JPS57115989A - Production of double-ply pipe - Google Patents

Abstract

PURPOSE: To produce robust self-tightening double-ply pipe with a simple heater at a low cost by exerting liquid pressure on an inner pipe inserted into an outer pipe, heating the outer side of the outer pipe circumferentially in a ring shape, and moving the heater in an axial direction.

CONSTITUTION: Water 5 of liquid for pipe expanding is fed into an inner pipe 3 made of stainless steel inserted to the inner side of an outer pipe 2 made of carbon steel. Water pressure is exerted to the water 5 to apply pipe expanding pressure (f) to the entire inside surface of the pipe 3. The applied liquid pressure gives plastic deformation to the pipe 3. A high frequency heater 11 enclosing the pipe 2 annularly is moved, by means of a roller carriage 9 having a driving motor 8 and inner idle rollers 10, on the plural rails 7, 7 along the axial direction on the outer side of a double-ply pipe 1 from one end A of the pipe 1 to the other end B to heat the pipe 2 successively locally in a ring shape to a set temp. Hence, pipe expanding stresses are concentrated by the liquid pressure applied in the pipe 3, and as the pipe 2 expands, the pipe 3 is increased of diameter. After shifting of a heating part 12, both pipes contract in diameter. Thereby, the self-tightening double pipes 1 having powerful degrees of fitting are obtained.

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