WO2015161253A1

WO2015161253A1 - Rope having a low-friction strand

Info

Publication number: WO2015161253A1
Application number: PCT/US2015/026471
Authority: WO
Inventors: Luis S. Padilla; Philip Samuel BULL; Randy S. LONGERICH; Aaron M. VODNICK; Wesley Conger
Original assignee: Actuant Corporation
Priority date: 2014-04-17
Filing date: 2015-04-17
Publication date: 2015-10-22

Abstract

A braided rope (10) includes a plurality of primary strands (12), and each of the primary strands (12) includes a plurality of fibers (16) which have a first coefficient of friction with itself. The rope (10) also includes a secondary strand resp. a core (14) surrounded by the plurality of primary strands (12). The secondary strand resp. core (14) includes a structurally-stable, non-flowable, material having a second coefficient of friction with the fibers (16) of the primary strands, wherein the second coefficient of friction is lower than the first coefficient of friction. The rope (10) may be of 12 x 12 braided construction and includes a core (14) for its length. The rope has reduced internal wear and therefore a longer service life and improved friction properties compared to braided ropes with a core, lubricated with flowable material. A method of constructing the rope is disclosed, too.

Description

ROPE HAVING A LOW-FRICTION STRAND

RELATED APPLICATIONS

[0001] This application claims the benefit of prior-filed, co-pending U.S. Provisional Application No. 61/981 ,039, filed April 17, 2014, and is related to U.S. Patent Application No. 14/155,317, filed January 14, 2014, which claims the benefit of prior-filed, co-pending U.S. Provisional Application No. 61/752, 195, filed January 14, 2013, the entire contents of all of which are hereby incorporated by reference.

FIELD

[0002] This invention generally relates to a reduced-wear synthetic fiber rope for various marine applications, particularly, a rope having a low-friction strand.

SUMMARY

[0003] Synthetic fiber ropes are used to carry tensile loads in various applications, such as working and lifting, towing, buoy mooring, tug and salvage operations, ship and barge mooring, commercial fishing, etc. The useful life of such ropes is limited due to wear of the individual fibers, which may be caused, to some extent, by the friction of the fibers rubbing against each other. The fibers rub against each other, for example, when a rope passes over a sheave or as the rope moves from a slack configuration to a configuration in which it carries a tensile load.

[0004] Prior attempts to alleviate friction and wear in the rope have included intertwining low-friction fibers with the high-friction fibers of the rope and adding lubricant or lubricating fibers to the rope. Such solutions may fail to achieve the desired reduction in friction and rope wear and may present independent shortcomings, for example, reduced rope performance (e.g., reduced friction in winching, splicing of the rope).

[0005] As such, a need exists for a rope with, for example, a longer useful life, improved performance, etc., compared to previous ropes. Such a rope may be subjected to less wear due to reduced friction between the rope's fibers while achieving acceptable performance in applications in which outer surface friction may be desired (e.g., winching, splicing, etc.).

[0006] In one independent aspect, a rope may generally include a plurality of primary strands each including a plurality of fibers formed of a high-friction material, the plurality of primary strands defining an outer surface and a longitudinal center passageway of the rope; and a non-load bearing secondary strand having a strand outer surface and disposed within the longitudinal center passageway of the rope, the secondary strand including, at least on the strand outer surface, a structurally-stable, non-flowable, low-friction material.

[0007] In another independent aspect, a rope may generally include a plurality of outer strands together defining an outermost surface of the rope and a longitudinally-extending center passageway of the rope, each of the plurality of outer strands including a plurality of fibers formed of a high-friction material, the high-friction material defining a first coefficient of friction with itself; and a core strand disposed within the longitudinally-extending center passageway of the rope and separated from the outermost surface of the rope by at least one of the plurality of outer strands at all positions along a length and about a circumference of the rope, the core strand including a structurally-stable, non-flowable, low-friction material, the low-friction material defining a second coefficient of friction with the high-friction material, the second coefficient of friction being less than the first coefficient of friction.

