WO2004020732A2

WO2004020732A2 - A high-strength light-weight rope with a shaped core

Info

Publication number: WO2004020732A2
Application number: PCT/IS2003/000025
Authority: WO
Inventors: Hjortur Erlendsson
Original assignee: Hampidjan hf
Current assignee: Hampidjan hf
Priority date: 2002-08-30
Filing date: 2003-09-01
Publication date: 2004-03-11
Anticipated expiration: 2005-02-28
Also published as: IS7779A; AU2003259549A1; WO2004020732A3; AU2003259549A8; NO331468B1; NO20050842L; EP1546449B1; NZ543203A; IS2927B; EP1546449A2

Abstract

A rope with high stiffness and breaking strength is provided. The rope is produced by providing a stiff core (1) and fibre rope jacket (4) surrounding the core and by changing the phase condition of the core while stretching the rope, such that inside vacancies between the fibre rope jacket (4) and the core (1)are eliminated permanently. A method and apparatus for producing such rope are provided, wherein the core (1) is heated up and stretched such that it will be permanently elongated. In a preferred embodiment the thermoplastic core (1) changes from solid phase to liquid phase by means of heating. While in liquid phase the core material adapts to the encapsulating space of the surrounding sheet. The rope is then cooled down under tension until the core has returned to solid phase.

Description

AN ULTRA HIGH-STRENGTH LIGHT-WEIGHT ROPE WITH A SHAPED CORE

Field of the invention

The present invention relates to a rope with high cross-sectional symmetry having high stiffness and breaking strength.

Background

Various types of ropes and cables exist for different operations. In some operations ropes are desired, that are twisted and braided with high breaking strength and simultaneously with low mass density. With improving technology in producing fibres (such as Aramids, Liquid Crystal Polymers, PBO and Ultra High Molecular Weight Poly Ethylene), ropes with high breaking strength have been produced, with a breaking strength that is greater than for steel wire of the same diameter. Furthermore, the weight of such ropes is only one-sixth of the weight of a same size steel wire. One of the advantages of such ropes is that they are much easier to handle than steel wire. Applications for such ropes are e.g. in fishing with nets and trawls, where the ropes are used for back strop attachments, bridles and sweep lines.

The problem with such ropes is that openings are formed in between the strands. Those openings or vacancies allow the strands to move and the cross-sectional stability is therefore low if the vacancies are not filled out.

A common type of ropes used for trawl warps, bridles and sweep lines are twisted steel wire ropes. In twisted steel wire rope the most common construction is based on seven strands where one is in the centre and the remaining six are twisted around the centre strand. The centre strand is therefore acting as a core filling up the void. In steel wire ropes the core is often made from other materials like a bundle of fibres, twine or even synthetic ropes. As the steel wire is very stiff and harder than such softer materials, the core will be clenched and fill eventual voids. The result is that these soft core steel ropes have high strength, excellent abrasion resistance, circular cross-section and the stiffness is high in axial as well as in radial directions. One of the advantages of using steel wire rope for warps is how accurately it can be wound on drum winches. This prevents tangling on the drum as the rope will not be buried down between previous layers, and ropes in the same layer will not cross each other and damage the underlying rope. Despite this, there are some drawbacks using steel wire ropes. The steel wires are very heavy and difficult to work with and the lifetime is often limited due to corrosion and bending fatigue. The weight of the rope once in the sea can make it difficult to tow trawls and particularly when the trawl is used in mid water or even close to the surface due to the high sinking force created by the high density of the warp.

This problem has partly been solved by providing synthetic fibre ropes with a stiff core that adds considerable stiffness to the rope without adding much to the diameter. Their strength is close to or higher than that of steel wire ropes of the same diameter. These stiff-core fibre ropes have been available for many years. In such fibre ropes the fibre is soft and the core is of similar material as the covering strands, but they will not be clenched in the same way as in steel wire ropes. If the core is stiff, the inside of the fibre rope will adjust to the contours of the core but not vice-versa. Therefore it is difficult to completely fill out the voids in fibre ropes and at the same time preserve the inside contour unless the core material is much softer than the fibre strands surrounding the core. Core material that is softer than the surrounding fibre material will therefore not enhance the stiffness of the rope.

There is therefore a need for a construction of a fibre rope, which gives it increased form stability.

