SPECIALTY TESTING & DEVELOPMENT COMPANY, INC.
A NEW DESIGN FOR SPIRAL CONTRACTOMETERS
KNOW THE STRESS IN YOUR APPLIED METALLIC COATINGS
Revised 02/03/2016
ADVANTAGES
IMPROVEMENTS
• Accurate repeatable results
• Thread stripping is prevented
• Perfect centering of the helix
• Reduced calibration wheel friction
• Perfect centering of the anode basket
• 25% glass filled Teflon construction
• Holes at helix ends - no slippage
• Inside spiral surface is shielded
• Simple and rapid calculations
• Minimal deposit on helix interior
• Guess steps are eliminated
• Precise scale to arrow view
For Applied Nickel Coating visit:
http://specialtytest.com/sprial-contractometer-method-for-nickel-deposit-stress/
SPIRAL CONTRACTOMETER MEASUREMENT METHOD AND
CALCULATIONS TO DETERMINE INTERNAL DEPOSIT STRESS IN
SPIRAL CONTRACTOR MEASUREMENT METHOD AND CALCULATIONS TO
APPLIED
METALLIC
COATINGS
DETERMINE INTERNAL
DEPOSIT
STRESS IN APPLIED
METALLIC COATINGS
Internal stress exists as an inherent force within electroplated and chemically applied metallic deposits.
This induced stress can be tensile or compressive in nature, causing the deposit to contract or expand in relation to
the base material. High levels of stress in deposits produce micro-cracking and macro-cracking, and in severe cases
produce a lack of deposit adhesion in the form of blistering, peeling, and flaking. In extreme cases, wave-like
ripples in electroforms, accelerated corrosion and deposit wear failure can also occur.
The two primary ways to evaluate the internal deposit stress in metallic coatings that are experiencing use
worldwide are the bent strip Deposit Stress Analyzer and the Spiral Contractometer methods. These represent the
only two stress test procedures that have approval status by the American Society for Testing Metals Standards.
Several other methods have been used in the past, but these have not been put into common practice. The Stress
Meter makes use of a disk that bows inward or outward as deposition commences depending on the nature of the
stressed deposit. Accuracy and stripping metallic layers from the disk remain problematic. Another method
measures the change in the length of the substrate material that is caused by an applied metallic coating. This
method yields consistent results, but the equipment set-up is complicated and there has never been a manufacturing
source for its use.
1. SPECIALTY TESTING & DEVELOPMENT COMPANY HELIX
Specialty Testing & Development Co. helices are constructed from 0.010 inch thick stainless steel and
each has a precise surface area of 13.57 square inches. The helix mounts on the contractometer in a
manner that permits plating on the entire outside surface of the helix and discourages deposition on the
interior of the helix. Thus, there is no need to estimate the surface area that has been plated. The
recommended average test deposit thickness is 500 microinches, (0.000500 inch) for nickel deposits.
2. PROPERTIES AND TEST CONDITIONS FOR STAINLESS STEEL HELIX
HELIX WITH
SPIRAL
A TEFLON
FOR THE
COATED
NEW CONTRACTOMETER
INTERIOR
DESIGN
Surface Area, in²
13.57
Square Feet
0.0942 Amps per sq. foot
30
Amps
2.90
Stock Thickness, inches
0.010
Avg. Deposit Thickness, µʺ
500
Plating Time, Min & Seconds
20 M & 48
40 S
Plating Solution Temperature
140º ± 1º F.
NOTE: For the purpose of illustration and explanation, electrolytic plating of nickel is used.
* Teflon coating can withstand temperatures up to 400°F
3. TEST PROCEDURE (SPIRAL CONTRACTOMETER METHOD - REFERENCE ASTM STANDARD B636)
A. Equipment.
-Spiral Contractometer with calibration weights (PN:2014SC)
-Adjustable Spiral Contractometer Support Stand (PN: 2014AS)
-Titanium anode basket 3.5ʺOD for Wood’s nickel strike (PN:14ABS)
-Titanium anode basket 5ʺOD for nickel bath (PN:14ABL)
-4,000 ml Pyrex beaker for plating bath (other source)
-DC Power Supply 0-5 Amperage output constant amp constant voltage (PN: HY3005-PS)
-2,000 or 3,000 ml beaker for Wood’s nickel strike bath (other source) around 9 1/2” tall beaker
-Magnetic Stirrer Hot Plate (PN:4000-S)
-Digital Temperature Controller prewired with probe (PN:590TC)
B. Helix Preparation and Use.
1. Place the anode basket containing nickel anode buttons in a 4,000 ml Pyrex beaker, then place the
beaker over a magnetic stirrer hot plate, add the desired plating solution to the beaker, then place the
adjustable spiral contractometer support stand over the beaker and anode basket and warm the plating
solution to the desired temperature.
