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Operation of the Spiral Contractometer

Test conditions for Nickel Plating A Spiral (Helix) using a Spiral Contractometer
Surface Area, 13.57 I n² Square Feet 0.0942
Stock Thickness, 0.010 inches Amps per sq. foot 30
Amps 2.90 Avg. Deposit Thickness, µʺ 500
Plating Time, 20 Minutes & 40 Seconds Plating Solution Temperature 130º ± 1.5º F
Test Procedure

Step 1: Place the anode basket containing buttons or anodes in a 4,000 ml Pyrex beaker, then place the beaker on a magnetic stirrer hot plate, add the desired plating solution to the beaker, then place the spiral contractometer adjustable support stand over the beaker and warm the plating solution to the desired temperature.

Note: Use gloves to prevent contamination of the spiral (helix).

Note: If a nickel Strike is necessary go to #2, if not go to #5.

Step 2: If a nickel strike is necessary for adhesion of the applied coating, pour the nickel strike solution into a beaker use a circular titanium anode basket containing Nickel anodes or buttons.

Step 3: Clean a spiral (helix) as the cathode (positive lead) in an alkaline steel electrocleaner at 3 amps for 30 seconds and warm water rinse.

Step 4: Nickel strike the spiral (helix) at 3 amps for 1 minute. Remove the spiral (helix) from the spiral contractometer and water rinse, isopropyl alcohol rinse and dry completely. Go to #6.

Step 5: Clean the Spiral (helix) in a soak clean solution water rinse and alcohol rinse, then dry completely.

Step 6: Weigh the spiral (helix) to the nearest milligram, record the starting weight in grams. (example 19.1649) SW=___________

Step 7: Mount the spiral (helix) onto the spiral contractometer and tighten the polycarbonate screws through the holes provided sufficiently to secure the spiral (helix) so as to prevent slippage during the plating process.

Note: That the wire contact end must be positioned over the top of the spiral (helix) with a screw.

Step 8: Place the spiral contractometer assembly and the attached spiral (helix) into the adjustable support stand center in the holes in the top surface of the stand. Then allow two minutes for the spiral (helix) to reach the plating bath temperature.

Calibration of the Spiral (Helix) How to Find Your (K)

For step by step instructions with photos

For more information visit:

Step 1: Loosen the pulley calibration wheel screw that holds the pulley calibration wheel tight against the top of the center rod and position the dial by rotating it to match the zero with the arrow, and then tighten the screw to secure the rod so slippage cannot occur.

Note: It is important that when the spiral (helix) is attached to the contractometer, a space of about 3/16 inch should be allowed between the bottom of the contractometer spiral shaft and the top of the spiral (helix) holder knob to which the spiral (helix) is attached.

Step 2: Attach the eye loop thread of one of the calibration weights over the pulley calibration pin at the zero and wrap the thread clockwise part way around the pulley calibration wheel and suspend the weight over the grooved guided wheel near the Kc marker.

Step 3: Attach the eye loop thread of second of the calibration weights over the remaining pulley calibration pin at the 180 degrees and wrap the thread clockwise ¾ way (making sure to put the thread under the previous one) around the pulley calibration wheel and suspend the weight over the grooved guided wheel near the Kc marker.

Step 4: Tap the pulley calibration wheel at the top of the contractometer lightly and read the degrees compressive stress. Note: Too much force taping could push the large bushing into the shaft causing the pully calibration wheel to not spin freely.

Step 5: Record this degree reading as Kc. Kc= -__________.

Note: The compressive stress values are identified with a minus sign.

Step 6: Remove the weights from the pins making sure the dial is at zero. Repeat step 2-4 procedure except wrap the strings counterclockwise 3/4 of the way and suspend the thread over the grooved guided wheel near the Kt marker. Again, tap the pulley calibration wheel at the top of the contractometer lightly and read the degrees tensile stress.

Step 7: Record this reading as Kt. Finally, remove the calibration weights. Kt=_____________.

