Improvements in or relating to electric plugs

Abstract

 A hollow electrically conductive pin (1) for use in an electric plug (6) is formed from sheet metal or metal alloy which has been folded or otherwise shaped to form the pin (1) and which carries on the outer surface of that part of the folded sheet metal or metal alloy forming a substantial part of the length of the pin which will project from a plug body, a covering of electrically insulating material (2).

Description

[0001] This. invention relates to electric plugs and is especially, but not exclusively, concerned with electric plugs for use in domestic and similar wiring systems.

[0002] When an electric plug is electrically connected in a socket outlet but the faces of the plug and outlet are not in interfacial engagement, there is a substantial risk that a child or other person will introduce a finger or other object between these faces and receive an electric shock. To reduce this risk, it has been proposed and is sometimes the practice to provide on at least each line pin of the plug an insulating protective covering which extends around and along a substantial part of the length of the pin projecting from the insulating plug body. Such insulating protective pin-coverings may be integral parts of the plug body but more recently it has been proposed to use, for each insulating pin-covering, a separate sleeve of insulating material which fits over a part of a length of a pin or a separate body of insulating material which is moulded in situ on a pin.

[0003] According to the present invention, a hollow electrically conductive pin for use in an electric plug is formed from sheet metal or metal alloy which has been folded or otherwise shaped-to form the pin, characterised in that the outer surface of that part of the folded sheet metal or metal alloy forming a substantial part of the length of the pin which will project from a plug body carries a covering of electrically insulating material.

[0004] The covering of insulating material preferably has a thickness lying in the range of 0.025mm to 0.1mm.

[0005] The pin is preferably formed from sheet metal or metal alloy which has a groove or other recess in the surface, and electrically insulating material at least partially fills the recess, preferably so as to fill it. In this way limitations on the thickness of the insulating material are considerably eased.

[0006] Preferably, the pin is folded or otherwise shaped so that the edges of that part of the folded sheet metal or metal alloy carrying the covering of electrically insulating material are turned inwardly. This arrangement has the advsatage that if the electrically insulating material becomes detached from these edges the metal or metal alloy underneath is not exposed. Also the distaace of these edges of the metal or metal from the surface of the pin is greatly increased, increasing the possible tracking distance and so making the pin less susceptible to high voltage breakdown.

[0007] Preferably, the insulating material is a hardenable thermosetting synthetic resin, for example an epoxy resin. Other suitable hardenable insulating materials that may be employed include systems based on polyurethane.

[0008] Where the pin is formed from sheet metal or metal alloy which has a groove or other recess in the surface, the insulating material may be a linear polymer such as PVC, polythene, nylon or PTFE.

[0009] The invention also includes a method of forming a hollow electrically conductive pin for use in an electric plug, which method comprises punching or otherwise cutting a sheet of metal or metal alloy to form a multiplicity of integral pin preforms and, before or after detaching a pin preform from the sheet, folding or otherwise shaping the preform to form a hollow pin, characterised in that before or after the sheet has been punched or otherwise cut, electrically insulating material is applied to a selected part of a surface of the sheet to cause a layer of electrically insulating material to adhere to said selected part of the surface to form a covering of electrically insulating material, the conered part of the sheet being such that, when each of said pin preforms is detached from the sheet and folded or otherwise shaped to form a hollow pin, the pin has on the outer surface of a substantial part of the length of the pin that will project frcm a plug body, a covering of electrically insulating material.

[0010] Preferably, a groove or other recess is formed in the surface of the sheet metal or metal alloy before the sheet is folded, the said selected part of the surface of the sheet being the surface of the groove or other recess.

[0011] In one preferred method, before or after the sheet has been punched or otherwise cut, the sheet is heated and electrically insulating material is applied to a selected part of a surface of the heated sheet in powdered form and is permitted or caused to coalesce, with or without pressure.

[0012] Any convenient method of applying powdered insulating material may be employed. For example, a stream of powdered insulating material may be directed on to the selected part of the surface by at least one appropriately shaped nozzle, if necessary the part of the surface of the sheet that is not to be so coated being suitably masked. Where the sheet is in the form of a strip with the pin preforms side by side, the stream of powdered plastics material may be directed on to the selected part of a surface of the strip as the strip is advancing in the direction of its length. ,

[0013] Other methods of applying electrically insulating material to a selected part of a surface of the sheet include electrostatic spraying of powdered material, painting, spraying or brushing a layer of a hardenable liquid material, silk screen techniques, and applying coated tapes.

[0014] Alternatively, where a groove or other recess is formed in the strip of metal or metal alloy, a preformed strip or other insert of insulating material may be laid in the groove or other recess and secured by the application of heat and pressure, or by an adhesive as appropriate for the particular material.

[0015] The invention further includes an electric plug which has at least one hollow electrically conductive pin substantially as hereinbefore described.

[0016] The invention is further illustrated, by way of example, by the accompanying drawlngs, in which:

Figure 1 is a pictorial view of a hollow electrically conductive plug pin in accordance with the invention;

Figure 2 is a similar view of a 13 amp three-pin plug with line pins as shown in Figure 1;

Figure 3 is a diagrammatic plan vlew of a strip of pin preforms;

Figure 4 is a diagrammatic view of a metal sheet having a recess;

Figure 5 is a diagrammatic view of the stages of forming a metal sheet into a hollow pin;

Figure 6 is a pictorial view of an alternative hollow electrically conductive pin in accordance with the invention; and

Figures 7 and 8 are alternative corss-sectionll views on the line in Figure 6.

