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Measurement Methods and Calculations to Determine Internal Deposit Stress

Measurement Methods and Calculations to Determine Internal Deposit Stress. Frank H. Leaman Specialty Testing & Development, Inc. York, PA. Methods for Deposit Stress Determination. Bent Strip (simple beam theory) Spiral Contractometer. Simple Beam Theory.

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Measurement Methods and Calculations to Determine Internal Deposit Stress

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  1. Measurement Methodsand Calculationsto Determine Internal Deposit Stress Frank H. Leaman Specialty Testing & Development, Inc. York, PA

  2. Methods for Deposit Stress Determination • Bent Strip (simple beam theory) • Spiral Contractometer

  3. Simple Beam Theory Where: N = Thickness of the plated coating (inches) T = Thickness of the test strip (inches) D = Deflection of the strip due to bending (inches) L = Length of the test section (inches) E = Modulus of elasticity of the test strip (lb/in2) I = Moment of inertia of the cross section of test strip about its neutral axis S = Stress in plated layer (lb/in2)  Then: S = 4E (N+T) D 3NTL

  4. Bent Strip Method(Initial Approach) • During the application of a coating, one end of the test piece is held in a fixed position and the other end is free to move. • It is difficult to measure the value for D.

  5. Bent Strip Method (Different Approach) • A test piece split into two legs spreads outward due to the deposit stress • The deflection is easily read by placing the test piece over a scale • Calculate the deposit stress value by using a simple formula

  6. Simple Beam Tensile and Compressive Stress Tensile Compressive

  7. Compressive and Tensile Stress Compressive Tensile

  8. Stress Evaluation Using the Bent Strip Method Test Strip in a Plating Cell

  9. In-Site 1 Plating Cell Ideal for small solution volumes and lab studies, particularly when working with precious metals

  10. Bent Strip Test Piece Measuring Stand

  11. Stress Evaluation Using the Bent Strip Method Bent Strip Plating Test Cell

  12. Test Strip Plating Cell with Accessories

  13. Typical Deposit Stress Evaluation Plating Set-Up

  14. Deposit Stress Calculations for Test Strips The Stoney Formula:  = E T² M δ  3 L² t E = Modulus of elasticity of the substrate = 120,655 kg/cm². T = Thickness of the substrate in millimeters = 0.05077 mm. δ = 1/2 the distance between the test strip leg tips in mm. Example: 0.540 inch spread ÷ 2 x 25.385 mm/inch = 6.85 mm.  = Stress in megapascals, MPa. Note: MPa x 145 = PSI. L = Length of substrate on which the deposit is applied in mm. For Deposit Stress Analyzer test strips, this value is 76.2 mm. t = Deposit average thickness in millimeters. M = Correction for modulus of elasticity difference between the deposit and substrate: M = EDeposit ÷ ESubstrate = 206,900 ÷ 120,690 = 1.714 = E (.05077 mm) ² M ( δ mm) = mm³= MPa 3(76.2 mm)²(.002538 mm) 44.21 mm³ Deposit Stress in PSI = MPa x 145 = PSI Note: MPa is Megapascals, kg/cm.²

  15. Spiral Contractometer Existing Design • The test piece is a spiral. • One end of the spiral is held, other end is free to move. • As the free end moves, a dial registers the movement in degrees. • The stress of the coating can be calculated.

  16. Spiral on an Existing Contractometer

  17. Spiral Plated on Existing Type Contractometer for Target Nickel Deposit Thickness of 500µ” in a Semi-bright Bath after 20 Seconds Wood’s Nickel Strike Deposit LocationThickness, µ” Outside Surface 410 Inside Surface 85 Deposit stress over a 2 minute strike = 26.4% less than the New Design Contractometer result

  18. New Spiral Properties • New design spirals are constructed from 0.010 inch thick stainless steel and have a precise surface area of 13.57 in2. • Spirals mount on the contractometer in a way that the entire spiral plates from end to end and deposition of metal on the inside of spirals is minimal even if they are void of a masking material. • The average test deposit thickness is 500 microinches.

