| 摘要 |
Pronounced surface roughness or undulations will sometimes be obtained on the unsized surface of plastic extruded hollow profiles. Particularly is this so for plastic resins containing fibres. In the invention smooth finishes are obtained on both external and internal surfaces of a hollow profile by passing the extruded resin first through or over a cooled sizing unit and then over or through a finishing unit in the form of a plug or a ring which will usually be heated. The heating will allow the asperities or the unsized surface to flow locally to conform to the plug or ring surface without disturbing the basic form of the pipe or tube wall. Subsequent cooling of the smoothed surface will be by heat loss to the interior of the pipe wall downstream of the finishing unit so that smoothed finishes are retained in the cooled pipe or tube. |
