GB766515A - Improvements in or relating to the method of and apparatus for producing metal tubes - Google Patents

Abstract

766,515. Making tubes; stamping; altering physical structure. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Feb. 28, 1955 [March 3, 1954], No. 5819/55. Classes 83 (2) and 83 (4). A method of producing a thin-walled metal tube from a tubular member of greater wall thickness, comprises rigidly supporting said tubular member at each of its ends against lateral expansion and longitudinal movement, placing said tubular member within a chamber having the same interior contour as the desired exterior contour of the thin-walled tube and expanding the intermediate portion of said tubular member into engagement with said chamber by force uniformly applied to the interior of the tubular member. A stainless steel tubular blank of thickness approximately 0.018 inch is clamped at its ends between discs 4 and outer clamping rings 7, the discs being held in position by a tie-rod 8. One of the discs 4 is provided with an opening 11 through which pressure fluid is supplied to the interior of the blank from an hydraulic pump 13. The other disc 4 has an opening 20 communicating with a release valve 26. Sealing rings 25 in the discs ensure a fluid-tight joint. The assembly is arranged inside a cylinder 1 and the blank expanded to the contour of the cylinder. Where a large percentage reduction is required the deformation is accomplished in stages, e.g. of 20 per cent increase in outside diameter, using progressively sized cylinders, annealing being carried out between successive stages. After the forming operation the wall thickness has been reduced from 0.018 inch to approximately 0.012 inch and the outside diameter increased from 2.7 inches to approximately 4.6 inches. The stresses in the formed tube, which tend to contract the tube, are relieved by an air hammer 15 operating on the outer surface of the cylinder 1. In a modification an upright sizing cylinder 102 is provided with a flange 104 for bolting to a bed-plate 108. The tie-rod assembly comprising tie-rod 114 and discs 120 and 126 is placed into a tubular blank 124 and the assembly lowered into the cylinder 102. The blank is filled with fluid and the air release valve 138 closed. The hydraulic pump 146 is then operated to produce a pressure of between 1000 to 2000 pounds per square inch to expand the blank into engagement with the cylinder. As in the previous embodiment the cylinder is subjected to shock waves by an air hammer 150 having a brass or bronze head. Thin-walled tubes of various cross-sections, e.g. triangular, rectangular or polyhedral may be made by this method.