US2431839A - Electrical insulator - Google Patents

Description

Dec. 2, 1947.

ELECTRICAL INSULATOR Filed Oct. 27. 1944 ENTOR Rawson Ei. tank R. E. STARK 2,431,839

v- )d y Patented Dec. 2, 1947 ELECTRICAL INSULATOR Rawson E. Stark, Greensburg, Pa., assignor to Stupakoi Ceramic & Manufacturing Co., Latrobe, Pa., a corporation o! Pennsylvania Application October 27, 1944, Serial No. 560,570

2 Claims. (Cl. 174-140) 'I'his invention relates to electrical insulators and especially those used in high frequency electrical systems.

Insulators used in electrical work commonly comprise a body of insulating material into or through which a metal object or conductor is entered or passed. For example, a ceramic insulator may have a hole therein which is threaded to receive a metal fixture that constitutes an anchor or support for an electric conductor. Frequently the contact between the threads of the metal fixture and the insulation is imperfect, leaving small air spaces between the insulator and the metal. Often the hole in the insulator is longer than the bolt or screw, leaving an air pocket inside the insulator.

If the insulator is used in a high frequency circuit or a high voltage circuit, ionization of the air in such spaces or cavities will occur, with a corona discharge radiating from the metal into the air. This results in the disintegration of the metal fixture and the straining and cracking of the insulator.

It has heretofore been known to eliminate this diiiiculty by pouring molten lead into a threaded cavity in the insulator and then tapping a threaded hole into the body of lead into which the metal xture in turn is screwed, but this is relatively expensive, requires two thread forming operations, and requires large dimensions for the insulator to accommodate the lead.

The present invention has for its object the elimination of corona discharges in such circumstances by cheap and eicient means and methods. According to my invention, the insulator is constructed as heretofore to receive the conductor or metal xture,

Thereafter a metal nlm is painted or sprayed over the interior of the cavity or threaded surface which receives the conductor or fixture. Silver paint is preferably used, as it may be deposited as a thin lm and will spread evenly over the ceramic surface. It may be iired at a low temperature to flx or set it.

The invention may be more fully understood by reference to the accompanying drawings in which:

Figure 1 is a view partly in section and partly in elevation of one form of insulator embodying my invention;

Figure 2 is a similar view of another form; and

Figure 3 is a view, partly in section and partly `in elevation of a through-wall insulator such as is used for the running out of'an aeroplane radio aerial during flight.

Referring to Figure 1 of the drawings, there is shown a simple insulator comprising a conven-y tionally shaped body 2 having a threadedcayity 3 in its upper end into which is screwed a metal conductor supporting ixture or pin 4 on which is carried a conductor 5. The interior of the cavity 3, including the threads, is covered with a thin film of metal, painted or sprayed and preierably fired thereon. This lm of metal forming a continuous lining in the cavity is designated 6. It is, of course, in intimate contact with the ceramic so that there is no air space between it and the ceramic insulator. Being in direct conducting contact with the fixture 4, it has, at any instant, the same potential as the iixture. Hence there can be no corona discharge between the fixture and the metal lm, and therein being no air space between the lm and ceramic insulator, no corona discharge occurs between the film and the insulation.

In Figure 2 the insulator 'I has a fixture 8 screwed into each end thereof. Both cavities 9 that receive the xtures are metalized, as described.

It will be seen that the insulator can be formed in the usual manner and the threads Cut therein after which the metalizing is effected and the film of metal is so thin that it does not appreciably alter the dimensions of the threads.

In Figure 3, the insulator is for a through-wall conductor. In this figure, I0 is a wall, as for example the shell of an aeroplane fuselage, It has a large opening Il therethrough. The insulator comprises two flanged substantially hemispherical bodies or shells I2, one on each face of the wall. There is a tubular insulator I3 passing through the opening I I and abutting at each end against one of the shells I2, each shell having an opening I2a that is in alignment with the end of the tube. Metal bushings I4 are passed through these openings and screwed into the tube I3 to hold the assembly together. The bushings I4 have a longitudinal bore so that a conductor, such as a retractable aerial I5 may pass through the insulator.

In this case, not only the threaded interior bore of the insulator I3 is metalized, but the entire interior of the tube is metal coated, as may also be the openings I2a in the insulator shells I2. Thus complete protection from corona discharge, even in a multipart insulator may be provided by my invention. Not only is the invention of advantage in eliminating corona, but it improves the Q factor of ultra-high frequency circuits 'because in such circuits, the elimination of insu- 3 lation with a poor power factor directly renects itself in the perfomance o! the circuit, and the silvering or otherwise rendering conductive insulators as indicated is beneilcial for this reason.

As previously indicated metal paints, such as silver paint of silver and lacquer may be used, the lacquer being burned out after the 111m has been formed, such materials being well known and forming no part of my invention.

While I have illustrated and described certain specific embodiments of my invention, it will be understood that this is by way of illustration and that various changes and modifications are within the contemplation of my invention, and that the specific forms of insulators are merely typical embodiments. Y

I claim:

1. An insulator for a through wall conductor comprising opposed bodies of insulating material adapted to be positioned on opposite sides of the wall, an insulating sleeve adapted to pass through the wall and having its ends adjacent said iirst two bodies, a metal bushing screwed into each end of the sleeve and holding the opposed bodies in assembled relation, the entire interior of the sleeve being covered with a thin conducting film thereover extending continuously therealong, the metal bushings ,being screwed into the sleeve where it carries such a 111m so as to make contact with such ilm, and a conductor passing through the bushings and the said sleeve.

2. An insulator for a through wall conductor comprising opposed cup-like bodies and insulat- 4 ing material positioned on opposite sides of the wall, each having a central opening therein, an insulating sleeve passing through the wall and having its ends abutted against said first two s bodies, a metal bushing entered in the opening of each of said vopposed bodies and screwed into the sleeve for holding the parts in assembled relation, the interior of said sleeve having a conducting illm over the entire interior thereof, the metal l0 bushing making contact with said 111m, and a conductor passing through the said bushings in the sleeve.

RAWSON E. STARK.

l5 REFERENCES CITED t The following references are of record in the ille of this patent:

UNITED STATES PATENTS zo Number Name Date 2,118,795 Littleton May 24, 1938 2,273,135 Ohnesorge et al. Feb. 17, 1942 2,133,768 Hostetter et al Oct. 18, 1938 2,274,955 Dykstra et al. Mar. 3, 1942 z5 1,205,971 Buschetti Nov. 28, 1916 1,516,585 Austin Nov. 25, 1924 227,370 Man May 11, 1880 1,997,666 Whisler Apr. 16, 1935 so FOREIGN PATENTS Number Country Date 340,371 Great Britain i931 233,880 Great Britain 1925

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