GB2488999A

GB2488999A - Cable gland with locking device

Info

Publication number: GB2488999A
Application number: GB201104246A
Authority: GB
Inventors: Geofrey Mood; Christopher Finn; David Southern
Original assignee: CMP Products Ltd
Current assignee: CMP Products Ltd
Priority date: 2011-03-14
Filing date: 2011-03-14
Publication date: 2012-09-19
Anticipated expiration: 2031-03-14
Also published as: GB2488999B; GB201104246D0

Abstract

A device and method for locking an article to an elongate member (e.g. cable), wherein the device comprises: a pair of retaining members 16, 18; at least one flexible elongate gripping member 20 (e.g. metal cables) with a gripping portion 22 extending between the retaining members 16, 18; and a locking device to lock the retaining members 16, 18 in position. When the retaining members 16, 18 are rotated relative to one another, the gripping portion 22 of the elongate gripping member 20 moves closer to an axis of the elongate member until it grips the elongate member. The locking device then locks the retaining members 16, 18 in the rotated position. The device may form part of a cable gland for connecting an article to a cable wherein the gland comprises: a gland body; a seal for sealing the body relative to the cable; and the aforementioned device for locking cable gland to the cable.

Description

A device for locking an article to an elongate member The present invention relates to a device for locking an article to an elongate member and relates particularly, but not exclusively, to a device for locking a cable gland into engagement with a sheathed electrical cable.

A cable gland, an article that carries an electrical cable and acts as the lunction between the outside world and internal workings of an electrical installation such as a metal box, has two main functions. Firstly, the gland acts as a seal preventing water and/or gases passing into the box.

Secondly, the gland grips the cable preventing it moving relative to the installation or even being pulled from the installation. To prevent axial movement of the cable, a gripping force is applied by the gland. Typically this is achieved by either using the compressive force applied by the seal in the gland against the cable or by fixing a part of the cable, typically a reinforcement wire from within the sheath, tc the cable gland.

In the example where the seal is used to grip the cable, the choice of material used in the seal becomes critical. In order to provide better grip, a harder material should be chosen. However, harder materials provide a less adequate seal. As a result, it is difficult to produce a cable gland that can pass the most stringent pull tests where only the seal is being used to grip the cable.

On the other hand, where a reinforcing wire or armour braid formed in the sheath is locked to the cable gland, a seal formed from the ideal sealing material can be chosen.

However, for hazardous area use safety regulation prevent the F use of the braid to secure the cable and so the seal must be used. It is also the case that the process of stripping the reinforcing wire from the cable sheath and locking it to the cable gland is time consuming. Furthermore, in some glands once the cable gland is assembled it is impossible to tell whether the reinforcing wire has been locked to the cable gland and therefore the cable gland correctly installed.

Preferred embodiments of the present invention seek to overcome the above described disadvantages of the prior art.

According to an aspect of the present invention, there is provided a device for locking an article to an elongate member, the device comprising:-at least one first retaining member; at least one second retaining member; at least one flexible elongate gripping member for gripping at least one elongate member, the or each gripping member defining at least one gripping portion extending between at least one said first retaining member and at least one second retaining member, such that rotation of at least one first retaining member relative to at least one second retaining member causes at least part of said gripping portion to move closer to an axis of said elongate member; and locking means for looking the first and second retaining members in said rotated position.

By providing a flexible elongate gripping member connected to first and second retaining members so that rotation of one rotating member relative to the other causes the gripping portion to move closer to the elongate member (the cable that is being locked to) and locking them in that position, provides the advantage that a grip that acts independently of the seal or armour wire is provided.

Furthermore, the grip is provided by simple rotation and then locking of one of the retaining members relative to the other.

This simple mechanism makes it easy to install and because the gripping portions of the gripping member are rotated into a locking position they can be usually set up to be positioned well away from the cable as it is installed.

Because the seal can also be made from a very soft material, it can provide the best possible seal and consideration of the grip provided by the seal need not be taken into account.

Furthermore, because there is no need to strip the sheath from the cable to access the reinforcing wires and grip them within the gland it is possible to provide a cable gland that can be inserted onto a cable without being dissembled but still provide sufficient grip to pass the most rigorous pull test. This provides significant time saving compared to existing glands that require the components to be dissembled, inserted onto the cable and reconnected. It may still be necessary to strip the sheath from the cable to access the reinforcing wire for the purposes of earthing.

However, this does not reguire that the gland be dissembled before insertion of the cable onto the gland.

