GB1387343A - Method of forming a tubular workpiece with a bend - Google Patents

Abstract

1387343 Bending tubes DEUTSCHE BABCOCK & WILCOX AG 24 Aug 1972 [28 April 1972] 39492/72 Heading B3E [Also in Division H5] During the bending of a tubular workpiece, a portion of the circumference thereof at the inside of the bend is heated to a first temperature whilst the remainder of the circumference is maintained at a temperature 100‹ to 500‹ C. lower than the first temperature. In Fig. 1, a series of inductors surrounding the workpiece 1 are fitted with laminated yokes which locally intensify the heating of the workpiece, and extend over a quater of the circumference at 2 furthest from the bend region, over a third of the circumference at 3, and over half the circumference at 4 in the region of the bend. The supply frequency on lines 5 is 1000 Hz, and 600 Hz on lines 6. In one example, the portion of the workpiece which is to become the inner part of the bend has a peak temperature of 1100‹ C., while the mean temperature of the outermost quarter of the circumference is 650‹ C. In another arrangement, Fig. 2, an inductor encircling the workpiece has axially extending portions 8 near the plane of bending, that portion nearest the plane being of greater axial extent than the others, and having laminated yokes 7 attached. In a further arrangement, the inductor extends helically around the workpiece. The heaters may include burners, or both burners and inductors and may be located inside the workpiece. Preferred limits to the ratio of wall thickness before and after bending are given, in respect of the outer portion of the bend and the inner portion.