GB2039654A

GB2039654A - Memory metal devices

Info

Publication number: GB2039654A
Application number: GB8000317A
Authority: GB
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1979-01-05
Filing date: 1980-01-04
Publication date: 1980-08-13
Also published as: DE3000204A1; IT8019045A0; JPS5598481A; FR2445753A1; CA1167224A; IT1196403B; FR2445753B1; JPS6346959B2; GB2039654B; BE880992A; NL8000055A

Abstract

The present invention concerns a [novel] device such as a pipe coupling for pipes 5, 6 comprising a heat- recoverable memory metal member 2 adapted on recovery to cause a plastically deformable member 1 of the device to be sealingly engaged with the pipes 5, 6, the inner surface of the member 1 being coated with a sealant having dispersed a particulate filler e.g. quartz which is adapted to bite into the pipes 5, 6 on recovery of the memory metal member. The device may also be used for correcting electrical conductors, in which case the filler should be of metal e.g. nickel or of silicon carbide. <IMAGE>

Description

SPECIFICATION Improvements in or relating to heat-recoverable devices The present invention relates to devices which are connectable to at least one substrate through the intermediary of a heat-recoverable memory metal member.

As is known, "memory metals", sometimes also called "memory alloys" are metallic material from which a heat-recoverable article can be made, that is an article which can be deformed from an original heat-stable configuration to a different heat-unstable configuration in which it will remain until raised above a temperature (or through a narrow temperature range) known as the transition temperature, when it will return or attempt to return towards its original configuration. It will be understood that the heat-recoverable article is capable of returning towards its original configuration withouth the further application of outside force.

Further information relating to such metals and their applications may be obtained by reference to US Patents Nos. 3,174,851; 3,351,463; 3,753,700; 3,759,552; 3,783,037; 4,019,925; 4,036,669; 4,067,752; 4,095,999 and UK Patents Nos. 1,327,441,1,327,442; 1,395,601; 1,488,393; 1,420,682; 1,504,707; 1,553,427; 1,548,965; 1,554,431; 1,554,432; and 1,544,423, the disclosures of which are incorporated herein by reference.

Devices which are connectable to at least one substrate through the intermediary of a heat-recoverable memory metal member are known, e.g. as pipe couplings or as connectors for electrical conductors. Such devices, whilst satisfactory in some situations, are less so in others, for example, in coupling thin walled pipes of relatively soft metal such as aluminium or copper especially where the pipes are subjected to relatively high fluid pressures, or in connecting certain electrical conductors especially where the conductors are coated with an oxide film as in aluminium conductors.

Accordingly, the present invention provides a device connectable to at least one substrate which comprises at least one heat-recoverable memory metal member adapted on recover to cause at least one surface of the device to be sealingly engaged with the substrate(s), said surface(s) being coated at least in part with a layer of a sealant having dispersed therein a particulate filler, said filler being adapted to bite into the substrate(s) on recovery of the memory metal member(s).

The present invention further provides a method of connecting a device to at least one substrate which comprises positioning at least one surface of the device adjacent the substrate(s) with a layer of sealant interposed therebetween, said sealant having dispersed therein a particulate filler, providing at least one heat-recoverable memory metal member adapted on recovery to cause said surface(s) of the device to be sealingly engaged with the substrate(s) and the filler to bite into the substrate(s) and heating the heat-recoverable member(s) to cause recovery thereof.

Preferably the device includes at least one non-heat-recoverable member, which is preferably plastically deformable, a surface of which is adapted to engage the substrate(s), the heat-recoverable member(s) acting as a driver to urge the non-heat-recoverable member(s) and the substrate(s) into engagement.

In one preferred form of the invention, the device is in the form of a fluid-tight coupling adapted to couple a plurality of pipes, particularly soft metal pipes, such as copper or aluminium. In such preferred form, a hollow non-heat-shrinkable "tubular" member is employed having the appropriate number of inlets and outlets for connection to the pipes to be coupled. (The term "tubular" is employed herein in a broad sense to include members of irregular and/or varying cross-section, Y-shaped, T-shaped and X-shaped members and members having one or more closed ends and is accordingly not limited to right cylindrical members).For example in the case where a pair of aligned pipes are to be joined, then a generally linear tubular non-heat-recoverable member is conveniently employed together with a memory metal member also of tubularform and coaxially disposed about the non-heat-recoverable member.

