Double-walled plastic tube with a low-grade foam interlayer

摘要

A recycled softened thermoplastic, which may be polyethylene or polypropylene, is extruded from an annular nozzle. The inner dia. is sized by a cooled inner mandrel. The tube passes through a former, extending over the length of the mandrel, and consisting of a pair of converging, floating die halves, lying closely together. The tube is coated by a pressed profile of encircling ridges. A transverse injection head completes the tube, covering the ridges with an outer casing of recycled plastic. Finally, the outer surface of the composite tube is sized and smoothed. A tube made in the manner described, is also claimed.