IMPROVED CLAMP

Abstract: A clamp for cables or other elongate articles comprises two body parts (1, 3) which are relatively movable in the axial sense. In use, a clamping element (6) extends helically around the article (C) and is tensioned as the parts (1, 3) move apart and thereby made to constrict about the article.

Description: TMPROVED CLAMP This invention relates to clamps suitable for application to elongate articles, for example electrical wires and cables, and ropes. United States patent specifications Nos. US-4 632 488 and US-4 834 571 each describe a clamp in which a clamping element in the form of a helically coiled wire or strip is retained within a tubular housing. An electrical cable may be inserted into the housing and one end of the coil rotated relative to the other about the axis of the housing to cause the coil to constrict and grip the cable. The coil has no freedom of movement in the axial sense. A ratchet device secures the rotated end of the coil in the position to which it has been turned. British patent specification No. GB 2 129 842 discloses a similar clamp for securing together the ends of two lengths of rope. A plurality of axially extending cords are arranged within the housing and surround a passage into which the rope ends may be inserted. At each end of the housing is a rotatable annular plate in which the ends of the cords are embedded. Midway between the ends of the housing is a partition through which the cords pass. The annular plates may be turned relative to the housing and a pawl cooperates with a ratchet formed on each annular plate in order to retain the plate in the position into which it has been turned. As each of the annular plates is rotated relative to the central partition, the cords are wound into helices and grip the associated rope end in the manner of the single coil of the clamps taught by the United States references mentioned above. Although clamps of these types may be used very effectively to grip an elongate article, they all depend upon parts of the housing being rotated relative to each other to bring about the gripping action of the clamping element, and then upon a ratchet mechanism being used to prevent the clamping element unwinding. The clamping elements of all of these known clamps have a frictional gripping action. It may happen that the clamping element is tightened insufficiently so that the clamped article is able to slip through the clamp when load is applied. Moreover, if such a clamp is repeatedly applied and released, the ratchet may become worn and tend to release accidentally. The present invention improves upon the known clamp by arranging for the clamping action to be brought about by applying tension axially to a helically coiled clamping element so as to cause the diameter of the coil to be reduced. With this arrangement, if the clamped article is placed under load in the sense of tending to pull it out of the clamp, the clamping element tightens about the clamped article and resists such extraction. This effect cannot be achieved with the clamps of the known types in which a clamping element is tightened merely by winding it about the article to be clamped. The clamping element may be pre-formed into a helical coil much as described in the United States patents mentioned above, or wound into a coil when in use, as described in the British patent. When a pre-formed helical clamping element is used, it is unnecessary for any twist to be applied to the coil in use. Tension may be applied simply by moving the ends of the coil apart. Alternatively, a combination of twisting and stretching motions may be combined in order to cause a straight cla ping element to be formed into a coil and constricted about the article to be clamped. A ratchet arrangement may be used to increase the number of turns in the coil and thereby reduce its initial internal diameter. With either arrangement, the clamp may include one, two or more clamping elements, although the invention is described hereinafter by way of example in connection with a clamp having a single clamping element. It will be self-evident how the invention may be applied to clamps having more than one clamping element. Preferably, clamping elements are employed which are inextensible under normal loadings. If use is made of clamping elements which do stretch under load, then the extension which does take place in use should not be such as to detract from the advantageous effects of the invention described herein. The clamping element may be moulded integrally with end pieces to form an inner clamp component. A tubular housing may be sleeved over the clamping element and made to interlock with one end piece. The other end piece may be screw-threaded and receive a nut or pressure member which bears on the end of the housing. Upon rotation of the pressure member, the screw-threaded end piece is moved relative to the housing and applies tension to the clamping element. In an alternative embodiment, one end of a filament-like clamping element is attached to one end of an internally screw-threaded tubular outer component. The other end of the clamping element is attached to the free end of an externally screw-threaded inner component which is screwed into the other end of the outer component. As the inner component is unscrewed from the outer component, the clamping element is both tensioned and wound about an elongate article passing through the clamp. A locking nut screwed onto the inner component bears against the end of the outer component to prevent the components unwinding. The use of a screw-threaded coupling to tension the clamping element has the advantage that a much greater clamping force may be applied than is practicable when a helical clamping element is tightened by rotating one of its ends relative to the other. This advantageous action is made possible only by applying force to the clamping element in the axial sense rather than in purely a circumferential sense as hitherto. In the drawings: Figure 1 is a perspective view of a first embodiment of clamp, Figure 2 is an axial section through the clamp shown in Figure 1, before application to a cable, Figure 3 is a view similar to Figure 2 but illustrating the arrangement after clamping of a cable, Figure 4 is a side view showing the individual components of a second embodiment, Figure 5 is an axial section through the second embodiment after assembly, Figure 6 is an axial section showing the second embodiment when assembled and coupled to a plug. Referring to Figures 1 and 2, a first embodiment of clamp comprises an outer component consisting of an internally screw-threaded sleeve 1 having a radially inwardly extending annular wall 2 at one end. An inner component consists of an externally screw-threaded cylinder 3 having a radially inwardly extending annular end wall 4. The clamp body is assembled by screwing the sleeve 1 onto the cylinder 3 so that the walls 2 and 4 are disposed at opposite ends of the clamp body. A retaining ring or lock nut 5 is screwed onto that portion of the cylinder 3 which projects from the sleeve 1. A clamping element is formed by a flexible filament conveniently formed by plastics line 6 which passes through holes in the end walls 2 and 4 and is knotted at both ends to prevent its escape. To apply the clamp to a cable C or other elongate article extending through the clamp, the sleeve 1 is rotated relative to the cylinder 3 in the direction of the arrow shown in Figure 1, in the sense of increasing the length of the clamp. The line 6 is drawn through the holes in the end walls and entwines itself around the cable C, as illustrated in Figure 4. When the cable is gripped tightly, the retaining ring 5 is screwed along the cylinder to abut the end of the sleeve and thereby prevent sleeve and cylinder tending to unscrew. Because the diameter of the coil formed by the line 6 reduces as the clamp body is lengthened, the line tends to bite into the cable, rather than apply a purely frictional force. If, now, the cable is loaded in the direction of the arrows in Figure 3 (or in the opposite direction) , the coil is stretched and tends to reduce still further in diameter, thereby clamping the cable all the more tightly. In the case of the known clamps, loading of the cable in this way could lead to the cable being pulled from the clamp. It may be demonstrated that the relationship between the length (L) of the coil considered along the axis of the clamp, the perceived diameter (d) of the coil core along its length, and the length (R) of the coil filament at each complete turn are governed by the relationship: R is a constant because any extension of the coil is matched by a corresponding reduction in the core diameter of the coil. Therefore d decreases at an increasing rate as L increases. A point is therefore reached where minute increases in the coil length L produce a greatly magnified reduction in the diameter of the coil core and the clamping effect it produces. The embodiment shown in Figures 4 and 5 comprises an outer component consisting of a metallic or plastics sleeve 21 conveniently formed with flats 28 for cooperation with a spanner or wrench. An inner component is moulded from plastics to include a flexible clamping element 26 in one piece with hollow end pieces 27 and 28. The clamping element is preformed as a helical coil. The end piece 27 is externally screw- threaded and may have a knurled pressure ring 25 screwed onto it. The end piece 28 is stepped, having a larger diameter portion for abutment with the end of the sleeve 21 and a smaller diameter portion 29 for reception within the end of the sleeve. Longitudinally extending grooves 30 in the inner surface of the sleeve are provided to mate with protrusions 31 on the end piece 24. The clamp is assembled by inserting the inner component 23 into the outer component 21 from the left and applying the pressure ring 25, so as to arrive at the arrangement shown in Figure 4. The protrusions and grooves interlock to prevent relative rotation between the inner and outer components. As the ring 25 is tightened against the end face of the sleeve, the inner component 23 is drawn out and the clamping element 26 is tightened about a cable extending through the clamp. Because application of the clamp shown in Figures 4 and 5 does not involve relative rotation between the inner and outer components, but is brought about solely rotating the pressure ring, clamping force is applied easily to the clamp. Because the clamping element 26 is relatively loosely wound, a load applied to the cable in the axial sense will displace the clamping element axially and constrict it still further. The sleeve 21 has a screw-thread 31 which may be used to screw the clamp into an aperture to allow the clamp to be mounted to other apparatus. Thus, as shown in Figure 6, the clamp may be screwed into the inlet opening of a conventional plug 40. A spanner or wrench being applied to the flats 28 to simplify assembly. A grommet 41 within the opening is compressed during such insertion to seal the plug. Both the inner and outer components of the clamp may be moulded from resilient plastics material which will allow the clamp to flex relative to the plug. Modifications may be made to the clamps described above. Thus, for example, the inner component 23 may be accommodated wholly within the outer component, so that the ring 25 is accessible through a slot in the outer component. The clamp is applicable to elongate articles other than cables, including ropes such as may be used in connection with machinery or in mountaineering.

