GB568660A - Improvements in or relating to heat exchange devices - Google Patents

Abstract

568,660. Making heat exchangers. COLTMAN, J. L., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Jan. 7, 1942, No. 240. [Classes 83 (ii) and 83 (iv)] Brazing.-The elements of heat exchangers comprising a matrix of thin-walled tubular or plate-like elements of copper or copper alloy, nickel or nickel alloy, or of a base metal such as steel or ferrous alloy coated with the abovenamed metals or alloys, are brazed together by interposing between the surfaces a thin film of an alloy of copper with tin comprising 60-95 per cent of copper and 40-50 per cent of tin, with or without up to 5 per cent of zinc, the alloy having a melting point below that of the elements or surfaces thereof, and heating in an inert atmosphere to a temperature between 700‹ C. and the melting point of the surface parts of the elements, which is sufficient to form a brazed joint. Heating may be effected so as either to melt the alloy film or to promote interdiffusion thereof. Where the surface preponderates in copper, the film may contain any proportion of copper within the above limits, but if the surfaces are of nickel or nickel alloy the film should contain a high proportion of copper. The alloy film may be applied by electrodeposition, hot-dipping, spraying, or as a dispersion in a liquid medium, or as a separate foil, and may be of thickness of the order of 0.0001-0.0003" for an element of the order of 0.005" in thickness. The atmosphere may comprise burnt coal gas or like hydrogen gases, hydrogen or cracked ammonia, a proportion of hydrogen being preferable. A plate-like type heat exchanger formed from steel strip 0.005" thick coated with 0.00025" of copper and then with a similar thickness of alloy of 60 per cent copper and 40 per cent tin, has the parts assembled in a jig and heated at 900-1000‹ C. for 10-20 minutes in a furnace with an atmosphere of burnt coal gas. The copper coating on the steel may be applied by rolling to prevent pin-holing. For a similar heat exchanger made from strips consisting of 80 per cent copper and 20 per cent nickel, a layer of 80/20 bronze powder formed into a paste with nitrocellulose solution is applied to the surfaces to give a film 0.00025" thick when molten and the elements are heated at 1000‹ C. under conditions as in the previous example. Specification 5232/10, [Class 83 (iv)], is referred to. According to the Provisional Specification, heating may be effected between 650‹ C. and the melting point of the surfaces.