SOLDERLESS WRAPPED CONNECTIONS PART I 



529 



stored up is therefore the sum of the energy in the screw and wire 

 (E = Es-{- Ew). 



Screws in terminal blocks are normally made of hard materials such 

 as brass or phosphor bronze. Wires used for the interconnection of com- 

 ponents are nearly always of a soft material and have a tendency to 

 creep. If creep takes place in the wire during the many years a screw 

 connection is in use, it is advantageous to have the loss of potential 

 energy in the wire compensated for by the energy stored in the screw. 



F=o 



F=o 



SPRING ANALOGUE 



Dw= D2-D, 

 Ds = D3-Dw 



Fig. 3 — Screw loosened and wire not compressed. The recovery of the wire 

 is denoted Dw. The recovery of the screw is Dz — Dw (with accompanying "Spring 

 Analogue"). 



A screw, for example, made of soft copper would not be expected to 

 make a lasting connection. If on the other hand the screw is made of a 

 material which has little creep and much elasticity, such as brass or 

 steel, it would act as a spring member and tend to keep the connection 

 tight. 



Several typical screw connections were measured to determine the 

 elastic reserve. It was found that on an average the potential energy 

 stored in the screw is about equal to that stored in the wire. Plastic 

 flow of the wire creates an effective bearing area comparable to the 

 area of the screw shank. 



THE SOLDERLESS WRAPPED CONNECTION 



The detailed analysis of the screw connection as an introduction to 

 the solderless wrapped connection was necessary not only because the 

 screw has such wide use as an electrical pressure connection but chiefly 

 because of its proven value as a (durable connection. When new types 

 of pressure connections are put into large scale production, the question 

 invariably arises. What is their life? While considerable analytical work 

 has been done on the cold flow of metals under stress* and while certain 



See Part II. 