[0008] In yet another independent aspect, a rope may generally include twelve outer strands together defining a longitudinally-extending center passageway of the rope, the twelve outer strands being braided in a single braid pattern, each of the twelve outer strands including twelve sub-strands braided in a single braid pattern, each of the sub-strands including a plurality of synthetic fibers; and a core strand disposed in the longitudinally-extending center

passageway over the length of the rope.

[0009] In a further independent aspect, a method of constructing a rope may generally include providing a non-load bearing secondary strand having a strand outer surface, the secondary strand including, at least on the strand outer surface, a structurally-stable, non-flowable, low-friction material; and surrounding the secondary strand with a plurality of primary strands each including a plurality of fibers formed of a high-friction material, the plurality of primary strands defining an outer surface and a longitudinal center passageway of the rope, the secondary strand being disposed within the passageway.

[0010] Independent features and independent advantages of the invention will become apparent to those skilled in the art upon review of the detailed description, drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a side view of a rope having a low-friction strand, with the low-friction strand shown in phantom lines.

[0012] FIG. 2 is a side view of the rope of FIG. 1 with a plurality of outer strands shown in phantom lines.

[0013] FIG. 3 is a side view of one of the outer strands of the rope of FIG. 1 .

[0014] FIG. 4 is a cross-sectional view of the rope of FIG. 1 , the space between the various strands is enlarged for clarity.

[0015] FIG. 5 is a cross-sectional view of an alternative construction of a center strand.

[0016] FIG. 6 is a schematic cross-sectional view illustrating use of the rope and

engagement of outer strands with the low-friction strand.

DETAILED DESCRIPTION

[0017] Before any independent embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other independent embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Use of "including" and "comprising" and variations thereof as used herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Use of "consisting of" and variations thereof as used herein is meant to encompass only the items listed thereafter and equivalents thereof.

[0018] Referring to FIGS. 1-4, the illustrated rope 10 generally includes a high-friction, load bearing outer jacket or envelope (e.g., high-friction, load bearing outer strands 12 including high-friction fibers 16) surrounding a low-friction core (e.g., a center strand 14 including a structurally-stable, non-flowable, low-friction material at least on its outer surface). As such, the rope 10 may provide one or more advantages associated with a high-friction outer jacket (e.g., acceptable surface coefficient of friction in applications in which outer surface friction may be desired (winching, splicing, etc.)), and with a low-friction core (e.g., reduced friction and wear on the load bearing strands 12 of the rope 10, as explained in greater detail herein). In other words, the illustrated rope 10 does not sacrifice rope performance to achieve reduced friction and wear.

[0019] In addition, because the illustrated low-friction material is separate from the outer strands 12, the low-friction material can be removed from the rope 10, as necessary. For example, the low-friction material can be removed at an end section of the rope 10 for splicing, for termination, etc. In such instances, the section of the rope 10 with the low-friction material removed will perform like a rope without any low-friction material.

[0020] It should be understood that the terms "high" and "low" are relative terms. For example, in the illustrated constructions, the outer strands 12 and fibers 16 have a higher coefficient of friction than the center strand 14 (at least its outer surface) which, in turn, has a lower coefficient of friction than the outer strands 12/fibers 16. Similarly, the outer strands 12 and fibers 16 may have a higher strength than the center strand 14 which, in turn, may have a lower strength than the outer strands 12/fibers 16.

[0021] The illustrated rope 10 includes a plurality of primary, load bearing strands 12 surrounding at least one auxiliary, non-load bearing strand 14. The illustrated center strand 14 is a low-friction strand (relative to the illustrated outer strands 12) to reduce the friction at the center of the rope 10, which is where most of the friction occurs. As such, the strands and fibers of the rope 10 are subjected to relatively little wear as they rub against each other, resulting in, for example, an increased useful life compared to previous ropes.

[0022] Turning to FIGS. 1 -3, each outer strand 12 includes a plurality of fibers 16 formed of a high-friction material (that is, not a low-friction material, or a higher friction material relative to the center strand 14 and permitting the rope 10 to be driven by a pulley, sheave, etc.). The material of the fibers 16 is also high strength (e.g., having, in an illustrated construction, a higher strength than the center strand 14). The outer strands 12 are thus high-strength, high-friction strands to provide a load bearing function and a high surface coefficient of friction for the rope 10.

