effects of the cleaner on the substrate that
might affect the integrity of downstream processes (anodizing, plating, paint-
ing, etc.). The impact of cleaner drag-out on the lifespan of downstream
process solutions should also be addressed.
Maximize cleaning efficiency If a cleaning step cannot be eliminated, and the least hazardous cleaning
material that is effective is already being employed, then it should be used as
efficiently as possible. From a waste reduction point of view, this means using
the least amount of cleaning medium to achieve an acceptable level of
cleanliness. Examples of ways to improve cleaning efficiency are cited in later
sections of this booklet for solvent cleaners, aqueous-based cleaners, and
abrasives, respectively.
Recycle and reuse waste The cleaning waste that cannot be eliminated through substitution or more
efficient use should be considered for recycling or reuse. The segregation of
different types of cleaning waste may be required for such recycling or reuse.
Specific examples of recycling and reuse are discussed for specific cleaning
media in later sections of this pamphlet.
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Waste Minimization in Metal Parts Cleaning Operations
3. WASTE MINIMIZATION APPROACHES
FOR SPECIFIC CLASSES OF CLEANING MEDIA
SOLVENTS
In the following sections, waste minimization strategies that are effective for
specific cleaning media are presented. The order of presentation solvents,
aqueous-based, and abrasive cleaners reflects the need to replace or reduce
the use of the most hazardous materials first. Also, a greater amount of
information is presented regarding ways to minimize solvent use than is
provided for aqueous or abrasive cleaners, since solvents are a greater concern
both environmentally and from a health standpoint.
Although organic solvents have excellent cleaning properties, many of them
are considered hazardous to human health and the environment. The negative
environmental and health-related attributes of solvents, particularly haloge-
nated ones include:
toxicity
flammability
ability to dissolve or penetrate polymeric landfill liners
high diffusivity through porous strata
ability to dissolve and serve as a carrier to other toxic organics
high volatility
photochemical reactivity
long half-life
toxic degradation products
resistance to biodegradation
depletion of stratospheric ozone
Solvent wastes were among the first to be banned from land disposal by EPA.
The 1984 RCRA amendments specify five categories of solvent waste (F-001 to
F-005) which are banned from land disposal effective November 1986 (RCRA
3004 (e)(l)). Due to the diverse problems associated with solvent use, solvents
should be used only when no other cleaner is suitable for the job. The major
ways to avoid or reduce the generation of solvent waste include eliminating the
need to use solvent; finding adequate substitutes for solvents; minimizing
losses associated with solvent use; and segregation, recycle, and reuse of waste
solvents.
3.1 Eliminate the Need for Solvents
The first priority in efforts to reduce solvent waste is to examine the cleaning
steps that require solvent. Such examination should aim to avoid solvent use
by eliminating or modifying the cleaning step. Special attention must be given
to the origin of soil and its composition.
Eliminate cleaning step
AT&TTechnologies, Inc. of Union, N. J., report that simple changes made in a testing operation enabled the com-
pany to eliminate a cable-end cleaning step that had employed 1,1,1-trichloroethane (Waste Reduction-The
Untold Story, 1985).
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Waste Minimization in Metal Parts Cleaning Operations
3.2 Substitution Alternatives for Solvents
SOLVENTS
Use less toxic solvents
Many firms have been successful in substituting less toxic cleaning media for
solvents. The alternatives include:
substitution of toxic solvents with less toxic solvents
substitution of solvents with aqueous cleaners
substitution of solvents with emulsion cleaners
substitution of solvents with mechanical and/or thermal methods
Discussion of each substitution approach is provided below. Most emphasis
is given to aqueous cleaners, since this is the major and often most effective
alternative.
In the case of halogenated solvents, media substitution will often require a
switch from vapor degreasing to cold tank cleaning with possible addition of
mechanical or ultrasonic agitation, A preliminary analysis of possible substi-
tutes for chlorinated solvents is available (US EPA 1983).
Substituting one solvent for another in cleaning applications has an extensive
history. Trichloroethylene (TCE) is being replaced by 1,1,1-trichloroethane
(TCA). Benzene and other toxic aromatic solvents were replaced by less toxic
aliphatic solvents such as Stoddard solvent and naphthas. Possible solvent
alternatives to halogenated compounds include:
aliphatic hydrocarbons (e.g. naphthas)
terpenes
N-methyl-2-pyrrolidone
dibasic acid esters
Although photochemically reactive, terpenes (derived from citrus plants and
pine trees) are "generally recognized as safe" substances (Hayes, 1988).
However, carcinogenicity of terpenes and other cycloalkenes has not been well
explored. The terpene cleaners are available commercially in neat form or as
water solutions with surfactants, emulsifiers, rust inhibitors, and other addi-
tives. Terpenes tested very favorably as substitutes for halogenated solvents
for removal of heavy greases, oily deposits, and carbonized oils. Terpenes are
being actively tested as alternatives to chlorofluorocarbons in electronic parts
cleaning.
Reported disadvantages of terpenes include inability to separate long chain
aliphatic oils for recycle of the cleaning solution both in neat form and in
aqueous emulsions. Ultrafiltration to remove oil is not viable for recycle and
is only useful for treating dilute emulsions prior to wastewater treatment.
Recovery by distillation is impractical since terpenes boil around 340°F, which
means that many light oils would be carried over with the solvent. Energy cost
for distillation recovery, even with vacuum assist, would be high. Difficulties
in rinsing residues from parts surfaces have been cited. Also, terpenes cost
three to five times more than traditional chlorinated and hydrocarbon sol-
vents. (Evanoff, 1988).
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
Other substitutes for halogenated solvents include N-methyl-2-pyrrolidone
(Taylor 1988), and dibasic acid esters (Lucas 1988). These substitutes are
considered to be safer and environmentally preferable to halogenated solvents
due to their low volatility and biodegradability. For additional information,
the reader should contact manufacturers of these products directly. It is
recommended that sol vent/cleaner recyclability be thoroughly investigated
along with cleaning properties, volatility, toxicity, cost, and other attributes.
Aqueous cleaners Historically, aqueous cleaners have been used extensively throughout the
industry. In recent years, their use has increased as environmental concerns
and regulatory restrictions placed solvent cleaners under more scrutiny.
The simplest aqueous cleaner is water, which can be used in conjunction with
mechanical or ultrasonic agitation. Hot water high pressure spray systems are
quite effective at removing caked-on dirt and grime. Where hard water
deposits may result in staining, use of demineralized or deionized water is
recommended. Use of demineralized water in a reuse bath preceding a plating
or process bath can help avoid the build-up of calcium and magnesium
contaminants in the bath. For example, hot deionized water has been success-
fully tested as a replacement for CFC-113 in certain critical cleaning applica-
tions hi the manufacture of disk drives in the electronic industry.
The cleaning action of aqueous cleaners relies mainly on displacement of soils
rather than dissolving them as is the case with organic solvent. Two classes of
aqueous cleaners, alkaline and acidic cleaners, are usually distinguished based
on pH. Application methods include soak cleaning, spraying, ultrasonic
cleaning, electrocleaning, and steam cleaning.
Alkaline cleaning solutions contain builders (sodium salts of phosphates,
carbonates, silicates, and hydroxides) and surfactants (detergents and soaps).
Other additives may include anti-oxidants and stabilizers as well as small
amounts of solvents. Acidic cleaning solutions may contain mineral acids
(nitric, sulfuric, phosphoric, or hydrochloric), organic acids (sulfamic, acetic,
oxalic, or citric), detergents, chelating agents, and occasionally small amounts
of solvents.
Use ivater in place of solvents
Certain electronic filter circuits are housed in aluminum casings. The casings are manufactured by an outside
sheet metal contractor who cleans the parts prior to shipment. Since delivered parts had occasional visible stains,
methyl alcohol was used to remove them. A simple investigation showed that hot deionized water was equally
effective (SFE, 1985).
