STEEL WIRE ROPE, COATED STEEL WIRE ROPE AND BELT COMPRISING STEEL WIRE ROPE

Abstract

A steel wire rope is presented for use in elevators and lifting applications. The steel wire rope contains a core surrounded by multiple strands. The outer filaments of the core and the outer filaments of the strands are likely to contact one another during used. The outer steel filaments of the core have an average Vickers hardness that is at least 50 Vickers hardness numbers lower than that of the outer filaments of the strands. As the hardness of the outer filaments of the core is substantially lower than that of the outer filaments of the strands, those softer filaments will preferentially abrade away during use. In this way the core is sacrificed while preserving the integrity of the outer filaments of the strands. The use of this ‘sacrificial core’ results in a higher residual breaking load after use.

Claims

1. A steel wire rope for use in lifting applications, said steel wire rope comprising a core and multiple strands twisted around said core, said core and each one of said strands comprising inner and outer steel filaments twisted together, said outer steel filaments being situated radially outward of said core and strands, the steel of said steel filaments being a plain high carbon steel that has been subjected to drawing, wherein the outer steel filaments of said core have an average Vickers hardness number that is at least 50 HV lower than the average Vickers hardness of the outer steel filaments of said strands, said Vickers hardness being measured with an indentation force of 500 gramforce for 10 seconds, said average being taken over ten measurement points in a perpendicular cross section of said steel filaments.

2. The steel wire rope according to claim 1 wherein the outer filaments of said core have a Vickers hardness number that is less than 600 HV.

3. The steel wire rope according to claim 2 wherein the inner filaments of said core have a Vickers hardness number that is less than 600 HV.

4. The steel wire rope according to claim 1 wherein the outer filaments of said strands have a Vickers hardness number that is larger than or equal to 600 HV.

5. The steel wire rope according to claim 1 wherein said multiple strands comprise five to eight intermediate strands and six to twelve outer strands, said intermediate strands being twisted around said core, said outer strands being twisted on said intermediate strands, wherein the outer filaments of said outer strands have a Vickers hardness number that is 40 HV or more higher than the Vickers hardness number of said outer filaments of said intermediate strands.

6. The steel wire rope according to claim 1 wherein the steel of the outer filaments of said core have a carbon content that is less than 0.80 weight percent.

7. The steel wire rope according to claim 6 wherein the steel of the inner filaments of said core have a carbon content that is less than 0.80 weight percent.

8. The steel wire rope according to claim 6 wherein said multiple strands comprise five to eight intermediate strands and six to twelve outer strands, said intermediate strands being twisted around said core, said outer strands being twisted on said intermediate strands, wherein the steel of the inner filaments and the outer filaments of said intermediate strands comprises less than 0.80 weight percent carbon and the steel of the inner filaments and the outer filaments of said outer strands comprises more than or equal to 0.80 weight percent carbon.

9. The steel wire rope according to claim 6 wherein said multiple strands comprise five to eight intermediate strands and six to twelve outer strands, said intermediate strands being twisted around said core, said outer strands being twisted on said intermediate strands, wherein the steel of the inner filaments and the outer filaments of said intermediate strands comprises more than or equal to 0.80 weight percent carbon and the steel of said inner filaments and said outer filaments of said outer strands comprises more than or equal to 0.80 weight percent carbon.

10. The steel wire rope according to claim 1 wherein said inner filaments and said outer filaments of said core have a tensile strength that is less than 2000 N/mm.sup.2 and said inner filaments and outer filaments of said multiple strands have a tensile strength that is larger than or equal to 2000 N/mm.sup.2.

11. The steel wire rope according to claim 10 wherein said multiple strands comprise five to eight intermediate strands and six to twelve outer strands, said intermediate strands being twisted around said core, said outer strands being twisted on said intermediate strands, wherein said inner filaments and said outer filaments of said intermediate strands have a tensile strength that is less than 2600 N/mm.sup.2.

12. The steel wire rope according to claim 10 wherein said multiple strands comprise five to eight intermediate strands and six to twelve outer strands, said intermediate strands being twisted around said core, said outer strands being twisted on said intermediate strands, wherein said inner filaments and said outer filaments of said outer strands have a tensile strength that is larger than or equal to 2600 N/mm.sup.2.

13. A coated steel wire rope for use in a lifting application comprising one steel wire rope according to claim 1 and a polymer jacket circumferentially surrounding said steel wire rope.