In a second preferred form of the invention, the device is in the form of an electrical connector for a plurality of electrical conductors, e.g. copper or particularly aluminium, especially high voltage conductors such as bus-bars in electrical switch gear. In such form, a plurality of non-heat-shrinkable shell members are provided adapted to be positioned about the ends of the conductors to form a generally tubular connection assembly. Furthermore, a plurality of heat-recoverable memory metal members in the form of bands or rings serving as drivers are also provided, each driver being adapted to be positioned about the connection assembly at or adjacent to an end thereof so that recovery of the drivers will cause the connection assembly to grip the conductors securely.Electrical connectors illustrative of the type to which the second preferred form of the invention relates are disclosed in co-pending UK Patent Application No. 47370178.

The choice of sealant will depend on the nature of the application. In the case of pipe couplings where, in use, high pressures are substained and the prime consideration is high shear strength, then preferably the sealant comprises an adhesive, and particularly an adhesive which is tack-free and solid at 25"C and softenable on heating so that on application of heat to cause heat-recovery, the adhesive will simultaneously soften and flow. Of particular interest are such adhesives which are also thermosetting and undergo a chemical transformation on heating, e.g. by a cross-linking reaction, serving to enhance or create the adhesive properties of the adhesive after cooling. Particularly good results have been obtained employing epoxy resin systems.

Suitable curable epoxy resins include resins which comprise 5 to 95 parts by weight of an epoxy resin, having an epoxy equivalent weight of 100 to 5,000, preferably 600 to 800, e.g. a bisphenol A epoxy resin, 5 to 95 parts by weight of an epoxy resin with at least 4 functional sites, e.g. a cresol-novolac resin having an epoxy equivalent weight of 200 to 500; and a substantially stoichiometric amount of a curing agent, e.g. a phenolic resin, preferably a bisphenol A polymer with a molecular weight of about 500, an anhydride, an amine or an amide. In order to improve the flexibility of the epoxy resin composition after curing, the composition may contain a small amount, e.g. 5 to 20% by weight of a carboxy-terminated butadiene-nitrile rubber which will react with the epoxide resin to give a cross-linkable graft copolymer resin.The rubber preferably has a molecular weight of 3,000 to 4,000, e.g. about 3,500, a percent nitrile content of 10 to 27%, e.g, about 18% and a carboxyl functionality of 1.5 to 3 per molecule, e.g. about 2 per molecule. When using such curable systems, heating should be continued for a sufficient time after the adhesive has flowed to provide the desired degree of cure. For example, for an epoxy resin system, heating for up to 3 minutes at 150 to 250 C is generally suitable.

In the case of electrical connectors where the prime consideration is a good electrical connection by penetration of low-conductivity or non-conducting surface films on the conductors to be connected, especially tough oxide layers, e.g. in the case of aluminium conductors, then any sealant may be employed that prevents re-estabilishment of such surface layers, e.g. a sealant to exclude oxidative influences such as oxygen. For electrical use, the sealant employed is preferably electrically conducting. The sealant may be a viscous mastic or may be non-flowable after installation, e.g. of the type hereinbefore described in relation to pipe couplings and preferably rendered electrically conducting by the inclusion of conducting fillers in manner known per se.

The sealant composition is preferably coated on the surface(s) of the member which is to contact the substrate, but it may be provided at the interface in any convenient manner, for example as a coating on the substrate(s). The initial thickness of the sealant coating i.e. before installation of the device is preferably 0.25 to 3 mils, especially 1 to 1.75 mils. The thickness of the sealant coating after recovery of the memory metal member will be substantially less, for example about 0.1 mail. Preferably at least one of the surfaces which contacts the sealant is treated to improve wettability by the sealant, e.g. to improve adhesion when an adhesive is employed, e.g. by sand-blasting.

