GB701112A - Improvements relating to the shaping of metal tubing - Google Patents

Abstract

701,112. Bending tubes. DRAPER, F. C., HOBSON, J. F., and SANG, W. Dec. 12, 1951 [Jan. 5, 1951], No. 405/51. Classes 83 (2) and 83 (4). [Also in Group XXIX] A method of forming a bend in a metal tube comprises compressing the walls of the portion of the tube to be bent so that they approach one another to give a cross section which is concave towards the side which is to be the outside of the bend, bending said compressed portion on a former to the required curvature and then expanding said portion to the desired final shape by fluid pressure whilst it is confined in a die. The portion to be bent of a tube 1 is placed in a member 3 of a press and compressed by a member 4 to the shape shown in Fig. 6. After annealing the compressed portion is bent on a former 5 by means of a roller 10 mounted between the side arms 9 of a lever 8 which is pivoted at the centre of curvature 7 of the semicircular contour of the former 5. The roller has a convex profile 12 for co-operating with the concave profile 6 of the former 5. One end of the tubing is gripped in a chuck 15. The bent tubing is then annealed and inserted in the lower half 19 of a split die one end of the tubing being plugged by a plug 21 provided with a sealing ring 22 the plug being held in position by a split bush 23. The plug 21 has an enlarged head 24 engaging with a recess in the die for locking the plug in position. An hydraulic fluid inlet valve 25 is inserted in the other end of the tube and is retained by a split bush 27. The upper half of the die (not shown) is then lowered into position by hydraulic pressure and hydraulic fluid of low pressure is introduced into the tube (see Group XXIX) the air in the tube escaping by means of a bleed passage 33 in the plug 21. The bleed passage is controlled by a cock 34. When the bleeding is complete the cock 34 is closed and the tube is initially expanded by a higher pressure of fluid and the tube removed and annealed. For the final expanding operation the end of the tube in which the pressure valve is inserted remains free to slide in the die by replacing the split bush 27 with a round bush in which the tube is a sliding fit. The full hydraulic pressure is then applied and the tube wall is expanded into contact with the die walls after which the tube is removed and annealed. The bent tube may be tapered by introducing a taper into the die so that the tube is expanded to give the desired taper. The invention relates to large diameter tubes of thin wall construction for use as short elbows for petrol and oil tanks in aircraft, ducts, fuel and air distributing rings on gas turbines and musical instruments.