As a further advantage it is also the case that the device of the present invention can be retrofitted to an existing cable gland or simply provided as an additional component to offer additional locking strength between a newly installed known cable gland and the cable.

The device may further comprise a plurality of elongate gripping members each defining a gripping portion.

By providing a plurality of gripping members, the advantage is provided that the amount of turning of one retaining member relative to the other that is required to provide a significant grip to the cable is reduced.

In a preferred embodiment at least one said elongate gripping member comprises a gripping cable.

In another preferred embodiment at least one of said first and second retaining members comprises an annular member adapted to surround said elongate member.

In a further preferred embodiment the gripping cables are spaced around the circumference of said annular member with a gap of between 10 and 20 times the diameter of the gripping cable between each gripping cable.

By providing equally spaced cables around the circumference of an annular retaining member with the cables separated by between ten and twenty times their diameter, the advantage is provided that this provides the ideal number of gripping members to provide sufficient grip to the cable.

The locking means may further comprise:-at least one first body member adapted to at least partially engage at least one said first retaining member and having a first threaded member; and at least one seoond body member adapted to at least partially engage at least one said second retaining member and having a second threaded member adapted to engage said first threaded member, wherein threaded engagement the first and second body members results in the locked engagement of the first and second retaining members.

By using two mutually threaded body members to engage the first and second retaining members, the advantage is provided that the rotation of the threaded members can be used to apply a rotation to the first and/or second retaining members and thereby apply the gripping force to the cable.

Furthermore, since the length of the retaining members is predetermined, the amount of thread taken up by moving the first and second body members into locked engagement with the retaining members will always be the same. /-ks a result, it is straightforward to see whether the first and second body members are fully engaged with each other and therefore determine that the first and second retaining members have been rotated into the correct locking mechanism and locked together, thus causing the device to be properly locked to the cable.

In a preferred embodiment rotation of the first and second body members into threaded engagement with each other causes rotation of the first and second retaining member relative to each other.

The device may further comprise at least one friction member for controlling the friction force between at least one body member and at least one retaining member.

In another preferred embodiment at least one friction member comprises an 0-ring.

Using a friction member, typically in the form of an 0-ring, the advantage is provided that the friction member ensures that the rotation of the second body member onto the first body member causes the correct amount of rotation of the first and second retaining members relative to each other. The 0-ring friction member acts a little like a clutch, ensuring that the correct amount of rotational force is applied to the retaining members to ensure the correct grip on the cable but preventing excessive rotation of the retaining members which could lead to damage of the cables.

In a further preferred embodiment said first and second retaining members and said gripping members are formed by moulding a thermoplastic material.

By forming the retaining members and the gripping member from moulded thermoplastic material, the advantage is provided that a very simple component is able to provide the additional grip required. This is particularly useful for retrofitting to existing glands or adding to an existing giand on installation, thereby utilising some existing grip of the gland and additional grip from the added component.

The device may also further comprise rotation means for causing one of said first and second retaining member to rotate relative to the other of said first and second retaining member.

According to another aspect of the present invention, there is provided a cable gland for connecting an article to a cable, the gland comprising:-a gland body; a seal for sealing the body relative to the cable; and a device fcr locking the cable gland to the cable as set out above.

According to a further aspect of the present invention, there is provided a method of locking an article to an elongate member, comprising the steps of:-locating at least one flexible elongate gripping member around at least one elongate member, the or each gripping member defining at least one gripping portion extending between at least one first retaining member and at least one second retaining member; rotating at least one first retaining member relative to at least one second retaining member so as to causes at least part of said gripping portion to mcve closer to an axis of said elongate member; and locking the first and second retaining members in said rotated position.

Preferred embodiments of the present invention will now be described by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which:-Figures 1 and 2 are side and perspective views of part of a device of the present invention in a first condition; Figures 3 to 6 are perspective sectional end and a further perspective view of the component of Figures 1 and 2 in a second condition; Figures 7 to 10 are views equivalent to Figures 3 to 6 in a third condition; Figures 11 to 14 are views equivalent to those of Figures 7 to 20 including further components of the device of the present inventicn; Figures 15 and 16 are perspective and side sectional views of a cable gland incorporating the device of the present invention; Figures 17 to 22 are sectional views of different embodiments of the present invention; and Figures 23 and 24 are perspective view of a cable gland engaged with a cable.

