US2756271A - Fitting for insulator assemblies and method - Google Patents

Description

July 24, 1956 R. 1 MERRIMAN FITTING FOR INSULATOR ASSEMBLIES AND METHOD Filed Aug. 8. 1950 RwhafidL.

United States Patent 'O FITTING FOR INSULATOR ASSEMBLIES AND METHOD Richard L. Merriman, Lansdale, Pa., assgnor to Lansdale Nipple Company, Lansdale, Pa., a corporation of Penu- Sylvania Application August 8, 1950, Serial No. 178,312

6 Claims. (Cl. V174-177) This invention relates to an improved connector assembly and is especially directed to the type of insulating connector used for suspending the lighting unit from an overhead street lamp.

In the conventional construction of overhead street lamps, it is customary to provide an insulator or connector between the lamp bracket and the lighting unit. This insulator carries the entire weight of the lamp and its associated structure, and in addition it must have an ample factor of safety to prevent failure under the severest wind, ice, and snow conditions. In standard practice the insulator is ellipsoidal in shape and is made of a ceramic material such as porcelain. An externally threaded metallic fitting is secured to the top and to the bottom of the insulator concentric with its vertical centerline. It has been found commercially impractical to use a threaded connection directly between the metallic fitting and the porcelain insulator with the result that no satisfactory inexpensive construction for securing the fittings to the porcelain has been proposed.

I have found that a modified pipe fitting such as a grooved close nipple may be cheaply and satisfactorily employed as the metallic fitting. This particular construction, as will be described more fully, enables a very satisfactory bond to be provided between the insulator itself and the fitting.

A primary object of the invention therefore, is to provide a threaded fitting which may be inexpensively manufactured and which can be securely bonded to a ceramic body subject to high tension and torque loads.

A further object is to provide a satisfactory porcelain insulator assembly that has sufficient strength in tension to enable its use on street lighting equipment.

A further object is to provide a method of fabricating an improved ceramic insulator assembly.

Further objects will be apparent from the specification and drawings in which:

Fig. l is a side View of a street lamp insulator assembly embodying my invention;

Fig. 2 is an enlarged sectional detail showing the joint between one of the metallic fittings and the ceramic insulator body;

Fig. 3 is a sectional perspective of one of the fittings;

Fig. 4 is a fragmentary sectional detail of a modified form;

Fig. 5 is a sectional detail of another modification; and

Fig. 6 is a sectional detail similar to Figs. 4 and 5, showing a further modification.

A feature of the present invention resides in the provision of a fitting which cannot be accidentally withdrawn axially or torsionally from its seat in the porcelain insulator body.

Referring now to the drawings, the conventional street lamp porcelain connector or insulator body 10 somewhat resembles a discus. From the top or bottom, the insulator is circular in appearance and from the side it is elliptical in shape. Identical bosses 11 and 12 are concentrically located on the top and bottom of the insulator and these 2,756,271 Patented July 24, 1956 bosses partially form the walls of concentric sockets 13 and 14. The diameter of the sockets is substantially larger than the outside diameter of the fittings 15 and 16 which are embedded in the sockets and thus secured to the insulator. It will be understood that the shape and dimensions of the insulator body, as well as the nature of the external threaded portions of fittings 15 and 16 extending beyond the insulator, follow conventional specifications and practice. In order however, to secure an absolutely permanent bond or joint between the fitting and the porcelain connector, I provide a helical thread 17 on the end of the fitting which is seated in the socketsy 13 and 14, This thread may be either cut or rolled and it may be, if desired, of the tapered or pipe thread form. After the fitting is threaded as described above, l cut one or more annular grooves 18 in one end of the fitting, making sure however, to leave several threads between the groove and one end of the fitting. After the grooved and threaded end of the fitting is placed in the socket, a bonding material such as lead is poured or packed into the cavity around the fitting.

Figs. 4-6 show several modifications which may be advantageously employed, depending upon the stresses likely to be present and the size of the fittings. Fig. 4 shows a construction in which the base 19 of the groove 18a is somewhat biased with respect to the centerline of the fitting. Likewise, the sides 20 of the socket in the insulator may be biased to provide increased bonding between the lead and the insulator.

Fig. 5 shows the expedient of providing two grooves 18h and 18C on each fitting. In this case, there is an unthreaded land 21 between the grooves. Fig. 6 is a construction quite similar to Fig. 5 in which the grooves 18d and 18e are spaced axially farther apart than shown in Fig. 5, and in this case the land 22 between the grooves 18aJ and 18e is also provided with threads.

