SPECIALTY TESTING SPIRAL CONTRACTOMER
TEST PROCEDURE
The new design for spiral contractometers corrects
problems that are common with earlier models. The basic
improvement is the addition of an interior 3/4th inch diameter
shaft over which the helix is attached. The shaft serves as a
shield to significantly reduce the quantity of the applied
deposit on the interior surface of the helix during the plating
test, producing results that are usually within a 4 -7% error
margin when using helices that are void of a mask material on
the inside diameter. Helices having an interior coating of
Teflon are only necessary for critical and certifiable
applications.
Helices recommended for use with the new design
contractometer are fully plated externally tip to tip so the
deposit surface area remains the same for each, avoiding an
estimated guess. The calculations are non-metric. Each helix
is 0.010 in thick, has a surface area of 13.57 in2 and has a hole
near each end through which a screw is used to fasten the
helix firmly to the shaft so helix slippage during the test
period is not possible. Also, stripping of threads is prevented
by the use of stainless steel inserts.
The recommended average test deposit thickness for
0.010 in thick helices is 5x10-4 in (1.27x10-3cm) for hard
deposits such as nickel. Deposit thickness values as great as
1x10-3 in (2.5x10-3cm) may become necessary for soft metallic
deposits.
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NEW DESIGN FOR SPIRAL CONTRACTOMETERS
The new geometry solves problems related
to an exposed interior that allows deposition of the applied
deposit to occur on the inside surface. Interior deposits reverse
the type of stress and reduce calculated results by as much as
30%, so interior masking is critical. The new design contains an
interior geometric shield that reduces the interior plating to the
degree that for process control helixes without an interior mask
can be used. However, for applications that require
certification, an interior mask is necessary. It is a real time saver
that offers more accurate results!
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HELIX ON AN OLDER MODEL SPIRAL
CONTRACTOMETER
Normally, the helix is attached at the top and bottom with a
polycarbonate ring and screw. Note how the interior surface
without a masked coating is totally exposed and receives
approximately 23% of the deposit. Since an interior deposit
reverses the type of the stress being applied to the outer surface,
the calculated result is very erroneous. The error is so great that
helices cannot be used in this manner for process control.
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THE SPECIALTY TESTING HELIX
ST&DC helices are constructed from 0.010 inch
thick stainless steel and have a precise surface
area of 13.57 in². Helices mount on the
contractometer in a way that the entire spiral
plates from end to end and deposition of metal
on the inside of helices is minimal even if they
are void of a masking material. The average
test deposit thickness is 500 microinches.
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Equipment for Determination of Internal Stress in Nickel
Deposits with the Spiral Contractometer
`
Spiral contractometer with calibration weights,
Spiral contractometer support stand,
Container 4ʺ dia. x 10 high for nickel strike anode
basket and bath (2,750 ml) only if a nickel strike is
required for adhesion of the applied deposit,
Titanium mesh anode basket 3.5ʺ outside and 2.25ʺ
inside diameter, 8ʺ high for Wood’s nickel strike if
desired,
Titanium mesh anode basket 5ʺ outside and 4ʺ inside
diameter with support tabs for the plating bath,
Nickel anode buttons to fill the anode baskets,
Pyrex 4,000 ml beaker for the nickel plating bath,
Magnetic stirrer hot plate,
Temperature controller prewired with probe,
Minutes and seconds timer, and
Power supply 0-10 amp constant amperage & voltage
output.
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CONTRACTOMETER PLATING SET-UP
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M Values to Determine Deposit Stress for Various Deposits
Stock Material
Cu-Fe Fe-Ni
Pure Nickel
E*
120,690 144,830 206,900
Stock Thickness, in
0.0020 0.0015
0.0008
Metal
M**
Values for M***
Cadmium
31,720
0.263
0.219
0.153
Chromium
248,280
2.06
1.71
1.20
Cobalt
206,897
1.72
1.43
1.00
Copper
117,240
0.971
0.810
0.567
Gold
74,480
0.617
0.514
0.360
Nickel
206,900
1.71
1.42
1.00
Platinum
146,900
1.22
1.02
0.710
Rhodium
289,650
2.400
2.000
1.400
Silver
75,860
0.629
0.524
0.367
Zinc
82,760
0.686
0.571
0.400
E*, modulus of elasticity of the substrate material.
M**, modulus of elasticity of the deposit.
M***, modulus of elasticity of the deposit ÷ modulus of
elasticity of the substrate in the modified Deposit Stress
Analyzer and Stoney Formulas.
