Electric power plug and method of producing the same

An electric power plug comprises blades, a bridge and a plug body. The bridge includes sleeves for covering the roots of the blades and a core for holding the lower ends of the blades. The blades and the core are integrally molded. The plug body is molded so that the plug body embeds the bridge except the upper portions of the sleeves. The core may embed the lower portions of the blades, cords, a caulking portion for connecting the lower ends of blades and wire conductors of the cords. A cavity may be formed at the central portion of the core. The plug body may be molded so that the plug body embeds the bridge and the cords except the upper portions of the sleeves.

TECHNICAL FIELD

This invention relates to an electric power plug and a method of producing the same, and more particularly an electric power plug provided with tracking resistance and a method of producing the same.

BACKGROUND OF INVENTION

A conventional electric power plug provided with tracking resistance is described in the Japanese Patent 3,327,093. The described electric power plug is of a construction that connecting terminal members or blades are inserted in the thermosetting resin and are connected at its bottom portion to power cords by caulking. The plug body is made of polyvinyl chloride material or the like. The connecting terminal members are provided with gap fillers or sleeves for wrapping or covering the roots of the connecting terminal members. When the resin such as polyvinyl chloride material or the like for making the plug body is injected or inpoured into die assembly, the gap fillers are made simultaneously with the plug body by inflow of the resin through connecting terminal inserting hole.

Since at the conventional power plug the surface of thermosetting resin is exposed to the front surface of the plug body, the thermosetting resin easily gets out of the plug body. In order to prevent the thermosetting resin from getting out of the plug body, the thermosetting resin is required to be provided with a relatively long leg portion which extends into the plug body. Although the gap fillers are made by inflow of the resin through connecting terminal inserting hole when the resin such as polyvinyl chloride material or the like is injected into die assembly, it is very difficult to mold or form a thin gap fillers by that step, and therefore it is believed that it is very difficult to mold a thin gap fillers simultaneously with the perfect molding of plug body.

Therefore, it is an object of the present invention to provide an electric power plug in which sleeves and a core can be integrally molded to prevent the thermosetting resin from getting out of the plug body.

It is the other object of the present invention to provide a method of producing an electric power plug in which sleeves and a core can be integrally molded to prevent the thermosetting resin from getting out of the plug body.

SUMMARY OF INVENTION

To accomplish the object, there is provided an electric power plug which comprises blades, a bridge including sleeves for covering the roots of said blades and a core for holding the lower ends of said blades which are integrally molded, and a plug body molded so that the plug body embeds said bridge except the upper portions of said sleeves.

There is also provided an electric power plug which comprises blades a bridge including sleeves for covering the roots of said blades and a core which are integrally molded, said core embedding the lower portions of said blades, cords, a caulking portion for connecting the lower ends of blades and wire conductors of said cords, and a cavity being formed at the central portion of said core, and a plug body molded so that the plug body embeds said bridge and said cords except the upper portions of said sleeves.

There is also provided a method of producing an electric power plug which comprises steps of integrally molding with hard resin a bridge including sleeves for covering the roots of sleeves and a core for holding the lower ends of said blades, caulking the lowermost ends of said blades and the wire conductors of cords at caulking portion, molding a plug body with soft resin so that said plug body embeds said bridge, said caulking portion and said cord at said caulking portion except the upper portion of said sleeves.

There is also provided a method of producing an electric power plug which comprises steps of caulking the lower ends of blades and the wire conductors of cords, integrally molding a bridge with hard resin, said bridge including sleeves for covering the roots of said blades and a core, said core embedding the lower portions of said blades, cords, a caulking portion for connecting the lower ends of blades and wire conductors of said cords, and a cavity being formed at the central portion of said core, and molding a plug body with soft resin so that said plug body embeds said bridge and said cord except the upper portion of said sleeves.

