| 摘要 |
PROBLEM TO BE SOLVED: To fix a mandrel ring stably, to perform maintenance simply and to maintain the strength of a die over a long term, with respect to an extruding die in which the mandrel ring is fit to the shaft externally. SOLUTION: The mandrel (30) for forming the inner surface of an extruded material has the shaft (32) and the mandrel ring (35) which is fit to the shaft externally. In the mandrel ring (35), a hard alkali-resistant coating film (39b) is formed at least on the outer peripheral surface of a base material (39a) which is composed of a material which is smaller in the coefficient of thermal expansion than that of the shaft (32). In the outer peripheral surface (32a) of the shaft (32) and the inner peripheral surface (35a) of the mandrel ring (35) are set so that there is a clearance between the both at room temperature in the state where the mandrel ring (35) is fit to the shaft (32) externally and, at the die temperature during extrusion, the clearance is disappeared and the both are brought into contact with each other at least in a part in the axial direction of the mandrel (30). COPYRIGHT: (C)2011,JPO&INPIT |
