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#319 Measurement of Stress in Electrodeposits of Nickel for Engineering Purposes and Electroformed Nickel

Category : Electroplating
November24, 2017

Forming a thick layer of plating, such as industrial nickel plating or electroformed nickel coatings, will leave stress in electrodeposits.The stress in electrodeposits comes in two forms: compression stress and tensile stress. If uncontrolled, they will lead to adhesion failures or deformation in sizes and shapes over time.

(1)Measurement method of stress in electrodeposits

The available methods are listed below.Since it is not possible to measure the actual stress in electrodeposits on the products, the stress will be calculated by using a dedicated test piece that will be plated or electroformed in the same conditions.

 1. Calculation of average stress in electrodeposits
 2. Measurement by spiral contract meter

(2)Calculation of average stress in electrodeposits

After applying plating on a rectangular test piece with insulation coating applied only one side (mild steel plate, 0.1 to 0.3mm thick, 10 to 15mm wide, and 50 to 100mm plating area), measure the force required to restore the deformation in the longitudinal direction, which was caused by electrodeposition stress, and calculate the average.
[Fig.1] is the illustration of a measuring device.
  [Fig.1]

(3)Measurement by spiral contract meter

Prepare a rectangular test piece (mild steel, 20 mm wide, and 0.2 to 0.5 mm thick) and wind it diagonally around the 20 mmΦ iron core, spaced approximately 0.5 mm apart. This will make a spiral (tabular spring) test piece (a). After insulating the internal surface, secure the top of the test piece onto the fixed axis of the top of the contract meter (b), while securing the bottom of the test piece onto the rotating shaft at the lower end. Apply plating over this test piece in the same conditions as those for the actual product.Using the gear mechanism, the dial gauge displays the angle of the twisted spiral that was caused by the electrodeposition stress.
[Fig.2] shows a structure of the device.
  [Fig.2]

(4)Reduction of stress in electrodeposits

The stress in electrodeposits can be reduced drastically by the plating conditions and using plating additives for stress reduction where appropriate. However, even these measures combined, it will not cover the entire surfaces.Heat treatment is generally adopted for reducing the stress in products. The conditions will be determined and agreed between the parties concerned.

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