GB1580036A

GB1580036A - Heat-recoverable composite coupling devices

Info

Publication number: GB1580036A
Application number: GB2207976A
Authority: GB
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1976-05-27
Filing date: 1976-05-27
Publication date: 1980-11-26
Also published as: FR2352629A1; BE889410Q; FR2352629B1; DE2724178A1; JPS5320042A; CA1068744A

Description

(54) HEAT-RECOVERABLE COMPOSITE COUPLING DEVICES (71) We, RAYCHEM CORPORA TION, a corporation organised according to the laws of the State of California, United States of America, of 300 Constitution Drive, Menlo Park, California 94025, United States of America, 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 heat-recoverable composite coupling devices.

German Offenlegungschrift 2448160 and British Application No. 14657/76 (Serial No. 1,554,432), the disclosures of which are hereby incorporated by reference, describe various composite coupling devices for joining generally cylindrical substrates. These devices comprise a first tubular sleeve which is made from a so-called memory alloy and is heat-recoverable in the radial direction, and a second tubular sleeve which is placed either within or around the first sleeve.

In the commonly used embodiment, the first sleeve recovers inwardly and has an inside diameter which is slightly larger than the outside diameter of the second sleeve; such devices are used to joint substrates whose outside diameter is slightly smaller than the inside diameter of the second sleeve.

In use, the substrates to be joined are placed within the second sleeve, and the first sleeve is recovered, thus driving the two sleeves and the substrates into tight radial abuttment. As described in OLS 2448160 the second sleeve (which is often called the insert) preferably (a) is provided with a plurality of teeth, usually in the form of radially extending rings, on the surface remote from the first sleeve (which is often called the driver), and/or (b) is structurally weakened, for example by longitudinal slots or grooves, to facilitate its deformation by the driver.

We have now discovered that couplings of improved strength are obtained if the insert is so shaped that in the recovered coupling, the internal diameter of the drive is greater at the center than it is at the ends, and at no point is substantially greater than the internal diameter of the adjacent section of the driver which is closer to the center of the driver. Thus the driver becomes slightly barrel-shaped. The barrel shape apparently causes an increased proportion of any tensile stress on the coupling to be born by the driver, which is the strongest part of the coupling, rather than the sleeve and frictional constraints. The extent of barrelling which will occur depends primarily upon the driver and the insert, but also on the substrate, as further described below. We prefer that in the finished coupling, the internal diameter of the driver should be greater at the center than at the ends thereof by a percentage which is at least 0.5%, preferably at least 0.7%, especially at least 0.9%, particularly at least 1.9%. A variety of factors place an upper limit on the barrelling which can be achieved, and we believe that in practice the said percentage will usually be 0.9 to 4.7% preferably 2 to 3.5%. These are the percentages typically obtained when the substrates are pipes made of BS 3602/23 (AISI 1016) carbon steel and having a wall thickness which is 20% of the outer diameter (e.g.

outer diameter 20 mm), and coupling devices which give rise to such percentages when used to couple such pipes are preferred.

In one aspect the invention provides a device for coupling together two cylindrical substrates, which device comprises a first tubular metal sleeve which is heat-shrinkable in the radial direction (the "driver") and a second tubular metal sleeve which fits within the first sleeve (the "insert"), the second sleeve being so shaped that, when the first and second sleeves are placed over two cylindrical substrates and the first sleeve is shrunk to couple the substrates together, the second sleeve provides a resistance to the shrinkable forces of the first sleeve which is less at the ends thereof than at the centre thereof and at no point is substantially greater than the resistance of the adjacent section of the second sleeve which is closer to the centre of the second sleeve, whereby the first sleeve shrinks to an internal diameter which is less at the end portions thereof than it is at the center thereof and which at all points is substantially the same as, or smaller than, the internal diameter of the adjacent section of the driver which is closer to the center of the driver.

