EP3967799A1 - Textile fibre rope comprising a plied yarn or core-sheath yarn and method of manufacturung such a yarn - Google Patents

Abstract

The invention relates to a rope (1) made of textile fiber material, comprising a rope core (2) and a sheathing (3) surrounding the rope core (2), the sheathing (3), a space between the sheathing (3) and the rope core (2 ) located intermediate sheath (4) and / or between the sheath (3) and the rope core (2) reinforcement comprises a twine (6) with excess length (Δ), the twine (6) with excess length (Δ) is thereby formed that it comprises at least a first yarn (7) and a second yarn (8) twisted together, the first yarn (7) having a greater length than the second yarn (8) measured in a untwisted state of a unit length of twine (6). In a further aspect, the invention relates to a method for producing a twine (6) with excess length (Δ) for the aforementioned cable (1).

Description

The invention relates to a rope made of textile fiber material, comprising a rope core and a sheath surrounding the rope core.

Fiber ropes from various fields of application are known from the prior art. For example, fiber ropes are used to secure people as climbing ropes, cords or lanyards. Ropes can also be used in the mechanical sector, for example as winch ropes. The cables described herein are all designed to have a diameter of 5 mm to 60 mm.

Depending on the desired application, the fiber ropes should have a predetermined cut resistance. For example, dynamic mountain ropes are used to secure the climber against falling and to slow down a fall. Mountain ropes are used in alpine terrain, among other things, where they are often exposed to rocky edges - both under static loads and under dynamic fall loads. It can be seen that such ropes should have a high cut resistance in order to avoid accidents.

A solution to increasing the lifespan of mountaineering ropes is in Scripture FR 2 951 743 disclosed showing a metal sleeve wrapped around a portion of the cable. If the rope is to be wrapped around a sharp edge, the cuff is guided over the rope in this area so that the sharp edge only affects the cuff and not the textile rope.

the EP 0 150 702 A2 proposes to make a mountain rope that should have a higher durability when detouring around sharp edges. For this purpose, the rope core or the entire rope is wrapped, braided or braided with monofilaments or wires.

It is also known from the prior art that high-strength fibers, in particular aramid, generally have a higher cut resistance than conventional fibers such as polyamide. From the US6,050,077 For example, it is known to produce a safety mountaineering rope that includes a sheath composed of a blend of high-strength and non-high-strength fibers, thereby making the rope better in the sharp edge test.

However, it has been found that the use of high-strength fibers also has disadvantages. In particular, high-strength fibers have very low elongation, making them poorly suited to braking a fall, i.e. absorbing energy through elongation.

Another disadvantage of fibers in general is that the cut resistance of the fibers decreases when the fibers are under tension. This means that the highest cut resistance is achieved when it is not under tension. In the aforementioned applications, however, the ropes are generally under tension during the cut, for example when the mentioned climber puts a load on the mountain rope and rubs it over a rock edge.

It is therefore the object of the invention to overcome the disadvantages of the prior art and to create a rope made of textile fiber material which has increased cut resistance even under tension.

This object is achieved by a rope made of textile fiber material, comprising a rope core and a sheath surrounding the rope core, the sheath, an intermediate sheath located between the sheath and the cable core and/or a reinforcement located between the sheath and the cable core having an excess length of thread wherein the overlength twisted yarn is formed by comprising at least a first yarn and a second yarn twisted together, the first yarn having a greater length than the second yarn measured in an untwisted state of a unit length of the twisted yarn .

The overlength twist in the rope of the present invention allows some fibers to be in a slack state even when the rope is taut. If the rope and the thread contained in it are stretched with excess length, only this thread is stretched due to the shorter length of the second thread and the first thread is still present without tension due to the greater length. Since, as already mentioned in the introduction, fibers have a lower cut resistance under tension, the longer length of the first yarn enables increased cut resistance in the tensioned state of the rope.

In contrast to the prior art, a fiber rope is thus created which has increased cut resistance and can be metal-free at least on the surface, whereby the risk of injury in the event of wire breakage is avoided. Furthermore, metal wires with an electrical conductivity could be present inside the cable, which means that they can be used, for example, as conductors or sensors. through the With the properties explained at the outset, the rope according to the invention is particularly suitable for use as a mountaineering rope, as a rope for connecting means, for slings or also as a winch rope.

