US1988155A - Insulator - Google Patents

Description

F. G. BOVARD INSULATOR Filed Oct. 24, 1931 m w m I O 5% Rd m mw R N/ 0 w m Patented Jan. 15, 1935 UNITED STATES PATENT OFFICE INSULATOR Application October 24, 1931, Serial- No. 570,794

4 Claims.

This invention relates to electrical insulators and especially to insulatorsof the suspension type, and'has-for one of. its objects the provision of an insulator which shallv have high mechanical strength without sacrificingitsinsulating properties. A further object. is to provide an insulator in which the load will be carried by the dielectric member chiefly in compression without undue tension or shear.

A further object is to provide an insulator pin which will automatically accommodate itself to variations in load and temperature.

A further object is to provide a. device of the class named which shall be of improved construction and operation.

Other objects and advantages will appear from the following description.

The invention is exemplified by the combination and arrangement of. parts shown in the accompanying drawing and described in the following specification, and it is more particularly pointed out inthe appended claims.

In the drawing:

Fig. 1 is a vertical, sectional viewof an insulater showing one embodiment of the present invention applied thereto.

Figs. 2m 5 inclusive are part elevations and part sections of modifications of the insulator pin.

Fig. 6 is a. plan view of the pin shown in Fig. 3.

In the drawing the numeral 11 designates the dielectric member of an insulator supported by a cap 12 secured to the member 11 by cement 13, in a well-known manner. The insulator 11 is provided with a central recess in which a. pin 14. is secured by cement 15. The surface of the pin 14 in contact with the cement 15 is preferably coated, as shown at 16, with a yielding material such as bitumen, wax or other material of a yielding nature which can be applied to the surface of the pin in a. well-known manner. The bearing. surface of the pin 14, which supports the load on the insulator, is divided into two portions, the lower, portion 1'7 being gradually flared outwardly, and an upper portion 18 which is more abruptly flared. The portion 17 may be in the form of an inverted-conical surface, as shown in Fig. 5, or may have the elements of the surface thereof slightly curvedinwardly, as in Figs. 1, 2, 3and 4.

In. order to prevent concentration of stress in the dielectric member, it is. desirable to have the force transmitting. surface of the pin extended over a considerable area. This result is secured by. the gradually flared portion 17. If the entire bearing surface were tapered at this angle, however, the wedging action would be excessive, tending to burst the dielectric member. When the insulator is subjected to temperature changes, the dielectric member and the pin will expand and contract unequally, due to differences in the coeflicient of. expansion for temperature changes. If the pin should contract, it would tend to move downwardly in its seat and the same effect would be produced. by a heavy load on the pin. If the conditions then should change and the pin expand, there would be a pressure developed, tending to burst the insulator.

With. the present construction, this result is prevented by the wider flared surface 18 which will restore the pin to its original position when the pin tends to expand or the load on the pin is decreased. The coating of yielding material on the surface 18 will permit the pin to be drawn downwardly sufficient to cause the surface 1'7 to transmit its load to the cement over the entire surface. By providing the two bearing surfaces at different angles, the load is therefore distributed over a large area but the wedging effect of the steeply tapered: portion is prevented from becoming excessive by the more widely flared surface 18.

Another beneficial result secured by the combination in the two bearing surfaces is that the direction of the resultant force in the dielectric member may be controlled so as to give the resultant any desired direction within certain limits. If a wider flared bearing surface 18 alone were used, the resultant force would be directed downwardly at a rather acute angle to the axis of the insulator so that the line of the resultant force would fall below the lower edge of the cap 12, and the porcelain would be placed under tension. If the surface having a steep angle alone were used, the resultant would be too nearly horizontal. and there would be a tendency to burst the dielectric member.

If. an attempt were made'to employ a conical surface having a uniform taper and this were made sufliciently steep to bring the resultant force within the cap, the pin would wedge into its seat and would not return when the conditions were changed but would tend to stick in the socket. Byproviding a bearing surface having different degrees of angularity, it is possible to secure the results of an extensive bearing surface without producing too great a wedging action upon the insulator and, at the same time, to control the direction of the resultant to accommodate the forces to capsof practically any character and bring the resultant sothat it falls within the cap and is taken up by the metal cap rather than by the insulator; the dielectric member being placed merely in compression between the pin and the cap.

In the form of the invention shown in Fig. 1, the pin 14 is bored out, or otherwise formed, with a central opening 19. The load on the pin will be transmitted to the cement over the surface above the point of minimum diameter of the pin, and the cross section of the shell 20 at this point is preferably approximately the same as the neck of the pin 21 so that the stress per unit area in the shell 20 will be substantially the same as that in;

the neck 21. For mechanical strength, the portion of the pin between the points 20 and 21 might have a substantially uniform diameter but it has been found that by enlarging the'pin at the point where it enters the opening in the dielectric member,better electrical properties are secured. Since the diameter of the pin increases from the point 20 upwardly, the thickness of the shell may be gradually decreased and yet maintain the .same sectional area. In fact, since a portion of the load is gradually transmitted tothe cement above the point 20, it is possible to decrease the total sectional area from the point 20 upwardly without increasing the stress per unit area. The top of the opening 19-may be left open or closed by a disc 22. In some cases, it may be desirable to form the disc 22 of a metal having a low coefiicient of expansion substantially the same as that of the porcelain. Invar metal may be used for this purpose so that when the temperature ofthe insulator rises, the tendency to expand and burst the insulator at the top of the pin is decreased.