In a second aspect, the invention provides a method of coupling together two cylindrical substrates by placing around the substrates a first tubular metal sleeve which is heat-shrinkable in the radial direction and a second tubular metal sleeve between the first sleeve and the substrates, and shrinking the first sleeve, in which method there is used a second sleeve which provides a resistance to the shrinkage forces of the first sleeve which is less at the ends thereof than at the center thereof and at no point is substantially greater than the resistance of the adjacent section of the second sleeve which is closer to the center of the second sleeve, whereby in the completed coupling, the internal diameter of the first sleeve is greater at the center than at the end portions thereof by a percentage which is at least 0.5%.

There are described below a variety of measures for shaping the insert so as to promote barrelling of the driver, and those skilled in the art will have no difficulty, having regard to the disclosure herein, and their own knowledge, in making and using the invention. On the other hand, it should be understood that in the absence of any appreciation of the benefit to be obtained from barrelling, and in the absence of the disclosure herein, adoption of one only (or even more than one) of some of the measures described herein will not necessarily result in a useful degree of barrelling. Thus we believe, for example, that none of the couplings disclosed in OLS 2448160 and British Application No.

14566/76 (Serial No. 1553427 will give rise to this very valuable effect.

It is preferred that each longitudinal half of the insert should be provided on its inner surface with at least two teeth which are in the form of radially extending rings which have an internal diameter d and which are longitudinally spaced apart from each other by a distance t such that t/d is at least 0.15, preferably 0.2 to 0.3, e.g. about 0.25. Typically there are four such rings on each half of the insert. The minimum spacing between the teeth helps to ensure that when the driver recovers, it exerts adequate radial force on the teeth so that they engage the substrate in a way which ensures adequate grip and sealing.

This first preferred feature does not in itself promote barrelling of the driver, and in order to promote barrelling of the driver, it is highly desirable that the insert should have at least one, and preferably both, of the features described below as the second and third preferred features. The presence of either of these features alone can be sufficient to give the desired effect. When the first feature is present with either one (and preferably both) of the second and third features, there is a cooperating relationship between them which greatly enhances the likelihood of barrelling.

The second preferred feature is that the end portions of the insert are structurally weakened so that when the driver recovers, the end portions are more readily distorted.

For this purpose, each longitudinal half of the insert preferably comprises weakened portions which extend longitudinally from the end of the insert, leaving a central portion of the insert free from such weakening. In an insert having teeth as described above, the weakened portions preferably pass through at least one (and preferably at least two) of the teeth and stop short of at least one (and preferably at least two) of the teeth. Preferably the weakened portions are in the form of open-ended slots, the slots preferably being of the same length and shape (e.g. generally rectangular); the length of the slots may be for example 0.6 to 0.9 cm., especially about 0.75 cm., per cm. of the internal diameter of the insert. The number of slots is conveniently four in each end portion.

It should be noted that even when the insert has weakened portions as described above, barrelling of driver will only take place if the other parameters permit it. Thus the presence of multiple closely spaced teeth on the interior of the insert can prevent the desired effect. This is because the difference between the pressure exerted on the substrate by the outer teeth (through which the weakened portions pass) and that exerted by the inner teeth (through which the weakened portions do not pass) may not then be sufficient to drive the outer teeth more deeply into the substrate than the inner teeth.

The third preferred feature is that the internal diameter of the insert increases from the center to each end. The diameter here referred to is the internal diameter of the main part of the insert, ignoring any teeth that may be present. The increase can be uniform or non-uniform and can be gradual or step-wise. In an insert having teeth as described above, the diameter between adjacent teeth can be constant, and preferably the average change in internal diameter of the insert between the center and the outermost tooth is 0.4 to 1.2 %, for example about 0.6%; for many couplings this will be from 0.2 to 0.6%.

A fourth preferred feature is that, in inserts having the first and third preferred features, in each longitudinal half of the insert, the internal diameter of the outermost tooth is greater than the internal diameter of the innermost tooth, and the internal diameter of any intermediate tooth is not less than the internal diameter of the innermost tooth and is less than that of the outermost tooth.

