US 3611257 A
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United States Patent  Inventor Carlton L. Carkhuli Evansville, Ind.  Appl. No. 853,170  Filed Aug. 26, 1969 [4S] Patented Oct. 5, I971  Assignee Springfield Wire of Indiana, Inc.
 ELECTRIC PLUG CONSTRUCTION AND METHOD OF MANUFACTURING SAME 5 Claims, 7 Drawing Figs. I  U.S. Cl 339/63 M, 339/l96 M, 339/2l8 M [SI] Int. Cl I-l0lr 13/08  Field of Search 339/63, I95, 196, 2l8
 Relerences Cited UNITED STATES PATENTS 2,047,094 7/1936 Bennett 339/63 Herman 339/63 M ABSTRACT: Electrical outlet plug which includes a core member encapsulated within a sheath. The core is formed with electrical contact blade-retaining bores through said core member opening in one direction to receive and retain the portion of the contact blades connected to a conductor wire, and opening in the other direction in close fitting peripheral relation about said blades. A pedestal projects outwardly of said core in a direction opposite the blades and is of sufficient size to serve as a base for supporting the core in a mold. The surfaces of the core peripheral to said blades extend outwardly of the core in a direction opposite the pedestal sufficiently to extend through said sheath and provide with the pedestal, mold bearing surfaces when the core is disposed in a mold cavity.
PATENIEDBCI SIB?! 3.611.257
- SHEEI 1 0F 2 INVENTOR. CARLTON L. CARKHUFF BY WWW! n0 M0015 1 ELECTRIC PLUG CONSTRUCTION AND METHOD OF MANUFACTURING SAME BACKGROUND In the fabrication of electrical plugs various methods and constructions have been developed over the years. In one method, final fabrication is essentially an assembly operation wherein conductor wires and contact blades are connected together and fitted. into a prefabricated housing or enclosure member. Another method widely used in recent years has been one in which a final molding operation is used to encapsulate the terminal ends of the conductor wires and the portions thereof connected to the contact blades. In this method some difficulty is encountered in quickly fitting the metal contact blades into the close fitting blade cavities in the mold and in insuring proper separation of the exposed conductor wires and correct encapsulation of the exposed wires within the molded body.
It has also been proposed, such as disclosed in U.S. Pat. No. 3,093,434, to fabricate molded plugs by a two-step molding operation. In the first step, contact blades and conductor wires are assembled and placed within a first mold cavity in much the same manner as described above in connection with the molding method. This unfortunately does not overcome the awkwardness involved in handling several loosely coupled terminal blades and conductor wires, nor does it facilitate placing the terminal blades in the close fitting mold cavities. A second molding operation is thereafter performed to wholly encapsulate the inner molded plug and to insure against any exposed wires.
As is well known, in any molding operation where a number of assembled elements must be molded into a final plug configuration, a great deal of care is required on the part of the operator to make certain that the assembled elements are properly separated, fitted and held within the mold cavity. In the patent referred to above, such care is required in placing the elements in the mold for the first molding operation. Thereafter the second molding operation is carried out which also requires some care in locating the first molded plug body with the second and larger mold cavity.
The principal object of this invention is to provide an improved simplified and economical method of fabricating electrical outlet plugs of the molded type.
Another object of this invention is to provide an improved electrical plug of molded construction which lends itself to efficient and economical manufacturing methods.
The above and other objects and advantages of this invention will be more readily apparent from the following description with reference to the accompanying drawing, in which FIG. 1 is a partial, exploded, perspective view showing assembly of the components in the method of fabricating an outlet plug according to this invention;
FIG. 2 is a cross-sectional view of the parts shown in FIG. 1 in an assembled condition;
FIG. 3 is a plan view of the core element of a plug;
FIG. 4 is a sectional view taken along line 44 of FIG. 2;
FIG. 5 is a cross-sectional view showing the assembly of FIG. 2 disposed in a mold;
FIG. 6 is a plan view of a completed electrical outlet plug of the type embodying this invention; and
FIG. 7 is an elevational view, partly in section of the plug shown in FIG. 6.
Referring in detail to the drawing, in FIG. 1 is shown a prefabricated or preformed core member 8, electrical prongs or contact blades 10 and 12 connected to the bared ends of the conductors of the lead wire or cable 14. A ground terminal 16 is also shown connected to the ground wire 18 which forms part of the cable 14.
The core member 8 comprises a stem, pedestal or base porportions 26 and 28 and are each further defined by an upstanding rim or boss portion 30. Similarly, the bore 24 extends through the portions 26 and 28 and is lengthened by an upstanding cylindrical rim or boss 32. The axial length and diameter of these sockets are selected so the blades 10 and I2 and terminal 16 are held securely in their assembled condition within the core member 8. As best shown in FIG. 4, a shoulder 34 is provided within each of the sockets 22 adjacent the outer wall of the sockets. The shoulders act as stops or supports for lugs 36 extending outwardly from the side of the blades 10 and 12. The openings of bores 22 in the direction of the pedestal are relatively large in cross section so that the tips of the blades can be readily located and fitted into the bores during assembly of blades and core member. Similarly the bore 24 is tapered as best shown in FIG. 4 and thereby adapted to facilitate location and insertion of the ground terminal 16 in the bore. The core member 28 thus serves to receive and hold securely in assembled relation the electrical contact blades l0, l2 and 16 and the conductor wires, and to facilitate and greatly speed up the time and care required for assembly and molding operations.
