Plastic pipe and method and appratus for manufacturing same

Abstract From the Canadian patent

A method of manufacturing a plastic pipe having a spiral ridge on an outer surface and a flat inner surface comprising the steps of: (a) supplying a plastic ribbon in a softened state onto a plurality of rotating forming rolls arranged circularly, so that the plastic ribbon is spirally wound around the forming rolls while partially overlapping to be fused with each other (b) spirally winding an endless forming core belt around the forming rolls in such a manner that the endless forming core belt is sandwiched between the plastic ribbon already wound around the forming rolls and the plastic ribbon newly supplied, thereby providing the resulting plastic pipe with a spiral ridge; (c) cutting …