[0023] The fibers 16 may comprise materials such as, without limitation, a recrystallized high modulus polyethylene (for example, Plasma®), a liquid crystal polyester (LCP; for example, Vectran® available from Kuraray Co., Japan), a gel-spun polyethylene (for example, Spectra® available from Honeywell International, Inc., New Jersey, U.S.A.), a para-aramid (for example, Kevlar® available from DuPont, Delaware, U.S.A. or Twaron® available from Teijin Aramid B.V., The Netherlands), a para-aramid copolymer (for example, Technora® available from Teijin Aramid B.V.), a polyamide (nylon), a polyester, or the like or combinations thereof. The fibers 16 may have a polyurethane finish, although other finishes may alternatively be used.

[0024] In some constructions, one or more of the outer strands 12 may include composite strands formed of more than one material, such as more than one of the exemplary materials identified above. In some other constructions (e.g., in which the coefficient of friction of the rope surface is of less importance) and for other aspects of the invention, one or more of the outer strands 12 may include composite strands formed of both high- and low-friction materials. For example, the rope 10 may include a structure similar to that described in U.S. Patent No.

6,945,153, entitled "Rope for Heavy Lifting Applications", the disclosure of which is also hereby incorporated by reference.

[0025] The plurality of outer strands 12 may be braided with one another. For example, the outer strands 12 may be braided in a "12x12" pattern like ropes provided by Cortland Cable of Cortland, NY. That is, there may be twelve outer strands 12 braided in a single braid pattern, and each of the twelve outer strands 12 may in turn include twelve sub-strands braided in a single braid pattern. The sub-strands may in turn include a plurality of synthetic fibers 16; each strand 12 may be braided with a center sub-strand formed of a low-friction material, at least on the strand outer surface, in a manner similar to the construction of the illustrated rope 10.

Similarly, the plurality of outer strands 12 may define a rope structure as described in U.S.

Patent No. 5,901 ,632, entitled "Rope Construction", the disclosure of which is hereby

incorporated by reference.

[0026] The rope 10 and/or the plurality of outer strands 12 may alternatively be braided using other patterns (e.g., 12x3, 12x8, etc.) in which the rope or strand is braided with its core separated from its outer surface. In any case, the plurality of outer strands 12 define the outer surface 18 of the rope 10 and an inner longitudinally-extending passageway 20 in which the center strand 14 is disposed.

[0027] Turning to FIGS. 2 and 4, the center strand 14 includes a structurally-stable, non-flowable, low-friction material (that is, a low-friction material with a coefficient of friction against the high-friction material lower than the coefficient of friction of the high-friction material against itself). In the illustrated construction, the material of the center strand 14 is also low strength (e.g., having a lower strength than the outer strands 12 and fibers 16). Thus, the illustrated center strand 14 is a low-strength (non-load bearing), low-friction strand providing reduced friction in the center of the rope 10 and, by being structurally-stable and non-flowable, does not impact the surface coefficient of friction of the rope 10.

[0028] The material of the center strand 14 may comprise, for example, without limitation, polyethylene (low, medium, and high density as well as cross linked), polypropylene, ethylene- propylene-copolymer, nylon, fluoropolymer-based materials, such as expanded

polytetrafluoroethylene (ePTFE; comprising non-flowable, stable, and solid fibers; for example, Omnibend® available from W. L. Gore & Associates, Inc., Delaware, U.S.A.), modified polytetrafluoroethylene, fluorinated ethylenepropylene (FEP), ethylene-chlorotrifluoroethylene (ECTFE), ethylene-tetrafluoroethylene (ETFE), a perfluoroalkoxy polymer (PFA), or the like or combinations thereof.

[0029] In one exemplary rope 10, the material of the center strand 14 may comprise a fluoropolymer-based material (e.g., PTFE), and the fibers 16 of the outer strands 12 may comprise a para-aramid copolymer (for example, Technora®). In another example, the material of the center strand 14 may comprise a fluoropolymer-based material (e.g., PTFE), and the fibers 16 may comprise UHMWPE.

