GB2265162A - Rope splice - Google Patents

Abstract

In a rope splice, an end portion 3a of each strand tail of one length of rope is connected end to end to an end portion 3b of a strand tail (or core portion) of the other length of rope, by connecting means such as a ferrule 1 with interposed adhesive 4. The ferrule may have a bore which tapers inwardly towards its ends (Fig. 2), may be waisted in the middle (Fig. 3), may comprise two end parts articulated together (Fig. 4), may be of metal or composite material, and may be internally grooved. <IMAGE>

Description

Rope Splice There are many materials handling and transportation systems around the world which operate with an endless loop of wire rope. Typically these members are formed by manufacturing one or more ropes of finite length, which are then jointed into an endless loop of the requisite size. A technique known as 'long splicing' is used to effect the necessary connections, producing what may be regarded as an invisible joint.

Long splicing is an effective and well proven technique, but it is known that, under the dynamic loading conditions to which it is usually subjected, the splice may "draw", that is the endless rope loop may elongate, due to gradual and progressive slip of the splice. Various treatments of the splice tails have been developed to minimise this effect and to prolong the useful life of the splice, but none of these have proved fully effective.

The present invention provides a long splice connecting two portions of a rope, and means for connecting together the strand tails from the adjacent tucks in the long splice, to resist relative movement (separation) of the tails when the rope is loaded and worked.

In this way it becomes possible to greatly reduce or totally obviate the occurrence of splice draw, which is expected to substantially improve the potential service life of endless rope haulage systems. An anticipated additional benefit is that appreciably shorter splice lengths will prove effective, with consequent savings in cost.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a connection between two strands of a long splice; Figure 2 is a similar view of another embodiment of the connection; Figure 3 is a similar view of a further embodiment of the connection; Figure 4 is a side view of an articulated connector; and Figure 5 is a plan view of the articulated connector.

In its most basic form1 the connection may be provided by a rigid tubular ferrule which extends longitudinally over the two strand ends, and is secured to them by a suitable bonding agent, such as an adhesive or thermosetting resin compound. Two exemplary forms of ferrule are illustrated in Figures 1 and 2.

Figure 1 illustrates a ferrule 1 with a parallel bore 2 which fits closely around the strand ends 3a,3b with interposition of a suitable adhesive compound 4, capable of transmitting axial load by means of shear transfer. Figure 2 is a variation of the concept, which incorporates a conical taper 6 at the exit of the ferrule 1, which entraps the bonding agent 7 (e.g. a thermosetting resin compound) and generates an additional radial gripping force when axial load is subsequently applied to the strands, by virtue of the wedging action of the (resin) cone.

The joints referred to above and located within the core of the rope (not shown), the strands 3a,3b being introduced into the ferrule 1 or 1t and positioned before the adhesive/resin curing takes place.

A recognised limitation of the foregoing connection means is that the ferrule will be subjected to bending stresses when the rope is worked over sheaves and pulleys. An alternative design of ferrule is therefore proposed which substantially reduces the ferrule stiffness and hence the stresses due to bending. Figure 3 illustrates part of a tubular ferrule 11 which incorporates a waisted central section 18, which may be introduced into the ferrule by machining, pressing, or swaging (or in composite form, by filament winding). For example a reduction of 25% in the diameter of the tube, at the waist, will reduce the flexural stiffness by more than 50% without any loss in sectional area, as illustrated in Table 1.

Table 1. Effect of Waisting on Ferrule Stiffness* % Reduction in diameter 0 10 15 20 25 30 35 40 at waist Relative Flexural 100 77 66 56 47 38 30 22 Stiffness * Assumes 10% wall thickness and constant cross-sectional area of ferrule at waist.

For applications where severe and frequently repeated bending is involved, the rigid tubular ferrule may be replaced by an articulated connector comprising two shorter closed ferrules la,lb flexibly linked together at their closed ends, as part-illustrated, for example, in Figures 4 and 5, although various other detailed arrangements are possible. The ferrules 1a,1b are again secured to the respective strand ends by the means described earlier and illustrated in Figures 1 and 2.

The degree of articulation required will depend upon the severity of bending, and the length of ferrule. Examples of typical service conditions are given in Table 2, together with the optimum range of joint articulation (for an assumed ferrule length of 1.5 x the rope diameter).

Table 2 Required Articulation of Ferrule Point Bending ratio: Sheave dia.

24 24 32 40 48 Rope dia.

Angular freedom (degrees) +7.2 +5.4 +4.3 +3.6 It is observed that from a design viewpoint the articulation requirement is in conflict with the need to maximise the tensile strength of the joint. The angular freedom of the joint should therefore be kept to an absolute minimum, i.e. say +5 for a bending ratio of 40:1 (allowing for manufacturing tolerances).

Using the techniques described above, it is possible to provide: (a) A wire rope splice incorporating a connecting means between the tails of adjacent strand tucks capable of transmitting axial load and resisting the separation of the strand tails as the rope is worked.

