METHOD FOR FINISHING A FIBER CABLE
The present invention relates to a method for terminating a fiber cable, which uses a device of the type which comprises a housing element, having a generally frustoconical bore, in which a terminal position of the cable can be retained in a wedged shape . It is known from GB 341 013 to terminate a fiber cable using a device of the type mentioned above. A wedge element, conically configured, is placed inside the frustoconical bore of the housing element, to trap, in wedged shape, fibers of the end portion of the cable into the bore of the housing element, thereby terminating the cable. This housing element includes resources to join it to an anchor, for example. It has been found that, with this method of terminating a cable, there is a tendency for the fibers of the end portion of the cable to wear out. The abrasion of the fibers occurs mainly in the region where these fibers make contact with the vertex portion of the wedge element, conically shaped, although abrasion may also occur in a narrow part of the mouth of the housing element, through the which extends the finished cable., The abrasion of the fibers of the cable substantially reduces the resistance to rupture of the cable.
A method for overcoming this problem is suggested in patent GB 2 236 546, in which the fibers of the end portion of the cable are treated with a resin composition. This resin composition is used to supply a lubricating effect on the fibers to reduce their abrasion around the vertex part of the wedge element, conically shaped. In spite of this, the combination of the tension load exerted on the cable, and the stress induced in the constituent fibers of the cable end portion by the compression action of the wedge element, results in the voltage failure of the cable. cable at a point generally in the region extending from about the apex part of the wedge element to the narrow part of the mouth of the housing element. US-A-4 184 784 discloses a method of terminating a braided fiber cable of small diameter. The cable has a diameter of approximately 2.54 mm and is combined with a plurality of parallel sections of this cable to be terminated in a single collar, which has a tapered inner channel. The collar is passed over the ends of the plurality of cables and each cable has a short tapered section of the same material, inserted into its braided core, as a means for swelling its end. The thickened ends of the plurality of parallel sections of cable are separated ("curled") in their individual fibers and a tube, having a tapered outer surface, is placed between them. The tube is driven inside the collar by a centering tool and firmly wedges the "curled" parts plus a significant portion of the braided lengths of the wires between the tube and the collar. This method is applied to the termination of bundles of very small diameter braided fiber cables in a single termination device, these terminated bundles of wires are used to retain conductor voltage loads in cables under water. This method is not suitable for terminating large diameter fiber cables, because their structures are more resistant to compression needed to secure the ends of the cable between the collar and the tube. It will be appreciated from the disclosure of US-A-4 184 784 that the amount of surface contact between each cable and the respective surfaces of the channel and the tube is restricted. It is an object of the present invention to obviate or mitigate the aforementioned problems associated with the prior art methods of terminating a fiber cable. It is a further object of the present invention to provide a method of terminating a fiber cable having a diameter of the order of 25.4 mm or greater. Fiber cables of this and many larger diameters are used in marine applications, when light weight, but high tensile strength, are required. According to a first aspect of the present invention, a method for terminating a fiber cable is provided, which comprises the steps of: introducing into or incorporating in an end portion of the cable an element for reinforcing the end portion of the cable; placing the reinforced portion of the cable end in a generally frustoconical bore of a housing element; and securing this end portion of the cable in the hole of the housing element. According to a second aspect of the present invention, a finished cable is provided using a device comprising a housing element having a generally frustoconical bore, by a metaccording to the first aspect of the invention. Additional features of the present invention are pointed out in the appended claims. The above and other features of the present invention will be more readily understood from the following description of the preferred embodiments, as an example thereof, with reference to the accompanying drawings, in which: Figure 1 is a side view in cross section of a cable and a cable end termination device, illustrating a prior art metof terminating a cable; Figure 2a is a cross-sectional side view of a cable and a cable end termination device, illustrating a first metof terminating a cable, in accordance with the present invention; Figure 2b is an amplified view of a portion of a braided layer of a fiber cable, reinforced according to the first metof the invention; Figure 3 is a cross-sectional side view of a cable and a cable end termination device, illustrating a second metof terminating a cable, in accordance with the present invention; Figure 4 is a cross-sectional side view of a cable and a cable end termination device, illustrating a third metof terminating a cable, in accordance with the present invention; Figure 5 is a cross-sectional side view of a cable and a cable end termination device, illustrating a fourth metof terminating a cable, in accordance with the present invention; and Figure 6 is a cross-sectional side view of a cable and a cable end termination device, illustrating a fifth metof terminating a cable, in accordance with the present invention; and Referring to Figure 1, which illustrates a prior art metof terminating a cable, which uses a cable end termination device 10, of the type comprising a housing element 12, having a generally tapered bore 14 , in which a wedge element 16, conically configured, is positioned to retain in wedged shape an end portion 18 'of the cable 18, trapping the fibers 20, comprising the end portion 18 * of cable. The metof the prior art comprises passing the end portion of the cable 18 through the hole 14 of the housing element 12, extending the fibers 20 of the end portion 18 * of the cable and inserting, first the apex, the wedge element. 