SOLDERLESS WRAPPED CONNECTIONS PART III 601 



In order to compare hoAV the solderless wrapped connection and 

 soldered connections are able to withstand the effects of vibration over 

 a period of time, several sets of terminals were mounted on a test table 

 and wires from a cable were wrapped or soldered to the terminals. The 

 cable was then oscillated through a small angle at 19 cycles per second 

 and the elapsed time until lead breakage occurred was recorded. Some 

 early similar tests indicated that soldered connections began to break 

 at about fifty hours and the solderless connections lasted several times 

 that long. In a more recent test where ten connections of each type were 

 set up three of the soldered connections broke within six hours and all 

 soldered connections broke within 1,000 hours. None of the wrapped 

 connections had broken in that interval. In another test using ten sol- 

 dered connections and twenty solderless connections, one of each broke 

 at nineteen hours and after fifty-seven hours two more soldered con- 

 nections broke with no further breakage of solderless connections. 

 Further tests are being made of resistance to vibration under various con- 

 ditions but the early indications are that the life of the solderless con- 

 nections is as good as and perhaps better than that of the soldered 

 connections. 



The increased resistance of the wrapped connection to vibration 

 breakage comes about because in the soldered connection the bending 

 stresses are concentrated at the point of emergency of the wire from the 

 solder, while in the wrapped connection the stresses tend to be dis- 

 tributed over the entire first turn of the connection. In order to obtain 

 long life, it is important to avoid any exposed nicks in the wire at the 

 first turn of the connection. Otherwise stress concentrations, perhaps as 

 severe as those in soldered connections may be set up. 



Incidentally, unless the wire has an enamel or similar coating it is 

 unnecessary to clean the wire or the terminal before wrapping, since 

 forces set up as the wire wraps on to the terminal shear off surface films 

 and the resultant gas-tight areas are immediately established on clean 

 surfaces. It is this intimate contact which also makes possible the dif- 

 fusion process between the wire and the terminal. 



A large number of parameters have an effect on the level of stripping 

 force which a given connection will Avithstand. Among these are the 

 number of wraps, tension on the wire during wrapping, sharpness of the 

 corners of the terminals, the elastic properties of both the terminal and 

 the Avire, the size of the terminal, the hardness of the terminal and wire, 

 the presence or absence of tin plating, taper of the terminal, aging, tool 

 design, etc. Tests have been run showing the effect of variations in these 

 parameters on the stability of the connections. Typical results of these 



