GB1343387A - Method and apparatus for the production of welded tubing - Google Patents

Abstract

1343387 Welding by fusion, making tubing D SCIAKY 22 Aug 1972 [7 Sept 1971] 39151/72 Headings B3A and B3R Continuous production of metal tubing 31 from flat metal strip 1 comprises the successive steps of (i) introducing said strip into a vacuum chamber 4 (ii) roll forming said strip into a tubular shape with strip edges overlapping or, as particularly described, abutting to form a seam, (iii) welding said seam by a beam from an electron gun 13, and (iv) passing the welded tubing 31 out from the vacuum chamber through a sealing means 18. As shown, the flat strip is drawn from a reel 2 through an edge scarfing device (not shown) and a sealing means 3, by forming roll stands 5 arranged in the chamber 4. The reel 2 is one of a pair on a rotatable reel stand 51, this arrangement, by weld connecting together ends of the strip on the two reels, providing for uninterrupted strip supply. The sealing means 3 comprises longitudinally hinged together bottom and top plates 22, 27 (Fig. 7) machined to provide a strip receiving slot of length several times the strip width. Bottom, top and side wear-preventing rollers may be provided spaced along said slot, and flexible seals 26 may be provided between the plates 22, 27. The chamber 4 may have the top and one side wall thereof longitudinally hinged to the bottom and the other side wall to provide for interior access. Within the vacuum chamber, the stands 5 are followed in succession by a roll stand having a tube twisting prevention disc 10 (Fig. 4, not shown), a seam closure roll stand 12, and, following the electron beam line, a cutter 15 for removal of protruding weld bead. The sealing means 18 comprises external and internal cylinders 28, 29 having respective internal and external diameters such that the diametral clearances between the cylinders and the welded tubing 31 are preferably less than 0À005 inches. Welded tubing cylinder centering rollers 30, 34 are provided in the cylinders 28, 29. The external cylinder 28 is flanged to the vacuum chamber and is provided with internal, spaced, air expansion cavities 44. The internal cylinder 29 is fixed to a hollow tube 35 which is supported inside the vacuum chamber by a sleeve 38 (Fig. 3, not shown). Pumps evacuate the vacuum chamber and the clearances between the welded tubing and the cylinders 28, 29. A tungsten disc 43 prevents beam penetration of the tube 35. For electron beam centering over the seam, there is provided an antenna 16 which collects secondary and reflected electrons generated at the point of beam impingement and a feed-back control which uses the signal from the antenna to deflect the beam to a position of minimum secondary electrons, i.e. over the seam centre. In Figs. 11, 12, twin electron guns 56, 57 may provide impingement areas which overlap, partially overlap, 58, 59, or are spaced, 60, 61. In the case of spaced areas, the first pre-heats and the second welds. In the case of partially overlapped areas, the leading portion pre-heats, the overlapped area penetrates, and the trailing portion retains metal fluidity for hole re-filling. Provision may be made for post-heating after welding. On leaving the sealing means 18, the welded tubing is cut up into lengths by a flying cutter 20. In alternative embodiments the flying cutter may be disposed in a further chamber following the sealing means 18, air-lock means being provided for removal of the cut lengths from said further chamber; and the coils of flat metal strip may be enclosed within the vacuum chamber 4.