Device and method for bending pipe material

Abstract

In the case of bending an outer pipe, a pressure die provided just in front of a bending section is provided with a groove, wherein the shape of the groove on the side far from the bending section is semi-circular and of which the diameter corresponds to that of the outer pipe before bending, while the shape of the groove on the side near the bending section is tapered semi-elliptically. With this, the cross-sectional shape of the outer pipe is caused to change into a substantially elliptical shape in which the outside of the section to be bent is tapered. The cross-sectional shape becomes substantially circular when bending is completed.

1 . A bending apparatus having a pressure die cramping a lateral surface to be bent of a pipe material provided just in front of a bending section of the pipe material, wherein the front surface of the pressure die is longitudinally provided with a substantially semi-circular groove that can fit a substantially half body of the outer circumferential surface of the pipe material, wherein a groove shape on a side far from the bending section is semi-circular and of which the diameter corresponds to that of the pipe material before bending, while a groove shape on a side near the bending section is semi-elliptically tapered.  
   
   
       2 - 3 . (canceled)  
   
   
       4 . The bending apparatus according to  claim 1 , wherein the semi-circular groove whose diameter corresponds to that of the pipe material before bending and the semi-elliptically tapered groove are provided on the pressure die continuously.