NZ543203A

NZ543203A - An ultra high-strength light-weight rope with a shaped core

Info

Publication number: NZ543203A
Application number: NZ543203A
Authority: NZ
Inventors: Hjortur Erlendsson
Original assignee: Hampidjan Hf
Priority date: 2002-08-30
Filing date: 2003-09-01
Publication date: 2007-06-29
Also published as: AU2003259549A8; EP1546449A2; EP1546449B1; WO2004020732A2; IS2927B; NO331468B1; WO2004020732A3; IS7779A; NO20050842L; AU2003259549A1

Abstract

A rope with high stiffness and breaking strength is provided. The rope is produced by providing a stiff core and fibre rope jacket 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 and the core are eliminated permanently. A method and apparatus for producing such rope are provided, wherein the core is heated up and stretched such that it will be permanently elongated. In a preferred embodiment the thermoplastic core 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

CS^Zo J> WO 2004/020732 PCT/IS2003/000025 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 5 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 10 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 15 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. 2 0 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 25 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 3 0 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 35 layer will not cross each other and damage the underlying rope. Despite this, INTELLECTUAL PROPERTY OFFICE OF N.Z. 23 JUN 2006 RECEIVED 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 5 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. 10 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 15 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 2 0 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 in such a way that the core will preserve its stiffness and fill out the 2 5 inside vacancies within the rope permanently, or to at least provide a useful choice.

Twisting or braiding a fibre jacket layer around a core which is made of thermoplastic material, can accomplish this. During the production process the rope is heated 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 30 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 jacket layer 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, e.g. overbraid, which has a higher 35 softening point than the core material. 2 INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 3 JUN 2006 RECEIVED 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 rope, thereby obtaining a relative movement of said at least one jacket layer and the core, so that the vacancies between the core and jacket layer are eliminated. A rope with stiffness and high breaking strength is thus obtained.

Specifically, the present invention relates to a rope having a thermoplastic core and at least one jacket layer enclosing the thermoplastic core, the rope comprising: at least one sheet formed and constructed so as to mainly be impermeable to a liquid phase of the thermoplastic core material, the at least one sheet selected from a group consisting of: a. a sheet layer; and b. a sheet cover, the thermoplastic core material mainly: i. contained within the selected sheet; and ii. formed to occupy a space between portions of the at least one jacket layer, whereby rope compactness is enhanced.

In one preferred embodiment, the core comprises a core material and a sheet, 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. 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. 3 INTELLECTUAL PROPERTY OFFICE OF N.2 1S MAR 2007 RECEIVED 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 layer. In preferred embodiments, the rope is treated such that the phase of the core changes while the phase conditions of the jacket layer 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-iiquid phase, though some parts/filaments may remain solid or semi-solid. In certain embodiments, the phase condition of the jacket layer is altered but generally, however, the jacket layer remains substantially solid during the processing. (In these embodiments, a portion of the jacket layer, e.g. filaments or threads with a lower 5 softening point than the main strands of the jacket layer, go through a phase transition and diffuse further in between the main strands of the jacket layer.) 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 layer may 10 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 one jacket layer are used, i.e. the jacket layer comprises an inner sheet with a plurality of strands (e.g. 3, 4, or 6) and one or more outer jacket layers of strands, each outer jacket layers comprising a plurality of strands, such as described above.

The jacket layer 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.

DyneemaTM (DSM, Herleen, Netherlands)), aramids, liquid crystal polymers, PBO 2 5 (polybenzoxazole polymer) or polyester, and any combination thereof. Such combinations may also comprise steel wires or in certain embodiment the jacket layer additionally comprises thermoplastic fibre threads, that during heating will soften or melt to blend in with the bulk material of the jacket layer. 3 0 The jacket layer is in certain embodiments enclosed by a sheet 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 35 Ethylene, (e.g. DyneemaTM), and any combination thereof.

NTELUECTUAL PROPERTY OFFICE OF i\I.Z 2 3 JUN 2006 INTELLECTUAL PROPERTY OFFICE 4 OF NX 2 3 JUN 2006 RECEIVED 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, 5 which co-operate. In order to increase the strength of the rope further, the at least one sheet is elongated such that the fibres in said at least one sheet have equal length. The load 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 layer (optionally with the core mounted inside) with an adhesive material, such as 10 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 15 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 2 5 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 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: INTELLECTUAL PROPERTY OFFICE OF N.Z. 23 JUN 2006 RECEIVED - providing a core, - enclosing the core with at least one jacket layer, - changing the phase condition of the core and optionally said at least one jacket layer from a first solid phase to a second phase condition, and - stretching said at least one jacket layer and optionally the core, wherein the stretching of the core and optionally said at least one sheet is adapted to eliminate vacancies between the core and said at least one sheet, whereby high stiffness and breaking strength is obtained.

