Patent GB-527093-A (GB)
Title: Improvements in the manufacture of multiply metal tubing
IPC: B21C37/09
Filed: 1939-03-31
Abstract: 527,093. Making multiply tubes. GENERAL MOTORS CORPORATION. March 31, 1939, No. 10095. Convention date, April 2, 1938. [Classes 83 (ii) and 83 (iv)] Angular bending ; soldering.-In a method of brazing multiply metal tubes, the tube is moved horizontally through a heater in a non-oxidizing atmosphere and then through a trough containing a molten brazing material such as copper also in a non-oxidizing atmosphere, a blast of heated non- oxidizing gas being directed opposite to the movement of the tube to remove excess copper &c. from the exterior of the tube, the blast further being directed against the molten copper so as to cause the copper &c. to pile up in the form of a wave to submerge the tube therein. The temperature surrounding the brazing trough is approximately 2100‹ F. so that the copper is safer molten and can run freely through the plies and seams of the tube. Two steel strips P 1 , P 2  are fed from reels R 1 , R 2  through a de greasing bath and then through a pair of wicks 21 under control of spring-pressed pads. The wicks carry lubricating oil, which vaporizes on heating, and coat the inner surface of the inner ply and the outer surface of the outer ply to facilitate passage over a forming mandrel and through forming rolls. The oil on the inner surface, on subsequently vapourizing in a heating furnace combines with the oxygen of the air so as to prevent oxidation of the surface whereas the oil on the outer surface, on subsequently vapourizing, mingles with the reducing gas in the heating furnace to prevent carburization of the surface. The strips after-being lubricated, pass through a series of guides and bending rolls. The strips are partially overlapped and are first bent as shown in Fig. 1, whereupon the lapped portion is bent to curved section and the inner ply then bent to form a substantially complete curved ply over the mandrel and the strip P 2  is then similarly bent. The tube so formed is passed through a rotary swager 26 to compact the plies. The tube then passes through a tubular guide 32 in an elongated electrically heated furnace 30 filled with a reducing atmosphere consisting approximately of 5.4 per cent. CO 2 , 8.5 per cent. CO, 2.5 per cent. CH 4 , 0.4 per cent. O 2 , 10 per cent. H 2 , and the remainder nitrogen. The tubular guide has two staggered rows of slots so that the gas may mingle with vaporized lubricating oil therein to prevent carburizing of the outer surface of the tube. The tube then passes through the brazing apparatus which may be removable as a unit from the furnace when replacement is necessary. This unit consists of a tray 41, Fig. 15, mounted on a track in the furnace and having supported thereon the brazing trough 42, gas wiper device 52 and heating pipes 71, 73, 75, Fig. 18, therefor. These parts are loosely assembled and fixed by wire bands. The tray has a bushing 112 to receive the tubular guide 32 and the brazing trough is closed at one end by a wall 47 carrying a boss 48 with flared opening 49. The trough carries a fire brick liner 44, Fig. 17, having inclined sides 45 merging into straight sides 46 and an arcuate base. Transverse metal pins 44a prevent bowing of the tube. The trough is closed by a cover 97 having a welded apron 97a resting on the inclined surfaces 98 of the tray. Copper wire 81 is fed from a reel 82 to the trough by rollers 83, 84 driven by gearing from an electric motor 92, the wire passing through a tubular guide 96 which rests on the sides of the liner. The guide 96 has a sealing collar resting on the flange of a fixed liner pipe 95 so that the guide 96 may be raised when a new brazing unit is to be inserted. The other end of the brazing trough is closed by the gas wiper device 52 which is provided with a lug fixed in a hole in the tray by a cross bar 56. The device 52 has an insert 53 with a stepped bore communicating by a hole 62a on the underside thereof and annular passage 62b with the pipe 63 through which the heated wiper gas is passed. This gas is preheated by passing from a pipe 70 through pipe 71, cross pipe 72, pipe 73, cross pipe 74 and pipe 75 to the pipe 63. The pipes 71, 73, 75 surmount a tubular guide 76 through which the tube passes. The annular jet of wiping gas impinges on the molten brazing material so as to form a wave 80 which submerges the tube, and further wipes the tube as clean of copper as possible. Any copper which splashes over the upper edge of the trough coating 42 is directed by the cover 97 and apron 97a to the bottom of the tray 41 from which it flows out through holes 100 and a spout 101 into a basin in the furnace bottom. The brazed tube passes out of the furnace through pipes 115, 116 through which gas from the tube 76 passes. Non- oxidizing gas is also forced into the tube 116 near its outlet end. The pipe 116 is surrounded by a water jacket 118 for cooling the tube. The tube then passes over a shelf 122 in a water trough 121 into pull-out rollers 130, 131 which assist the forming rolls in bending the tube. The roller 131 is mounted on a weighted arm 138 and the roller 130 is driven by gearing and friction clutch 136 from an electric motor 135 at a speed which is slightly faster than the tube travels when the rollers are running free, so that if the tube breaks any loose pieces are pulled clear of the oncoming tube. The tube is finally wound on a reel 150 with detachable end plate 152, driven by an electric motor .158 through gearing 154, 155 and friction clutch 157. The coils are tested by hydraulic pressure and are then connected, straightened and cut into lengths. They are finally coated inside and outside, preferably by electro deposition with zinc, tin or cadmium. Each furnace may be provided with duplicate apparatus for bending and brazing two tubes at the same time.