GB2152301A

GB2152301A - A non-rewirable electrical plug and a method of moulding therefor

Info

Publication number: GB2152301A
Application number: GB08431088A
Authority: GB
Inventors: Dermot Hurst; Raymond Kenny; Patrick Mannix Brannigan
Original assignee: IRISH DRIVER HARRIS Co LI
Current assignee: IRISH DRIVER HARRIS Co LI
Priority date: 1983-12-13
Filing date: 1984-12-10
Publication date: 1985-07-31
Also published as: GB2152301B; IE832928L; IE54984B1; GB8431088D0

Abstract

A non-rewirable electrical plug 1 comprises a base member 2 mounting pins 4, 5 to which a corresponding conductor of an electric cable 10 is attached to form connections. In moulding the plug the pins 4, 5 are mounted in a mating recess in a mould and insulating material is moulded around the pins 4, 5 to form the base member 2 which is keyed to the pins 4, 5 through a groove 25 extending around each pin 4, 5. The connections between the pins 4, 5 and conductors are then made and the inner layer 15 is moulded around a portion of the base member 2 to enclose the connections. The outer layer 16 is then moulded around the inner layer 15 to form the body of the plug 1. A lug 45 formed integrally with the inner layer 15 projects to the outer surface of the outer layer 16 to indicate the presence of the inner layer 15 in the finished plug 1. <IMAGE>

Description

SPECIFICATION A non-rewirable electrical plug and a method of moulding therefor The invention relates to a non-rewirable electrical plug and a method of moulding therefor.

In one known method of moulding a non-rewirable plug the body of the plug is either moulded in one or two layers around the contacts of the pins to which corresponding conductors have been previously attached.

The principal disadvantage of this method is that stray strands of conductor wire may migrate to the surface ofthe plug body during thefirst moulding operation. This presents a serious safety hazard to the plug user.

In another known method of moulding a nonrewirable plug the pins are inserted in corresponding holes in a preformed base insert either before or after the electrical connections are made between the contact pins and conductors.

The principal disadvantage ofthe use of a premoulded insert is that a complex construction of base insert is required. Such inserts generally include various ramps and shoulders for holding the pins and conductors in position. In addition, the requirement of shoulders or protrubences on the pins to retain them in position in the holes in the preformed base insert leads to a complex and hence costly construction of pin with various changes in cross-section.

This invention is directed towards providing an improved method of moulding an electric nonrewirable plug which will overcome the problems with the presently known methods. The invention is also directed towards providing an improved construction of non-rewirable plug.

According to one aspect ofthe invention there is provided a method of moulding non-rewirable electrical plug having at least a pair of pre-formed plug pins comprising the steps of: mounting a portion of each step in a predetermined position in a mating recess in a mould; moulding insulating material around portion ofthe pins to form a base member mounting the pins; electrically connecting each pin to a corresponding current carrying conductor of an electric cable to form a connection; and moulding a body of insulating material around portion ofthe base member to enclose the connections and conductor cable and to form an outer body ofthe plug.

In a preferred embodiment of the invention the body of insulating material is formed by: moulding a first layer of insulating material around portion ofthe base member to substantially enclose the connections to form a sub-assembly, and moulding a second layer of insulating material around the first layer.

Preferablythe method includes the step of, after moulding of the first layer of insulating material and before moulding ofthe second layer, checking the sub-assembly to ensure that no stray strands of conductor have risen to the outerface ofthe first layer.

In a preferred embodiment of the invention the base member is moulded from a dimensionally stable and electrically resistant thermoplastics material such as glass filled polyester.

In a preferred embodimentoftheinventionthe body may be of any suitable thermoplastic orthermosetting material preferably of a plastisised polyvinyl chloride material.

In another aspect of the invention provides a non-rewirable electrical plug ofthetype comprising a base member mounting at least a pair of plug pins to each of which a corresponding current carrying conductor of an electric cable is electrically connected to form a connection and a body of insulating material moulded around portion ofthe base member wherein at least one pin is formed with a pin keying means for inter-engagementwiththe base member on moulding ofthe base member around portion ofthe pins before the conductors are electrically connected to the pins.

In one embodiment ofthis aspect ofthe invention the pin keying means comprises an undercut groove formed intermediate the ends of the pin.

Usuallythe grooves extend transversely around at least portion ofthe pin.

Alternatively the pin keying means comprises a hole extendingthrough a pin intermediatetheends thereof.

As a further alternative the pin is knurled intermediate its ends to provide the pin keying means.

As a still further alternative the pin is formed with a flange extending transversely around at least portion ofthe pin to provide the pin keying.

In a further embodiment of this aspect ofthe invention the body of insulating material comprises a first layer of insulating material moulded around portion ofthe base memberto substantially enclose the connections and a second layer of insulating material moulded around the first layer.

