EP1564846A1

EP1564846A1 - Prong structure of a plug

Info

Publication number: EP1564846A1
Application number: EP04003381A
Authority: EP
Inventors: Tun-Li Su
Original assignee: Gem Terminal Industry Co Ltd
Current assignee: Gem Terminal Industry Co Ltd
Priority date: 2004-02-16
Filing date: 2004-02-16
Publication date: 2005-08-17

Abstract

A conductive prong structure for a plug is provided. The prong includes a neck (31; 31A) covered by a plastic material (312; 312A; 312B) for forming an inner frame (4) in an injection molding process. The neck (31; 31A) includes an arc-shaped bottom wall (311, 311A) that has a center (X') offset from a longitudinal axis (X) of the prong. In an embodiment, the neck (31) includes a crescent cutout (312) is delimited by the arc-shaped bottom wall (311). In another embodiment, the neck (31 A) includes an annular groove (314A) having a bottom wall (310A), and wherein a crescent cutout (312A) is defined in a portion of the bottom wall (310A) and delimited by the arc-shaped bottom wall (311).

Description

Background of the Invention

The present invention relates to a prong structure of a plug.
A plug is generally coupled with a receptacle for supplying power to an electric appliance or the like. A typical plug includes at least two prongs made of conductive metal. The prongs are supported by an inner frame. In particular, the prongs are placed in a mold, and molten plastic material is poured into the mold, forming an inner frame that is bonded with the prongs. A semi-product is thus formed after hardening of the plastic material. A housing is then formed to provide a final plug product. Torque testing is carried out to test the bonding strength between the inner frame and the prongs. Namely, the anti-torque characteristic has become one of the specifications of the plug. It is, therefore, an important issue to the manufacturers to provide reliable bonding between the prongs and the inner frame and to provide a plug with better anti-torque characteristic.
Referring to Fig. 1 of the drawings, DE 38 40 140 C2 discloses a prong structure 1 including a neck 11 that is rolled before it is covered by the plastic material for forming the inner frame. After rolling, a patterned annular groove 111 is defined in the neck 11. The annular groove 111 includes recessed portions and protruded portions, providing improved bonding between the neck 11 and the plastic material before complete hardening of the plastic material for forming the inner frame.
Referring to Fig. 2 of the drawings, DE 196 27 335 C1 discloses a prong structure 2 including a neck 21 that is rolled before it is covered by the plastic material for forming the inner frame. After rolling, a plurality of patterned annular grooves 211 are defined in the neck 21. The respective annular groove 211 includes recessed portions and protruded portions, providing improved bonding between the neck 21 and the plastic material before complete hardening of the plastic material for forming the inner frame.
In both prior art prong structures, the prongs are covered by the plastic material in a more compact manner before complete hardening of the plastic material. Further, the prongs have improved anti-torque characteristic after hardening of the plastic material. Thus, the prongs would not become loosened, assuring safety during use of the plug.
However, in the prior art prong structures, formation of the patterned the annular groove(s) in the neck of the prong is difficult, which leads to many disqualified products while increasing the cost.

Summary of the Invention

The present invention provides a prong structure including a neck to be covered by a plastic material before hardening of the plastic material for forming an inner frame, characterized in that the neck includes an arc-shaped bottom wall that has a center offset from a longitudinal axis of the prong.
In an embodiment of the invention, the neck includes a crescent cutout delimited by the arc-shaped bottom wall.
In another embodiment of the invention, the neck includes an annular groove having a bottom wall, and wherein a crescent cutout is defined in a portion of the bottom wall and delimited by the arc-shaped bottom wall.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
Fig. 1 is a plan view, partly sectioned, of a conventional prong structure;
Fig. 2 is a plan view, partly sectioned, of another conventional prong structure;
Fig. 3 is a perspective view of a prong structure in accordance with the present invention;
Fig. 4 is a sectional view taken along plane 4-4 in Fig. 3;
Fig. 5 is a plan view of the prong structure in accordance with the present invention;
Fig. 6 is a plan view similar to Fig 5, wherein the neck of the prong structure is covered by a plastic material;
Fig. 7 is a perspective view of a modified embodiment of the prong structure in accordance with the present invention;
Fig. 8 is a sectional view taken along plane 8-8 in Fig. 7;
Fig. 9 is a plan view of the prong structure in accordance with the present invention;
Fig. 10 is a plan view, similar to Fig. 9, wherein the neck of the prong structure is covered by a plastic material.
Fig. 11 is a perspective view of the plug in accordance with the present invention and an inner frame.
Fig. 12 is a final product of a plug in accordance with the present invention.

