| 摘要 |
<P>PROBLEM TO BE SOLVED: To reduce the risk of breakage of a mandrel ring in a mandrel in which the mandrel ring is attachable to and detachable from a stem and to secure the high positional accuracy of the mandrel ring even when the difference between the coefficients of thermal expansion of the stem and the mandrel ring is large. <P>SOLUTION: The mandrel 30 has the stem 32 and the mandrel ring 35, the mandrel ring 35 is composed of a material with a coefficient of thermal expansion smaller than that of the stem 32. The outer circumferential surface of the stem 32 and the inner circumferential surface of the mandrel ring 35 are set in such a manner that in a state in which the mandrel ring 35 is fitted externally to the stem 32: a clearance S<SB POS="POST">1</SB>is present between both surfaces at ordinary temperature; and at the die temperature at extrusion, the clearance S<SB POS="POST">1</SB>eliminates in at least a part in the axial direction of the mandrel 30 and both surfaces are brought into contact with each other as a result, wherein the stem 32 is provided with at least one slit 40, 41 which are cut from the downstream side-end face of the stem 32 toward the upstream side and which divides the stem 32 at a plane vertical to the axial line. <P>COPYRIGHT: (C)2012,JPO&INPIT |
