258 



BELL SYSTEM TECHNICAL JOURNAL 



Melling and Casting 



For experimental investigation of magnetic materials in the laboratory, 

 the raw materials easily obtainable on the market are generally satisfactory. 

 When high purity is desirable specially prepared materials and crucibles 

 must be used and the atmosphere in contact with the melt must be con- 

 trolled. The impurities that have the greatest influence on the magnetic 

 properties of high permeability materials are the non-metallic elements, 



Vig. 10 — Induction furnace designed for small niclts in controlled atmosphere, as de- 

 signed hy J. H. Scaff and constructed by the Ajax Northrup Company. 



j)articularly oxygen, carbon and sulfur, and the presence of these im[)urities 

 is therefore watched carefully and their analyses are carried out with special 

 accuracy. Impurities are likely to change in important respects during the 

 melting and pouring on account of reactions of the melt with the atmos- 

 phere, the slag or the crucible lining, or because of reactions taking place 

 among the constituents of the metal. 



Melting of small lots (10 pounds) is best carried out in a high-frequency 

 induction furnace, l-'igure 10 shows such a furnace designed for melting ten 

 to lifty pounds, and casting by tilting the furnace, the whole operation being 