In a particularly preferred embodiment, the first yarn comprises high-strength fibers, preferably p-aramid fibers, m-aramid fibers, UHMWPE fibers or PBO fibers. This enables the twine to have a particularly high cut resistance when taut, since high-strength fibers have better cut resistance than conventional fibers. In other embodiments, however, it is also possible to make the first yarn from non-high-tenacity fibers in order to achieve at least some increase in cut resistance.

In a further embodiment, the second yarn comprises non-high-strength fibers, preferably PA fibers, PES fibers or PP fibers. Since non-high tenacity fibers usually have a higher elongation than high tenacity fibers, it is preferable for some applications to make the load-bearing part of the twisted yarn, i.e. the second yarn, from non-high tenacity fibers. This is particularly preferred for mountain ropes so that the second yarn can better absorb energy through stretching.

It is preferred if the first yarn is at least 5%, preferably at least 8%, particularly preferably at least 12% longer than the second yarn, measured in the untwisted state of the unit length of the thread. As a result, the first yarn is long enough to be tension-free in the tensioned state of the cable or the overlength twine or the second yarn, even if the cable or the excess length twine or the first yarn is stretched.

Furthermore, the twine is preferably designed in such a way that the proportion by weight of the second yarn in the twine with excess length is 30% to 90%, preferably 40% to 75%. This provides a good ratio between the first yarn and the second yarn, allowing the second yarn to absorb sufficient energy under tension while allowing the first yarn to have sufficient levels to perform its cut-resistance function.

Moreover, it is advantageous if the proportion by weight of the overlength thread in the sheath, in the intermediate sheath and/or in the reinforcement is 50% to 100% of the sheath, the intermediate sheath or the reinforcement. It goes without saying that the choice of the proportion of twine in the rope depends to a large extent on the desired depends on the application, so that less yarn with excess length can be used for other applications.

The rope core of the rope according to the invention can also be structured differently depending on the application. The cable core is preferably made up of one or more twisted or braided cores. In particular, when the rope is designed for mountaineering applications, it is customary to provide several cores in the rope core. When used as a winch rope, however, the rope according to the invention generally comprises only one core as the rope core.

If the rope core is to have a high degree of elongation, for example in order to absorb energy through elongation in the event of a fall, the rope core can comprise non-high-strength fibers, preferably PA fibers, PES fibers or PP fibers. In this embodiment, the rope can be designed, for example, as a climbing rope according to the EN892 standard. In these embodiments, the use of the rope as a climbing rope is particularly appropriate.

However, if the elongation of the rope core only plays a minor role or should be small for the application, the rope core can also include high-strength fibers, preferably aramid fibers, UHMWPE fibers, PBO fibers or Vectran fibers. This embodiment is preferred in particular for use as a winch cable.

Regardless of the application, it is preferred for the cable according to the invention if the diameter of the cable is 5 mm to 60 mm, preferably 5 mm to 13 mm.

The extra-long twine for the rope according to the invention can be produced in various design variants. However, the following two alternative production processes are particularly preferably used.

• Bereitstellen des ersten Garns und des zweiten Garns;
• Verzwirnen bzw. Verdrehen des ersten Garns mit dem zweiten Garn;

wobei das erste Garn und das zweite Garn mit im Wesentlichen derselben Spannung und derselben Länge miteinander verdreht werden und der Zwirn nach dem Verdrehen einem Schrumpfvorgang ausgesetzt wird.The first preferred method of manufacturing the overlength twine includes the steps of:

• providing the first yarn and the second yarn;
• twisting the first yarn with the second yarn;

wherein the first yarn and the second yarn are twisted together at substantially the same tension and length and the twisted yarn is subjected to a shrinkage process after twisting.

In this first preferred manufacturing method, two yarns are used which are manufactured in such a way that they shrink at different rates. For example, fibers of different materials can be used for this.

The shrinking process is preferably carried out in an autoclave. Before the twine is introduced into the autoclave, it is preferably prepared to enable defined shrinkage. The processing can particularly preferably be carried out by knitting, the knitted fabric being separated again after the shrinking process. The type of processing of the threads, e.g. by knitting, the selection of the temperature and/or the pressure in the autoclave can be made by a person skilled in the art.

