SOLDERLESS WRAPPED CONNECTIONS — PART I 533 



solderless wrapped connection there is no sudden change in cross section 

 and therefore no locahzation of stresses. The term commonly used to 

 indicate the gradual change in rigidity of the wire as it approaches the 

 anchoring point is "tapered stiffness." (See Fig. 8.) 



HEAT AND COLD FLOW 



When a pressure connection is subjected to high temperatures, which 

 may be due to large current or to heat transfer from adjacent com- 

 ponents, the pressure at the joint is relaxed. This is true in the solder- 

 less wrapped connection as well as in the screw connection. The same 

 process of relaxation takes place in normal temperature with time. The 

 relaxation of pressure with temperature and time will be shown in an- 

 other part of this paper. Under ordinary conditions the relaxation of 

 pressure in a solderless wrapped connection is not sufficiently large to 

 indicate any change in resistance during a forty-year life. Furthermore, 

 as Mason and Osmer point out in their paper, solid state diffusion takes 

 place as time goes on. This process strengthens the joint mechanically 

 and improves it electrically. 



QUANTITATIVE EVALUATION OF ELASTIC RESERVE 



Because of the above mentioned disturbances to which a pressure 

 connection may be subjected, it is important to know how much elastic 

 reserve is stored in a connection. If no potential energy were stored in 

 the wire and in the terminal, no contact pressure would be produced. 

 If little potential energy were stored in a connection, a slight change in 

 temperature due to differential expansion of the metals would loosen 

 the connection. The same would be true with vibration and handUng. 



A rough comparison with other pressure connections will serve to 

 illustrate how much elastic reserve a solderless wrapped connection has 

 to have in order to withstand the disturbances to which it may be sub- 

 jected. The best known pressure connection, and the most universally 

 used, is the screw connection. On a No. 4 screw (0.112"), the force ex- 

 erted in clamping the No. 24 gauge (0.020") wire is about 135 lbs. The 

 elastic energy is stored by compressing the wire and by elongating the 

 screw shank. Similarly, in a solderless wrapped connection as shown in 

 Fig. 9 a total force of 90 lbs is exerted on the edges of the terminal 

 (24 corners) . Here the greater part of the energy is stored in the terminal 

 which receives torsional as well as compressional stress from the tension 

 in the wrapped wire. (See Figs. 10(a) and 10(b)). 