The very important and unusual benefit derived from this construction is due to the fact that the bonded joint between the fitting and the insulator body cannot be removed by tension or by twisting. The length and depth of the threads together with the dimensions of the annular groove are ample to withstand any axial load imposed on the insulator assembly. Since there is an annular land 24 of unthreaded lead or packing interposed between two threaded portions of the fitting, it will be seen that this land serves as a lock to prevent the fitting from unscrewing. Before the terminal threaded portion 25 of the fitting could be turned past the land 24, it would be necessary that new threads be cut in the land. Since there is no void to take any of the displaced metal incident to such a thread cutting, the land securely locks the fitting so that it cannot be unscrewed.

In the form of Fig. 5, I provide the above-described locking feature which takes place with regard to the terminal threaded portion 25a. In addition, land 21 seats securely under the lead in groove 181'; to provide additional strength both axially and torsionally. It will be apparent that any turning of the fitting must be accompanied by axial movement so that the locking is enhanced.

The form of Fig. 6 combines the above-described fea-` tures of the form of Fig. 5, as well as a double thread locking land since it would be necessary for the threads. on land 22 to cut through the lead in groove 18d, as well as the threads on land 33 to cut through the lead in groove- 18e. It will be understood that the depth of the various. grooves as well as their axial length, depends largely upon the particular materials being used and the conditions likely to be encountered in service. It is desirable however, that the groove be cut to the root diameter of' the threads at least, so that there will be no starting grooves in the lead through which the terminal threadsl might ultimately turn.

Furthermore, the above-described locking features may be employed regardless of the shape of the socket; it is not essential that the fittings be tubular as shown in Figs. 2 and 3. However, an important feature of the invenn tion is derived from the fact that the cost of manufacturing satisfactory locking features can be cut to a fraction as compared to any other form. lt is not necessary to provide axial grooves or ilutes to resist torsion. Furthermore, the cost and equipment required to provide even a knurled surface for the fitting that would approximate the strength of the present invention, is also prohibitive. It is only necessary to ultilize a standard close pipe nipple which may be readily grooved in one or more places with conventional machine tool equipment and without excessive radial pressures, with standard cutting tools.

Having thus described my invention, i claim:

1. A connector assembly for suspending street lamps and the like from hangers, comprising a ceramic insulator body having at least one socket therein, a metallic fitting embedded in said socket, walls defining an annular groove around the periphery of the fitting, said groove being axially spaced from the embedded end of the fitting, a helical thread on the periphery of the tting between the groove and the embedded end, and sealing means between the insulator body and the fitting, said sealing means iilling the groove and said threads.

2. A connector assembly for suspending street lamps and the like from hangers, comprising a ceramic insulator body having at least one socket therein, a metallic fitting embedded in said socket, a helical thread on the outer periphery of said fitting within the borders of the cavity, walls defining an annular groove around the periphery of the fitting, said groove being positioned to separate the thread into at least two discontinuous segments, and sealing means between the insulator body and the fitting, said sealing means lling the grooves and at least one of said thread segments.

3. Apparatus in accordance with claim 2, in which the walls of the fitting define a plurality of grooves.

4. Apparatus in accordance with claim 2, having a plurality of annular grooves, and an unthreaded land between two of said grooves.

5. Apparatus in accordance with claim 2, in which the base of the groove is biased with respect to the centerline of the fitting.

6. The method of fabricating an insulator assembly having a ceramic insulator body and at least one cylindrical metallic fitting bonded to said body, which comprises the steps of forming a helical thread on one end of said fitting, forming an annular groove intermediate the termini of said thread, inserting the threaded end of the fitting into a socket on the insulator body, and embedding said fitting in the socket by pouring therein a molten metallic bonding material to fill the threads and the groove.

References Cited in the tile of this patent UNITED STATES PATENTS 352,437 Winton' Nov. 9, 1886 476,207 Locke May 3l, 1892 878,870 Creaghead Feb. l1, 1908 1,160,546 Steinberger Nov. 16, 1915 1,483,022 Stewart Feb. 5, 1924 1,652,835 Peirce Dec. 13, 1927 1,653,437 Liversidge Dec. 20, 1927 1,882,312 Aspinwall Oct. 11, 1932 1,898,574 Card Feb. 21, 1933 2,191,152 Hammel Feb. 20, 1940 2,407,904 Rosan Sept. 17, 1946

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