METHOD OF MANUFACTURING A TUBULAR CONDUCTOR COMPRISING A LAYER OF NIOBIUM SUPERCONDUCTOR AND A LAYER OF METAL WHICH IS NOT SUPERCONDUCTIVE AT A TEMPERATURE AT WHICH THE NIOBIUM IS SUPERCONDUCTIVE

摘要

1397785 Making super-conductive cables; welding by fusion SIEMENS AG 18 Aug 1972 [19 Aug 1971 (2) 2 Nov 1971] 38749/72 Headings H1A and A4D A method of making a tubular conductor comprising a niobium layer and a layer of another metal includes making a strip of the two layers with fillets of niobium along its edges, bending the strip into a tube so that the niobium fillets abut one another and securing the fillets together. Niobium strips (4), 5 Fig. 1 (not shown), are drawn between rollers 24, 25 by a support 10 and a strip 2 of niobium foil is simultaneously drawn on to the strips. The edges of the foil strip are electron beam welded to the strips (4), 5 to form a channel section strip. The welding apparatus and support are located in a housing 12 provided with a branch 14 leading to a vacuum pump. The channel section niobium strip is fed to a vacuum housing (12SP1/SP), Fig. 4 (not shown), where a copper strip (3) is fed into the channel. The copper strip is melted in a narrow region transversely of the foil by an electron beam gun (32) and it is bonded by diffusion to the still solid niobium. The electron beam may be directed either on to the copper or niobium face of the strip and it may be deflected in steps over the width of the strip or guided linearly across its width. Alternatively niobium strips 4, 5 Fig. 5, and a copper strip 3, are fed simultaneously into a vacuum housing (12SP11/SP), Fig. 6 (not shown), where electron beams 7SP1/SP, 8SP1/SP melt the copper in narrow regions b to bond it by diffusion to the niobium strips 4, 5. Recesses 38, 39 reduce heat-transfer to the roller 10SP11/SP, which is usually cooled by water. The electron beams 7SP1/SP, 8SP1/SP may be directed at the strips 4, 5 and the copper melted by heat conduction. The composite strip 50, Fig. 7, is passed through a fusion electrolysis installation, which comprises an electrolyte housing 40 and a furnace 51. A connection 52 is provided for a vacuum pump and a connection 54 for the supply of protective gas. The electrolyte is alkaline niobium fluoride at a temperature of about 740‹C. With a current density of about 40 mA/cmSP2/SP between an anode 47 and the strip 50, which serves as a cathode, niobium is deposited at a rate of about 0À6 Ám./min. The strip made by the foregoing methods is bent to bring the niobium strips 4, 5 into abutment and they are welded together, preferably by an electron beam 58. An alternative form of strip is made by filling a channel-section niobium tape (82), Fig. 9 (not shown), with copper and rolling it to the required thickness prior to bending and welding. The niobium layer 2, Fig. 8, may be located either on the inside or outside of the tubular conductor. The copper may be replaced by aluminium or nickel or their alloys.