Elastomeric Shield For An Electrical Conductor Connector Module And Method Of Making Same

Abstract

An electrical conductor connector module of the type having a passageway through it to receive one or more electrical cables, which are sealed in water-tight relationship by the module and electrically coupled therein, is provided with a thin electrostatic shield that surrounds a middle portion of the passageway. The electrostatic shield is in the form of a relatively thin coating of electrically conductive elastomeric material. The coating can be formed by either a dip-forming type of process or, by a transfer process in which the electrostatic shielding material is first coated on a mandrel and then transferred from the mandrel to the inner surface of the module passageway, when the module housing is molded around the mandrel.

Description

BACKGROUND OF THE INVENTION

In the field of underground electric power distribution, it is well known to utilize elastomeric conductor termination modules to effect coupling and switching functions at the junctions between associated components in the distribution system. Such modules commonly are provided with some means for electrostatically shielding the potential corona sources within the modules that are formed by electrically stressing air which is entrapped in the connector couplings made within the module. Prior to the present invention, such electrostatic shields were generally formed in two different manners. First, a metallic conductor in the form of a screen or metal sleeve has been mounted in some conductor termination modules to afford such shielding. An example of this first type of metallic electrostatic shield is illustrated in U.S. Pat. No. 2,967,901-Priaroggia, which issued Jan. 10, 1961 and is assigned to Pirelli Societa per Azioni. A second kind of electrostatic shield is more generally used in the electric power distribution field currently. This second type of shield comprises a fixed, molded sleeve of electrically conductive elastomeric material that is mounted within a conductor module around the conductor coupling area that is to be shielded. An example of this type of electrostatic shield is illustrated in U.S. Pat. No. 3,344,391-Ruete, which issued Sept. 26, 1967 and is assigned to Elastic Stop Nut Corporation of America (Elastimold Division of Amerace-ESNA Corporation).

While both of these prior art types of electrostatic shields for conductor termination modules have proven to be satisfactory for given applications, they have several common disadvantages. Perhaps the major disadvantages of such prior art electrostatic shield means is that they are very expensive to install within a conductor module. A second significant disadvantage inherent in these prior art electrostatic shielding techniques is that they are difficult to accurately position within a predetermined section of a conductor termination module due to distortion which often results during injection molding operations used to form the dielectric material. Accordingly, it has been found necessary to employ relatively expensive, highly plastic dielectric materials to form the housing of such modules, thereby to reduce the risk of such undesirable distortion of the electrostatic shield sleeve. As a result, the moldability of the dielectric material to prevent distortion of the molded conductive elastomeric inserts takes precedence over the desired physical and electrical properties of the dielectric material which could be easily obtained without this constraint. Of course, it would be desirable to provide an electrostatic shield means that would enable the dielectric housing to be molded, and still be formed of a relatively inexpensive, less plastic material, which contains a high percentage of low-cost fillers.

Accordingly, it is an object of the present invention to provide a reliable and inexpensive electrostatic shield for an underground electrical conductor termination module.

Another object of the invention is to provide an electrical conductor termination module with an electrostatic shield that is easily placed within a given section of the module during an injection molding operation.

A further object of the invention is to provide an electrical conductor termination module having a conductor-guiding sleeve and an electrostatic shield mounted, in combination, therein in a manner that affords a smooth electrostatic shield around the junction of the sleeve and the dielectric material of the module.

Still another object of the invention is to provide a method for forming an electrostatic shield within an electrical conductor termination module that is inexpensively and accurately formable by an injection molding operation.

Yet another object of the invention is to provide a method for forming a relatively thin, flexible electrostatic shield on a precisely predetermined portion of the inner surface of a conductor termination module by a dip-forming or transfer process.

Additional objects and advantages of the invention will be apparent to those skilled in the art from the description of it that follows, taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention relates to electrical conductor termination modules of a type having an electrostatic shield means mounted therein; and the invention also comprises a method of manufacturing such a module. In one preferred form of the invention, a relatively thin electrostatic shield formed of an electrically conductive elastomeric material is bonded on a predetermined portion of an inner dielectric wall of a conductor termination module during an injection molding operation in which the module dielectric housing is formed. Pursuant to the invention, the electrostatic shield is formed by coating a mandrel with a predetermined thickness of conductive elastomeric material, mounting the mandrel in a mold cavity, then forcing a dielectric plastic material into the cavity around the mandrel, under a given temperature and pressure, thereby to form the dielectric housing and simultaneously cause the electrostatic coating to be bonded to an interior portion thereof. Finally, the mandrel is withdrawn from the dielectric housing of the module, thereby transferring the conductive coating from it to the walls of the dielectric housing. In a modification of the invention, an electrostatic shield is formed within an electrical conductor termination module by dip-forming a thin dielectric coating on a predetermined portion of the interior surface of the housing after the molding operation. In another modification of the invention, an electrostatic shield is formed by painting a coating of electrically conductive elastomeric material on a contact or other rigid article and the supporting mandrel. Subsequent molding of the dielectric material then assures a continuous electrostatic shield from the surface of the rigid insert to the dielectric material in the area that is to be shielded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view, partly in cross-section, showing an electrical conductor termination module embodying one form of the invention.

