AU674295B2 - Improved core for wire rope - Google Patents

Abstract

A tubular outer member 1 of plastics material is extruded onto an extruded solid cylindrical central member 3 of plastics material. The outer member 1 has symmetrically spaced helical grooves 2 for receiving respective wire strands 4. Plastics materials are specified, and may incorporate fibres. Member 3 may be lubricated.

Description

OPI DATE 03/03/94 APPLN. ID 32610/93 III111 1 liii lIIIII AOJP DATE 26/05/94 PCT NUMBER PCT/GB93/00008 11 11 1111 II III 1111111 II AU9332610

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(51) International Patent Classification 5 (11) International Publication Number: WO 94/03672 D07B 1/16 Al (43) International Publication Date: 17 February 1994 (17.02.94) (21) International Application Number: PCT/GB93/00008 (74) Agent: GODWIN, Edgar, James; Marks Clerk, 57-60 Lincoln's Inn Fields, London WC2A 3LS (GB).

(22) International Filing Date: 6 January 1993 (06.01.93) (81) Designated States: AT, AU, BB, BG, BR, CA, CH, DE, Priority data: DK, ES, FI, GB, HU, JP, KP, KR, LK, LU, MG, MN, 9216482.1 3 August 1992 (03.08.92) GB MW, NL, NO, NZ, PL, PT, RO, RU, SD, SE, UA, US, European patent (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OAPI patent (BF, (71) Applicant (for all designated States except US): BRIDON BJ, CF, CG, CI, CM, GA, GN, ML, MR, SN, TD, TG).

PLC [GB/GB]; Carr Hill, Doncaster, South Yorkshire DN4 8DG (GB).

Published (72) Inventors; and With international search report.

Inventors/Applicants (for US only) WALTON, John, Mawson [GB/GB]; 101 Park Drive, Sprotborough, Doncaster 7LP BURTOFT, Michael, Thomas [GB/ GB]; 16 Hennings Close, West Bessacarr, Doncaster DN4 7SA (GB).

(54)Title: IMPROVED CORE FOR WIRE ROPE (54) Title: IMPROVED CORE FOR WIRE ROPE (57) Abstract A tubular outer member of plastics material is extruded onto a solid cylindrical central member of plastics material.

The outer member has symmetrically spaced grooves for receiving respective wire strands WO 94/03672 PCT/GB93/00008 Improved Core for Wire Rope This invention relates to cores for wire ropes, particularly steel wire ropes.

GB-A-2 219 014 describes a core for wire rope comprising a fluted member of polymeric or elastomeric material having helical grooves symmetrically spaced around its outer surface, each groove in cross-section (in a plane normal to the longitudinal axis of the core) having the form of an arc of a ellipse. The properties and control of manufacture of the core may be substantially improved by incorporating within the extrusion a reinforcing member or cord constituted by a fibre core or independent wire rope.

However, the use of conventional types of reinforcing members such as are illustrated in GB-A-2 219 014, has certain drawbacks. Both fibre cores and independent wire rope cores, by the very nature of their helical construction, entrap a quantity of air which has a detrimental effect on the solidity of support that the core is able to provide in the rope. This is especially important in a wire rope, where the core is typically subjected to very high radial pressures; any compressibility of the core results in a reduction in rope diameter with tension and, hence, an increased rope stretch characteristic, which is often undesirable in service. Additionally, any pronounced reduction in rope diameter will result in the outer strands of the rope coming into contact with one another at the wire crowns, with very high stresses at the contact points. In a rope which is working backwards and forwards over sheaves or is otherwise -2repetitively flexed, these stresses will cause fretting damage to the outer wires, with a consequent loss of fatigue performance.

Practical experience wich the conventional types of reinforcing member disclosed in GB-A-2 219 014 has also revealed that it is possible for the reinforcing member to fail prematurely, before there has been any significant deterioration of the outer strands of the rope (which are readily inspectable). This mode of failure is not only undesirable from an inspection viewpoint, but can also lead to a loss of load carrying capacity and structural integrity of the wire rope.