  19. Properties and Plating Conditions for Spiral Contractometer Tests • Spiral Material Stainless Steel • Spiral Surface Area, in2 13.57 • Square Feet 0.0942 • Amps per square foot 30 • Amps 2.90 • Stock Thickness, inches 0.010 • Avg. Deposit Thickness, µ” 500 • Plating Time, Minutes 21 • Solution Temperature 140° ± 1° F

  20. A 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 as much as 30%. Interior masking is critical.

  21. The new design provides masking of the interior surface by geometry and enables spirals to be plated tip to tip so the plated surface area is a constant value. Other advantages: • Stainless steel inserts • 30% glass filled nylon construction which prevents thread damage and spiral slipping • More accurate results • Saves time

  22. Spiral Contractometer Equipment to Determine Internal Nickel Deposit Stress • Spiral Contractometer with calibration weights, support stand and spiral test pieces. Container 4” diameter and 10” height for nickel strike anode basket and bath (1750 ml) • Titanium Mesh Anode Basket 3.5” outside and 2.25” inside diameter, 8” high with support contact tabs and cover for Wood’s nickel strike • Titanium Mesh Anode Basket 5” outside and 4” inside diameter with support contact tabs and cover for the plating bath • Nickel anode buttons to fill the anode baskets • Pyrex beaker 4000 ml for a nickel plating bath • Support stand – designed to perfectly center over beaker • Magnetic stirrer hot plate, 115 volt • Digital temperature Controller pre-wired with probe to control ± 10 F • Power Supply constant current, constant voltage, 0-5 amps, 0-30 volts • Magnetic stirrer hot plate, 115 volt

  23. Contractometer Stand, Anode Basket & Beaker

  24. Contractometer Plating Set-Up

  25. Data Recording 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 subraction: ________ ________ Deposit thickness in microinches: ________ ________

  26. Average Deposit Thickness Calculation in Inches T = _________W____________ = Inches D (87.55 cm2) (2.54 cm/inch) W = Grams of nickel D = Density of nickel = 8.90 g/cm3, and T = Deposit thickness in inches For the new spirals plated on the new design contractometers, the constant spiral plated surface area is 13.57 in2 and the following shortened formula applies: T = W = Inches 1979.2

  27. Calculating Deposit Stress Stress = 13.02 (D) (M) ÷ w x d = PSI D = Degrees caused by the deposit, M = Modulus of Elasticity of the deposit ÷ that of the substrate = 206,897 ÷ 198,186 = 1.044 for nickel deposits over new spirals that are 0.010 inch thick, w = degrees Kt from spiral calibration if the stress is tensile or degrees Kc if the stress is compressive, and d = Deposit thickness in inches. Calculation Example: S = 13.02 (26) (1.04897) ÷ 33 (0.000536) = 20,073 PSI

  28. Modulus of Elasticity Values Stock Material Cu-Fe AlloyNi –Fe Alloy Ni-Fe AlloyPure Ni ES* 120,690 144,830 179,310 206,900 Stock Thickness, in 0.0020 0.0015 0.0010 0.0010 Metal ED** Values for M*** • Cadmium31,720 0.263 0.219 0.177 0.153 • Chromium 248,280 2.06 1.71 1.39 1.20 • Cobalt 206,897 1.72 1.43 1.15 1.00 • Copper 117,240 0.971 0.810 0.654 0.567 • Gold 74,480 0.617 0.514 0.415 0.360 • Nickel 206,900 1.71 1.42 1.14 1.00 • Platinum 146,900 1.22 1.02 0.819 0.710 • Rhodium 289,650 2.40 2.00 1.62 1.400 • Silver 75,860 0.629 0.524 0.423 0.367 • Zinc 82,760 0.686 0.571 0.462 0.400 • ES*, modulus of elasticity of substrate material in the Stoney Formula. • ED**, Modulus of elasticity of deposit for use in modified Deposit Stress Analyzer and • Stoney formulas. • M***, modulus of elasticity of deposit ÷ modulus of elasticity of substrate for deposit • stress determinations using the modified Deposit Stress Analyzer and Stoney Formulas.

