ASTM B636-84(2006)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
SIGNIFICANCE AND USE
The spiral contractometer, properly used, will give reproducible results (see 8.5) over a wide range of stress values. Internal stress limits with this method can be specified for use by both the purchaser and the producer of plated or electroformed parts.
Plating with large tensile stresses will reduce the fatigue strength of a product made from high-strength steel. Maximum stress limits can be specified to minimize this. Other properties affected by stress include corrosion resistance, dimensional stability, cracking, and peeling.
In control of electroforming solutions, the effects of stress are more widely recognized, and the control of stress is usually necessary to obtain a usable electroform. Internal stress limits can be determined and specified for production control.
Internal stress values obtained by the spiral contractometer do not necessarily reflect the internal stress values found on a part plated in the same solution. Internal stress varies with many factors, such as coating thickness, preparation of substrate, current density, and temperature, as well as the solution composition. Closer correlation is achieved when the test conditions match those used to coat the part.
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 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.
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Designation:B636–84 (Reapproved 2006)
Standard Test Method for
Measurement of Internal Stress of Plated Metallic Coatings
with the Spiral Contractometer
This standard is issued under the fixed designation B636; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Note 2 was editorially updated in May 2006.
1. Scope tensile (+). From the amount of needle deflection and other
data, the internal stress is calculated.
1.1 This test method covers the use of the spiral contracto-
3.2 With instrument modifications, the movement of the
meter for measuring the internal stress of metallic coatings as
helixcanbemeasuredelectronicallyinsteadofmechanicallyas
produced from plating solutions on a helical cathode. The test
described in 3.1.
method can be used with electrolytic and autocatalytic depos-
its.
4. Significance and Use
1.2 This standard does not purport to address all of the
4.1 The spiral contractometer, properly used, will give
safety concerns, if any, associated with its use. It is the
reproducible results (see 8.5) over a wide range of stress
responsibility of the user of this standard to establish appro-
values. Internal stress limits with this method can be specified
priate safety and health practices and determine the applica-
for use by both the purchaser and the producer of plated or
bility of regulatory limitations prior to use.
electroformed parts.
2. Terminology 4.2 Platingwithlargetensilestresseswillreducethefatigue
strengthofaproductmadefromhigh-strengthsteel.Maximum
2.1 Definitions:
stresslimitscanbespecifiedtominimizethis.Otherproperties
2.1.1 compressive stress (−)—stress that tends to cause a
affected by stress include corrosion resistance, dimensional
deposit to expand.
stability, cracking, and peeling.
2.1.2 internal stress—thenetstressthatremainsinadeposit
4.3 In control of electroforming solutions, the effects of
whenitisfreefromexternalforces.Theinternalstresstendsto
stress are more widely recognized, and the control of stress is
compress or stretch the deposits.
usuallynecessarytoobtainausableelectroform.Internalstress
2.1.3 tensile stress (+)—stress that tends to cause a deposit
limits can be determined and specified for production control.
to contract.
4.4 Internal stress values obtained by the spiral contracto-
3. Summary of Test Method
meterdonotnecessarilyreflecttheinternalstressvaluesfound
onapartplatedinthesamesolution.Internalstressvarieswith
3.1 The test method of measuring stress with the spiral
many factors, such as coating thickness, preparation of sub-
contractometer is based on plating on the outside of a helix.
strate, current density, and temperature, as well as the solution
The helix is formed by winding a strip around a cylinder,
composition. Closer correlation is achieved when the test
followed by annealing. In operation, one end of the helix is
conditions match those used to coat the part.
fixedandtheotherisallowedtomoveasstressesdevelop.The
free end is attached to an indicating needle through gears that
5. Apparatus
magnify the movement of the helix.As the helix is plated, the
5.1 The spiral contractometer is described by A. Brenner
stress in the deposit causes the helix to wind more tightly or to
and S. Senderoff.
unwind, depending on whether the stress is compressive (−) or
NOTE 1—Spiral contractometers are available from many of the sup-
pliers of nickel sulfamate.
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
Test Methods.
Current edition approved April 1, 2006. Published May 2006. Originally
approved in 1978. Last previous edition approved in 2001 as B636–84 (2001). Brenner, A., and Senderoff, S., Proceedings of the American Electroplaters
DOI: 10.1520/B0636-84R06E01. Society, Vol 35, 1948, p. 53.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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B636–84 (2006)
5.2 Helices shall be stopped-off on the inside to prevent 6.4.1 Testsrunonelectroplatingsolutionsusinginsolubleor
plating.Helicesareavailablewithorwithoutapermanentinert inefficient anodes could result in significant solution changes
coating on the insides (see Appendix X1). during the test.
