OPERATION OF THE SPIRAL CONTRACTOMETER

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 center shaft and the top of the free end to which the spiral (helix) is attached.  This space prevents binding as the spiral (helix) turns during the test plating period.  The spiral (helix) 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 (helix) by using the counterweights.  Fasten the loop of a counterweight string over the pin at the zero degree mark of the pulley wheel and take the string 3/4th way around the pulley in a clockwise direction.  Place it over the grooved Teflon wheel of the contractometer near the K compressive stress label. Then fasten the loop of a counterweight string over the pin on the left side at the 180 degree mark of the pulley wheel and take the string 3/4th way around the pulley in a clockwise direction (make sure the string goes below the pin at Zero). Place it over the grooved Teflon wheel of the contractometer near the K compressive stress label. Note Compressive stress values are identified with a minus sign.

Kc= -____________.

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 counterweight string over the pin at the zero degree mark of the pulley wheel and take the string 3/4th way around the pulley in a Counterclockwise direction.  Place it over the grooved Teflon wheel of the contractometer near the K tension stress label. Then fasten the loop of a counterweight string over the pin on the left side at the 180 degree mark of the pulley wheel and take the string 3/4th way around the pulley in a counterclockwise direction (make sure the string goes below the pin at Zero). Note: Tension stress values are positive. 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. 

Kt = ________________.

Confirm that the desired plating conditions are correct, then begin the plating test procedure. Tap the top of the contractometer every few minutes. After the plating is completed, tap the top of the contractometer until an equilibrium reading is reached and 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 (helix) and rinse it again.  Note that the spiral (helix) can be dried in a short time by rolling up a paper towel and pulling it through the interior of the spiral (helix).  When it is completely dry, weigh it and calculate the weight of the applied deposit in grams.

Since all of the Specialty Testing spirals (helices) have the same external surface area and all of that area is plated, the average deposit thickness can be calculated in inches by dividing the deposit weight by 1978.7.  In the stress formula, d = the deposit weight.  For the deposit stress nonmetric calculation formula, see Item 4 in our Spiral Contractometer brochure on our home page.

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.

 

Spiral (Helix) preparation and use (visit:https://specialtytest.com/video-how-to-use-the-spiral-contractometer/

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.
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.
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.
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.
5. Clean the Spiral (helix) in a soak clean solution water rinse and alcohol rinse, then dry completely.
6. Weigh the spiral (helix) to the nearest milligram, record the starting weight in grams. (example 19.1649) SW=___________
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.
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 photo instructions visit our web site at: https://specialtytest.com/calibration-of-the-helix/

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.
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 Teflon guided wheel near the Kc marker.
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 Teflon guided wheel near the Kc marker.
4. Tap the pulley calibration wheel at the top of the contractometer lightly and read the degrees compressive stress.                                                                                                                Record this degree reading as Kc. Kc=_-__________.
Note: The compressive stress values are identified with a minus sign.
5. Remove the weights from the pins making sure the dial is at zero. Repeat step 2-4 procedure except wrap the strings counterclockwise ¾ of the way and suspend the thread over the grooved Teflon 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.             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)

  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.                                                                                                                                          THIS IS YOUR (d) value__________.
  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.                                                                                                                                         FW=_________________________

 

Calculations for the Deposit Thickness

  1. Subtract the start weight from the finished weight to obtain the weight of the metal deposited.       FW – SW = W
  2. Calculate the average deposit thickness in inches. (See chart 1 below for density values)

T =                        W                             = Inch                               Where 

     D (13.57in²)(6.45cm²/in²)( 2.54 cm / inch) 

W = Grams of nickel deposit

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

 T = Deposit thickness in inches

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 =           W        = Inch                    
D(222.32cm² / 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  

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

 

CHART 1.  Density and Modulus of Elasticity

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

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

                Stress =     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, (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