ASTM B635-91(1997)
(Specification)Standard Specification for Coatings of Cadmium-Tin Mechanically Deposited
Standard Specification for Coatings of Cadmium-Tin Mechanically Deposited
SCOPE
1.1 This specification covers the requirements for a coating that is a mixture of cadmium and tin mechanically deposited on metal products. The coating is provided in various thicknesses up to and including 12 μm.
1.2 Mechanical deposition greatly reduces the risk of hydrogen embrittlement and is suitable for coating bores and recesses in many parts that cannot be conveniently plated electrolytically. (See Appendix X1.)
1.3 This standard does not purport to address all of the safety problems 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 specific hazards statements, see Section 7.
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Designation: B 635 – 91 (Reapproved 1997)
Standard Specification for
Coatings of Cadmium-Tin Mechanically Deposited
This standard is issued under the fixed designation B 635; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope B 697 Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
1.1 This specification covers the requirements for a coating
E 87 Methods for Chemical Analysis of Lead, Tin, Anti-
that is a mixture of cadmium and tin mechanically deposited on
mony, and Their Alloys (Photometric Methods)
metal products. The coating is provided in various thicknesses
E 396 Test Methods for Chemical Analysis of Cadmium
up to and including 12 μm.
2.2 U.S. Federal Standard:
1.2 Mechanical deposition greatly reduces the risk of hy-
FED-STD-141 Paint, Varnish, Lacquer, and Related Mate-
drogen embrittlement and is suitable for coating bores and
rials; Methods of Inspection, Sampling and Testing
recesses in many parts that cannot be conveniently plated
2.3 U.S. Military Standard:
electrolytically. (See Appendix X1.)
MIL-L-7808J Lubricating Oil, Aircraft Turbine Engine,
1.3 This standard does not purport to address all of the
Synthetic Base
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Classification
priate safety and health practices and determine the applica-
3.1 Classes—Cadmium-tin coatings are classified on the
bility of regulatory limitations prior to use. For specific hazards
basis of thickness, as follows:
statements, see Section 7.
Class Minimum Thickness, μm
12 12
2. Referenced Documents
2.1 ASTM Standards:
B 117 Practice for Operating Salt Spray (Fog) Apparatus
3.2 Types—Cadmium-tin coatings are identified by types on
B 183 Practice for Preparation of Low-Carbon Steel for
the basis of supplementary treatment required, as follows:
Electroplating
3.2.1 Type I—As coated, without supplementary chromate
B 201 Practice for Testing Chromate Coatings on Zinc and
treatment (see X1.1).
Cadmium Surfaces
3.2.2 Type II—With supplementary chromate treatment (see
B 242 Practice for Preparation of High-Carbon Steel for
X1.2).
Electroplating
B 322 Practice for Cleaning Metals Prior to Electroplating
4. Ordering Information
B 487 Test Method for Measurement of Metal and Oxide
4.1 To make the application of this specification complete,
Coating Thicknesses by Microscopical Examination of a
the purchaser needs to supply the following information to the
Cross Section
supplier in the purchase order or other governing document:
B 499 Test Method for Measurement of Coating Thick-
4.1.1 Class, including a maximum thickness, if appropriate,
nesses by the Magnetic Method: Nonmagnetic Coatings on
type, and need for supplemental lubricant (3.1, 3.2, and
Magnetic Basis Metals
5.2.4.2).
B 567 Test Method for Measurement of Coating Thickness
4.1.2 Nature of substrate, for example, high-strength steel,
by the Beta Backscatter Method
need for stress-relief, and cleaning precautions to be followed
B 571 Test Methods for Adhesion of Metallic Coatings
(5.2.2).
B 602 Test Method for Attribute Sampling of Metallic and
4.1.3 Significant surfaces (5.3).
Inorganic Coatings
4.1.4 Requirements and methods of testing for one or more
of the following requirements: need for and type of test
specimens (8.1), composition (8.2), thickness (8.4), adhesion
This specification is under the jurisdiction of ASTM Committee B-8 on
Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee
B08.04 on Soft Metals.
Current edition approved Feb. 22, 1991. Published May 1991. Originally Discontinued—See 1984 Annual Book of ASTM Standards, Vol 03.05.
published as B 635 – 78. Last previous edition B 635 – 90. Annual Book of ASTM Standards, Vol 03.05.
