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BELL SYSTEM TECHNICAL JOURNAL 



of the gases given off by magnetic metals during heating are formed from 

 the impurities carbon, oxygen, nitrogen and sulfur; CO is usually given off 

 in greatest amount from cast metal, and some No and H2 are also found. 

 Refining of the melt is therefore of obvious advantage, and the furnace of 

 Fig. 10 is especially useful for this purpose. 



Small ingots are sometimes made by cooling in the crucible. Usually, 

 however, ingots are poured into cast iron molds for subsequent reduction 

 by rolling, etc.; permanent magnet or other materials are often cast in si;nd 



Fig. 13 — Design of rolls in a blooming mill for hot reduction of ingots to rod. Carnegie 

 Illinois Steel Corp. 



in shapes which require only nominal amounts of machining or grinding 

 for use in apparatus or in testing. Special techniques are used for specific 

 materials. 



Other considerations important in the melting and pouring of ingots are 

 proper mixing in the melt, the temperature of pouring, mold construction, 

 inclusions of slag, segregation, shrinkage, cracks, blow holes, etc. 



Fabricalioii 



Magnetic materials require a wide variety of modes of fabrication, which 

 can best be discussed in connection with the specific materials. The methods 

 include hot and cold rolling, forging, swaging, drawing, pulverization, elec- 



