GB2269274A

GB2269274A - Bend limiter

Info

Publication number: GB2269274A
Application number: GB9315103A
Authority: GB
Inventors: Ian Mathieson
Original assignee: ORCINA CABLE PROTECTION LIMITE
Current assignee: ORCINA CABLE PROTECTION LIMITE
Priority date: 1992-07-22
Filing date: 1993-07-21
Publication date: 1994-02-02
Also published as: GB9215581D0; GB9315103D0

Abstract

A bend restrictor for flexible cabling, resists tensile forces and produces an acceptable diameter bend using two or more relatively movable housing members 11 and link means (3, 5) comprising a spherical joint, coupling adjacent housing members in a manner allowing relative angular movement thereof. The housing members and link means have respective communicating passageways 8, 7 to accommodate the cabling. The link members 3 have a pair of part spherical formations 3a, 3b which cooperate with two part concave spherical formations 5a, 5b which are located in the intermediate housing members. Rib and recess arrangements on the frusto-conical surfaces of the housing members may be used to take radial forces and hence avoid unwanted loading on the joint arrangement. <IMAGE>

Description

Title: Bend limiter DESCRIPTION The present invention relates to a bend limiter for cabling or otherwise.

Sub-sea telecommunications cables require repeater units at intervals which will introduce short stiff,sections into the cabling. Furthermore, repair to the cabling introduces short stiff sections. There is a potential problem with over bending of flexible cabling adjacent to such short stiff sections. The cabling is deployed under tension over a sheave and is commonly required to be buried using a standard sub-sea plough.

Passage over the sheave calls for a bend restrictor to prevent damage to the cable from overbending adjacent to the stiff section, whilst passage through the plough sets a limit on the maximum diameter of the unit. With telecommunication cabling a combination of a large heavy moment with a small diameter leads to inherently high stress Bend restrictors are known from GB 2142788 and US 4703135 which have attempted to provide a solution and comprise flanged sleeve-like devices which are connected by a series of loosely fitted bolts allowing a limited degree of angular movement. Bending moments are restricted by tension in the bolt on the outside of the bend. Regardless of how many bolts are used between the adjacent segments, only one takes the tensile load at any time. The tension can be extremely high (for example of the order of 10 tons or more) requiring a large bolt diameter.The associated parts are also very highly loaded. Furthermore, it may be impossible to accommodate such a design within the diameter limits imposed by the plough - even when the highest strength materials are employed.

The present invention aims to provide a solution to the above problems.

Accordingly the present invention provides a bend restrictor comprising at least two relatively moveable housing members, link means comprising a spherical joint coupling adjacent housing members in a manner allowing angular movement of the adjacent housing members with respect to one another, and wherein the housing members and link means have respective communicating passageways to accommodate cabling or other elongate means whose permitted bend radius is to be restricted.

Using a spherical joint of ball and socket type has the advantage that axial forces are distributed over the cooperating surfaces thereof. Bending moments experienced in operation are resisted by couples consisting of tensile forces in the link means and opposing compressive forces. Advantageously the compressive forces are taken by cooperating engagement of the adjacent housing members. Bending movements in individual components are minimised. The detail design can protect the individual parts from bending loads.

The spherical joint conveniently comprises cooperating spherically shaped surfaces, ie.

cooperating members having concave and convex components .

More particularly the link means comprises a link member having say convex part spherical surfaces at opposite ends to couple with respective housing members by way of respective mating locators, say concave spherical, which are secured to the housing members.

The mating locators are constructed in a manner which allows assembly round the respective convex spherical surface of the link member to entrain same when the locators are secured to the housing member.

Conveniently this is achieved by making the locators in two halves, ie split longitudinally and having a cylindrical outer surface received in a cylindrical bore of the housing member.

The ends of the adjacent housing members make contact at the maximum bend condition to take compression loads. In one embodiment the ends of the housing members are frusto-conical so that at the maximum permitted bend the adjacent housing members make a radial line contact at their end surfaces.

Advantageously however, the adjacent ends of the housing member have interengageable complimentary formations, for example, ribbing and recessing, which take radial loading in the limit condition.

For most applications a plurality of housing members and associated link means will be provided, each joint, allowing a prescribed angular movement whereby the permitted bend radius is made up of several joints disposed one after the other. Thus, with the exception of end housing member, intermediate housing members will receive two link members - one in each end. Thus the intermediate housing members are preferably cylindrical sleeves with frusto-conical end surfaces. The locators are formed to accommodate the respective link members.

The present invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a bend restrictor according to the present invention, Figure 2 is a view of an end of the connector, and Figure 3 is an enlarged detail view within circle A of Figure 1.

