GB336710A - Improvements in or relating to thermionic cathodes - Google Patents

Abstract

336,710. Robinson, E. Y., and Associated Electrical Industries, Ltd. Aug. 14, 1929. Addition to 320,866, [Class 39 (i), Electric lamps, Arc &c.]. Extrusion machines; rolling - machines. - In applying insulating coatings to the heater wire of indirectly - heated ther - mionic cathodes by extrusion as in the parent Specification, the wire is first drawn through a plastic sludge &c. of the insulating substance and a vehicle or agglutinant and is then passed through a die to form and limit the coating before it is dried or baked. The two operations may be carried out in a single process, the wire from a drum 3 being drawn through a vessel 12 containing porcelain sludge 13 and out through an extrusion aperture 14, a weight 17 and plunger 15 applying pressure to the sludge. The coated wire passes through an oven 20 and blow-pipe. flame 21, the aperture 14 being shielded from heat by a baffle 22 and air-jets 23. The wire may be given two coatings in this manner in succession and may be heated by a blow-pipe flame before passing into the first vessel 12, and the first coating may be heated to biscuit state and the final coating sintered. Alternatively, two initial coatings, preparatory to the coating in the vessel 12, may be given by passing the wire successively over two wheels each driven in the opposite direction to the wire and having a V or U groove dipping into the sludge, the wire being passed through three blow-pipe flames separated by the wheels. In a modification of the vessel 12, the wire passes into the vessel through a narrow tube and the vessel is provided with a compressed-air supply and a variable air-leak, a paper washer on top of the sludge preventing it from drying. In a modified process, the wire is coated by drawing over a driven wheel dipping into the sludge and the coating is at once moulded by passing the wire through a die or through co-operating semi-circular grooves on two driven rollers. These two rollers may be lubricated with oil to prevent the sludge from sticking. The coated wire may be cut into lengths.