Abstract
A mash seam welder is widely used for a continuous annealing and galvanizing line, but it is not applied to a continuous cold rolling line. The cross section of mash seam welding is characterized by steps at the edge of the lap seam. Analyzing by FEM and experimentally, the steps are found to be transformed to surface defects by rolling. There are two forms of defects: double-deformed and open. The former appears at the stepping-up part of the edge, and the latter appears at the stepping-down part. The potential of rolling fracture in double-deformed defects increases when the angle of step forms more steeply. The conventional flattening mechanism of steps at the lap seam is a swage by narrow wheels after welding, but a conventional swaging mechanism forms double-deformed defects. By crossing the upper and lower swaging wheels, shear force at the surface smoothen the steps without forming double-deformed defects. By using a mash seam welder with a cross swaging mechanism, lapped welding sheet specimens of 6 mm thickness are flattened without causing surface defects. The welded specimens can be rolled to 3.4 mm thickness without inducing fracture.