In a further embodiment of this aspect ofthe invention layer keying means are provided between the base member and at least one layer of insulating material.

In another embodiment of this aspect of the invention indicating means are provided for indicating the presence ofthe first layer of insulating material afterthe second layer has been moulded on.

The indicating means may comprise an indicating lug formed integrally with the first layer and projecting to the outersurface of the second layer.

The keying means between the base member and thefirstlayercomprisestheindicating lug.

Usually the second layer of insulating material extends over portion of the base member to provide at least portion ofthe keying means.

The base member may be moulded from a dimen sionally stable and electrically resistantthermoplastics material such as glass filled polyester.

The invention will be more clearly understood from thefollowing descriptionthereofgiven byway of example only with reference to the accompanying drawings in which: Fig. lisa perspective view of a first sub-assembly comprising a base member, mounting plug pins, forming part of a non-rewirable plug according to the invention.

Fig. 2 is a top plan view ofthe sub-assembly of Fig. 1, Fig. 3 is across-sectionalview in the direction of the arrows Ill-Ill in Fig. 2, Fig. 4 is a perspective view of an electric cable with terminalsandfuseclips attached, Fig. 5 is a perspective view of a second subassembly comprising the first sub-assembly of Figs. 1 to 3 with the cable, terminals and fuse clips of Fig. 4 connected to the pins, Fig. 6 is a top plan view of the sub-assembly of Fig. 5, Fig. 7 is a cross-sectional view in the direction ofthe arrowsVII-VII in Fig. 6, Fig. 8 is an underneath plan view of a third sub-assemblycomprising the sub-assembly of Figs. 5 to 7 with a first layer of insulating material mouldedon, Fig. 9 is a cross-sectional view in the direction ofthe arrows VIIII-VIIII in Fig. 8, Fig. 10 is a cross-sectional view in the direction of the arrows X-X in Fig. 8, Fig. 11 is a perspective view of an electric plug according to th invention, Fig. 12 is another perspective view ofthe plug of Fig.

11 in a different position, Fig. 13 Is a further perspective view ofthe plug of Figs. 11 and 12 in a different position, Fig. 14 is an exploded perspective view ofthe plug of Fig. 12, Fig. 15 is an underneath plan view of the plug of Figs. 11 to 13, and Fig. 16 is a cross-sectional view in the direction of the arrows XIV-XIV in Fig. 15.

Referring to the drawings there are illustrated various parts of sub-assemblies used in forming a non-rewirable electrical plug in accordance with the invention. The finished plug is illustrated particularly in Figs. 11 to 16 and is indicated generally by the reference numeral 1. The plug 1 comprises a base member 2 mounting at least a pair and in this case three plug pins namely a live pin 3, a neutral pin 4 and an earth pin 5. A corresponding current carrying conductor respectively indicated by reference numerals 7,8 and 9 of an electric cable 10 is electrically connected to the pins 3,4,5 to form a connection.A body of insulating material which in this case comprises a first inner layer 15 and a second outer layer 16 is moulded around the connections and portion ofthe base memberto form the body ofthe plug.

The plug is moulded by first mounting a portion of each pin 3,4,5 in a predetermined position in a mating recess in a mould and then moulding insulating material around portion ofthe pins 3,4,5 to form the base member 2. The base member 2 with the pins mounted therein forms a first sub-assembly which is illustrated in Figs. 1 to 3. Each pin 3,4,5 is them electrically attached to its corresponding current carrying conductor7, 8,9 of a cable lOtoform a connection. A second sub-assembly which comprises the first sub-assembly with the pins electrically connected to its corresponding current carrying conductor is illustrated in Figs. 5 to 7.The first layer of insulating material is then moulded around portion of the base member to enclose the conductor connections forming a third sub-assembly as illustrated in Figs. 8to 10. Asecond layer 16 of insulating material is moulded around the first layer 15, the cable 10 and portion ofthe base member 2 to form the outer body oftheplug 1.

Referring particularlyto Figs. 1 to 3 pin keying means are provided on each pin 3,4,5 for interen gagementwith the base member 2. In this case the pin keying means comprises a transverse groove 25 extending around portion of each pin 3,4,5 and into which the material of the base member 2 flows on moulding to retain the pins in position.

It will be noted thatthe side edges of each ofthe pins 3,4,5 are radiussed to reduce stress concentration particularly in the area ofthe keying grooves 25. The head of each pin is hollowed out at 60 to facilitate rivetting on ofthe ring terminals or fuse clips as required.