Thus the teeth may have progressively greater internal diameters the nearer they are to the end. When such an insert also has the second preferred feature described above, as is preferred, it is preferred that each longitudinal half of the insert comprises a plurality of longitudinally extending open-ended slots which pass through the outermost tooth but not through at least two inner teeth and that said at least two inner teeth have the same internal diameter.

It has also been found that when an insert is provided on its inner surface with teeth in the form of radially extending rings, improved results are obtained when at least the outer ring at each end, and preferably the two outer rings at each end, is formed with a flat surface facing generally towards the axis of the sleeve but inclined to the axis at a small outward facing angle, preferably of 3 to 10 degrees, especially about 5 degrees. The provision of such teeth on any insert forms part of the present invention, but is particularly useful in devices according to the first aspect of the invention, especially those having the fourth preferred feature described above. As a result of their configuration, the teeth have a substantially reduced tendency to be forced out of the indentations which they form in the substrate.

Another preferred feature is that in an insert whose inner surface is provided with teeth, the outermost tooth at each end is separated from the end of the sleeve by an end portion which has a gradually, and preferably uniformly, reducing thickness, the reduction in thickness being at least in part achieved by an increase in the internal diameter. A suitable reduction can be achieved for example, by a taper of 4 to 15 degrees. The said end portions preferably have a length of 0.2 to 0.3 cm., especially about 0.25 cm., per cm. internal diameter of the insert. This feature is of assistance in assembling the coupling over the substrates, especially when they are misaligned, as also is the third preferred feature.

It is also preferred that the outer surface of one end of the insert should be flared slightly outwards. This enables the driver to be slipped over the insert and be retained in the correct position.

The drivers used in the present invention can readily be prepared by those skilled in the art. The driver is preferably the same length as the insert, but may be shorter or longer. The couplings are useful for joining substrates of outer diameter from 6 mm.

upwards, generally less than 10 cm., for example 1.25 to 3.8 cm., especially high strength pipes such as those used in hydraulic systems, e.g. of annealed 70-30 copper nickel, 304 stainless steel, 316 stainless steel, mild steel and high strength alpha brass.

The barrel shape of the driver appears to be particularly important in meeting tensile conditions that greatly exceed the yield strength of the pipe. As the pipe is pulled beyond its yield point, it elongates and diminishes in diameter and so tends to disengage from the gripping teeth. The insert in this coupling is designed to yield and elongate and follow with the pipe to a limited extend as the pipe is being pulled from the coupling. As the insert ends move axially outward in the driver, they are forced radially inward by the inward taper of the barrel shaped driver ends, thus following the diminishing diameter of the pipe and maintaining penetration of the gripping teeth in the pipe wall. This feature can make possible a coupling whose ultimate tensile strength exceeds 150% of the pipe yield strength.

The invention is illustrated in the accompanying drawings, in which Figure 1 is a cross-section of one half of a coupling device of the invention, and Figure 2 is a crosssection of a coupling device as shown in Figure 1 which has been shrunk to couple together a pair of pipes.

Referring now to Figure 1, there is shown a cylindrical driver 1 which is made of a memory metal such as a nickel-titanium alloy and is in the expanded condition. The driver 1 is placed around a generally cylindrical metal insert 2 whose outer diameter is very slightly smaller than the inner diameter of the driver 1 except at outwardly flared end portion 3 which is slightly distorted by pushing the driver over it. The insert 2 has four teeth 4, 5, 6 and 7 on its inner surface and four longitudinal slots 8 at 900 intervals. The inner diameter of the insert remains contant between adjacent teeth, but increases stepwise from center to end. Teeth 4 and 5 have the same inner diameter. Tooth 6 has an inner diameter larger than teeth 4 and 5. Tooth 7 has an inner diameter larger than tooth 6. The periphery of each of teeth 6 and 7 is a flat surface which is inclined to the axis of the insert at an outward-facing angle OL of about 5 degrees.

The other half of the coupling device shown in the drawing is a mirror image except that it does not have a flared end portion.