16, generally at the center of the extended fibers 20, before stretching the cable end portion 18 'back into the housing element 12, so that the wedge element 18 is placed inside the hole 14 of the housing element 12, trapping the fibers there. In addition, the tension load exerted on the cable 18 will cause the end portion 18 'of cable to be securely retained within the housing element 12, but the wedge member 16 will exert a greater compression force on the trapped fibers 20 of the end portion 18 'of cable, which may result in damage thereto. A further problem with this metof terminating a cable is that the fibers 20 of the cable end portion 18 'in a region surrounding a vertex portion 16' of the wedge element 16 tends to wear out, thereby substantially reducing the resistance to the breaking of the cable 18. The fibers 20 of the cable can be treated with a resin to lubricate them and reduce their abrasion in and around the vertex portion 16 * of the wedge element 16. However, the fibers 20 of the cable 18 can also become worn in a region surrounding a mouth portion 12 'of the housing element 12 and experience has shown that this is most likely the voltage failure point of the cable 18. The Figure 2a illustrates a method of terminating a cable end portion, according to a first method of the present invention. The device for terminating the cable has a structure similar to that used in the method of the prior art and, therefore, similar numbers will be used to denote similar parts. The first method of the invention comprises introducing into or incorporating into the end portion 18 'of the cable, an element for its reinforcement, so that the breaking strength of this end portion 18 • of the cable, in the surrounding region the vertex part 16 'of the wedge element 16, is increased. In the preferred form of the first method, the reinforcing element comprises a portion 22 of a fiber cable of structure similar to that of the cable 18 to be terminated and is incorporated in the end portion 18 'of the cable, by splicing. A stress load, exerted on the cable 18, causes it to constrict, so that the load on the cable 18 is transferred through the friction to the fibers of the reinforced cable portion 22, thereby transferring part of the load of the cable. tension in the fibers 20 of the cable away from the apex portion 16 'of the wedge element 16. In a most preferred form of the first method, the cable 18 to be terminated is a braided cable having a hollow construction and the portion The reinforcement fiber cable 22 is placed in the hollow part of the cable 18 or is preferably connected to the filaments comprising the cable 18. The constriction of the cable 18 under the tension load causes part of the load to be exerted on the cable. portion of reinforcing fiber cable 22, thereby substantially increasing the breaking strength of the reinforced cable end portion 18 '. This reinforced end portion 18 'may be reinforced so that its reinforced part extends over at least the apex portion 16 * of the wedge element 16. While the diameter of the mouth portion 12' of the housing element is shown to be greater than the diameter of the cable 18, it will be appreciated that, in practice, this is not necessary. Figure 2b shows an amplified view of a braided layer of a fiber cable, reinforced over a part of its length by splicing filaments 19 of a reinforcement section of the cable of the same structure as the filaments 18a of the fiber cable 18. For convenience, only one filament 19 of the reinforcing cable is shown in the figure. It will be appreciated that the splicing of the filaments (18a and 19) is impractical with fiber cables of relatively small diameter. However, for cables with a diameter greater than 25.4 mm, the filaments comprising the cable are of a size that allows the connection to be achieved relatively easily. The splicing of the reinforcing filaments 19 with the filaments 18a of the cable 19 greatly increases the transfer of the stress load within the structure of the reinforced cable end, when comparing a reinforced cable end with a reinforcing cable section. merely inserted into the core of the braided fiber cable. Figure 3 illustrates a second method, according to the invention. This method is similar to that of the first method. However, it differs in that an end portion 18 of greater length of the cable 18 is reinforced with a portion 22 of fiber cable, so that the reinforced cable end portion 18 'extends beyond the mouth portion. 12 'of the housing element 12. In this way, a tension load exerted on the cable 18 is transferred away from both the region surrounding the vertex part 16' of the wedge element and also the mouth part 12. 