The base member 2 is of a relativelysimple construction and is formed with fourflared keying holes 30 for engagement with the insulating material ofthefirst layer 15 as illustrated in Figs. 5 to 7. A recess 31 is also provided for reception offuse clips 20, 21 in which is mounted a conventional fuse 32 which is retained in a fuse carrier 35. In the particular arrange- ment illustrated in Fig. 14the fuse carrier 35 is fully removable from the recess 31 however it will be appreciated that the fuse carrier may also be of the captive type, for example the carrier may be slidably, hingedly or in any convenient manner mounted on the base member 2 to facilitate replacement ofthe fuse 32 without detaching the carrier 35from the base member2.A ramp 36 providesaccessforascrew- driverorsimilartool for removal of the carrier 35 and fuse 32 from the clips 20,21. Grooves 37 guide the conductors 7,8 and 9 ofthe cable to their appropriate locations. Portion ofthe fuse clips 20, 21 are inserted into the recess 31 through appropriately shaped channels 38. A keying ledge 38 off-set from the back base 2 is provided for interengagement with the second layer 16 of encapsulation as will be apparent particularly from Fig. 7.

Referring to Figs. 4to 7 after the base member 3 has been moulded around the pins 3,4,5 the neutral and earth conductors 8,9 of the cable 10 are mechanically by rivetting attached through ring terminals 40 to the appropriate pins respectively 4,5. The live conductor7 is mechanically attached to one fuse clip 20. The fuse clip 20 and the other clip 21 are then inserted in their appropriate recesses 31 to form a second base sub-assembly which is illustrated in Figs. 5 to 7. The cable 10 with ring terminals 40 and fuse clips 20, 21 is illustrated in Fig. 4. When the fuse is in place electrical connections between the live conductor7 and the live pin 3 is made.

When the connections have been made and the fuse clips 20, 21 are loaded, the innerfirst layer of insulating material is moulded around the connections and portion ofthe base member 2 to encapsulate the connections and form a third sub-assembly. The third sub-assembly with the first layer 15 in place is illustrated in Figs. 8to 10.

Insulation material forthe first layer 15 is keyed to the base member 2 through the keying holes 30 as will be particularly apparent from Fig. 10. An indicating lug 45 projects proud of at least one of the keying holes 30 to a position flush with the backface ofthe base member 2 and may be clearly viewed when the second layer 16 of insulatingmaterial is moulded on.

Thus a visual inspection ofthefinished plug reveals thatthe inner layer 15 has been included. To facilitate ease of inspection the material ofthe inner layer 15 may be of a different colourthan that of the outer layer 16. A pair of keying holes 47 are formed overthe fuse clips 20 for bonding the outer layer 1 6to the inner layer 15.

Referring to Figs. 11 to 16 there is illustrated a finished plug included a second layer 16 of insulating material moulded over the first layer 15. The insulation material ofthis layer 16 engages in the keying holes 47 in the first layer 15 and behind the ledge 38 of the base member 2. The insulation material also engages around the cable 10 to form a sleeve 15 having a numberof cut-out grooves 51 to allow sufficient flexibility while preventing removal ofthe cable from the plug. Two sidewardly extending ribs 55 on each side of the outer body ofthe plug facilitate finger gripping on insertion and withdrawal ofthe plug into and from a socket.

Referring particularly to Fig. 4 the fuse clip 20 to which the live conductor 17 ofthe cable 10 is attached is illustrated. The clip 20 comprises a fuse receiving portion formed from a generally channel-shaped member 60 including a slightlyarcuate portion 61 for reception of a conventional fuse 32 and a cap 62 spot welded to the channel-shaped member 60. It will be noted thatthe cap is widerthan the channel in which the fuse 32 is received and therefore acts as a seal or shut-offforthefuse clip recesses in the base member 2to preventflash particularly during moulding on of the first layer 15 of insulating material. The cap 62 includes a pair of upstanding lugs 63 which are crimped to engage with the wires ofthe live conductor 7.

The other fuse clip 21 is also illustrated in Fig. 4 and is similar to the clip 20, and like parts being assigned the same reference numerals. The fuse clip 21 is for rivetting to the live pin 3 and consequently the cap 62 is formed with an L-shaped extension 65 having a through hole 66 for engagement overthe head ofthe live pin 3 on rivetting on.

Referring particularlyto Fig. 1 4the fuse carrier 35 includes a generally rectangular shield 70 and a central collar 71 for accommodating the fuse. Viewing apertures 72 are provided in the shield 70.

The base member 2 is preferably of 30% glassfilled thermoplastic polyester material. The first 15 and second 16 layers of encapsulation are usually of a plastisised polyvinyl chloride material however both the layers and base member may be of any suitable thermoplastic orthermo-setting material.

One advantage ofthe method according to the invention is that because the base member is moulded around the pins it is of very simple construction.

Consequently the tooling required is also a simple construction and the construction of pin is considerabley less complex than that required in previous methods of moulding such plugs.

It will be appreciated that in some cases instead of a first layer of insulating material moulded on or around the connections and base member a preformed cap or gaiter may be provided.