It is important, in order to achieve the objectives of the present invention, that the particulate filler should cause localized deformation of the substrate(s) and preferably also the surface(s) of the device which engages the substrate(s), when the surface(s) and the substrate(s) are caused to engage, with the sealant, e.g. the heat-softened adhesive composition, between the surface(s) and the substrate(s). In the case where shear strength is of prime importance and an adhesive is employed, after installation of the device at which stage the adhesive is in the solid state, the filler particles provide a plurality of anchors between the adhesive and at least one of the adjacent surfaces, thus improving the shear strength of the bond between the surfaces.Particularly good results are obtained if individual particles of the filler are partially embedded in both the adjacent surfaces, thus forming a locking bridge between them. For this reason, it is preferred that the filler should comprise particles having at least one linear dimensin greater than 0.05 mil, preferably greater than 0.1 mil. On the other hand, the extent of available recovery of the heat-recoverable member (and in some cases the method used to form the layer of adhesive composition) limit the maximum size of the filler particles, which are, therefore, preferably less than 5 mils in their maximum linear dimension.

In the case where a satisfactory electrical connection is the prime consideration, then the filler particles after installation of the device should be such as to penetrate the surface layers, e.g. oxide layers, on the conductor. It is, however, preferable to take advatage of the high shear strength aspect of the present invention also in the case of electrical connectors and accordingly filler particle dimensions as hereinbefore defined are preferably also employed for electrical use.

Preferably the filler particles have an aspect ratio of less than 2 to provide the desired degree anchoring or surface layer penetration.

The fillers employed in the present invention should be such as to bite into the substrate(s) and preferably also the engaged surface(s) of the device. To this end, the hardness number of the filler should be greater than that of the substrate(s) and preferably also the engaged surface(s) of the device. Appropriate fillers have been found to be inorganic fillers such as quartz, alumina and other ceramics, silicon carbide and metals such as nickel. For electrical use, conducting fillers such as metals, particularly nickel, or silicon carbide are appropriate.

The amount of filler present in the sealant is preferably 10 to 50 weight % of the total sealant system, more preferably 20 to 40 weight 'O, e.g. about 30 weight per cent.

When a non-heat-recoverable member is used in addition to the heat-recoverable member, it should naturally have a melting point substantially greater than any temperature reached during installation, e.g.

above 300go, preferably above 500"C, and it is preferably composed of a metal or a composite material of similar properties. As hereinbefore explained it is also preferable that is should undergo plastic deformation as a result of recovery of the heat-recoverable member. In a preferred arrangement which results in such deformation and which is suitable for use with tubular substrates, the non-heat-recoverable member which is preferably composed of a metal, is in the form of a tube and the memory metal member is in the form of a radially heat-recoverable tube which is positioned co-axially with and adjacent to the non-heat-recoverable member. The memory metal member is preferably heat-shrinkable and is placed around the non-heat recoverable member.The surface of the non-heat-recoverable member remote from the memory metal member is generally smooth, but it may comprise radial teeth in the form of annular rings which subsequently engage the substrates. It should, however, be noted that if such teeth are present, it is generally necessary for the adhesive composition to be coated relatively thinly, or not at all, on the edges of the teeth. This is because the extent of radial deformation which can be provided by the second member is limited. The non-heat-recoverable and memory metal members and the substrates are preferably of annular cross-section. Often their cross-sections will be substantially the same throughout their length. However, where substrates of different outer diameters are being coupled together, at least the inside diameter of the inner member may have a stepped configuration.

Part or all of the exposed surface of the non-heat-recoverable member may have a coating thereon of a thermochromic paint to indicate when it has been heated to a certain temperature, in order to provide a guide to the temperature reached by the adhesive composition when a heat softenable adhesive is employed. Alternatively the softenable adhesive composition itself when employed may, incorporate a thermochromic paint and be applied so that part of it is visible when the heat-recoverable member is recovered.