Referring now to Figure 2, this shows a coupling device as illustrated in Figure 1 which has been used to couple together two cylindrical pipes 9 and 10. Shrinkage of the driver 1 has compressed the insert 2, espe cially where it is weakened by the slots, forcing the teeth 4, 5, 6, 7 of the insert partially into the surfaces of the pipes (the outer teeth being driven further into the pipes than the inner teeth) and the driver has assumed a barrel shape, the extent of the barrelling being exaggerated for illustrative purposes.

The coupling devices of the invention are preferably used to couple together two substantially identical substrates in a symmetrical assembly. The gap between the substrates should preferably be small and, when the coupling has teeth as described in the first preferred feature, substantially less than the gap between the two innermost teeth; thus the substrate should preferably extend inwards from the innermost tooth by at least 1/8 of the outer diameter of the substrate.

WHAT WE CLAIM IS: 1. A device for coupling together two cylindrical substrates, which device comprises a first tubular metal sleeve which is heat-shrinkable in the radial direction and a second tubular metal sleeve which fits within the first sleeve, said second sleeve being so shaped that, when the first and second sleeves are placed over two cylindrical substrates and the first sleeve is shrunk to couple the substrates together, the second sleeve provides a resistance to the shrinkage forces of the first sleeve which is less at the ends thereof than at the centre thereof and at no point is substantially greater than the resistance of the adjacent section of the second sleeve which is closer to the centre of the second sleeve, whereby the first sleeve shrinks to an internal diameter which is less at the end portions thereof than it is at the center thereof and which at all points is substantially the same as or smaller than the internal diameter of the adjacent section of the first sleeve which is closer to the center of the first sleeve.

2. A device according to Claim 1, wherein each longitudinal half of the second sleeve is provided on its inner surface with at least two teeth which are in the form of radially extending rings.

3. A device according to Claim 2, wherein the rings have an internal diameter d and are longitudinally spaced apart from each other by a distance t such that t/d is at least 0.15.

4. A device according to Claim 3, wherein t/d is 0.2 to 0.3.

5. A device according to any one of Claims 2 to 4, wherein each longitudinal half of the second member comprises weakened portions which extend longitudinally from the end of the sleeve, which passes through at least one of said teeth and which stop short of at least one of said teeth.

6. A device according to any one of the preceding claims wherein the internal diameter of the second member increases from the center to each end.

7. A device according to Claim 7 wherein the second sleeve comprises teeth as defined in any one of claims 2 to 4 and the average change in the internal diameter of the second sleeve between the center and the outermost tooth thereof is 0.4 to 1.2%.

8. A device according to Claim 7 wherein, in each longitudinal half of the second sleeve, the internal diameter of the outermost tooth is greater than the internal diameter of the innermost tooth, and the internal diameter of any intermediate tooth is not less than the internal diameter of the innermost tooth and is less than that of the outermost tooth.

9. A device according to Claim 8 wherein each longitudinal half of the second member comprises a plurality of longitudinally extending open-ended slots which pass through the outermost tooth but not through at least two inner teeth and that said at least two inner teeth have the same internal diameter.

10. A device according to Claim 8 or 9 wherein the periphery of each of the outermost teeth is a flat surface which is inclined to the axis of the member at an outward-facing angle of 3 to 100.

11. A device for coupling together two cylindrical substrates, which device comprises a first tubular metal sleeve which is heat-shrinkable in the radial direction; and a second tubular metal sleeve which fits within the first sleeve; which is provided on its inner surface with at least four teeth which are in the form of radially extending rings which have an internal diameter d and which are longitudinally spaced apart from each other by a distance t such that t/d is at least 0.15; which comprises weakened portions which extend longitudinally from the end of the member, which pass through at least one of said teeth and which stop short of at least one of said teeth; and whose diameter increases from the center to each end.

12. A device according Claim 11 wherein the average change in the internal diameter of the second sleeve between the center and the outermost tooth thereof is 0.4 to 1.2%.

