US 3358073 A
Description (OCR text may contain errors)
Dec. 12, 1967 Filed March 5, 1966 J- R. GAMBLE PORCELAIN CASING BEAD CONSTRUCTION 5 Sheets-Sheet 1 FIG. 5.
WiTNESSES: j W
INVENTOR v James R. Gamble ATTORNEY Dec. 12, 1967 J. R. GAMBLE PORCELAIN CASING BEAD CONSTRUCTION 3 Sheets-Sheet 2 Filed March 5, 1966 FIG-9.
Dec. 12, 1967 J. R. GAMBLE PORCELAIN CASING BEAT) CONSTRUCTION Filed March 3, 1966 3 Sheets-Sheet 5 FIG. 6
United States Patent 3,358,073 PORCELAIN CASING BEAD CONSTRUCTION James R. Gamble, Unity Township, Greensburg, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of lennsylvania Filed Mar. 3, 1966, Ser. No. 531,598 6 Claims. (Cl. 174-137) ABSTRACT OF THE DISCLOSURE To enable a much better securement of a metallic mounting flange to the end of a porcelain casing, the end of the porcelain casing has a formed bead construction of particular dimensions and curvatures. In more detail, the bead height (H) should be between 0.06 inch and 0.12 inch, the bead spacing (S) between 0.38 inch and 1.00 inch, and the radius of curvature (R of the individual beads should be between 0.06 inch and 0.15 inch. The curvature (R extending from the crest of each bead to the root thereof should vary between 0.12 inch to 0.38 inch. The bead curvature (R should have the following relationship with respect to the bead height (H): R 517.
This invention relates generally to porcelain casing bead construction and, more particularly, to an improved casing bead construction for a porcelain casing adaptable for use in lightning-arrester applications, for example.
A general object of the present invention is to provide an improved bead construction for a porcelain casing which greatly enhances the effective strength of the joint between a porcelain casing and an associated metallic mounting flange ring.
A further object of the present invention is to provide an improved bead construction for a porcelain casing which will eliminate cracking between adjacent beads and, in addition, will reduce costs of manufacture by eliminating rejects, and generally will facilitate the manufacture of sound, high-quality, porcelain casings.
Still a further object of the present invention is the provision of an improved casing bead construction which is adaptable to high-volume production, and which will diminish the possibility of operator error and, in addition, will obviate the need for additional secondary tooling. Still a further object of the present invention is the provision of an improved end construction for a porcelain casing which will result in a secure attachment of the associated metallic flange ring.
In order to attach a flange to a porcelain cylinder with Fortland cement or sulphur base cement, it is necessary to roughen the outer surface of the porcelain in the area of flange attachment. The most common method of accomplishing this is to use a sanded surface attached to the porcelain surface with glaze.
There are some applications where the use of a sanded surface is not practical and for these applications, previous solutions have been the use of a knurled surface, ground grooves or closely spaced, sharply defined beads that approximated the appearance of the sand band. These closely spaced, sharply defined beads were the most common.
All of these solutions suffer from one serious defect in that they are sources of stress concentration. Stress concentrations occur at points on the surface where there is some sort of discontinuity. The closely spaced, sharply defined beads, in particular, have an adverse effect on the load-carrying ability of a porcelain assembly. They introduce sources of high stress concentration in several ways: (a) Their configuration, using very sharp radii and abrupt changes in section, result in sharp discontinuities which increase the magnitude of stress concentration. (b) During drying of a porcelain part, shrinkage takes place. These sharp, closely spaced beads or projections will dry more rapidly than adjoining heavy sections. A tensile stress results which tends to cause cracks at the spot where the contrasting sections meet. (c) During machining of the porcelain part, these small projections are relatively fragile and are subject to small tears or cracks that result from the loads applied during machining.
These sources of stress concentration greatly affect the load-carrying properties of brittle materials such as porcelain. The final fraceture of brittle material is the direct result of a localized failure. This localized failure is most likely to occur at some point of stress concentration. In order to reduce the degree of stress concentration that results from discontinuities, it is necessary to blend as gradually as practicable so as to alleviate the sharp discontinuities.
