ASTM B322-99(2004)
(Guide)Standard Guide for Cleaning Metals Prior to Electroplating
Standard Guide for Cleaning Metals Prior to Electroplating
SIGNIFICANCE AND USE
The performance and quality of electroplated articles depend upon the surface cleanliness and condition. Various metals are electroplated for decorative or engineering finishes. The common electroplates applied are usually copper, nickel, and chromium for decorative and functional uses. Electroplated articles are used in many industries such as the marine, automotive, plumbing fixtures, and appliance industries.
SCOPE
1.1 This guide describes the procedure for cleaning metal surfaces to obtain good adhesion of electrodeposited metals. The degree of cleanliness required for metals to be electroplated is greater than for most other finishes. Methods of removal of heat-treat or mill scale are not included in these methods, because they are covered in practices referring to specific metals. It should also be understood that while these procedures are broadly applicable, particular substrates may require certain specific cleaning procedures.
1.2 Adequate cleaning requires a proper combination of cleaning procedures. The choice of these procedures must be based on a knowledge of the metals to be cleaned and of the soils to be removed. Because most experience and knowledge in cleaning have been obtained by suppliers of proprietary processes and formulations, these sources should be consulted before setting up a cleaning process.
1.3 A treatment to remove tarnish, light rust, fingerprints, or oxides is usually provided before immersion of the piece in the electroplating tank. This treatment activates the metal and is usually accomplished in acid baths which also serve to neutralize the residual alkaline film from alkaline cleaning. Alkaline chelated derusting and cleaning solutions, alone or with sodium cyanide, used as a soak or electrocleaner, are often preferred before electroplating on ferrous alloys.
1.4 Invariably several stages are necessary to provide adequate cleaning. These stages are discussed in three parts:
Part I-Precleaning (use of a solvent, emulsion, or alkaline spray) to remove the bulk of the soil.
Part II-Intermediate (alkaline) cleaning.
Part III-Final electrocleaning, to remove trace solids and especially adherent impurities.
Part IV-Trouble shooting.
Often, depending largely on the amount and type of soil on the workpieces as received, one or more of these stages may be eliminated or modified. Usually, even with light soils, it is advisable to retain multistage cleaning, thereby increasing the life and efficiency of the cleaning solutions.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (For more specific safety precautionary statements see Sections 11 and 16.)
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Standards Content (Sample)
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Contact ASTM International (www.astm.org) for the latest information.
Endorsed by American
Designation:B322–99(Reapproved 2004) Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Guide for
Cleaning Metals Prior to Electroplating
This standard is issued under the fixed designation B322; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
INTRODUCTION
This guide is intended to illustrate general principles of cleaning prior to electroplating. It is not
meant to apply to every specific application. In specific cases, cleaning practice may depart from the
general principles given in this guide.
1. Scope Part III—Final electrocleaning, to remove trace solids and
especially adherent impurities.
1.1 This guide describes the procedure for cleaning metal
Part IV—Trouble shooting.
surfaces to obtain good adhesion of electrodeposited metals.
Often, depending largely on the amount and type of soil on
The degree of cleanliness required for metals to be electro-
the workpieces as received, one or more of these stages may be
plated is greater than for most other finishes. Methods of
eliminated or modified. Usually, even with light soils, it is
removal of heat-treat or mill scale are not included in these
advisable to retain multistage cleaning, thereby increasing the
methods, because they are covered in practices referring to
life and efficiency of the cleaning solutions.
specific metals. It should also be understood that while these
1.5 This standard does not purport to address all of the
procedures are broadly applicable, particular substrates may
safety concerns, if any, associated with its use. It is the
require certain specific cleaning procedures.
responsibility of the user of this standard to establish appro-
1.2 Adequate cleaning requires a proper combination of
priate safety and health practices and determine the applica-
cleaning procedures. The choice of these procedures must be
bility of regulatory limitations prior to use. (For more specific
based on a knowledge of the metals to be cleaned and of the
safety precautionary statements see Sections 11 and 16.)
soils to be removed. Because most experience and knowledge
in cleaning have been obtained by suppliers of proprietary
2. Significance and Use
processes and formulations, these sources should be consulted
2.1 The performance and quality of electroplated articles
before setting up a cleaning process.
depend upon the surface cleanliness and condition. Various
1.3 Atreatment to remove tarnish, light rust, fingerprints, or
metals are electroplated for decorative or engineering finishes.
oxides is usually provided before immersion of the piece in the
The common electroplates applied are usually copper, nickel,
electroplating tank. This treatment activates the metal and is
and chromium for decorative and functional uses. Electro-
usually accomplished in acid baths which also serve to
plated articles are used in many industries such as the marine,
neutralize the residual alkaline film from alkaline cleaning.
automotive, plumbing fixtures, and appliance industries.
Alkaline chelated derusting and cleaning solutions, alone or
withsodiumcyanide,usedasasoakorelectrocleaner,areoften
3. Nature of the Soil
preferred before electroplating on ferrous alloys.
