GB728131A - Improvements in and relating to composite tubes - Google Patents

Abstract

728,131. Metal tubes. FOSTER WHEELER, Ltd. Oct. 31, 1952 [Nov. 16, 1951 ; April 21, 1952], Nos. 26948/51 and 10041/52. Class 99 (2). [Also in Groups XIII and XXII] In a method of making composite tubes, particularly for heat exchangers, wherein two metal tubes are placed one within the other, their surfaces brought into dose contact by deformation of at least one of them, e.g. by shrinking, drawing, swaging, and their interfaces metallically bonded, the bonding metal is stored in a cavity or cavities in one or the other of the tubes, and the bonding is effected by heating the composite tube to a temperature above the melting point of the bonding metal so that the bonding metal flows into the spaces between the interfaces. The tubes are preferably heated in a non-oxidising atmosphere, e.g. hydrogen or commercial hydrogen and coal gas, the bonding metal, e.g. copper in the form of wire or strip .being attracted by capillary action into the interstices of the joint. When grooves such as helical grooves 12, Fig. 1, extend the length of the composite tube, and the amount of bonding metal is so chosen that substantially the whole of it is used for bonding, the grooves may communicate with leak detecting devices, since should a fault develop it is probable that the heat exchanger medium which is thus allowed to leak out will enter one of the grooves 12. In one example both tubes are of mild steel. In another, Figs. 6, 7, the outer tube is of cast iron sections 30, 32, and the inner tube 10 is of mild steel. The tube 10 is bent to the required shape, the U-portion enclosed in split, cast iron bends 30, and the sections 32, having longitudinal grooves 34, shrunk on with spigots 35 interengaging and copper wires dropped into the grooves. The composite tube is then heated. Alternatively the inner tube may have a helical or other groove or grooves cut into it. Specification 703,081 is referred to.