GB745016A - Improvements in or relating to surface discharge sparking plugs or other igniters - Google Patents

Abstract

745,016. Ceramic-metal seals. LODGE PLUGS, Ltd. Oct. 31, 1952, No. 23508/53. Divded out of 26027/51. Class 36. [Also in Group XXVII] A surface discharge sparking plug or other igniter includes a pair of electrodes of a metal having a higher sintering or fusion temperature than that of copper oxide, an electric insulator separating said electrodes, and a continuous semi-conducting spark discharge path of copper oxide extending between said electrodes and intimately uniting the insulator therewith. In one arrangement, Fig. 1, the central electrode 11 is separated from the earthed electrode 12 by an insulator 10 which may be of ceramic material such as alumina, and the spark discharge path is formed by a layer 13 of copper oxide the active face of which is flush with the ends of the electrodes. In a modified arrangement, Fig. 2, the copper oxide layer 13 is formed on an insulating pellet 15 abutting the main insulator and a nickel-iron earthed electrode 14 is separate from but lies in contact with the plug body 16. The air gaps between the electrodes and insulator and the exposed surface of the latter are filled or coated with copper oxide which is fused or sintered at a temperature below the fusion or sintering temperature of the electrodes or ceramic insulating material. The copper oxide may be in either the cuprous or cupric form or may be a mixture of these, and may be applied by painting or spraying and adhesion and compacting obtained by heating above or preferably just below the oxide melting point of 1250‹ C. Control of the conducting properties of the oxide layer may be effected by adjustment of the sintering temperature and furnace atmosphere. Heating for five minutes at 1100‹ C. in an oxidizing atmosphere produces satisfactory results. The electrodes may be assembled on to the ceramic base after the copper oxide layer has been applied and fired, but it is preferred to assemble the electrodes on to the ceramic base before firing the copper oxide layer. The electrodes may be coated with copper before the firing operation to ensure more intimate contact.