According to one aspect of the present invention, a bead construction is provided having particular dimensional limits, and resulting in a stress-free attachment to the associated metallic mounting flange ring. This is accomplished by the use of formed beads of particular configuration, spacing and height, provided on the ends of the insulating casing element to coact with the cement to fixedly secure the associated end casting rigidly into position.
The advantages of the type of bead construction of the present invention are:
First, it minimizes the degree of stress concentration. Second, it is easier to machine. Third, it increases the effective strength of the porcelain casing.
Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:
FIGURE 1 is a side elevational view of a porcelain casing embodying the principles of the present invention, with a quarter section removed to more clearly illustrate the bead configuration;
FIGS. 2-4 are fragmentary cross-sectional views of limiting bead constructions which may be provided at the ends of the porcelain casing of FIG. 1 illustrating a certain leeway of dimensional relationships;
FIG. 5 is a fragmentary sectional view indicating the attachment of a mounting flange ring through a cemented construction with the beaded end of the associated porcelain casing;
FIG. 6 is a top plan view 0 fan end casting, which is employed to encircle the end of an associated porcelain casing;
FIG. 7 is a sectional view of the metallic flange ring of FIG. 6, taken substantially along the line VII-VII of FIG. 6;
FIG. 8 illustrates a modified construction involving a tapered enlargement of the end portion of a porcelain casing for increased strength in attachment; and,
FIG. 9 illustrates, in side elevation, a complete high voltage lightning-arrester assembly, indicating the superpositioning of several arrester sections, each of which embodies principles of the present invention.
The present invention is particularly concerned with a novel bead construction, which prevents stress concentration at the beads. As well known by those skilled in the art, it is necessary to provide an attachment arrangement which results in a strong joint with favorable distribution of the stress between the jointing material and the porcelain casing.
With particular reference to the drawings, it is noted that FIGURE 1 illustrates a side elevational view of a Edward F. W. Beck and Otto Ackermann, and assigned to the assignee of the instant application, as a typical example of use of a cemented joint construction between a porcelain outer casing and a metallic mounting flange element, which encircles each end of the casing.
FIG. 2 illustrates in vertical section, and fragmentarily, the improved bead construction 2 of the present invention, as applied to the porcelain casing element 1 of FIG. 1. The dimensional relationships are indicated in the figure and have been found to provide a stress-free attachment.
Using the bead construction 2 of the present invention, the effective strength in tension of the joint between the end support casting 4 and the porcelain casing increased from approximately 16,000 pounds to 43,000 pounds using the same porcelain and flange assembly with the only change being the bead construction 2.
FIGS. 2-4 illustrate the dimensional limits which are to be applied to take advantage of the improved stressfree bead construction 2 of the present invention. It is to be noted that the bead height H may range between .06 inch to .12 inch, the bead spacing 8 may range between .38 inch to 1.00 inch, the bead spacing S being approximately equal to 6 R which is the radius of the curvature of the individual beads 3.
It is desirable to make R equal to or greater than H, a preferable range being from .06 inch to .15 inch. The radius R of the curved surfaces preferably ranges between .12 inch to .38 inch, but may be as large as conveniently possible.
It is to be noted that FIGS. 2-4 illustrate the lower limit, most practical dimensions, and the practical upper limit to clearly indicate the dimensional limits of the bead construction 2 of the present invention.
FIG. 5 fragmentarily illustrates, partially in section, the cemented attachment of a metallic end ring 4 with the end 8 of a porcelain casing 1. As well known by those skilled in the art, the end casting 4- may be securely fastened to the end of the porcelain casing 1 by Mineralead cement 10, a high-melting-point sulfur cement, which contains no corrosive constitutents.
The formulation of the Mineralead cement is as fo1 lows:
Material: Content, percent Refined sulfur, min. Inert aggregate 35-45 Plasticizer, max 3 1 NoTE.-Suitable nonvolatile plasticizer in sufficient quantity so that cement conforms to requirements of this specification.
