METALLIC MATERIALS IN THE TELEPHONE SYSTEM 141 



was also stronger than lead and more resistant to abrasion and the 

 cutting action of the galvanized steel rings which usually fasten aerial 

 cable to its supporting strand. As the quantity of alloy required for 

 cable sheathing increased, however, it became evident that a large 

 portion of the world's supply of tin would be needed, and this would 

 cause a prohibitive rise in its price. A search was made, therefore, for 

 an alloy of at least equal quality which would be less expensive. 



As a result of investigation of the properties of twenty or more 

 different alloys, an alloy of lead containing one per cent antimony was 

 selected. After extensive manufacturing and field trials this alloy 

 was adopted in 1912 as the standard for Bell System use. Had the 

 lead-tin alloy been continued as a sheathing material to the present 

 time the cost would have been twenty-five million dollars greater 

 (figured on the amount of cable sheath used during the intervening 

 years and on the price of tin which actually prevailed during this time). 



Standardization of an alloy of lead with one per cent antimony for 

 cable sheath was not accomplished without the appearance and solu- 

 tion of many technical problems. For example the extrusion of sheath 

 around the cable core has been an intermittent process, since the cylin- 

 der of the extrusion press is not large enough to contain sufficient lead 

 to cover a full length of cable. It was necessary, therefore, to stop 

 extrusion to recharge the cylinder with the molten lead alloy which 

 must weld to the previous charge, a slug of solid metal. If a layer of 

 dross was present on the surface of this material remaining in the 

 cylinder, a faulty weld was formed which would be subsequently ex- 

 truded into the sheath. Also, during the recharging interval, the lead 

 alloy remaining in the extrusion die receives a different thermal treat- 

 ment from that of the previously extruded sheath. Since the proper- 

 ties of the lead-one per cent antimony alloy are markedly affected by 

 thermal treatment, there were frequently abrupt differences in stiffness 

 of the sheath extruded just before and just after the charging interval. 

 When this change in stiffness was sufficiently great, serious buckles 

 occurred during reeling and installation of the cable. 



Through a knowledge of the constitution and characteristics of the 

 alloy, and by continual improvement in the extrusion process, it has 

 been possible to overcome obstacles such as these and to manufacture 

 cable sheath of improved quality from the one per cent antimony 

 alloy. 



The telephone metallurgist is also concerned with the life of the 

 alloy in service. Many samples from sheath which has failed are ex- 

 amined annually and compared with samples from sheath which is 

 giving satisfactory service. Microscopic examination in some in- 