All general features relating to the method and components of the rope (the core, the 15 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 adhesive material as described 2 0 above, so that the fibres in the sheet 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 adhesive material.

Preferably the method further comprises removing the excess of said adhesive 2 5 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 adhesive material, (d) removing an excess of the adhesive material and the moisture in the rope by 35 means of drying, and INTELLECTUAL PROPERTY OFFICE OF N.Z. 6 2 3 JUN 2006 RECEIVED (e) tensing the rope, so that the length of the fibres in the strands obtain an equal length so that the load is equally divided among the fibres while heating the core and the strands. In one embodiment the optimal core temperature is 110-117°C during the heating.

Specifically, the present invention relates to a method for producing a rope comprising the steps of: a. providing a thermoplastic core; b. enclosing the core within at least one sheet; c. forming the at least one sheet so as to mainly be impermeable to a liquid phase of the core material; d. enclosing the core within at least one jacket layer; e. changing the phase condition of at least a portion of the thermoplastic core from a solid phase condition to a liquid phase condition; and f. applying tension forces to the at least one jacket layer sufficient to stretch both the at least one jacket layer and the core, wherein the applying tension forces to the at least one jacket layer causes constriction of the at least one jacket layer about the core sufficient to force deformation and flow of the at least a portion of the core in the liquid phase condition, the at least one sheet formed so as to mainly be impermeable to the liquid phase of the core material mainly containing the at least a portion of the core in the liquid phase condition within the at least one sheet, thereby forming the core into a shape that eliminates vacancies between the core and at least one jacket layer, whereby rope compactness is enhanced.

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

In another preferred embodiment the apparatus further comprises means for introducing a fastening or adhesive 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 adhesive 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 7a drawings in which, Fig. 1 shows the thermoplastic 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 thermoplastic core (1) as well but in the centre there is a central inner core (2) which can be useful for some thermoplastic core materials, as discussed herein.

Fig. 3 is a view of the thermoplastic core (1) with a surrounding sheet layer (3) from a material, which has higher thermal stability than the core material. This sheet layer (3) 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 jacket layer (4) around the thermoplastic core (1). The jacket layer (4) can be braided or twisted. The particular jacket layer (4) illustrated in the drawing is a braided jacket layer (4). Each strand (5) of the jacket layer (4) is a twisted bundle of filaments or yarns.

Fig. 5 shows the thermoplastic 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 sheet cover (6) can be co-extruded, pulltruded, wrapped, twisted or overbraided or made by a combination of two or more of said methods.

The thermoplastic core (1) is extruded with or without a central inner core (2) in the middle. The material used is thermoplastic material of any kind but preferably a polymer. The core (1) is cooled down until it reaches solid state. If desired, a sheet layer (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 layer (3) is to prevent uncontrolled flow of the liquid or semi-liquid core during processing. In some cases however, it INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 3 JUN 20% RECEIVED is desirable to have the core (1) flowing out to the surface of the jacket layer (4) and in such embodiments sheet layer (3) is not present in the construction. The thermoplastic core(1) with or without sheet layer (3) is fed into the jacket layer (4) centre during braiding or laying of the strands (5). The rope is now ready for 5 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 sheet cover (6) can be added at this stage or after 10 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. However, the cover material has to be able to withstand the temperature used in the process. The rope with core (1) 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. 15 During the heating, the thermoplastic 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 sheet layer (3) allows the penetration of the core material. If 2 0 the sheet layer (3) is absent, the thermoplastic core (1) material when in the second phase condition, (typically liquid or semi-liquid phase), it will penetrate in-between the strands of the jacket layer (4) and eventually to the surface of the jacket layer (4). If the sheet cover (6) has been applied prior to the process, it will stop the fluid core material from entering the surface of the rope. The rope construction is now cooled 2 5 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. 9 INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 3 JUN 2006 RECEIVED

Claims

1. A rope having a thermoplastic core and at least one jacket layer enclosing the thermoplastic core, the rope comprising: at least one sheet formed and constructed so as to mainly be impermeable to a liquid phase of the thermoplastic core material, the at least one sheet selected from a group consisting of: a. a sheet layer; and b. a sheet cover, the thermoplastic core material mainly: i. contained within the selected sheet; and ii. formed to occupy a space between portions of the at least one jacket layer, whereby rope compactness is enhanced.

