Surface Roughness

thyssenkrupp Laboratory Services is equipped with a Taylor-Hobson S-100 Profilometer, which detects the surface roughness and waviness of materials. The two values most widely used to quantify surface texture are: Ra, which is the arithmetic mean of the distance of the profile from the mean line and the peak count (PPI), which is the number of peaks per inch that project through a selectable ‘band width’ (usually 50 µin).

Sheet steel or other metal surfaces carry the imprints of the last rolling passes of the production mill. Sheets subjected to temper rolling exhibit the surface finish of the temper rolls superimposed on the prior finish, to an extent determined by the temper reduction. The roughness of a sheet is not constant due to the wear of rolls; peaks are worn off and both Ra and Peak Count diminish.

Surface texture can influence appearance of exterior auto body panels whether painted or unfinished. Surface texture / topography determine the distribution contact points between die and sheet, and the quantity and distribution of entrapped lubricants. Thus, topography affects press performance and the onset and consequences of lubricant breakdown.