FIG. 2 is a top plan view of one portion of an injection mold, showing a mold cavity and associated mandrels used in practicing the present invention to form an electrical conductor termination module similar to that illustrated in FIG. 1.

FIG. 3 is a side elevation view, partly in cross-section, showing an electrical conductor termination module during a manufacturing sequence in which an electrically conductive coating is being formed on an interior mid-portion of the module, pursuant to a manufacturing technique of the present invention.

FIG. 4 is a side elevation view, partly in cross-section, illustrating an electrical conductor termination module having a contact member molded therein and incorporating electrostatic shield means that are constructed pursuant to the present invention.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

There is shown in FIG. 1 of the drawing an electrical conductor termination module 1 comprising an elongated housing 2 that is formed of elastomeric insulating material. Many examples of suitable insulating materials for such applications are well known in the field of underground power distribution systems. Any suitable insulating material may be used to form the housing 2, but in the preferred embodiment of the invention a material similar to the dielectric housing material disclosed in the above-identified Ruete patent may be employed. As seen in FIG. 1, the housing 2 includes wall means 3 that define a passageway through the housing 2 from a first end 4 to the other end 5 thereof.

In order to electrostatically shield a predetermined mid-portion of the passageway, i.e., the portion lying between the points 3a and 3b, an electrically conductive coating 6 of elastomeric material is bonded to the wall means 3 between the points 3a and 3b of the passageway. Pursuant to the present invention, the coating 6 may be formed of various suitable electrically conductive materials. However, in the preferred embodiment of the invention, the coating 6 is formed of a sulfur-cured elastomeric material similar to that disclosed and claimed in co-pending United States Patent application, Ser. No. 36,051-Ryder, entitled "Electric Cable Termination Modules Having Peroxide-Cured Elastomeric Insulating Bodies and a Low-Electrical-Resistance Conductive Coating on the Exterior Thereof," which was filed on May 11, 1970 and is assigned to the assignee of the present invention. In other words, the coating 6 may be formed of material similar to that used to coat the exterior of the conductor termination modules disclosed in the Ryder application. An important characteristic feature of the coating 6 is that it is greater than 0.0001 inch thick and less than 0.040 inch thick over substantially its entire surface area.

As noted above during the discussion of the background of the present invention, it is known in the prior art to use relatively thick, molded coatings to form an electrostatic shield around a mid-portion of an internal passageway in a conductor termination module. The unique feature of the relatively thin coating 6 illustrated in FIG. 1 is that it affords all of the desirable advantages enumerated above, while providing the electrostatic shielding capability that is necessary in such a module.

In addition to the coating 6, a hollow sleeve 7 is mounted in the passageway, with its outer surface in electrically conducting contact with the coating 6. In the form of the invention shown in FIG. 1, the sleeve 7 has both of its ends positioned between the ends 3a and 3b of the coating 6. It should be understood that in other embodiments of the invention it may be desirable to position the sleeve 7 with relation to the coating 6 so that only one of its ends is between the longitudinally spaced-apart ends 3a and 3b of the coating 6. The intended function of the sleeve 7 is to provide a means for guiding a terminal inserted into the module through the end 4 thereof, into contact with a second terminal inserted into the module through the end 5 thereof. Thus, it will be apparent that the sleeve 7 may be formed of either a dielectric material or an electrically conductive material. In the embodiment of the invention shown in FIG. 1, the sleeve 7 is formed of an electrically conductive material such as copper.

In order to assure the formation of a void-free bond between the sleeve 7 and the conductive coating 6, a bonding material 8 is mounted on the outer surface of the sleeve 7. Any suitable conventional bonding material may be used for this purpose, and it will be understood that the bonding material need not be electrically conductive, since the necessary electrostatic shielding is afforded by coating 6 in the illustrated embodiment of the invention. Of course, it should also be appreciated that is some embodiments of the invention it may not be desirable to extend the coating 6 along the entire length of the sleeve 7. In such modifications of the invention, if the sleeve 7 is formed of electrically conductive material, it affords adequate electrostatic shielding over its central portion. However, in order to assure a smooth transition of the electrical field from the respective ends of the sleeve 7 to the coating 6 in such a modification, the coating 6 would be formed to extend beyond the ends of the sleeve 7, by the method to be described below.