2. Pour the nickel strike solution into a 2,000 ml beaker containing an anode basket with nickel anode
buttons along the beaker's inside parameter.
3. Clean a helix as the cathode in an alkaline steel electrocleaner at 53 amps for 30 seconds and
water rinse. If the helix is clean skip step 4.
4. Treat the helix with anodic current (positive charge) for 10 seconds at 25amps, then change the
current leads to bring negative contact to the helix and nickel strike the helix at 35amps for 30
60seconds.
Remove the helix, water rinse, acetone rinse and dry.
5. Weigh the helix to the nearest milligram and record its weight. Note: use finger cots since the
deposited nickel is approximately 0.0545 grams. For non-critical applications, step 5 can be eliminated.
Deposit weight in grams:
6. Mount the helix onto the helix holder and tighten the nylon screws through the holes
provided sufficiently to secure the helix so as to prevent slippage during the plating process.
7. Place the spiral contractometer assembly on the adjustable support stand and center it by
engaging the centering holes in the top surface of the stand.
C. Calibration of the Helix.
1. Loosen the screw that holds the pulley wheel tight against the top of the center rod and position
the dial by rotating it to match the zero with the arrow, then tighten the screw to secure the rod so
slippage cannot occur.
2. Put the loop of a calibration thread over a pulley calibration pin and wrap the string around the
pulley wheel clockwise, and place the thread and 0.5 avoir dupois ounce weight over the extended
Teflon guide wheel near Kc.
3. Put the loop of the second thread over the remaining calibration pin, wrap clockwise and hang
the weight over the remaining Teflon guide wheel. Lightly tap the top of the contractometer pulley
to equalize the dial position. Record the Kc degrees. As an option, the spiral calibration steps can
be repeated and this data can be averaged.
Kc degrees:
Average:
4. Repeat this process again, this time wrapping the threads in a counterclockwise direction and
looping the weights over the Teflon guide wheels near Kt. Record the degrees tensile as Kt.
Then remove the calibration strings and weights. Repeat and average the results if desired.
Kt degrees:
Average:
D. Plating the Helix.
1. Plate the helix at 2.90 amps (30 asf) for 20m and 40s.
48s. As soon as possible after the helix
has been plated, tap the top of the contractometer lightly, observe and record the degrees
deflection at the arrow point and the nature of the stress as tensile or compressive.
Compressive stress is indicated by a negative sign.
Degrees deflection caused by the deposit:
2. With the helix on the contractometer, rinse it in water and isopropyl alcohol, then remove the
helix from the contractometer using finger cots so as to not adversely affect the weight of the
helix and dry it thoroughly.
E. Calculations.
1. Weigh the dry spiral and record its weight in grams.
Helix weight in grams:
Subtract from this weight the before plating weight to obtain the weight of metal deposited.
Deposit weight in grams:
2. Calculate the average deposit thickness in inches.
T=
W
=
Inch
D (87.55
87.53 cm²) (2.54 cm / inch)
W = Grams of deposit,
D = Density of deposit = 8.90 g/cm³ for
pure nickel, and
T = Deposit thickness in inches.
Where
For Specialty Testing helices, the helix plated surface area is 13.57 in² and the following formula
applies for nickel:
T=
W
= Inches
1978.7
1979.2
For a helix attached by circular rings, the plated surface area must be determined by wrapping the helix
tightly around a 3/4 inch diameter rod. Then the diameter & estimated plated length in inch values are
used to calculate the plated surface area as follows:
Surface Area = πdh = inch²
This surface area value replaces the 87.53
87.55 cm² value in the above equation. See E.2.
3.�Record the average deposit thickness of the helix as microinches.
Deposit thickness in microinches:
4. CALCULATE THE DEPOSIT STRESS OF THE APPLIED COATING.
A. Calculate the Deposit Stress in PSI.
x 1 + EO (d) = PSI
Stress= 13.02 (D)
E (t)
w (d)
D = Degrees caused by the deposit,
w = degrees Kt from the helix calibration,
t = Helix material thickness = 0.010 inch
d =Deposit thickness in inches,
Eo= the Modulus of Elasticity of the deposit = 30,000,050 PSI for nickel, and
E = the Modulus of Elasticity of the helix substrate = 28,600,000 PSI,
Record the Internal Deposit Stress as PSI:
PSI
5. STRIPPING OF HELIX FOR REUSE.
A. Plated helices can be stripped of nickel deposits repeatedly in a 50% by volume nitric acid solution for reuse.
Do not heat the solution above 90°F. The Teflon coating remains in place.
SPECIALTY TESTING & DEVELOPMENT COMPANY, INC.
137 Reynolds Mill Road, York, PA 17403 USA
Phone (717) 428-0186 Fax (717) 428-0294 www.specialtytest.com