Replace solvent with aqueous cleaning medium
An electronic manufacturing facility of a large corporation originally cleaned printed circuit boards with
solvents. The company found that by switching from a solvent-based cleaning system to an aqueous-based
system the same operating conditions and workloads could be maintained. The aqueous-based system cleaned
6 times more effectively. This resulted in a lower product reject rate, and eliminated a hazardous waste (USEPA,
1983).
14
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
Emulsion cleaners
It is important to evaluate the wastewater quality issues and recyclability
aspects when selecting an aqueous cleaner. Generally, selection of non-
emulsifying cleaners which promote oil separation will enhance recyclability.
Process equipment involves a heated tank equipped with oil skimmer and
mechanical agitation, spraying, or ultrasonic devices. The cleaning step is
usually followed by water rinsing and air drying.
Quite often, solvent is employed for cleaning because an attempt to utilize an
aqueous cleaner was unsuccessful. Before committing to solvent, one should
investigate the compounds requiring removal. High melting temperature
compounds are often used in forming compounds, lubricants and preserva-
tives, making removal with aqueous cleaners difficult. Suppliers of metal
processing chemicals can recommend substitutes that can be cleaned with
aqueous cleaners thus eliminating solvent and emulsion cleaners. General
studies are available (Briggs, 1976; Wagner, 1984; USEPA, 1983; Evanoff, 1988);
however, each application is highly specific and generalizations are difficult.
Testing of a number of potential substitutes is recommended (see Table 5). The
reader is advised to contact aqueous cleaner manufacturers for specific recom-
mendations. A comprehensive list of manufacturers and trade names can be
found in recent issues of Metal Finishing's "Guidebook & Directory" or other
standard buying guides.
Emulsion cleaners combine solvent cleaning with aqueous cleaning so that
water-immiscible solvent is dispersed in the aqueous phase with the aid of
emulsifiers, surfactants, and coupling agents. The large surface area of the
dispersed solvent phase often allows the attainment of results achievable with
direct solvent cleaner. Solvent vapor pressure and evaporation losses are
suppressed.
Emulsion cleaners are used for immersion or spray cleaning in cold baths
predominantly in metal fabrication facilities. Disadvantages include residual
oil film on the parts (which necessitates an additional cleaning step in applica-
tions where a high degree of cleanliness is required), relatively low saturation
capacity, and difficulties in recycling by separation of oil and reconstituting the
cleaner. Emulsion cleaning is no longer a widespread technology and is being
quickly replaced by aqueous cleaners. For more information on emulsion
cleaners, the reader is referred to USEPA, 1983.
Replace solvent with alkaline cleaning media
The Torrington Company in Walhalla, S.C, was using vapor degreasers containing 1,1,1-TCE to clean metal
bearings for the automotive industry. Because of concern about worker health and increasing solvent prices, the
company installed an alkaline degreaser that employed a two-stage washer and hot air drier. The waste water
from this system can be discharged directly to the sewer system because the alkaline cleaner is considered non-
hazardous (Kohl, 1984).
Reduction of solvent use
A company that reduced TCE use is the Hamilton Beach Division of Scovill, Inc. in Clinton, N.C., which
manufactures small electric appliances. Scovill found that a water-soluble synthetic cleaner manufactured by
Cincinnati Milacron Co. could be used in place of the TCE organic solvent degreaser for some applications,
reducing TCE use overall by 30 percent. This saved $12,000 per year. (Huising, et al. 1985).
-------
Waste Minimization in Metal Parts Cleaning Operations
Mechanical/thermal methods In addition to aqueous cleaners, mechanical and/or thermal methods are quite
effective at eliminating the need for solvents. Solvents are often used to dry
parts following a water rinse operation. As an alternative, air blast systems
utilize a high velocity air jet that blows water droplets and other contaminants
from glass, metal, or wood parts. Abrasive blast cleaning methods use a plastic
blast media to clean and strip parts. Dry stripping and cleaning can reduce
disposal costs and water usage and have been shown to reduce labor costs
significantly. The plastic media are recycled.
SOLVENTS
Table 5. Selection of an Aqueous Cleaner1
1. Review cleaner composition. Hazardous or undesirable components are identified on
material safety data sheets. Many candidate cleaners can be eliminated on this basis.
2. Identify contaminants to be cleaned from parts, and obtain samples of each.
3. Apply each contaminant to representative metal panels and immerse in each candidate
cleaner in laboratory scale cleaning tanks. Use manufacturer's recommendations for
concentration and temperature, and provide mechanical agitation. After periods of 5,10,
and 15 minutes, remove panels from bath, rinse, and evaluate cleanliness. Cleanliness
can be ascertained by (a) water break, (b) fluorescence under UV light (applicable for
soils that fluoresce), and (c) by immersing in a cupric chloride solution and observing
uniformity of copper deposited.
4. If a contaminant was cleaned (from Step 3), lower the temperature and re-test until the
minimum effective temperature is identified. Also determine the minimum effective
cleaner concentration in a similar manner. If the contaminant from Step 3 was not
cleaned, increase temperatures and concentrations to identify minimum effective para-
meters. These data will permit selecting the optimum operating conditions for any
contaminant or mixtures thereof of any of the cleaners evaluated.
5. Using a series of standard tests, determine etch rates, staining characteristics, effects on
coatings' adhesion, and corrosion characteristics.
6. Evaluate cleaner performance including tank maintenance, recyclability, and disposal re-
quirements in a pilot plant-scale tank prior to full scale implementation.
; Selection process developed by General Dynamics/Fort Worth Division (Evanoff et al 1987).
Abrasive substitutes for solvents in paint stripping
Conventional paint stripping of aircraft may use 8,000 gallons per aircraft of such solvents as methylene chloride
or hot caustic. Hill Air Force Base in Ogden, Utah, has successfully employed plastic beads propelled by high
pressure air j'ets (bead blasting) to remove paint from aircraft exteriors. Besides not generating hazardous waste,
the use of bead blasting improved personnel working conditions, was easier to perform than solvent paint
stripping, and cost less and used less raw material.
16
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
To replace the use of chlorinated solvents in paint stripping operations, heat or
flame cleaning ovens are becoming more common. Heat cleaning ovens burn
off paint and other organic compounds from metal parts. Specifically, these
techniques have been successful in cleaning paint hangers and hooks. A dis-
advantage of heat cleaning ovens is the production of combustion emissions.
3.3 Minimize Solvent Losses
Once it has been determined that the use of solvent cannot be avoided, all
efforts to reduce solvent use in a facility should be made. The following options
are grouped according to their application (general, cold cleaning, and vapor
degreasing).
General options Waste minimization options that apply to solvent use in general are discussed
below. These options include standardizing solvent use, consolidating solvent
cleaning operations, maintaining solvent quality, increasing cleaning effi-
ciency, and reducing solvent evaporation.
Standardize solvent use
Standardization means using the least number of different solvents in the
facility. A reduced inventory helps track solvent consumption, reduces the
risk of cross contamination, and eases waste handling. In addition to simpli-
fying cleaning operations, standardization also helps promote the potential for
downgrading or recycling waste solvents. Using fresh solvent for the most
critical cleaning applications and reusing solvent sequentially for less de-
manding cleaning operations can reduce overall solvent consumption and
waste production.
Consolidate cleaning operations into one centralized degreasing operation
Centralization helps in the effort to standardize solvent use. It also eases the
effort it would take to supply many solvent users dispersed throughout a
facility. A centrally-located solvent issue and waste collection station was
found to be useful in solvent control and in proper waste handling in the multi-
user facility (SFE Technologies, 1985).
Maintain solvent quality
By maintaining solvent quality, the need for solvent replacement and disposal
is reduced. Ways to achieve this goal include contamination avoidance,
equipment maintenance, solvent monitoring, proper solvent addition, and
prompt sludge removal. These approaches are discussed below.
