GB2324542A - Rope with additional reinforcing members - Google Patents

Abstract

A wire rope 1 includes reinforcing members 4 of substantially triangular cross-section, each having an apex located between adjacent strands 3 and continuously aligned with them. The member 4 may be a triangular wire, a triangular plaited arrangement of wires, or a triangular strand, for example.

Description

ROPE WITH ADDITIONAL REINFORCING MEMBERS This invention relates to rope including at least one layer of strands and a plurality of reinforcing members.

In practical applications of wire rope there is a continuing desire for higher breaking strength from a given size of product. This may be achieved by making advances in one or more of the following areas: the tensile strength of the constituents e.g. the steel wire components; the amount of load bearing material available, i.e.

higher fill factor; and the efficiency with which this material is used, i.e. lower spinning losses. What is desired is a rope structure that enables advances to be made simultaneously in all three areas.

The present invention provides a rope comprising one or more layers of strands together with a plurality of substantially triangular reinforcing members located between adjacent strands of a layer and orientated to align with the interstices between the strands.

Preferred features of the rope are set forth in the claims.

In particular the invention provides a stranded wire rope in which the strands of an outer layer (at least) are supported by reinforcing members which are generally triangular in cross-section and disposed in such an orientation that a longitudinal apex of each reinforcing member points radially outwards in the gap between adjacent strands. Ideally the number of reinforcing members will be the same as the number of strands in the layer with which they are associated. The reinforcing members may be of high tensile material, e.g. similar to that of the wire rope strands, so as to maximise the radial support given to the strands and contribute a significant additional strength to the wire rope. The cross-sectional shape of the reinforcing members will preferably correspond to an isosceles or equilateral triangle, although in practice the actual profile will be curvilinear.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which : Figure 1 is a schematic cross-section of a wire rope structure; and Figure 2 is a schematic cross-section of another wire rope structure.

The wire rope 1 illustrated in Figure 1 comprises a core 2, which may be an independent wire rope core (IWRC), and a layer of six strands 3 helically wound around the core. Each strand 3 is a round strand comprising helically wound steel wires. Only the envelope of each strand is shown, being slightly oval, since each strand intersects the plane of the drawing at an angle. The strands 3 are equally spaced around the core 2, with gaps between them.

The wire rope 1 includes six reinforcing members 4 of substantially triangular cross-section, one between each pair of strands 3, located in the interstitial spaces between the strands 3 and the core 2. Accordingly, each reinforcing member 4 has a longitudinal apex which is directed radially outwards. The longitudinal apex is continuously aligned with the associated strands 3 and is located between them.

For ropes of modest size the reinforcing members 4 may comprise single substantially triangular filaments, e.g. of steel. For larger ropes it is preferably to use substantially triangular reinforcing members comprising a plurality of wires which have been stranded or plaited together. For example, each triangular reinforcing member 4 may comprise one or more layers of helical wires over a centre element; the helical wires may be round wires or flat strips. Each centre element will preferably be triangular in shape, e.g.

a solid triangular wire; three parallel round wires arranged in a triangular bundle; an initially round wire which if deformed into a triangular shape during the manufacturing process; or a plurality of round wires plaited into a triangular shape, e.g. 3x2 + 3 fillers.

The last-mentioned (plaited) centre element may be used as a reinforcing member in its own right, without recourse to covering layers of wires. Where it is necessary to cause substantial plastic deformation in order to achieve the desired triangular shape, one or more of the wires (e.g. in the centre) may comprise a softer material, such as a lower tensile grade steel, or zinc or a plastics material.

It is to be understood that the triangular reinforcing members 4 will be manufactured and shaped prior to their introduction into the rope, for example by pulling the wire or strand through a die or a set of three rollers. During closing of the rope strands 3 together, the reinforcing members 4 may be paid off bobbins which rotate with the machine (i.e. fixed bobbins) and thereby maintain the correct orientation of the cross-sectional shapes, led down between the strands 3 and fed into the appropriate interstitial spaces prior to the rope closing die. Alternatively, the reinforcing members may be pre-twisted to an appropriate degree and paid off floating bobbins in the usual way. Additional triangular shaped fairleads may be provided to control the approach angle if required.

In a practical application to a high tensile steel rope of 90mm diameter and 6x47 IWRC construction, triangular reinforcing strands of 7.5mm altitude, each comprising twelve (9/3) steel wires have been incorporated into the product as shown in Figure 1.

Destruction tests on this product showed a resulting strength increase of 5%, equivalent to the aggregate strength of the reinforcing members, i.e. indicating a tensile efficiency of 100% from the additional material.

The concept may also be applied to ropes having more than six outer strands, for example to eight-strand ropes or even to multistrand ropes which comprise more than one layer of strands over a core.

In the above-described six-strand rope 1 the strands 3 are 60 degrees apart and it is preferable to use triangular reinforcing members 4 which approximate to an equilateral triangle, because this has perfect symmetry and is easier to control and manufacture. In some instances, however, an alternative triangular profile may be selected which better suits the natural geometry of the interstitial spaces. Where ropes with a larger (or smaller) number of strands are being considered then the angular separation of the strands will be 360/N, where N is the number of strands in the layer under consideration. It may then be preferable to select reinforcing members with triangular profiles which correspond to the changed inter-strand geometry. For example, in an eight-strand rope this would suggest reinforcing members which approximate to an isosceles triangle with an included angle at the apex of 45 degrees.