Description of the invention

The object of the present invention is to provide a strong rope by implementing a stiff core in a rope jacket in such a way that the core will preserve its stiffness and fill out the inside vacancies within the rope permanently. Twisting or braiding a fibre rope around a core which is made of thermoplastic material, can accomplish this. During the production process the rope is heated up and stretched in such a way that it will be permanently elongated. The thermoplastic core goes through a transition from a first solid phase to second phase (typically a liquid or semi-liquid phase) and back to solid phase by means of the heating. During the second phase the core material will adapt to the void space within the rope jacket in which it is enclosed. The rope is then cooled down under tension until the core has regained its solid phase. To control the movement of the thermoplastic material in the liquid phase, it may be covered by a sheet layer, e.g. overbraid, which has a higher softening point than the core material. It will be particularly appreciated that ropes of the present invention have sufficient strength for use as towing wires for towing fish trawls, where conventionally much heavier steel wires have been used, which are sensitive to corrosion.

According to a first aspect, the present invention relates to a rope having high stiffness and breaking strength, comprising a core, and at least one jacket layer enclosing the core, wherein the high breaking strength is obtained by changing the phase condition of the core and optionally said at least one jacket layer from a first phase condition to a second phase condition while stretching the cable, thereby obtaining a relative movement of said at least one jacket layer and the core, so that the vacancies between the core and jacket are eliminated. A rope with stiffness and high breaking strength is thus obtained.

In one preferred embodiment the core comprises a core material and a cover sheet layer, e.g. braided cover, enclosing said core material. Thereby it is prevented that the core material diffuses, in the second phase condition, towards the surface of the at least one sheet layer/jacket. The core material may be selected from any of a number of suitable thermoplastic materials (i.e., materials that become reversibly softer when heated and retain original properties (hardness) when cooled down). Preferably, the core is made of a plastic material, such as typically a thermoplastic polymer, a suitable polymer can be selected e.g. from nylon, olefin, or high-density polyethylene (HDPE), chlorinated polyethylene (CPE), polyester, or a combination thereof.

In certain useful embodiments, the core comprises additionally a central inner core (or "strength member") with different material properties than the main core material, for added strength and/or stiffness. The central inner core is preferably made from a fibre thread or filament, twinned or braided, from a suitable polymer, a single thread or metal wire, e.g. a lead or steel wire.

As mentioned, the first phase condition is typically a solid phase condition for both the core and the jacket. In preferred embodiments, the rope is treated such that the phase of the core changes while the phase conditions of the jacket remain unchanged. The second phase condition for the core is preferably a liquid phase condition but may also be an intermediate phase (semi-liquid phase) or a mixture of a liquid and solid phase, e.g. such that substantially all of the core is in a liquid or semi-liquid phase, though some parts/filaments may remain solid or semi-solid. In certain embodiments, the phase condition of the jacket is altered but generally however, the jacket remains substantially solid during the processing. (In these embodiments, a portion of the jacket, e.g. filaments or threads with a lower softening point than the main strands of the jacket, go through a phase transition and diffuse further in between the main strands of the jacket.)

The at least one jacket layer is preferably made of a plurality of strands where each strand typically is a bundle of fibre filaments, threads or yarns; the jacket may be braided in such a way that the strands form at least three-strand laid rope, such as a four- or six-strand laid rope. However, other arrangements are as well workable for the rope of the invention, hence, the strands may form a strand braided rope, with, e.g. 6, 8, 10, 12, 14, 16, 18, 20, 24, 28 or 32 strands braided. In one embodiment the strands form a 6 braided rope with the core in the middle, i.e. a 1+6 construction.

In other embodiments more than jacket layer are used, i.e. the jacket comprises an inner sheet layer jacket with a plurality of strands (e.g. 3, 4, or 6) and one or more outer sheet jackets of strands, each outer sheet jacket comprising a plurality of strands, such as described above.

The jacket may be made of one or more suitable materials, typically from one or more polymer fibre material such as but not limited to nylon, polyethylene, including high-density and ultra high-molecular weight polyethylene polymers (e.g. Dyneema™ (DSM, Herleen, Netherlands)), aramids, liquid crystal polymers, PBO (polybenzoxazole polymer) or polyester, and any combination thereof, such combinations may also comprise steel wires or in certain embodiment the jacket additionally comprises thermoplastic fibre threads, that during heating will soften or melt to blend in with the bulk material of the jacket.