Staged solvent use and standardization of solvent
A Massachusetts electronics firm switched from using three different solvents mineral spirits for degreasing
machine parts, perchloroethylene for computer housings, and a fluorocarbon-methanol blend for printed circuit
boards to a single solvent mixture. The mixture of 1,1,1-trichloroethane and alcohol is used for all three
applications in a staged system. Fresh solvent is used for the printed circuit boards, then is reused to degrease
the computer housings and, last, the machine parts. Besides reducing solvent consumption and waste, this
practice has eliminated potential cross contamination of solvents, generated a single waste stream that can be
recycled, simplified safety and operating procedures, and increased purchasing leverage (Traverse, 1984).
1
17
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
Contamination avoidance
Parts should be checked for undue contamination, including moisture, before
being cleaned. Often, parts stored outside will pick up a large amount of con-
densation. The introduction of water from condensation into a bath of
chlorinated solvent can acidify the solvent. When this occurs, the solvent must
be replaced and all equipment in contact with the solvent thoroughly flushed
and rinsed. Another problem is that water contamination can lead to increased
air emissions because of azeotrope formation. To avoid this problem, the parts
should be stored indoors. Precleaning inspections can help point out potential
problems that are due to upstream operations.
Another purpose of precleaning inspections is to promote workload segrega-
tion. In some situations, a given bath of solvent is more than adequate for
cleaning the normal production workload but it fails to thoroughly clean
heavily soiled pieces. As these pieces pass through production and yield
rejects, the solvent bath is blamed for inadequate cleaning. Rather than having
to replace the bath due to an occasional heavily soiled object, it is better to
segregate these objects and to preclean or spot-clean them before the bath.
Material and/or process substitution can be another effective way of avoiding
undue bath contamination. Use of newer, water emulsifiable metal forming
lubricants that require less material, and spray/mist application devices will
minimize the amount of material applied (Evanoff, 1988).
Equipment maintenance
Racks and barrels should be maintained so as not to introduce corrosion
products (such as rust) into the solvent. Corroded racks can also remove liquid
from the bath by way of capillary action.
Solvent monitoring
The military is currently developing solvent test kits (Joshi et al, 1988) for
cleaning operations using Stoddard solvent (PD-680) and chlorinated solvents
(1,1,1 trichloroethane, methylene chloride, trichloroethylene, and perchlo-
roethylene). The purpose of these kits is to provide operators with simple,
reliable and repeatable testing means for determining when solvent is spent.
Due to the often arbitrary nature in which the need for solvent replacement is
now determined, much solvent may be disposed of prematurely. The most
reliable tests developed to date include light transmittance @ SOOnm, electrical
conductivity, and specific gravity for PD-680 and acid acceptance value, light
transmittance, and electrical conductivity for the chlorinated solvents.
18
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
After establishing a proper monitoring program, work should be undertaken
to correct identified problems. Chlorinated solvents contain stabilizers to
prevent acid forming reactions with water, metal, heat, and oil. When an acid
acceptance test indicates that the solvent is near the point of "going acid," the
solvent is either disposed of or fresh solvent is added in an attempt to boost
stabilizer levels. Addition of fresh solvent is a poor solution since it results in
the degradation of the fresh solvent. A better solution is to analyze the solvent
and add only the specific components required (see example below). Since
each type of solvent may employ a different mix of stabilizers, the solvent
manufacturer should be contacted before any additions are made.
Careful solvent addition
Care should be taken whenever solvent is added to the tank to ensure that
proper solvent is being added. For example, as little as 0.1% TCA mistakenly
added to a tank of TCE can cause an acid condition requiring disposal of the
entire contents.
Sludge removal
Metal fines can catalyze reactions that lead to decomposition of the solvent.
Paint chips can absorb solvent and swell, forming a viscous sludge. Routine
maintenance should be performed to remove sludge. Continuous filtering is
often helpful.
Increased cleaning efficiency
As the level of contamination increases, the rate of solvency slows down.
While cold cleaning operations can be successfully performed at up to 10%
contamination, solvent baths are often replaced due to slow cleaning action,
when the contamination level reaches 2 to 3%. A simple way to increase
cleaning efficiency is to employ manual brushing. Manual brushing is ex-
tremely effective at removing caked-on soils and is a very common precleaning
technique. Disadvantages include exposure of workers to solvents, high labor
costs, and the need for high ventilation rates to protect workers. High
ventilation rates can, in turn, lead to excessive solvent evaporation.
Maintaining solvent quality
The Ogden Air Logistic Center generates about 6500 gallons of waste 1,1,1 trichloroethane (TCA) from 21 va-
por degreasing operations. In an effort to reduce this waste, the chemical laboratory personnel determined that
the TCA was being disposed of because it did not meet an acid acceptance value of 0.10 weight percent NaOH.
Oil contamination levels were less than 10 percent at the time of disposal, far less than the expected 30 percent
level. To restore acid acceptance levels, 1,2 butylene oxide was added to the solvent. No adverse reactions or
detectable problems were observed when the butylene oxide was added to the vapor degreasers. Ogden Air
Logistics Center expects to reduce disposal volumes by 4000 gallons (60 percent) and save $30,000 per year
(Christensen, 1988).
19
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
Cleaning efficiency can also be increased by increasing the degree of agitation
in the bath. Methods include use of mechanical agitators, ultrasonic devices,
liquid sprays, and liquid jet pump-around arrangements. Great care should be
taken with these methods to ensure that undue splashing does not occur.
Systems are available that provide a raising and lowering (or pumping) action
of the parts trays inside the bath while the unit is closed. Increased temperature
maybe employed to increase cleaning efficiency but this method leads to larger
evaporative losses.
Cleaning speed can be maintained effectively at high contamination levels
using ultrasonic agitation. High frequency sound waves are transmitted
through the solvent, causing formation and collapse of small vapor bubbles at
solid surface (micro-cavitation). The agitation assists in the removal of
insoluble soils. This supplementary cleaning action is not expensive, and it can
prevent the need for hand cleaning and reduce the number of rejects. Ultra-
sonic transducers may be added to existing equipment, and they can be used
in both vapor degreaser and cold cleaning applications.
Control of evaporative losses
The first step in controlling evaporative losses is the selection of the proper
location for cleaning operations. The area should be free from drafts and away
from any heat source, which can cause large evaporative losses. These large
losses can result in problems elsewhere in a facility.
The second step in controlling evaporative losses is through the proper use of
lids. Tank lids, even on cold tanks, are very effective in reducing solvent loss.
For vapor degreasers, roll-type covers are recommended over hinged covers
because they are less disturbing to the vapor zone.
Other methods that are effective in controlling evaporative emissions from all
solvent cleaning operations are the proper monitoring of temperature (if the
solvent is heated) and avoiding the use of porous items such as ropes or bags
for handling parts. Additional air emission control methods are discussed in
the subsequent sections.
Cold cleaning Of the total number of cold cleaner soak tanks in use, it has been estimated that
70 percent are used for maintenance operations. Typically, most tanks hold 30
or more gallons of solvent and have about four square feet of open area. Cold
tanks used in manufacturing operations range from desktop sized units used
for cleaning small parts to units designed to clean large sections of aircraft.
Maintenance cleaning usually employs mineral spirits (petroleum distillates
such as Stoddard solvent) while manufacturing operations employ a wider
variety of solvents.
Locate solvent tank properly
One manufacturer placed a tank of chlorinated solvent near his paint cure oven. Heat from the oven caused
excessive emissions which were picked up by the oven's combustion fan. The emissions were burned, forming
hydrochloric acid, which ruined the finish on the painted parts in the oven. The manufacturer had to strip, clean,
and repaint all of the parts. All of the waste (not to mention the cost) associated with this event could have been
avoided if the tank was properly located (Durney, 1984).
20
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Waste Minimization in Metal Parts Cleaning Op.erations
SOLVENTS
Some waste minimization options specific to cold cleaning soak tank opera-
tions include reducing the degree of drag-out and using a counter-current
cleaning arrangement. In addition to these methods, the reader should review
all of the general options discussed in the preceding section.
