US1998549A - Insulator construction - Google Patents

Description

April 23, 1935. G. w. LAPP AL 1,998,549

INSULATOR CONSTRUCTION Filed Feb. 15, 1934 INVENTORJ rower WI 3 YMA 256a; AT ORNEY Patented Apr. 23 1935 PATENT OFFICE msum'roa coss'rauc'nos Grover W. Linn and Ralph L. Jenner, Le Roy, N. Y., minors to Lapp Insulator Company Inc., Le Roy, N. Y., a

corporation of New York Application February 15, 1934, Serial No. 711,386

10 Claims.

This invention relates to insulators and more particularly to compression insulators designed for resisting compressive stresses.

An object of the invention is to provide an 5 insulator of improved design which, for a given quantity of material, will have substantially greater compressive strength than those heretofore known.

Another object of the invention is to provide an insulator which, when subjected to too great stress, will provide warning of failure in ample time before it fails, so that the warning may be observed and the insulator may be replaced. A

A further object is the provision of a generally improved and more satisfactory insulator, capable of withstanding great stresses in proportion to its size and weight.

To these and other ends the invention resides in certain improvements and combinations of parts, all as will. be hereinafter more fully described, the novel-features being pointed out in the claims at the end of the specification.

In the drawing:

Fig. 1 is a diagrammatic view partly in eleva- 25 tion and partly in vertical section illustrating an 50. its tensile strength. This causes longitudinal insulator constructed in accordance with one embodiment of the present invention;

Fig. 2 is a view of a slightly different form of insulator according to the present invention;

Fig. 3 is a view of still another form of insulator, and

Fig. 4 is a vertical section illustrating another embodiment of the invention.

The same reference numerals throughout the several views indicate the same parts.

Insulators are usually made of a material which has substantially greater compressive strength than tensile strength. This characteristic is exhibited by all or practically all of the ceramic materials, among which may be mentioned specifically porcelain and glass, which are frequently used in insulator constructions.

When a ceramic material or other material having substantially less tensile strength than compressive strength is subjected to compression of high degree, it frequently fails or breaks, not because-its compressive strength is exceeded, but because the longitudinal compressive force produces a lateral or transverse tensile strain in the material, which stresses the material beyond cracks in the material, and ultimately further breakage or failure of the material.

The ratio of the lateral or transverse tensile 56 strain produced by thelongitudinal ve strain to this longitudinal cpmpressive strain which produces it, is known 'in mechanics as Poissons ratio, and for porcelain and similar ceramic materials this ratio has a value of about one-fifth or 0.2. Good grades of porcelain have a compressive strength often running as high as eighty thousand pounds to the square inch, or higher, whfle the tensile strength thereof is of the order of about five to eight thousand pounds per square inch. Consequently when subjected to compression, a piece of such material will ordinarily fail due to lateral or transverse tension long before the compressive strength limit is reached. In an isotropic, material, such as porcelain, stress is proportional to strain both longitudinally and laterally. In all cases, the stress is equal to the modulus of elasticity times the strain. v f

As a practical matter, it has heretofore been thought that an insulator of porcelain or other ceramic material, of conventional' shape, could not safely be subjected to compressive stress of more than about twenty-five thousand pounds per square inch, without danger of cracking and ultimate failure due to lateral or transverse tension stress set up as above mentioned,

With insulators made according to the present invention, on the contrary, the limit has been very materially raised and in some case'smore than doubled, so that thepresent invention constitutes an important contribution to the art and permits the same amount of insulatingmaterial, when properly shaped according to the present invention, to carry a materially greater load than heretofore.

The present invention involves the shaping of the body of insulating material so that its sides curve inwardly or may be said to be bowed inwardly. Consequently a compressive force exerted longitudinally or axially of the insulating body tends to bend the sides still further inwardly, and this tendency counteracts or counterbalances the circumferential tension stress which might otherwlsecrack the material, due to its low tensile strength. The inward curving *of the side walls in accordance with this invention may not counterbalance the radial tension stresses produced in the material by the longitudinal compressive stress, but it does coundone by the present invention, then the insulator is made materially stronger, even though radial tension may not be counterbalanced t0 any marked degree.

This action may be readily visualized if one will consider a barrel madeup o1. staves curved inwardly instead of in the conventional outward manner, so that the barrel is of smaller diameter at its middle than at its ends. Then if one presses downwardly on the end of the barrel, it is obvious that the downward pressure on any stave will tend to bow this stave still further inwardly, and will set up a circumferential com-.

pressive stress between the staves.

