Some Aspects of the Production Problem in Sparking Plugs for Aircraft Engine

Abstract

T. E. L. CO. sparking plugs have been designed and developed by the writer and are manufactured by the Tachikawa Engineering Laboratory Company, from which the plug derives its name. The factories of T. E. L. CO. were established in 1921,at Tachikawa Machi, near Tokyo, to make aircraft accessories and other instruments, by the present proprietor, Mr. M. Nosawa. In 1925-1926,the writer was able to produce sparking plugs with Mica insulator, commercially known as T. E. L. CO. M. 1. and M. 11., and has achieved several noteworthy successes on mail planes, between Tokyo, Osaka and Sendai. At the end of March, 1927,three types of T. E. L. CO. sparking plug were firs adopted by the Military Air Service as standard equipments, as they passed very severe tests which were carried out the Technical Division of Imperial Army, Tokorozawa. Now there are more than eight types of T. E. L. CO. sparking plugs which have been adopted in a large number by the Military Air Service and the Air Transport Company of Japan, with several records for the safety, soundness of construction and the low cost. The total number of types of all T. E. L. CO. sparking plugs which were actually designed and constructed, exceeds seventy three. So far as the question of production is concerned, a mass production system has been fully adopted throughout the shop, and the present capacity of production has been greatly increased to meet all demands. Parts such as plug shells and gland nuts are turned up by a number of gangs for turret lathes, and the grinding operation of insulators as well as assembly being conducted on line methods. Insulated electrodes are examined for the insulating property and gas leakage at various stages of manufacture, and after being assembled to shells, they are subjected to further leakage tests and spark tests under a high pressure. The advantages of using mica as insulating material, can not be over-estimated. Its chemical, electrical and mechanical properties are unique. It has an extremely good insulating resistance even at a very high temperature, as well as a high heat resisting property, an ample flexibility and a sufficient hardness. There are many kinds of mica, but they all belong to the same chemical family. They are silicates of alumina and alkalis, sometimes combined with magnesia and iron oxide. Although mica is one of the most universally distributed minerals on the globe, localities where the deposits consist of pieces large enough for sparking plugs are rare. India, America, Canada and Siberia produce most of mica used for sparking plugs, and a particular kind known as "RUBY" mica is the most suitable."BLACK" mica is also used for special sparking plugs, as it possesses a very high heat resisting property. Its laminar structure is well known, and the consequent absence of effective lateral cohesion is one of its outstanding characteristics. Great care has to be exercised in selecting mica, as it must be free of impurities as far as possible. The latest type of T. E. L. CO. sparking plug is M. 80. series, which has been designed for the particular use of modern high compression engines of air or water cooled types with a horse power between 400 and 800. M. 80. series embodies the same standards of design and workmanship as the previous model M. 54., the chief characteristics of M. 82. and M. 84. plugs being of the reliability, lightness and durability. In the history of mechanical engineering, the rapidity of progress in the development of aircraft engines is unparalleled. The requirement of the last few years inspired a great advance in the perfection of high compression and high power engines of both air-cooled and watercooled types, and consequently, severe conditions have been placed to the plugs, which necessitated quite special designs and materials to be used. At the immediate present, T. E. L. CO. M. 82. and M. 84. plugs consequently well

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