GB1579734A

GB1579734A - Methods of making electrical connections and connectors for use therein

Info

Publication number: GB1579734A
Application number: GB1011776A
Authority: GB
Original assignee: Raychem Ltd
Current assignee: Raychem Ltd
Priority date: 1977-03-11
Filing date: 1977-03-11
Publication date: 1980-11-26
Also published as: BE888940Q

Description

(54) METHODS OF MAKING ELECTRICAL CONNECTIONS AND CONNECTORS FOR USE THEREIN (71) We, RAYCHEM LIMITED, a British Company, of Moor House, London Wall, London, E.C.2, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement-: This invention relates to methods of making electrical connections and connectors for use therein.

The usual method for attaching an earth lead to a solid outer conductive sheath of an electrical cable is by soldering. However, although a good electrical connection can be obtained by this method, it is both operator dependent and time consuming, and the resultant connection is not mechanically strong. Furthermore, it is not easy to form soldered connections to aluminium sheathed cables, and difficulties have also been experienced in soldering an earth lead to the copper sheath of a mineral insulated cable, of the type found for example in fire protection systems, since the copper sheath is frequently covered with a tightly adhering coating of oxide, which necessitates vigorous abrasion of the surface to expose the metal, with the consequent risk of damage to the copper sheath.

In certain types of electrical apparatus there is a need to connect an earth lead to an edge of a metal surface, and it is known to use a clamp connector provided with a screw for this purpose. However with such edge connectors it is frequently difficult to obtain a connection having a good long term electrical performance.

There is thus a need for a method of connection which provides a good mechanical and electrical connection between a variety of substrates and for a connector which is simple to install and reliable in service.

The present invention is based on our observation that mechanically strong electrical connections to conductors can be made by employing dimensionally heatrecoverable memory metal connectors which have a discontinuous cross-section.

Accordingly, in one aspect, the present invention provides a method of making an earth connection to a conductor in which there is used a connector comprising a dimensionally heat-recoverable memory metal member which has a discontinuous cross-section and which is fitted wholly or partly around the conductor and is recovered into gripping engagement therewith.

Such a method can simply be carried out by using a split heat-recoverable band which is positioned around the conductor and, for example, a further conductor such as an earth lead, and is caused to recover whereupon it grips the conductors and forces them together to make the electrical connection.

However, in most applications it will be preferable for the connector to have means for facilitating the attachment of, and preferably, independently receiving, the second conductor. Accordingly, in a second aspect, the present invention provides a method of electrically connecting a first conductor to a second conductor. which comprises placing at least partly around said first conductor a dimensionally heatrecoverable memory metal connector which has a discontinuous cross-section and which is provided with means integral therewith for facilitating attachment of the said second conductor, heating said conductor so that it recovers into gripping engagement with said first conductor, and before, during or after said heating step attaching said second conductor to the connector.

The present invention also provides a connector comprising a dimensionally heat recoverable memory metal member which has a discontinuous cross-section and which is constructed so as to fit wholly or partly around, and be recovered into gripping engagement with, a first conductor and which is provided with means integral therewith for independently receiving, and facilitating the mechanical attachment of, a second conductor.

Whilst the present invention will, for conveniencc, be described in more detail with reference to the formation of connections between earth leads and sheathed cables, it will be appreciated that the term "conductor" as used herein is not limited to the material(s) or the shape(s) of the objects being connected.

The means for facilitating the attachment of the second conductor may, for example, simply be a surface on the connector which is receptive to the formation of a soldered connection with the second conductor or to the formation of a crimped connection with the second conductor although the connectors may, if desired, be provided with means such as for example, a flange, or lug or a solder pot, for enhancing such connections.

However, the connectors will, in general, be provided with means for inde pendently receiving and facilitating the mechanical attachment of the second conductor. For example the connector may be provided with an upstanding screw threaded portion and a complementary nut for attachment of the earth lead. However where the connector is provided with means for independently receiving and mechanically attaching the second conductor these means are preferably also adapted to grip or attach to the conductor indepcndently after recovery, for example, the heat-recoverable member may be provided with channels or grooves adapted to receive the earth lead and the cable sheath and to grip the lead and the sheath after recovery and, in general, it will be preferred that the recovery of the heat-recoverable member acts as the sole agent for forming the connection between the two conductors.

For example, in one preferred embodiment of the present invention, there is used a connector which is capable of independently receiving two or more conductors in side-by-side relationship so that on re covcry, the conductors are gripped by the electrical conductive memory metal so as to establish electrical connection between them. Such a connector may, for example, have the form, in cross-section, of a broken figure eight thereby providing two discontinuous bands in side-by-side relationship.

