Patent GB-613118-A (GB)
Title: Improvements in method and apparatus for bending metal tubes
IPC: B21C37/29
Filed: 1945-11-15
Abstract: 613,118. Bending tubes. WURZBURGER, P. D. Nov. 15, 1945, No. 30648. [Classes 83 (ii) and 83 (iv)] Mandrels ; restoring shape of articles.-A method of making elbows by bending a length of tubular stock comprises two successive operations, firstly forcing the tube longitudinally into a channel conforming to the external shape of the elbow and secondly removing the wrinkles or distortions thereby produced in the leading end of the tube by means of internal radial pressure. The method is particularly applicable to work having a bend radius smaller than the diameter of the tube. The blank tube is inserted into a pair of split dies D, Fig. 6, and acted on by a ram R having a pilot P engaging the inside diameter and a shoulder S abutting the end of the tube. The tube is' bent to right angle form, but one arm is deformed with wrinkles 13, 14 and the lower mouth 11 is raised from the side of the die. The ram is held in the down position and a mandrel M, operated as by a hydraulic cylinder H is introduced into the mouth 12 of the tube. The mandrel has a rounded nose 20 conforming to the inside contour of the outer bend radius of the tube and runs in a sleeve 21 having the same wall thickness as the tube. In Fig. 7, the mandrel has operated to remove and iron out the wrinkles in the tube and set the outer wall 16 of the bend. The finished elbow has an oblique edge 12<SP>1</SP> which may be further worked and trued. For larger pipes the leading edge 11 of a blank tube may be cut at an angle to be longer than the edge 10 and so make allowance for the shortening in bending. In a modification, a specially shaped mandrel N, Fig. 10, is used with the same dies as before, said mandrel having a tapering portion 30 acting to guide the upper leading edge of the tube being bent, and a bulb end 31 whose lower curvature is of the same form as the inside radius of the outer wall of the tube. The mandrel is inserted in the dies and its shank 32 runs in a sleeve 33 of the same dimensions as the tube so that a space substantially 'the thickness of the tube is left between the mandrel and lower wall of the dies. The ram is then operated to bend the tube to elbow form around the mandrel which is withdrawn to remove the wrinkles formed. If desired, the mandrel may commence its withdrawal before the ram R has completed its stroke. In yet another modification, an elbow is formed from a blank tube, having a sealed end, which is partially filled with a material F, Fig. 20, which may be oil, water, or a dry granular material such as salt or sand, polyethylene glycol or " carbowax " or other granulated filler. The tube is inserted in the die D and acted on by a ram Q having an outer sleeve member 40 to abut the tube end and an inner punch member 41. The outer part of the ram operates to force the tube around the bend in the dies where the closed end comes into contact with the end 44 of a second ram V occupying the whole diameter of the channel in the die. The inner member 41 of the ram is then operated to compress the liquid or other material inside the tube, to remove the wrinkles formed in bending and impart a substantially squared end 46 to the tube by reason of its bearing against the ram V. This end may later be removed. Where liquid or substantially liquid fillers are used they may be fed into the tube through the ram after or during the bending operation to remove wrinkles or the like, the pressure of such fluids being controlled externally of the ram. Specification 552,857 is referred to.