摘要：

A plurality of metal sheets disposed on a roller conveyor in end-to-end relation are tack welded to form a continuous sheet. The continuous sheet is passed through a series of forming rolls by which it is progressively formed into a tube with abutting side edges lying in a straight line along the underside of the tube. These side edges are seam welded on the inside of the tube, after which the individual sheets (now in tube form) are separated from one another and removed from the conveyor. Each tube is again seam welded, this time along the outside of the tube.

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