METHOD AND APPARATUS FOR MAKING PLASTIC PIPE WITHOUT MECHANICAL PRESSURE ON INNER PIPE WALL

摘要

A method of making double wall plastic pipe (8) having inner (8) and outer (5) pipe walls adhered to one another without mechanically holding the inner pipe wall against the outer pipe wall comprises extruding separate streams of molten plastic into a mold tunnel (3) to form the inner and outer pipe walls and producing a positive gas pressure which acts internally of and forces the inner pipe wall (8) outwardly against the outer pipe wall (5) while the pipe is being formed in the mold tunnel (3).