GB805981A - - Google Patents

Abstract

805,981. Sparking plugs. GENERAL MOTORS CORPORATION. April 16, 1956 April 15, 1955], No. 11450/56. Class 7(4) A sparking plug, particularly for use with gas turbine engines, has a tubular metal shell within which is secured an insulator comprising two elongated substantially cylindrical sections, each of which is composed of ceramic material, and one of which is bonded at one end to an end of the other so that the ends of the insulator and the shell are in substantial axial alignment, the ends of the metal shell being substantially coextensive with or projecting beyond the ends of the insulator. The upper and lower sections 24, 26 of the insulator are formed in known manner for example by injection or compression moulding using an organic resin as a binder which is subsequently burned out during the firing operation; by the rubber moulding technique using paraffin as a binder which is burned out during firing or by grinding or turning. The insulator is preferably made from a sintered high alumina composition. At least those portions of the insulator sections 24 and 26 to be joined are coated with a thin layer of ceramic bonding material and fired until the material is fully matured. After cooling at least the mating portion of one of the sections 24 or 26 is coated with a second layer of ceramic bonding material after which the two sections are fitted together and fired while pressure is applied. The pressure may be 3 to 4 pounds. The centre electrode may be filled before the firing operation. A variety of ceramic bonding materials can be used ranging from those which mature at the relatively low temperature of about 1600‹F. to those which mature at the relatively high temperature of about 2500‹F. The composition of a preferred known low temperature maturing glaze is quoted. The final step in the plug manufacture is a weld operation whereby the thin shell section 54 is softened by passage of electric current while pressure is applied on the ends of the shell so as to tightly clamp the insulator shoulder 25 between the shield 14 and sleeve 27 and firmly seat the base of the insulator against the flange 22. A conductive glass seal is indicated at 34. Fig. 4 shows a modification. The plug includes seals 78, 80. The insulator is seated and sealed within the shell by means of a gasket 86 and by a gasket 90 which is pressed between the top surface of the insulator and the shell. The shell sections may be secured together by welding or brazing.