PURPOSE: To easily observe a hole expanded state and to easily find and repair flaws, etc., in advance of pipe manufacturing by force-feeding a hole expanding plug into an opening part of the end of a guide hole to provide a tapered guide hole before a hole expanding process of a hollow billet.
CONSTITUTION: In a hollow billet 1, one end of a guide hole 1a is expanded in advance and the diameter is expanded with the approach to the termination to form an expanded part 1b. The hollow billet 1 is heated and one opened end of a guide hole 1a which has not yet formed an expanded part 1b is expanded by a hole expanding machine 3. When the heated billet 1 is laid horizontally on a receiving base 3a of the hole expanding machine 3, the hole expanding plug 3d projects into the billet 1, the conical shape part of the hole expanding plug 3d is force-fed to form a hole expanded part 1c for expanding an inner diameter. Then, the billet is charged with a chamfered end part upward in a cylindrical container 9 with a shear ring 8 on the lower end part and a lubricated ball 6a is dropped into the expanded part 1b to close the guide hole 1a and then lubricating powder 6b is dropped to penetrate the hole expanding plug 10 down to the lower end.
MORIYOSHI SHINJI
YAMADERA YOSHIMI
