GB2065991A - Sleeved plug pin - Google Patents

Abstract

A pin 22, 24, 26 has a reduced portion 24 of dumb-bell shape in cross-section to receive a plastics sleeve 28 of similar internal cross- section. This cross-section avoids many problems in moulding and handling which arise with the more usual rectangular cross-section of prior art sleeves. The pin may be of diecast, brass-plated, zinc-alloy construction. <IMAGE>

Description

SPECIFICATION Electrical plugs This invention relates to electrical plugs, and in particular is concerned with sleeved conductor pins for electrical plugs.

It is a criticism of many plugs that it is possible to touch accidentally the live and neutral pins of a plug when the pins are partially inserted into a socket, with consequent danger of receiving an electric shock. Danger may particularly arise when the plug is tilted during engagement with the socket. To reduce the danger it is known to provide insulating sleeves (for example, moulded of a plastics material) around portions of the pins which are otherwise exposed and liable to be accidentally touched.

Conductor pins to be sleeved usually comprise a portion of reduced cross-section to receive the insulating sleeve; the insulating sleeve usually has an outer cross-section which is the same as that of an adjacent unsleeved outer end portion of the pin, so that the sleeved pin is of a uniform crosssection over at least that part of its length which will enter a socket with which the plug is engaged.

Conventionally, the cross-section of the reduced portion of the pin, and correspondingly the inner cross-section of the sleeve, is of an oblong rectangular shape where the pin is of a so-called flat pin type (for example complying with British Standard No. 1363).

Various problems arise with the conventional sleeve arrangements, many of these stemming from the shape of the sleeve. The sleeves are usually relatively thin-walled, and this can result in moulding difficulties leading to poor quality mouldings, including the production of nonstraight sleeves which are at worst scrap and at best difficult to assemble on to pins. Furthermore the relatively thin walls, and the sharp-cornered inside shape of a rectangular sleeve, can mean that the sleeves are relatively frail and may suffer damage in handling before assembly on to pins.

Thin walls also tend to mean that the sleeves ale easy to distort, even to the extent of allowing the insertion of a plug pin in a wrong orientation within a sleeve, and flexibility in the sleeve generally tends to make assembly with a pin more difficult. A disadvantage also arises from the sharp-cornered shape of the reduced portion of a pin which is of rectangular cross-section, in that there can be a tendency for the sharp corners of the pin to cut into the sleeve as a sleeve is slid on to the pin; lack of straightness in the moulded sleeve and thinness of the sleeve wa!!, tend to make this problem worse.

It is an object of the invention to provide an improved sleeved conductor pin.

In one of its aspects the invention provides a sleeved conductor pin comprising an electrically conductive pin, comprising an outer end portion and a reduced portion adjacent said outer end portion having a cross-sectional area less than that of said outer end portion, and an electrically insulating sleeve mounted on said reduced portion of the pin, the cross-section of said reduced portion, and correspondingly the inner crosssection of the sleeve, having a wholly curvilinear non-circular periphery.

The use of a shape with a wholly curvilinear periphery can be found to be advantageous in various ways. For example, it can be beneficial as regards strength of the sleeve, ease of moulding the sleeve in an injection moulding process, avoidance of damage to the sleeve during assembly with a pin, and ease of formation of the pin by a diecasting process.

In another of its aspects the invention provides a sleeved conductor pin comprising an electrically conductive pin, comprising an outer end portion and a reduced portion adjacent said outer end portion having a cross-sectional area less than that of said outer end portion, and an electrically insulating sleeve mounted on said reduced portion of the pin, the cross-section of said reduced portion of the pin, and correspondingly the inner cross-section of the sleeve, being of a dumb-bell shape (as hereinafter defined).

By a "dumb-bell shape" is meant, where the expression is used herein, the shape of an axial cross-secticn through a solid of revolution comprising two similar, axially spaced, head portions connected by an elongate body portion of which the diameter where it joins each of the head portions is less than the maximum diameter of the head portion. Preferably the maximum diameter of the body portion is not greater than the maximum diameter of the head portions. In one preferred dumb-bell shape the diameter of the body portion is a maximum at a position mid-way between the head portions, where it may be equal to the maximum diameter of the head portions.

The dumb-bell shape enables the reduced portion of the pin to be constructed with a generally rounded periphery which militates against damage being done to a sleeve in assembly of the sleeve with the pin. Furthermore the dumb-bell shape can provide a locking engagement between the sleeve and the pin which resists relative rotation between the sleeve and the pin and reduces the likelihood of the sleeve being mounted on the pin in an incorrect orientation. In relation to the sleeve, the dumb-bell shape of the inner cross-section of the sleeve can be of assistance in moulding the sleeve from a plastics material, and can help to overcome some of the moulding problems experienced hitherto.

Parts of the sleeve can be of a greater wall thickness than has been usual hitherto, and the use of curved shapes can improve the flow of material in an injection moulding process and avoid points of high stress concentration in the moulded sleeve. The dumb-bell shape can assist in providing a sleeve which is sufficiently strong to withstand rough handling, and suitably stiff for ease of assembly with a pin.