[0030] The material of the center strand 14 is structurally stable and non-flowable, meaning that it stays positioned in the passageway 20 and does not flow, creep or get squeezed out between the outer strands 12 to the outside of the rope 10. In the construction shown in Fig. 4, the low-friction material of the center strand 14 is extruded.

[0031] The center strand 14 is disposed in the passageway 20 defined by the outer strands 12 over the entire length of the rope 10. Furthermore, the center strand 14 is separated from the outer surface 18 by at least one of the outer strands 12 at all points along the entire length and about the entire circumference of the rope 10. As such, the center strand 14 reduces the friction at the center of the rope 10, and the fibers 16 of the strands 12 and the center strand 14 are subjected to relatively little wear as they rub against each other.

[0032] The diameter of the center strand 14 (or the largest cross-sectional dimension if the strands 12 are compressed against one another) is such that the center strand 14 does not adversely affect the performance of the outer stands 12 and the rope 10 (e.g., does not interfere with the load-carrying capabilities of the outer strands 12). As a practical example, a center strand 14 that is at most one-third of the diameter of each of the outer strands 12 (or the largest cross-sectional dimension) will generally not affect the performance or the outer diameter of a given rope 10. However, it should be understood that the center strand 14 may be smaller or larger (even as large as or larger than the outer strands 12).

[0033] In some constructions, the center strand 14 may be formed of a low-friction, high- strength material. In some constructions, the center strand 14 may include a composite strand formed of more than one material, such as more than one of the exemplary materials identified above. In some constructions (not shown), the rope 10 may include more than one center strand 14.

[0034] In some other constructions (see FIG. 6) and for other aspects of the invention, the center strand 14a may include a hybrid strand formed of one or more of the exemplary low- friction materials identified above in combination with other materials In such constructions, the center strand 14a may include a center or core element 24, formed of a material having a relatively higher coefficient of friction than the low-friction material. The core element 24 is surrounded by a low-friction material (e.g., as an extrusion, a coating, etc.), with the low-friction material being between the inner surface of the outer strands 12 and the core element 24 at all points along the entire length and about the entire circumference of the passageway 20.

[0035] The core element 24 may be braided. To surround the core element 24, the low- friction material may, for example, be extruded around, coated onto, etc. the core element 24 to define the low-friction strand 14a.

[0036] In another example, the low-friction material may be formed into a tape and wrapped onto the core element 24. The wrapped low-friction tape may be heated (e.g., baked) to conform to the core element 24 and/or to provide a unitary outer surface of the low-friction strand 14a.

[0037] The core element 24 may comprise, for example, without limitation, a multi-filament polyester (available from Kuraray, Co., Japan; Teijin Limited, Japan; or Unifi, Inc., North

Carolina, U.S.A.), a para-aramid copolymer (for example, Technora® available from Teijin Aramid B.V.), a liquid crystal polyester (LCP; for example, Vectran® available from Kuraray Co., Japan), a polyamide, a polyester, or the like or combinations thereof. [0038] Because of the low-friction material on the outer surface, the material of the core element 24 may be a high-friction material with the low-friction outer surface separating the high-friction material of the outer strands 12 and such a core element 24. The material of the core element 24 may be high-strength such that the center strand 14a is capable of bearing a load.

[0039] Such a hybrid center strand construction may be used in larger ropes (e.g., having a diameter of 3 ¾" or greater or a circumference of 80 mm or greater) in which a larger passageway 20 can be formed. Relatively-expensive low-friction material can be used with less expensive material of the core element 24 to form a larger center strand 14a to occupy the larger passageway 20.

[0040] When the rope 10 is used, all strands 12, 14 move relative to each other. As the rope 10 is used and tension added (see FIG. 6), the "void" area in the center passageway 20 disappears, and the center strand 14 is in contact with the outer strands 12. The low-friction strand 14 keeps the outer strands 12 from contacting each other at the center and allows the outer strands 12 to move against a low-friction material that will not cause damage to the strands 12.

