File:Bell telephone magazine (1922) (14570141958).jpg

Identifier: belltelephonemag26amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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stability combinedwith reasonable strengthis important. It is usedfor our telephone handset. This particular com-pound consists of phenolformaldehyde resin with50 percent filler, the lat-ter being a mixture ofwood flour or groundwood and cotton floe orlinters. It is cheap,strong, mechanically sta-ble, and chemically inert.As a rule, and this is trueof most plastics, the partscome from the moldingdie substantially readyfor use with excellentsurface finish. Akin to phenol plasticis phenol fibre. This ismade by impregnatingvarious types of absorb-ent paper with phenolformaldehyde laminatingvarnishes. After dryingor partially curing theresins, the sheets of var-nish-impregnated paper are stackedin a press and cured under a pressureof one-half to one ton per squareinch at a temperature of approxi-mately 325°?. for about one hour. Plastics as Insulators Various grades or kinds of phenolfibre are used. These vary in resincontent and formulation and in thecharacter of the surface sheet. High
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A new operator head set, with plastic caps on transmitterand receivery gets a talk test cloth may be employed to obtain vari-ations in strength and appearance. Organic plastics do not conductelectricity, and hence form insulators.These insulators must be very good,so that the telephones comparativelyfeeble electric currents will not leakaway or be lost in transmission.Telephone apparatus must also bestable, so that the adjustment of re-lays, keys, switches will be reason-resin content produces good electrical ably permanent. Insulators must notcharacteristics; lower resin content, deteriorate chemically or affect ad-good mechanical strength; and for jacent parts nor cause corrosioncertain grades a tung oil plasticized or deterioration. Consequently, thevarnish is used. Instead of paper, properties of mechanical and chemi- 132 Bell Telephone Magazine AUTUMN

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