The measurement and prediction of coin wear in circulation

CIM Bulletin, Vol. 81, No. 911, 1988

M.J.H. RUSCOE, Sherritt Research Centre, Sherritt Gordon Mines Limited, Fort Saskatchewan, Alberta

The circulation wear rates of pure nickel, cupronickel and nickel-plated-steel coins were measured and found to be in the ratio 1:3:1. The relative wear rates of nickel and cupronickel coins were similar to those reported in earlier studies, and the circulation wear data for nickel were used as a reference in laboratory wear tests. A correlation between circulation wear rates and laboratory wear rates formed the basis for a prediction of service life using relief legibility as an 'end of life' criterion. This criterion was determined to be an average surface thickness loss of 12 pm. The surfaces of nickel and Nickel-Bonded-Steel (N-B-S™) coins were observed to harden both in circulation and in the laboratory tests at a rate of approximately 1 VHN/year of actual or simulated service life. It was also observed that the laboratory wear rate of N-B-S coins increased as nickel cladding thickness increased and this effect was attributed to differences in surface hardness. Wear test results are also reported for the new Canadian dollar coin material which shows a better wear resistance than pure nickel.

Keywords: Wear testing, Coinage, Nickel-bonded steel, Aureate Nickel, Cupronickel, Hardness, Friction.