Detailed Description of illustrative Embodiments

Referring to Figs. 3 through 5, a prong structure 3 in accordance with the present invention generally comprises a neck 31 on an end thereof. The prong structure 3 is substantially cylindrical and made of a conductive metal. At least two prong structures 3 are placed in a mold, and molten plastic material is poured into the mold, forming an inner frame 4 that is bonded with the prongs 3. A semi-product is thus formed after hardening of the plastic material, as shown in Fig. 11. A final plug product 5 (Fig. 12) is obtained after a wire-attaching process and formation of a housing. The neck 31 is the portion that is covered by the plastic material before hardening of the plastic material for forming the inner frame 4.
The neck 31 includes a crescent cutout 312. As illustrated in Fig. 4, in this embodiment, the crescent cutout 312 is delimited by an arc-shaped bottom wall 311 that has a center (X') offset from a longitudinal axis (X) of the prong 3. The neck 31 is covered by a plastic material 313 (Fig. 6) for forming the inner frame 4 (Fig. 11) in the above-mentioned injection molding process. The bonding effect between the arc-shaped bottom wall 311 and the inner frame 4 is improved before and after hardening of the plastic material 313 for forming the inner frame 4. This is because the arc-shaped bottom wall 311 has a center X' offset from a longitudinal axis X of the prong 3. Further, the inner frame 4 thus formed provides improved anti-torque effect.
Figs. 7 through 10 illustrate a modified embodiment of the invention, wherein the neck 31A of the prong 3A includes an annular groove 314A having a bottom wall 310A. A crescent cutout 312A is defined in a portion of the bottom wall 310A. The crescent cutout 312A is delimited by an arc-shaped bottom wall 311A that has a center X' offset from a longitudinal axis X of the prong 3A, as shown in Fig. 8. The neck 31 A is covered by a plastic material 313A (Fig. 10) for forming an inner frame 4 (Fig. 11) in the above-mentioned injection molding process. The bonding effect between the arc-shaped bottom wall 311A and the inner frame 4 is improved before and after hardening of the plastic material 313 for forming the inner frame 4. This is because an arc-shaped bottom wall 311A has a center offset X' from the longitudinal axis X of the prong 3. Further, the inner frame 4 thus formed provides improved anti-torque effect.
The quality of the plug 5 having the prong structure 3, 3A in accordance with the present invention is stable through provision of the arc-shaped bottom wall 311, 311A that has a center X' offset from a longitudinal axis X of the prong 3, 3A. The anti-torque characteristic of the plug meets the safety requirements. Another advantages of the arc-shaped bottom wall 311, 311A are that the bonding effect between the arc-shaped bottom wall 311, 311 A and the inner frame 4 is improved before and after hardening of the plastic material 313, 313A for forming the inner frame 4 and that the frame 4 thus formed provides improved anti-torque effect. Further, the crescent 312, 312A receives the plastic material before hardening, providing products with a stable structure.
Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.

Claims

A prong structure for a plug, the prong (3; 3A) being made of a conductive metal, the prong comprising a neck (31; 31A) covered by a plastic material (312; 312A) for forming an inner frame (4) in an injection molding process, characterized in that:

the neck (31; 31A) includes an arc-shaped bottom wall (311, 311A) that has a center (X') offset from a longitudinal axis (X) of the prong.
The prong structure as claimed in claim 1, wherein the neck (31) includes a crescent cutout (312) is delimited by the arc-shaped bottom wall (311).
The prong structure as claimed in claim 1, wherein the neck (31A) includes

an annular groove (310A) having a bottom wall (310A), and wherein a crescent cutout (312A) is defined in a portion of the bottom wall (310A) and delimited by the arc-shaped bottom wall (311).