The pin preferably comprises a core of a zinc alloy material formed in a diecasting process, the casting subsequently being brass plated. Hitherto, pins have usually been machined out of solid brass material, and by employing a diecasting process the cost of manufacturing sleeved pins may be reduced.

There now follows a description, to be read with reference to the accompanying drawings, of an electrical plug comprising two sleeved conductor pins which each illustrate the invention by way of example.

In the accompanying drawings: Figure 1 is a view in longitudinal section through earth and neutral pins of the plug; Figure 2 is a view in elevation of a conductor pin of the plug; and Figure 3 is a magnified view in plan of the pin shown in Figure 2.

The plug comprises a base member 10, to an outer side of which is secured a faceplate member 12, the faceplate member being retained by shoulders of live and neutral conductor pins 14 (one only shown) and an earth pin 16, which pins extend through the faceplate member and the base member to an inner side of the base member for electrical connection in a conventional manner to leads of a flexible cord 1 8. A cover member 20 is secured to the assembly of the base member 10 and the faceplate member 12 to prevent access to otherwise exposed electrical conductors adjacent the inner side of the base member. The plug is constructed in accordance with British Standard No.1363.

Each of the live and neutral pins 14 comprises an outer end portion 22, a reduced portion 24 adjacent the outer end portion, and a cylindrical inner end portion 26 which in the assembled plug is rivetted over to secure an electrical connection.

The reduced portion 24 has a cross-sectional area less than that of the outer end portion 22 (see especially Figure 3). In the assembled plug (Figure 1), an electrically insulating sleeve 28, provided by a sleeve portion ofthefacepiate member 12, is mounted on the reduced portion 24 of each of the live and neutral conductor pins 14. Each sleeve has an outer cross-section which is substantially the same as the cross-section of the outer end portion 22 of the pin, and an inner cross-section which is substantially the same as the cross section of the reduced portion 24 of the pin, so that the sleeved pin is of uniform cross-section over at least that part of its length which will enter a socket with which the plug is engaged.

The cross-section of the reduced portion 24 of each pin 14, and correspondingly the inner cross section of the sleeve 28, is of a dumb-bell shape (as hereinbefore defined) as shown in Figure 3. In chain-dot outline, in Figure 3, the cross-section of the reduced portion of a conventional pin is indicated, from which it can be seen that the maximum longitudinal and transverse dimensions of the two cross-sections are the same. The cross section of the reduced portion 24 can be notionally divided into two identical head portions connected by an elongate body portion. The width of the body portion is a maximum at a position mid-way between the head portions, where it is equal both to the maximum width of the head portions and to the diameter of the inner end portion 26 of the pin.As seen in Figure 3, the perimeter of the cross-section is made up entirely of curves, so that the cross-section has a wholly curvilinear non-circular periphery.

The live and neutral pins 14 comprise a core of a zinc alloy material formed in a diecasting process, the casting so formed being subsequently brass plated to provide the pin. The faceplate 12, comprising the sleeve portions providing the sleeves 28 for the pins 14, is moulded by injection moulding of a nylon material.

For electrical connection to the inner end portions 26 of the live and neutral pins 14, it is preferred to employ terminations of a phosphor bronze material, as compatible with the largely zinc alloy pins as regards thermal expansion and cuntraction during use.

The use of diecasting to manufacture the live and neutral pins 14 allows considerable flexibility in the design of the cross-sectional shape of the reduced portions of the pins, and other pins in accordance with the invention might have different dumb-bell shapes from that of the pin shown in Figure 3. For example, the body portion of the cross-section could be rectangular in shape, or have concave, rather than convex, sides extending between the head portions.

Claims (8)

1. A sleeved conductor pin comprising an electrically conductive pin, comprising an outer end portion and a reduced portion adjacent said outer end portion having a cross-sectional area less than that of said outer end portion, and an electrically insulating sleeve mounted on said reduced portion of the pin, the cross-section of said reduced portion of the pin, and correspondingly the inner cross-section of the sleeve, being of a dumb-bell shape (as hereinbefore defined).

2. A sleeved conductor pin according to Claim 1 in which the maximum diameter of the body portion (of the dumb-bell shape) is not greater than the maximum diameter of the head portions.

3. A sleeved conductor pin according to Claim 2 in which the diameter of the body portion is a maximum at a position mid-way between the head portions.

4. A sleeved conductor pin according to Claim 3 in which the maximum diameter of the body portion is equal to the maximum diameter of the head portions.

5. A sleeved conductor pin comprising an electrically conductive pin, comprising an outer end portion and a reduced portion adjacent said outer end portion having a cross-sectional area less than that of said outer end portion, and an electrically insulating sleeve mounted on said reduced portion of the pin, the cross-section of said reduced portion, and correspondingly the inner cross-section of the sleeve, having a wholly curvilinear non-circular periphery.

6. A sleeved conductor pin according to any one of Claims 1 to 5 in which the electrically Conductive pin comprises a brass-plated core of a zinc alloy material formed in a diecasting process.

7. A sleeved conductor pin substantially as hereinbefore described with reference to the accompanying drawings.

8. An electrical plug comprising a sleeved conductor pin according to any one of Claims 1 to 7.