Before describing the method of manufacturing the coating 6, another aspect of the unique electrostatic shield of the invention will be discussed. Referring to FIG. 1, it will be seen that if sleeve 7 is made of electrically conductive material it can cooperate with the coating 6 to form an electrostatic shield, even if the coating 6 does not directly contact the sleeve 7, provided an electrical connection is formed between sleeve 7 and coating 6. Thus, in some embodiments of the invention the coating 6 may be terminated at a predetermined point adjacent the end of sleeve 7 if it is known that during normal use of module 1 an electric circuit will be completed between these members. For example, if during such normal use a copper conductive rod were to be inserted in sleeve 7 and the rod was also in contact with the coating 6, it would serve to eliminate electric field stresses between the inserted sleeve 7 and the coating 6.

The method in which the coating 6 is manufactured, and in which the layer of bonding material on the sleeve 7 is used, in cooperation with the coating material 6, forms an important part of the invention, which will now be described in greater detail. Referring to FIG. 2, it will be seen that there is provided a mold 9 having a mold cavity 9a in the form of the elongated housing of module 1. Pursuant to the present invention, the mold 9 forms one-half of an injection mold cavity, the other half of which (not shown) is formed by a cooperating mold having a complementary cavity engraved therein. In order to form the passageway that extends between the ends 4 and 5 (see FIG. 1) of the module 1, a pair of mandrels 10 and 11 are provided. The mandrels 10 and 11 are adapted to be inserted into the cavity 9a, as shown in FIG. 2. In this inserted position, the mandrels 10 and 11 seal the respective ends of the cavity 4' and 5', thus, leaving only the sprue 12 open; so that plastic dielectric material may be forced into the mold cavity 9a from a suitable reservoir (not shown) through an injection nozzle 13, which is adapted to be moved into sealing relationship with the upper end of the sprue 12, in a well-known conventional manner. Of course, before such plastic dielectric material is forced into the cavity 9a the complementary half of mold 9 would be sealed in position over the mandrels 10 and 11, thereby to define a closed cavity having the form of module 1. It is not necessary to an understanding of the present invention to describe further refinements of the mold cavity configuration, or the provision of various inserts within the cavity, such as metal support members for the hot stick ring of module 1, or capacitance-tap inserts for the housing. Obviously, such component parts may be incorporated in the module 1 in a conventional manner.

In order to understand the unique features of the present invention, only the portion of the molding operation necessary to form the unique, relatively thin type of coating 6, discussed above, with reference to FIG. 1, is necessary. Pursuant to the present invention, the coating 6 may be formed satisfactorily in either of two novel processes. First, the coating 6 may be formed by applying a coating 6' to at least a portion of the mandrels 10 and 11, as shown with the dotted design in FIG. 2. Alternatively, the coating 6 may be formed by a dip-forming process that will be discussed in greater detail below.

Pursuant to the first of these processes, the respective enlarged inner end portions of mandrels 10 and 11 are coated with an uncured elastomeric material, similar to that described above, prior to the insertion of the mandrels in the cavity 9a. When the cavity 9a is filled with elastomeric insulating material, under a predetermined pressure and temperature, as described above, the coating 6' is securely bonded to the insulating material 2 (see FIG. 1) of the module 1. It has been found that this bonding is sufficient to allow removal of the mandrels 10 and 11 from the molded module 2, thereby to separate it from the coating 6' which then defines the desired electrostatic shield around the predetermined portion of the passageway between the points 3a and 3b (see FIG. 1) of the housing 2. It should be noted that pursuant to this embodiment of the invention the two outer end surfaces of conductive sleeve 7, which is held in position between the mandrels 10 and 11 during the molding operation, are coated with the coating 6. Thus, the sleeve 7 serves to complete the electrostatic shield between the points 3a and 3b as discussed above with reference to FIG. 1. Of course, as noted above, if desired, the coating 6 could extend over the entire outer surface of sleeve 7 in some embodiments of the invention, or both the inner and outer surfaces of sleeve 7 may be covered by coating 6, or only the inner surface may be coated.

Now, the second embodiment of the coating method of the present invention will be described with reference to FIG. 3 of the drawing. In FIG. 3, there is shown a module 1', which has been formed in a manufacturing process similar to that described above with reference to FIG. 2, except for the fact that during the molding operation the mandrels 10 and 11 were not provided with an electrically conductive coating 6', and the sleeve 7 was omitted. It will be understood that in such a modified form of the invention, the mandrel 10 includes an integral extension that is equal in diameter to the sleeve 7, thereby to complete the passageway through the module 1', as shown in FIG. 3. In this form of the invention, in order to provide a coating 6' between the points 3a' and 3b', it is necessary to mask a predetermined portion of the passageway formed between the ends 4" and 5" of module 1'. This masking is accomplished by inserting a plug 14 through the end 4" of module 1' to form a fluid-tight seal with the walls of the passageway at point 3a'. Then, a hollow tube 15 is inserted through the end 5" of module 1' to the point 3b', thereby to mask the passageway from the end 5" up to the point 3b'. Next, a suitable body 6a of fluid elastomeric, electrically conductive material is introduced, in an uncured state, into the passageway through the tube 15, as shown in FIG. 3. After the level of the body 6a of conductive material reaches the point 3b', the body of conductive material 6a is drained from the passageway through the tube 15, leaving a coating 6' coextensive with the wall means defining the passageway between the points 3a' and 3b'. To complete the manufacture of the module 1', the coating 6' is then cured by baking the module at a suitable temperature for a given period of time. Of course, such a cure cycle may vary for the given electrically conductive coating materials that might be used, but an example of suitable cure times, as well as suitable conductive materials, is given in the above-identified Ryder application.

