The effects of bead surface roughness on friction, die pickup, and sheet surface damage in the drawbead test were investigated. Beads of HRC 58 hardness were prepared from centerless-ground rod by circumferential honing to 0.05 μm roughness, followed by finishing with 100, 400, or 600 grit SiC paper in the axial direction. Paraffinic base oils with viscosities of 4.5, 30, and 285 mm2/s were used neat and in conjunction with stearic acid.
The effects of bead roughness depended on the nature of metal transfer, especially its distribution and firmness of attachment.
The presence of a boundary additive increased, decreased, or had no effect on friction depending on the particular coating and bead finish.