14. A belt for use in a lifting application comprising a plurality of steel wire ropes according to claim 1 and a polymer jacket, said polymer jacket encasing and holding said plurality of steel wire ropes in a side-by-side relationship.

15. A method to produce a steel wire rope according to claim 1 comprising the following steps: providing one or more steel wire rods having a plain carbon steel composition; drawing said wire rod to one or more intermediate steel wires having an intermediate steel wire diameter; patenting said intermediate steel wires; coating said intermediate steel wires with a metallic coating; drawing said intermediate steel wires to said inner filaments or outer filaments of said core and/or said strands; assembling said inner filaments and outer filaments of said core into said core by twisting, assembling said inner filaments and outer filaments of said strands into said strands by twisting; assembling said core and said strands into a steel wire rope by twisting; wherein the steel of said inner filaments and said outer filaments of said core have been subjected to a true elongation of less than 2.85.

16. The method according to claim 15 wherein said multiple strands comprise five to eight intermediate strands and six to twelve outer strands, said intermediate strands being twisted around said core strand, said outer strands being twisted on said intermediate strands, wherein the steel of said inner filaments and said outer filaments of said intermediate strands has been subjected to drawing with a true elongation of less than 2.85 and the steel of said inner filaments and said outer filaments of said outer strands have been subjected to drawing with a true elongation larger than or equal to 2.85.

17. The method according to claim 13 wherein said multiple strands comprise at least five to eight intermediate strands and at least six to twelve outer strands, said intermediate strands being twisted around said core strand said, said outer strands being twisted on said intermediate strands, wherein the steel of said inner filaments and said outer filaments of said intermediate strands have been subjected to drawing with a true elongation of larger than or equal to 2.85 and the steel of said inner filaments and said outer filaments of said outer strands have been subjected to drawing with a true elongation larger than or equal to 2.85.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0090] FIG. 1 shows an exemplary construction of a coated steel wire rope according the invention that is particularly suitable as an elevator rope.

[0091] FIG. 2 shows an exemplary construction of a coated steel wire rope according the invention that is designed for use on a crane.

[0092] FIG. 3 shows an exemplary construction of a belt for use in an elevator.

MODE(S) FOR CARRYING OUT THE INVENTION

[0093] FIG. 1 shows a cross section of a coated steel wire rope according the invention. The coated steel wire rope comprises a steel wire rope 110 encased, enrobed in a polymer jacket 180. The polymer jacket 180 completely surrounds the steel wire rope 110. The steel wire rope 110 consists of a core 120 and multiple strands 140, 140′, . . . and 160, 160′, . . . that are twisted around the core 120. The core comprises a single inner filament 122 and six outer filaments 124. The intermediate strands 140 also have an inner filament 142, surrounded by six outer filaments 144. The outer strands 160 have seven inner filaments 162 and twelve outer filaments 164. The outer strands have a Warrington geometry. The outer filaments are situated at the outer periphery of the strands thereby covering the inner filaments.

[0094] Polymer jacket 180 is made of an ester polyol based polyurethane, for example EL1190 as obtainable from BASF. It is extruded around the steel wire rope. During extrusion care is taken that the elastomer fully penetrates the steel wire rope down to the core wire 122.

[0095] The detailed construction of the wire rope of FIG. 1 can be summarised in the following formula:

{[(0.34+6×0.31).sub.10.0z+6×(0.25+6×0.25).sub.10.0S].sub.20z+7×(0.34|6×0.31|6×0.33|6×0.25).sub.20S}.sub.45Z

[0096] The brackets indicated different levels of assembly. All elements within one bracket level are combined in one cabling operation.

[0097] The numbers with decimal point refer to the diameter of the filaments (in mm) while the whole numbers indicate the number of filaments. The subscripts are the lay lengths inclusive their lay direction by which the filaments respectively strands are twisted together.

[0098] The outer filaments of the core have a diameter of 0.31 mm, the outer filaments of the intermediate strands have a diameter of diameter of 0.25. The outer filaments of the outer strands have diameters of 0.33 mm and 0.25 mm.