• Bereitstellen des ersten Garns und des zweiten Garns;
• Verzwirnen bzw. Verdrehen des ersten Garns mit dem zweiten Garn;

wobei das erste Garn und das zweite Garn mit unterschiedlicher Spannung miteinander verdreht werden und der Zwirn nach dem Verdrehen entspannt wird.The second preferred method of manufacturing the overlength twine includes the steps of:

• providing the first yarn and the second yarn;
• twisting the first yarn with the second yarn;

wherein the first yarn and the second yarn are twisted together with different tension and the twisted yarn is relaxed after the twisting.

In the second preferred manufacturing method, two yarns can also be used that are manufactured in the same way and whose fibers are made of the same materials.

The production of the rope according to the invention is usually carried out in one step, with the rope core or cores being introduced into a braiding machine and, among other things, being braided with extra-long thread, whereby the sheath and, if necessary, the intermediate sheath and/or the reinforcement arises.

• Figur 1 zeigt den Querschnitt des erfindungsgemäßen Seils.
• Figur 2 zeigt einen Zwirn mit Überlänge, der im Seil von Figur 1 eingearbeitet ist.
• Figur 3 zeigt den Zwirn von Figur 2 im entdrehten Zustand.
• Figur 4 zeigt eine Versuchsanordnung zur Ermittlung der Schnittfestigkeit.

Advantageous and non-limiting embodiments of the invention are explained in more detail below with reference to the drawings.

• figure 1 shows the cross section of the rope according to the invention.
• figure 2 shows an overlength of twine used in the rope of figure 1 is incorporated.
• figure 3 shows the twine of figure 2 in the untwisted state.
• figure 4 shows a test arrangement for determining the cut resistance.

figure 1 shows the cross section of a rope 1. The rope 1 comprises a rope core 2 and a sheathing 3 surrounding the rope core 2. The rope 1 is made of a textile fiber material, ie both the rope core 2 and the sheathing 3 are made of textile fiber material made. The rope 1 is preferably made metal-free, apart from optional connecting elements or clamps that are attached to the ends of the rope 1 or at another point on the rope 1, or functional, electrically conductive wires routed in the rope 1, which can be used, for example, as current conductors, information conductors or sensor serve.

The cable 1 can optionally have an intermediate sheath 4 which is provided between the cable core 2 and the sheath 3 . Depending on the embodiment, this intermediate jacket 4 can also be made of textile fiber material and be metal-free. As an alternative or in addition to the intermediate jacket 4, a textile, preferably metal-free, reinforcement (not shown) can also be used, which is understood here to mean a non-covering intermediate jacket.

How out figure 1 As can be seen, the rope core 2 has twelve cores 5 . In general, however, the rope core can also have only one core 5 or more than one core 5 . The cores 5 are, for example, twisted or braided, but could also be made in a different way.

The rope 1 described herein can be used in various applications, for example as a mountain rope, as a rope for lanyards, for slings or as a winch rope. When used as a mountaineering rope, the rope 1 is used, for example, by a climber to protect against falls or is also used as a static accessory cord for makeshift rescue techniques. For example, when used as a lanyard rope, an arborist can use the rope 1 as a lanyard/lanyard, where the rope 1 is looped around the tree 1 and hooked into an arborist's harness, allowing the arborist to brace themselves on the tree in any vertical position can. When used as a rope for slings, the rope 1 is used as an auxiliary rope when climbing. When used as a winch cable, this is wound up on a winch and is therefore used in mechanical operation, in contrast to the aforementioned uses, and not to prevent people from falling.

In all of the aforementioned applications, the rope 1 can have a diameter of 5 mm to 60 mm, preferably 5 mm to 13 mm.

In particular, when the rope 1 is used to prevent falls, the rope core 2 should have advantageous dynamic properties. In these embodiments, the Rope core not high-strength fibers, preferably polyamide (PA) fibers. In other applications, the non-high-strength fibers can also be polyester (PES) fibers or polypropylene (PP) fibers.

In other embodiments, for example when the cable 1 is used as a winch cable, the cable core 2 can also have high-strength fibers. For the purposes of the present invention, “high-strength” is understood to mean fibers with a tensile strength of at least 14 cN/dtex, preferably a tensile strength greater than 24 cN/dtex, particularly preferably greater than 30 cN/dtex. UHMWPE fibers (including ^Dyneema® ), aramid fibers, LCP fibers (including Vectran) or PBO fibers are known as high-strength fiber types with corresponding tensile strengths.

Depending on the embodiment, the rope core 2 or the cores 5 can also comprise a mixture of high-strength fibers and non-high-strength fibers.