In practice, however, the equilateral triangle may still be the preferred solution, provided that it is properly sized to suit the specific rope design.

Evidently it is possible to vary the dimensions of the core and triangular reinforcing members relative to the outer strand diameter to achieve a desired level of gap or clearance between the strands of the outer layer (in this case). This is a potent benefit, since with a conventional rope and core it is not possible to increase the interstrand clearances gap appreciably without the likelihood of the gaps becoming irregular, with the attendant risk of rope distortion (waviness) in service.

When the reinforcing members 4 are in the form of strands, the actual size of the triangular reinforcing strand is selected to accommodate a degree of interference with the surrounding strands 3, and the optimum level of interference will vary with the constructional details of the rope, such as the surface topography of the strands 3 and the core 2 (dependent on the size and number of outer wires and their helical pitch).

The gussets between the adjacent outer wires of a strand 3 will allow the reinforcing members 4 and strands 3 to approach one another more closely than their nominal outlines would suggest, particularly when the relative angular orientation of the wires can be arranged to closely align. The triangular reinforcing members 4 when viewed on the rope cross-sectional view may therefore appear larger in area than the inter-strand voids can apparently accommodate, e.g. by 10 or 20%. The controlling factor in specifying the interference level is likely to be the achievement of an optimum distribution of the radial stresses, since these play a decisive role in the mode of failure of wire rope when loaded to destruction. A lower level of such interference may need be specified when the outer strands are of the compacted variety, because there will be less scope for intermitting of the adjacent wires. The wire rope structure shown in Figure 2 exhibits such interference effects.

It will be appreciated that various modifications may be made to the structures described above.

Where the core 2 of the wire rope 1 itself comprises a (smaller) wire rope, i.e.

an independent wire rope core (IWRC), then triangular reinforcing members may be applied to the external gussets of the core. In this case the triangular reinforcing members will be arranged so that they each lie between a pair of strands of the IWRC, with the longitudinal apex of the reinforcing member pointing radially inwards. A similar arrangement of reinforcing members may be provided on an inner layer of strands between the core and an outer layer of strands. The core reinforcement may be specified in conjunction with the use of reinforcing members in one or more overlying layers of strands, for the purpose of optimising the level of support provided by the core. Alternatively, a similar support effect may be achieved (with less strength increase) by filling the gussets of the core with a softer, e.g. non-metallic, material such as plastics, either by laying in yarns and/or monofilaments, or by extruding material into the voids of the core.

Where a triangular reinforcing member 4 is composed of helical stranded wires then the preferred lay direction for constituent wires is in the opposite direction to that of the pair of strands 3 between which it is located, in order to optimise the contact conditions therebetween. For example, if the outer strands of the rope are Right-hand Ordinary lay, then the reinforcing members should preferably comprise wires laid up with a right-hand lay. If the same rope has an IWRC with a Right-hand Langs lay which has reinforcing members in the outer gussets, then the reinforcing members should preferably comprise wires laid up with left-hand lay.

To provide further amelioration of the said contact conditions the stranded reinforcing members may be beneficially filled with a cushioning material such as plastics (or zinc), for example by passing the triangular stranded member through an extruder (or a galvanising bath). This also has the effect of enhancing the corrosion protection of the wire rope.

Substantial additional benefits may be obtained in rope strength and axial stiffness by compacting the (or at least the outer) strands of the rope to improve the contact conditions further and to increase still further the cross-sectional area of steel.

This compaction may be achieved by rolling or swaging the strands or drawing them through a tapered reducing die as in the so-called "Dyform" process.

The improved contact conditions between the adjacent strands of the rope, as referred to above, have been shown to enhance the tensile efficiency of the rope, by reducing the inter-wire contact stresses which have a critical influence on the failure mechanisms under extreme loading conditions. It has also been shown that it is these same contact stresses which control the upper limit of wire tensile strength that can be effectively employed without exceeding the ductile/brittle transition phase. It may therefore be concluded that when the inter-wire contact stresses are mitigated by the means described above, the strength and efficiency enhancements will have a compound influence on the actual rope strength.

Claims (6)

CLAIMS:

1. A wire rope including a layer of strands, each strand comprising helical wound wires, and a plurality of reinforcing members associated with the said layer, each reinforcing member being of substantially triangular cross-section and substantially consisting of a material similar to the material of the said wires, each reinforcing member having a longitudinal apex located between and continuously aligned with adjacent strands of the said layer.

2. A wire rope as claimed in claim 1, in which the said apex is directed radially outwards.

3. A wire rope as claimed in claim 1 or 2, in which each reinforcing member comprises a plurality of wires.

4. A wire rope as claimed in claim 3, in which at least one of the said plurality of wires has been deformed from a round shape.

5 A wire rope as claimed in any preceding claim, in which each strand of the said layer has a compacted structure.

6. A wire rope as claimed in any preceding claim, in which the said layer is an outer layer.

7 A wire rope as claimed in any preceding claim, in which the strands of the said layer are supported in circumferentially spaced relationship by the triangular reinforcing members.

8 A wire rope as claimed in any preceding claim, including an inner layer of strands and reinforcing members, each reinforcing member having a longitudinal apex located between and continuously aligned with adjacent strands of the inner layer and directed radially inwards.

9 A wire rope substantially as described with reference to, and as shown in, Figure 1 or Figure 2 of the accompanying drawings.