What is desired is a core which avoids or mitigates these disadvantages.

The present invention provides a core for a wire rope, comprising a fluted tubular outer member of extruded plastics material and a stiffer solidcylindrical central member of extruded plastics material, the outer member having a cylindrical inner surface in intimate contact with the central member and having a fluted outer surface, formed by extrusion, with symmetrically-arranged spaced-apart continuous helical grooves for receiving respective wire strands of the wire S"rope, the diameter of the central member being at least 25 70% of the root diameter of the fluted outer surface, and the cross-sectional area of the central member being at least 40% of that of the core.

Preferred and optional features are set forth in the subsidiary claims.

30 The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Sc Figure 1 is a diagrammatic cross-section through a core for a wire rope; and S 35 Figure 2 is a diagrammatic cross-section through a wire rope incorporating the core.

S:13678[ WO 94/03672 PCT/GB93/00008 3 The core illustrated comorises a tubular cuter memoer :f plastics material arc a sclid cylindrical central memoer 3 f elastics material. The outer member 1 has a cylindrical inner surface in intimate contact with the central member 3 Optionally there may be a film of luoricant or release agent at the interface between the members 1,3. The outer member 1 as a fluted outer surface with symmetrically spaced helical grooves 2 for receiving respective steel wire strands 4.

In the illustrated example of a wire rope, shown in Figure 2, there are six strands 4. However, it will be appreciate: :nat a different number of strands may be used 5, 7, or Each strand 4 is a round strand whose circumscribing envelope E in a cross-section perpendicular to the strand axis is a circle of diameter dl. Since each strand extends helically, the envelope E appears slightly elliptical in a cross-section in :he plane of the drawings, whicn plane is perpendicular to the axis of the core. Each groove 2 in a cross-section perpendicular to the groove is an arc of a circle of diameter d.

To maximise the area of contact between the wires of the strand 4 and the core, the strand is a Dyform (Trade Mark Bridon pci) strand which in cross-section perpendicular to its axis has a compacted structure in which the outer wires 6 nave eternal edges 6a which are arcs of a circle of diameter d.

However, conventional strands made up of round wires may be used instead. Also, non-round strands may be used, with grooves cf suitable cross-section.

WO 94/03672 PCr/GCB93/00008 -4support to ne strancs c. rcr"; cere with a sufficienty large cross-secti:n with grooves 2 cf sufficient :eptn. a working clearance Detwuen the adjacent strands can ce ensured, even up to the breaKing load of the race. The use of two distinct (outer and central) members 1.3 enables one to select the properties of the memoers to satisfy various requirements for the physical (and chemical) properties of the core as a whole.

In order to define the preferred size of core, reference is made to Figure 1, wherein dimension d represents tne diameter cf the outer strands 4 of the rope and diameter d 2 denotes tr.e root diameter of the fluted memoer 1, i.e. the minimum distance between the bottoms of any two diametrically opposing grooves.

For any given rope type and construction the minimum root diameter d 2 may be expressed as a function of the outer strand diameter dl. The exact relationship will depend primarily upon the number of outer strands in the rope and the lay anale (or pitch) at which they are closed together, although additional account may be taken of the strand construction and service zuty.

For example, different factors will be required for ropes in which the strands are of quasi-triangular shape. For the more common round-strand rope constructions and lays, the following relationships are recommended WO 94/03672 WO 9403672PCT/G B93/00008 Number of outer strands 6 8 Lay ratios in closing 6 7 6 7 Mean lay angle (degrees) 19.5 17.0 21,01 18.2 Miaimum diameter ratio 1.20 1.18 1.90 1.8 7h~e 'Iwo members 1,3 may be made cf- the sane :ype :-pas-c material or diffeert types. :n each case the clastics ma~r= may, ror example. te selected from the :ollowing types: Polypropylene Polyethylene (medium to high density) Polyester (such as Hytrel Trade Mark of DuPont) 'zoecifi: zrades of material, and their characteristic physical properties. are shown in the following Table 2 WO 94/03672 PCT/GB93/00008 6 -able 2 Type of plastic PoLpropylene Polyethylene Hytrel 6346 Density (g /cm 3 0.90 0.91 0.93 0.95 1.22 Hardness (Shore D) 62 66 58 60 63 Yield Strength (MPa) 27 31 20 22 17 Flexural Modulus (MPa) 600 1000 600 800 350 The above properties are cited for the purpose of illustration only. Additional property enhancement may be obtained by going to harder grades of material or incorporating reinforcing fibres glass-fibre) into the polymer, albeit with some loss of rope flexibility.