[0099] The properties of the different filaments are summarised in the Table I (filaments are ordered from the inside to the outside of the strand):

TABLE-US-00001 TABLE I details of Rope I Filament Vickers True Carbon Tensile diameter Hardness elongation content strength (mm) Number applied. class (N/mm.sup.2) Core 0.34 513 1.61 0.70 1791 0.31 524 1.79 0.70 1859 Intermediate strands 0.25 594 2.69 0.70 2315 0.25 613 2.69 0.70 2315 Outer strands 0.34 667 3.05 0.80 2742 0.31 664 3.23 0.80 2865 0.33 653 3.20 0.80 2703 0.25 661 3.23 0.80 2782

[0100] The Vickers hardness has been measured in line with ISO 6507-1 (2018 Edition) with an indentation force of 500 gramforce for a duration of 10 seconds. All filaments in a specific layer have been measured and averaged. The carbon content is the lower class limit as is usually specified in the world of steel wire rod. The tensile strength is measured on the straight wire by determining the breaking load (in N) and dividing it by the cross sectional area of the steel filament (in mm.sup.2).

[0101] As one can verify the outer 0.31 mm filaments of the core are in contact with the 0.25 outer filaments of the intermediate strands. The difference between the Vickers hardness numbers are 524 HV and 613 HV respectively which differs by more than 50 HV namely 89 HV.

[0102] Both outer and inner filaments of the core are soft compared to the outer filaments of the intermediate strand as the former have a hardness that is below 600 HV, while the latter have a hardness above 600 HV. The outer filaments of intermediate strands have a Vickers hardness above 600 HV.

[0103] The outer filaments of the outer strands 0.33 mm and 0.25 mm have a Vickers hardness that is 40 HV higher than the Vickers hardness of the outer filaments of the intermediate strands.

[0104] The outer filaments of the core have a carbon content that is below 0.80% C as they are from 0.70 class, as well as the inner filament.

[0105] All the filaments of the core and the intermediate strands are made of steel that comprises less than 0.80 wt % C, while the inner and outer filaments of the outer strands comprise more than 0.80 wt % C.

[0106] The true elongation to which the inner and outer filaments of the core have been subjected is 1.61 and 1.79 which is well below the limit of 2.85. The inner and outer filaments of the intermediate strands have been subjected to true elongation of 2.69 that is below the limit of 2.85. The inner filaments of 0.34 and 0.31 of the outer strands have been subjected to a true elongation of 3.05 and 3.23 respectively, while the 0.25 and 0.33 outer filaments have been subjected to a true elongation of 3.20 and 3.11 respectively that are well above the limit of 2.85.

[0107] The tensile strength of the inner (1791 N/mm.sup.2) and outer (1857 N/mm.sup.2) filaments of the core are well below 2000 N/mm.sup.2. The tensile strength of the inner and outer filaments of the intermediate strand is (2315 N) that is higher than 2000 N/mm.sup.2 but below 2600 N/mm.sup.2. The tensile strength of the inner and outer filaments of the outer strands is always higher than 2600 N/mm namely 2742 (0.34 mm), 2865 (0.31 mm), 2696 (0.25 mm) and 2782 (0.33 mm) N/mm.sup.2). The higher tensile in the outer strands ensures a high enough total breaking load for the overall rope that is 31 kN.

[0108] Although in the metal industry it is many times mentioned that hardness measurements correlate with the tensile strength of the steel this is only valid within the lower range of the steel—say below 2000 N/mm.sup.2—and for non-cold worked steels for example in a range of steels that have different carbon contents. See ISO 18265 and the warnings given therein.

[0109] The inventors remark that currently used steel wire ropes for elevators do not use filaments with a hardness in excess of 600 HV. They also observe that the use of different hardnesses, different degrees of true elongation, different carbon contents or different tensile strengths are not common in the field of steel wire design. In common art ropes the tensile grade of the wires used is always less than 2000 N/mm.sup.2. In any case the number of nominal tensile grades ropes are limited to one or two. The so called dual tensile grades are all limited to tensile strengths below 2000 N/mm.sup.2 for example Grade 1370/1770 ropes as per ISO 4344. Moreover common art ropes have the lowest tensile filaments as the outer filaments of the outer strands while the higher tensile filaments are situated at the inner part of the core and ropes.

[0110] In a comparative embodiment of the same construction and make, only the intermediate diameters D2 and carbon contents were changed (see Table II)

TABLE-US-00002 TABLE II details of Rope II Filament Vickers True Carbon Tensile diameter Hardness elongation content strength (mm) Number applied. class (N/mm.sup.2) Core 0.34 677 3.05 0.80 2742 0.31 629 2.77 0.70 2376 Intermediate strands 0.25 627 2.69 0.70 2315 0.25 621 2.69 0.70 2315 Outer strands 0.34 727 3.05 0.80 2742 0.31 727 3.23 0.80 2865 0.33 681 3.20 0.70 2696 0.25 713 3.11 0.80 2782

[0111] As the difference between the hardness between the outer filaments of the core and the outer filaments of the intermediate strands is less than 50 HV, the conditions of the invention are not met.