The jacket is in certain embodiments enclosed by a cover (6) which may be braided, coextruded or pulltruded and is preferably from a material selected from any of the materials listed above or a combination thereof (such as, e.g., from nylon, olefin, polypropylene, thermoplastic filaments, polyester, aramids, liquid crystal Polymers, PBO and polyethylene, including Ultra High Molecular Weight Poly Ethylene, (e.g. Dyneema™), and any combination thereof. Furthermore, in order to enhance the strength of the at least one jacket layer, the threads and the strands in the at least one jacket layer are preferably internally fixed together. The force is thereby divided between all the strands and their threads, which co-operate. In order to increase the strength of the rope further, the at least one sheet layer is elongated such that the fibres in said at least one sheet layer have equal length. The strength is therefore not imposed on one or several fibres but on all the fibres. Such internal fixing may be obtained by contacting (impregnating) the jacket (optionally with the core mounted inside) with an adhesion material, such as preferably polyurethane or another material with similar suitable properties, e.g. by immersion, or by other suitable techniques such as spraying or using wet rollers.

The changing of the phase condition is preferably by heating the core and optionally said at least one jacket layer. Preferably, the temperature for the phase change is in the range of 50-180°C, and preferably in the range of 100-130°C, or in the range of 110-120°C, such as, e.g., about 110, 112, or 115°C. The exact temperature or temperature range will, however, depend on the material or combination of materials comprised in the core, and their properties and softening point(s).

In other embodiments of the present invention, further means for coverbraiding the rope are used, mainly in order to increase the lifetime of the rope.

The relative movement of said at least one jacket layer and the core is preferably effected through elongating lengthwise said at least one jacket layer, and optionally also the core. The elongation results in that the at least one jacket layer is clenched widthwise (cross-sectional), such that the core material when softened fills up in vacancies between the core and said at least one jacket layer. The cross- sectional symmetry of the rope may after the clenching be circular. However, other cross section symmetries are also possible.

According to a second aspect, the present invention provides a method for producing rope with high stiffness breaking strength, such as described above, the method comprising the steps of: - providing a core,

- enclosing the core with at least one jacket layer,

- changing the phase condition of the core and optionally said at least jacket layer from a first solid phase to a second phase condition, and

- stretching said at least one jacket and optionally the core,

wherein the stretching of the core and optionally said at least one sheet layer is adapted to eliminate vacancies between the core and said at least one sheet layer, whereby high stiffness and breaking strength is obtained.

All general features relating to the method and components of the rope (the core, the jacket layer, the phase conditions, stretching and the relative movement) is as described above.

In one preferred embodiment of the method the at least one jacket layer and optionally the core are brought in contact with an adhesion material as described above, so that the fibres in the sheet layer are internally joined together prior to the changing of the phase condition of the core. Polyurethane, which optionally can be diluted in aqueous solution, is preferred as an adhesion material.

Preferably the method further comprises removing the excess of said adhesion material and/or optionally moisture from said at least one jacket layer and the core prior to the stretching step.

The following protocol describes the currently most preferred embodiment for producing a rope with high breaking strength according to the invention:

(a) providing a core material with a braided cover enclosing said core material,

(b) braiding a plurality of strands around the core,

(c) contacting the core and the strands with an adhesion material,

(d) removing an excess of the adhesion material and the moisture in the rope by means of drying, (e) tensing the rope, so that the length of the fibres in the strands obtain an equal length so that the strength is equally divided between the fibres while heating the core and the strands. In one embodiment the optimal core temperature is 110-117°C during the heating.

In a third aspect, the present invention relates to an apparatus for producing rope as described above, with high stiffness and breaking strength comprising:

means for arranging at least one jacket layer around a core,

means for changing the phase condition of the core and said at least one jacket layer from a first phase condition to a second phase condition, and

- means for stretching said core and at least one jacket layer, preferably such as to obtain a relative movement between said at least one sheet layer and the core.

In one preferred embodiment said means for arranging at least one sheet layer around the core is a braid mechanism. Changing the phase condition may suitably be effected through any type pf heat supply mechanism.

