Development of on-line measurement system of surface roughness for cold-rolled steel sheet

The optical measurement of surface roughness for cold-rolled steel sheet has been studied experimentally. Two parameters of the surface roughness, such as root-mean-square (rms) roughness and auto-correlation length are measured by optical method and converted into average surface roughness (Ra) and the number of peaks per inch (PPI), respectively. The rms roughness shows the linear relationship with Ra UP to certain limit that depends on the wavelength of a laser. We have developed an automatic surface roughness measurement system and installed at cold-rolled mill, and tested in-situ. The system is verified to be able to measure Ra in the range of 0.1-2.0 /spl mu/m and PPI of 100-600 per inch.