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July, 1921 Westinghouse Strain Insulators Section G-A--Part III

WOOD STRAIN INSULATORS

In the production of wood strain insulators the Westinghouse Company claims first position in points of quality in- put and quantity out-put. The eyes, clevises and tapped fittings are malleable iron sherardized, with the metal properly distributed to insure maximum strength and adaptability.

One of the most important considerations in the design of these insulators is the angle at which the malleable iron caps are swaged on, which angle must be exactly parallel to the reverse cone seat of the insulator proper. We have determined conclusively that there is only one angle for each diameter of insulator which gives the maximum holding power. Obviously, the more this angle is increased the greater is the disturbance to the metal under the swaging process, while on the other hand, the more the angle is reduced the less becomes its resistance to the action of the cone.

Westinghouse wood strain insulators are made of straight-grained, well-seasoned, air-dried, selected hickory. After being accurately turned to size, the sticks are oil-impregnated and given two coats of transparent insulating varnish which makes possible an inspection of the grain of the wood. The end castings are pressed tight on the stick, giving a watertight joint. Great care is taken so that the pressure not great enough to injure the wood.

Every wood strain insulator is subjected to a test load before shipment so as to eliminate defective wood or end- castings. The end-castings are sherardized and are strong enough to part the best hickory obtainable.