Spiral reinforcement thread in wall of extruded plastic tube - is introduced at a fixed station, as the extruded material spirals past

摘要

In contrast to known methods, the invention requires the material that is to form the spiral to be introduced at a fixed station, while the still-liq. material of the tube spirals past. Pref. the plastic is extruded into an annular channel formed between a fixed wall and a rotating peg. At a certain point the peg narrows, the channel correspondingly widening, and the stream of plastic divides into two. The outer part passes round a stationary ring that stands at this point, while the rest of the plastic passes through borings that perforate the ring. The reinforcing material is introduced at this point, between the two streams of molten plastic. The two streams re-unite as the peg that forms the core of the extrusion channel resumes its full dia.