GB1440933A - Electromagnetic waveguides - Google Patents

Abstract

1440933 Making waveguides; extruding BICC Ltd 20 Nov 1973 [21 Nov 1972] 53700/72 Headings B3A and B3P [Also in Division H1] A method of making a waveguide of circular cross-section comprises forming a composite tubular billet of circular cross-section by introducing into or forming within a pre-formed tubular sheath 1 a continuous wall 2 of a metal or alloy suitable for forming the electrical conductor of a waveguide, the metals or alloys of the sheath and wall being mutually compatible, extruding the billet between a die 14 and a mandrel 8 to form a composite tubular shell in which the wall is metallurgically bonded to the sheath and applying a layer of insulating material to the internal surface of the shell. The sheath is of aluminium alloy and a seamless copper or silver lining is inserted inside it, preferably in a non-oxidizing gas atmosphere, e.g. nitrogen, after the mating surfaces have been cleaned. The inserted wall is sealed to the sheath by inwardly deforming the sheath at a tapered end 4 and outwardly deforming the wall at the other end of the sheath or by means of a sealing ring (7), Fig. 3 (not shown), in the end face of the sheath. The mandrel 8 is inserted in the prepared billet and it is sealed to the stem 9 of the mandrel by further inward deformation. Alternatively the mandrel stem may have an enlarged end (11), Fig. 7 (not shown). The billet/mandrel assembly is placed in a chamber 13 of a hydrostatic extrusion machine with its end 3 in sealing engagement with the die 14 and pressure of the fluid in the chamber is raised by a ram 15. A head 10 on the mandrel transmits a secondary force on the billet and the mandrel advances through the die as extrusion proceeds. Alternatively a shoulder (16), Fig. 7, may be located in the chamber 13 to hold the mandrel stationary. The mandrel is then removed and an insulating sleeve is inserted in the billet, the sleeve and/or the bore of the billet having a coating of adhesive. The sleeve is sealed to both ends of the billet and the space between the sleeve and billet is evacuated. Fluid under pressure may also be injected into the sleeve bore. Alternatively the bore of the billet is heated and powdered plastics material is applied to it. Another method of forming the composite billet comprises electroplating a layer of copper on to the internal surface of an aluminium or aluminium alloy sheath. This may be effected after depositing a layer of zinc or copper-tin alloy on the internal surface of the sheath. The bond resulting from electro-plating is consolidated by the extrusion process.