'of the housing element 12. It has been found that by incorporating a portion 22 of reinforcing fiber cable of a structure similar to that of the cable 18 to be terminated., it is possible to transfer up to half of the tension load exerted on the cable distally of the housing element 12 and thus the resistance to rupture of the cable is substantially increased. The point of failure of the cable 18, therefore, will be transferred by some distance from the mouth portion 12 'of the housing element 12. The end portion 18' of the reinforced cable can be reinforced over a length which is several. times the length of the hole 14 of the housing element 12, thereby transferring a portion of the tension load exerted on the cable 18 by a substantial distance distally away from the housing element 12. The reinforcement fiber cable portion, 22, it is preferably formed with a decreasing number of filaments or fibers by its length so that, when it is introduced into or incorporated into the end portion of the cable, it results in a generally continuous increase or in increases in the number of fibers that it comprises the end portion 18 'of the reinforced cable, in a direction toward a free end of the end portion 18' of the cable. This contrasts with the rather abrupt increase in the diameter of the cable at a point distant from the housing element 12 which would be the case if the portion of the reinforcing fiber cable 22 was not formed with a tapered structure. The conicity of the reinforcing fiber cable portion 22 has the advantage of transferring a portion of the tension load exerted on the cable 18 remote from the housing element 12, and to avoid an abrupt change in the number of fibers in which it is it exerts the tension load at a distance distant from the housing element 12. It has been found that with this arrangement, the breaking strength of the cable is further increased, since there is a moderate transition between the number of fibers comprising the portion of the cable. end 18 of the reinforced cable and the smaller number of fibers comprising the main or constant part of the finished cable 18. The fibers of the end portion 18 * of reinforced cable can be treated with a resin composition of the type disclosed in the patent UK 2 236 546. The method may include placing a further resin composition 24 in an end portion of the bore 14 of the housing element, behind the element d e wedge 16 for joining the loose fibers 20 of the end portion 18 * of the cable at its rear end of the housing element 12.
Figure 4 illustrates a third method of terminating a cable according to the present invention. This method involves reinforcing the end portion 18 'of the cable in a manner similar to any of the methods described respectively with reference to Figures 2 and 3, but a wedge element is not required to secure the end portion 18' of the cable. in the housing element 12. In this method, the end portion 18 • of the reinforced cable is secured by placing it inside the bore 14 of the housing element 12 and emptying a resin composition 26 into the bore 14 of the housing, to adhere to the fibers 20 comprising the reinforced end portion 18 'of the cable in a conical configuration defined by a frustoconical bore 14 of the housing element 12. Once the resin has hardened, a tension load, applied to the cable 18, will cause the resin cone 26, formed by the above method, becomes secured in a wedge-shaped manner, in the bore 14 of the housing element 12. The transfer of the charge of The tension exerted on the cable 18 occurs by the same mechanism as in the methods described with reference to Figures 2 and 3, respectively. Figure 5 illustrates a four method, according to the present invention. This method is similar to that described with respect to Figure 3, but differs in that the reinforcing fiber cable portion 22 is preformed with a resin cone 28 at its end and combined with the cable portion 22 and the resin cone 28 is inserted into the end portion 18 'of cable. This end portion 18 'of cable is then stretched in the bore 14 of the housing member, where the resin cone 28 retains, in wedged shape, the end portion 18' of the cable within the housing element 12 and the portion of the cable. cable 22 reinforces the end portion 18 'of the cable. This method has the advantage of reducing the number of components to be combined, when the cable 18 is terminated. Figure 6 illustrates a fifth method of reinforcing a fiber cable, according to the present invention. This method is particularly applicable to the termination of fiber cables of a relatively large diameter, that is, with a diameter of 10 cm or larger. This method employs a housing element 12 having a frustoconical hole 14. A plurality of hollow elements 15 are placed, in use, within the bore 14 of the housing element in a side-to-side relationship. Each hollow element 15 has a frustoconical outer surface 15a and a frustoconical chamber 15b, to retain, in wedged shape, one end of one of a multiplicity of filaments comprising a cable (not shown). Each end filament of the cable can be retained in its respective hollow element 15, according to any of the first to fourth methods of the invention or any combination thereof, although, for purposes of illustration, a frustoconical wedge element 16 is shown placed in the center of one of the hollow elements 15. This method of the invention can also be used to terminate a bundle of fiber cables, comprising a plurality of parallel stretches of fiber cables of similar construction, for use in marine applications heavy work. The methods of the present invention make use of the transfer of charge by means of introducing into or incorporating in an end portion of a cable, to be terminated, a material or element that increases the carrying characteristics of the portion of the cable. end of the cable, so that a portion of the tension load exerted on the cable is transferred down the cable away from the reinforced end portion. While several of the methods of the present invention have generally been described with reference to the termination of a fiber cable having a braided construction, using a reinforcing portion of fiber cable also of a braided construction, it will be appreciated that the method it can be applied to any fiber cable that is capable of exerting a transverse compression load when subjected to an axial force (tension load).