In another preferred embodiment, the connector comprises a heat-recoverable band constructed so as to fit wholly or partly around a first conductor, the band being provided with at least one peripheral slot adapted to receive a second conductor and the band and the slot being so shaped that upon recovery the first and second conductors are each independently gripped by contraction of the band and the slot, respectively. For example the band may be formed with a channel shaped deformation extending across the width of the band in an axial direction, there being situated within the channel an upstanding bridge portion bounded on each side by slots cut in the channel, the slots being adapted to receive the second conductor therethrough.

In yet another embodiment the connector may comprise a heat-recoverable band having a recess in one or both of its jaws.

The heat-recoverable memory metal member used in the connectors of the present invention is of discontinuous crosssection and is, therefore, able to recover in a bending mode. For example, where the connector comprises a heat-recoverable band the band is provided with a gap in its circumference, the width of the gap preferably being small relative to the diameter of the band. A discontinuous band has the advantage that it can be given a bending deformation which combines both tensional and compressive stresses with the result that higher effective degrees of dimensional recovery can be attained as compared with a continuous band. This extra recovery is especially advantageous because memory metals exhibit a relatively low degree of recoverable strain. Furthermore, these metals are usually resilient in their recovered state and the presence of a discontinuity similarly increases the degree of resiliently recoverable deformation which can be imparted to them. Thus members exhibiting such a discontinuity are more able to accommodate dimensional changes which may occur in the conductors after the connection has been made (for example during heat aging).

The provision of a discontinuity also greatly facilitates the application of the connector to conductors with edges. A further advantage, where the connector is used to form a connection to a cabled sheath, is that on recovery the edges of the discontinuity in the band are forced into a firmer gripping relationship with the sheath and, if the sheath is sufficiently malleable, a small portion thereof may even be extruded into the discontinuity thus providing an additional protection against circumferential movement of the connector relative to the sheath.

Amongst suitable memory metals for use in the present invention there may be mentioned various alloys of titanium and nickel which are described for example in U.S. Patent Nos. 3,174,851, 3,351,463, 3,753,700, 3,759,552, British Patent Nos.

1,327,441, and 1,337,442 and NASA Publication SP 110, "55-Nitinol - The alloy with a Memory, etc" (U.S. Government Printing Office, Washington D.C. 1972).

The property of heat-recoverability has not, however, been solely confined to such titanium-nickel alloys. Thus, for example, various beta-brass alloys have been demonstrated to exhibit this property in e.g. N. Nakanishi et al, Scripta Metallurgica 5, 433-433 (Pergamon Press 1971) and such materials may be doped to lower their transition temperatures to cryogenic regimes by known techniques.

Similarly, 304 stainless steels have been shown to enjoy such characteristics, E. Enami et al, id at pp 663-68.

In general these metals have a transition temperature within the range of from - 196"C to + 1350C, especially from - 196"C to -700C (this being the lowest temperature they are liable to encounter during everyday use), and thus may be brought to their martensitic state by immersion in liquid nitrogen. However, more recently, it has been found possible to "precondition" memory metals so as transiently to raise their transition temperature. This enables the articles made from such alloys to be kept at room temperature prior to use, when they can be recovered by heating. Such preconditioning methods, which eliminate the need for liquid nitrogen during storage and transportation, are described, for example, in German Patent Application OS 26 03 878 and OS2603911.

The preferred memory metal for use in the present invention is heat-recoverable brass since this has excellent electrical properties and permits soldered connections to be made.

As previously mentioned, the present invention is especially suitable for making connections between earth leads and the conducting sheaths of electric cables and, in a particularly preferred embodiment according to this aspect of the invention, the connector is positioned within a heatrecoverable plastics sleeve so that on recovery the sleeve provides an environmental seal for the connection made by the article. In terminations and splices for mineral insulated cables the heatrecoverable sleeve is preferably provided with a fusible insert as described in British Patent No. 1,098,304. Such an arrangement provides a single heat-recoverable part which in one operation is capable of providing an earth connection and a seal for the mineral insulated cable termination or splice. Preferably, the temperature at which the connector recovers is lower than the temperature of recovery of the heatrecoverable sleeve and the temperature of fusion of the fusible insert.

Another application for the connectors of the present invention is in the earthing of leads to edges of electrical apparatus. In such an edge connector, one part is adapted to receive and grip the edge upon recovery and another part is adapted to receive the earth lead. For example, as mentioned above, such a connector may comprise a discontinuous band having a recess in one or both of its jaws. The discontinuous band may be positioned about the edge and the earth lead is positioned in a recess. Upon recovery, the jaws move together to grip the edge and thereby force the earth lead into connection with it.