The pedestal or base portion 20 extends outwardly of the platform 26, as shown in FIGS. 1, 3 and 4, a sufficient distance and is of sufficient cross-sectional size whereby it serves as a base support for the assembled core, terminal blades and conductor wires within the cavity of a mold 40 where an encapsulating sheath is molded about the core and blade assembly. The height of the core a measured from the outer surface of the pedestal 20 to the outer surface of the rims 30 and 32 is preferably somewhat greater than the height of the mold whereby the resilient core material is compressed somewhat and the outer surfaces of rims 30 and 32 act in effect as integral sealing rings about the blades 10 and I2 and ground terminal 16. Thus an excellent seal is achieved whereby flash over from the molding operation is prevented from forming about the base portions of the metallic blades. Thus the blade cavities 42 of the mold may be made more commodious to assist the operator in quickly and efficiently locating and inserting the blades into the cavities of the mold. With this arrangement not only is assembly time reduced but it is accomplished with substantial elimination of flash which often forms about the terminal blades.
The pedestal or stem 20 as well as being a bore support for the core in the mold also serves in the nature of a separator wall or partition to protect against accidental shorting of any of the conductor wires connected to the respective contact blades 10 and 12. Thus this is a safety factor during molding.
The core may be formed in any suitable manner of any suitable electrical insulating material, preferably a flexibly resilient plastic or elastomer such as rubber or a suitable synthetic plastic, such as a polyvinyl chloride, silicone rubber, neoprene, polyolefin or the like. These core members may be and preferably are molded as an entirely independent operation entirely unrelated to plug assembly.
In the assembly operation, the blades l0, l2 and 16 are first connected to the appropriate bared lead of the cable 14 in the manner shown in FIG. 1. The prefonned core member and blades are then fitted together by the operator who inserts the free end portions of the blades into the enlarged end portion of the appropriate bore, as shown in FIGS. 1 and 3. Once this simple assembly operation is completed, all these elements are thereafter registered and maintained in proper relationship for further processing or handling. Thus the core-retained blades may be readily fitted into the blade cavities 42 which are engineered to register with and receive the terminal blades when in assembled condition with the core member 8.' The pedestal portion 20 of the core 8 as discussed above serves to support the core and wire assembly in a central location within the mold cavity 44. When the mold is closed, as shown in FIG. 5, the inner surfaces of the mold, surrounding the blade cavities 42 contact and rim portions of the core and compress the core sufficiently to sealingly engage the mold cavity about the periphery of the terminal blades. A suitable material is then injected into the mold to encapsulate and form a sheath about the interconnected portion of the lead wires and the terminal blades. Suitable materials for this molding operation include various plastics and elastomers such as rubber or synthetic plastics, including neoprene, silicone, polyvinyl chloride, suitable polyoleftn and the like. It has been found that with a given number of mold cavities, where a skilled operator can produce 250 molded plugs per hour using the conventional techniques, that the same operator can produce about 425 molded plugs per hour when using the preformed core member embodying the invention.
After the molding operation a sheath 48 wholly encapsulates the core, the inner ends of the terminal blades and the connecting portion of the conductor wires with the exception that the outer surfaces of the rims 30, 32 and the stem 20 facing in opposite directions are exposed having served as bearing surfaces in contact with the mold cavity. Thus the rims and stem 20 extend through the sheath 48 as shown in FIG. 7 so as to be exposed. The rims may either be flush or slightly raised with respect to the outer surface of the sheath surrounding the terminal blades.
Having disclosed the invention what is claimed is:
1. Electrical plug for insulated conductor wire comprising a preformed core member formed of electrical insulating material having sockets formed in said core, a terminal blade disposed in each of said sockets, the inner end of each blade connected to the bared end of said insulated conductor wire, said core including outwardly extending rim portions around said sockets and through which the outer portions of the ter-- minal blades project, said core also including a stem portion projecting outwardly opposite said rim portions and a sheath of insulating material encapsulating the end portion of the blades and bared conductor wires with outer surfaces of the rims projecting through said encapsulating material to at least the outer surface thereof.
2. Electrical plug for insulated conductor wire comprising terminal blades extending outwardly of a plug body having an inner preformed core of electrical insulating material and an encapsulating sheath, the inner ends of said blades connected to the bared ends of said insulated conductor wire, said inner core having sockets formed therein in which the inner end portions of the terminal blades are disposed, said core including rim portions closely surrounding the blades and being exposed through the sheath and a stem on said core extending opposite the rim portions thereof and having a portion of its outer surface exposed through the sheath, said stem and rim portions serving as oppositely extending mold bearing surfaces, said rim portions providing for sealing engagement with the mold cavity when said sheath is molded about the core.
3. Electrical plug for insulated conductor wire comprising terminal blades extending outwardly of a molded plug body comprising an inner preformed core of flexibly resilient insulating material and an encapsulating sheath molded about said core, the inner ends of said blades connected to the bared ends of said insulated conductor wire, said core having sockets formed therein in which the inner end portions of the terminal blades are supported for assembly, said core including outstanding rim portions circumferentially disposed about said sockets and disposed around the portion of the blades extending from said sockets, a stem extending opposite said rim portion, outer surface portions of the rims and stem being unencapsulated having provided mold bearing surfaces within the cavity of the mold when the sheath is molded about said core.
4. Electrical plug as set forth in claim 3 in which said cavities comprise bores extending through said core with enlarged entry openings for ease of assembly with said blades, said stem being disposed between said enlarged openings and providing a pedestal for supporting said core on one wall of a mold cavity with said rims sealingly engaged with the opposite wall of said cavity.
5. Electrical plug as set forth in claim 4 in which said bores include shoulders for retaining therein the inner end portion of said terminal blades, said core being formed of synthetic plastic material.