MILL ROLL TEXTURING USING EDT

Thee surface texture of sheet steel of the type used for automotive ap plications plays an important role during subsequent processing operat ions. With textured steel, ''sticker wrench'' marks are less likely to occur during batch annealing, formability is improved due to the rete ntion of lubricant and the visual integrity of any paint finish applie d to the sheet, is enhanced. Currently, shot blasting (SB), laser beam texturing (LBT) and electrical discharge texturing (EDT) are the thre e principal methods used to texture mill rolls, however, electron beam texturing (EBT) is being evaluated. Although widely used, conventiona l SB has major limitations due to the lack of adequate process control and its inability to deal with hard alloys. The paper discusses the t echniques 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 te sts 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. S urface 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 w ith some 3-D surface maps.