The memory metal member is preferably composed of a memory metal which has (either inherently or as a result of a pretreatment) an As (austenite start) temperature above 40 C, e.g. 40-1 500C., so that is can be stored at room temperature and so that recovery thereof and when a heat softenable adhesive is employed, softening of the adhesive composition, can be effected in the same heating operation. Notable results are obtainable using members composed of p-brass, as disclosed for example in co-pending and commonly assigned US Patent Application Serial Nos. 783,040,783,041 and 797,621, the disclosures of which are incorporated herein by reference.The heat-recoverable member, after it has recovered, generally remains in position, but when it is used to effect plastic deformation of another member which contacts the substrate, it can in some cases be removed once it has effected the desired deformation of the other member. When it is to remain in position, it is preferably composed of a memory metal whose normal As temperature is below room temperature but which has been pre-treated so that its initial As temperature is above room temperature (20 C) - for example by the method disclosed in co-pending and commonly assigned US Patent Applications Serial Nos. 550,847,735,737 and 779,360, the disclosures of which are incorporated by reference herein. On the other hand, if the first member is to be removed, then its transformation temperature is preferably above room temperature.

When a non-heat-recoverable member is used in addition to the heat-recoverable member, it will generally be the same length as or shorter than the heat-recoverable member. As hereinbefore explained however there may be two or more heat-recoverable members which are the same or different and which exert force on different parts of the non-heat-recoverable member, as for example two cylindrical heat-recoverable members.

As hereinbefore described, the invention is particularly valuable for coupling together substrates, especially pipes, made of soft metals such as aluminium or copper, particularly thin-walled pipes e.g. of wall thickness such that the ratio w/d, where w is the wall thickness and d the outer diameter, is less than 0.15, e.g. less than 0.1, generally a wall thickness less than 100 mils, e.g. 20 to 50 mils, of the kind widely used in refrigeration and air-conditioning equipment. Such pipes will normally have an outer diameter of 0.25 to 100 inch. The substrates to be coupled together may be of the same or different materials and of the same or different dimensions. Where a non-heat-recoverable member is used in addition to the heat-recoverable member, it is preferably composed of the same metal as one or both of the pipes to be joined.It is preferred that a substantially uniform pressure should be exerted on the substrate by the contacting surface.

Embodiments of the present invention will now be described with reference to the accompanying drawings wherein; Figure 1 is a plan view, partly in cross-section, of a coupling member of the invention in position, priorto recovery, around two tubes to be coupled together; Figure2 is a cross-section on line AA of Figure 1; Figure 3 is a cross-section of a part of the interface between the coupling member and one of the tubes, after recovery of the coupling; and Figure 4 is a plan view, partly in cross-section of another coupling member of the invention in position, prior to recovery, around two tubes to be coupled together.

Referring to Figures 1 and 2 of the drawings, two pipes 5 and 6 are shown which are to be coupled together by means of a coupling member which comprises a tubular plastically deformable member 1 and a heat-shrinkable tubular member 2. The deformable member 1 has a coating of an adhesive composition 3 on its inside surface. Adhesive composition 3 comprises a partially cured epoxy resin and about 20% by weight, based on the composition, of quartz particles. The end portions of the outer surface of the deformable member 1 have a coating 4 thereon of thermochromic paint. Figure 3 shows the interface between the pipe 5 and the deformable member 1 after the assembly shown in Figures 1 and 2 has been heated to cause recovery of member 2 and melting and curing of composition 3. Quartz particles 33 in the adhesive composition have become embedded in both surfaces. Figure 4 shows heat-shrinkable tubular member 2 having a coating 3 on its inside surface and part of its outside surface of an adhesive composition as just described, in position around pipes 5 and 6 which are to be coupled together.

The adhesive composition employed above and which is suitable for powder coating was prepared by classifying a milled composition containing: Parts by weight Bisphenol A epoxy resin of epoxy 38 equivalent weight about 750 ("Epon 2001") Multifunctional epoxy cresol novolac 4.25 resin of epoxy equivalent weight about 230 ("ECN 1280") Bispheol A polymer curing agent 17.75 of colecular weight about 500 ("XD 8062.01") *Quartz particles ("P Quartz") 20.00 TO2 19.5 Carbon black (Statex 160) 0.5 * The particle size distribution of the quartz particles was as follows:: Retained by 80 mesh screen 0 % by weight Retained by 100 mesh screen 0.1 Retained by 120 mesh screen 0.1 Retained by 140 mesh screen 0.9 Retained by 160 mesh screen 0.7 Retained by 200 mesh screen 3.3 Retained by 270 mesh screen 5.9 Retained by 325 mesh screen 8.8 Pass through 325 mesh screen 80.2 The classified composition was applied by powder coating to the previously sand-blasted interior surface of a right cylindrical copper tube of inner diameter 0.764, outer diameter 0.848 inch and length 1.5 inch, the exterior of the tube being masked by a tube of polyethylene which had been heat-shrunk around it. The coated tube was heated sufficiently to cause the particles of the adhesive composition to coalesce and form a layer about 2 mils thick. The masking tube of polyethylene was then removed.