2 6
Annual Book of ASTM Standards, Vol 03.02. Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Annual Book of ASTM Standards, Vol 02.05. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
B 635
(8.6), and absence of hydrogen embrittlement and the waiting appearance or serviceability of the article when assembled in
period prior to testing and testing loads (8.8) and lubricating
normal position; or which can be the source of corrosion
resistance (S2). products that deface visible surfaces on the assembled article.
4.1.5 Sampling plan for each inspection criterion and re-
When necessary, the significant surfaces shall be indicated on
sponsibility for inspection, if necessary (Section 6 and Supple- the drawing of the article, or by the provision of suitably
mentary Requirement S1).
marked samples.
4.1.6 Requirements for certified report of test results (Sec-
NOTE 1—The thickness of mechanically-deposited coatings varies from
tion 10).
point-to-point on the surface of a product, characteristically tending to be
thicker on flat surfaces and thinner at exposed edges, sharp projections,
5. Requirements
shielded or recessed areas, interior corners and holes, with such thinner
5.1 Nature of Finish—The coating shall be 45 to 75 mass %
areas often being exempted from thickness requirement.
cadmium, the remainder tin.
5.3.3 When significant surfaces are involved on which the
5.2 Process:
specified thickness of deposit cannot readily be controlled, the
5.2.1 Stress Relief Treatment—All steel parts that have
purchaser and manufacturer should recognize the necessity for
ultimate tensile strength of 1000 MPa and above and that
either thicker or thinner deposits. For example, to reduce
contain tensile stresses caused by machining, grinding,
buildup in thread roots, holes, deep recesses, bases of angles,
straightening, or cold forming operation shall be given a stress
relief heat treatment prior to cleaning and metal deposition. and similar areas, the deposit thickness on the more accessible
surfaces will have to be reduced proportionately.
The temperature and time at temperature shall be 1906 15°C
for a minimum of3hso that maximum stress relief is obtained
NOTE 2—The coating thickness requirement of this specification is a
without reducing the hardness below the specified minimum.
minimum requirement; that is, the coating thickness is required to equal or
5.2.2 High-strength steels that have heavy oxide or scale
exceed the specified thickness everywhere on the significant surfaces.
shall be cleaned before application of the coating in accordance
Variation in the coating thickness from point to point on a coated article
with Practice B 242. In general, non-electrolytic alkaline,
is an inherent characteristic of mechanical deposition processes. There-
fore, the coating thickness will have to exceed the specified value at some
anodic-alkaline, and some inhibited acid cleaners are preferred
points on the significant surfaces to ensure that the thickness equals or
to avoid the risk of producing hydrogen embrittlement from the
exceeds the specified value at all points. Thus, in most cases, the average
cleaning procedure.
coating thickness on an article will be greater than the specified value;
5.2.3 For preparation of low-carbon steels, see Practice
how much greater is largely determined by the shape of the article and the
B 183. For cleaning, useful guidelines are also given in
characteristics of the deposition process. In addition, the average coating
Practice B 322.
thickness on articles will vary from article to article within a production
5.2.4 Supplementary Treatments:
lot. Therefore, if all of the articles in a production lot are to meet the
5.2.4.1 Chromate treatment for Type II shall be done in a thickness requirement, the average coating thickness for the production lot
as a whole will be greater than the average necessary to ensure that a
solution containing hexavalent chromium. This solution shall
single article meets the requirement.
produce a bright or semi-bright continuous, smooth, protective
film. This film may have a slight yellowish or iridescent color.
5.4 Adhesion—The cadmium-tin coating shall be suffi-
The absence of color shall not be considered evidence of the
ciently adherent to the basis metal to pass the tests specified in
absence of a Type II film or as a basis for rejection of the parts.
8.6.
Only post treatments that contain salts that yield films contain-
5.5 Corrosion Resistance:
ing hexavalent chromium are permitted as treatments for
5.5.1 The presence of corrosion products visible to the
producing Type II coatings.
unaided eye at normal reading distance at the end of the
5.2.4.2 Waxes, lacquers, or other organic coatings may be
specified test period as stated in Table 1 shall constitute failure,
used to improve lubricity, and the need for them should be
except that corrosion products at the edges of specimens shall
supplied in the purchase order or other governing document
not constitute failure. Slight “wisps” of white corrosion, as
(4.1.1). Such supplemental lubrication treatments shall not be
opposed to obvious accumulations, shall be acceptable.
used to ensure conformance to the salt spray corrosion resistant
requirements or to enhance the test results of the lead acetate
NOTE 3—The hours given in Table 1 are the minimums required to
spot test (8.5.2).
guarantee satisfactory performance. Longer periods before the appearance
of white corrosion products and rust are possible, but salt spray resistance
5.3 Thickness:
does not vary in exact proportion with increased plating thickness. The
5.3.1 The thickness of the coating everywhere on the
hours given for Type II reflect the added protection of chromate treatments
significant surfaces shall be at least that of the specified class
without requiring impractical testing periods.
as defined in 3.1.