Referring to the figures and with particular reference to Figures 1, 2, 15, 16, 23 and 24, a device 10 for locking an article, such as a cable gland 12, to an elongate member, such as a cable 14, includes first and second retaining members 16 and 18. The locking device 10 also has at least one, but preferably a series of, flexible elongate gripping members in the form of gripping cables 20. These gripping cables 20 are attached to first and second retaining members 16 and 18 with gripping pcrtions 22 extending between the first and second retaining members 16 and 18. The gripping cables 20 also have fixed ends 24 that are fixedly connected to the retaining members 16 and 18. The fixed ends 24 are clamped between inner portions 26 and 28 and outer portions 30 and 32 of first and second retaining nenbers 16 and 18 (shown most clearly in Figure 4) The inner portions 26 and 28 and outer portions 30 and 32 are annular and sized to provide an interference fit when cable ends 24 are inserted between them, thereby fixedly retaining the fixed cable ends 24 of gripping cables 20 between the annular first and second retaining members 16 and 18. The gripping cables 20 are preferably regularly spaced around the circumference of the annular retaining members 16 and 18 and the distance between the gripping cables around the diameter of the retaining members is between ten and twenty times the diameter of the gripping cable and most preferably fifteen times the diameter.

The device also includes locking means in the form of first and second body members 34 and 36 which engage each other on respective mutual threaded portions 38 and 40. The first threaded portion 38 of first body member 34 is an external thread and the second threaded portion 40 of second body member 36 is an internally threaded portion. The first and second body members enclose the first and second retaining members 16 and 18. An outer end surface 42 of first retaining member 16 engages an abutment surface 44 of first body member 34 and an outer end surface 46 of second retaining member 18 engages an abutment surface 48 of second body member 36. The first and second retaining members 16 and 18 have inner end surfaces 50 and 52 that in use engage each other. Outer annular surfaces 54 and 56 of first and second retaining members 16 and 18 engage internal annular surface 58. As a result, the first body member 34 almost entirely encloses the first and second retaining members 16 and 18 and the only engagement between the first and second retaining members and the second body member 36 is between the outer end surface 46 and abutment surface 48.

First body portion 34 has an internal threaded portion 60 that engages an external threaded portion 62 of cable gland 12 for connecting the lccking device 10 to the cable gland 12. The cable gland 12, shown in Figures 15 and 16, is a simplified gland having mutually threaded gland members 64 and 66 and a compressible seal 68 that is compressed by the axial movement of the gland members and, due to its engagement with cam surface 70, moves radially inwardly in a manner familiar to those skilled in the art.

An externally threaded body portion 72 of gland member 64 extends through, for example, a box (not shown) for connection of the gland 12 to that box. At the junction between outer end surface 42 and abutment surface 44, a friction member in the form of 0-ring 45 is provided. The 0-ring 45 is secured to a recess formed in abutment surface 44 of first body member 34. Similarly, at the junction between outer end surface 46 and abutment surface 48 a second 0-ring 49 is retained within a recess in second body member 36.

Operation of the locking device 10 will now be described. The first and second retaining members 16 and 18 are formed with fixed cable ends 24 clamped between inner portions 26 and 28 and outer portions 30 and 32 and as shown in Figures 1 and 2. In order to assist the description of the present invention, the operation of the first and second retaining members will initially be described in theoretical terms with the retaining members illustrated outside of the device. When the first and second retaining members 16 and 18 are separated at the greatest extent possible the gripping portions 22 of gripping cables 20 are ideally aligned parallel to each other. Slight rotation of second retaining member 18 relative to the first retaining member 16, as seen in Figures 3 tc 6, causes the opposing ends of the gripping portion 22 to rotate away from each other around the circumference of the annular retaining member 16 and 18.

The gripping cable 20 becomes stretched across the circumference thereby drawing the gripping portion radially inwards when viewed along the axis of the cable (see Figure 5) . This in turn draws the first and second retaining members closer to each other and further rotation still causes the inner end surfaces 50 and 52 to engage each other, as seen in Figures 7 to 10 with the gripping portions moving further radially inwards. When a cable 14 is present running through the retaining members radially inward movement of the gripping portions is prevented by the cable and instead a gripping force is applied in a radially inward direction to the outer surface of the sheath of the cable. The gripping cables 20 are therefore acting like an iris closure to apply a gripping force to the cable 14 allowing a single device to grip cables of various diameters.

When the first and second retaining members 16 and 18 are used in the device 10, the starting position for the retaining members is such that the inner end surfaoes 50 and 52 are engaged or nearly engaged with each other between the first and second body members 34 and 36. The first and second body members are only partially threaded over each other ieaving the first and second retaining members loosely fitting within the internai annular surface 58 of first body member 34. With the first and second retaining members free to move, they are able to rotate relative to one another and the gripping portions 22 of gripping cables 20 can be moved apart with the gripping portions 22 able to move into the recess formed between the two inner portions 26 and 23 of first and second retaining members 16 and 18 and also potentially between the separated inner surfaces 50 and 52.