(b) A wire rope splice incorporating a connecting means between the tails of adjacent strand tucks, comprising a rigid tubular ferrule within which the two ends of strand are secured.

(c) A splice as in (b), with internal parallel bore and adhesive bonding.

(d) A splice as in (b), with internal tapering section and potting compound to generate self-wedging gripping action.

(e) A splice as in (a) to (e), with a waisted central section.

(f) A wire rope splice incorporating a connecting means between the tails of adjacent strand tucks, comprising a pair of flexibly coupled tubular ferrules within which the ends of the strands are secured.

(g) A splice as in (f), with a means of articulation between the two interconnected ferrules.

(h) A splice as in (g) in which the articulation is limited to +5 .

(i) A splice as in (a) to (h), in which the ferrule(s) is/are metallic.

(j) A splice as in (a) to (h), in which the ferrule(s) is/are manufactured from composite material, such as CFRP (carbon fibre reinforced plastics).

(k) A splice as in (a) to (j), in which the connecting means are located in the centre of and coaxial with the rope, and are surrounded by the outer strands.

The above-described method of splice enhancement is most applicable to ropes of 6 to 9 strand construction where the core accommodation within the rope is larger than the diameter of the outer strands. The lengths of strand tail not covered by the connection means, may be built up to support the outer strands, in the usual way.

In addition to being used to connect adjacent strand tails to one another, the method may also be used to connect the first and last strand tucks of the splice to the adjacent core ends, if the core is capable of carrying an appreciable load and can be reduced to a size which is compatible with the connection means.

The preferred length of ferrule should be sufficient to accommodate strand ends of length equivalent to 4-8 times their own diameter, although alternative gripping lengths of between 2x and tOx the strand diameter may be considered, depending on the service duty.

The taper angle of the conical bore section of the ferrule, if used, is preferably 2-6 (i.e. 4-12 included angle), although a wider range of angles could be considered, depending on detailed design considerations. The resin or adhesive bonding compound may be introduced into the ferrule before or after the strand insertion. Injection holes may be provided in the ferrule if the potting material is to be introduced last. If the resin injection is not the final operation, then all necessary adjustments must be completed before the potting material begins to set.

The connection means will ordinarily be manufactured from metal (which term includes alloys) e.g. high strength steel, but aleternatively non-metallic materials, such as carbon fibre reinforced plastics, may be considered for some duties, for example where the rope itself is fabricated from such advanced fibre material.

To assist bonding, the area of the strand tail that will be located within the connection means, is thoroughly cleaned and degreased. Similarly the internal bore of the parallel ferrule shown in Figure 1 will also be thoroughly cleaned and for some adhesive systems the surfaces may be advantageously pre-treated with a priming agent. Additional gripping advantage may be obtained by grooving the internal bore of the ferrule in a substantially transverse (or hoop) direction (not shown).

Where the tapered or conical ferrule is adopted, then a bond to the ferrule is no longer desirable as it would resist the movement required to achieve the wedging action. The internal bore of the ferrule 1' shown in Figure 2 may therefore be advantageously pre-treated with a release agent which prevents the potting material adhering to it, whilst not impairing the bond to the strand.

Claims (13)

CLAIMS:

1. A rope splice formed between two lengths of rope of similar construction, each length of rope comprising strands extending helically around the rope axis, and optionally a core extending along the rope axis, the two lengths of rope overlapping in the region of the splice, where their strands form strand tails of finite length and their cores, if any, form core portions of the finite length, characterised in that an end portion of each strand tail of one length of rope is connected end-to-end to an end portion of a strand tail or core portion of the other length of rope, by connecting means.

2. A rope splice as claimed in claim 1, in which the connecting means comprises a rigid tubular ferrule within which the said end portions are secured.

3. A rope splice as claimed in claim 2, in which the ferrule has a parallel bore and is adhesively bonded to the said end portions.

4. A rope splice as claimed in claim 2, in which the ferrule has a bore which tapers towards its ends and potting compound is interposed between the bore and the said end portions.

5. A rope splice as claimed in any of claims 2 to 4, in which the ferrule has a waisted central section.

6. A rope splice as claimed in claim 1, in which the connecting means comprises a pair of flexibly coupled ferrules within which the said end portions are secured.

7. A rope splice as claimed in claim 6, including means for permitting articulation of the ferrules.

8. A rope splice as claimed in claim 7, in which the articulation is limited to a range of at most i 5-.

9. A rope splice as claimed in any of claims 2 to 8, in which the or each ferrule is metallic.

10. A rope splice as claimed in any of claims 2 to 8, in which the or each ferrule is of composite material.

11. A rope splice as claimed in any of claims 2 to 10, in which the length of each said end portion within the ferrule is equal to 2 to 10 times, preferably 4 to 8 times, the diameter of the said end portion.

12. A rope splice as claimed in any preceding claim, in which the connecting means is located in the centre of the rope splice and is coaxial with the two length of rope.

13. A rope splice substantially as described with reference to Figure 1, Figure 2, Figure 3, or Figures 4 and 5 of the accompanying drawings.