In another preferred embodiment the apparatus further comprises means for introducing a fastening or adhesion material within said at least one jacket layer. Such means may be immersing means to immerse said at least on jacket layer and optionally the core into said fastening or adhesion material, as described above. The excess of said material is preferably removed from the rope and optionally the moisture. This may be done in drier or similar means. Subsequently, a tensing mechanism is applied to apply tension to the rope and preferably to effect relative movement between said at least one jacket layer and the core.

Detailed description

In the following the present invention, and in particular preferred embodiments thereof, will be described in greater detail in connection with the accompanying drawings in which, Fig. 1 shows the core (1) as a cylindrical bar but other cross-sectional shapes may equally be used as the core is reshaped during the production process according to the invention.

Fig. 2 shows the core 1 as well but in the centre there is a strength member 2 which can be useful for some thermoplastic core materials, as discussed herein.

Fig. 3 is a view of the core with a surrounding sheet 3 from a material, which has higher thermal stability than the core material. This sheet can be co-extruded, pulltruded, wrapped, twisted or overbraided or made by a combination of two or more of said methods.

Fig.4 is showing the rope jacket 4 around the core. The rope jacket can be braided or twisted. The particular jacket illustrated in the drawing is a braided rope jacket. Each strand 5 is a twisted bundle of filaments or yarns.

Fig. 5 shows the core 1 unravelled after the phase change process. The pattern 7 is created by the clenching and elongation during the phase shifts of the core material.

Fig. 6 shows a view of a processed rope with a sheet cover 6. The cover can be co-extruded, pulltruded, wrapped, twisted or overbraided or made by a combination of two or more of said methods.

The core 1 is extruded with or without a strength member 2 in the middle. The material used is thermoplastic material of any kind but preferably a polymer. The core is cooled down until it reaches solid state. If desired, a sheet 3 is applied with a co-extrusion, pulltrusion, wrapping, twisting or overbraiding or a multiple or combination of the methods. The function of the sheet 3 is to prevent uncontrolled flow of the liquid or semi-liquid core during processing. In some cases however, it is desirable to have the core flowing out to the surface of the rope jacket and in such embodiments sheet 3 is not present in the construction. The core 2 with or without sheet 3 is fed into the rope 4 centre during braiding or laying of the strands 5. The rope is now ready for impregnation. Dipping into suitable solution is the most effective method but there are other alternative methods, which involve spraying or wet rollers. The impregnation materials can be solvents of polymers, polyurethane, bitumen or latex or a blend of those materials. Prior to the stretching and heat processing the solvent should be dried out of the rope. A cover 6 can be added at this stage or after the processing. If the core 1 is used without a sheet layer 3 it is advantageous to add such cover 6 prior to the processing but the cover material has to be able to withstand the temperature used in the process. The rope with core is now tensioned and heated up, by means of suitable medium, liquid or air, to the appropriate temperature and simultaneously stretched until it elongates permanently. During the heating, core 1 shifts from solid phase to a liquid or semi- liquid phase. The force applied to the axial direction of the rope will partly be transferred into forces working perpendicular to the rope. These perpendicular forces will move the now liquid core material into the inside voids of the rope and fill them up, to the extent that the core sheet layer 3 allows the penetration of the core material. If the sheet layer 3 is absent, the core 1 material when in the second phase condition, (typically liquid or semi-liquid phase), it will penetrate in-between the strands of the rope jacket and eventually to the surface of the jacket. If the cover sheet 6 has been applied prior to the process it will stop the fluid core material from entering the surface of the rope 4. The rope construction is now cooled down and the tension is simultaneously lowered. The rope has now undergone permanent change involving shifting phase of the core and both axial and radial stiffness has been achieved by rearranging the rope sub-elements.

Claims

1. A rope having high stiffness and breaking strength comprising:

a core (1),

- at least one jacket layer (4) enclosing the core,

wherein the high breaking strength is obtained by changing the phase condition of the core from a first solid phase condition to a second phase condition and concurrently stretching said at least one jacket layer and the core so that the vacancies between the core and said at least one jacket layer are substantially eliminated, and subsequently returning the core to a solid phase condition, thereby obtaining a rope with stiffness and high breaking strength.

2. The rope according to claim 1 , wherein the second phase condition for the core material is a liquid phase condition.

3. The rope according to claim 1 , wherein the second phase condition for the core material is a solid phase condition.

4. The rope according to claim 1 , wherein the second phase condition for the core material is a mixture of solid and liquid phase condition.

