GB1571627A

GB1571627A - Heat-recoverable coupling

Info

Publication number: GB1571627A
Application number: GB231677A
Authority: GB
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1976-01-22
Filing date: 1977-01-20
Publication date: 1980-07-16
Also published as: FR2339121B1; DE2702542C2; CA1079328A; DE2702542A1; FR2339121A1

Description

(54) HEAT-RECOVERABLE COUPLING (71) We, RAYCHEM CORPORATION, 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 relåtes to couplings, especially for line members such as tubing.

Over the years many types of coupling for joining and terminating pipes and conduits have been proposed, many of these being complicated in design and necessitating the expenditure of considerable time and effort in their installation.

Quite recently, however, it has been proposed to use so-called "memory metals" to make much simpler couplings. Thus, for example, British Patent No. 1,327,441 describes and claims a tubular coupling member made from a memory metal and provided on its inner surface with one or more inwardly projecting teeth, the coupling member being radially shinkable upon being heated to the transition temperature of the memory metal. Other couplings of this type may be provided with smooth or serrated bores.

In Belgian Patent No. 820,880 it is proposed to make composite coupling members in which an insert makes contact with the line substrate, such as tubing, under the recovery force of a heat-recoverable metal tubular driver member. The insert may be provided with teeth or serrations and/ or may be made from a material chosen for its compatibility with the line substrates, for example it may be made from a gallprone material. These composite couplings have advantages in certain applications insofar as they are easier to manufacture without damaging their structural features, such as teeth, and insofar as they can avoid problems of incompatibility between certain memory metals and the metal tubing.

These recoverable metal couplings are especially suitable for use in joining the tubing of, for example, aircraft hydraulic systems. In such applications they are often tapered towards their ends in order to reduce the stress loading on the hydraulic tubing under bending loads. By tapering the ends of the coupling, it is .more able to flex and thus distribute the load over a greater area of the tubing. This prevents or significantly reduces failure of the tubing caused by high stress concentration.

However, although high bending stress may be substantially reduced in this manner, the flexure of the tubing within the coupling causes relative movement between the ends of the coupling and the underlying tubing. This relative movement, which is especially acute in - aircraft and other applications where vibration occurs for long periods, is generally longitudinal and causes chafing, fretting and galling of the tubing. The roughened, pitted area thus formed results in high stress concentration in the tubing which, through continued flex cycling, leads to the propagation of cracks through the tubing wall ultimately resulting in complete failure.

Attempts have been made to reduce chafing at the interface between the coupling and the tubing. For example, lubricants have been used in an effort to reduce friction at the tubing/coupling interface.

However, none of the attempts have proved successful and the problem of failure at locations near the end of the coupling because of relative movement between the components has remained unsolved.

The present invention provides a heatrecoverable hollow metal coupling comprising a main body portion and at least one terminal stress distribution portion having an opening for receiving a line member, the wall thickness of the coupling in the or each terminal stress distribution portion being less than that in the main body portion, characterised in that the or each terminal stress distribution portion is provided at its end remote from the main body portion with an outer collar of increased wall thickness.

In certain advantageous forms of coupling according to the present invention the or each terminal stress distribution portion, apart from the collar, includes a section of substantially constant wall thickness which is preferably connected to the main body portion by a tapered section, the thickness of which increases towards the main body portion, these two sections together acting to provide stress distribution.

The length of the section of substantially constant wall thickness is preferably in the range of from 20% to 100% of its outer diameter.

In other advantageous embodiments, the section of substantially constant wall thickness may be omitted, the collar then being connected to the main body portion by a tapered section which acts on its own to provide stress distribution. In these embodiments, the tapered section will in general preferably be longer and more gradually tapered than the tapered section in embodiments also including a thin-walled section of constant wall thickness.

The collar is preferably formed integrally with the terminal stress distribution portion and is advantageously positioned at the extreme end thereof but it will be appreciated that, whilst the provision of a large section of thin-walled coupling beyond the collar would effectively negate the function of the collar, it may in some cases be convenient to form the collar slightly back from the extreme end of the coupling.

