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US 4,305,899 AGranted
Method of manufacturing a plastic tube with longitudinal channels in the wall
AssigneeWavin B.V.
InventorJan P. van Dongeren
Life of this patent
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Abstract
This invention relates to a method of making a tube of thermoplastic material, comprising longitudinal channels of circular cross-section and having such wall stresses that, after axially cutting the tube, the edge parts along the cut edge overlap each other for less than 8% of the outer circumference of the tube.
Claims8
A method of manufacturing a tube of thermo-plastic material having an inner wall and an outer wall being interconnected by partitions thereby forming longitudinal channels which are interspaced along the circumference of the tube, comprising the steps of:
- extruding a plastic material,
- sizing the tube and cooling said tube to a temperature distribution whereby the tube is form stable, and thereafter
- reheating the outer wall of the tube to a temperature over 50.degree. C. by applying heat from the outside such that the tube is not form-destabilized,
- such that a tube is obtained wherein the internal stresses are such that, after axial cutting of the tube, the overlap of the edge parts along the cut edge of the tube amounts to less than 8% of the total circumference of the tube.
1 more element
Dependencies are inferred from the claim text.