This simile furnishes a likely explanation of the reason for the greatly improved result obtained by curving the sides of the insulator body inwardly according to the present invention. Whether or not this reason is correct, and whatever the true reason may be, the fact remains that insulators constructed according to the present invention have been actually tested and tried out under operating conditions and are found to give better service and to have materially greater compressive strength than in- I sulators of similar size made according to prior designs.

It can be demonstrated mathematically, taking Poisson's ratio for the material to be used as 0.2, that for a theoretical thin membrane, the radius of curvature of the longitudinal curve of the side walls should be approximately five times the radius of transverse curvature at any point under consideration. As a practical matter, more or "less departure from this theoretical radius may be advisable, as indicated by experience and the skill of the designer.

This invention of curving the side walls of the insulator body inwardly may be applied, of course, to insulators of various shapes as well as of various materials. It is particularly useful when dealing with materials having considerably less tensile strength than compressive strength, such as porcelain or other ceramic materials, and ordinarily it is applied to shapes which are in general frusto-conical or cylindrical. The outer surfaces of such shapes may be conveniently described as surfaces of revolution formed by the revolution of a curved line about an axis lying on the convex side of the line. According to the above mentioned theoretical relationship between the curvatures, the radius of curvature of the curved line at any point would be approximately five times the distance of that point from the axis 'of revolution, although as stated this theoretical curvature may'frequently be modified in practice.

, In Fig. 1 of the drawing there is shown one arrangement suitable, for example, in supporting a heavy mast or other member Ill. The structure includes two insulators II and I2 which may be substantial duplicates of each other, each being shaped generally as the frustum of a hollow cone, but with its sides curved or bowed inwardly, as plainly shown in the drawing. In other words, each insulator may be described as having its outer surface concave in a direction lengthwise of the insulator (or in a direction along a plane passing through the axis of the insulator) while it is convex in a direction around the insulator (or in the direction of a plane perpendicular to the axis of theinsulator) The mast l0 may be bolted-to a base member l6 of cast or forged metal which is provided with a suitable socket for receiving one end 0! the upper insulator The lower end 01 the upper insulator II has the cap i8 interengaged with and resting upon a cap H at the top of the lower insulator I2, while the lower end of the insulator |2 rests in the base 20 which may be similar to the base l6 and which is mounted on any suitable foundation 2|. Cement or other suitable substance 22 may be interposed between the ends of the insulators and the caps or bases in which they fit.

An arrangement of this kind is intended to be subjected at all times to compressive stress. Due to the inward curving of the sides of the two insulators, as shown, the load which may be safely carried is materially increased over what it would be if the sides were of conventional straight or strictly conical shape. If the mast or other structure Ill sways or tilts slightly, the cap I8 may roll slightly on the cap l9, but the insulators still remain under compression at all times.

In Fig. 2 of the drawing there is shown a slightly different form of construction intended for resisting tension stress, although the insulating body itself is always under compression. The

insulating body 30 may be of frusto-conical shape similar to the bodies ii and I2 above mentioned, and is similarly provided with a cap ll of cast or forged metal or the like, through which passes a tension rod 32. The base of the insulator 30 is held in a socket 33 fixed to or formed integral with a yoke 34 which has an eye 35 at its upper end. It is seen that if the eye 35 be pulled upwardly and the rod 32 be pulled downwardly, as would be the case when resisting tension, the insulator 30 is placed under compression and acts to resist the tension in the members to which it is connected. In this example, as in the previous one, the insulator is of generally frusto-conical shape, with its sides curved inwardly.

In Fig. 3 there is shown a slightly diiferent arrangement which is adapted to resist both compression and tension, but with the insulating bodies themselvesalways in compression. Here there are two insulating bodies 4| and 42 which may be of the same shape as the bodies |2, and 30, above mentioned, placed base to base in a metal base member 43, cement or other suitable material 44 being employed in the socket in known manner. Each of the insulators has a cap 45 as shown. A washer 46 rests on the upper cap and downward pressure on this washer causes compression of the upper insulator 4|, which is transmitted to the socket 43 and from it to any suitable support such as the arms 48 securely mounted on a base. Thus the upper insulator 4| takes care of downward or compressive stress.

A rod 49 passing through both insulators is provided with a nut or other fastening means 50 underlying the bottom cap 45. Upward tension on the rod 45 does not affect the upper insulator 4| but places the lower insulator 42 in compression. In this manner, both compressive and tension stress are provided for, the former being resisted by the insulator 4| and the latter by the insulator 42.