2. The rope according to claim 1 wherein the at least one jacket layer includes strands braided around the thermoplastic core.

3. The rope according to claim 1 or claim 2 wherein the thermoplastic core additionally includes a central inner core.

4. The rope according to claim 3, wherein the central inner core includes a material selected from a group consisting of: a. a fiber thread; and b. metal wire.

5. The rope according to any one of claims 1 to 4 wherein the sheet layer is selected as the at least one sheet and is situated between the thermoplastic core and the at least one jacket layer.

6. The rope according to any one of claims 1 to 5 wherein the selected at least one sheet includes sheet cover, sheet cover disposed so as to enclose the at least one jacket layer. 10 INTELLECTUAL PROPERTY OFFICE OF N.Z. 13 MAR 2007 RECEIVED WO 2004/020732 PCT/IS2003/000025

7. The rope according to any one of claims 1 to 5 wherein : a. the selected at least one sheet is sheet layer, and the selected at least one sheet encloses the thermoplastic core; and b. the at least one jacket layer encloses the selected sheet.

8. The rope according to claim 7 wherein sheet cover encloses the jacket layer.

The rope according to claim 1 or claim 5 wherein the core material includes a polymer material selected from a group consisting of: a. nylon; b. olefin; c. high-density polyethylene (HDPE); d. chlorinated polyethylene (CPE); e. polyester; and f. various combinations of group elements a through e.

10. The rope according to claim 1 or claim 5 wherein the jacket layer is formed from a material selected from a group consisting of: a. nylon; b. polyethylene; 5 c. ultra high molecular weight polyethylene; d. polyester; e. aramids; f. liquid crystal polymer; 9- polybenzoxazole polymer (PBO); 10 h. steel wire; and i. combinations of group elements a through h

11. The rope according to any one of claims 1, 6, and 8, wherein the sheet cover is formed of a construction selected from a group consisting of: a. a braided construction; b. a coextruded construction; and 5 c. a pulltruded construction. ii INTEllECTUAi PROPERTY OFFICE OF (M.2. 2 3 JUN 2006 RECEIVED

12. A method for producing a rope comprising the steps of: a. providing a thermoplastic core; b. enclosing the core within at least one sheet; c. forming the at least one sheet so as to mainly be impermeable to a liquid phase of the core material; d. enclosing the core within at least one jacket layer; e. changing the phase condition of at least a portion of the thermoplastic core from a solid phase condition to a liquid phase condition; and f. applying tension forces to the at least one jacket layer sufficient to stretch both the at least one jacket layer and the core, wherein the applying tension forces to the at least one jacket layer causes constriction of the at least one jacket layer about the core sufficient to force deformation and flow of the at least a portion of the core in the liquid phase condition, the at least one sheet formed so as to mainly be impermeable to the liquid phase of the core material mainly containing the at least a portion of the core in the liquid phase condition within the at least one sheet, thereby forming the core into a shape that eliminates vacancies between the core and at least one jacket layer, whereby rope compactness is enhanced.

13. The method of claim 12, wherein the step of changing the phase condition of at least a portion of the core from a solid phase condition to a liquid phase condition is effected by heating the core to a temperature in the range of 50-180 °C.

14. The method of claim 13, wherein the core is heated to a temperature in the range of 100-130°C.

15. The method according to any of claims 12 to 14 including the further step of contacting the at least one jacket layer with an adhesive material so that the fibers in the at least one jacket layer are internally joined together prior to the changing of the phase condition of the core.

16. The method according to any of claims 12 to 14 including the further step of 12 INTELLECTUAL PROPERTY OFFICE OF N.2 13 MAR 2007 RECEIVED WO 2004/020732 PCT/IS2003/000025 contacting the at least one sheet with an adhesive material so that the fibers in the at least one sheet are internally joined together prior to the changing of the phase condition of the core.

17. The method according to claim 15 or claim 16 wherein the adhesive material is polyurethane.

18. The method according to claim 17 including the further step of removing excess of the adhesive.

19. The method according to claim 17 including the further step of removing a maximal amount of moisture.

20. The method according to claim 18 or claim 19 wherein the steps of removing excess of adhesive and moisture include the further step of drying in hot air.

21. A high breaking strength rope substantially as herein described with reference to any one of Figures 1 to 6.

22. A method for producing a rope according to claim 12 substantially as herein described with reference to any one of Figures 1 to 6. OF CLAIMS END I WTELutCTlWr 3Rf)0pHTv 0FFICE Oh iM i 2 3 JUN 2006 RECEIVFn