906 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1 954 



a. V) 



ULi Q. 



5^ 



8 



18 20 22 24 26 



Fig. 



10 12 14 16 

 WELD POSITIONS 



Weld strength versus resistance adjustment. 



The welds occur in rapid succession in each head thereby preventing 

 electrical interference between the many circuits involved. When combs 

 which require less than a full complement of contacts are to be welded, 

 the tapes in the not wanted positions are removed from the feed rolls 

 and the toggle switches on the control cabinet are set to direct the weld 

 energy in the sequence desired. To aid in obtaining uniform weld strength 

 from the 24 circuits, all secondary leads from the transformers to the 

 upper welding electrodes are of the same length. To further aid in effect- 

 ing uniform weld strength, rheostats are provided in the high voltage 

 side of the discharge circuit. Fig. 8 shows the result of adjusting these 

 rheostats to balance the weld strengths produced by all circuits. A 

 longer pulse would give the heat produced more time to be conducted 

 away from the weld zone and would tend to heat more of the wire end, 

 to the point, perhaps, of melting it completely. The three millisecond 

 welding time has proven to be satisfactory for this job. However, the 

 shorter the duration of the weld the higher will l^e the current peak re- 

 quired to obtain the necessary heat; the higher the current peak, the 

 greater will be the likelihood of burning the electrodes and shortening 

 electrode life. Adjustment of the pressure on the electrodes can be em- 

 ployed as a compensating factor. As the pressure is increased the tend- 

 ency to burn the contacting surfaces is decreased, but the weld pro- 

 jection on the palladium is flattened correspondingly and the tempera- 

 ture of the weld, for a given current, is lowered accordingly. These 

 variables can be adjusted to maintain optimum balance between uni- 

 formity of weld strength and electrode life. 



CONCLUSIONS 



More than ten million welds from this automatic machine have offered 

 convincing proof of its capabilities. Fig. 9 indicates that good weld 



