. The Bell System technical journal . esides, the coil is generally womid tightly on the relaycore. These factors, to a large extent, preclude lead breakage. With thecellulose acetate filled coil it is desirable to bring the winding wire di-rectly to terminals on the terminal spoolhead to which the end of thecoil is later bonded. Since the filled coil must slide loosely over the corefor assembly reasons, it can have a small lateral motion at the non-ter-minal end. To eliminate this movement a motion limiting washer hasbeen provided to fit snugly over the core and which is bonded to thisend of
. The Bell System technical journal . esides, the coil is generally womid tightly on the relaycore. These factors, to a large extent, preclude lead breakage. With thecellulose acetate filled coil it is desirable to bring the winding wire di-rectly to terminals on the terminal spoolhead to which the end of thecoil is later bonded. Since the filled coil must slide loosely over the corefor assembly reasons, it can have a small lateral motion at the non-ter-minal end. To eliminate this movement a motion limiting washer hasbeen provided to fit snugly over the core and which is bonded to thisend of the coil.^ The washer and the way it is used is illustrated in In assembly, the thin cellulose acetate faced phenol fibre washer andthe non-terminal spoolhead are forced over the knurl on the core and thewasher is bonded to the end of the coil. The tight fit of the washer onthe knurl is the feature that pre\ents lateral movement of the coil. Thereis always some slight shrinkage of the cellulose acetate filled coil in the KNURL. Fig. 5—Relay coil employing a molion limiting washer to prevent lead breakage. 986 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 longitudinal direction, but the washer can move with the coil, althougheliminating lateral movement. Use of this washer has practically elimi-nated fatigue lead breakage. CONTACT RELIABILITY Since the opening and closing of contacts are the prime objectives ofa relay, it is extremely important that the contacts themselves are madereliable. To realize these objectives, several factors should be taken intoconsideration. First is the contact material. While much could be saidregarding the behavior of contact metals, space does not permit morethan a brief treatment. The contact should maintain reasonably low re-sistance and under the environment in which it is used, be able to with-stand the erosion. Electrical resistivity of most metals is low enough tobe satisfactory from the resistance standpoint, but unfortunately^
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