It should be understood that the method defined above with reference to FIG. 3 may be modified by providing a hollow sleeve, such as the sleeve 7, within the module 1', in a manner similar to that discussed with reference to FIGS. 1 and 2 above. In such a modification of the invention, it would only be necessary during the molding operation to coat the respective opposite ends of the sleeve 7 with an electrically conductive coating, and to similarly coat a portion of the respective enlarged inner ends of the mandrels 10 and 11 with a conductive coating, such as the coating 6' shown in FIG. 2, in order to form a portion of the electrostatic shield that would operate in cooperation with a dip-formed coating similar to the coating 6' formed by the fluid body of conductive material 6a in the embodiment of the invention described with reference to FIG. 3.

Turning now to FIG. 4 of the drawing, it will be seen that there is shown still another embodiment of the invention. FIG. 4 depicts an electrical conductor connector module 21 comprising an elongated housing 22 of dielectric material, which may be similar to the material used to form the dielectric housing of module 1 described above with reference to FIG. 1. In general, the module 21 is similar in structure and function to the module 1 discussed above, except for the fact that module 21 includes an electrically conductive contact member 23 mounted therein. Also, the passageway extending between the ends 24 and 25-25a is bifurcated so that two conductor-receiving terminals are afforded therein, spaced inwardly from the respective ends 25 and 25a. An electrostatic shield is formed around the terminal 23 and predetermined portions of the passageway by a coating 26 (comprising sections 26a and 26b) of electrically conductive material, which is similar in composition to the material of coating 6, for module 1, discussed above. In this embodiment of the invention, contact 23 is provided with a layer of bonding material 28 which is electrically conductive, at least in the areas thereof adjacent the opposite ends of the contacts 23, i.e. around the resilient-fingered terminals 23a and 23b and the threaded aperture 23c. Thus, it will be seen that the first section 26a of coating 26 is positioned in electrically conducting relationship with one end of the bonding layer 28, adjacent the fingers 23b, and the second section 26b of coating 26 is positioned in electrically conducting relationship with the other end of coating 28 adjacent the threaded bore 23c.

Of course, as described above with regard to the bonding layer on sleeve 7, illustrated in FIG. 1, substantially all of the electrically conductive bonding layer 28 on contact 23 can be electrically conductive, rather than just being conductive adjacent its respective ends. This second alternative is particularly desirable if there is some risk of the bonding layer 28 becoming separated from the contact 23, when it is molded into the housing 22, because the layer 28 would then shield any air voids formed between the contact 23 and the dielectric of housing 22.

In an alternative embodiment of our invention, the conductive bonding layer 28 may be formed of a suitable conductive adhesive, rather than being formed of a moldable conductive elastomer. Such conductive adhesives are well known in the rubber molding field. It should be appreciated that in practicing the invention in any instance where an insert is to be molded into a dielectric insulating body, and electrostatically shielded, such a coating of conductive adhesive can be applied either to the insert, or the area of the housing to be occupied by the insert, thereby to afford the desired thin electrostatic shield of the invention.

It should be apparent from the description of the invention given above, that the sections 26a and 26b of coating 26 can be formed by a dip-forming process similar to that described with reference to FIG. 3. Accordingly, further detailed description of the embodiment of the invention illustrated in FIG. 4 is not deemed to be necessary in order to enable those skilled in the art to practice the invention.

Obviously, additional modifications and embodiments of the invention will occur to those skilled in the art from the description of it that has been given herein. Accordingly, it is our intention to encompass all such modifications of the invention within the scope of the following claims.

Claims

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical conductor connector module comprising:

an elongated housing formed of elastomeric insulating material,

wall means defining a passageway in said housing,

an electrically conductive coating of elastomeric material bonded to a predetermined portion of said wall means thereby to form an electrostatic shield around said predetermined portion, said coating being greater than 0.0001 inch thick and less than 0.040 inch thick over substantially its entire surface area, and

an insert member mounted in said passageway adjacent said coating, said insert being formed of a dielectric material, and including a layer of electrically conductive bonding material mounted on a predetermined portion of at least one surface of said insert member thereby to form an electrostatic shield around said insert member.