The wall thickness of the collar is greater than that of the terminal stress distribution portion in the immediate vicinity thereof but, in general, will not be as great as the wall thickness of the main body portion.

In preferred embodiments of the present invention the hollow metal coupling will have a generally cylindrical bore; that is to say the wall thicknesses of the main body portion and the stress distribution portion(s) are adjusted by variations in the configuration of the outer surface. The hollow member is preferably generally tubular. The term "tubular" as used herein is not limited to members of hollow cylindrical configuration, but includes, for example, members of non-circular crosssection and for example, T-shaped, Xshaped and Y-shaped members. It will be appreciated, therefore, that the couplings will, in general, comprise at least two terminal stress distribution portions, each baving an opening for the reception of a line member, although the present invention also encompasses a coupling for the termination of a single line member which has only one terminal stress distribution portion comprising an opening for said member.

In many applications the couplings of the present invention will be formed as unitary structures and may, in accordance with British Patent Specification No.

1,327,441, be provided with one or more internal teeth designed to bite into the line member(s), e.g. hydraulic tubing, upon recovery. If present, such teeth will preferably be provided internally of the main body portion, although in some cases it may be advantageous to provide them internally of the terminal portion(s).

In other applications it may be advantageous to form the coupling as a composite member in accordance with Belgian Patent Specification No. 820,880 in which case the coupling will be provided with an insert which, for example, may itself be provided with internal teeth and/or may be made from a gall-prone material. Such an insert may be provided, for example, in order to prevent corrosive action between the heat-recoverable metal member and the line member, in which case it will be advantageous to have the insert extend beyond the end(s) of the heat-recoverable coupling. In such an instance the insert will preferably be made from a flexible or structurally weak material in order that the action of the collar(s) will not be diminished.

The heat-recoverable metal couplings of the present invention may be made from any suitable memory metal, the nature of the memory metal chosen depending upon the particular application for the coupling.

Amongst suitable memory metals there may be mentioned, for example, various alloys of titanium and nickel which are described, for example in U.S. Patents Nos.

3,174,851, 3,351,463, 3,753,700, 3,759,552, British Patents Nos. 1,327,441 and 1,327,442 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 betabrass alloys have been demonstrated to exhibit this property in, e.g. N. Nakanishi et al, Scripta Metallurgma 5, 433-440 (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. 66348.

In general these metals have a transition temperature within the range of from --196"C to +135"C, especially from -1960C to -700C (this being the lowest temperature they are liable to encounter during everyday use), and thus may be brought into 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 Offenlegungschrifts Nos. 2,603,911, 2,603,863 and 2,603,878.

Nickel-titanium alloys of the type mentioned above are especially suitable for use in the present invention.

It will be appreciated from the foregoing that the present invention is designed to eliminate relative movement at the ends of heat-recoverable metal couplings so as to prevent chafing, fretting or galling of the tubing and thus avoid eventual tube failure. To accomplish this end, the heatrecoverable metallic couplings are provided with stress distribution portions having rigid terminal collars. The entire structure is of a heat-recoverable nature and is usually of a unitary construction, although a composite construction using an insert of another metal or material may be desirable in certain applications, where, for example, the tubing comprises a substance which is corrosive to the heat-recoverable metal.

In preferred embodiments the stress distribution portions of the couplings include tapered sections which provide a transition from the thick-walled main body portion, which is preferably cylindrical, to the thinwalled terminal sections, if present, and the collar. At the main body portion, the coupling is in most applications more rigid than, i.e. has a substantially greater flexural strength than the line member, e.g. the tubing, with which the coupling is to be employed. At the outer ends of the stress distribution portions, the walls of the coupling are thin and the coupling is preferably at least as flexible as the tubing.

Thus, the construction of each end of the coupling ensures that the tubing extending into the coupling will experience a stress loading from flexure of the tubing which is spread over a broad area rather than concentrated at a rigid edge.