Note: The tensile stress values are positive.

Plating the Spiral (Helix) How to Find Your (d)

Step 1: Make sure the solution temperature is the desired temperature within ± 3°F.

Step 2: Set the timer for the desired plating time.

Step 3: Connect the positive lead (usually red) of the power supply to the anode basket and the remaining lead (usually black) to the metal contact at the top of the spiral contractometer.

Step 4: With the rectifier plugged into the timer, turn on the timer and begin the plating process. For critical work, maintain the bath temperature within ± 3°F. It is helpful to tap the top of the pulley calibration wheel every 3 minutes or so with a blunt instrument to assist in stabilizing the degree reading.

Step 5: When the plating time expires, tap lightly on the top of the pulley calibration wheel to stabilize the degree value, then read the final degrees value and note if the stress is compressive (negative) or tensile (positive). Record the degree value as Kc- or Kt+ accordingly.

THIS IS YOUR (d) value__________.

Step 6: Remove the spiral contractometer from the adjustable support stand, rinse the spiral (helix) in water, and rinse it in 70 % isopropyl alcohol. Remove the spiral (helix) from the contractometer using gloves. Dry thoroughly. Note: It is helpful to pull part of a rolled sheet of paper towel gently through the interior of the spiral (helix) to assist in drying.

Step 7: When the spiral (helix) is completely dry, weigh the spiral (helix) and record the weight in grams.


Calculations for the Deposit Thickness

Step 1: Subtract the start weight from the finished weight to obtain the weight of the metal deposited.

FW – SW = W

Step 2: Calculate the average deposit thickness in inches. (See chart 1 below for density values)

T  =    ────────────────────────────   =   Inch     Where
            D (13.57in²)(6.45cm²/in²)( 2.54 cm / inch)

T = Deposit thickness in inches

D = Density plated material (If using Nickel the plated material is 8.88g/cm³)

W = Grams of nickel deposit

Note: For the Specialty Testing spirals (helices) plated on the new design contractometer, the constant spiral (helix) plated surface area is 13.57 in² since the entire spiral (helix) receives plating on the outside diameter, and the following shortened formula applies:

T  =    ────────────────────────────   =   Inch     Where
            D(222.32cm² / inch)

Note: For the spirals (helices) plated on the old design spiral contractometers, the surface area plated must be determined by wrapping the spiral (helix) tightly around a 3/4 inch diameter rod. Then the diameter and estimated plated length in inch values are used to calculate the plated surface area as follows: Surface Area = πdh = cm²

Step 3: Record the average deposit thickness of the spiral (helix) in microinches. Deposit thickness in microinches: T= ____________ inches.

CHART 1. Density and Modulus of Elasticit
Deposited Metal (D)Density (Edeposit)Modulus of Elasticity
Cadmium 8.80 30,600,000
Copper 8.93 16,000,000
Gold (Soft) 19.30 11,200,000
Gold (Hard) 19.32
Nickel 8.88 30,000,500
Palladium 12.02
Platinum 21.45 24,800,000
Rhodium 12.45 52,100,000
Silver 10.50 11,000,000
Tin 7.26 5,900,000
Zinc 7.10 14,000,000

Step 4: Calculate the Deposit Stress in PSI

Note that compressive stress is indicated by use of a negative sign.

Calculating Spiral Contractometer Deposit Stress Results on Helices

                     13.02 (d)                   EDeposit(T)
Stress  =    ───────   X   1 + ────────── = PSI      where
                        (K)(T)                  ESubstrate (t)

d = deflection of the spiral (helix) caused by the deposit in degrees, (before plating)

K= deflection of spiral (helix) on calibration in degrees,(after plating)

T = deposit thickness in inches,

t = substrate thickness in inches, for Specialty Testing Spiral(helix) 0.010 inch

EDeposit = Modulus of elasticity of the plated material _____________ PSI, (See chart 1)

ESubstrate = Modulus of elasticity of the helix substrate= 28,600,000 PSI