ASTM B636-84(1992)e1
(Test Method)Standard Test Method for Measurement of Internal Stress of Plated Metallic Coatings with the Spiral Contractometer
Standard Test Method for Measurement of Internal Stress of Plated Metallic Coatings with the Spiral Contractometer
SCOPE
1.1 This test method covers the use of the spiral contractometer for measuring the internal stress of metallic coatings as produced from plating solutions on a helical cathode. The test method can be used with electrolytic and autocatalytic deposits.
1.2 This standard does not purport to address all of the safety problems, 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.
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e1
Designation: B 636 – 84 (Reapproved 1992)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Measurement of Internal Stress of Plated Metallic Coatings
with the Spiral Contractometer
This standard is issued under the fixed designation B 636; 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.
e NOTE—Section 12 was added, the title changed to “Test Method,” and other editorial changes made in January 1992.
1. Scope 4. Significance and Use
1.1 This test method covers the use of the spiral contracto- 4.1 The spiral contractometer, properly used, will give
meter for measuring the internal stress of metallic coatings as reproducible results (see 8.5) over a wide range of stress
produced from plating solutions on a helical cathode. The test values. Internal stress limits with this method can be specified
method can be used with electrolytic and autocatalytic depos- for use by both the purchaser and the producer of plated or
its. electroformed parts.
1.2 This standard does not purport to address all of the 4.2 Plating with large tensile stresses will reduce the fatigue
safety problems, if any, associated with its use. It is the strength of a product made from high-strength steel. Maximum
responsibility of the user of this standard to establish appro- stress limits can be specified to minimize this. Other properties
priate safety and health practices and determine the applica- affected by stress include corrosion resistance, dimensional
bility of regulatory limitations prior to use. stability, cracking, and peeling.
4.3 In control of electroforming solutions, the effects of
2. Terminology
stress are more widely recognized, and the control of stress is
2.1 Definitions: usually necessary to obtain a usable electroform. Internal stress
2.1.1 compressive stress (−)—stress that tends to cause a
limits can be determined and specified for production control.
deposit to expand. 4.4 Internal stress values obtained by the spiral contracto-
2.1.2 internal stress—the net stress that remains in a deposit
meter do not necessarily reflect the internal stress values found
when it is free from external forces. The internal stress tends to on a part plated in the same solution. Internal stress varies with
compress or stretch the deposits.
many factors, such as coating thickness, preparation of sub-
2.1.3 tensile stress (+)—stress that tends to cause a deposit strate, current density, and temperature, as well as the solution
to contract.
composition. Closer correlation is achieved when the test
conditions match those used to coat the part.
3. Summary of Test Method
5. Apparatus
3.1 The test method of measuring stress with the spiral
contractometer is based on plating on the outside of a helix. 5.1 The spiral contractometer is described by A. Brenner
The helix is formed by winding a strip around a cylinder,
and S. Senderoff.
followed by annealing. In operation, one end of the helix is
NOTE 1—Spiral contractometers are available from many of the sup-
fixed and the other is allowed to move as stresses develop. The
pliers of nickel sulfamate.
free end is attached to an indicating needle through gears that
5.2 Helices shall be stopped-off on the inside to prevent
magnify the movement of the helix. As the helix is plated, the
plating. Helices are available with or without a permanent inert
stress in the deposit causes the helix to wind more tightly or to
coating on the insides (see Appendix X1).
unwind, depending on whether the stress is compressive (−) or
5.3 The clamps holding the helix to the contractometer shall
tensile (+). From the amount of needle deflection and other
be coated with an inert nonconductive coating to prevent their
data, the internal stress is calculated.
plating and acting as thieves.
3.2 With instrument modifications, the movement of the
5.4 For testing electroplating solutions, anodes are placed
helix can be measured electronically instead of mechanically as
equidistant from the helix and symmetrically positioned to
described in 3.1.
produce even plate distribution. A minimum of four anodes is
required. A concentric anode arrangement is preferred.
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.10on
General Test Methods.
