Patent GB-708397-A (GB)
Title: Improvements in the manufacture of metal tubing
IPC: B21B17/14
Filed: 1952-05-27
Abstract: 708,397. Making tubes. GENERAL MOTORS CORPORATION. May 27, 1952 [June 15, 1951], No 13362/52. Classes 83 (2) and 83 (4) Rolling.-A method of making tubes by forming metal strip into tubular form and welding the edges of the strip together is characterized in that the tubing is initially formed to a larger diameter than required and after welding is progressively reduced to the desired diameter, without substantial reduction in wall thickness, by alternating applications of pressure one of which forms the tubing into an elliptical cross-sectional shape while the next rectifies the tubing to a circular cross-sectional shape the diameter of which approximately corresponds to the length of the minor axis of the previous elliptical cross section. A steel strip S is formed into a tube C by rolls 20-21, 22-23, 24-25 and 26-27. The edges of the formed strip are welded together by an electric welding unit comprising a pair of spaced coaxial rolls 30 and a back-up roll 31 supported by a pivoted lever 32 forced upwardly by fluid pressure in a bellows 34. The interior of the tube is protected by a non-oxidizing gas introduced through a pipe 35. The external bead formed during the welding is removed by a trimmer having a cutting tool 41 and a supporting roll 42. After removal of the bead the welded tube is formed into the crosssectional shape 53, Fig. 3, by a two-roll elliptical unit 50 and then to circular shape 63 by a rectifying roll unit 60. The tube next passes between two pairs of rolls 71, 72 at right angles in an elliptical-forming four-roll unit 70, then between rolls 81, 82 in rectifying unit 80 which restores the tube to circular form 83 but of less diameter. The tube is then fed successively through another four-roll elliptical unit 90, a rectifying unit 100, a third four-roll elliptical unit 110, a rectifying roll unit 120, a fourth four-roll elliptical unit 130 and finally through two rectifying units 140 and 145. The diameter of the tubing after passing the last unit 145 is approximately half the initial diameter of the tube and the wall thickness of the tube remains unchanged throughout the forming operations. Finally the tube passes through an annealer 150 comprising pairs of electrode rolls 151 and 152 in a housing 153 connected by a tube 154 with another housing 155 containing electrode rolls 156. The housings and the tube 154 contain reducing or non-oxidizing gas. From the annealing device the tube passes through a cooler 160 having an inner pipe 161, through which the tube T passes, and which is surrounded by a water jacket 162. The rolls of the various forming roll units are all driven from a single lay shaft 170 through chain and sprocket and reduction gearing which varies the speed of the roll units as the rate of travel of the tube increases due to the elongation caused by the reduction in cross-sectional area. A different combination of forming roll units may be used, for example, the tubing could be passed through a two-roll elliptical unit, two four-roll elliptical units and four rectifying roll units instead of the six shown in Figs. 1 and 2, whereby the tube reduction would not be so great. The rolls of the four-roll elliptical units run on pins 200 supported by blocks 201 having ribs engaging grooves 203 in upper and lower plates 205a and 205b, Fig. 6, connected by side bars 208. The blocks 201 are adjusted in the plates 205a and 205b by means of screws 206 and 209 and the plates and their bars 208 are adjustably located in slots in frames 213 attached to a base 214.