GB702390A - Improvements in or relating to turbo-machines or the like and to the manufacture of parts thereof - Google Patents

Abstract

702,390. Making turbines and compressors; welding by pressure. ROLLS-ROYCE,'Ltd. July 19, 1951 [Aug. 1, 1950], No. 19182/50. Classes 83 (2) and 83 (4). [Also in Group XXVI] In manufacturing turbo machines &c. one part to be pressure butt resistance welded is formed with tapered grooving to produce a series of spaced lands, several of which are contacted by the other part during welding to provide an initial reduced contact area which increases as the other part penetrates the lands against increasing resistance. The sides of the grooving are preferably inclined at about 55 degrees to one another. In an embodiment, a turbine rotor disc 10, Fig. 3; is provided with circumferential V grooves 13 by turning, milling, knurling, punching &c. to leave spaced lands having surfaces 12l-i. These surfaces vary in width with the thickness of the section of the blade which is preferably solid but may be hollow and which is to be welded thereto. The land surfaces may all have the same width. The grooves 13 may be separate and circumferentially continuous or a continuous thread like groove may be provided. The lands may extend only over the rotor disc surface only where each blade is to be attached. Where the grooves are continuous a tubular shroud 14, Fig. 6 having slots 16 for the blades is tack welded at 15 to the lands 12, before the blades are welded, to provide a smooth rotor surface. In a modification a tubular shroud 17, Fig. 7, having slots for the blades is welded to an annular disc 18 which is welded to the disc 10 before the blades 11 are welded. Another disc 19 is then welded in position and tack welds as at 20 may secure the shroud 17 to the blades. Air holes 21 are provided to allow cooling of the roots of the blades. To insulate the blades from the shrouds during welding, thin mica or vitreous enamel is introduced between the blades and the edges of the slots. To weld a blade to a rotor disc, the latter is mounted on a fixed table and the blade in contact blocks is pressed into engagement therewith by means of a pneumatic ram. Pressure sufficient to forge the weld is exerted. A small A.C. e.m.f. of 3 volts is applied across the abutting surfaces for say <SP>1</SP>/ 5 second when the blade end and lands fuse and move together for a limited distance.