The stress distribution portions provide a strength gradient with respect to tensile and compressive loading, the tensile and compressive strengths of the couplings decreasing from the comparatively rind main body, preferably cylindrical, portions to the collars. If the couplings include thinwalled terminal sections, the compressive and tensile strengths of the couplings in these sections are preferably less than those of the lines, e.g. tubing, with which the couplings are to be employed.

The collars of the stress distribution portions have a transverse wall thickness which is substantially greater than the adjacent thin-walled sections. The thickness and recovered inside dimension of each collar provide a hoop strength on recovery such that the coupling tightly grips the tubing.

This hoop strength is sufficient to overcome the linear flexural strength of the stress distribution section. The linear flexural strength is that strength tending to create relative longitudinal movement between the coupling and the underlying tubing when the tubing is subjected to flexure.

In other words, the gripping of the tubing is such that the collars will not slide longitudinally along the tubing during flexure.

Thus, compression and elongation is experienced inwardly of the collars in the stress distribution portions. As a result, little or no relative longitudinal movement between the coupling and the tubing is experienced and chafing, fretting and galling is eliminated or is significantly reduced.

Various embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a coupling assembled with tubing according to the present invention; Figure 2 is a cross-sectional elevation taken along line 2-2 of Figure 1; Figure 3 is an end view of the coupling; Figure 4 is a cross-sectional end view taken along line 44 of Figure 2; Figure 5 is a cross-sectional elevation of a second form of coupling according to the present invention; Figure 6 is an elevation, partially in section, of an unrecovered coupling including an insert according to the present invention; and Figure 7 is an elevation, partially in section, of the embodiment of Figure 6 recovered about the tubing.

Referring now to the drawings, and more especially Figure 1 thereof, the coupling shown comprises a unitary hollow member 10 fabricated from a heat-recoverable metal.

The hollow member 10 includes a main, substantially cylindrical hollow body portion 14, a substantially cylindrical bore 12 extending throughout the length of said hollow member 10. Two annular teeth 13 are provided on each side of the coupling to improve the sealing capabilities thereof.

Stress distribution portions 15 and 17 extend longitudinally from each end of the hollow body portion 14 t collars 26 and 28. The stress distribution portions 15 and 17 include tapered sections 16 and 18 and thin-walled sections 20 and 22, respectively.

The tapered sections 16 and 18 act to distribute the resistance to bending of the hollow member 10 when the tubes extending into the hollow member 10 are strained under a bending load. The tapered sections 16 and 18 offer decreasing resistance to the strain imposed by the tubes because of the decreasing cross-section of the walls of these tapered sections. This allows distribution of the load across a greater length of the tubes and thus obviates fatigue failure at a specific high stress point at the edge of a stiff untapered coupling.

The thin-walled sections 20-and 22 ex tend from the tapered sections 16 and 18 to the collars 26 and 28, respectively. The length of each thin-walled section is pre ferably from one-fifth-to equal its outside diameter. The bore of each thin-walled section is generally smooth, although properly designed inward projections may be incorporated. The thin-walled sections 20 and 22 act to extend the relatively flexible ends of the tapered sections 16 and 18 to eliminate the edges formed by more conventional couplings at the end of similar tapered portions. The conventional coupl ings tend to promote chafing, fretting or galling because of relative longitudinal mo tion at the ends of the coupling between the coupling and the tubing extending therethrough. The thin-walled sections displace the ends of the coupling away from the heavier portions of the taper.

The collars 26 and 28 are located at the extended ends of the thin-walled sections 20 and 22, respectively. The collars 26 and 28 are substantially thicker in transverse cross-section than the thin-walled sections 20 and 22. These collars 26 and 28 are also of heat-recoverable metallic material and are sized tightly to conform to tubing positioned within the coupling upon heat recovery of the collars. The collars 26 and 28 may have a transverse wall thick ness which is equal to the thickness of the main wall portion of the coupling. How ever, in most applications, it is not neces sary to have a collar as thick as the main wall portion.