In Fig. 4 there is shown by way of example an insulator 55 of generally cylindrical form, with its sides curved or bowed inwardly in a longitudinal direction. The ends of such an insulator may be mounted in socket members 56 and 51, through which compressive stress may be applied to the insulator.

the exterior surface of its load carrying walls The preferredmaterial of which the insulators are made is porcelain, and extremely satisfactory results have been secured with this material,

' shaped according to the present invention. In-- sulators'have been produced which will safely stand approximately double the amount of compressive stress which insulators of the conven tional straight sided shape will stand.

Another advantage of insulators shapedaccording to the present invention is that when cracks occur in an insulator, they are not followed shortly by failure of the insulator as a whole, as is frequently the case with prior types of insulators, but on the contrary these cracks serve as warnings or danger signals of excessive load, while the insulator remains in this cracked condition and continues to carry its load for a long period of time. When the cracks are observed, there is'ordinarily still ample time for replacement of the insulator before it fails as whole. This is not true of insulators with straight sides or outwardly curving sides, as such insulatorsusually fail and break down completely as soon as cracks occur.

Insulators constructed according to the present invention are intended for use wherever electrical insulation is desired under mechanical loading, whether of high or low electrical frequency.

When the shape of the insulator is referred to, both in this specification and in the accompanying claims, it is to be understood that the shape of the main load-carrying part of the insulator body is meant. Petticoats or other flanges or protuberances may obviously be applied as is frequently done, to either the exterior or the interior surfaces of the body, or to both, without departing from the spirit of the invention. Those is intended to cover all variations and modiflca-. 'tions thereof falling within the spirit of the invention or the scope'of the appended claims.

skilled in the art will readily understand that if petticoats were applied-to the exterior surfaces of any of the insulators shown in the acompanying drawing, the outward appearance and apparent shape of the insulators would thereby be materially changed, but the main load-carrying parts of the bodies would nevertheless still be inwardly curved in accordance with the present invention.

While certain embodiments of theinvention have been disclosed, it is to be understood that the inventive idea .may be carried out in a number' of ways. This application is, therefore, not to be limited to the precise details described, but

We claim: 1. An insulator for resisting compression loads,

comprising a base member having means forming a socket, a second member spaced from said base member and also having means forming a socket, a compression resisting body of dielectric material interposed between said base member and said second member and extending into the sockets therein, said body having load carrying securing said ing with the sockets therein, said body having substantially in the shape of a surface of revolution formed by revolution of a curved line about an axis on the convex side of the curved line.

3. An electrical insulator for resisting compression loads, comprising asocket member, a.

second socket member, and a dielectric body interposed between said socket members and adaptmembers, said body being of generally cylindrical shape having its sides curved inwardly in the direction of the axis of the cylinder.

5. As a new article of manufacture, an electrical insulator for use in resisting compression stress, said insulatorcomprising a body of material having substantially less tensile strength than compressive strength'and having inwardly curved sides, means forming a socket for receiving a portion of said body and adapted to apply pressure to said body in a direction longitudinally thereof, and other means forming a socket for receivinganother portion of said body spaced from the first mentioned portion and adapted to resist a longitudinal thrust from said body.

'6. An electrical insulator for resisting compression s n comprising a hollow body of material having tantially less tensile strength than compressive s ength, the side walls of said body being bowed wardly so that when said body is subjected to compression stress said side walls will tend to. bend inwardly and will tend to resist internal tension-stress caused by said compression stress, a metallic member for thrusting. against one end of said hollow body, and another metallic member for thrusting against another portion of said hollow body.

'7. A- compression insulator comprising a cap and a base against which pressure may be applied, and a body of ceramic material interposed between said cap and said base and having its side walls bowed inwardly.

8. A' compression insulator comprising a cap and a base against which pressure may be applied, and a body of ceramic material interposed between said cap and-said base, said body having its exterior walls shaped concavely in the direction of any plane passingthrough the axis of compression' and shaped convexly in the direction of any plane perpendicular to said axis of compression. I 1 9.. A compression insulator comprising a metal lic cap, a metallic-base, and a dielectricsbody 10. A compremion insulator comprising a metallic cap, a metallic base, and a dielectric body of ceramic material of generally cylindrical shape interposed between said-cap and said base and having its sides curved inwardly in the direc- -tionof'theaxisofthecylinder.-

' .GROVERW.LAPP. RALPHLJENNER.

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