[0017] The hollow electrically conductive pin 1 shown in Figure 1 has a covering 2 of hardened epoxy resin over the outer surface of a substaatial part of its length. The pin 1 is formed from one of a plurality of metal strip preforms 3 (Figure 3) which have a selected part of their surfaces covered by hardened epoxy resin 4 which was applied to the strip after it had been cut to farm the preforms. Each preform 3 is then folded into a pin 1 shown in Figure 1. These pins 1 can be used as line pins 5 in a thirteen amp three-pin plug 6 as shown in Figure 2.

[0018] In an alternative embodiment a metal sheet 7 shown in Figure 4 has a recess 8. A preformed strip 9 (Figure 5) of PVC is secured in the recess 8. The metal sheet 7 is then cut into preforms 10 as shown in Figure 5, in which PVC strip 9 is inlaid in the recess 8 on the underside of each preform 10. Each preform 10 is then folded into a hollow conductive pin 11 with the edges 12 and 13 of the preform 10 abutting, before it is detached from the metal sheet 7.

[0019] Another hollow conductive pin 14 is shown in Figure 6. In this case, the edges 15, 16 (Figure7) of that part of the folded metal sheet 17 carrying the covering of insulating material 18 are turned inwardly. An alternative arrangement is shown in Figure 8, where the inturned edges 15¹, 16 are contiguous.

[0020] A method of attaching an electrical conductor to the pin 14 in Figure 6 is by crimping. The fingers 19, 20 are cut and formed as an integral extension of the pin 14 when the pin is cut and folded. These fingers 19, 20 can be folded around a conductor to make a crimped connection.

[0021] One alternative method of attaching an electrical conductor to a hollow conductive pin is described and claimed in the specification of BICC-Bumdy Limited's U.K. Patent Application No. 7901361,

Claims

1. A hollow electrically conductive pin for use in an electric plug formed from sheet metal or metal alloy which has been folded or otherwise shaped to form the pin, characterised in that the outer surface of that part of the folded sheet metal or metal alloy forming a substantial part of the length of the pin which will project from a plug body carries a covering of electrically insulating material.

2. A hollow electrically conductive pin for use in an electric plug formed from sheet metal or metal alloy which has been folded or otherwise shaped to form the pin, characterised in that the outer surface of that part of the folded sheet metal or metal alloy forming a substantial part of the length of the pin which will project from a plug body carrles a covering of electrically insulating material, and in tbat the pin is so folded or otherwise shaped that the edges of that part of the folded sheet metal or metal alloy carrying the covering of electrically insulating material are turned inwardly.

3. A hollow electrically conductive pin for use in an electric plug formed from sheet metal or metal alloy which has been folded or otherwise shaped to form the pin, characterised in that the pin has a groove or other recess in the outer surface of that part of the folded sheet metal or metal alloy forming a substantial part of the length of the pin which Will project from a plug body, and electrically insulating material at least partially fills the groove or recess.

4. A hollow electrically conductive pin for use in an electric plug formed from sheet metal or metal alloy which has been folded or otherwise shaped to form the pin, characterised in that the pin has a groove or other recess in the outer surface of that part of the folded sheet metal or metal alloy forming a substantial part of the length of the pin which will project from a plug body, in that electrically insulating material at least partially fills the groove or recess, and in that the pin is so folded or otherwise shaped that the edges of that part of the folded sheet metal or metal alloy carrying the covering of electrically insulating material are turned inwardly.

5. A hollow electrically conductive pin as claimed in any one of Claims 1 to 4, characterised in that the insulating material is a hardenable thermosetting synthetic resin.

6. A hollow electrically conductive pin as claimed in any one of Claims 1 to 4, characterised in that the insulating material is a linear polymer.

7. A method of forming a hollow electrically conductive pin for use in an electric plug, which method comprises punching or otherwise cutting a sheet of metal or metal alloy to form a multiplicity of integral pin preforms and, before or after detaching a pin preform from the sheet, folding or otherwise shaping the preform to form a hollow pin, characterised in that before or after the sheet has been punched or otherwise cut, electrically insulating material is applied to a selected part of the surface of the sheet to cause a layer of electrically insulating material to adhere to said selected part of the surface to form a covering of electrically insulating material, the covered part of the sheet beiag such that, when each of said pin preforms is detached from the sheet and folded or otherwise shaped to form a hollow pin, the pin has on the outer surface of a substantial part of the length of the pin that will project from a plug body, a covering of electrically insulating material.

8. A method as claimed in Claim 7, characterised in that before or after the sheet has been punched or othewise cut, the sheet is heated and electrically insulating material is applied to a selected part of a surface of the heated sheet in powdered fom and is permitted or caused to coalesce, with or without pressure.

9. A method as claimed in Claim 7, characterised in that a groove or other recess is formed in the surface of the sheet before the sheet is folded, and in that, before or after the sheet has been punched or otherwise cut, a preformed strip or other insert of insulating material is laid in the groove or other recess and is secured by the application of heat and pressure or by an adhesive.

10. An electric plug characterised in that at least one of the line pins is a hollow electrically conductive pin as claimed in any one of Claims 1 to 6.

Drawing