JPS5794434A - Tube expanding method in uoe tube making method - Google Patents

Abstract

PURPOSE: To reduce bendig of a tube after tube expanding by increasing the frictional resistance between tube expanding segments and inner face of a tube and thereby making strain due to elongation uniform in a peripheral direction of the tube.

CONSTITUTION: A rugged pattern 11 is worked on the surface of plural segments 10 constituting a tube expanding head 1 to increase the coefficient of friction at the time of tube expanding. The rugged pattern is provided only on the surface of the segments 10 that contacts with the inner face of the tube, and provided over the whole surface uniformly except a part 12 that contacts with the weld bead 21 of the welded tube 2. The rugged pattern 11 may be provided in various forms such as vertical stripes, cross stripes, dots, etc. By the above, slipping on the contact surface between the tube expanding segments 10 and the inner face of the tube is prevented, and elongation at the time of tube expanding is generated only in the part where the segments 10 do not come into contact, and strain is distributed uniformly in peripheral direction. Thus, bending after tube expanding can be reduced remarkably.

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