Mill roll texturing using EDT

Abstract

The surface texture of sheet steel of the type used for automotive applications plays an important role during subsequent processing operations. With textured steel, “sticker wrench” marks are less likely to occur during batch annealing, formability is improved due to the retention of lubricant and the visual integrity of any paint finish applied to the sheet, is enhanced. Currently, shot blasting (SB), laser beam texturing (LBT) and electrical discharge texturing (EDT) are the three principal methods used to texture mill rolls, however, electron beam texturing (EBT) is being evaluated. Although widely used, conventional SB has major limitations due to the lack of adequate process control and its inability to deal with hard alloys. The paper discusses the techniques now available for roll texturing, the developments that have occurred over the last decade and the main advantages provided by EDT over traditional SB methods. The results of an extensive series of tests aimed at evaluating operating variables when texturing steel work rolls using EDT are presented. Test parameters included peak current, on/off-time, capacitance, electrode material and electrode polarity. Surface texture parameters relevant to sheet-metal characterisation are outlined and typical topographies presented. In addition a number of SEM photographs are shown of the various textured surfaces, together with some 3-D surface maps.