Method and apparatus of extruding a plastic pipe under control o

Details Method and apparatus of extruding a plastic pipe under control o Method and apparatus of extruding a plastic pipe under control o

1986-07-14

1988-06-07

Thurlow, Jeffery

Plastic and nonmetallic article shaping or treating: processes

With measuring, testing, or inspecting

Controlling heat transfer with molding material

264 407, 425141, 425144, B29C 4792, B29C 4786

Patent

active

047495316

ABSTRACT:
A pipe of thermoplastic polymer, e.g. polyvinylchloride is extruded by an extruder comprising an extrusion die (2) having a moulding end part (2a) with heating elements (11) located about said end part. The wall thickness of the pipe is controlled in order to obtain a pipe of a substantially even wall thickness. For said control the wall thickness of the extruded pipe is measured at 360 points equally distributed over the circumference and moreover the average is determined in eight measuring sectors comprising 45 measuring points per sector. The average of the measuring values of one measuring sector is compared with the circumferential average of the 360 points, the deviation of the desired wall thickness in said one sector being counter balanced by the action of the heating elements. In a preferred embodiment a polyvinylchloride pipe obtained by means of a two screw extruder presents an even wall thickness over the circumference.

REFERENCES:
patent: 3212127 (1965-10-01), Flook, Jr. et al.
patent: 3974248 (1976-08-01), Atkinson
patent: 4000402 (1976-12-01), Higham
patent: 4152380 (1979-05-01), Graves et al.
patent: 4426239 (1984-01-01), Upmeier
patent: 4464318 (1984-08-01), Upmeier et al.
patent: 4512943 (1985-04-01), Hahn et al.
patent: 4548570 (1985-10-01), Hahn et al.
Rotherham and Haynes, "Control of Adiabatic Heat in the Extrusion of Rigid PVC Pipe", British Plastics, 7-1969, pp. 125-127.

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