It will also be appreciated that after moulding on of the first layer a suitable check may be made to ensure that no stray strands of conductor have migrated to the surface ofthe layer. This check may be conducted either electrically or by visual inspection. However, it is envisaged that even if such strands were present these would be safely confined to the outer surface of the first layer which is covered by the outer layer or layers.

It will be appreciated that a dummy earth pin may be provided in the plug in some cases.

It will also be appreciated that as a safety feature the pins may be sleeved over portion oftheir length. For examplewhen forming the base insert.

It will also be appreciated that any number of layers of insulation material may be employed.

It will be appreciated that in the case where the pin keying means is provided bya groovethegroovemay extend either partially or fully around the pin. The pin keying means may also be provided by a flange extending transversely around at least portion of the pin. A hole or a numberofblindorthrough holes may be provided in the pin intermediate the ends thereofto provide the keying means. As a further alternative the pin may be knurled to provide the keying means.

It will also be appreciated that each of the fuse clips may be formed from a single piece of electrically conductive material.

Claims

1. A method of moulding a non-rewirable electrical plug having at least a pair of preformed plug pins comprising the steps of: mounting a portion of each pin in a predetermined position in a mating recess in a mould; moulding insulating material around portion of the pins to form a base member mounting the pins; electrically connecting each pin to a corresponding current carrying conductor of an electric cable to form a connection; and moulding a body of insulating material around portion ofthe base memberto enclose the connections and conductor cable and to form an outer body ofthe plug.

2. A method as claimed in claim 1 in which the body of insulating material is formed by: moulding a first layer of insulating material around portion of the base member to substantially enclose the connections to form a sub-assembly, and moulding a second layer of insulating material around the first layer.

3. A method as claimed in claim 2which includes the step of, after moulding of the first layer of insulating material and before moulding ofthesecond layer, checking the sub-assembly to ensure that no stray strands of conductor have risen to the outerface ofthefirst layer.

4. A method as claimed in any of claims 1 to 3 in which the base member is moulded from a dimen sionally stable and electrically resistantthermoplastics material.

5. Amethod as claimed inclaim4inwhichthe base member is moulded from a glass filled polyester material.

6. A method as claimed in any preceding claim in which the body is of a thermoplastic orthermosetting material.

7. A method as claimed in claim 6 in which the body is of plastisised polyvinyl chloride material.

8. A method substantially as hereinbefore de scribed with reference to the accompanying drawings.

9. Anon-rewirable electrical plug ofthetype comprising a base member mounting atleasta pairof plug pins to each of which a corresponding current carrying conductor of an electric cable is electrically connected to form a connexion and a body of insulating material moulded around portion of the base memberwherein at least one pin is formed with a pin keying means forinter-engagementwith the base member on moulding of the base member around portion of the pins before the conductors are electrically connected to the pins.

10. A plug as claimed in claim 9 in which the pin keying means comprises an undercut groove formed intermediate the ends ofthe pin.

11. A plug as claimed in claim 10 in which the groove extends transversely around at least portion of the pin.

12. A plug as claimed in clam lOin which the pin keying means comprises a hole extending through a pin intermediate the ends thereof.

13. A plug as claimed in claim 10 in which the pin is knurled intermediate its ends to provide the pin keying means.

14. A plug as claimed in claim 10 in which the pin is formed with a flange extending transversely around at least portion ofthe pin to providethe pin keying means.

15. A plug as claimed in claims 9to 14 in which the codyofinsulating material comprises a first layer of insulating material moulded around portion of the base member to substantially enclose the connections dnd a second layer of insulating material moulded around the first layer.

16. A plug as claimed in any of claims 9 to 15 in which layer keying means are provided between the base member and at least one layer of insulating material.

17. Aplug as claimed in any of claims 9 to 16in which indicating means are provided for indicating the presence of the first layer of insulating material afterthe second layer has been moulded on.

18. A plug as claimed in claim 17 in which the indicating meanscomprises an indicating lugformed integ rally with the first layer and projecting to the outer surface ofthe second layer.

19. Aplug as claimed in claim 18 in which the keying means between the base member and the first layer comprises the indicating lug.

20. A plug as claimed in claim 19 in which the second layer of insulating material extends over portion ofthe base memberto provide at least portion ofthe keying means.

21. A plug as claimed in any of claims 9 to 20 in which the base member is moulded from a dimen sionallystable and electrically resistantthermoplastics material.

22. A plug as claimed in claim 21 in which the base member is mouldedfrom a glass filled polyester material.

23. A plug as claimed in any of claims 9to 22 in which the body is of a thermoplastics orthermosetting material.

24. A plug as claimed in claim 23 in which the body is of a plastisised polyvinyl material.

25. A plug substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.