It has been found advantageous in some cases when the loads are sufficiently heavy to produce the required operation to curve the elements of the surface 17 inwardly so that this surface is not a true frustrum of a cone but is slightly concave. Where this is done, there is a. tendency for the curved elements to straighten under the force of the load, which produces an outward pressure, and thus tilts the resultant force upwardly, assisting in keeping the resultant above the lower edge of the cap. This is especially true where the shell of the pin is slotted, as shown at 23 in Fig. 3.

The pin in Fig. 2 is similar to that in Fig. 1 except that there is no marked division line between the bearing surfaces of different angularity but instead, the bearing surface 26 is curved throughout its entire length; the amount of ourvature being increased at the upper part 27 to secure the effect of the wider flaredportion 18, shown in Fig. 1. In Fig. 2 the upper end of the pin is left open. It will be noted that Fig. 3 is provided with a portion 30 below the flared portion 26 which is cylindrical. It is apparent that no load will be transmitted to the cement by this cylindrical portion and the position at which the load is transmitted is thus raised inside of the porcelain member. The height at which the load is transmitted may be regulated by regulating the length of the cylindrical portion 30. I

In the modification shown in Figs. 3 and 6, the bearing surface 26 is similar to that of Fig. 3 but the upper end of the pin isslotted, as shown at 23, and is provided with a disc 22 for preventing the upper end of the pin from closing inwardly when the load is applied to the insulator. The slots 23 add resiliency .to the shell of the pin so that the tendency to straighten under the load is in creased and the resiliencyfor overcoming the tendency to burst the insulator is increased.

The form of pin shown in Fig. 4 is similar to that in Fig. 1 except that the upper bearing surface 27 is more widely flared than in Fig. 1. In fact, the bearing surface 2'7 could be made substantially horizontal if its lower face were sufiiciently coated to permit the steeply tapered portion to transmit a sufiicient portion of the load to keep the resultant above the lower edge of the cap 12.

In Fig. 5 the steeply tapered bearing surface 17 is made in'the form' of a frustruin'of a cone, and its, elements are not curved inwardly as in some of the other figures.

I claim:

1. .An insulator comprising a dielectric member having asupporting boss provided with a recess therein, aeap surrounding said boss and having a tapered bearing surface for supporting said dielectric member, a pin disposed in said recess and having a tapered bearing surface offset inwardly of said recess relative to the plane normal to the axis of said pin and passing through the upper edge of the bearing surface of said cap, the portion of the outer surface of said pin in horizontal registration with the bearing surface of said'cap being concave longitudinally of said pin, said pin being hollow to provide relatively thin walls which tend to straighten and produce outward pressure under the force of the load on said pin to oppose the inward pressure exerted by the bearing surface of said cap and cement filling the space about said pin in said recess and being unbon'ded to said '2. An insulator comprising a dielectric member having a boss thereon, a cap surrounding saidboss and having a tapered bearing surface, cement interposed between said cap and boss for securing said cap to said boss, said boss having a recess therein, a pin disposed in said recess, cement surrounding said pin for retaining said pin in said recess, said pin having a tapered bearing surface comprising a zone disposed at a wide angle relative to the axis of said pin, and a second zone disposed at a more acute angle relative to the axis of said pin, said bearing surface being unbonded to said cement to permit movement of said pin in the direction of its axis in said recess, the wide angle bearing zone of said pin serving to shift said pin in said recess to avoid excessive bursting force due to expansion of said pin, said pin being hollow and having inner reinforcement adjacent the wide angle tapered portion of its bearing surface but having the walls thereof free to yield radially adjacent the more acute angle portion of said bearing surface.

3. An insulator comprising a dielectric member having a recess therein, a cap for supporting said dielectric member, a pin disposed in said recess and cement surrounding said pin for retaining said pin in said recess, said pin being hollow and having a longitudinally concave bearing surface unbonded to said cement and tending to straighten under the force of the load on said pin to exert outward pressure on saidcement but free to yield inwardly to avoid excess pressure when said pin expands.

4. An insulator comprising a dielectric member having a recess therein, a pin disposed in said recess and cement surrounding said pin for retaining said pin in said recess, said pin being unbonded to said cement and having an inner tapered bearing surface disposed at a wide angle relative to the axis of the pin, and a second bearing surface disposed at a more acute angle relative to the axis of the pin, said second bearing surface extending a greater distance longitudinal- 1y of said pin than said first bearing surface and being longitudinally concave, said pin being ho1- low to provide relatively thin side walls which tend to straighten under the force of the load so 5 that the concave portion thereof exerts outward pressure on said cement, said pin having an internal reinforcing member in registration with the wide angle bearing surface thereof but being unsupported inwardly adjacent the acute angle portion of the bearing surface thereof to prevent excessive pressure on said acute angle portion.

FLOYD G. BOVARD.

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