Claims: CLAIMS 1. A method of clamping an elongate article wherein a clamping element is made to encircle the article and is subjected to tension, characterised in that such tension is applied in a direction generally axially of the article so as to cause the clamping element to constrict about the article. 2. A method as claimed in claim 1 characterised in that the clamping element is pre-formed as a helical coil. 3. A method as claimed in claim 1 or claim 2, characterised in that the clamping element is wound about the article during or before the application of tension. 4. A method as claimed in any preceding claim, characterised in that loading of the article in the axial sense causes the clamping element to constrict further. 5. A clamp comprising a body through which an elongate article to be clamped may be passed, the body including two relatively movable parts, a clamping element extending between said parts, characterised in that said parts are movable relative to each other in a direction generally parallel to the path to be followed by the article through the body, thereby to cause the clamping element to be tensioned and made to constrict about an article to be clamped. 6. A clamp as claimed in claim 5, characterised in that the one of said parts is rotatable relative to the other. 7. A clamp as claimed in claim 5, characterised in that one of said parts is movable linearly without rotating relative to the other. 8. A clamp comprising a hollow body including two relatively movable parts, a clamping element extending helically between said parts, characterised in that said parts are movable relative to each other in the longitudinal direction to cause the clamping element to be tensioned and the diameter of the helix to reduce, and means to retain said parts in the relative positions to which they have been moved. 9. A clamp as claimed in claim 8, characterised in that said body parts and clamping element constitute an inner component housed at least partly within an outer component, means interlocking one of said parts with the outer component, the other of said parts being screw threaded to receive a pressure member bearing on the outer component, whereby rotation of the pressure member displaces the said other part. 10. A clamp as claimed in any of claims 5 to 9, characterised by a plurality of clamping elements.

Inventors: HARDY KELVIN RHYS, HARDY LEONARD RHYS, HARDY, KELVIN, RHYS, HARDY, LEONARD, RHYS
Applicants: HARDY KELVIN RHYS, RHYS HARDY LEONARD, HARDY, KELVIN, RHYS, HARDY, LEONARD, RHYS
Application year: 1995
Main classification: F16G11
IPC codes: F16G11