The relative longitudinal holding capa city of the collars 26 and 28 based on the hoop strength of the collars 26 and 28 and the stress induced by the recovery of the undersized collars about the tubing is de signed to withstand the longitudinal force that can be generated by elastic deforma tion of the thin-walled sections 20 and 22.

Consequently, the collars 26 and 28 will ~ieniain fixed relative to the tubing regardless of the flexure of the tubing. With the tubing strained in a bending mode, the thinwalled sections 20 and 22 experience elastic deformation thereby allowing the tubing to flex relative to -the main, cylindrical hollow body portion 14 without displacing the collars. The thin-walled sections 20 and 22 preferably also have a flexural strength which is no greater than that of the tubing with which the coupling is to be employed.

-If the strength of the thin-walled sections -20 and 22 were greater than -the tubing, the tubing could be excessively stressed at the ends of the coupling which could result in early failure of the tubing. A gradual decrease in the bending moment in the tubing from a maximum stress at the coupling which could result in early failure of the tubing. A gradual decrease in the bending moment in the tubing from a maximum stress at the coupling ends to zero stress near the centre is necessary for good flex life. Thus, it will be apparent that the function of the thin-walled exten sions between the tapered sections and the collars is to permit the collars to move with the tubing as it bends and also to transmit linear stress to the tapered sections so that they will also move with tubing. In this way, all, or nearly all, relative movement between the tubing and coupling is eliminated.

The heat-recoverable properties of a hollow member 10 are advantageous for both the main, hollow body portion 14 and the collars 26 and 28. The main, hollow body portion 14, when recovered about tubes 30 and 32, prevents longitudinal ex traction of the tubes from the coupling and provides a seal to prevent leakage of high pressure fluid which may be contained within the tubing. At the same time, the recovery of the collars 26 and 28 acts to ensure that no chafing, fretting and galling will occur.

One specific coupling of this type, made from a nickel-titanium alloy, was designed to couple tubing of 127 cm outer diameter to provide a connection capable of with standing hydraulic pressures of up to 8,000 p.s.i. The machined coupling in its unex panded form has an overall length of 4 13 cm, the length of the central main body portion being 1 9 cm, the length of each tapered section being 0 64 cm, the length of each thin-walled section being 0 32 cm, and the length of each collar being 0 16 cm. The main body portion has an outer diameter of 1-80 cm and a thickness of 0-27 cm. The thin-walled sections have an outer diameter of 126 cm and a thickness of 0 025 cm. The wall thickness of each collar is 0-13 cm.

Figure 5 shows a second form of coupling -in accordance with the present invention.

The coupling 40 has a main body portion 44 and two terminal stress distribution portions comprising tapered sections 46 and 48 and collars 56 and 58, respectively.

A series of internal circumferential teeth 43 is provided on the inner surface of the central portion of the coupling. In this type of coupling no thin-walled sections of constant wall thickness are provided between the tapered sections 46 and 48 and their collars 56 and 58, respectively. One specific coupling of this type, again made from a nickel-titanium alloy and designed to couple 127 cm OD tubing to withstand hydraulic pressures of up to 8,000 p.s.i., had in its machined unexpanded form an overall length of 4-19 cm, the length of the main body portion being 1 27 cm, the length of each tapered section being 121 cm and the length of each collar being 0-25 cm. The outer diameter of the main body portion was 185 cm, the thickness of this portion was 0-31 cm. The thickness of the tapered section adjacent the collar was 0 060 cm and the wall thickness of the collar was 0-178 cm. It will be seen that in this coupling the tapered sections 46 and 48 are longer and more gradually tapered than the tapered sections in the coupling shown in Figures 1 to 4.

