MANUFACTURE OF STEEL TUBES FROM STEEL STRIP BY ELECTRON BOMBARDMENT

1,261,551. Welding by fusion; making longitudinally seamed tubes. VALLOUREC USINES A TUBES DE LORRAINE-ESCAUT ET VALLOUREC REUNIES. 23 Jan., 1969 [23 Jan., 1968], No. 3779/69. Headings B3A and B3R. [Also in Division H1] In electron beam longitudinal beam welding of continuously delivered steel, particularly alloy or stainless, tube 1, an electron gun 21 is connected to a housing 8 connected to a main evacuating pump 11 and extended upstream and downstream by sleeves 9, 10 the lengths of which co-operate with means near the sleeve ends to maintain partial vacuum in the housing. The welding is effected at a station preceded by stations (not shown) converting a continuously delivered strip into a circular cross-section tube 1. Rollers 2 co-operate with a fixed or displaceable blade 2a to open up the tube for admission of a rod or tube 23 (Fig. 2). Rollers 12 cooperate with a blade 13 for aligning the tubeforming strip edges with the electron gun, and rollers 14, 15 respectively close the tube and nip the edges together before and after welding. Seals 24, 25 (Fig. 2), e.g. of plastics such as P.T.F.E., are provided in contact with the inner surface of the tube 1 upstream and downstream of the housing and may be carried by the rod or tube 23 which may carry a tool 22 for scraping or flattening the weld bead. The seal 24 may have an outwardly projecting longitudinal rib to close the opening provided by the blade 2a. Seal-efficiency-increasing, low vapour pressure, liquid may be fed, through a tube 26 incorporated in the rod or tube 23, to the upstream side of the seal 25. The rod may also be used to connect an additional pump to the tube 1 interior for evacuation thereof. To protect the lower inside surface of the tube 1, and the rod or tube 23, against the effect of the electron beam, the rod or tube 23 is either in part formed by (Fig. 3A, not shown), or carries in a nacelle (Fig. 3B, not shown), refractory material such as a molybdenum bar positioned in the beam path. The refractory material may be cooled by circulating water. Preferably, chambers 18, 19 provided near the ends of the housing sleeves are gently evacuated by pumps 16, 17 (e.g. vane pumps), and, in addition, mechanical, hydraulic or pneumatic sleeve/tube seals 20, 21 are provided at the tube ends. Other pumps, such as 16, 17, may be provided in the vicinity of the housing 8, and two pumps, such as 11, may be provided on either side of the beam. An annular pump may be arranged, at the position 20