. The Bell System technical journal . ilter coils and associatedequipment. To secure low losses the powder particles are each insu-lated with a high resistivity, heat resistant material prior to pressinginto cores. Manufacture of this fine alloy powder is a unique metal-lurgical process taking advantage of the effects of small amounts ofadded elements to achieve a desired result. The presence of a fewthousandths per cent of sulphur in the iron-nickel alloys in the rangeof 80 per cent nickel results in a structure which can be rolled to small * The term soft is used to designate materials of re
. The Bell System technical journal . ilter coils and associatedequipment. To secure low losses the powder particles are each insu-lated with a high resistivity, heat resistant material prior to pressinginto cores. Manufacture of this fine alloy powder is a unique metal-lurgical process taking advantage of the effects of small amounts ofadded elements to achieve a desired result. The presence of a fewthousandths per cent of sulphur in the iron-nickel alloys in the rangeof 80 per cent nickel results in a structure which can be rolled to small * The term soft is used to designate materials of relatively high permeability andlow magnetic loss. Likewise, permanent magnet materials are frequently referred toas hard. METALLIC MATERIALS IN THE TELEPHONE SYSTEM 149 section when hot, but when cold it is exceedingly brittle and can bepulverized to fine powder. The manganese content of the alloy mustalso be controlled since it has an effect opposite to that of iron-cobalt system yields a useful magnetic material, the one. Fig. 6—Twenty roll cold-reduction mill for producing thin sheetmaterials for experimental studies. containing approximately equal percentages of iron and cobalt. Thisalloy, called perniendur, is characterized by high permeability at highflux densities and by a high reversible permeability when subjected tosuperposed direct current magnetizing forces. The binary alloy can- 150 BELL SYSTEM TECHNICAL JOURNAL not be fabricated cold and this appeared at first to limit seriously theapplications for the otherwise promising material. Brittleness incold-rolling was overcome through the addition of approximately cent of vanadium, whereupon the alloy can be cold rolled after aquench from a high temperature. Fortunately the vanadium does notmaterially impair the useful magnetic characteristics. The alloyfinds its chief application in the form of .010 inch sheet in the telephonereceiver diaphragm. Substantial tonnages of permanent magnet materials are
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