908 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



the automatic multiple percussion welding of contact blocks to the ends 

 of an array of small wires extending less than a quarter of an inch from 

 molded phenolic plastic. This array, fixed in plastic, forms a comb which 

 is illustrated in Fig. 10. WTien completed this comb becomes the station- 

 ary contact member of the ^^'ire spring relsiy. The small blocks of metal 

 on the ends of the wires are cut from a composite tape of which a small 

 portion near the top and/or the bottom surface is palladium. There is 

 a family of combs to be welded, depending on the number and type of 

 contacts required by the code of relays into which each comb is assem- 

 bled. Unlike the twin wire combs, wires which do not require contacts 

 are left in the single wire combs, primarily to facilitate reading terminal 

 locations during wiring into equipment. All top palladium contact 

 surfaces must be located in the same plane across the 12 wire positions 

 of the comb within a tolerance of dzO.002 inch to meet design reciuire- 

 ments. In addition, other dimensions for locating the precious metal 

 must be held to close limits for reasons of precious metal economy. 



The contact blocks for the wire comb are welded to the wire ends by 

 the automatic percussion welder. Fig. 11, which is a unit in an automatic 

 welding and forming line, Fig. 12, similar to but not identical with the 



FORMED TERMINALS 



THE FOUR CONTACT 

 CONDITIONS 



(l) NO CONTACT 



(2) MAKE- PA 

 CAP 



[3) BREAK -PA 



CAP DOWN 



(4) TRANSFER -PALLADIUM 

 CAP UP S. DOWN 



0.042"-: 

 0.010" 



O.IOI" 



K- I C 



f^ 



^ 



^ I I <J„ 0.040" 



0.010" / '7i-T3 SILICON COPPER 



PERCUSSION 

 WELD 



LLADIUM f^i>f^- 



LLADIUM f>r:^ 

 OWN y/ 



0.040" 



Fig. 10 • — Single-wire coml) with percussion welded contacts. Also view of wire 

 spring relay. 



