| 摘要 |
PURPOSE:To enable the resin-blocking or the breakage of a hollow body in the beginning of extrusion forming to be remarkably reduced by using the sizing die in which the ratio of the length of the sizing die to the inner diameter thereof satisfies a specified formula. CONSTITUTION:As a sizing die 4, the sizing die in which the ratio of its length (Lmm) to its inner diameter (Dmm) satisfies following formula is used, and said formula is 0.46XDp+0.16<L/D<0.65XDp+3.23, and then Dp is the outer diameter (mm) of a polyoxymethylene hollow body and is equal to or larger then 3.5. In the case of L/D<=0.46XDp+0.16, at the beginning of extrusion, the resin-blocking or the breakage of a hollow body in the sizing die does not occur easily, but a prescribed wall thickness is not easily obtained, whereby only the hollow body with thin wall thickness is obtained, and the dimension control of the outer diameter is not sufficient, whereby the deviation of the outer diameter becomes large. On one hand, in the case of L/D>=0.65XDp+3.23, the resin-blocking or the resin breakage at the beginning of extrusion occurs easily and stable forming is not achieved. |