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PLATING CONDITIONS FOR SPIRAL
CONTRACTOMETER TESTS
Helix Material
Stainless Steel
Helix 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
20m 40s
Solution Temperature
140º±1ºF
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Current Density, Amperage and Plating
Time at 95% Cathode Efficiency
Amps/ Ft²
Amps
Time
10
15
25
40
50
100
150
180
200
1.04
1.72
2.60
4.16
5.19
10.39
17.18
18.75
20.84
57M
38M
22M
14M 15S
11M 24S
5M 42S
3M 48S
3M 10S
2M 52S
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CONDITIONS FOR NICKEL PLATING HELICES
Current Density, Amperage and Plating Time at 95%
Cathode Efficiency
Amps/ Ft²
10
15
25
30
40
50
100
150
180
200
Amps
1.04
1.72
2.60
3.12
4.16
5.19
10.39
17.18
18.75
20.84
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Time
57M
38M
22M
19M
14M 15S
11M 24S
5M 42S
3M 48S
3M 10S
2M 52S
CALCULATING NICKEL DEPOSIT STRESS
A. Calculate the Deposit Stress in PSI.
Note the formula first used. This one fails to include the
influence of the helix material thickness and it produces for
instance about 5% error for nickel deposits.
Stress = 13.02 (D) (M) ÷ w x d = PSI
Where
D = Degrees caused by the deposit,
M = Modulus of Elasticity of the deposit ÷ Modulus of
the substrate Elasticity = 30,000,050 PSI ÷ 28,600,000
PSI = 1.04895 for nickel deposits over Specialty
Testing helices 0.010 inch thick,
w = degrees Kt from helix calibration if the stress is
tensile or degrees Kc if the stress is compressive,
d = Deposit thickness in inches, and
t = Helix material thickness in inches.
The improved formula is as follows:
S = 13.02(D) ÷ w (d) x 1 + ED (d) ÷ ES (t)
B. Calculation Examples.
First Used Formula:
S = 13.02 (26) (1.04897) ÷ 33 (0.000536) = 20,073
Second Used Formula:
S = 13.02 (26) x 1 + ED (d) = PSI
w (d )
S=
PSI
Es (t )
338.52
x 1 + 30,000,050 PSI (0.000536)
33 (0.000536)
28,600,000 PSI (0.010)
S = 19,138 ( 1 + 16,080 ÷ 286,000) = 20,209 PSI
S = 19,138 ( 1.056224 ) = 20,214
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PSI
Recording Data for Spiral Contractometer Tests
Deposit weight in grams:
Kc degrees:
Kt degrees:
Degrees deflection caused by the deposit:
Spiral weight in grams:
Deposit weight in grams by subtraction:
Deposit thickness in inches:
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OPERATION OF THE SPIRAL CONTRACTOMETER
It is important that when the spiral is attached to the
contractometer, a space of about 1/4 inch should be allowed between
the bottom of the contractometer center shaft and the top of the free
end to which the spiral is attached. This space prevents binding as the
spiral turns during the test plating period. The spiral is calibrated while
it is on the contractometer and immersed in the plating solution at the
plating bath temperature. Loosen the screw at the top of the
contractometer and adjust the zero of the dial to line up with the arrow
point. Use a blunt instrument in a tapping motion and make
adjustments as necessary to get a reading at the zero mark. Next,
calibrate the spiral by using the counterweights. Fasten the loop of a
counterweight string over the pin on the right side of the pulley wheel
and take the string around the pulley in a clockwise direction. Place it
over the Teflon grooved pin of the contractometer near the
Kcompressive stress label. Use tapping to get a stabilized degree of
stress from the zero point. Record this value as the calibration degrees
for compressive stress. Remove the counterweights and strings. If the
dial zero doesn't match the arrow with tapping, repeat this
procedure. To determine the tensile calibration value, fasten the loop
of a counter weight string over the pulley pin on the left side of the
pulley wheel. Wrap it in a counterclockwise direction and place the
string and counterweight over the Teflon pin near the Ktensile stress
label. Use tapping to get a stabilized degree of stress from the zero
point. Record this value as the calibration degrees for tensile
stress. Remove the calibration weights and strings.
Confirm that the desired plating conditions are correct, then
begin the plating test procedure. After the plating is completed, tap
the top of the contractometer until an equilibrium is reached and
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record the internal deposit stress value as the compressive or tensile
degrees caused by the deposit.
Remove the contractometer from the plating cell and rinse in water
and isopropyl alcohol. Remove the plated spiral and rinse it
again. Note that the spiral can be dried in a short time by rolling up a
paper towel and pulling it through the interior of the spiral. When it is
completely dry, weigh it and calculate the weight of the applied deposit
in grams.
Since all of the Specialty Testing spirals have the same surface
area and all of the external surface area is plated, the average deposit
thickness can be calculated in inches by dividing the deposit weight by
1,979. In the stress formula, d = the deposit weight. For the deposit
stress nonmetric calculation formula, see Item 4 in our Spiral
Contractometer brochure.
Note that compressive stress is indicated by use of a negative
sign.
Note also that is very important to loosen the screw at the top
of the contractometer and lift off the dial and remove the center
rod. Do this step over a sink and force water through the hole to
remove solution that could over time form a salt that could bind the
rod and prevent turning of the lower piece that must remain free to
turn as the deposit stress is applied.
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