Other objects, features, and advantages of the present invention will be explained in the following detailed description of the invention having reference to the appended drawings:

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

Now referring toFIG. 1, blades12are covered by sleeves16binjection molded with hard thermosetting resin for imparting tracking resistance to the roots of the blades. These sleeves16bare integrally molded or formed with a core16awhich holds the bottom ends of the blades12and the bottom end of an earth pin14. For convenience of explanation, The assembly of integrally molded sleeves16band core16ais hereinafter referred to as a bridge16. The power plug which is not provided with the earth pin is applicable to the present invention, as shown inFIGS. 2 and 3.

The blades12and the earth pin are provided with caulking portions18at their bottommost ends, and are caulked or pressure connected to the wire conductors of the cords20at the caulking portions18. The plug body22is injection molded with soft resin such as soft polyvinyl chloride, soft polyethylene resin, soft polyolefin resin or the like so as to embed the bridge16, caulking portions18and cords20except the upper portions of sleeves16b. Since the bridge16is embedded within the plug body22, it cannot get out of the plug body22. Furthermore, since the sleeves16bare molded without thermosetting resin being flowed in through connecting terminal inserting hole, the sleeves are molded almost perfectly.

Second Embodiment

InFIG. 2, the blades12are covered by sleeves30binjection molded with hard thermosetting resin for imparting tracking resistance to the root of the blades. These sleeves30bare integrally molded or formed with a core30a. The core30ais injection molded with thermosetting resin so as to form a cavity30cat its central portion, and to embed the core30a, the lower portions of the blades12, the cords20, and the caulking portions18where the blades12and the wire conductors of the cords20are caulked. For convenience of explanation, The assembly of integrally molded sleeves30band core30ais hereinafter referred to as a bridge30.

The plug body22is injection molded with soft resin such as soft polyvinyl chloride, soft polyethylene resin, soft polyolefin resin or the like so as to embed the bridge30and the cords20except the upper portions of sleeves30b. Since the bridge30(except the upper portions of the sleeves) is embedded within the plug body22, it cannot get out of the plug body22. Furthermore, since the sleeves30bare molded without thermosetting resin being flowed in through connecting terminal inserting hole, the sleeves are molded almost perfectly.

Now main steps of production of power plug will be explained with reference toFIG. 3. InFIG. 3A, as a first step the blades12and the wire conductors of cords20are connected to each other by caulking. The caulked product of the blades12and cords20is disposed within die assembly, not shown. Thereafter, as shown inFIG. 3B, the bridge30comprising core30aand sleeves30bis injection molded with thermosetting resin so that the cavity30cis formed at the central portion of the bridge, and the lower portion of the blades12, the cords20and the caulking portions18are embedded within the bridge. Finally, The plug body22is injection molded with soft resin so as to embed the bridge30within the plug body22except the upper portions of sleeves30b.

The second embodiment has the following advantages over the first embodiment:

(1) Since in the first embodiment caulking portions are molded integrally with plug body made of soft resin, in the unlikely event that wire conductors get out of caulking portions, one or a few wire conductors are exposed to the surface of plug body, which would result in electric shock accident. Even if one or a few wire conductors are not exposed to the surface of plug body, insulation distance between the wire conductors and the surface of plug body would become remarkably short.
Meanwhile in the second invention even if the wire conductors get out of caulking portions, since insulation distance is maintained by the outside plug body made of soft resin insulator, electric shock accident or lowering of insulation distance does not occur.
(2) Since in the first embodiment the cords are fixed at its outer surface to soft resin, when strong force is applied to the caulking portions by strong tensile force applied to the cords, overload would be applied to wire conductors.
Meanwhile in the second embodiment the cords are fixed to the core by injection molding pressure and the cords and the core are injection molded integrally with soft resin, durability for tensile force is enhanced several times.
(3) In the first embodiment, air bubbles due to gases generated at the time of molding stay within the core.
Meanwhile in the second embodiment since the cavity or opening is formed at the central portion of the core, gas retention is suppressed, and since the thick portion of the core does not exist, the gases easily flow out.

It is understood that many modifications and variations may be devised given the above description of the principles of the invention. It is intended that all such modifications and variations be considered as within the spirit and scope of this invention, as it is defined in the following claims.