On optimizing the zinc coating surface by an improved temper rolling process

摘要

Skin pass rolling (temper rolling) combines the adjustment of mechanical properties like suppression of the yield point elongation with defining surface topography and roughness needed for consecutive process steps such as forming and painting. It is also being used to homogenize features to enhance the visual aspect of a high quality surface. These detrimental features usually are changes of the galvanized surface, caused by an uneven surface of the cold rolled steel substrate or local coating weight differences. Different skin pass roll textures are being used in-line during hot-dip galvanizing nowadays, which are typically described by 2-d-parameters like peak count and average roughness. Unlike all other textures the Topocrom~R roll surface consists of convex hemispheres and offers the opportunity for a wide range of different resulting topographies on the zinc coating by adapting the mean radius, size distribution and number of these hemispheres per unit area. Different steel grades allow different temper rolling forces. Dependent on these values and the size of the detrimental features, different mechanisms during skin pass rolling and various consequences for the resulting product are possible. These will be explained in this paper in detail with some examples and strategies how to optimize the skin pass roll texture depending on the various demands on surface and mechanical properties of the galvanized steel sheet.