A process for producing improved weather-resistant pearlescent pigment

摘要

pThe invention provides an improvement in the method of forming a skelp into a rounded tubular form in the preparation of an electric resistance welded steel pipe. Different from conventional methods, the skelp in bent in the initial and intermediate forming stages within a limited region alone along the centerline thereof to have a U-shaped forming flower. Thereafter, the edge portions of the bent skelp are bent in the upstream fin pass rolls to have a curvature of at least 80% of the final curvature with simultaneous overbending in the boundary regions on both sides of the side portions of the rounded skelp. Finally, the rounded skelp is pressed down in the direction to decrease the vertical diameter to bulge out in the transverse direction with simultaneous unbending the overbent portions into the final curvature./p [EP0133245A2]