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# Metric Formula for the Spiral Contractometer System

Calculations for the Deposit Thickness using Specialty Testing Spirals (Helices)
Step 1: Subtract the start weight (SW) from the finished weight (FW) to obtain the weight of metal deposited.

FW – SW = W

Step 2: Calculate the average deposit thickness in inches. (for D density, see Chart A below)
W
T  =    ────────────
D (87.548212 cm²)

For Specialty Testing Spirals/ Helices the surface area is 87.548212 cm ²

W = Grams of deposit
D = Density of plated material, g/cm³
T = Deposit thickness in cm.

Step 3: Record the average deposit thickness of the spiral (helix) in cm: T = ______________cm
Chart A, Density and Modulus of Elasticity for Metric Systems
Deposited Metal (D) Density (Edeposit) Modulus of Elasticity in kg/cm2
Chromium 7.19 2,528,896
Cobalt 8.80 2,151,601
Copper 8.93 1,121,688
Gold (Soft) 19.30 787,221
Gold (Hard) 19.32
Nickel 8.88 2,110,813
Platinum 21.45 1,743,715
Rhodium 12.45 3,660,781
Sliver 10.50 774,984
Tin 7.26 414,820
Zinc 7.10 984,026
Step 4: Calculate the Deposit Stress in kg/cm² using Specialty Testing Spirals/Helices only
2.54 (d)                         EDeposit(T)
Stress  =    ───────   X   1 + ────────────── = kg/cm²
(K)(T)                            4926656

d = deflection of the spiral (helix) caused by the deposit in degrees after plating,
K = deflection of spiral (helix) on calibration in degrees= before plating Kt or –Kc, if the bath is tensile use (Kt value) or compressive use (-Kc value).
T = deposit thickness in cm, (found in #2 on previous page)
t< = substrate thickness in cm, for Specialty Testing Spiral (helix) is .0254 cm,

EDeposit = Modulus of elasticity of the plated material ___________kg/cm², (see Chart A on previous page).

ESubstrate = Modulus of elasticity of the helix substrate= 2,010,880 kg/cm² for Specialty Testing Spiral (helix).

NOTE: If using Other Spirals/ Helices the Metric Formula would be (if using other Spiral Contractomters we can not guarantee these results-due to slippage and other issues)

2.54 (d)                         EDeposit(T)
Stress  =    ───────   X   1 + ────────────── = kg/cm²
(K)(T)                  ESubstrate ((t) x 100)

Step 5: Stripping spirals (helices) for reuse

1. Plated spirals (helices) can be stripped of deposits repeatedly in a 50% by volume nitric acid solution for reuse. Do not heat the solution above 32°C

2. When the exterior surface of a spiral (helix) shows visible etching, the helix should be discarded.

Note: If stripping Silver, Gold, or Copper see our website under Procedures / Stripping Deposits from Spirals (Helices).