Reduce drag-out
Drag-out is the term applied to the liquid that comes along on the part as it is
removed from the tank. Excessive drag-out can result in increased solvent
replenishment costs, increased air emissions, and upset of downstream proc-
esses. Methods for reducing drag-out include proper racking, increased
drainage, and installation of drain boards.
Proper racking
Careful attention should be given to the design of work baskets and to methods
of racking so as to ensure that a minimum amount of solvent will be trapped
either in the work or in the baskets (Figure 3).
Figure 3. Racking For Maximum Drainage
No
Yes
21
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Waste Minimization in Metal Parts Cleaning Operations
Increase drainage
Parts should always be allowed to drain inside the tank before being removed.
The installation of a rest shelf inside the tank allows the operator to better drain
the parts, especially heavy ones. Depending on the size, shape, and function
of the part, some fabricators design the part to include inconspicuous drainage
holes.
Install drain boards
Drain boards are often helpful in recovering solvent that drips from a part.
Drain boards which extend from one tank to the next help to keep the area
between tanks clean (Figure 4).
Use counter-current cleaning
Parts should be passed through a series of cleaning tanks or compartments.
The first tank consists of used solvent, the last rinse consists of very clean
solvent. When the first tank of solvent is spent, it can be pumped out for
disposal and each subsequent tank pumped into the previous tank. For
facilities with limited space, existing tanks can be segmented. Staging will
reduce the amount of solvent use by maintaining solvent quality for a longer
period.
Figure 4. Installing Drain Boards Conserves Solvent, Keeps Floor Clean.
Without Drain Board
With Drain Board
T^
: w/ss/s/s/z/ww/w//////?//?/^^^
22
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
Vapor degreasing In industries that perform a large amount of cleaning, vapor degreasing
systems are common. Available sizes for open-top units range from 1x2 feet,
up to 6 x 100 feet. The typical unit size is approximately 3x6 feet. Open-top
units are commonly employed in the electroplating and electronics industries
where easily handled parts are cleaned. Conveyorized (or fully automated)
units are more common in the aerospace and large appliance product coating
industries.
Vapor degreasing systems usually consist of a tank of halogenated solvent that
is heated to the solvent's boiling point. Parts to be cleaned are placed in a basket
or on a rack and lowered into the vapor zone. As the solvent condenses, the
contamination is dissolved and the parts are rinsed and cleaned. To increase
cleaning efficiency, the parts may be immersed into the solvent bath or a
solvent spray unit may be employed. When the temperature of the parts finally
reaches the temperature of the solvent vapor, condensation of the vapor onto
the part ceases. The parts can then be removed from the unit clean and dry.
Solvent use in vapor degreasing can be minimized by many of the general
options discussed previously and by the options listed below:
Limit entrance/exit speeds
Solution and vapors are removed from the tank when a part is inserted or
withdrawn too quickly. Avoid speeds greater than 11 feet per minute to limit
excessive dragout.
Limit workload size
The use of baskets having an area of less than 50% of the degreaser opening
will limit vapor dragout due to piston effect (Figure 5).
Avoid work shock
Work shock occurs when a heavy load is introduced into the degreaser,
resulting in collapse of the vapor blanket and infiltration of air into the cleaning
unit (Figure 6). The solvent-saturated air will be expelled from the unit when
the vapor layer is reestablished.
Maintain temperature of solvent
The temperature of the solvent in the degreaser should be maintained at a level
adequate for vapor production, to ensure that the degreaser functions effi-
ciently.
Allow sufficient time in the degreaser
Ensure that parts have reached the temperature of the vapor so that conden-
sation has ceased.
23
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Waste Minimization in Metal Parts Cleaning Operations
Figure 5. Piston Effect
Wide Workload
Wide Workload
Spray only below the vapor zone
The spray pattern should be a solid stream, not a fine mist.
Maintain proper solvent level in sump
In addition to excessive water contamination, a major cause of chlorinated
solvents going acidic is exposure of the heating coils to the solvent vapor.
Exposure causes localized overheating which results in decomposition of the
solvent. These items can be kept in check by inspecting the parts for excessive
water and by regularly checking the operation of the water separator and
solvent level controls.
Minimize vapor diffusion
Vapor diffusion, which results in air emissions, can be reduced through
the following means:
Check parts for excessive water contamination.
Cover water separator to prevent vapor loss.
Check water jacket for proper water flow and temperature on outside
of degreaser.
24
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Waste Minimization in Metal Parts Cleaning Operations
Figure 6. Work Shock
Workload
Air
A 1. Work introduced
2. Rapid condensation on work
3. Vapor blanket collapses
4. Air pulled in
Workload
B
Vapor-laden
Air
B 5. Condensation on work stops
6. Vapor blanket re-established
7. Vapor-laden air expelled
SOLVENTS
Extend freeboard. Increasing the freeboard/width ratio of a vapor
degreaser can reduce solvent air emissions (see Figure 7).
Use cold traps above freeboard chillers.
Locate the degreaser away from drafts or use baffles to prevent upset
of the vapors. Proper location can reduce solvent loss by 30 percent.
For additional information on ways to reduce emissions associated with vapor
degreasing, the reader should contact the solvent supplier. Most if not all of
the major chlorinated solvent manufacturers have information available on the
proper way to utilize, maintain, and eventually dispose of their products.
25
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Waste Minimization in Metal Parts Cleaning Operations
Figure 7. Effect of Changes in Freeboard/Width Ratio (Figur
EFFECT OF FREEBOARD/WIDTH RATIO AND
CONDENSER TEMPERATURE ON DIFFUSIONAL LOSSES
FROM IDLING DEGREASER CONTAINING
FREONSTFSOLVENT
o o OT
i 1
3 a: a ,
o B g
en
in g z wo
O Q ui
_J (^j Q
O < 2
i- O O w
UJ CQ CJ
tlj ^
t; o* <
3!tQ "°
[jj -L, 2
W ^ "^ .
S 3-
* |«
d. n
Freeboard/Width
Ratio = 0.46
Freeboard/Width
Ratio = 0.75
Freeboard/Width
Ratio = 1.0
30 40 50 60 70 80
AVERAGE CONDENSER TEMPERATURE °F
3.4 Solvent Segregation and Recycling/Reuse
SOLVENTS
In addition to the savings in solvent that result from minimizing losses during
use, overall solvent consumption can be reduced by segregating solvent
wastes and recycling or reusing them. EPA estimates that up to 50% of all
solvent wastes are currently being segregated and managed for energy recov-
ery, reclamation or recycling.
To simplify waste solvent handling and to make recycling feasible, the follow-
ing procedures should be followed (Kohl, 1984 and California DHS, 1986):
Keep solvents segregated In the recycling process, it is much easier to separate a solvent from its
impurities than to separate two solvents. Specific recommendations are
always to segregate:
Chlorinated from non-chlorinated solvent wastes.
Aliphatic from aromatic solvent wastes.
Freon from methylene chloride.
Water waste from flammable waste.
26
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W a s t e M inimization in M e t a I Parts Cleaning Operations
SOLVENTS
Keep waste solvents as free from water, solids, and garbage as possible
Label the container clearly, keep the container closed and, if possible, sheltered
from rain. Drums should be covered to prevent contamination with water.
Label the chemical content on each waste container
Record the exact composition and method by which the solvent waste was
generated.
Recycling Where recycling of solvent waste is viable, the choice between on-site versus
off-site recycling must be made. Major factors that may influence a decision are
shown in Table 6.
Table 6. Factors Influencing the Decision to Recycle
Solvent Wastes on Site
Advantages
Less waste leaving the facility.
Owner's control of reclaimed solvent's purity.
Reduced liability and cost of transporting waste
offsite.
Reduced reporting (manifesting).
Possible lower unit cost of reclaimed solvent.
Perceived Benefits
Favorable economics for recovery
(e.g. reduced solvent requirements).
