FORMING METHOD OF SYNTHETIC RESIN COVERING LAYER ON OUTER CIRCUMFERENCE OF STEEL PIPE

摘要

PURPOSE:To positively form a cylindrical denatured polyolefine resin covering layer which is excellent in adhesive strength and free from breakage on the outer circumference of a thermosetting type epoxy resin covering layer formed on the outer circumference of a steel pipe by generating a specific negative pressure at the interface between two films. CONSTITUTION:A steel pipe 2 on which a thermosetting type epoxy resin covering layer 2a is formed around its outer circumference is supplied to a circular die 1 of which inlet side and the steel pipe 2 are sealed with a circular packing 3 and molten cylindrical denatured polyolefine resin covering layer 2b is extruded from the circular die 1 and at the same time air inside the circular die 1 is sucked by a vacuum pump 5 through a blower pipe 4 and the covering layer 2b is caused to adhere to the outer circumference of the covering layer 2a by reducing the pressure of the interface between the covering layers 2a, 2b to a negative pressure of 100-200mm.Hg.