In order to ensure that the gripping cables do not extend into the area through which the cable will extend as it is inserted into the cable gland 12 and locking device 10, an object, such as a long conical object, can be inserted into the device 10 through the opening in second body member 36.

As the object introduced engages the cables and pushes then apart it will cause either or both of the first and second retaining members to rotate in opposite directions.

The second body member 36 is threaded onto the first body member 34 so that external end surfaces 74 and 76 are displaced away from each other sufficiently far that that recess 78 is visible between the external end surfaces 74 and 76. As shown in the examples in Figures 18 and 19, this recess can house a further 0-ring So. If this 0-ring is brightly coloured it can be used to assist in showing that the device 10 has been correctly used since in the locked position, shown in Figures 15 and 16, external end surfaces 74 and 76 should be engaged with each other. If the 0-ring 80 is still visible, the locking device 10 is not correctly locked. Similarly, the recess 78 could be painted with a bright colour.

In order to insert a cable into a box connected to gland 12, and lock it thereto, the external threaded portion of gland member 64 is inserted into an aperture in a box (not shown) and fixed on the inside by an internally threaded nut (not shown). Alternatively, the box may be provided with an internally threaded aperture into which the external threaded portion of gland member 64 is directly connected. The gland member 66 is rotated relative to gland member 64 causing seal 68 to compress against cam surface 70 and move radially inwardly engaging the external surface of the sheath of cable 14 thereby sealing the inside of the box. First body member 34 is already in fully threaded engagement with gland member 66. Second body member 36 is rotated so as to bring it into further thread engagement with first body member 34. Until the outer end surfaces 42 of first retaining member 16 and 46 of second retaining member 18 engage 0-rings 45 and 49 and the inner end surfaces 50 and 52 engage with each other, the rotation of second body member 36 is unlikely to cause any rotation of the second retaining member 18 relative to the first retaining member 16.

However when the inner end surfaces 50 and 52 are pressed into engagement with each other and the outer end surfaces 42 and 46 are pressed into engagement with 0-rings 45 and 49, further rotation of the second body member will cause the second retaining member 18 to rotate with the second body member. This rotation of the second retaining member 18 relative to the first retaining member 16 causes the gripping portions 22 of gripping cable 20 to be tightened across the outer surface of the cable 14. If the cable 14 were not present, the cables 20 would move radially inward as shown going from the view shown in Figure 5 to the view shown in Figure 9. This rotation causes the gripping portions 22 of gripping cables 20 to apply a gripping force to the outer sheath of cable 14 and thereby grip and lock the cable 14 to cable gland 12.

The 0-rings 45 and 49 act in two ways during the rotation of the second body member 36. Initially they ensure that the second retaining member 18 begins to rotate with the rotation of the second body member 36 by expanding into the small gap between the end surfaces 12 and 46 and abutment surfaces 44 and 48 as the second body member comes into closer engagement. They also maintain the friction between these surfaces during the continued rotation of the second body member 36 but prevent excessive constriction of the gripping cables 20 around the sheath of cable 14 by, if necessary, allowing the outer end surfaces 42 and 46 to slip relative to the abutment surfaces 44 and 18, thereby acting in a similar manner to a clutch. As a result, the degree of grip applied by the gripping cables can be controlled.

When the external end surfaces 74 and 76 are almost engaged with each other, as shown in Figures 11, 12, 15 and 16, the abutment surface 44 of first body member 34 is pressed into engagement with outer end surface 42 of first retaining member 16. At the same time, the outer end surface 46 of second retaining member 18 is pressed into engagement with abutment surface 48 of second body member 36 and the inner surfaces 50 and 52 of the first and second retaining members are also pressed into engagement with each other. As a result, further rotation of the second retaining member 18, or reverse rotation of the second retaining member is prevented and the first and second retaining members and first and second body members 36 and 36 are all locked together in these final positions..

