GB676234A - Improvements in or relating to method of bending tubular thermoplastic bodies - Google Patents

Abstract

676,234. Angular bending. STEVENS, A. H. (Kellogg Co., M. W.). Aug. 30, 1949, No. 22510/49. Class 83 (iv). [Also in Groups V and XI] A method of bending metal bodies comprises heating successive unit bands of width not greater than one half the natural buckling wavelength of the body, the heating being so rapid that the material of the body adjacent the heated band resists deformation during the bending of the heated band. Apparatus for bending a pipe 10 comprises a support 11, an annular heater 12, cooling rings 13 situated on each side of the heater 12 and bending means 14. The heater 12 and rings 13 are preferably fixed in position and the pipe 10 is moved in steps. The heater may be an oxygen-acetylene or other hydrocarbon burner (see Group XI) or a highfrequency induction or resistance heater capable of producing a zero slope heat gradient throughout the unit band and a steep slope heat gradient in the material adjacent the band. The rings 13 are internally liquid cooled but may be of solid metal and cooled by water sprays. Buckling is avoided by selecting a width of unit band calculated from the ratio of unit band width to pipe thickness for the particular percentage deformation necessary to effect the desired bend. The width will generally be less than one half the buckling wavelength of the pipe and greater than the thickness. Localized upsetting is prevented by choosing an increment of movement of the pipe so that the unit bands overlap. The pipe 10 is positioned in support 11 relative to the heater 12 so that the first band is at one end of the desired bend. This band is brought to the prebending temperature by repeated heating and cooling. Then it is heated for a predetermined time interval after which the heater is shut off and the bending force applied. The pipe 10 is then moved through the chosen increment and the next band heated and bent. By shortening the time interval between the bending of one unit band and heating the next, the operation can be converted into a continuous one. The bending force may be applied by maintaining a minimum load at all time and increasing the load to a maximum during bending or maintaining the maximum load on the pipe during the whole of the heating and bending operation. The annular heater 12 may be replaced by a conventional burner oscillating along the width of the unit band.