Abstract:
A HALLOW, ELONGATED, THIN-WALLED BODY IS FORMED BY WELDING AT LEAST ONE SEAM TO CLOSE THE BODY AROUND A MANDREL OF A MATERIAL HAVING A GREATER COEFFICIENT OF THERMAL EXPANSION THAN THE MATERIAL OF THE BODY, WHEREAFTER THE BODY AND MANDREL ARE HEATED UNTIL THE THERMAL STRESSES IN THE BODY ARE GREATER THAN THE YIELD STRENGTH OF THE MATERIAL OF THE BODY. THE MANDREL HAS PROJECTING RIDGES RUNNING LONGITUDINALLY AT ITS CORNERS, AND LONGITUDINAL GROOVE IN WHICH IS MOUNTED A SUPPORT MEMBER WHICH UNDERLIES THE SEAM. THE BODY IS THEN PASSES BETWEEN ROLLERS TO FINISH THE SEAM.