| 摘要 |
PURPOSE:To produce easily a good plastic covered pipe, by covering the tube under the condition of specifying the drawdown ratio and the diameter contraction ratio thereof. CONSTITUTION:Plastic 2 is extruded in a semi-molten state from a co-extrusion round die 1 fixed to an extruder, in order to cover a pipe 3 moving relatively in an axial direction of the round dice 1. The pipe covering operation is effected to satisfy a relative relation Y=1.8X+(0.7+ or -0.25), wherein Do is a diameter of a mouthpiece 4 in the round die 1, Di is an outer diameter of a core metal 5, do is an outer diameter of a plastic cover 2', di is an outer diameter of a pipe 3, a drawdown ratio R=Do<2>-Di<2>/do<2>-di<2> is represented by axis Y, and a diameter contraction ratio is represented by axis X. If the above relation is set to be maintained, a covering condition is obtained wherein a breakage of semi-molten plastic, unevenness of the covering, generation of creeps may almost be neglected. |
