INDUCTIVE LOADING FOR TELEPHONE FACILITIES 



169 



None of the early work by these and other investigators, however, had 

 resulted in commercially usable iron powder cores. It was not until the 

 Western Electric concept of pressures sufficient to deform the magnetic 

 particles, and of an insulating medium of such character as to withstand 

 these high pressures and provide an exceedingly thin insulating film be- 

 tween particles, was developed, that commercially usable results were ob- 

 tained. 



The Western Electric compressed powdered-iron development was carried 

 out in two distinct steps, one after the other, using the same basic magnetic 

 material. In the early work, consideration was given to the use of chemically 

 produced iron powder. Then, mainly for cost reasons, the development 



Fig. 5— Early cable loading coils and their cores. At left: Iron wire core coil; core has 

 insulating-binding tape partly removed to show core construction. At right: Compressed 

 iron powder core coil; 7-ring core has binding tape partly removed. Also 2 individual 

 core rings. 



efforts were concentrated upon the use of electrolytically deposited iron 

 which was processed so that it could easily be ground into particle sizes of 

 the required fineness. The iron particles were thoroughly mixed with suit- 

 able insulating material and then moulded into thin core rings of desired 

 over-all dimensions under moulding pressures of about 100 tons per square 

 inch. These core rings were stacked vertically and bound with insulating 

 tape for use as loading coil cores. 



In the first commercially usable product, the iron-powder was annealed 

 prior to the insulating and ring-moulding operations. When a higher-grade 

 loading coil core material became necessary for reasons subsequently dis- 

 cussed, the iron-powder annealing process was omitted and a larger amount 

 of insulation was mixed with the magnetic material, which changes resulted 

 in a substantial reduction of effective permeability. Other process dif- 