Figures 17 to 21 show further embodiments of the invention in which alternatives to the friction members, 0-rings 45 and 49, are included. It should be noted that Figure 21 is the embodiment previously described. In the embodiment shown in Figure 17, the 0-rings 45 and 49 have been replaced with a wave spring 82. In this version the annular retaining members 16 and 18 have hexagonal outer profiles. The wave spring 82 holds the retaining members cut of a hexagonal socket in the second body portion 36 until the spring has been compressed enough. In this way the second body portion can be tightened by a few threads, but the retaining members are only twisted a small amount. In Figure 18 the 0-rings 45 and 49 have been replaced by tapered cam surfaces 84, 86, 88 and 90 which gradually increase the friction between body members 34 and 36 and retaining members 16 and 18. In Figure 19, the tapered surfaces remain present and 0-rings 92 and 9 have been introduced. The embodiment in Figure 20 a rubber seal 96 has been provided and ensures gentle pressure of the engaging surfaces against each other until the seal becomes sufficiently compressed to induce rotation in the second retaining member as the second body member 36 is rotated. The seal also acts to provide further sealing against the sheath of cable 14. Finally, in Figure 22 the embodiment shown is like that in Figure 21 and as previously described except that the 0-ring 45 has been removed and the first retaining member 16 is fixed to the l6 first body member 34 by an interference fit between the surfaces indicated at 98.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of F example only and not in any limitative sense, and that the various alterations and modifications are possible without departure from the scepe of the invention as defined by the appended claims.

For example, instead of using a piurality of gripping cables 20 to provide a plurality of gripping portions, as shown in Figures 1 and 2, a single gripping cable 20 could be used to provide a plurality of gripping portions by looping the cable backwards and forwards between the first and second retaining members 16 and 18 and the fixed ends 24 being joined sections of the gripping cable 20. Furthermore, a single cable could be used where it is fixed at both ends and wrapped at least once around the cable 14. A multiplicity of cables could be used and they could be arranged In a crossing over or woven form forming a woven tube of wires. Materials other than metal cables could be used or the wires could be coated. Rubber tubes can be used, preferably with reinforcing cable contained within the wall of the tube.

Claims

Claims 1. A device for locking an article to an elongate member, the device comprising:-at least one first retaining member; at least one second retaining member; at least one flexible elongate gripping member for gripping at least one elongate member, the or each gripping member defining at least one gripping portion extending between at least one said first retaining member and at least one second retaining member, suoh that rotation of at least one first retaining member relative to at least one second retaining member causes at least part of said gripping portion to move closer to an axis of said elongate member; and locking means for locking the first and second retaining members in said rotated position.
2. A device according to claim 1, further comprising a plurality of elongate gripping members each defining a gripping portion.
3. A device according to claim 1 or 2, wherein at least one said elongate gripping member comprises a gripping cable.
4. A device according to any of the preceding claims, wherein at least one of said first and second retaining members comprises an annular member adapted to surround said elongate member.-IB-
5. A device according to claim 4, wherein said gripping cables are spaced around the circumference of said annular member with a gap of between 10 and 20 times the diameter of the gripping cable between each gripping cable.
6. A device according to any of the preceding claims, wherein said locking means comprises:-at least one first body member adapted to at least partially engage at least one said first retaining member and having a first threaded member; and at least one second body member adapted to at least partially engage at least one said second retaining member and having a second threaded member adapted to engage said first threaded member, wherein threaded engagement the first and second body members results in the locked engagement of the first and second retaining members.
7. A device according to claim 6, wherein rotation of the first and second body members into threaded engagement with each other causes rotation of the first and second retaining member relative to each other.
8. A device according to any of the preceding claims, further comprising at least one friction member icr controlling the friction force between at least one body member and at least one retaining member.
9. A device according to claim 8, wherein at least one friction member comprises an 0-ring.
10. A device according to any of the preceding claims, wherein said first and second retaining members and said gripping members are formed by moulding a thermoplastic material.
Il. A device according to any of the preceding claims, further comprising rotation means for causing one of said first and second retaining member to rotate relative to the other of said first and second retaining member.
12. A device for locking an article to an elongate cylindrical member substantially as hereinbefore described with reference to the accompanying drawings.
13. A cable gland for connecting an article to a cable, the gland comprising:-a gland body; a seal for sealing the body relative to the cable; and a device for locking the cable gland to the cable according to any one of the preceding claims.
14. A cable gland for connecting an article to a cable substantially as hereinbefore described with reference to the accompanying drawings.
15. A method of locking an article to an elongate member, comprising the steps of:-locating at least one flexible elongate gripping member around at least one elongate member, the or each gripping member defining at least one gripping portion extending between at least one first retaining member and at least one second retaining member; rotating at least one first retaining member relative to at least one second retaining member so as to causes at least part of said gripping portion to move closer to an axis of said elongate member; and locking the first and second retaining members in said rotated position.
16. A method of locking an article to an elongate member substantially as hereinbefore described with reference to the accompanying drawings.