  29. A Frequent Mistake in Test Procedure Spiral Test Strips 1 2 3 Deposit Thickness To Stock Ratio 1:20 1:20 1:5 Stock Thickness, Inches 0.010 0.002 0.002 Deposit Thickness, µ Inches 500 500 100 Minutes Plated 20 4 20 Current Density, ASF 30 30 30 Deposit Stress, PSI 14,060 14,127 6,865 Note: Extra thick deposits of the harder metals increases the degree of stiffness which results in lower proportional test strip spread.

  30. Formulas for Bent Strip with One End Stationary* Bent Strip Stress Curve For the comparison of equations that follow that apply to calculating the internal deposit stress of applied metallic coatings over various substrate materials, the value of U = 8.5 units = 0.780 inch will consistently be used as a basis. It will be noted that the calculated internal deposit stress values vary from equation to equation, particularly where the equation fails to address Modulus of Elasticity differences between the substrate and the deposit. Relationship between δ and Z. Example: For a given test strip, U = 8.5 units = 0.780 inch, and δ = U in inches x 25.385 mm/inch ÷ 2, so in this case δ = 9.90 mm. δ = 4Z Z = δ ÷ 4 L = 76.155 mm Using δ = 9.900 mm, Z = 9.90 mm ÷ 4 = 2.475 mm R = L² + 4Z² = 5824.1 = 303.34 mm 8Z 19.2 *Note: These formulas only work for bent strip applications and are not applicable for the spiral contractometer method.

  31. Stoney Formula Without and With Correction for Modulus of Elasticity Differences Between the Deposit and the Substrate Example: For a Cu-Fe test strip, U = 8.5 units = 0.780 inch δ = U in inches x 25.385 mm/ inch ÷ 2 = 9.900 mm WITHOUT σ = 4ET²Z = ET² δ= 91.137 MPa = 13,214.9 PSI 3L²t 3L²t L = test strip plating length = 76.2mm, T = Stock thickness = 0.05077mm and t = Deposit thickness = 0.000075 inch = 0.001904mm WITH M = Edeposit ÷ Esubstrate = 206900 ÷ 120690 = 1.714 σ = ET² δM = 120690(0.05077)²(9.900mm)(1.715) = 156.30 MPa 3 L² 3(76.2mm)²(0.00194mm) σ = MPa (145 PSI/MPa) σ = 22,663.5 PSI

  32. Other Bent Strip Formulas to Determine Internal Deposit Stress in Applied Metallic Coatings Barklieand Davies Formula σ = ET² 6Rt (1 – t/T) Heussner, Balden and Morse Formula σ = 4ET²Z 3t (T + t) L Brenner and Senderoff Formulas σ = ET(T+ ᵦt) ᵦ = Edeposit ÷ Esubstrate 6Rt σ = E (t + T)³ 3Rt (2T + t)

  33. Brenner and Senderoff Formula for Bent Strip Applications Brenner and SenderoffFormula σ = ET(T+ ᵦt) ᵦ= Edeposit ÷ Esubstrate= 1.714 6Rt σ = 120690 MPa (.05077mm)(.05077mm +1.714(.001904mm) = 95.538 MPa 6(303.34mm)(.001904mm) 95.538 MPa x 145PSI/MPa = 13,853 PSI Note: This formula doesn’t correct for large differences in Modulus of Elasticity values. The uncorrected Stoney result was 13,215 PSI. To be correct, this Brenner and Senderoff formula requires modification as follows: σ = ET²ᵦ = 22,310 PSIwhereᵦ= 1.714 6Rt

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