Measurement of hard chrome plating with a UCI tester

Measurement of hard chrome plating with a thickness of 0.003–0.005 inches

The hardness of the chrome coating itself must be considered for the calculation. Assuming a hardness of 65 HRC, which approximately corresponds to 832 HV, the penetration depth is calculated using the ASTM A1038 formula:

h [mm] = 0.062 × √(F [N] / HV)

The standard also states that the minimum coating thickness should be at least ten times the indenter penetration depth:

Smin = 10 × h

Calculations for the main test loads:

Load

Penetration depth h

Minimum coating thickness 10 × h

1 kgf / 10 N

0.00680 mm / 0.000268 inches

0.0680 mm / 0.00268 inches

5 kgf / 50 N

0.01520 mm / 0.000598 inches

0.152 mm / 0.00598 inches

10 kgf / 98 N

0.02128 mm / 0.000838 inches

0.213 mm / 0.00838 inches

A coating thickness of 0.003–0.005 inches corresponds to 0.0762–0.127 mm.

Therefore, at a test load of 10 N, the coating thickness of 0.0762–0.127 mm exceeds the calculated minimum requirement of 0.0680 mm. According to the ASTM A1038 criterion, a coating of this thickness should be sufficiently thick to limit the influence of the substrate.

At a load of 50 N, the required minimum coating thickness is 0.152 mm, and at 98 N, it is 0.213 mm. Therefore, these loads are too high for a coating 0.003–0.005 inches thick, and the influence of the substrate may be significant.

Consequently, of the listed options, the 1 kgf / 10 N load, i.e. the LAB UCI PRO 10N, is suitable for this coating. However, at the lower end of the thickness range, approximately 0.003 inches, the safety margin is small, so the results should ideally be confirmed through practical measurements on the actual part.