Alternatively, the earth lead may, in some cases, be simply positioned within the discontinuous band next to the edge.

When, as described above, the heatrecoverable member has the form, in crosssection, of a broken figure eight, thereby effectively providing two discontinuous bands in side-by-side relationship, for example, the edge may be placed within one band and the earth lead within the other.

Various embodiments according to the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a first connector; Figure 2 shows the connector of Figure 1 heat recovered in position about the solid outer sheath of a mineral insulated cable; Figure 3 shows a cross-section through lines I-I of Figure 2; Figure 4 illustrates a second connector; Figure 5 shows a third connector heat recovered in position about the solid outer sheath of a cable and protected by a heat recovered moulded sleeve; Figure 6 shows a fourth connector heat recovered in position about the solid outer sheath of a cable; Figure 7 illustrates a previously proposed edge connector; Figure 8 illustrates one form of edge connector Figure 9 illustrates a second form of edge connector; Figure 10 represents a third form of edge connector; Figure 11 represents a fourth form of edge connector; Figure 12 illustrates a connector for joining cables; and Figure 13 illustrates the use of a connector for joining a power cable to its branch cables.

Referring to Figure 1, there is shown a connector comprising a discontinuous band 1, formed from a memory metal, having a gap 2 and a channel portion indicated generally by reference numeral 3. The channel portion 3 comprises a channel 4 having a raised bridge portion 5 defined by slots 6 cut into the channel 4.

Figure 2 shows the connector of Figure 1 recovered about the solid outer conducting sheath 7 of a cable 8 and connecting an earth lead 9 thereto. The earth lead 9 is stripped to expose the centre conductor 10 which is inserted into the channel 4 through slots 6 and under the bridge portion 5. The band I is positioned about the outer sheath 7 and heated to cause it to recover towards its original configuration.

On recovery the band 1 tightens radially about the outer sheath 7, and the raised bridge portion 5 and the channel 4 tend to flatten so as to grip the conductor 10 in the slots 6.

Figure 3 shows a cross-section through lines 1-1 of Figure 2. The conductor 10 of the earth lead 9 is clamped against the outer sheath 7 of the cable 8 by the bridge portion 5.

Figure 4 shows a second form of connector according to the present invention comprising a discontinuous memory metal band 11 having a single circumferential slot 12 therein. The material of the band in the area of the slot 12 has been formed to provide a channel 13 extending from the slot 12 to the edge of the band 11 and a raised portion 14 extending from the slot 12 to the opposite edge of the band 11.

The connector of Figure 5, shown recovered about the sheath of a cable, comprises a discontinuous band 15 of memory metal having a gap 16 therein.

The conductor of an earth lead 17 has been soldered at 18 to the band 15 and a heatrecoverable plastic moulded part 19 has been heat recovered about the connector to provide an environmental protection.

The connector of Figure 6 has also been recovered about the sheath of a cable. The connector, indicated generally by reference numeral 20 comprises a band 21 of memory metal having a raised lug 22 to which has been soldered an earth lead 23.

Clearly the lug may have a configuration other than that shown, for example it may comprise a deformable portion which may be crimped about the conductor of the earth lead, or may have a screw threaded portion and a mating nut.

In Figure 7 there is illustrated an edge connector representative of those at present used in the art. As can be seen, the edge connector comprises a generally U-shaped member 31 adapted to receive the edge concerned between the arms of the U, and which may also be provided with a groove or recess 32 adapted to receive an earth lead which is to be connected to the edge.

When the two components are in position the connection is made by tightening screw 33 until the head 34 breaks off.

In Figure 8 there is shown a heatrecoverable memory metal edge connector in accordance with the present invention.

This comprises a band 35 which is split longitudinally so as to form two jaw portions 36 and 37, the jaw 37 having a recess 38 adapted to receive an earth lead.

(If desired the edge 36 may also be provided with such a recess in order to accommodate a second earth lead.) In use the band 35 is deformed by bending it so as to open the jaws 36 and 37 and, upon subsequent recovery these jaws move together in the direction shown by the arrows so as to grip edge 39 and form a secure connection to the earth lead.

In Figure 9 there is shown a second heat-recoverable memory metal edge connector in accordance with the present invention, the cross-section of which is generally of the form of a figure eight, each of the rings of the eight being longitudinally split. In use an edge 10 may be positioned within one ring 41 and an earth lead or second edge may be positioned within the other ring 42. Upon recovery in the direction shown by the arrows the two components are securely gripped so as to form the desired connection. The connector may, of course, equally well be used to connect the earth lead to a cable or, indeed, to connect two cables or two sheets of material.