Inert aggregate composition The chemical composition of the inert aggregate shall conform to the following:
Chemical: Content, percent Carbon 1.0 to 2.0 SiO 97.0- to 98.5 A1 0 0.3 to 0.7 Fe O 0.1 to 0.5 CaO none MgO none K 0 none NazO i none NaCl or other inorganic halides none Instead of Mineralead, a Portland cement could be used in the lightning arrester casing construction. This cement 10 has been found to be extremely strong, as shown by cantilever strength tests, and preferably contains a plasticizer, which prevents mechanical stresses. As well known by those skilled in the art, the end castings 4 may be formed of an aluminum alloy and have considerable mechanical strength to support the lightning arrester and, additionally, provide a means of stacking units to form a column. The purpose and function of a lightning arrester device is set forth in detail in the aforesaid US. Patent No. 2,858,476, which may be referred to in this connection.
FIGS. 6 and 7 respectively illustrate top and vertical sectional views of a typical metallic end support casting 4. It will be noted that the support casting 4 (FIG. 7) has internally-provided beads 41;, which cooperate with the cement 10 to provide a secure attachment. It will moreover be noted that the end flange support ring 4 has outwardly-extending mounting ears 4b with mounting apertures 40 provided therein, which may accommodate mounting bolts, not shown.
FIG. 8 illustrates a modified construction of a porcelain insulator casing 1a having a tapered enlarged end portion 12, which additionally may be provided to increase the strength of attachment. It is to be noted that the end 12 of the casing section 1a is tapered so as to increase the resistance of the metallic end flange ring 4 from pulling off of the end of the insulator casing in.
FIG. 9 illustrates in side elevation a self-supporting high-voltage lightning-arrester. For the higher voltages, say, for example, 336 kv., the lightning-arrester assembly 20 may have a height A of 239.5 inches and a grading ring radius B of 164 inches. The weight of the assembly 20 may, for example, be 2643 pounds. It is evident, therefore, that wind stresses, weight loading and other forces come into play to result in heavy cantilever loading forces being imposed upon the lightning-arrester assembly 20, and the attachments between the porcelain casings 1 and the end castings 4, the latter bolted together, must be secure and not loosen during the operational life of the device. The bead construction 2 of the present invention has overcome this severe problem, and has provided a secure attachment between the casing elements 1 and the end castings 4.
Although there has been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the invention.
I claim as my invention:
1. An insulating cylindrical porcelain casing having an externally-provided circumferentially-extending bead configuration adaptable to fixedly secure an encompassing mounting flange ring, or the like, by a cemented construction, said bead configuration providing a bead spacing between 0.38 inch and 1.00 inch and a bead height between 0.06 inch and 0.12 inch.
2. The insulating cylindrical porcelain casing according to claim 1, wherein the beads in cross-section have a circular configuration with a radius of curvature (R of between 0.06 inch and 0.15 inch.
3. The insulating cylindrical porcelain casing according to claim 2, wherein the curvature (R extending from the crest of each bead to the root thereof varies from 0.12 inch to 0.38 inch.
4. An insulating cylindrical porcelain according to claim 1 wherein said head configuration provides a bead spacing (S) of substantially 0.75 inch with a bead height (H) of substantially 0.09 inch.
5. The combination of claim 4, wherein the curvature (R extending from the crest of each head to the root thereof is substantially 0.3 8 inch.
6. An insulating cylindrical porcelain casing having an externally-provided circumferentially-extending bead configuration adaptable to fixedly secure an encompassing mounting flange ring, or the like, by a cemented construction, said bead configuration providing a bead spacing 5 a 6 (S) which is approximately equal to 6R ,where (R is FOREIGN PATENTS the radius of curvature of the individual beads. 300,419 11/1928 Great Britain.
References Cited OTHER REFERENCES UNITED STATES PATENTS 5 Picard, German application No. 1,097,502, published 1,812,713 6/1931 Proctor et a1. 28789.365X 2,542,798 2/1951 Cumming 1'7 15 X LARAMIE E. ASKIN, Primary Examiner.