MANUFACTURING PROCESS FOR POLYETHYLENE THICK FILM-SHEATHED STEEL PIPE, AND POLYETHYLENE THICK FILM-SHEATHED STEEL PIPE

摘要

PROBLEM TO BE SOLVED: To provide a polyethylene thick film-sheathed steel pipe suitable for being buried underground in an area where a thunderbolt occurs frequently.

SOLUTION: A 4.7-7.2 mm thick polyethylene film is formed around the outside surface of a moving 100-180°C steel pipe by moving the steel pipe at a velocity of V0m/min using a cross head die which ejects polyethylene at V1m/min through its ring-shaped ejection hole. The ejected polyethylene has a density of 0.937-0.965 g/cm3and a melt tension of 1.5-2.5 g at 230°C. V0/V1is 2.3-3.7. D1/D0is 1.1-1.5. h is 10-13 mm. A chromate layer, an epoxy primer layer or a modified polyethylene layer may be formed on the steel pipe, before the thick film is formed.

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