GB577979A - Improvements in or relating to heat exchange devices - Google Patents

Abstract

577,979. Making heat exchangers. COLTMAN, J. L., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Jan. 19, 1943, No. 986. [Classes 83 (ii) and 83 (iv)] Soldering.-In making heat exchange devices, such as intercoolers, radiators or oil coolers for internal-combustion engines, of the kind having primary and secondary heat exchange surfaces formed of thin-walled copper or copper alloy sheet, strip or tubular elements by coating the parts with silver and heating in a non-oxidising or reducing atmosphere above 780‹ C. so as to form a silver-copper eutectic which solders the parts together, only one of each pair of contacting surfaces is so coated and the coating is limited to a thickness not exceeding 0.0002" and the surfaces are held in mutual contact under pressure during the soldering operation. The silver coating, which may be 0.0001"- 0.00015" and preferably not less than 0.000075" thick may be applied by coating a copper billet on one or both sides with a thin sheet of silver, rolling to sheet or strip form and then forming into heat-exchange elements, or by electro-depositing the silver on a sheet or strip or applying a paste of silver powder in collodion, or the coating may be effected during or subsequent to formation of the elements. Elements left uncoated or only coated on one side should be formed of deoxidised or oxygen-free copper or copper alloy. For a heat exchanger comprising alternate plain and corrugated platelike elements, the plain elements may be coated on both sides and the corrugated elements left uncoated. For a finned tube heat exchanger, the tubes, which extend through flanged apertures in the fins and are reinforced internally by stiffening members, may be coated internally and externally or. only internally, in which latter case the fin elements are also coated on one side. The parts are held in mutual contact when joining plain and corrugated elements by an earthenware tile or like. When elements are sufficiently resilient they may be assembled under initial compression in a jig. When joining fins to flattened tubes threaded therethrough, the flanges of the apertures in the fin elements may be radiused so as to exert resilient pressure on the walls of the tube. Soldering may be effected in a furnace containing an atmosphere of nitrogen or hydrogen or a mixture thereof formed by admixing the gases or by employing dissociated or cracked or cracked and burnt ammonia. Alternatively, the atmosphere may comprise carbon dioxide or burnt coal gas or like hydrogen gases. In joining flattened tubes to corrugated strips of deoxidised copper, the tubes may be coated on both sides with a layer of silver 0.00015" in thickness and the parts assembled in a jig and soldered at 820‹ C. in an atmosphere of cracked ammonia. Specifications 540,961 and 548,515 are referred to.