Reduction in disposal costs.
Reduction in reporting (manifesting)
Lower liability.
Source: California DHS, 1986.
Disadvantages
Capital outlay for recycling equipment.
Liabilities for worker health, fires, explosions, leaks,
spills, and other risks as a result of improper equip-
ment operation.
Possible need for operator training.
Additional operating and maintenance costs.
Reported Difficulties
Loss of solvent during distillation process.
Low solvent recovery efficiency.
Installation problems.
Maintenance problems.
27
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
On-Site Recycling
On-site recycling is economical when approximately 8 gallons of solvent waste
is generated per day (Schwartz, 1986). The simplest form of solvent reuse is
termed "downgrading," which is the use of a solvent that has become contami-
nated through initial use for a second cleaning process. For example, precision
bearings need very high purity solvents for cleaning. The solvent acquires very
little contamination in usage and can be downgraded or used for less demand-
ing cleaning operations.
More effort is required to recycle solvent that has become heavily contami-
nated, and the possibilities for both on-site and off-site recycling or reclamation
need to be explored. In vapor degreasing and cold cleaning, the soil removed
accumulates in the equipment. Eventually the solvent becomes too contami-
nated for further use and it must be reclaimed or disposed of via incineration.
For on-site recycling, many different separation technologies are available.
Commonly used separation technologies for contaminated solvents include
gravity separation, filtration, bath distillation, fractional distillation, evapora-
tion, and fuel use.
Gravity separation
The use of settling to separate solids and water from solvent often permits the
reuse of solvent. For example, paint thinners may be reused many times if
solids are allowed to settle out.
Filtration
Filters can be used to remove solids from many solvents thus extending
solvent life.
Batch distillation
A batch still vaporizes the used solvent and condenses the overhead vapors in
a separate vessel. Solids or high boiling residues (>400° F) remain in the still
as a residue. Solvent stills range in size from 5 gallon to 500 gallon capacity. A
vapor degreaser can be used as a batch still for recycling solvent. This is often
done by employing proper boil-down procedures. Detailed discussion of
these procedures is available from major solvent suppliers.
In many applications, it is necessary to keep the water content of the recovered
solvent to less than 100 ppm. This can often be accomplished by distilling off
the solvent-water azeotrope, decanting the water, and then drying the remain-
ing solvent with a molecular sieve, or other desiccant. The water removed in
this operation must then be either treated or drummed for disposal.
On-site recycling
A company that used trichloroethylene in degreasing was able to cut its solvent waste from 20 drums a month
to five drums a montha 75 percent reduction. Virgin solvent consumption was reduced by 15 drums a month.
Formerly, the company removed solvent waste from degreasers into a storage tank every other day. The stored
waste was transferred to drums for disposal. Now, the solvent waste is pumped into a holding tank; every two
weeks this collected waste is redistilled to recover as much solvent as possible, leaving only 5 drums per month
requiring off-site disposal (USEPA1988 A).
28
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Waste Minimization in Metal Parts Cleaning Operations
SOLVENTS
(For a survey of small still manufacturers and other technical information, the
reader is referred to "Guide to Solvent Waste Reduction Alternatives" avail-
able from the State of California Department of Health Services (Calif. DHS,
1986).
Fractional distillation
Fractional distillation is carried out in a refluxed column equipped with either
trays or packing. Heat is supplied by a reboiler located at the bottom of the
column while heat is removed at the top of the column by a condenser.
Fractional distillation allows for separation of multi-component mixtures or
mixtures of solvent and oils with very similar boiling points.
Evaporation
Evaporation can be employed for solvent recovery from viscous liquids,
sludges, or still bottoms resulting from distillation. Scraped or wiped-film
evaporators utilize revolving blades which spread the liquid against a heated
metal surface. The vapors are recovered by means of a condenser. Another
type of system, a drum dryer, employs two heated counter-rotating drums
through which the liquid feed must pass. While both systems can handle
viscous wastes, the drum dryer is more tolerant of polymerizable
contaminants.
Off-Site Recycling
If recycling of waste solvent on site is impractical, several off-site recycling
schemes are available. One should consider or investigate all of the items listed
in Table 7 when selecting an off-site recycling scheme. Some viable off-site
Recycling solvents efficiently
Segregating solvent wastes is usually an essential step prior to recycling. IBM Corporation reported that
segregation may also increase recycling efficiency; segregating non-chlorinated from chlorinated solvents
resulted in 15 to 20 percent greater yields (Waste Reduction - The Untold Story, 1985).
Mobile solvent degreasing units
Automobile repair shops in California can lease fully-contained degreasing systems from Safety Kleen Inc.
Safety Kleen provides a batch-tolling service for degreasing solvents; it leases its mobile units, including
solvents, as one system. Safety Kleen periodically replaces the spent solvent with fresh solvent, and recycles the
spent solvent at a separate facility.
Waste exchanges
Waste exchanges generally exchange some 20 to 30 percent of the wastes they list (Banning, 1983,1984). At
present, the most common wastes listed are solvents and metal wastes. Other wastes listed include acids, alkalis,
other inorganic chemicals, organics and solvents, and metals and metal sludges.
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Waste Minimization in Metal Parts Cleaning Operation
recycling arrangements include toll recyclers, and waste exchange/brokerage.
Toll recyclers
Toll recyclers offer services to generators by supplying solvent wash equip-
ment and solvent and waste recycling services. The solvent wash equipment
is maintained by these companies and the solvent is replaced periodically. The
used solvent is recycled at an off-site facility. Costs for these services range
from 50-90% of new solvent cost.
Waste exchange and brokerage
This is not a technology but an information service. A waste exchange can
match a generator of waste with a facility that can use the waste as a raw
material. Commercial waste brokerage services are also available. A waste
generator is matched with a potential waste user who can utilize the waste as
a feedstock. Matching generators and users is based on the knowledge of raw
material inputs and wastes and product outputs of individual industries and
firms.
Table 7. Facility Characteristics to Be
Considered in Choosing an Off-Site Recycler
Permits held by the facility.
Types of solvent wastes managed.
Ability to meet solvent purity specifications if solvent is to be returned to the generator.
Availability of registered trucks to transport the solvent wastes.
Distance to the recycling facility and associated transportation costs.
Available laboratory facilities and analytical procedures.
Record keeping practices.
Availability of custom recycling services (e.g., vendor-owned recycling units that can be operated on the
generators property).
Expertise on in-plant waste management strategies and process controls.
Insurance for recycling/treatment/disposal operations.
Disposal procedures for still bottoms and solvents that cannot be recycled.
State regulatory agency's compliance records on the facility.
Current customers' comments on the facility.
Facility's financial stability.
Source: Radimsky, 1984.
30
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Waste Minimization in Metal Parts C I
n g Operations
AQUEOUS
Aqueous cleaning comprises a wide range of water-based cleaning methods
that use water, detergents, acids, and alkaline compounds to displace soil
rather than dissolving it in organic solvent. Aqueous cleaning has been found
to be a viable substitute for many parts cleaning operations currently using
solvents. Its principal disadvantage is that the parts are wet after cleaning and
ferrous parts easily rust in this environment. (However, the use of warm (140-
150°F) air for drying is less costly than the cost associated with solvent usage
and disposal and there are additives available to prevent short term rusting).
Also, aqueous cleaning may not be suitable for electronic components since it
may leave conductive residue.
Waste minimization techniques for reducing wastes from aqueous cleaning
include substitution alternatives, use of less hazardous compounds, and
maintaining solution quality.
3.5 Substitution Alternatives for Aqueous Cleaners
Abrasives, water, or steam are less hazardous than acid or alkaline cleaners,
and may be equally or more effective. An example in which an abrasive
cleaning system was successfully substituted for an alkaline cleaner is pro-
vided below.
