GB548841A - Improved spark plug and method of making same - Google Patents

Abstract

548,841. Sparking plugs. AC-SPHINX SPARKING PLUG CO., Ltd., and BARRING- TON, R. R. July 10, 1941, Nos. 8692 and 8693. [Class 7 (iv)] [Also in Groups XXXVI and V] A resistance element is made by mixing finely divided conductive refractory material, such as silicon carbide, with a finely divided metallic conductor and a glassy bonding element, the percentage of the metallic conductor being sufficient to prevent a gradual increase of resistance and insufficient to cause increase in conductivity. The preferred metallic conductor is copper and forms from 5-10 per cent. of the whole mixture. In an example 18 per cent. of very finely divided copper is mixed with 18 per cent. of equally finely divided dehydrated boric acid. These are ground together and then mixed with 64 per cent. of finely divided silicon carbide. The mass is compacted to the desired shape and heated to about 800‹C., the mixture being sealed from the atmosphere to prevent oxidation of the metal. Metal contacts may be provided on the container or in the sealing materials. The resistance may be incorporated in a spark plug as shown.' Within the outer shell a is the insulator c having a bore which contains at its lower end an electrode d. On top of this is a small pellet of ground mixture e of copper (55 per cent.) and a borosilicate glass (45 per cent.) bonded with dextrine. A small copper disc f is then pressed down on to the pellet and on top of that is placed a mixture g of powdered silicon carbide (64 per cent.) powdered copper (18 per cent.) and dehydrated boric acid (18 per cent.). A further copper disc h is then pressed on to the resistance mixture and covered by a further pellet i of a ground mixture of equal parts of copper powder and a glass of low melting point. The whole mass is then compressed by the screwed centre conductor j and heated to 900‹C. Alternatively the resistance element may be preformed and sealed, and more than one such element may be combined serially with several glass seals. Other carbides such as those of boron and tungsten may be used instead of silicon carbide.