The invention relates to a device for tension relief of a cable, of the kind indicated by the preamble of the attached independent claim pertaining to a device.

The invention also relates to a method for effecting tension relief for a cable, according to the preamble of the attached independent claim pertaining to the method.

A previously known practice is to apply an annular element made of plastically deformable material round a cable and to deform the annular element in radial and circumferential directions so that its inside circumference engages with the cable's outside surface round the cable's circumference.

The cable is usually an electrical cable, e.g. a power cable or a signal cable, and the radially inside surface of the annular element is pressed with relatively great force onto the cable's outside circumference, whereby the reaction forces from the electric cable influence the shape of the element's inside circumference. At the location of the element's elastic engagement with the cable's outside circumference, the cable undergoes a local diameter decrease. The result is that the deformed element provides a good seal relative to the cable's outside surface round the latter's circumference and that the annular element provides good anchoring to the cable in axial directions. The element may be linked directly or indirectly to a lead-through aperture in a wall through which the cable extends. The element may for example be provided with an axial tubular extension bearing a thread (or some other connection means) which makes it possible for the device to be connected to the wall, or any connection means appropriate to the purpose which is associated with the wall.

Previously known tension relief devices of the kind indicated function well in many embodiments, but there is always risk of the cable being damaged by the fact that the annular element engages directly with the cable. The plastically deformable ring element is usually supported by or integrated in a sleeve which, for example, is provided at one end with a coupling means whereby the sleeve can be sealingly and reliably linked to a coupling element cooperating with it which is connected to a wall round a wall aperture through which the cable is to be led.

In the previously known devices, the ring element needs also to be well-adapted to the diameter of the cables concerned, thereby making it necessary to provide for each cable diameter a specially adapted device.

One object of the invention is to indicate a new tension relief device which can be fitted to the cable by a single contact pressing operation and which provides tight and good tension relief of the cable and can easily be adapted to different sizes of cable.

A further object of the invention is to indicate a technique which makes it possible to reduce the costs involved in providing devices which are adapted to different sizes of cables.

A further object of the invention is to indicate a technique which makes it possible to use one and the same contact pressing tool for a number of different devices which are adapted to respective different sizes of cable, whereby the contact pressing tool is drivable to a predetermined contact pressing final position (crimping final position).

These objects are achieved in whole or in part by the invention.

The invention is defined in the attached independent claims.

Embodiments of the invention are indicated in the attached dependent claims and in the ensuing description of the invention.

In an at present particularly preferred embodiment of the invention, standard sleeves with a predetermined inside diameter are provided for cables having different outside diameters within a predetermined diameter range. A tubular elastomer bushing whose inside diameter corresponds to the outside diameter of the cable concerned is provided for each standard diameter of cable. At least one, preferably at least two, axially separated ring elements made of plastically deformable material are accommodated in the elastomer bushing. The inside circumference of the ring elements is situated in the vicinity of the inside surface of the elastomer bushing. The inside circumference surface of the ring elements is preferably covered with an approximately 2 mm thick layer of the elastomer bushing. The outside surface of the rings is selected to closely correspond to the inside diameter of the standard sleeve so that the bushing, with the rings borne by it, can be inserted axially into the sleeve. The cable may be introduced into the bushing before or after the bushing is introduced into the sleeve. The bushing may be provided with an end stop which ensures correct axial positioning of the bushing in the sleeve. The sleeve may be made of a plastically deformable material such as stainless steel or brass. The ring elements may be made, for example, of aluminium. The ring elements have an axial thickness which is sufficient for preventing shearing relative to the cable and for preventing the rings from buckling outwards when the device is contact-pressed onto the cable. For example, the thickness may be within the range 3-10 mm for cables in the diameter range 14-30 mm.

For cables with an outside diameter in the range 30-14 mm, the standard sleeve may have a wall thickness of about 1 mm and an inside diameter of 33 mm, in which case the ring elements will have a radial thickness of from about 1.5 mm to about 1 cm in order to interact correctly with the respective sizes of cable. During the clamping of the device onto the cable, the tool effects for example crimping of the device from a circular outside diameter of 35 mm to the shape of a regular hexagon with a diagonal dimension of 32 mm. In cases where the device comprises two ring elements, the distance between them is with advantage somewhat larger than the diameter of the cable concerned. The radial deformation of the rings during the contact pressing (crimping) operation is selected so as to impart to the cable a deformation which does not damage the cable but which brings about the best possible tightness and tensile load transmission between the ring and the cable.

The invention achieves particularly good tightness between the device and the cable round the latter' s circumference and also achieves very good axial tension relief for the cable.

The invention is described below in the form of examples with reference to the attached drawing.

Fig. 1 depicts schematically an axial section with a device according to the invention as placed on a cable.

Fig. 2 depicts the subject matter of Fig. 1 after radial pressing of the device onto the cable.

Fig. 3 depicts schematically a tool for application of the device, as fitted on the cable.

Fig. 4 depicts the tool in a closed state.

Fig. 1 depicts a circular cylindrical sheetmetal sleeve 2 made of a plastically deformable material, e.g. stainless steel or brass. The sleeve 2 has a material thickness of, for example, 1 mm. On the inside of the sleeve 2 there is a tubular rubber bushing 4. The latter 's inside surface 42 has a diameter substantially corresponding to the outside diameter of a cable 5 which extends through the bushing 4.