Referring to the drawings, a bend restrictor as illustrated in the example comprises a plurality of housing members 1 (referred to as intermediate housing members la and end housing members lb, lc) and link means comprising a plurality of link members 3 and locators 5 The link members 3 have to their opposite ends respective convexly spherical formations 3a, 3b and an internal through bore 7. The through bore is generally toroidal whose curvature is equal to the minimum permitted bend radius, and the adjacent members are disposed so that the curves run one into the other as illustrated in Figure 1.

The intermediate housing members comprise cylindrical sleeves with an internal bore 8 which receives a respective locator 5. The locator is made up of two halves - split in a plane along their longitudinal axis and having concave spherical surface formations 5a, Sb to fit around the respective formations 3a, 3b of the link members 3.

Once assembled around the link member the locator can be slid into the housing member and is secured against axial displacement and against shear forces using the likes of a locating pin 10 received in a bore of the housing member la and aligned recessing of the locator Thus the adjacent housing members are connected in a manner which permits a limited angular movement with 360 degrees of movement about the joint axis, whilst the spherical surfaces ensure that the tension forces are distributed over the mating joint surfaces. By this means component sizes and/or material specifications may be reduced whilst meeting the design load requirements.

The ends 11 of the housing members 1 are frustoconical and adjacent ends cooperate at the minimum permitted bend radius, ie. in the limit condition and thus compression forces are transmitted through the housing members.

The end housing members ib, 1 are configured to receive the spherical surface of a link member by provision of a concavely spherical locator. These are made up of two halves held together by a locating sleeve In the case of end housing lb in the illustrated embodiment, the locator halves 5',5" are held together by a cylindrical sleeve lla, secured by screw 12 and have tapped holes 13 for coupling to the stiff section of the cable by way of bolts or the like.

The other end lc has locator halves 5',5" coupled by an end sleeve 116 whose internal bore 15 is curved radially outwardly at the end to limit cable stressing where it emerges from the restrictor.

The cable is shown in dotted outline at 17. the illustrated example of bend restrictor allows 1000 movement before the housing members come to their end positions. Altering the number of links in the restrictor or their length can serve to adjust the permitted angular range over which the restrictor exerts its influence Reference to Figure 3, shows in detail the end configuration of the facing member according to one embodiment It will be seen that the adjacent ends of the housing members comprising complimentary recessing 21 and ribbing 22 which extend circumferentially with generally tapered mating side frees 23, 24. These take radial forces in the limit condition and by this means avoids introducing bending movements in the link members and local loading of the locators. It will be seen that there is a clearance between the adjacent ends of the link members 5 in the limit position

Claims

CLAIMS 1. A bend restrictor comprising at least two relatively moveable housing members, link means comprising a spherical joint coupling adjacent housing members in a manner allowing angular movement of the adjacent housing members with respect to one another, and wherein the housing members and link means have respective communicating passageways to accommodate flexible cabling or other flexible elongate means whose permitted bend radius is to be restricted.
2. A bend restrictor as claimed in claim 1 in which the spherical joint is of ball and socket type.
3 A bend restrictor as claimed in claim 1 or 2 in which bending moments experienced in operation are resisted by couples consisting of tensile forces in the link means and wherein the compressive forces are taken by cooperating engagement of the adjacent housing members
4 A bend restrictor as claimed in claim 1, 2 or 3 in which the link means comprises a link member having convex part spherical surfaces at opposite ends to couple with respective housing members by way of respective mating concave spherical locators, which are secured to the housing members.
5. A bend restrictor as claimed in claim 4 in which the mating locators are constructed in a manner which allows assembly round the respective convex spherical surface of the link member to entrain same when the locators are secured to the housing member
6. A bend restrictor as claimed in claim 5 in which the locators are made in two halves, being split longitudinally and having a cylindrical outer surface received in a cylindrical bore of the housing member.
7. A bend restrictor as claimed in any one of the preceding claims in which the ends of the housing members are frusto-conical so that at the maximum permitted bend the adjacent housing members make a radial line contact at their end surf aces
8. A bend restrictor as claimed in any preceding claim in which the adjacent ends of the housing member have interengageable complimentary formations, which take radial loading in the limit condition.
9. A bend restrictor as claimed in claim 8 in which the interengageable complimentary formations comprise ribbing and recessing.
10. A bend restrictor as claimed in any one of the preceding claims comprising a plurality of said housing members and associated link means, each joint allowing a prescribed angular movement whereby the permitted bend radius is made up of several joints disposed one after the other 11 A bend restrictor as claimed in claim 10 in which said housing members intermediate the ends of the restrictor comprises cylindrical sleeves with frustoconical end surfaces 12. A bend restrictor as claimed in claim 11 in which the intermediate housing members receive locators which two part concave spherical surfaces for engagement by a respective part convex spherical link members 14. A bend restrictor as claimed in claim 10, 11 or 12 in which an end housing member comprises mounting means for the bend restrictor 14 A bend restrictor constructed and arranged substantially as hereinberore described with reference to and as illustrated in the accompanying drawings