3.6 Use of Less Hazardous Acid or Alkaline Compounds
The aluminum processing industry widely uses deoxidizers and desmutters
based on chromic acid which is highly toxic and a possible carcinogen. By
substituting a nonchromated deoxidizer, use of a hazardous product can be
eliminated. The latter products are based on ferric sulfate which is easily
treated for disposal (Weast 1988).
3.7 Maintain Solution Quality.
As was discussed under general waste minimization options for solvent use,
maintaining solution quality reduces the need for replacement and disposal.
Ways to achieve this goal include precleaning inspection, avoiding unneces-
sary loading, providing continuous heating, proper solution make up, remov-
ing sludge promptly, and monitoring cleaning solution strength.
Precleaning inspection All parts entering the tanks should be free of solvents and other cleaners. For
parts that are first mechanically cleaned, water-based abrasives and cutting
oils should be used to reduce the cleaning load. Precleaning of the parts in a
hot water bath is often effective in reducing the load on the cleaner. This initial
precleaning stage can often be made up from the last rinse stage of the cleaning
operation and should employ demineralized water.
Substituting an abrasive cleaning system for an alkaline bath
A manufacturer of fabricated metal products cleaned nickel and titanium wire in an alkaline chemical bath prior
to using the wire in its product. In 1986, the company began to experiment with a mechanical abrasive system.
The system worked, but required passing the wire through the unit twice for complete cleaning. In 1987 the
company bought a second abrasive unit and installed it in series with the first unit. This system allowed the
company to completely eliminate the chemical cleaning bath (USEPA, 1988B).
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Waste Minimization in Metal Parts Cleaning Operations
~.^/.i.ji|
AQUEOUS
Precleaning inspections of the parts may also help in establishing the proper
temperature and concentration at which to operate the bath. Quite often, bath
temperatures and/or concentrations are increased in an attempt to improve
efficiency. While this works in many cases, some soils can become set at higher
temperatures and concentrations. When bath oils and solids are present on a
part, the rapid removal of the oil due to higher bath temperature creates a
difficult-to-remove solid. Proper cleaning may require a lower temperature,
longer soak time, and some form of agitation.
Avoid unnecessary loading When using an alkaline cleaner, alkalinity may be reduced by the acidity of the
soils removed, reaction of the alkali with carbon dioxide in the air used for
agitation, and reaction of the cleaner components with hard water salts
(Spring, 1963). In some applications, the detrimental effects of carbon dioxide
and hard water can be as significant as the effect of soil loading. Quite often,
10 to 25 percent of the cleaner can be consumed due to water softening.
In addition to consuming expensive cleaner, large amounts of solids form in
the bath which may then interfere with cleaning. These solids can also form
scale on the heating tubes and reduce heat transfer efficiency. Cleaner con-
sumption can be very high when heated cleaning baths are used and large
amounts of hard water are added as evaporation make-up. Solutions to these
problems include use of mechanical agitation instead of air and use of softened,
demineralized, or deionized water.
Provide continuous heating For tanks containing alkaline cleaner that are well insulated, properly covered,
and located where ambient temperatures are not too low, there are benefits to
be gained if the tank is not allowed to cool overnight. Derived benefits include
reduced absorption of carbon dioxide (i.e. less reduction of alkalinity) and
fewer rejects during production start-up due to inadequate temperature.
Occasional cooling of the tank should be performed to allow for the split out
and removal of oil. Proper heating and cooling cycles will depend on the types
of air encountered, the types of cleaning agents used, and the workload on the
system.
Proper solution make-up Great care should be exercised when making up cleaning solutions. If the
water is too hot, boil over can occur due to the heat of solution. If the water
temperature is too low, the liquid or solid cleaner will sink to the bottom and
not mix properly. With cleaners that contain inhibitors, failure to allow for
complete mixing can lead to attack of metal parts or the tank itself. A helpful
procedure is to formulate baths at the end of a shift so that the components have
time to dissolve and mix before the start of production. For systems without
good mixing controls, the use of liquids should be favored over solids or
powders.
32
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Waste Minimization in Metal Parts Cleaning Operations
AQUEOUS
Good mixing is achieved by adding a mixing system to the tank. By installing
a three way valve on the main header of the pump exit, solution can be re-
diverted to the chemical entry area instead of through the spray nozzles. This
provides for easier dissolution of chemicals through a greater number of
turnovers (less pressure drop means higher pumping rates), and elimination
of potential plugging of the nozzles when dissolving solids.
Remove sludge and soils
promptly
Removing sludge and soils from aqueous cleaning soak tanks will reduce
chemical use by increasing the permissible time interval between dumping
and total cleanout of the tank.
Alkaline cleaners are available which allow the separation of excess oily soil
from the cleaner. These formulations involve the use of surfactants that are
good detergents but poor emulsifiers. Agitation of the bath during the work
shift causes a temporary emulsification which keeps the soil in suspension.
After a prolonged period of inactivity (usually overnight), the oily soils float
to the surface where they are skimmed off. This method is quite effective with
mineral oil-type soils but is less so with fatty oils.
Monitor cleaning solution
strength
Analytical checks of solution strengths should be made on a routine basis. The
correction of solution strength by making small and frequent additions is
much more effective than making a few large additions. Analytical checks can
be performed by the operator utilizing simple titration techniques (does the
addition of a given amount of reagent to a known volume of cleaner and
indicator result in a color change?). Full scale titration tests may be performed
by the lab on a less frequent basis. An accurate log of all tests and cleaner
additions should be kept at all times. Occasional testing of the reagents should
also be performed.
Equipment maintenance As discussed under solvent cleaning, rack systems should be maintained in
good condition, free from cracks, rust, and corrosion. Metal tanks should be
properly coated with protective finishes both inside and out. Plastic linings
should be used in deionized water rinse tanks since these tanks tend to rust
rapidly. Use of plastic tanks can eliminate this problem. Spray nozzles should
be inspected regularly to avoid clogging.
Reducing chemical use and waste in a bath cleaning system
Liquid-Life makes a 100-gallon per minute separator unit that operates in conjunction with a cleaning bath
(solvent, alkaline or acid). The separator unit continuously removes sludge and particulate matter from the bath.
A pump, hydrocyclone, and sludge retention tank make up the unit. Waterloo Industries Inc., of Waterloo, Iowa,
installed the Liquid-Life unit for its alkaline cleaning system, used to clean the steel cabinets it manufactures prior
to phosphate-coating the cabinets. The Liquid-Life unit has enabled Waterloo to reduce its chemical costs by 20
percent, clean out its alkaline bath system every 13 weeks instead of every four weeks, and do less maintenance
on the cleaning operation since the pump is the only moving part in the system (Anonymous, March 1982).
3.3.
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Waste Minimization in Metal Parts Cleaning Operations
AQUEOUS
Another important item to maintain regularly is the float valve that supplies
make-up water to tanks of heated cleaning solution. Float valves are used to
maintain the level in the tank so that the heating coils / elements do not become
exposed. While maintaining an adequate level is extremely important, it is also
important that the valve does not leak and result in dilution of the cleaner. In
addition to maintenance, making frequent analytical checks is a good way to
detect slow leaks.
Reduce drag-out If possible parts should be racked so that surfaces are nearly vertical and the
longer dimensions are horizontal. (For example, a rectangular part should be
racked so that while its planes are vertical, its long axis is horizontal.) If the
lower edge is tilted, the run-off will occur at a corner rather than the entire edge.
As shown in Table 8, proper racking can reduce solution drag-out. Racking
parts so that their planes are vertical is preferable to racking the planes
horizontally (i.e., oriented like the top of a table). Drag-out can also be reduced
by draining parts thoroughly, installing drain boards, reducing the concentra-
tion of cleaner, and by increasing solution temperature.
