SPECIALTY TESTING and DEVELOPMENT COMPANY SPIRAL CONTRACTOMETER Measurement Method for Nickel Plating
Specialty Testing and Development Company spirals (helices) are constructed from 0.010 inch thick stainless steel and have a precise surface area of 13.57 square inches. The spiral (helix) mounts on the contractometer in a manner that the entire spiral (helix) receives the nickel deposit from end to end and deposition of nickel does not occur on the inside of the spirals (helices) even if they are void of a masking material. The recommended average test deposit thickness is 500 microinches, (0.000500 inch).
A 500 microinch average deposit thickness over one square foot requires 9.5 ampere hours.
Current Density, Amperage and Plating Time at 95% Cathode Efficiency
Spiral contractometer (PN: KSC114)with calibration weights, support stand (PN: SAS141), and a spiral (helix) test piece(PN: CTS214 Teflon coated or PN: NCS314 non-coated).
Titanium anode basket (PN: ABL14 Large to hold pure nickel buttons.
4,000ml Pyrex beaker – for nickel plating.
Power supply (PN: HY3005 0-5 Amp) sufficient for the amperage desired.
Magnetic stir hot plate (PN: MHS4000)
Digital Temperature Controller (PN: TC590) with probe to place within the plating solution – recommended since the deposit stress varies with the bath temperature.
Spiral (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 spiral contractometer adjustable support stand over the beaker and anode basket and warm the plating solution to the desired temperature.
2. If a nickel strike is necessary for adhesion of the applied coating, pour the nickel strike solution into a beaker (approx. 9.5″) use a circular titanium anode basket containing nickel anodes or buttons.
3. Clean a spiral (helix) as the cathode (positive charge) in an alkaline steel electrocleaner at 3 amps for 30 seconds and water rinse.
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.
5. Weigh the spiral (helix) to the nearest milligram and record the weight in grams. Note: use gloves to prevent contamination of the spiral (helix).
6. 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: the wire contact end must be positioned over the top of the spiral (helix) with the screw provided.
7. Place the spiral (helix) contractometer assembly and the attached spiral (helix) into the adjustable support stand holes located on 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)
1. Loosen the pulley wheel 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 during the plating cycle.
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 at the bottom where the spiral (helix) is attached.
2.Place the eye loop thread of one of the calibration weight string over the pulley calibration pin at the zero and wrap the thread clockwise part way around the pulley calibration wheel, then suspend the thread and weight over the grooved Teflon guide wheel near the Kc marker.
3. Place the eye loop thread of second calibration weight string over the remaining pulley calibration pin and wrap the thread clockwise part way around the pulley calibration wheel, then suspend the weight over the grooved Teflon guide wheel near the Kc marker.
4.Tap the pulley calibration wheel at the top center of the contractometer lightly and read the degrees compressive stress. Record this degree reading as Kc.
Note: The compressive stress values are identified with a minus sign.
5.Remove the eye loop threads from the pins and repeat the above procedure except for wrapping the strings counterclockwise and suspending the threads over the grooved Teflon guide wheels near the Kt markers. Again, tap the pulley calibration wheel at the top center of the contractometer lightly and read the degrees tensile stress. Record this reading as Kt. Finally, remove the eye loop calibration string and weights.
Plating the Spiral (Helix)
1. Make sure the solution temperature is the desired temperature within ± 3°F.
2. Set the timer for the desired plating time.
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.
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.
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.
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.
7. When the spiral (helix) is completely dry, weigh the spiral (helix) and record the weight in grams.
Calculations for the Nickel Deposit Thickness
1. Subtract the start weight from the finished weight to obtain the weight of material deposited. FW – SW- = W
2. Calculate the average deposit thickness in inches.
T = W =Inch
D x 13.57in² x 6.45cm²/in² x 2.54 cm/in
W= Grams of nickel deposit
D= Density of Nickel plated material is 8.88g/cm3
T= Deposit thickness in inches
Note: The surface area for Specialty Testing spirals (helices) is 13.57 in² or 13.57 square inches.
For nickel deposits: T = W = ________________Inch
Note: If calculation of the internal deposit stress is desired based on the pitch of the spiral (helix), since all of the Specialty Testing and Development stainless steel spirals (helices) are manufactured in the same manner from 0.0100 inch thick stainless steel, t = 0.0002540 meters, and are formed in the same manner, the pitch, p, of each spiral (helix) is 0.000254 meters. The pitch is determined by slipping a spiral (helix) over a 0.019 m, 0.75 inch, diameter rod, compressing the spiral (helix) so the edges of the loops tightly touch each other and dividing the length in meters by the number of loops. This length is 14.3 cm = 0.143 m, and 0.143m ÷ 7.73 loops equals 0.0196 m.
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
b. Solve the equation for PSI internal deposit stress as follows:
S = 13.02 (d) X 1 + EDeposit(T) = PSI where
(K) (T) ESubstrate (t)
d = deflection of the spiral (helix) caused by the deposit in degrees,
K = deflection of spiral (helix) on calibration in degrees,
T = deposit thickness in inches,
t = substrate thickness in inches, Specialty Testing Spiral (helix) material thickness =0.010 inch
EDeposit = Modulus of elasticity nickel = 30,000,500 PSI, and
ESubstrate = Modulus of elasticity of the helix substrate= 28,600,000 PSI
Record the Internal Deposit Stress as PSI: _________________
STRIPPING OF NICKEL FROM SPIRALS (HELICES) FOR REUSE.
1. Plated spirals (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.
2. When the exterior surface of a Spiral (helix) shows visible etching, the helix should be discarded.