5. The rope according to any of the preceding claims, wherein the jacket (4) comprises strands (5) braided around the core.

6. The rope according to claim 5, wherein the strands (5) form at least a four- strand braided rope.

7. The rope according to any of the preceding claims, wherein the core additionally comprises a central inner core (2).

8. The rope according to claim 7, wherein the central inner core (2) comprises a material selected from a fibre thread and metal wire, such as a lead wire.

9. The rope according to any of the preceding claims, wherein the core comprises a core material and a cover sheet layer (3) enclosing said core material.

10. The rope according to any of the preceding claims, wherein the core material is a plastic material.

11. The rope according to claim 10, wherein the core material is from polymer.

12. The rope according to claim 11 , wherein the core material is from a polymer selected from the group consisting of nylon, olefin, high-density polyethylene (HDPE), chlorinated polyethylene (CPE), polyester, and a combination thereof

13. The rope according to any of the preceding claims, wherein the jacket (4) is from a material selected from nylon, polyethylene, including ultra high molecular weight polyethylene, polyester, aramids, liquid crystal polymer, polybenzoxazole polymer (PBO), steel wire and a combination thereof.

14. The rope according to any of the preceding claims, wherein the jacket (4) is enclosed by a cover (6) which is braided, coextruded or pulltruded from a material selected from nylon, olefin, polypropylene, polyethylene, including ultra-high molecular weight polyethylene, thermoplastic filaments, polyester, Aramids, Liquid Crystal Polymers, PBO, and any combination thereof.

15. The rope according to any of the preceding claims, wherein changing the phase condition of the core is effected by heating the core and optionally said at least one jacket layer.

16. The rope according to claim 15, wherein the core is heated to a temperature in the range of 50-180°C to effect the phase changing.

17. The rope according to any of the preceding claims, wherein said stretching results in that said at least one jacket (4) is clenched widthwise such that the core material (1) substantially fills up in vacancies between the core and said at least one sheet layer.

18. A method for producing a rope with high stiffness and breaking strength comprising: providing a core (1),

- enclosing the core with at least one jacket (4),

changing the phase condition of the core (1) from a first solid phase condition to a second phase condition, and

- stretching said at least one jacket (4) and the core (1),

wherein the stretching of the core and said at least one jacket is adapted to eliminate vacancies between the core and said at least one sheet layer, whereby a high stiffness and breaking strength is obtained.

19. The method according to claim 18 wherein the second phase condition is a liquid phase condition.

20. The method according to claim 18 wherein the second phase condition is a solid phase condition.

21. The method according to claim 18 wherein the second phase condition is a mixture of solid and liquid phase condition.

22. The method of claim 18, wherein changing the phase condition is effected by heating the core to a temperature in the range of 50-180°C.

23. The method of claim 22, wherein the core is heated to a temperature in the range of 100-130°C.

24. The method according to any of the claims 14-23, further comprising contacting said at least one sheet layer and optionally the core with an adhesion material so that the fibres in the sheet layer are internally joined together prior to the changing of the phase condition.

25. The method according to any claim 24, wherein said adhesion material is polyurethane.

26. The method according to claim 24, further comprising removing excess of said adhesion material and optionally moisture from said at least one sheet layer and the core prior to said stretching.

27. The method according to claim 26, wherein removing excess of said adhesion material and optionally moisture is conducted by drying in hot air.

28. An apparatus for producing rope with high stiffness and breaking strength comprising:

- means for arranging at least one jacket layer (4) around a core (1), - means for changing the phase condition of the core (1 ) from a first solid phase condition to a second phase condition, and means for stretching said at least one jacket layer (4) and the core (1).

29. The apparatus according to claim 28, wherein said means for arranging at least one jacket layer around the core is a braid mechanism.

30. The apparatus according to claim 28, wherein said means for changing the phase condition is a heating mechanism.

31. The apparatus according to claim 28 further comprising means to contact said at least sheet layer and optionally the core with an adhesion material.

32. The apparatus according to claim 31 , wherein said means to contact said at least sheet layer and optionally the core with an adhesion material comprises means to immerse said at least one sheet layer and optionally the core into an adhesion material.

33. The apparatus according to 31 further comprising means for removing excess adhesion material and/or excess moisture from said sheet material, such as a hot air supply.