| 摘要 |
PURPOSE:A specifically structured ''parasol'' is inserted into a plastic tube and the die is pushed to expand the tube into polygonal prism, thereby making residual stress-free tubes that shrink only in the radial direction. CONSTITUTION:Said system mainly comprises (A) a die consisting of shaft 25, which is fixed by boss 23, straps 26, 27 with holes 26', 27' through which a plurality of flexible strings 5 as piano or stainless wires pass so that they form the edges of polygonal prism, and support 34, (B) a parasol consisting of a plurality of strings 5, the one end 37 and the other end of string-collecting plate 29 both of which support the strings so as to form a polygonal prism, (C) a means for moving the die in the direction of pipe shaft, and (D) a heating means. A tube 28, which is fitted on the parasol and heated beforehand, is taken out of the heater and immediately expanded by pushing the die until the straps 26, 27 sufficiently approach the string- collecting plate 29. The tube 28 is expanded into a polygonal prism, cooled, and taken out of the parasol by pulling back the die. |