[0041] From the above description, it should be apparent that the present invention provides a rope 10 that may include a structurally stable, non-flowable, low-friction center strand 14, 14a to reduce the friction at the center of the rope 10 while maintaining the coefficient of friction of the rope surface. As such, the fibers 16 and the strands 12, 14 of the rope may be subjected to reduced wear as they rub against each other, resulting in increased useful life and improved performance compared to previous ropes.

[0042] One or more independent features and independent advantages of the invention may be set forth in the following claims:

Claims

CLAIMS What is claimed is:

1. A rope comprising:

a plurality of primary strands each including a plurality of fibers formed of a high-friction material, the plurality of primary strands defining an outer surface and a longitudinal center passageway of the rope; and

a non-load bearing secondary strand having a strand outer surface and disposed within the longitudinal center passageway of the rope, the secondary strand including, at least on the strand outer surface, a structurally-stable, non-flowable, low-friction material.

2. The rope of claim 1 , wherein the low-friction material is configured to remain in the longitudinal center passageway of the rope and not creep or flow to the outer surface of the rope.

3. The rope of claim 1 , wherein the secondary strand is separated from the outer surface of the rope by at least one of the plurality of primary strands at all positions along a length and about a circumference of the rope.

4. The rope of claim 1 , wherein the low-friction material includes one of low-friction polyethylene, polypropylene, ethylene-propylene-copolymer, nylon, expanded

polytetrafluoroethylene, modified polytetrafluoroethylene, fluorinated ethylenepropylene, ethylene-chlorotrifluoroethylene, ethylene-tetrafluoroethylene, a perfluoroalkoxy polymer or combinations thereof.

5. The rope of claim 1 , wherein the high-friction material is also a load bearing material.

6. The rope of claim 5, wherein the low-friction material is also a non-load bearing material.

7. The rope of claim 5, wherein the high-friction material includes one of an ultra-high molecular weight polyethylene, a recrystallized high modulus polyethylene, a liquid crystal polyester, a gel-spun polyethylene, a para-aramid, a para-aramid copolymer, a polyamide, polyester, or combinations thereof.

8. The rope of claim 1 , wherein the plurality of primary strands forms a braid around the secondary strand.

9. The rope of claim 1 , wherein the entire secondary strand is formed of the low-friction material.

10. The rope of claim 9, wherein the secondary strand is extruded.

1 1 . The rope of claim 1 , wherein the secondary strand includes a non-load bearing core element surrounded by the structurally-stable, non-flowable, low-friction material.

12. The rope of claim 1 1 , wherein the low-friction material is extruded onto the core element.

13. The rope of claim 1 1 , wherein the low-friction material coats the core element.

14. The rope of claim 1 , wherein each of the primary strands is free of low-friction material.

15. A rope comprising:

a plurality of outer strands together defining an outermost surface of the rope and a longitudinally-extending center passageway of the rope, each of the plurality of outer strands including a plurality of fibers formed of a high-friction material, the high-friction material defining a first coefficient of friction with itself; and

a core strand disposed within the longitudinally-extending center passageway of the rope and separated from the outermost surface of the rope by at least one of the plurality of outer strands at all positions along a length and about a circumference of the rope, the core strand including a structurally-stable, non-flowable, low-friction material, the low-friction material defining a second coefficient of friction with the high-friction material, the second coefficient of friction being less than the first coefficient of friction.

16. The rope of claim 15, wherein the low-friction material includes one of low-friction polyethylene, polypropylene, ethylene-propylene-copolymer, nylon, expanded

17. The rope of claim 16, wherein the high-friction material includes one of an ultra-high molecular weight polyethylene, a recrystallized high modulus polyethylene, a liquid crystal polyester, a gel-spun polyethylene, a para-aramid, a para-aramid copolymer, a polyamide, polyester, or combinations thereof..

18. The rope of claim 15, wherein the high-friction material includes one of an ultra-high molecular weight polyethylene, a recrystallized high modulus polyethylene, a liquid crystal polyester, a gel-spun polyethylene, a para-aramid, a para-aramid copolymer, a polyamide, polyester, or combinations thereof.