[0112] Concealed field trials have been conducted with both coated steel wire ropes Rope I and Rope II in elevators. Although cross sections of the used ropes reveal that the outer filaments of the core of Rope I do show an increased wear (as expected) the fatigue life of Rope I turns out to be as good as that of Rope II while having an improved residual breaking load.

[0113] FIG. 2 illustrates a coated steel wire rope 200 that is designed for a crane rope application consisting of the steel wire rope 210 and a jacket of polymer 280 that has a circular cross section. The rope comprises a core 220 consisting of one inner filament 222 surrounded with six outer filaments 224. The core 220 is surrounded by 18 strands that can be divided into six intermediate strands 240 immediately surrounding the core 220 and twelve outer strands 260, 270. The intermediate strands likewise comprise one inner filament 242 surrounded by six outer filaments 244. The twelve outer strands consist of six lower diameter strands 270 and six higher diameter strands 260. Again the outer strands consist of inner filaments 262, 272 around which six outer filaments 264, 274 are twisted. The core and all the strands are twisted together in one closing operation i.e. all strands have the same lay length and lay direction. The diameters of the six lower diameter strands 270 and six higher diameter strands 260 are chosen as to form a Warrington assembly of strands. The steel wire rope can conveniently designated as a (19×7) W. The steel wire rope is further provided with a polyurethane elastomer coating 280 that is extruded around the steel wire rope.

[0114] In detail the make up of the steel wire rope can be written as:

[(0.63+6×0.62).sub.28 s|6×(0.61+6×0.60).sub.28 z|6×(0.46+6×0.45).sub.20 z|6×(0.61+6×0.60).sub.28 z].sub.60 s

[0115] All wires are galvanised with a thin hot dip coating with a weight of about 15 grams of zinc per kilogram of filament.

[0116] Details of the filaments are shown in Table III

TABLE-US-00003 TABLE III details of Rope III Filament True Carbon Tensile diameter elongation content strength (mm) applied. class (N/mm.sup.2) Core 0.63 1.60 0.65 1750 0.62 1.63 0.65 1760 Strands Intermediate strands 0.61 2.74 0.70 2350 0.60 2.77 0.70 2380 Outer strands Smaller diameter outer strands 0.46 2.94 0.80 2670 0.45 2.98 0.80 2700 Larger diameter outer strands 0.61 2.90 0.85 2670 0.60 2.93 0.85 2690

[0117] The outer filaments of the core that are in contact with the outer filaments of the intermediate layer are lower in by 75 HV Vickers hardness points. Moreover all the filaments of the core have a Vickers hardness of less than 600 HV points.

[0118] The steel wire rope prior to coating has a diameter of 8.1 mm and after coating a diameter of 8.5 mm inclusive the polyurethane. The coated steel wire rope has a weight of 270 grams per meter and a breaking load of about 70 kN.

[0119] FIG. 3 shows a belt 300 consisting of four steel wire ropes 302 encased and held parallel by a polymer jacket 380. The steel wire ropes 302 are of the (19×7)W build with the following formula:

[(0.38+6×0.36).sub.16 z|6×(0.35+6×0.33).sub.16 z|6×(0.30+6×0.28).sub.12 z|6×(0.38+6×0.36).sub.16 z].sub.38 s

[0120] The steel wire rope 302 has a diameter of 4.8 mm, a breaking load of 27 kN and a linear density of 92 grams per meter. The belt has a thickness of 7 mm and a width of 26 mm.

[0121] The filaments have the following properties (Table IV):

TABLE-US-00004 TABLE IV Filament True Carbon Tensile diameter elongation content strength (mm) applied. class (N/mm.sup.2) Core 0.38 1.94 0.70 1750 0.36 2.04 0.70 1830 Strands Intermediate strands 0.35 2.77 0.70 2380 0.33 2.89 0.70 2460 Outer strands Smaller diameter outer strands 0.30 3.08 0.80 2760 0.28 3.22 0.80 2860 Larger diameter outer strands 0.38 3.22 0.80 2860 0.36 3.33 0.80 2929

[0122] The outer filaments of the core have a Vickers hardness that is lower with 55 HV than the Vickers hardness of the outer filaments of the intermediate strands.