| 摘要 |
<p>A perforated, weldless plastic plane tube having slits, cuts or lines of weakness is drawn so that the edges of the slits are separated so as to form orifices. The slits may be parallel, perpendicular or at an angle to the axis of the tube, as may the direction of drawing. The slits are formed during extrusion by cutting, and so that there ae no residual stresses in the tube. Opening of the slits may be by a template, pref. of larger diameter than the tube, or of increasing diameter. The slits may be formed by a tool with knives its inner surface which is given an alternating motion in the extruder head. The process gives tubes of constant wall thickness and the drawing of the tube increases its mechanical properties.</p> |