Figures 6 and 7 show the employment of a composite device comprising a substantially cylindrical insert 34 having inwardly extending teeth 36. The inwardly extending teeth are intended further to deform the underlying tubes 30 and 32 as can be seen in Figure 6. Thus, the insert 34 is designed as a means for further increasing the holding capacity of the coupling. Inserts designed to accomplish other functions, such as galling the inner ends of the tubes 30 and 32, are also contemplated by the present invention. A more detailed description of such inserts can be found in Belgian Patent No. 820,880, referred to above. The insert disclosed is shown to be shorter in length than the overall length of the heat-recoverable coupling member.

However, where the insert is designed as a means for preventing corrosive action between the heat-recoverable coupling and the tubing, it is advantageous to have the insert extend beyond the ends of the heatrecoverable coupling. In the latter instance, the insert is preferably of a flexible or structurally weak nature in order that the advantages obtained by the location of the rigid collars 26 and 28 will not be compromised.

It will be seen, therefore, that the coupling provided by the present invention reduces or eliminates longitudinal motion between flexing tubing and the associated coupling and reduces the maximum bending stress experienced by the tubing at the coupling. In this way, chafing, fretting or galling of the tubing at the outer ends of the coupling is substantially avoided.

The present invention further provides methods for forming a termination of a single line member or a connection between two or more line members using such a coupling.

WHAT WE CLAIM IS: - 1. A heat-recoverable hollow metal coupling comprising a main body portion and at least one terminal stress distribu tion portion having an opening for receiv ing a line member, the wall thickness of the coupling in the or each terminal stress distribution portion being less than that in the main body portion, characterised in that the or each terminal stress distribution portion is provided at its end remote from the main body portion with an outer collar of increased wall thickness.

2. A coupling as claimed in claim 1, wherein the or each terminal stress distri bution portion includes a section of sub stantially constant wall thickness which is connected to the main body portion by a tapered section, the thickness of which in creases towards said main body portion.

3. A coupling as claimed in claim 2, wherein the section of substantially con stant wall thickness has a length which is 20% to 100% of its outer diameter.

4. A coupling as claimed in claim 1, wherein the or each terminal stress distri bution portion comprises a tapered section the wall thickness of which increases to wards the main body portion, the collar being positioned adjacent the narrow end of said tapered section.

5. A coupling as claimed in any one of claims 1 to 4, wherein the collar is formed at the extreme end of the or each terminal stress distribution portion.

6. A coupling as claimed in any one of claims 1 to 5, wherein the collar has a wall thickness which is less than the wall thickness of the main body portion.

7. A coupling as claimed in any one of claims 1 to 6, wherein the inner bore of the coupling is generally cylindrical.

8. A coupling as claimed in any one of claims 1 to 7, wherein the coupling has at least two terminal stress distribution por tions.

9. A coupling as claimed in claim 8, wherein the main body portion is substan tially cylindrical and includes an opening at each end thereof.

