PURPOSE: To enable residual stress to be extremely lowered or eliminated, by providing a rod form body with a hole in a central or substantially central part thereof, and specifying the crystallinity distribution of a plastic constituting the rod form body.
CONSTITUTION: A rod form body 1 is provided with a continuous hole 2 in a central or substantially central part thereof. The distribution of crystallinity of a plastic material constituting the rod form body 1 is as indicated by a curve 4, wherein a point (e) indicating the highest point of the curve 4 is present between an outermost end part (a) of the hole 2 and an outermost end part (c) of the rod form body 1. The crystallinity (b) at the left end of the curve 4, namely, the outermost end part (a) of the hole 2 is higher than the crystallinity (d) at the outermost end part (c) of the rod form body 1. With the two requirements fulfilled, residual stress in the rod form body 1 is extremely lowered.
OTSUJI MASAAKI
ARIMA TORU
