"MULTI-STRAND STEEL WIRE ROPE"

BACKGROUND TO THE INVENTION

THIS invention relates to a multi-strand steel wire rope and to individual strands of a wire rope.

A multi-strand steel wire rope has steel wires spun into strands, and the strands are then laid up helically, typically about a core, in one or more layers. Figure 1 shows a typical example of a conventional single layer multi-strand steel wire rope, indicated generally by the numeral 1. The rope 1 has a core 2 about which a single layer of strands 3 is laid up. The core 2 is typically made of a fibre such as sisal, a synthetic polymeric material such as polypropylene or another steel wire strand, or the core area may be vacant. In this example of a conventional construction, the numeral 4 designates the core of each strand, the numeral 5 an inner wire of the strand and the numeral 6 an outer wire of the strand. If the outer wires 6 are laid up in a helical direction opposite to the helical direction of the strand as a whole, the rope is referred to as being of ordinary or regular lay construction. If the wires 6 are laid up in the same helical direction as the strand itself, the rope is referred to as being of Lang's lay construction.

Ropes with a single layer of strands, for convenience referred to in this specification as "single layer ropes", generally generate a torque when subjected to tensile load. The result of this is that if one end of the rope is free to rotate the rope as a whole will tend to untwist in order to alleviate the torque which is generated. This untwisting may be highly undesirable in certain applications, for example where the rope is used to raise a load which is not restrained from spinning. In such cases, non-spin ropes are used. Such ropes generally have more than one layer of strands, with an outer layer of strands laid up on an inner layer of strands but in the opposite helical direction to the strands of the inner layer. In this way an attempt is made to balance the torque generated by the respective layers when the rope is under tensile load.

For convenience in this specification, ropes with more than one layer of strands are referred to as "multi-layer" ropes.

Although multi-layer ropes can counter the tendency of the rope to untwist they are generally less stable and robust than single layer ropes. Also, magnetic non-destructive testing of single layer ropes tends to be more accurate and reliable than is the case with multi-layer ropes.

The strands of known steel wire ropes may take different forms. An example of a round strand is shown in Figure 2 in which the numerals 7 and 8 respectively indicate the "height" and "width" of the strand. The "height" of the strand is the cross-sectional dimension of the strand measured, in the laid up rope, in a radial direction corresponding to the indicated Y-Y axis.

The "width" of the strand is the cross-sectional measured, in the laid up rope, in a circumferential or tangential direction corresponding to the indicated X-X axis. In the case of a round strand such as that of Figure 2, the ratio heightwidth is substantially equal to unity and the bending stiffness of the strand about the X-X axis is substantially equal to the bending stiffness about the Y-Y axis.

Figure 3 shows an example of a known triangular strand in which the core 4 has the cross-sectional shape of an equilateral triangle. In this case, the ratio heightwidth will typically be of the order of 0.98, i.e close to unity. As a result the bending stiffness about the X-X axis is again substantially equal to the bending stiffness about the Y-Y axis.

Figure 4 shows an example of another known strand form known as an "8 over 2 wire" strand composed of wires 9. In this case, the ratio height:width is substantially less than unity and may for instance be about 0.69. The bending stiffness of such a strand about the X-X axis is substantially less than its bending stiffness about the Y-Y axis.

SUMMARY OF THE INVENTION

According to the present invention there is provided a multi-strand steel wire rope comprising multiple strands laid up helically on a core, at least some of the strands being deep strands, i.e. strands with a heightwidth ratio greater than unity, preferably 1.04 or greater.

In the preferred embodiments, the rope is of a single layer construction. There may for instance be a single layer of deep strands, and no other strands, laid up helically on the core. Alternatively there may be a single layer of strands, including both deep strands and other strands, laid up on the core.

Each deep strand may includes a core having the cross-sectional shape of a non-equilateral triangle. Alternatively each deep strand may comprise, in cross-section, parallel rows of wires arranged generally radially.

Further according to the invention there is provided a strand for a multi- strand steel wire rope, the strand being a deep strand having a ratio heightwidth of 1.04 or greater. As indicated above, the strand may have a core with the cross-sectional shape of a non-equilateral triangle and wires laid up on the core, or it may comprise, in cross-section, parallel rows of wires arranged generally radially.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 illustrates a conventional multi-strand steel wire rope;

Figures 2 to 4 illustrate different, conventional strand configurations used in multi-strand steel wire ropes;

Figure 5 illustrates a deep strand of a multi-strand steel wire rope according to the present invention; and

Figures 6 to 10 illustrate different multi-strand steel wire ropes according to the invention.

SPECIFIC DESCRIPTION

The multi-strand steel wire rope seen in Figure 1 has been described above, as have the different strand configurations seen in Figures 2 to 4.

Figure 5 illustrates a deep strand 10 according to this invention. The strand 10 has a core 12 having the cross-sectional shape of a non-equilateral isosceles triangle, with two sides 14 and 16 of equal length and a shorter third side 18. An inner layer of steel wires 20 is laid up helically on the core 12 and an outer layer of steel wires 22 is laid up helically on the inner wires.