Figure 10 shows a simple form of heatrecoverable connector comprising a discontinuous memory metal band 43 used to form a connection between an earth lead 44 and an edge member 45 in accordance with the method of the present invention.

Upon recovery the jaws of the band 43 move together in the direction shown by the arrows so as securely to grip the earth lead 44 to the edge member 45.

The connector shown in Figure 11 operates in a similar fashion in that the jaws of heat-recoverable memory metal band 46 move together as indicated by the arrows to grip edge member 47. However, in this case the earth lead 48 is attached to the band 46 by soldering within the channel 49 which is provided for this purpose.

Figure 12 shows how a connector in accordance with the present invention may be used to join cables. The connector comprises a heat-recoverable memory metal member 50 provided with grooves 51 and 52 adapted to receive cables 53 and 54, respectively. Upon recovery, the member 50 moves in the direction indicated by the arrows so as to form a secure connection between the cables.

Finally, in Figure 13 there is shown a somewhat similar memory metal connector designed to join a power cable 55 to two branch cables 56 and 57. In this case the connector 58 is provided with gripping arms 59 and 60 for connection with the power cable 55 and is also provided with grooves 61 and 62 adapted to receive the branch cables 56 and 57, respectively.

Upon recovery the connector 58 moves in the direction shown by the arrows so as to form the connection.

The present invention has been specifically described with reference to the embodiments shown in the accompanying drawings, but many other variations and modifications falling within the scope of the present invention will be apparent to those skilled in the art.

WHAT WE CLAIM IS: 1. A method of electrically connecting a first conductor to a second conductor, which comprises placing at least partly around said first conductor a dimensionally heat-recoverable memory metal connector which has a discontinuous cross-section and which is provided with means integral therewith for facilitating attachment of said second conductor, heating said connector so that it recovers into gripping engagement with said first conductor and, before, during or after said heating step attaching said second conductor to the connector.

2. A method as claimed in claim 1, wherein the connector is provided with means for independently receiving, and facilitating mechanical attachment of, the second conductor.

3. A method according to claim 1 or claim 2, wherein the memory metal is a brass.

4. A method according to any one of claims 1 to 3, wherein the connector is arranged to recover in a bending mode.

5. A method according to any one of claims 1 to 4, wherein the connector comprises a heat-shrinkable band provided with a gap in its circumference.

6. A method according to claim 5, wherein the width of the gap is small relative to the diameter of the band.

7. A method according to any one of claims 1 to 6, wherein the connector comprises means for independently receiving a plurality of conductors prior to recovery.

8. A method according to claim 7, in which the conductors are positioned within the heat-recoverable member in side-by-side relationship, the heat-recoverable member being provided with parts adapted to receive the conductors in such an arrangement, and wherein said member is caused to recover to make the connection.

9. A method according to claim 7, or claim 8, in which the heat-recoverable member has the form, in cross-section, of a broken figure eight, thereby providing two discontinuous bands in side-by-side relationship.

10. A method according to any one of claims 1 to 6, in which the connector com prises a heat-recoverable band constructed so as to fit wholly or partly around a first conductor, the band being provided with at least one peripheral slot adapted to receive a second conductor and the band and the slot being so shaped that upon recovery the first and second conductors are each inde pendently gripped by contraction of the band and the slot, respectively.

11. A method according to claim 10, in which the band is formed with a channel shaped deformation extending across the width of the band in an axial direction there being situated within the channel an upstanding bridge portion bounded on each side by slots cut in the channel, the slots being adapted to receive the second conductor therethrough.

12. A method according to any one of claims 1 to 4, in which the connector comprises a heat-recoverable discontinuous band having a recess in one or both of its jaws.

13. A method according to any one of claims 1 to 12, in which the connector is positioned within a heat-recoverable plastics sleeve so that on recovery the sleeve provides an environmental seal for the connection.

14. A method according to any one of claims 1 to 13, wherein the recovery of the connector acts to form connections to both the first and second conductors.

15. A method according to any one of claims 1 to 6, in which the connector is provided with means adapted to grip or attach to one of the conductors independently after recovery.

16. A method according to any one of claims 1 to 15, in which there is formed a connection between an earth lead and the conducting sheath of an electrical cable.

17. A method according to any one of claims 1 to 15, in which there is formed a connection between an earth lead and an edge of an electrical apparatus.

18. A method of making an earth connection to a conductor in which there is used a connector comprising a dimensionally heat-recoverable memory metal member which has a discontinuous crosssection and which is fitted wholly or partly around the conductor and is recovered into gripping engagement therewith.