13. A device according to Claim 11 or 12 wherein, in each longitudinal half of the second sleeve, the internal diameter of the outermost tooth is greater than the internal diameter of the innermost tooth, and the internal diameter of any intermediate tooth is not less than the internal diameter of the innermost tooth and is less than that of the outermost tooth.

14. A device according to any one of claims 11 to 13 wherein each longitudinal half of the second sleeve comprises a plurality of longitudinally extending open-ended slots which pass through the outermost tooth

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. cially where it is weakened by the slots, forcing the teeth 4, 5, 6, 7 of the insert partially into the surfaces of the pipes (the outer teeth being driven further into the pipes than the inner teeth) and the driver has assumed a barrel shape, the extent of the barrelling being exaggerated for illustrative purposes. The coupling devices of the invention are preferably used to couple together two substantially identical substrates in a symmetrical assembly. The gap between the substrates should preferably be small and, when the coupling has teeth as described in the first preferred feature, substantially less than the gap between the two innermost teeth; thus the substrate should preferably extend inwards from the innermost tooth by at least 1/8 of the outer diameter of the substrate. WHAT WE CLAIM IS:

1. A device for coupling together two cylindrical substrates, which device comprises a first tubular metal sleeve which is heat-shrinkable in the radial direction and a second tubular metal sleeve which fits within the first sleeve, said second sleeve being so shaped that, when the first and second sleeves are placed over two cylindrical substrates and the first sleeve is shrunk to couple the substrates together, the second sleeve provides a resistance to the shrinkage forces of the first sleeve which is less at the ends thereof than at the centre thereof and at no point is substantially greater than the resistance of the adjacent section of the second sleeve which is closer to the centre of the second sleeve, whereby the first sleeve shrinks to an internal diameter which is less at the end portions thereof than it is at the center thereof and which at all points is substantially the same as or smaller than the internal diameter of the adjacent section of the first sleeve which is closer to the center of the first sleeve.

4. A device according to Claim 3, wherein t/d is 0.2 to 0.3.

but not through at least two inner teeth and that said at least two inner teeth have the same internal diameter.

15. A device according to Claim 13 wherein the periphery of each of the outer most teeth is a flat surface which is inclined to the axis of the member at an outward-facing angle of 3 to 100.

16. A device according to any one of the preceding claims wherein the second sleeve comprises outwardly tapered sections between the outermost teeth and the ends of the sleeve.

17. A device substantially ns hereinbefore described with reference to and as illustrated in the accompanying drawings.

18. A method of coupling together two cylindrical substrates by placing around the substrates a first tubular metal sleeve which is heat-shrinkable in the radial direction and a second tubular metal sleeve between the first sleeve and the substrates, and shrinking the first sleeve, in which process there is used a second sleeve which provides a resistance to the shrinkage forces of the first sleeve which is less at the ends thereof than at the center thereof and at no point is substantially greater than the resistance of the adjacent section of the second sleeve which is closer to the center of the second sleeve, whereby in the completed coupling. the internal diamcter of the first sleeve is greater at the center than at the end portions thereof by a percentage which is at least 0.5%.

19. A method according to Claim 18 wherein said percentage is at least 1.9%.

20. A method according to Claim 18 or 19 wherein said percentage is 0.9 to 4.7%.

21. A method according to any one of claims 18 to 20 wherein the second sleeve is as defined in any one of claims 2 to 17.

22. A method according to anyone of claims 18 to 21 wherein the substrates are pipes.

23. A method according to Claim 22 wherein the pipes form part of a hydraulic system.

24. Two cylindrical substrates coupled together by a method as claimed in any one of claims 18 to 23.

25. A device according to any one of claims 1 to 17 which, when used to couple together two pipes made of BS 3602/23 carbon steel and having a wall thickness which is 20% of the outer diameter, give rise to a coupling in which the internal diameter of the first sleeve is greater at the center than at the end portions thereof by a percentage which is at least 0.9%

26. A device according to Claim 25 wherein said percentage is at least 1.9%.

27. A device according to Claim 25 or 26 wherein said percentage is 0.9 to 4.7%