A radially heat-shrinkable right cylindrical tube having a length of 1.2 inch an external diameter of 1 inch and internal just over 0.848 inch (so that is was a close tolerance fit over the copper tube) was made by radially expanding a tube of a íA-brass which had been cooled in liquid nitrogen. The lS-brass had been treated so that it had an As of about 40 - 50 C. The heat-shrinkable (3-brass tube was removed from the liquid nitrogen and placed centrally over the ocpper tube, which was sufficiently strong to resist any radial shrinkage of the í,-brass tube under normal storage conditions.

The ends of two copper tubes of outer diameter 0.75 inch and wall thickness 35 mils were placed within the adhesive-coated copper tube in the manner shown in Figure 1. The assembly was then heated to a temperature of about 200'C for about 1 minute to cause recovery of the lS-brass tube and melting and subsequent curing of the epoxy resin composition.

The coupling produced in this was very strong, having a pull-out strength greater than 1,000 psi at room temperature and at 150"C and being capable of holding an internal pressure of 3,000 psi at room temperature and at 150go.

Similar results were achieved when using an aluminium tube instead of the copper tube in the coupling member, and when replacing one or both of the copper tubes to be joined by aluminium tube of the same dimensions.

Claims

1. A device connectable to at least one substrate which comprises at least one heat-recoverable memory metal member adapted on recovery to cause at least one surface of the device to be sealingly engaged with the substrate(s), said surface(s) being coated at least in part with a layer of a sealant having dispersed therein a particulate filler, said filler being adapted to bite into the substrate(s) on recovery of the memory metal member(s).

2. A device according to Claim 1 wherein the sealant is an adhesive.

3. A device according to Claim 2 wherein the adhesive is softenable on heating.

4. A device according to any one of the preceding claims wherein the adhesive is a thermosetting adhesive.

5. A device according to Claim 4 wherein the adhesive is a curable epoxy resin.

6. A device according to any one of the preceding claims, wherein the thickness of the sealant before installation of the device is in the range 0.25 to 3 mils.

7. A device according to any one of the preceding claims wherein the thickness of the sealant after installation of the device is less than 0.25 mils.

8. A device according to any one of the preceding claims wherein the aspect ratio of the particulate filler is less than 2.

9. A device according to any one of the preceding claims wherein the hardness number of the particulate filler is greater than that of the surface(s) of the device and the substrate(s) to be engaged.

10. A device according to Claim 9 wherein at least some of the individual filler particles, after installation of the device bite into the surface(s) of the device and the substrate(s) to form locking bridges therebetween.

11. A device according to any one of the preceding claims wherein the filler comprises particles having at least one linear dimension thereof greater than 0.05 mil.

12. A device according to Claim 11 wheein the filler comprises particles having at least one linear dimension thereof greater than 0.1 mil.

13. A device according to to any one of the preceding claims wherein the filler comprises quartz, alumina, silicon carbide or metal particles.

14. A device according to any one of the preceding claims where the amont of filler in the sealant is between 10 to 50 weight per cent of the total sealant system.

15. A device according to any one of the preceding claims including at least one non-heat-recoverable member, at least one surface of which is adapted to engage the substrate(s), the heat-recoverable member(s) acting as a driver to urge the non-heat-recoverable member(s) and the substrate(s) into engagement.

16. A device according to Claim 15 wherein the non-heat-recoverable member(s) is plastically deformable.

17. A device according to either of Claims 15 or 16 wherein the non-heat-recoverable member(s) is a metal.

18. A device according to any one of Claims 15 to 17 including a non-heat-recoverable member of tubular form.

19. A device according to Claim 18 including a radially heat-recovery memory metal member of tubular form co-axially disposed about the non-heat-recoverable member.