19. The rope of claim 15, wherein the plurality of outer strands forms a braid around the core strand.

20. The rope of claim 15, wherein the high-friction material is also a load bearing material.

21 . The rope of claim 15, wherein the low-friction material is also a non-load bearing material.

22. The rope of claim 15, wherein the entire core strand is formed of the low-friction material.

23. The rope of claim 22, wherein the core strand is extruded.

24. The rope of claim 15, wherein the core strand includes a non-load bearing core element surrounded by the structurally-stable, non-flowable, low-friction material.

25. The rope of claim 24, wherein the low-friction material is extruded onto the core element.

26. The rope of claim 24, wherein the low-friction material coats the core element.

27. The rope of claim 15, wherein each of the primary strands is free of low-friction material.

28. A rope comprising:

twelve outer strands together defining a longitudinally-extending center passageway of the rope, the twelve outer strands being braided in a single braid pattern, each of the twelve outer strands including twelve sub-strands braided in a single braid pattern, each of the sub- strands including a plurality of synthetic fibers; and

a core strand disposed in the longitudinally-extending center passageway over the length of the rope.

29. The rope of claim 23, wherein the plurality of synthetic fibers of the twelve outer strands include a high-friction material.

30. The rope of claim 29, wherein the high-friction material defines a first coefficient of friction with itself, and wherein the core strand includes a low-friction material, the low-friction material defining a second coefficient of friction with the high-friction material less than the first coefficient of friction.

31 . The rope of claim 30, wherein the high-friction material is also a load bearing material.

32. The rope of claim 28, wherein the core strand includes a non-flowable, low-friction material.

33. The rope of claim 32, wherein the low-friction material is also a non-load bearing material.

34. The rope of claim 32, wherein the entire core strand is formed of the low-friction material.

35. The rope of claim 34, wherein the core strand is extruded.

36. The rope of claim 28, wherein the core strand includes a non-load bearing core element surrounded by the structurally-stable, non-flowable, low-friction material.

37. The rope of claim 36, wherein the low-friction material is extruded onto the core element.

38. The rope of claim 36, wherein the low-friction material coats the core element.

39. A method of constructing a rope, the method comprising:

providing a non-load bearing secondary strand having a strand outer surface, the secondary strand including, at least on the strand outer surface, a structurally-stable, non-flowable, low-friction material; and

surrounding the secondary strand with a plurality of primary strands each including a plurality of fibers formed of a high-friction material, the plurality of primary strands defining an outer surface and a longitudinal center passageway of the rope, the secondary strand being disposed within the passageway.

40. The method of claim 39, wherein the low-friction material is configured to remain in the longitudinal center passageway of the rope and not creep or flow to the outer surface of the rope.

41 . The method of claim 39, wherein surrounding includes separating the secondary strand from the outer surface of the rope by at least one of the plurality of primary strands at all positions along a length and about a circumference of the rope.

42. The method of claim 39, wherein the low-friction material includes one of low-friction polyethylene, polypropylene, ethylene-propylene-copolymer, nylon, expanded

43. The method of claim 39, wherein the high-friction material is also a load bearing material.

44. The method of claim 43, wherein the low-friction material is also a non-load bearing material.

45. The method of claim 43, wherein the high-friction material includes one of an ultra-high molecular weight polyethylene, a recrystallized high modulus polyethylene, a liquid crystal polyester, a gel-spun polyethylene, a para-aramid, a para-aramid copolymer, a polyamide, polyester, or combinations thereof.

46. The method of claim 39, wherein surrounding includes braiding the plurality of primary strands around the secondary strand.

47. The method of claim 39, wherein providing includes providing a secondary strand formed entirely of the non-flowable, low-friction material.

48. The method of claim 47, wherein providing includes extruding the secondary strand.

49. The method of claim 39, wherein providing includes providing a secondary strand including a non-load bearing core element surrounded by the structurally-stable, non-flowable, low-friction material.

50. The method of claim 49, wherein providing includes extruding the low-friction material onto the core element.

51 . The method of claim 49, wherein providing includes coating the low-friction material on the core element.

52. The method of claim 39, wherein each of the primary strands is free of low-friction material.