The optimum blend of core properties may be obtained by using two dissimilar materials to produce the core. For example.

the outer member 1 may comprise a material with good elongaticn properties to accept the high bending strains and also be caDable of deforming locally to provide close conformance with the 7 surface geometry of the outer strands of the rope, whereas the central member 3 may be beneficially composed of a harder and more rigid material, perhaps incorporating reinforcing fibres.

Whatever the choice of materials, the core is preferably prepared in two separate extrusion operations, the first of which produces the solid cylindrical member 3. Optionally, a lubricant or a release agent is applied to the solid cylindrical member 3. This is then fed into an extruder for a further operation which produces the fluted member 1, the central member 3 greatly assisting in the control of the second extrusion operation.

The size of the central member 3 in relation to the size of the core may vary, so that one size of central member can be used for a range of core sizes, thereby achieving an economy in manufacturing costs. However, the cross-sectional area of the central member 3 is at least 40% (preferably at least 45%) and preferably at o a most 60% (more preferably at most 55%) of the cross- 20 sectional area of the core, a convenient ratio being about 50% (enabling extrusion speeds to be equalised) Accordingly, the central member 3 has a circular cross- .section whose diameter dl is at least 70% (preferably at least 75%) of the root diameter d 2 preferably d 3 is at 25 most 90% (more preferably 85%) of d 2 a convenient ratio being about a.o o S:135781

Claims (14)

1. A core for a wire rope, comprising a fluted tubular outer member of extruded plastics material and a stiffer solid-cylindrical central member of extruded plastics material, the outer member having a cylindrical inner surface in intimate contact with the central member and having a fluted outer surface, formed by extrusion, with symmetrically-arranged spaced-apart continuous helical grooves for receiving respective wire strands of the wire rope, the diameter of the central member being at least 70% of the root diameter of the fluted outer surface, and the cross-sectional area of the central member being at least 40% of that of the core.

2. A core as claimed in claim 1, in which the outer member is longitudinally slidable relative to the central member.

3. A core as claimed in claim 1 or 2, in which the central member is harder than the outer member.

4. A core as claimed in any preceding claim, in 20 which the plastics material of the central member *n contains discontinuous reinforcing fibres.

5. A core as claimed in any preceding claim, in which the plastics material of the central member and the plastics material of the outer member are of the same 25 type.

6. A core as claimed in any preceding claim, for a wire rope comprising round strands each having a circumscribing circle, in which each groove in a cross- section perpendicular to the groove describes a substantially circular arc. S:136781 -9-

7. A core as claimed in claim 6, which is of sufficient size to prevent contact between the strands in the rope when the radius of the said circumscribing circle is equal to the radius of the said arc.

8. A method of manufacturing a core according to claim 1, in which the core is formed by two separate successive extrusion operations, the first of which forms the central member, and the second of which forms the outer member around the central member.

9. A wire rope comprising a core according to any of claims 1 to 7, and wire strands received in the respective grooves.

A wire rope as claimed in claim 9, in which the core prevents contact between the strands.

11. A wire rope as claimed in claim 10, in which the strands are round strands each having a circumscribing circle.

12. A core for a wire rope, substantially as Sdescribed herein with reference to Figure 1 of the 20 accompanying drawings.

13. A wire rope substantially as described herein with reference to Figure 2 of the accompanying drawings.

14. A method of manufacturing a core for wire rope, substantially as described herein with reference to the accompanying drawings. DATED this 23rd day of October 1996 S* BRIDON plc By their Patent Attorneys GRIFFITH HACK S: 16781