5.5.2 There are no requirements for corrosion of base metals
5.3.2 Significant surfaces are defined as those normally
visible (directly or by reflection) that are essential to the other than steels.
A
TABLE 1 Minimum Hours to Failure (White Corrosion and Red Rust for Cadmium-Tin Coatings on Iron and Steel)
Type Class 12 Class 8 Class 5
White Corrosion Rust White Corrosion Rust White Corrosion Rust
I not applicable 144 not applicable 120 not applicable 60
II 96 168 96 168 96 168
A
Corrosion products are those visible to the unaided eye at normal reading distances after gentle washing to remove salt deposits.
B 635
NOTE 4—Mechanical deposition is exclusively a barrel-finishing pro-
accordance with the criteria of the sampling plans in Test
cess. It is recognized that mechanical deposition on parts may therefore
Method B 602.
produce surfaces which have a different characteristic from those on parts
NOTE 8—Test Method B 602 contains three sampling plans that are to
which are finished exclusively by racking. Similarly, corrosion testing of
be used with non-destructive test methods and a fourth to be used with
actual parts may produce different results from those on test panels. Salt
destructive test methods. The three methods for non-destructive tests differ
spray requirements that are appropriate to indicate the technical quality
in the quality level they require of the product. Test Method B 602
with which a process is carried out may be impractical for acceptance of
requires use of the plan with the intermediate quality level unless the
actual parts. In such cases the purchaser should indicate his requirements
purchaser specifies otherwise. The purchaser should compare the plans
on the purchase order (see 4.1.4).
with his needs and state which plan is to be used. If the plans in Test
NOTE 5—In many instances, there is no direct relation between the
Method B 602 do not serve the needs, additional ones are given in Guide
results of an accelerated corrosion test and the resistance to corrosion in
B 697.
other media, because several factors that influence the progress of
NOTE 9—When both destructive and non-destructive tests exist for the
corrosion, such as the formation of protective films, vary greatly with the
measurement of a characteristic, the purchaser needs to state which is to
conditions encountered. The results obtained in the test should not,
be used so that the proper sampling plan is selected. Also, a test may
therefore, be regarded as a direct guide to the corrosion resistance of the
destroy the coating but in a noncritical area. Or, although it destroys the
tested materials in all environments where these materials may be used.
coating, it may be the tested article can be reclaimed by stripping and
Also, performance of different materials in the test cannot always be taken
recoating. The purchaser needs to state whether such a test is to be
as a direct guide to the relative corrosion resistance of these materials in
considered destructive or non-destructive.
service.
6.2 An inspection lot shall be defined as a collection of
5.6 Absence of Hydrogen Embrittlement— Steel springs and
coated articles that are of the same kind, that have been
other high-strength steel parts subject to flexure shall be held
produced to the same specifications, that have been coated by
for a minimum of 48 h at room temperature after coating,
a single supplier at one time or at approximately the same time,
before being loaded, flexed, or used. Such parts shall be free
under essentially identical conditions, and that are submitted
from hydrogen embrittlement. When specified in the purchase
for acceptance or rejection as a group. In no case shall the lot
order, freedom from embrittlement shall be determined by the
exceed production for one week.
test specified herein (see 4.1.4 and 8.8).
6.3 If separate test specimens are used to represent the
5.7 Workmanship—The coating shall be uniform in appear-
coated articles in a test, the specimens shall be of the nature,
ance and substantially free of blisters, pits, nodules, flaking and
size, and number, and be processed as required in 8.1.
other defects that can adversely affect the function of the
coating. The coating shall cover all surfaces as stated in 5.3,
7. Hazards
including thread roots, thread peaks, corners, recesses, and
7.1 Warning—Cadmium is toxic and must not be used in a
edges. The coating shall not be stained or discolored through-
coating for articles that can come into contact with food or
out to an extent that would adversely affect appearance as a
beverages, or for dental or other equipment that can be inserted
functional requ
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