In Figure 5 the numeral 24 indicates the cross-sectional height of the strand 10. As in the above description of conventional ropes and strands, this is the radial dimension of the strand, i.e. the cross-sectional dimension of the strand, when laid up in a multi-strand steel wire rope, measured in a radial direction with respect to the central axis of the rope.

The numeral 26 indicates the cross-sectional width of the strand 10, i.e. the circumferential or tangential cross-sectional dimension of the strand, measured perpendicularly to the radial direction, when laid up in the rope. In Figure 5 the parameters are such that the ratio heightwidth is of the order of 1.12.

For convenience the strand 10 of Figure 5 is referred to as a deep triangular strand. It will be understood that a deep strand according to the invention may comprise a shaped core, as in Figure 5, with only a single layer of wires instead of multiple layers of wires.

Figure 6 shows a cross-sectional view of a multi-strand steel wire rope 28 which has a core 30 and five closely adjacent and equally spaced deep triangular strands 10 of Figure 5 type laid up helically in a single layer on the core.

Figure 7 shows a cross-sectional view of a single layer multi-strand steel wire rope 32 which has a core 34 and nine closely adjacent and equally spaced deep triangular strands 10 of Figure 5 type laid up helically in a single layer on the core.

Figure 8 shows a cross-sectional view of a single layer multi-strand steel wire rope 36 which includes deep strands having a form different to the deep triangular strand 10 of Figure 5. In this case each deep strand 38 has ten steel wires 40 arranged in generally radially extending, parallel rows 41 , such that the height 42 of the strand is greater than the width 44 thereof, i.e. the ratio heightwidth is greater than unity. The ratio heightwidth may, for instance be of the order of 1.46: 1.

In Figure 8, three deep strands 38 are spaced apart from one another and alternate circumferentially with three conventional, round strands similar to the strand 3 described previously with reference to Figure 2.

Figure 9 shows a cross-sectional view of a single layer multi-strand steel wire rope 46 which includes deep strands 38. Once again, the ratio heightwidth of each deep strand 38 is greater than unity and may, as in Figure 8, be of the order of 1.46: 1.

The embodiment of Figure 9 differs from that of Figure 8 in that there are four spaced apart deep strands 38 alternating with four round strands 3 of Figure 2 type.

Figure 10 shows a cross-sectional view of a single layer multi-strand steel wire rope 50 which includes four closely adjacent deep strands 38 and four round strands 3.

The round strands 3 are laid up helically as fillers between the deep strands 38 but do not cover them so that the construction does, in effect, remain a single layer construction.

As indicated above, it is recognised that tensile force applied to a single layer multi-strand rope will generate a torque, i.e. a force tending to untwist the rope, when the rope is subjected to tensile load. The present invention is based upon the recognition by the inventor that the tensile force in a rope can be resolved into components of torque-generating shear force and longitudinal force. The inventor has furthermore recognised that in order to reduce the tendency of a single layer multi-strand rope to untwist under tensile load, the bending stiffness of the strands of the rope about the appropriate axes should be increased relative to the torsional stiffness of the strands, i.e. the resistance of the strands to twisting under the shear- generated, applied torque forces acting about the axes of the strands.

As a result of the fact that its ratio heightwidth exceeds unity, in most cases by a substantial amount, the deep strands 10 and 38 described above will exhibit increased bending stiffness about the axis A-A in Figure 6, perpendicular to the radial direction and corresponding to the axis X-X in Figures 2 to 4, compared to conventional strand configurations where the corresponding ratio is unity or less.

It is accordingly perceived that the ropes illustrated in Figures 6 to 10 will have a reduced tendency to untwist under tensile toad, or that such ropes may have no such tendency at all to untwist or even a tendency to twist up slightly when loaded.

It is furthermore considered most beneficial, in order for the rope as a whole rope to enjoy an appropriately reduced tendency to untwist under tensile load, that there should be three or more deep strands having the desired, increased bending stiffness about the axis A-A, although it will be understood that some beneficial anti-twist effect will be experienced even if there are less than three deep strands.

It is noted that the principles of the invention are applicable to various different types of multi-strand steel wire ropes, including ropes with right hand or left hand lay, ropes with Lang's lay or ordinary lay, ropes in which the strands are simple strands with a single layer of wires over the core, ropes in which the strands are compound strands with two or more layers of wires laid up on the core, irrespective of whether the wires are laid up in the same or different helical directions in the different layers, ropes in which the strands have metallic or non-metallic cores, irrespective of whether the strand cores are of plaited or other construction, ropes in which the rope core is metallic or non-metallic or in the form of a strand or otherwise, and ropes in which the strands and/or ropes themselves are encapsulated.

The major benefits of the invention will be realised in single layer ropes, but it is envisaged that a reduced tendency of a rope to untwist can also be achieved in the case of multi layer ropes.