Process and apparatus for bending thin-wall plastic tubing
AssigneeDana Corporation
InventorsPatrick Powell, Russell Manning
Life of this patent
Estimating the term…
Abstract
Process and apparatus for bending thin-wall thermoplastic tubing utilizing pressure inside the tube portion being bent to thereby maintain the shape of the tube during bending, and applying heat only in the zone of the tube that is stretched by pulling it axially during continuous incremental bending around a rotatable bend die to thereby maintain the original cross-sectional shape of the tubing. The tube inside radius surface is continuously supported during application of bending-induced tensile stress by causing the tube to track or wrap partially around a rotatable bend die in a generally linear (minimum slip) tracking mode.
Claims42
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.
Apparatus for bending a thermoplastic tube to impart a permanent bend curvature to a portion of the tube including in combination:
- (1) a bending die having a rotatable 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) tube positioning means for positioning a forming length of the tube relative to said die means such that the tube portion to be bent is juxtaposed to said die working surface,
- (3) means for forcing one side of the 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) means for heating a backside portion of said tube portion diametrically opposite the 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 while such bending stress is being exerted while lowering the tensile reaction stress exerted by bending the 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.
Dependencies are inferred from the claim text.