Patent GB-581024-A (GB)
Title: Improvements relating to resistance assemblies for ignition circuits of internal combustion engines
IPC: H04B15/02
Filed: 1944-05-12
Abstract: 581,024. Glass manufacture. GENERAL MOTORS CORPORATION. May 12, 1944, No. 9045. Convention date, May 24, 1943. [Class 56] [Also in Group XXVII] In a sparking-plug, or the high-tension lead thereof, a resistance assembly for suppressing high - frequency oscillation, comprises a sleeve of insulating material within which is sealed at each end, by a conductive gas-tight seal, a resistance element composed of a fused mixture of glass and a carbon black produced by thermally cracking natural gas in an oxygen-free atmosphere, and having particles whose structure is of minute spheroids joined by rods and whose size is preferably 1.12 microns. The glass may, however, be replaced by sintered oxides or mixtures thereof and silicates. The insulator sleeve 14 is preferably of the sintered oxide type consisting either wholly or chiefly of aluminium oxide together with other oxides, e.g. magnesium or beryllium oxide, or silicates such as mullite. It may be a porcelain body composed of mullite, zircon, zirconia and glass. A lower seal 26 is made from a mixture comprising 55 parts by weight of powdered copper, 45 parts borosilicate glass and 3 parts of a binder, e.g. hydrogenated cotton seed oil. An upper seal 28 comprises a lower portion having a similar composition to the lower seal and an upper portion composed of a mixture of copper, glass and a binder, the glass preferably including a lead borosilicate. The preferred composition of the resistance element 30 is 62.4 per cent borosilicate glass, 25.2 per cent fluorspar, 7.8 per cent magnesium borate glass and 4.6 per cent of the carbon black. These materials are mixed and water is added in the proportion of 40 parts to 100 parts of mixture. The wet mass is then dried to permit granulation through a 20-mesh screen and then completely dried and passed through a similar screen. The resistance may be varied by adjusting the amount of carbon, but if a very high resistance is required, 15 per cent of whiting or beryl should be added, the carbon being reduced to from 1.5 per cent to 1 per cent. Boron carbide and tungsten carbide or boron metal may be added. When making an insulator for a sparking-plug, a lower section 18 preferably of a nickel alloy sleeve filled with copper as described in Specification 549,281, [Group XXVII], is first inserted in the insulating sleeve. The seals and resistance element are then placed and stamped in succession and an upper section 24 of steel is inserted. The whole is then heated to a temperature of 870‹ C. and when the glass is soft, the section 24 is then forced into the bore. An application to the high-tension lead of a distributer is also described in which the insulating sleeve is mounted in a metal sleeve having cooling fins and attached to the distributer cover. The insulating sleeve may be coated with silver to provide better heat conductivity. Specification 558,497 also is referred to. The Specification as open to inspection under Sect. 91 comprises also a resistance element in which boron carbide and tungsten carbide are used with, or in place of, the carbon black. This subject-matter does not appear in the Specification as accepted.