In order to increase the cut resistance of the rope 1, said sheath 3, the intermediate sheath 4 and/or the reinforcement comprises the following with reference to FIG Figures 2 and 3 explained thread 6 with excess length Δ. The casing 3, the intermediate casing 4 and/or the reinforcement can be made entirely or partially from a plurality of threads 6 with an excess length Δ. The sheathing 3 and the intermediate sheathing 4 are usually braided, so that a plurality of threads 6 with an excess length Δ can be braided together, optionally with the addition of other threads. Usually, however, the proportion by weight of the thread 6 with excess length Δ in the sheath 3, in the intermediate sheath 4 and/or in the reinforcement is 50% to 100% in each case.

In figure 2 the thread 6 is shown with excess length Δ, which can be produced with an indefinite length and wound up on at least one bobbin before the production of the casing 3, the intermediate casing 4 or the reinforcement. In figure 2 an arbitrarily selected unit length E of the twisted yarn 6 with excess length Δ is also shown. The numerical size of the unit length E can be chosen arbitrarily, for example as 1 m. However, the invention is completely independent of the length actually chosen, as will be explained below, and is only used to determine the excess length Δ of the yarn 7 in the twine 6 with excess length Δ.

As known to those skilled in the art, twisted yarns are made by twisting multiple yarns. The thread 6 explained here with excess length Δ comprises a first yarn 7 and a second yarn 8 twisted together. The twisted state of the twisted yarn 6 with excess length Δ is in figure 2 shown.

figure 3 12 shows the section of unit length E of twisted yarn 6 with excess length Δ in an untwisted state. It can be seen that the first yarn 7 is longer than the second yarn 8 . In a practical example, E = 1 m was chosen for the unit length. However, as already from figure 2 As can be seen, the first yarn 7 is twisted with the second yarn 8 so that small loops of the first yarn 7 form around the second yarn 8 in some cases.

How out figure 3 As can be seen, the actual length of the first yarn 7 in the untwisted state is greater than the length of the second yarn 8 or the unit length E. In the above example, in which the unit length E=1 m was selected, the result was in the untwisted state of the thread 6 with excess length Δ for the first yarn 7 a length L1 = 1.15 m and for the second yarn 8 a length L2 = 1 m. In this example the first yarn 7 is in the untwisted state of the thread 6 with excess length Δ thus around 15 % longer than the second yarn 8, where the percentage P is calculated by P = 100 ^* (L1-L2)/L2.

From the above example it can be seen that the choice of the unit length E is arbitrary and is only used to determine the relative length of the first yarn 6 to the second yarn. If the unit length E = 2 m were chosen, the length L1 of the first yarn 7 in the untwisted state of the twisted yarn 6 with excess length Δ would be 2.3 m and the length L2 of the second yarn 8 would be 2 m, so that the first yarn 7 would turn around 15% longer than the second yarn 8.

In general, the first yarn 7 is at least 5%, preferably at least 8%, more preferably at least 12% longer than the second yarn 8, measured in the untwisted state of the unit length E of the thread 6. The percentage P is as described above given in each case with respect to the length L2 of the second yarn 8, ie P=100 ^* (L1-L2)/L2. These length ratios ensure that the first yarn 7 is not stretched even when the second yarn 8 is stretched. An upper limit of the length by which the first yarn 7 is longer than the second yarn 8 can be 30%, for example, this upper limit usually being limited only by the manufacturing process.

At this point it should be noted that measuring the length of the first yarn 7 and the second yarn 8 in the untwisted state of the unit length E either in the tension-free State or under a certain bias, for example 0.5 +/- 0.1 cN / tex, can take place. It may be necessary to pretension the yarns in order to achieve a correct, comparable measurement result. Standards for measuring the length of yarns are known in the prior art, such as DIN 53830-3, which among other things specifies a pretension of 0.5 +/- 0.1 cN/tex for measuring the length of yarns, and can also be used to determine the lengths of the yarns of the rope 1 described herein.

Usually, the first yarn 7 comprises high-tenacity fibers and the second yarn 8 non-high-tenacity fibers, the definition of high-tenacity being as given above with regard to the rope core 2 . For example, the high tenacity fibers of the first yarn 7 could be p-aramid fibers (para-aramid fibers), m-aramid fibers (meta-aramid fibers), LCP fibers, UHMWPE fibers, or PBO fibers. Fibers marketed under the names Kevlar, Twaron and Technora are particularly suitable. For example, PA fibers, PES fibers or PP fibers could be selected for the non-high-strength fibers of the second yarn 8 .

