1054 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



welded to the armature. The special features consist largely of variations 

 in finish and material which do not greatly affect the manufacturing 

 processes. The only added parts are the damping members. These are 

 molded from soft but stable polyisobutylene with grooves to receive the 

 twin wires. One damper is attached to each side of the shelf provided on 

 the stationary wire assembly. The twin wires pass through the grooves 

 and are cemented in place. As shown in Fig. 25, these dampers reduce 

 the vibration of the twin wires between the card and the molded section 

 at the rear, thereby reducing the slide between the wires and the card. 

 Early designs of relays indicated that wear between the twin wires 

 and the card was excessive and that changes in materials would not 

 produce the improvement needed for very long life, particularly with 

 high-speed relays. A fundamental study^" of the conditions which cause 

 wear was made and it was found that reduction of the sliding motion 

 between the wires and card to 0.001 inch or less was necessary to sub- 

 stantially eliminate such wear. The AF relay meets this requirement. The 

 necessity for such a requirement will be better understood when it is 



uj 90 



80 



y 20 



0.004 0.008 0.012 0.016 



WEAR OF THE CONTACTS AND SOME 

 OTHER RFi AY PARTS IN INCHES 



Fig. 23 — Contact forces on the AF relay remain almost constant with wear, 

 while U relay contacts lose force rapidly. 



low. P. Mason and S. D. White, "New Techniques for Measuring Forces and 

 Wear in Telephone Switching Apparatus", Bell System Tech. J., May, 1952, p. 469. 



