GB680374A - - Google Patents

Abstract

680,374. Sparking plugs. LODGE PLUGS, Ltd. March 16, 1951 [June 3, 1950; March 3, 1951], Nos. 13927/50 and 5187/51. Class 7 (iv). In a sparking plug central electrode assembly having a thimble 17 at the sparking end which is adapted to be filled with silver 16 or other metal or alloy of good heat conductivity in electrical and thermal contact with the firing tip of the central electrode 15, the thimble is provided with an inner shoulder, flange or other projection 18 at its open end or intermediate its ends for engagement with an internal shoulder 14 in the bore of the insulator 12 to be supported thereby and a second projection 25 located at the closed end of the thimble 17 for abutment against the end of the insulator 12, the two projections 18, 25 serving to maintain a radial clearance between the thimble and the insulator bore throughout the length of the thimble 17 between the projections. An extension 19 at the end of the central electrode 15 passes through a seal 20 into the mass of silver 16 or similar material which has the thimble 17 on the outer end to form the sparking tip, the thimble being held in spaced relationship with the bore of the insulator 12 by the projections 18, 25 to avoid damage to the insulator upon expansion of the metal parts. The thimble 17 is made of such. material as platinum, nickel, alloys containing either of these metals or any suitable heat resisting alloy steel. In a modification, a separate sparking tip of platinum or platinum alloy is formed on the end of the thimble by riveting, welding or brazing, in the former case the inner rivet head abuts the silver core to enhance the electrical and thermal contact therewith. In another modification, the inner projection is moved nearer the seal so that the length of the thimble is increased. In a further modification, the thimble is increased in length and the inner projection is arranged intermediate its ends. The inner projection is formed after the thimble has been inserted in the insulator; the silver in the bore may be subjected to both heat and pressure during assembly of the plug. The first Provisional Specification describes also a sparking plug in which the thimble is unsupported at the firing tip end by the outet projection.