Depending on the embodiment, yarns 7, 8 made of different materials can thus be selected for the twisted thread 6 with excess length Δ. In other embodiments, however, yarns made of the same materials can also be selected, with limitations resulting from the production processes described below.

As a rule, the ratio of the first yarn 7 to the second yarn 8 is chosen such that the proportion by weight of the first yarn 7 with excess length Δ in the thread is 30% to 90%, preferably 40% to 75%.

However, the construction of the thread 6 is not limited to the twisting of only two yarns, but more than two yarns could also be twisted together. In the untwisted state of the twisted thread 6 with excess length Δ, all the yarns could then have a different length. In other embodiment variants, only one yarn could be longer than the other yarns of the same length, or only one yarn could be shorter than the other yarns of the same length. Again, for example, two yarns of the same length could be longer than two other yarns of the same length. It can be seen that there are no limits to the structure of the twisted yarn 6 with excess length Δ, as long as at least one yarn has a greater length than another yarn, measured in an untwisted state of a unit length E of the twisted yarn 6. In these embodiments, it is particularly preferred if the longest yarn is at least 5%, preferably at least 8%, particularly preferably at least 12% longer than the shortest yarn, measured in the untwisted state of the unit length E of the thread 6.

The twisted yarn 6 with excess length Δ can be produced in a wide variety of ways and is not restricted to a specific production method. In particular, however, production methods by means of a shrinking process or under different tension are available, which are described below.

In the production method using the shrinking process, first the first yarn 7 and the second yarn 8 are provided. In this case, the two yarns 7, 8 are usually without tension or have the same tension. Thereafter, the yarns 7, 8 are twisted together, resulting in a twist without excess length Δ. In a further process step, the twine without excess length Δ is exposed to a predetermined temperature in an autoclave after suitable preparation, e.g. knitting, so that the first yarn 7 and the second yarn 8 shrink. In this embodiment, the yarns 7, 8, in particular their materials, were selected in such a way that they shrink to different extents under the predetermined conditions, resulting in the twisted yarn 6 with excess length Δ.

In the differential tension manufacturing method, the first yarn 7 and the second yarn 8 are twisted together with different tension, and the twisted yarn 6, i.e., its yarns 7, 8, is relaxed after twisting. The selection of the tensions in order to achieve a desired excess length Δ of the first yarn 7 compared to the second yarn 8 can be determined by the person skilled in the art on the basis of the modulus of elasticity of the two yarns 7, 8. It can be seen that, for example, a thread in which PA 940 dtex is twisted with aramid 1660 dtex requires a different pretension to achieve thread 6 with excess length Δ than a thread in which PA1400 dtex is twisted with aramid 1660 dtex.

The measurement described below was carried out in order to empirically test whether the rope 1 explained above with the twisted yarn 6 with excess length Δ processed therein has a higher cut resistance than a comparable rope without twisted yarn 6 with excess length Δ. However, it goes without saying that other measurement methods can also be used to determine the cut resistance.

Initially, a height-adjustable test carrier was provided, on which an 80 cm long granite block 9 with a naturally broken edge 10 (granite curb) was fastened. Starting from a fixed anchorage point above, a test mass (80 kg steel cylinder) was lowered over edge 10 with the rope to be tested. through the Depending on the position of the attachment point, the rope is deflected at the edge 10 in a deflection angle α, as shown in FIG figure 4 is evident. Edge 10 is located at a distance of 4 m from the anchor point (belay). Immediately after edge 10, the proof mass is freely suspended. The forces occurring at the attachment point were recorded by installing a load cell.

• Am Anschlagpunkt wird eine Kraftmessdose installiert und das Prüfseil daran befestigt.
• Die Masse wird jeweils stoßfrei knapp unterhalb der Steinkante in das Prüfseil gehängt und anschließend um 2 m abgelassen.
• Das Seil wird mittels seitlich angebrachten Seilzügen horizontal bewegt (Dies könnte einer Situation entsprechen, bei welcher der abgelassene Kletterer seitlich zum nächsten darunterliegenden Standplatz pendelt). Das Prüfseil wird so entlang der scharfen Kante 10 in beide Richtungen gezogen bis zum Riss. Die Kantenlänge, die bis zum Riss überstrichen wurde, wird gemessen und als Bruchlänge bezeichnet.

