Patent ID: 6309588
Filing Date: 2001-10-30
Classification: B29C

Abstract:
Process for bending a thermoplastic tube to impart a permanent bend curvature to a portion of the tube comprising the steps of:(1) providing a rotatable bending die having a bending working surface of revolution contoured in a bending plane with a curvature complemental to the desired final inside radius curvature of the tube in the plane of the desired tube bend,(2) providing a forming length of a thermoplastic tube positioned relative to said die such that the tube portion to be bent is juxtaposed to said die working surface,(3) forcing one side of said tube portion to be bent into continuous incremental wrap contacting conformity with said die working surface by exerting bending stress incrementally on said forming length of tube with said die resisting such stress by acting as a bending fulcrum while rotating during such tube bending, and(4) heating a backside portion of said tube portion diametrically opposite said tube portion one side along a sufficient axial length and to a sufficient processing temperature such as to sufficiently weaken the tensile strength thereof to thereby enable stretching of the outside radius curvature of the tube in step (3) while lowering the tensile reaction stress exerted by bending said backside portion such that any corresponding resultant compressive stress developed in said tube portion one side is insufficient to cause unwanted deformation of the tube wall along the inside radius curvature portion of the resultant tube bend as so formed.