Increase the degree of Rinse tanks should be agitated for maximum rinsing efficiency. Heating the
rinsing efficiency while water may also be effective but care should be taken that the soils present do
reducing water use not become set. Ways to further increase efficiency while reducing water usage
include:
Use of demineralized water
Following a final rinse, the contaminants contained in the rinse will remain on
the workpiece. As the parts dry, spotting or rusting may occur. For items on
which minor residues cannot be tolerated, the use of demineralized water is
standard. Using demineralized water will also reduce the amount of sludge
generated during wastewater treatment and may allow the direct reuse of rinse
water as make-up to the cleaning bath.
Reducing drag-out
Parts that have recesses or cavities may carry significant amounts of cleaning solution with them when they are
removed from a bath. Improved rack design, including proper tilting of long horizontal bars, reduced the
amount of drag-out from a cleaning bath associated with an electroplating operation, according to a report by
Pioneer Metal Finishing Inc., of Franklinville, New Jersey. Other drag-out reducing measures include tilting a
part during withdrawal, or drilling small holes in the part to provide for drainage during removal.
Using deionized water rinse
It has been reported (Spring 1963; Brown, Spring, and Hennessy 1955) that many in the steel fabricating industry
were troubled with the pinpoint rusting of steel "blackplate." Experiments showed that a residual amount of
alkaline cleaner residue plus hard water produced this type of rusting during storage at slightly humid
conditions. Lab tests showed that this type of rusting only occurred when hard water and alkaline salts were
present. Rinsing in hard water only resulted in heavy streak rust while use of deionized water produced trace
or no rust. A final rinse in distilled water was utilized to prevent rusting.
34
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Waste Minimization in Metal Parts Cleaning Operations
AQUEOUS
Table 8. Drag-Out for Various Rack Configurations
Item
Vertical parts, well drained
Vertical parts, poorly drained
Vertical parts, very poorly drained
Horizontal parts, well drained
Horizontal parts, very poorly drained
Cup-shaped parts, very poorly drained
Source: Durney, 1984.
Drag-out, gal/100 ft2
0.4
2.0
4.0
0.8
10.0
8.0 to > 24.0
Table 9. Flow Rates for Five Rinsing Systems
System
Single rinse
Two rinses in series, equal flow of fresh rinse
water to each tank
Three rinses in series, equal flow of fresh rinse water
to each tank
Two counterflow rinses, fresh water feed to second tank only
Three counterflow rinses, fresh water feed to third tank only
Source: Durney, 1984.
Flow (gpm)
10.0
0.6
0.3
0.3
0.1
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Waste Minimization in Metal Parts Cleaning Operations
AQUEOUS
Counterflow rinsing
Counterflow rinse systems should always be used to reduce overall water
consumption and subsequent treatment requirements. A comparison of 5
rinse systems is illustrated in Table 9.
Spray rinsing
Rinsing efficiency can be increased by installing spray systems. Spraying parts
with fresh water as they are raised above the rinse equals the equivalent of
1/2 of a counterflow bath.
Installation of fog nozzles
Fog nozzles use much less water than conventional spray systems. Fog nozzles
also benefit aqueous cleaned parts by covering the parts, thus preventing
solution from drying on parts. Solution drag-out is reduced.
Employ closed loop systems For pickling applications, consider a closed loop acid pickle system as shown
in Figure 8. This system consists of four essential items (Krofchak and Stone
1975):
A synthetic fiber fume filter to recover acid vapors
Unlike wet scrubbers/ these filters do not produce large volumes of
waste water and the recovered acid can be returned directly to the
bath.
Use of indirect heating (instead of live steam inj ection) and agitation
to maintain cleaning efficiency and acid concentration.
Employment of a multistage counter-current rinsing sequence
Rinse water from the first stage can be used as make-up to the acid
tank. This avoids the need for treating a stream that contains 70 to 80
percent of the dragged-out acid. Rinse water from subsequent stages
can be used as make-up for preceding stages.
Use of a cooling or evaporative crystallizer to recover ferrous sulfate
from spent sulfuric acid baths
Proper parts drying
For facilities employing hydrochloric acid, proven commercial proc-
esses can be employed to recover iron and hydrochloric acid.
After a water rinse, it is quite common to dry the parts using compressed air.
Unless great care is taken to ensure the removal of oil, water, and dirt from the
air stream, resoiling of the parts will almost certainly occur. Automated drying
ovens might be a more viable alternative.
36
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Waste Minimization in Metal Parts Cleaning Operations
Figure 8. Acid Pickle Closed-Loop System
Fresh_
Acid
Recovered
Acid
Evaporation
Water & Acid Mist
Make-Up
' -~-.:.. ~
»^^:^»;^^4^-^fc.ji;^ -'* ir/s
lipiclcie'Bath '"
Spent
Acid
Acid
Regeneration
Overflow
Rinse 1
^Iron Sulfate
Iron Hydroxide
Rinse 2
_ Fresh
Water
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Waste Minimization in Metal Parts Cleaning Operations
ABRASIVES
Abrasives can be used in tumbling barrels or applied to a buffing wheel or
machine. Other mechanical abrasive cleaning methods include air-assisted or
water-assisted blasting, brushing, vibratory processes, centrifugal barrel fin-
ishing (CBF), centrifugal disc finishing, spindle finishing, and use of natural
mass finishing abrasives.
Waste from buffing operations consists of worn out cloth wheels saturated
with abrasives, metal particles, binder, and various oxides. Waste from liquid-
based mass finishing operations consists of abrasives, metal particles, and
water and oxides dispersed in a slurry. Alkaline and acid cleaners are
sometimes added to abrasive slurries in order to improve cleaning action.
These slurries are discharged when the abrasive has undergone a given
amount of attrition.
Options for reducing wastes associated with abrasive cleaning include:
Use of greaseless
or water-based binders
for buffing or polishing
When oil-based binders are used, the frictional heat generated during buffing
can cause the binders to burn. This in turn leads to the requirement for
additional cleaning with alkaline soaks. When properly used, greaseless
compounds produce parts that leave the wheel clean and dry. Greaseless
compositions also tend to adhere to the surface of the wheel so that wheel life
is extended.
Use of liquid spray compositions Liquid spray abrasive systems are usually water-based abrasives that are
applied directly to the buffing wheel. Wheel wear due to compound defi-
ciency, compound waste due to over-application, and post-cleaning require-
ments are all significantly reduced or eliminated when a spray gun with liquid
abrasive spray is used.
Control water level in mass
finishing equipment
Mass finishing operations are carried out in aqueous solutions using abrasives
or non-abrasive compounds. Water level control is extremely important in
order to achieve maximum efficiency in mass cleaning operations. If not
enough water is used, parts leaving the equipment will be dirty. Too little
water will increase the attrition rate of the abrasive and increase replacement
frequency.
38
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Waste Minimization in Metal Parts Cleaning Operations
4. IMPLEMENTATION
5. CONCLUSIONS
After promising waste minimization measures for a parts cleaning operation
have been identified, they should be evaluated for technical and economic
feasibility and, if found satisfactory, they should be implemented. For those
methods that are found to be economically infeasible, additional analysis
including consideration of "hidden " cost, liability, public image and other
components (USEPA, 1988C) should be performed before dropping an option.
Adopting specific waste minimization measures may not be easy or straight-
forward. A number of factors (Table 10) may affect the readiness of an
organization to implement measures that require changes in procedures,
equipment, or employee responsibilities. Developing a strategy to overcome
these barriers should be an integral part of waste minimization planning. This
strategy should include establishment of a working group of personnel repre-
senting the affected departments: Health and Safety, Production, Mainte-
nance, Process Control, Purchasing, and Facilities, for example. (USEPA,
1988B)
As increased regulation raises the cost of waste treatment and disposal, efforts
to decrease waste volumes and toxicity become more economically justifiable.
Implementing waste minimization techniques to reduce cleaning waste can
produce treatment and disposal cost savings which more than offset the expen-
diture. In additionfmaterial costs, regulatory compliance, and other costs can
be cut since the life of the cleaning solutions will be lengthened.