19. A method according to claim 18, in which the connector comprises a heatrecoverable band which is positioned

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. between the cables. Finally, in Figure 13 there is shown a somewhat similar memory metal connector designed to join a power cable 55 to two branch cables 56 and 57. In this case the connector 58 is provided with gripping arms 59 and 60 for connection with the power cable 55 and is also provided with grooves 61 and 62 adapted to receive the branch cables 56 and 57, respectively. Upon recovery the connector 58 moves in the direction shown by the arrows so as to form the connection. The present invention has been specifically described with reference to the embodiments shown in the accompanying drawings, but many other variations and modifications falling within the scope of the present invention will be apparent to those skilled in the art. WHAT WE CLAIM IS:

1. A method of electrically connecting a first conductor to a second conductor, which comprises placing at least partly around said first conductor a dimensionally heat-recoverable memory metal connector which has a discontinuous cross-section and which is provided with means integral therewith for facilitating attachment of said second conductor, heating said connector so that it recovers into gripping engagement with said first conductor and, before, during or after said heating step attaching said second conductor to the connector.

around the conductor and a second conductor and is caused to recover whereupon it grips the conductors and forces them together to make the earth connection.

20. A method according to claim 18 or claim 19, wherein the connector is arranged to recover in a bending mode.

21. A method according to any one of claims 18 to 20, in which the connector comprises a discontinuous heat-recoverable band provided with a gap in its circumference.

22. A method according to claim 21, in which the width of the gap is small relative to the diameter of the band.

23. A connector comprising a dimensionally heat-recoverable memory metal member which has a discontinuous crosssection and which is constructed so as to fit wholly or partly around, and be recovered into gripping engagement with, a first conductor and which is provided with means integral therewith for independently receiving, and facilitating the mechanical attachment of, a second conductor.

24. A connector according to claim 23, wherein the memory metal is a brass.

25. A connector according to claim 23 or claim 24, wherein the connector is arranged to recover in a bending mode.

26. A connector according to any one of claims 23 to 25, wherein the connector comprises a heat-shrinkable band.

27. A connector according to claim 26, wherein the width of the gap is small relative to the diameter of the band.

28. A connector according to any one of claims 23 to 27, wherein the connector comprises means for independently receiving a plurality of conductors prior to recovery.

29. A connector according to claim 29, in which the conductors are positioned within the heat-recoverable member in sideby-side relationship, the heat-recoverable member being provided with parts adapted to receive the conductors in such an arrangemcnt, and wherein said member is caused to recover to make the connection.

30. A connector according to claim 28 or claim 29, in which the heat-recoverable member has the form, in cross-section, of a broken figure eight, thereby providing two discontinuous bands in side-by-side relationship.

31. A connector according to any one of claims 23 to 28, in which the connector comprises a heat-recoverable band constructed so as to fit wholly or partly around a first conductor, the band being provided with at least one peripheral slot adapted to receive a second conductor, the second conductor being of smaller diameter than the first conductor, and the band and the slot being so shaped that upon recovery the first and second conductors are each independently gripped by contraction of the band and the slot respectively.

32. A connector according to claim 31, in which the band is formed with a channel shaped deformation extending across the width of the band in an axial direction there being situated within the channel an upstanding bridge portion bounded on each side by slots cut in the channel, the slots being adapted to receive the second conductor therethrough.

33. A connector according to any one of claims 23 to 27, in which the connector comprises a heat-recoverable discontinuous band having a recess in one or both of its jaws.

34. A connector according to any one of claims 23 to 28, in which the connector is provided with means constructed so as to grip or attach to one of the conductors independently after recovery.

35. A connector according to any one of claims 23 to 34, which is provided with an outer heat-recoverable plastics sleeve so that on recovery the sleeve provides an environmental seal for the connection.

36. A connector according to claim 35, in which the sleeve is provided with a fusible insert.

37. A method as claimed in claim 1, carried out substantially as described herein with reference to, and as illustrated in, Figures 1 to 6 of the accompanying drawings.

38. A method as claimed in claim 1, carried out substantially as described herein with reference to, and as illustrated in, Figures 8, 9 and 11 to 13 of the accompanying drawings.

39. A method as claimed in claim 18, carried out substantially as described herein with reference to, and as illustrated in, Figure 10 of the accompanying drawings.

40. A connector as claimed in claim 23, substantially as described herein with reference to, and as illustrated in, Figures 1 to 4, and 6 of the accompanying drawings.

41. A connector as claimed in claim 23, substantially as described herein with reference to, and as illustrated in Figures 8, 9 and 11 to 13 of the accompanying drawings.

42. An electrical connection whenever made by a method as claimed in any one of claims I to 22, 37, 38 or 39.