5.3 Theclampsholdingthehelixtothecontractometershall 6.4.2 When testing autocatalytic plating solutions, the con-
be coated with an inert nonconductive coating to prevent their
stituents of the plating solution may be significantly depleted
plating and acting as thieves. during the test, unless replenished.
5.4 For testing electroplating solutions, anodes are placed
6.5 Arelationship between the surface area to be plated and
equidistant from the helix and symmetrically positioned to the volume of autocatalytic plating solutions exists that may
produce even plate distribution. A minimum of four anodes is
affect the character of the deposit. In testing autocatalytic
required. A concentric anode arrangement is preferred. plating solutions, the ratio of plated surface area to the volume
5.5 Laboratory tests on electroplating solutions shall utilize
of solution that is normally used in the plating tank shall be
at least 3.7 L of solution.A4-L beaker with an annular anode maintained. When using proprietary solutions, the supplier’s
arrangement is convenient. Use of this volume or larger will
recommendation shall be followed.
minimize solution changes due to electrolysis during the test.
5.6 Laboratory tests on autocatalytic plating solutions are
7. Calibration
doneina1-L,tall-formbeaker.Obviously,noanodesareused.
7.1 Calibrate the instrument as directed in the manufactur-
er’s instructions.
6. Factors Affecting Accuracy
7.2 The frequency of calibration will vary with use and
6.1 Variations in the preparation of the helix may cause
extent of attack on the helices from the chemical stripping.
substantial variations in results.
When visible attack is noted, discard the helix.
6.1.1 Stop-off material shall be applied properly to the
7.3 The calibration procedure consists essentially of deter-
interior of the helix. The stop-off material shall be thin and
mining the force required per degree of dial deflection. A
flexible to permit the helix to move freely during the test. A
known mass is suspended over a small pulley on a lever arm
coating weight of less than 50 mg/dm is satisfactory.
with the helix mounted in place. The degree of deflection is
read from the dial. The data required for the calibration
NOTE 2—The inside must be stopped-off with some inert, flexible
calculations as expressed in metric units are as follows:
coating. One acceptable stop-off material is “Microstop.” One part of
“Microstop” is diluted with two parts of acetone before use. Any nickel
deposited on the inside of the helix will exhibit an opposing effect.
w = mass used in calibrating, kg,
6.1.2 Helices that have been permanently coated on the
a = length of lever arm, m,
inside with TFE-fluorocarbon may give variable results when
p = pitch of helix, m,
testing near-zero stresses.
t = thickness of the strip used to make the helix, m,
6.1.3 Cleaning variations and surface preparation of the deg = degree deflection; difference in dial readings
def
helix before the test can produce varying results. For example, caused by mass,
g = 9.8 m/s (acceleration of free fall), and
electrocleaning of the helix shall always be cathodic and
MPa
Z =
controlled with respect to current, time, and temperature.
calibration constant of the helix
S D
mdeg
Anodic cleaning at this stage can give wide variations. Abra- def
where
sive cleaning of the helix and the use of etchants shall be
2~w!~a!~g!
avoided.
Z 5 3 10
p~t!deg
def
6.1.4 Very thin deposits of less than about 3 µm are
influenced more by the surface conditions and preparation of
8. Procedure
the helix than are thicker deposits.
6.2 Internal stress varies with current density used in elec- 8.1 The procedure will vary with the solution being tested.
Follow the instructions given by the supplier carefully. Varia-
troplating. The variation is not predictable and depends on the
metal being deposited, impurities or additives, and the current tions in the procedure can produce variations in results. Give
appropriate attention to the factors in Section 6. A detailed
density range under consideration. It is important that the
current be measured and controlled closely throughout the procedurefornickelplatingsolutionsappearsinAppendixX1.
8.2 Position the spiral contractometer in electroplating so-
stress test.Variations in currents shall be held to less than 2%.
6.3 Because the temperature of the plating solution may lutions so that it is equidistant from the anodes. Position the
anodesonatleastfoursideswhentheyareusedinaproduction
affect the internal stress, it shall be maintained within 2°C
during the test. The initial rest point of the indicator and the tank or use a concentric anode arrangement. Do not place the
spiral contractometer between the tank anodes and the work
final rest point are both taken at the op
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