The test procedure is as follows:

• A load cell is installed at the anchor point and the test rope is attached to it.
• The mass is hung in the test rope just below the edge of the stone without hitting it and then lowered by 2 m.
• The rope is moved horizontally by means of laterally attached pulleys (this could correspond to a situation in which the lowered climber swings sideways to the next belay below). The test rope is thus pulled in both directions along the sharp edge 10 until it breaks. The edge length that was swept up to the crack is measured and referred to as the break length.

In order to achieve a sideways movement that is as uniform as possible, the force of the sideways pull is introduced directly below the edge 10 . Stop bolts at each end of the edge 10 prevent the cable from moving beyond the edge 10. At the end of the tests, the sharpness of the edge 10 is verified by a rope model that has already been tested. The edge 10 remained unchanged.

The first test rope was a prior art rope designed to EN892 with a diameter of 9.8mm. This was a core-sheath rope with a polyamide sheath. The deflection angle was 45°. A fracture length of approx. 200 cm could be achieved.

The second test rope was a rope according to the invention with aramid in the intermediate sheath in the construction according to the invention, designed according to EN892 with a diameter of 9.8 mm. A fracture length of approx. 340 cm could be achieved. The breaking length could thus be increased by 70% compared to the rope according to the prior art.

Claims (14)

Rope (1) made of textile fiber material, comprising a rope core (2) and a sheathing (3) surrounding the rope core (2),
characterized in that
the sheath (3), an intermediate sheath (4) located between the sheath (3) and the cable core (2) and/or a reinforcement located between the sheath (3) and the cable core (2), a twine (6) with excess length ( Δ) includes,
the overlength (Δ) thread (6) being formed by comprising at least a first yarn (7) and a second yarn (8) which are twisted together, the first yarn (7) having a greater length than that second yarn (8) measured in an untwisted state of a unit length of the thread (6). Rope (1) according to claim 1, wherein the first yarn (7) comprises high-strength fibers, preferably p-aramid fibers, m-aramid fibers, LCP fibers, UHMWPE fibers or PBO fibers. Rope according to claim 1 or 2, wherein the second yarn (8) comprises non-high-strength fibres, preferably PA fibres, PES fibers or PP fibres. Rope (1) according to one of claims 1 to 3, wherein the first yarn (7) is at least 5%, preferably at least 8%, particularly preferably at least 12% longer than the second yarn (8), measured in the untwisted State of the unit length of the thread (6). Rope (1) according to one of claims 1 to 4, wherein the proportion by weight of the first yarn (7) in the twisted thread (6) with excess length (Δ) is 30% to 90%, preferably 40% to 75%. Rope (1) according to one of Claims 1 to 5, the proportion by weight of the thread (6) with excess length (Δ) in the sheath (3), in the intermediate sheath (4) and/or in the reinforcement being 50% to 100% of the Sheathing, the intermediate shell or the reinforcement is. Rope (1) according to one of Claims 1 to 6, in which the rope core (2) is made up of one or more twisted or braided cores (5). Rope (1) according to one of claims 1 to 7, wherein the rope core (2) comprises non-high-strength fibers, preferably PA fibers, PES fibers or PP fibers. Rope (1) according to claim 8, wherein the rope (1) is designed as a climbing rope according to the EN892 standard. Rope (1) according to one of claims 1 to 7, wherein the rope core (2) comprises high-strength fibers, preferably aramid fibers, UHMWPE fibers or PBO fibers. Cable (1) according to one of claims 1 to 10, wherein the diameter of the cable is 5 mm to 60 mm, preferably 5 mm to 13 mm. Use of a rope (1) according to Claim 8 or 9 as a climbing rope. Method for producing a twisted yarn (6) with excess length (Δ) for a rope (1) according to one of Claims 1 to 11, comprising the steps: - Providing the first yarn (7) and the second yarn (8); - twisting the first yarn (7) with the second yarn (8); wherein the first yarn (7) and the second yarn (8) are twisted together at substantially the same tension and length and the twine (6) is subjected to a shrinkage process after twisting; or wherein the first yarn (7) and the second yarn (8) are twisted together with different tension and the twisted yarn (6) is relaxed after twisting. A method according to claim 13, wherein the shrinking operation is carried out in an autoclave.

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