20. A device according to any one of Claims 15 to 17 including an assembly of non-heat-recoverable members, the assembly being of generally tubular form.

21. A device according to Claim 20 including a plurality of radially heat-recoverable rings or bands, each ring or band being positioned at or adjacent to an end of the generally tubular assembly of non-heat-shrinkable members.

22. A device according to any one of the preceding claims wherein the heat-recoverable member(s) comprises p-brass.

23. A device according to Claim 1 substantially as described herein with reference to the accompanying drawings.

24. A device which comprises a memberwhich is heat-recoverable and is composed of a memory metal and which, when it is heat-recovered, causes movement of a surface of the device which has a coating thereon of an adhesive composition, the adhesive composition being softenable by heating and comprising a polymeric phase having dispersed therein a particulate filler, said filler having an aspect ratio less than 2 and having a hardness greater than said surface at a temperature at which said adhesive composition is softened.

25. A method of connecting a device to at least one substrate which comprises positioning at least one surface of the device adjacent the substrate(s) with a layer of sealant interposed therebetween, said sealant having dispersed therein a particulate filler, providing at least one heat-recoverable memory metal member adapted on recovery to cause said surface(s) of the device to be sealingly engaged with the substrate(s) and the filler to bite into the substrate(s) and heating the heat-recoverable member(s) to cause recovery thereof.

26. A method according to Claim 25 wherein the device is as defined in any of claims 1 to 24.

27. A method according to either of Claims 25 or 26 wherein the device is connected to a plurality of substrates serving to connect the substrates one to another.

28. A method according to Claim 27 wherein the device is connected to a plurality of pipes providing a fluid tight coupling between the pipes.

29. A method according to Claim 28 wherein each of the pipes has a wall thickness, w, and an outer diameter, d, such that wid is less than 0.1

30. A method according to Claim 29 wherein the wall thickness is 20 to 50 mils.

31. A method according to Claim 28 wherein the device is connected to a plurality of electrical conductors and provides an electrical connection between the conductors.

32. A method according to Claim 25 substantially as described herein with reference to the drawings.

33. A method of joining a member to at least one substrate, the to-be-joined surface of said member being composed of a first material and the to-be-joined surface of said substrate being composed of a second material, which method comprises: (a) positioning said surfaces adjacent to each other; (b) providing between surfaces a layer of an adhesive composition, the adhesive composition being softenable by heating and comprising a polymeric phase having dispersed therein a particulate filler, said filler having an aspect ratio less than 2 and having a hardness greater than at least one of said first and second materials at a temperature at which said adhesive composition is softened;; (c) providing a member which is heat-recoverable and is composed of a memory metal and which, when it is heat-recovered, causes said surface composed of a first material to contact said surface composed of a second material through said layer of adhesive composition; and (d) heating said adhesive composition to a temperature at which it is softened and heating said heat-recoverable member to cause recovery thereof, thereby forcing said surfaces into sealing contact with each other and causing localized deformation of at least one of said surfaces by said particulate filler.

34. A method according to Claim 33 which comprises: (a) placing a first member which is not heat-recoverable adjacent said substrate, the surface of said first member adjacent said substrate being composed of a first material and the surface of said substrate adjacent said first member being composed of a second material; (b) providing between said first member and said substrate a layer of an adhesive composition, the adhesive composition being softenable by heating and comprising a polymeric phase having dispersed therein a particulate filler, said filler having an aspect ratio less than 2 and having a hardness greater than at least one of said first and second materials at a temperature at which said adhesive composition is softened; (c) positioning a second member adjacent said first member, said second member being heatrecoverable and being composed of a memory metal; and (d) heating said adhesive composition to a temperature at which it is softened and heating said second member to cause recovery thereof, thereby forcing said first member into sealing contact with said substrate and causing localized deformation of at least one of said substrate and said first member by said particulate filler.

35. A non-heatrecoverable member wherein a surface thereof is coated at least in part with a layer of a sealant having dispersed therein a particulate filler, and adapted for use in a device as defined in any of of claims 15 to 21.

36. A non-heat-recoverable member according to Claim 35 substantially as described herein with reference to the drawings,

37. A substrate connnected to a device as defined in any of of Claims 1 to 24.