10. A coupling as claimed in any one of claims 1 to 9, wherein the coupling is made from a nickel titanium alloy.

11. A coupling as claimed in any one of claims 1 to 10, wherein the coupling is of unitary construction.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The coupling 40 has a main body portion 44 and two terminal stress distribution portions comprising tapered sections 46 and 48 and collars 56 and 58, respectively. A series of internal circumferential teeth 43 is provided on the inner surface of the central portion of the coupling. In this type of coupling no thin-walled sections of constant wall thickness are provided between the tapered sections 46 and 48 and their collars 56 and 58, respectively. One specific coupling of this type, again made from a nickel-titanium alloy and designed to couple 127 cm OD tubing to withstand hydraulic pressures of up to 8,000 p.s.i., had in its machined unexpanded form an overall length of 4-19 cm, the length of the main body portion being 1 27 cm, the length of each tapered section being 121 cm and the length of each collar being 0-25 cm. The outer diameter of the main body portion was 185 cm, the thickness of this portion was 0-31 cm. The thickness of the tapered section adjacent the collar was 0 060 cm and the wall thickness of the collar was 0-178 cm. It will be seen that in this coupling the tapered sections 46 and 48 are longer and more gradually tapered than the tapered sections in the coupling shown in Figures 1 to 4. Figures 6 and 7 show the employment of a composite device comprising a substantially cylindrical insert 34 having inwardly extending teeth 36. The inwardly extending teeth are intended further to deform the underlying tubes 30 and 32 as can be seen in Figure 6. Thus, the insert 34 is designed as a means for further increasing the holding capacity of the coupling. Inserts designed to accomplish other functions, such as galling the inner ends of the tubes 30 and 32, are also contemplated by the present invention. A more detailed description of such inserts can be found in Belgian Patent No. 820,880, referred to above. The insert disclosed is shown to be shorter in length than the overall length of the heat-recoverable coupling member. However, where the insert is designed as a means for preventing corrosive action between the heat-recoverable coupling and the tubing, it is advantageous to have the insert extend beyond the ends of the heatrecoverable coupling. In the latter instance, the insert is preferably of a flexible or structurally weak nature in order that the advantages obtained by the location of the rigid collars 26 and 28 will not be compromised. It will be seen, therefore, that the coupling provided by the present invention reduces or eliminates longitudinal motion between flexing tubing and the associated coupling and reduces the maximum bending stress experienced by the tubing at the coupling. In this way, chafing, fretting or galling of the tubing at the outer ends of the coupling is substantially avoided. The present invention further provides methods for forming a termination of a single line member or a connection between two or more line members using such a coupling. WHAT WE CLAIM IS: -

1. A heat-recoverable hollow metal coupling comprising a main body portion and at least one terminal stress distribu tion portion having an opening for receiv ing a line member, the wall thickness of the coupling in the or each terminal stress distribution portion being less than that in the main body portion, characterised in that the or each terminal stress distribution portion is provided at its end remote from the main body portion with an outer collar of increased wall thickness.

12. A coupling as claimed in claim 11,

wherein the main body portion includes means which protrude inwardly for gripping the line member upon recovery.

13. A coupling as claimed in claim 12, wherein said means comprise one or more internal teeth.

14. A coupling as claimed in claim 12 or claim 13, wherein the bore of the terminal stress distribution portion is smooth and continuous.

15. A coupling as claimed in any one of claims 1 to 10, wherein the coupling is a composite device including an insert member.

16. A coupling as claimed in claim 15, wherein the insert member is a sleeve which is provided with internal teeth and/or which is made from a gall-prone material.

17. A method for forming a termination or connection with at least one line member which comprises the steps of (a) positioning the line member within a heat-recoverable hollow metal coupling comprising a main body portion and at least one terminal stress distribution portion having an opening for receiving said line member, the wall thickness of the coupling in the or each terminal portion being less than that in the main body portion and the at each terminal portion being provided at its end remote from the main body portion with an outer collar of increased wall thickness; and (b) causing said heat-recoverable hollow metal coupling to recover and grip the line member.

18. A method as claimed in claim 17.

wherein the or each terminal stress distribution portion of the coupling includes a section of substantially constant wall thickness which is connected to the main body portion by a tapered section, the thickness of which increases towards said main body portion.

19. A method as claimed in claim 18, wherein the or each thin-walled section has a flexural strength which is not greater than that of the line member.

20. A method as claimed in claim 17, wherein the or each terminal stress distribution portion comprises a tapered section the wall thickness of which increases towards the bain body portion, the collar being positioned adjacent the narrow end of said tapered section.

21. A method as claimed in any one of claims 17 to 20, wherein the main body portion has a substantially greater flexural strength than the line member.

22. A method as claimed in any one of claims 17 to 21, wherein the recovered internal dimension of the collar is less than the outer corresponding dimension of the line member.

23. A method as claimed in any one of claims 17 to 22, wherein the line member is tubing.

24. A coupling as claimed in claim 1, substantially as described herein with reference to and as illustrated in the accompanying drawings.

25. A method as claimed in claim 17, carried out substantially as described herein with reference to and as illustrated in the accompanying drawings.