Most of the measures discussed in this pamphlet would involve minimal
capital outlays. For example, proper equipment operation requires only that
management thoroughly train the employees using the equipment and that the
equipment be correctly maintained. These low-cost measures generally have
a fast payback and are among the first a firm should implement. Making
employees aware of the cost of waste generation due to cleaning operations
and involving them in identifying solutions may encourage the design of
more efficient production processes.
With the adoption of efficient production processes and the waste-minimizing
measures presented here, companies with parts cleaning operations should be
able to reduce their waste disposal costs and liabilities, and reduce their
contribution to the environmental problems associated with waste disposal.
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Waste Minimization in Metal Parts Cleaning Operations
Table 10. Some Barriers to Waste Minimization
Pmlitction
A new operating procedure will reduce waste but may also be a bottleneck that decreases the
overall production rate.
Production will be stopped while the new process equipment is installed.
A new piece of equipment has not been demonstrated in a similar service. It may not work here.
Facilities/Maintenance
Adequate space is not available for the installation of new equipment.
Adequate utilities are not available for the new equipment.
Engineering or construction manpower will not be available in time to meet the project schedule.
Extensive maintenance may be required.
Quality Control
More intensive QC may be needed.
More rework may be required.
Client Relations/Marketing
Changes in product characteristics may affect customer acceptance.
Inventory
A program to reduce inventory (to avoid material deterioration and reprocessing) may lead to
stockouts during high product demand.
Finance
Inadequate cost evaluations or coordination with financial department.
Purchasing
Existing stocks (or binding contracts) will delay the replacement of a hazardous material with a
nonhazardous substitute.
Eiwironmental
Accepting another plant's waste as a feedstock may require a lengthy resolution of regulatory
issues.
Waste Treatment
Use of a new nonhazardous raw material will adversely impact the existing wastewater treat-
ment facility.
Source: USEPA, 1988B.
40
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Waste Minimization i n M e t a I Parts Cleaning Operations
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41
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IV a S t e Minimization in Metal Parts Cleaning Operations
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Waste Minimization in Metal Parts Cleaning Operations
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Waste Minimization in Metal Parts Cleaning Operations
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El
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Waste Minimization in Metal Parts Cleaning Operation
7. SOURCES OF INFORMATION ON WASTE MINIMIZATION 1
Associations That Can Provide Information and Direction
Relating to Waste Minimization in Parts Cleaning
Abrasive Engineering Society (AES)
1700 Painters Run Rd.
Pittsburg,PA 15243
(412) 221-0900
Aerospace Industries Association
of America (AIA)
1725 DeSales St., NW
Washington, DC 20036
(202) 347-2315
Air Pollution Control Association
(APCA)
P.O. Box 2861
Pittsburgh, PA 15230
(412) 621-1090
American Chemical Society
1155 16th St., NW
Washington, DC 20036
(202) 872-4600
American Electronics Association
(AEA)
2600 El Camino Real
Palo Alto, CA 94306
(415) 327-9300
American Electroplaters Society
(AES)
1201 Louisiana Ave.
Winter Park, FL 32789
(305) 647-1197
American Society for Metals (ASM)
Metal Parks, OH 44073
(216) 338-5151
American Society for Testing
and Materials (ASTM)
1916 Race St.
Philadelphia, PA 19103
(215) 299-5400
Association for Finishing Processes
(AFP)
P.O. Box 930
One SME Dr.
Dearborn, MI 48128
(313) 271-1500
Chemical Coaters Association
(CCA)
Box 241
Wheaton,IL 60187
(312) 668-0949
Chemical Manufacturers
Association (CMA)
1825 Connecticut Ave., NW
Washington, DC 20009
(202) 328-4200
Chemical Specialties
Manufacturers Association
(CSMA)
1001 Connecticut Ave., NW
Washington, DC 20036
(202) 872-8110
Electrochemical Society (ECS)
P.O. Box 2071
Princeton, NJ 08540
(609) 924-1902
Electronic Industries Association
(EIA)
2001 Eye St., NW
Washington, DC 20006
(202) 457-4900
Fabricating Manufacturers
Association (FMA)
7811 N. Alpine
Rockford,IL 61111
(818) 654-1902
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Waste Minimization in Metal Parts Cleaning Operations
Federation of Societies for
Coatings Technology (FSCT)
1315 Walnut
Philadelphia, PA 19107
(215) 545-1506
Halogenated Cleaning Solvents
Association (HCSA)
Affiliate of Synthetic Organic
Chemical Manufacturers
Association Inc.
1075 Central Park Ave.
Scarsdale,NY 10583
Institute for Interconnecting and
Packaging
Electronic Circuits (IPC)
3451 Church St.
Evanston, IL 60203
(312) 677-2850
Metal Fabricating Institute (MFI)
710 S. Main St.
Rockford, IL 61105
(815) 965-4031
Metal Finishing Suppliers
Association (MFSA)
1025 E. Maple Rd.
Birmingham, MI 48011
(313) 646-2728
National Association of
Corrosion Engineers (NACE)
1440 S. Creek Dr.
Houston, TX 77084
(713) 492-0535
National Association of
Manufacturers (NAM)
1776 F St., NW
Washington, DC 20006
(202) 331-3700
National Association of Metal
Finishers (NAMF)
HIE. WackerDr.
Chicago, IL 60601
National Solid Wastes
Management Association
(NSWMA)
1120 Connecticut Ave., NW
Washington, DC 20036
(202) 659-4613
Semiconductor Equipment
and Materials Institute (SEMI)
625 Ellis St., Suite 212
Mountain View, CA 94043
(415) 964-5111
Semiconductor Industry
Association (SIA)
20380 Town Center Lane, Suite 155
Cupertino, CA 95014
(408) 255-3522
Society of Automotive Engineers
(SAE)
400 Commonwealth Dr.
Warrendale, PA 15096
(412) 776-4841
Water Pollution Control
Federation (WPCF)
2626 Pennsylvania Ave.
Washington, DC 20037
(202) 337-2500
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Waste Minimization in Metal Parts Cleaning Operations
List of Periodicals That May Contain Information
Relating to Waste Minimization in Parts Cleaning
American Paint and
Coatings Journal
American Paint Journal Co.,
2911 Washington Ave.,
St. Louis/MO 63103.
Assembly Engineering
Hitchcock Publishing Co.,
Geneva Rd.,
Wheaton,IL 60187
Cleaning - Finishing - Coating
Digest
American Society for Metals,
Metals Park, OH 44073
Electronic Packaging
and Production
Milton S. Kiver Publications, Inc.,
222 W. Adams St.,
Chicago, IL 60606
Industrial Finishing
Hitchcock Publishing Co.,
Hitchcock Building,
Wheaton,IL 60187
Iron Age
Chilton Co., Inc.,
Radnor, PA 19089
Journal of Coatings Technology
Federation of Societies for Coating
Technology,
1315 S. Walnut St., Suite 830,
Philadelphia, PA 19107
List of Abstract Publications
American Society for Metals
Annual Review of Metals Literature
Cleaning and Finishing, Section L.
American Society for Testing
and Materials
Special Technical Publication 90
Metal Cleaning Abstracts
Metal Finishing
Metals and Plastics
Publications, Inc.,
One University Plaza,
Hackensack, NJ 07601
Metal Finishing Guidebook
and Directory
Metals and Plastics
Publications, Inc.
One University Plaza,
Hackensack, NJ 07601
Metal Finishing Journal
Fuel and Metallurgical
Journals Ltd.,
John Adam House,
John Adam St.,
London WC 2N 6JH, England
Metal Finishing Plants
and Processes
Finishing Publications Ltd.,
28 High St.,
Teddington, Middlesex, England
Metal Progress
American Society for Metals,
Metals Park, OH 44073
Plating and Surface Finishing
American Electroplaters Society,
Inc.
1201 Louisiana Ave.,
Winter Park, FL 32789
Metal Finishing Abstracts
Finishing Publications Ltd.,
28 High St.,
Teddington, Middlesex, England
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