Ceramics
in the Telephone A . G. JOHNSON
AND
L. 1. SIIAW
Western Electric Company, Chicago, Ill.
N OltLUEii to unify a discussion of specific ceramic itenis used in the telephoiie, it s e e m advisable to classify broadly and define the field covered. The primary characteristic of ceramic products is that they are inorganic and are made principally from flint or sand, clays, feldspars, cryolite, floorspar, soda ash, sodium nitrate, lead oxide, and in some instances other materials including magnesium carbonate, borax, boric aoid, iron oxides, potassiuni carbonate, barium carbonate, as ell as coloring materials such as clrroiniurn oxide, cobalt oxide, etc. A second characteristic of ceramic parts is that a high temperature is used in the process of manufacture, resulting in a partial or complete fusion of the constituents and the formation of cossipounds not presetit in the raw materials. The bonding niatcrial is generally a glass and even after cooling is noncrystalline iu nature. The finished i:eramic prodiict is resistant t,o decomposition at temperaitires a.t wliic'i organic materials, such a i woo&, plasbics, paint, and lacquers would be ilet!onipoi;ed. T l i c ainoiiirt and kind of fused inraterial or glws prciciit is the key to most its properties. For example, t,he degree of pwwity of pwcelain is determined by the arisount of vitrification. Tljis also affects veather resistance, dielectric cliaracteristics, and iiieclrauical strength. Tlie strength or iirittleness of pircdain, cnairieli, and glass is goverricil hy the aoiount and liiud of ginss and affects r nce tu impact, dxwion, am1 clieiuical action. T h e specific clcctriral resistix-ity is also influeneed by the arnormt i d of gItL3S IJrCSCIlt &lid, together witli o t h factors, the iisc oi the product :is insulation for high ~r low w and high or l o ~ vfrer~ricneies. Tiecause the enlargerrieiit arid improvernent of telrphorir t years bas requirod new product3 with specific uses of ceramic products have been extendod o tlist they now comlirisc nearly every type of time jrmrlucti, irwliiding electrical porcelain, vitreous enameled parts, glass, arid heavy clay products. Part of the iiicreasn in the uses of ceramic materials has been brought abnut because advances in ceramic art independent, of teleplionc rriariufactrire have made available ceramic parts of iinproved hiracteriatics. In some cases it lias been possible to iise coniriierrial products or to ohtain desired clsaract,eristics by working with manisSacturars. In other cases d i e r e the rcqriirmicnts are iiii13:'6
usual, peculiar to telepiioiie usage, aiid closely asiociatid with other operations in the manufacture of telephone apparatus, the control arid developinent required have made it neccssary not only to develop methods of rnannfactiire but actually to manufacture these products. In this discussion the general distribution of each gencrnl rlitss of major ceramic parts in the telephone system, the requirements that t h y mnst meet for satisfactory fiinct.ioning, their advantages and disadvmtages, :ind a brief description of iniseellaneous nietliods and sonic ~~robletna of ilianufacture will IJe given.
Electrical Porcelain I ' e r h p t i l e i r m t gericrally used ceramic lmrduct in tile t,clephie system is electrical porcelain. l'arts of this mat,erial vary in size from ssiiall beads For wire insultition tu Large tcrmirml blocksusedat the joining of cahleeonducl.ors and opeu mire. Tliew imrr:cleiii parts vary in physical cliara.o ncr tabes to dense, t h o u g l i l y Y 1-nciiuni-tithe insulators. Tlie material is used for isisulatiou in t.rarrsniittcws aiid vaciiuiii tubes, for fastening and insulatirig i~iiscellaiieorii wiring betxecii siihcriber's apparatus and iiiaiii telepiioiie lines, in protection apparatus for both eeiibral offices and su1)scriber's eqiiipnrent, and in the insulatioii of maiii telepliune lincs. Tire quality of parts used in lucations d i e r e a degree of high-tension irisulation is desirable or wlierc ilinlcetric properties are iinportant., such as insulaling aerial constnict,ion,dead-ending wire sections, or in radio frequency .*\.ark, is controlled by the density or porosity, and by iriecliairieal arid r:lect,rical cbaracteristics. Porwlairi for relat,ively liigI~-t~ei~sim uses, such as the strain insulators shown in tlii: upper part (if Figure 1 iiiust he sufficiently dense and well vitrified to withstand (1) any penetratioii through hroken .surfaces by a fudisin dye solution under a pressure of 4000 ~ ~ ~ i i uper i l ssquare inch for 15 Iioiirs, (2) tensile loads
i n t l i c mat.erial ma