The bushing has an outside surface adjacent to the inside surface of the sleeve 2. The bushing 4 has recesses open outwards which accommodate two axially separate annular elements 3 made of plastically deformable material, e.g. aluminium. Between the inside surface of the bushing 2 and the outside surface of the ring elements 3 there is a clearance of, for example, 0.1 mm. The inside circumference surface of the ring elements 3 is situated at a distance of about 2 mm from the outside circumference of the cable 5 so that the rubber bushing 4 has material bridges 45 with a corresponding thickness between the annular elements 3 and the cable 5. The material bridges 45 hold together the portions of the bushing 4 which are delineated by the ring elements 3.

The sleeve 2 is depicted with a funnel shape widened at one end to limit the risk of damage to the cable 5 if the latter is bent out to contact with the sleeve 2.

At its other end, the sleeve 2 has a coupling means which provides tight and reliable linking to corresponding contact elements on a wall 8 which has a lead-through aperture 9 for the cable 5. The coupling means on the sleeve 2 may comprise a radial end flange 74 with an external thread 71 which cooperates with an internal thread 72 on the wall 8, whereby the flange 74 rests against a wall surface via an annular seal 76. One skilled in the art will nevertheless appreciate that tight or untight linking of the sleeve 2 to a loadbearing element 8 can be established in many already well- known ways.

The tension relief device illustrated in Fig. 1 is anchored to the cable 5 by the fact that the device 1, e.g. the rubber bushing 4 with the annular elements 3 and the surroun¬ ding sleeve 2, is compressed radially by a contact pressing tool so that at least the annular elements 3 and the adjacent portions of the sleeve 2 undergo plastic deformation radially inwards and in the circumferential direction, to the shape schematically illustrated in Fig. 2. It may be appreciated from Fig. 2 that the annular elements 3 engage with, and form annular indentations in, circumferential regions of the cable 5, while the circumferential surface of the cable 5 is protected by the rubber bridges 45 from direct influence of the ring elements 3. The result is that it is possible to increase the grip of the ring elements 3 on the cable 5 without damaging the latter. It may also be seen that the rubber bushing is clamped between the sleeve 2 and the cable 5, particularly the portion of the bushing which is situated between the ring elements 3, which means that this portion of the bushing provides substantial strengthening of the axial anchoring of the sleeve and the ring elements 3 to the cable 5.

According to an important aspect of the invention, the tension relief devices 1 need to be readily adaptable to different sizes of cable. To reduce the costs involved in pro¬ viding such a range of devices 1 for different standard cable sizes within a predeter¬ mined diameter range, a standard sleeve 2 with a predetermined inside diameter is provided for the diameter range concerned. Depending on the outside diameter of the cable 5 concerned, a corresponding rubber bushing 4 with inside diameter corres¬ ponding to the outside diameter of the cable and with its own outside diameter cor¬ responding to the inside diameter of the standard sleeve 2 is provided.

The annular elements 3 are fitted in this bushing 4 in such a way that they are protec¬ ted inside by the material bridges 45. The bushing 4 with the rings 3 can easily be inserted in the standard sleeve 2 before or after the cable is threaded through the bushing 4.

For each size of cable 5, an appropriate bushing 4 with relating rings 3 is therefore manufactured so that the bushing adapted to the cable 5 can be inserted in the sleeve 2, which can therefore be used for all sizes of cable within the predetermined dia¬ meter range.

The fact that the tension relief device 1 thus has one and the same outside diameter for all the tension relief devices within the group concerned means that the device 1 can be applied firmly to the cable 5 by a single conventional crimping operation resulting in a crimping final position which is the same for all sizes of cable within the group. It is for example possible to use as crimping tool 10 two clamping jaws 11 movable in a linear manner relative to one another and having mutually similar recesses which together, in the final position when the parts 11 are brought together, define a regular hexagonal space which defines a crimping final position for the device 1 on the cable 5 concerned, as illustrated in Fig. 4. It may be appreciated from Fig. 3 that the tool parts 11 are movable in a linear manner relative to one another by means of a pair of parallel screws which extend perpendicularly to the parting line between the tool parts 11. The tool according to Figs. 3 and 4 is known per se.

Upon completion of a crimping operation, the tool 10 opens, while the cable 5, the bushing 4 and the sleeve 2 exhibit a certain resilience from the crimped state, which resilience is of course less in the region of the ring elements 3. The crimping operation is with advantage performed only in a longitudinally middle region of the sleeve 2 comprising the ring elements 3.

The cable 5 has a certain elasticity and resilience and interacts with the rings 3, with relatively high outward pressure via the material bridges 45, resulting in the cable portion between the rings 3 having an outward curvature which counteracts an axially outward tension of the cable relative to the rings 3. The rubber bushing portion confined between the cable 5, the sleeve 2 and the two ring elements 3 undergoes a compression which contributes to the cable being firmly held axially in the device 1.

In the example referred to, the invention has been described in relation to an embodiment with two annular elements 3, but it should be clear that in certain embodiments it is possible to achieve advantages by the invention even if the tension relief device has only one annular element 3, particularly if some portion of the rubber bushing 4 can be confined between the single ring element 3 and some other similar annular supporting surface, e.g. against the wall 8, provided of course that the device is subjected to a crimping operation which comprises the confined portion of the bushing. However, even without any confining effects upon any portion of the bushing 4, the objects of the invention are achieved by a tension relief device which comprises only a single annular element 3.