Importance

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Abstract

Tube bending apparatus in which a tube is clamped between a U-shaped bend die and a cooperating pressure die, the pressure die being advanced in a linear direction as the bend die is rotated, a tube groove in each of the dies embracing diametrically opposite sides of the tube. The tube groove on the bend die is of generally U-shaped configuration having a semi-circular bend section and opposite sides extending in tangential directions to define tangential grooves along opposite sides of the bend die, the cross-sectional radii of curvature of the tube groove along the bend section and tangential sections are closely controlled to impart some temporary distortion to the tube which will resist wrinkling or collapse. Similarly, the tube groove on the pressure die has cross-sectional radii of curvature corresponding to those of the bend section of the bend die in order to cooperate with the bend die. In carrying out the method of the present invention, the tube to be bent is clamped between the pressure die and bend die so that it is forced to assume the configuration of the tube grooves on the pressure die and the bend section of the bend die as the bend die is rotated and the pressure die is advanced while maintaining a constant pressure on the tube. Preferably, the pressure die is advanced at variable pressure rates as the tube is bent around the bend section of the bend die so that the pressure die will impart a force tending to minimize the reduction of the outer wall of the tube as the inner wall of the tube is compressed.

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First Claim