Current edition approved Feb. 24, 1984. Published April 1984. Originally Brenner, A., and Senderoff, S., Proceedings of the American Electroplaters
published as B 636 – 78. Last previous edition B 636 – 78. Society, Vol 35, 1948, p. 53.
B 636
5.5 Laboratory tests on electroplating solutions shall utilize affect the character of the deposit. In testing autocatalytic
at least 3.7 L of solution. A 4-L beaker with an annular anode plating solutions, the ratio of plated surface area to the volume
arrangement is convenient. Use of this volume or larger will of solution that is normally used in the plating tank shall be
minimize solution changes due to electrolysis during the test. maintained. When using proprietary solutions, the supplier’s
5.6 Laboratory tests on autocatalytic plating solutions are recommendation shall be followed.
done in a 1-L, tall-form beaker. Obviously, no anodes are used.
7. Calibration
6. Factors Affecting Accuracy
7.1 Calibrate the instrument as directed in the manufactur-
6.1 Variations in the preparation of the helix may cause
er’s instructions.
substantial variations in results.
7.2 The frequency of calibration will vary with use and
6.1.1 Stop-off material shall be applied properly to the
extent of attack on the helices from the chemical stripping.
interior of the helix. The stop-off material shall be thin and
When visible attack is noted, discard the helix.
flexible to permit the helix to move freely during the test. A
7.3 The calibration procedure consists essentially of deter-
coating weight of less than 50 mg/dm is satisfactory.
mining the force required per degree of dial deflection. A
known mass is suspended over a small pulley on a lever arm
NOTE 2—The inside must be stopped-off with some inert, flexible
coating. One acceptable stop-off material is “Microstop.” One part of with the helix mounted in place. The degree of deflection is
“Microstop” is diluted with two parts of acetone before use. Any nickel
read from the dial. The data required for the calibration
deposited on the inside of the helix will exhibit an opposing effect.
calculations as expressed in metric units are as follows:
6.1.2 Helices that have been permanently coated on the
inside with TFE-fluorocarbon may give variable results when
w 5 mass used in calibrating, kg,
testing near-zero stresses.
a 5 length of lever arm, m,
6.1.3 Cleaning variations and surface preparation of the
p 5 pitch of helix, m,
helix before the test can produce varying results. For example,
t 5 thickness of the strip used to make the helix, m,
electrocleaning of the helix shall always be cathodic and
deg 5 degree deflection; difference in dial readings
def
controlled with respect to current, time, and temperature.
caused by mass,
Anodic cleaning at this stage can give wide variations. Abra-
g 5 9.8 m/s (acceleration of free fall), and
sive cleaning of the helix and the use of etchants shall be MPa
Z 5
calibration constant of the helix
S D
avoided.
m deg
def
6.1.4 Very thin deposits of less than about 3 μm are where
2 w! a! g!
influenced more by the surface conditions and preparation of ~ ~ ~
Z 5 3 10
the helix than are thicker deposits. p~t!deg
def
6.2 Internal stress varies with current density used in elec-
8. Procedure
troplating. The variation is not predictable and depends on the
8.1 The procedure will vary with the solution being tested.
metal being deposited, impurities or additives, and the current
Follow the instructions given by the supplier carefully. Varia-
density range under consideration. It is important that the
tions in the procedure can produce variations in results. Give
current be measured and controlled closely throughout the
appropriate attention to the factors in Section 6. A detailed
stress test. Variations in currents shall be held to less than 2 %.
procedure for nickel plating solutions appears in Appendix X1.
6.3 Because the temperature of the plating solution may
8.2 Position the spiral contractometer in electroplating so-
affect the internal stress, it shall be maintained within 2°C
lutions so that it is equidistant from the anodes. Position the
during the test. The initial rest point of the indicator and the
anodes on at least four sides when they are used in a production
final rest point are both taken at the operating temperature of
tank or use a concentric anode arrangement. Do not place the
the plating solution to eliminate thermal stresses.
spiral contractometer between the tank anodes and the work
6.4 The solution composition shall not vary during the test.
being plated in a production tank. A separate ammeter and
Usually, if the repeatability tests in 8.5 are met, the solution can
current control a
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