Effect of Sampling Length and Testing Speed on Measurement of Roughness Average Ra on Cold Rolled Steel Sheet

For solving the problem of differences between 2.5 mm sampling length adopted by European standard (SEP 1940－2002) and 0.8 mm sampling length adopted by national standard (GB/T 2523－2008) in measurement of roughness average Ra on cold rolled steel sheet, special contrast test was carried out, and the absolute error and relative error of the testing data were analyzed. The results indicate that facing with the actual condition in China, the Ra on cold rolled steel sheet at 0.5-2.0 μm, adopting 0.8 mm sampling length corresponded to testing parameter setting requirement of European and Japanese surface roughness average testing instruments, and the sampling length of 2.5 mm and 0.8 mm had less impact on the testing results. What’s more, contrast test was also carried out between 0.2 mm·s-1 testing speed adopted by material laboratory of Japanese automobile factory and 0.5 mm·s-1 testing speed adopted by GB/T 2523－2008, and the testing data indicate that the actual Ra testing results with two different testing speeds were the same.