3.1 Some of the soils commonly encountered in electroplat-
1.4 Invariably several stages are necessary to provide ad-
ing are:
equate cleaning. These stages are discussed in three parts:
3.1.1 Solid buffing compounds containing waxes, fatty ac-
Part I—Precleaning (use of a solvent, emulsion, or alkaline
ids, and abrasives.
spray) to remove the bulk of the soil.
3.1.2 Liquid buffing compounds.
Part II—Intermediate (alkaline) cleaning.
3.1.3 Drawing and stamping compounds including those
containing fillers (pigments).
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
3.1.4 Machining oils.
Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 on Pre
3.1.5 Rust-preventive slushing oils or greases.
Treatment.
3.1.6 Electroplater’s stop-off residues.
Current edition approved Oct. 1, 2004. Published October 2004. Originally
approved in 1958. Last previous edition approved in 1999 as B322 – 99. DOI:
10.1520/B0322-99R04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B322–99 (2004)
3.1.7 Fingerprints. procurement since, even in the same category, not all cleaners
3.1.8 Dry dirt from storage or dry pickling smut formed are equally effective. A cleaner may be very effective for one
during derusting by pickling. group of soils, yet poor for other soils. This is true of
3.1.9 Rust or oxide scales, especially admixed with oil, electrocleaners as well as soak or spray cleaners. Soil, type of
including heat-treat scales after oil quenching. water, available time, rinsing facilities, type of metal, heating,
3.1.10 Phosphate coating with or without lubricant. and agitation available, facilities for disposal of cleaner, and
3.1.11 Smut resulting from improper vapor degreasing of type of personnel and equipment all influence the selection of
heavily buffed work. cleaners. Obviously, economics must be considered but an
3.1.12 Smut resulting from annealing parts without pre- initialorperpoundcostmustbebalancedagainstotherfactors.
cleaning between drawing operations. 5.2 Cleaners do not work effectively indefinitely. The effec-
3.1.13 Heat-treating salts, with or without quenching oils. tive life of a cleaning bath must be estimated and baths
3.2 Consideration should be given to control of the soil. For discarded when exhausted. Bath life is influenced by some of
example, efforts should be made to avoid overbuffing, leaving the factors mentioned above as well as by the volume of work
excessivecompoundonthework,oragingofthecompoundon processed. The concentration of the cleaner should be con-
the part before cleaning. Substitution of liquid for solid buffing trolled by analysis at regular intervals.
compound, if work permits, often gives easier cleaning, if
6. Rinses
properly applied, but may require use of a different type of
cleaner. Drawing compounds with polymerizing oils or white
6.1 Water hardness, acidity or alkalinity, and impurities are
lead pigment are to be avoided because of difficulty in
important factors in rinsing (1). Distilled or demineralized
cleaning. Additives for lubricating and sulfurized cutting oils
water is preferred where impurities in rinse water must be kept
are chosen for their ability to adhebe tenaciously and are
to a minimum. Boiler condensate may also be used advanta-
difficult to remove. Prolonged storage or drying of emulsion
geously. If the plant conditions water for acidity or alkalinity
drawing compounds after metal working should be avoided so care must be taken to be sure the solids content is not too high
that slimy water-in-oil emulsions do not form. In-process
(Note 1). Impurities derived from processing cannot be ig-
cleaning or even a hot-water flush before storage is helpful. nored; that is, rinse waters must be changed frequently or
Emulsion machining lubricants (soluble oils) should be used in
overflowed continuously (Note 2). Counterflowing rinses are a
place of sulfurized cutting oils if operations permit. Lower- distinct advantage in obtaining good rinsing with economical
viscosity machining and rust-preventive oils are more easily
use of water.
removed. Stop-off materials, when used, should be applied
NOTE 1—Boiler waters which contain cationic corrosion inhibitors may
carefully in order to avoid contaminating significant surfaces.
be quite detrimental to the plating process.
The use of clean gloves should be mandatory after buffing or
NOTE 2—Floating oil on water can cause poor adhesion.
polishing to avoid fingerprints on the work.Airborne contami-
7. Equipment
nants can be avoided by using covers over stored work. It is
desirable to perform a cleaning operation as soon as possible
7.1 It is important to provide enough room in the plant for
after metal forming, polishing, or buffing to reduce the de-
an adequate cleaning cycle. A discussion of equipment is
mands on subsequent cleaning operations, because many soils
beyond the scope of this practice (2, 3).
are more easily removed when fresh.
