Telephone Apparatus Springs^ 



A Review of the Principal Types and the Properties Desired 

 of These Springs 



By J. R. TOWNSEND 



This article describes the types of springs employed in telephone apparatus 

 and enumerates the engineering requirements both from the standpoint 

 of mechanics and the quality of materials desired. The chemical and 

 physical requirements of the spring materials are given. The importance 

 of fatigue is emphasized and the endurance limit is given for spring brass, 

 nickel silver and phosphor bronze. 



THE proper functioning of telephone apparatus springs depends 

 upon careful design and selection of material. In many instances 

 the springs must occupy small space and maintain delicate adjustment 

 throughout the life of the apparatus with a minimum of attention. 

 Whereas the physical size of these springs is small, the forces are 

 sometimes necessarily large due to space limitations and this requires 

 careful choice of material. It is believed that the use of these small 

 springs is not unique to the telephone art and a discussion of materials 

 and methods of test used should have broad interest and application. 

 There are three general classes of springs employed in telephone 

 apparatus. For the purposes of this discussion the springs may be 

 classified as follows: 



Springs of sheet non-ferrous metal 

 Springs of clock spring steel 

 Helical springs. 



Sheet Non-Ferrous Springs 



Sheet non-ferrous springs usually consist of punched and formed 



parts made from brass, nickel silver, or phosphor bronze. These 



serve as electrical contact carrying members that are deflected or 



operated either electromagnetically or mechanically. Such springs 



are essentially cantilever springs clamped at one end and bearing 



near the other end one or more precious-metal contacts that are 



spot welded in place. The precious-metal contacts are employed to 



reduce contact resistance and the destructive eff"ects of arcing when 



circuits are broken. The apparatus employing such springs are keys 



1 Presented at the Annual Meeting, New York, N. Y., Dec. 3 to 7, 1928, of The 

 American Society of Mechanical Engineers, 29 West 39th Street, New York, N. Y. 



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