8. Criteria of Cleanliness
4. Metal
8.1 This subject has been treated exhaustively in the litera-
4.1 The properties of the metal and the method of fabrica-
ture (4). The atomizer test is the most sensitive one, but the
tion and handling of parts play a role in cleaning. The softness
water-break test is most commonly used. This involves visual
and surface finish of the metal are factors in selecting handling
observation after a final rinse in clear, cool water.Acontinuous
methods.Thechemicalactivityofthemetalisanimportantand
sheet of water on the part usually indicates a clean surface.
determining factor in cleaner selection. Aluminum requires
(Certain precious-metal surfaces, such as gold, may exhibit
care to avoid overetching in alkaline cleaners; both aluminum
water break, even though clean.) Some experience is necessary
and zinc are sensitive to pitting attack, zinc and brass to
to judge the appearance of a break in the film of water. A
tarnishing. Zinc die castings have surfaces that require special
specific drainage time, about 30 s, should be used before
care because of sensitivity to attack by cleaning solutions. If
observation.
possible, design of parts should avoid small indentations that
8.2 A dip in clean, dilute acid and reexamination are
tend to trap solid particles or buffing compositions. With die
desirable to avoid false water-film continuity due to adsorbed
castings, care must be exercised to avoid cutting through the
soaps. Other methods, including electroplating and testing of
surface by excessive buffing. The subsurface is usually more
the electroplate, should be used occasionally to confirm visual
sensitive than the“ skin” of the casting. Some surface defects
examination. (One procedure involves scrubbing with pumice
may not show up until cleaning and electroplating cycles are
and then comparing the surface produced by this method with
completed.
that produced under production conditions.)
5. Cleaner
5.1 It is essential that proper cleaners and operational
The boldface numbers in parentheses refer to the reports and papers appearing
conditions be selected. Attention should be given to proper in the list of references at the end of this practice.
B322–99 (2004)
PART I—PRECLEANING cleaning methods. Its lower equipment, floor space, and heat
requirements offset the higher cost of solvent.
9. Purpose
10.3.3 For some applications (steel stampings, buffed zinc-
base die castings, etc.), the degreased work can go directly to
9.1 Precleaning is designed to remove a large excess of soil,
especially deposits of buffing compound or grease. It is also mild electrolytic cleaning and subsequent electroplating with-
useful in reducing the viscosity of waxes and heavy oils, to out the need for an intermediate alkaline cleaning step.
enablelatercleaning stages to be more effective, or tosurround
10.4 Emulsion Cleaners—Oils and high-boiling hydrocar-
fingerprints and dry dust with an oily matrix to facilitate
bonssuchaskerosenehavetheabilitytodissolvemostgreases,
removal by alkaline cleaners.
particularly at high temperatures. The addition of emulsifiers,
soaps, and wetting agents enhances the penetrating power of
10. Types
the organic solvent and permits removal of the latter and
10.1 Cold solvent, vapor degreasing, emulsifiable solvent,
associated soil by power flushing. Further, intimate contact of
solvent emulsion spray, invert-type emulsion cleaners, or hot
the metal surface with the aqueous phase permits removal of
alkaline spray with or without solvent emulsion can be used
materials not soluble in the hydrocarbon phase.
(5).
10.4.1 The principle of emulsion cleaning can be applied in
10.2 Cold Solvent (6)—Mineral spirits; trichloroethylene;
a variety of ways including the use of straight emulsifiable
perchloroethylene; 1,1,1,-trichloroethane (methylchloroform);
solvents, unstable emulsions (diphase cleaners), invert-type
methylene chloride; or trichlorotrifluoroethane can be used for
emulsion cleaners, and stable emulsions. Additions of rust
coldcleaning.Combiningthesewithhandbrushingisexcellent
inhibitors or of alkali cleaners can be made to the water phase.
but does not lend itself to production conditions. On the other
Since agitation is important to good cleaning, the power-spray
hand, simple dipping in solvent is frequently ineffective. The
cleaners find wide applications.
chlorinated solvents are very effective for many soils, but not
10.4.2 Emulsion cleaners are used at temperatures up to
as effective in removing soap-based or other solvent-insoluble
82°C. The higher temperatures remove soils more quickly and
soils. Before electroplating, cold cleaning with solvents must
effectively, but caution must be used with cleaners containing
be followed by additional cleaning such as alkaline cleaning to
organics of low flash point. Some cleaners containing chlori-
remove slight oily residues.
nated solvents are used above the flash point of some of the
10.3 Vapor Degreasing (7)—Trichloroethylene and, to a
components since the chlorinated portion will volatilize to
lesser extent, perchloroethylene, trichlorotrifluoroethane, and
extinguish flashes.
methylene chloride are used for vapor degreasing. In vapor
degreasing, the work is usually sprayed with clean solvent or 10.5 Biological Cleaners (14)—Highly emulsifying soak
given a thorough immersion in boiling or warm solvent for
cleaners are combined with living microorganisms to permit
mechanical removal of tenacious soil or solids. This is fol-
the removed oils, greases, and other complex organic com-
lowed by immersion in cold solvent to cool the parts. Then
pounds to undergo a natural process known as bioremediation.
follows exposure to condensation of hot, clean solvent vapors
Living microbes break down organic compounds, such as oil
on the work. This final step also removes any last traces of oil
and grease into carbon dioxide and water and the cleaners, if
and grease and dries the part. For removal of caked-on oils and
properly maintained, may run for years without changing the
compounds, a predip in cool solvent can be used to wet and
bath at all. Since the cleaning fluid is kept free from conta
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