Patent Application
20180023221
The present invention is related to a yarn construction comprising fibres A and at least one indicator fibre, wherein the indicator fibre comprises fibre B and an elemental metal at least partially coating the surface of fibre B. Such yarn constructions may be available in different forms, amongst others in ropes, straps, slings, fabrics and synthetic chains.
Yarn constructions from UHMWPE fibres such as ropes, slings, fabrics and synthetic chains are used in a multitude of applications such as lifting, securing, protecting loads, goods or people. Failure of said yarn constructions may result in substantial damage, replacement costs if not casualties.
Damages, especially when occurring through wear of the yarn construction can most often no be detected by contactless, visual inspection of the construction while a manual inspection is labor intensive and often subject to further deterioration of the yarn construction. Readiness for replacement is hence difficult to identify, requiring an additional safety margin at increased cost.
Monitoring systems for yarn constructions, especially for ropes and cables, have been reported in the past. These systems aim at providing improved detection and monitoring of the state of wear of the ropes and cables, allowing timely replacement.
Ropes and cables comprising conductive indicator yarns are for example known from EP 2499291. EP 2499291 describes a conductive monofilament or multifilament HPPE yarn and a rope or cable comprising the conductive HPPE yarn, whereby the aging of the rope could be tracked by the decrease of conductivity of the indicator yarn.
U.S. Pat. No. 8,360,208 describes monitoring the lifetime of a rope of an aramid fibres with an indicator yarn. The indicator yarn consisting of carbon indicator fibres surrounded by aramid fibres with a higher modulus of elasticity than the aramid fibres. The construction provides an early deterioration of the indicator yarn, resulting in a failure of a signal transmitted through the indicator yarn.
From EP 0731209 an layered aramid rope is known with carbon fibres present in each layer. The amount of snapped carbon fibres provides an indication of wear of the rope, assuring the residual load-bearing capacity of the synthetic fibre rope.
Although the yarn constructions described above represent improvements regarding lifetime monitoring of synthetic ropes and cables there is a constant demand for further improvements, especially there is a need for monitoring systems with less complex yarn constructions and/or increased adjustability.
Accordingly is it the aim of the present invention to provide a yarn construction with a further improved life-time monitoring. In particular it is an objective of the present invention to provide yarn constructions with a less complex construction, such as a reduced number of individual yarn components. A further objective of the invention may be to provide a yarn construction with broader diversity of the monitoring system.
Surprisingly the aim of the invention is achieved by a yarn construction comprising fibres A and at least one indicator fibre, wherein the indicator fibre comprises fibre B and an elemental metal at least partially coating the surface of the fibre B, wherein fibre A and fibre B are dissimilar ultra high molecular weight polyethylene (UHMWPE) fibres.
By fibre is herein understood an elongated body, the length dimension of which is much greater that the transverse dimensions of width and thickness. Accordingly, the term fibre includes filament, ribbon, strip, band, tape, and the like having regular or irregular cross-sections. The fibres may have continuous lengths, known in the art as continuous filaments or filaments, or discontinuous lengths, known in the art as staple fibres. A yarn for the purpose of the invention is an elongated body containing many individual fibres. By individual fibre is herein understood the fibre as such.
By yarn construction is herein understood a construction comprising or consisting of at least two yarns such as for example a braid, a textile, a woven, a non-woven, a knitted, a twisted, laid, parallel or otherwise formed structure.
In one embodiment of the present invention, the yarn construction such as a twisted, laid, braid, a textile, a woven, a non-woven, a knitted, a parallel or otherwise formed structure can be combined with other type of yarn. Preferably, the other type of yarn is a high-performance one such as for example, polyaramid yarns, polyamide yarns, teflon yarns, polypropylene yarns, etc.
The term yarn construction also encompasses an array of fibres such as a unidirectional (UD) monolayers. Unidirectional monolayers are produced by positioning yarns in parallel arrangement on a suitable surface and embedding the fibres in a suitable matrix material. The thus prepared network is unidirectionally aligned yarns in parallel to one another along a common yarn direction.
Preferably the yarn construction according to the invention is a rope, a sling, a fabric or a synthetic chain link. More preferably the yarn construction is a rope, wherein the rope contains a plurality of strands comprising the ultra high molecular weight polyethylene (UHMWPE) fibres A and B.
UHMWPE fibres are herein understood to be fibres made from ultra-high molar mass polyethylene and having a tenacity of at least 1.5, preferably 2.0, more preferably at least 2.5 or at least 3.0 N/tex. Tensile strength, also simply strength, or tenacity of fibres are determined by known methods as described in the experimental section. There is no reason for an upper limit of tenacity of UHMWPE fibres in the rope, but available fibres typically are of tenacity at most about 5 to 6 N/tex. The UHMWPE fibres also have a high tensile modulus, e.g. of at least 75 N/tex, preferably at least 100 or at least 125 N/tex. UHMWPE fibres are also referred to as high-modulus polyethylene fibres or high performance polyethylene fibres.
The UHMWPE yarns preferably have a titer of at least 5 dtex, more preferably at least 10 dtex. For practical reasons, the titer of the yarns of the invention are at most several thousand dtex, preferably at most 4000 dtex, more preferably at most 3000 dtex. Preferably the titer of the yarns is in the range of 10 to 10000, more preferably 15 to 6000 and most preferably in the range from 20 to 3000 dtex.
The UHMWPE fibres preferably have a filament titer of at least 0.1 dtex, more preferably at least 0.5 dtex, most preferably at least 0.8 dtex. The maximum filament titer is at most 50 dtex, preferably at most 30 dtex and most preferably at most 20 dtex.
The UHMWPE fibres may be manufactured according to any technique known in the art, e.g. by melt, solution or gel spinning. Preferably the UHMWPE filaments are manufactured according to a gel spinning process as described in numerous publications, including EP 0205960 A, EP 0213208 A1, U.S. Pat. No. 4,413,110, GB 2042414 A, GB-A-2051667, EP 0200547 B1, EP 0472114 B1, WO 01/73173 A1, EP 1,699,954 and in “Advanced Fibre Spinning Technology”, Ed. T. Nakajima, Woodhead Publ. Ltd (1994), ISBN 185573 182 7.
UHMWPE is understood to be polyethylene having an intrinsic viscosity (IV, as measured on solution in decalin at 135° C.) of at least 5 dl/g, preferably of between about 8 and 40 dl/g. Intrinsic viscosity is a measure for molar mass (also called molecular weight) that can more easily be determined than actual molar mass parameters like Mn and Mw. There are several empirical relations between IV and Mw, but such relation is dependent on molar mass distribution. Based on the equation Mw=5.37*104 [IV]1.37 (see EP 0504954 A1) an IV of 8 dl/g would be equivalent to Mw of about 930 kg/mol. Preferably, the UHMWPE is a linear polyethylene with less than one branch per 100 carbon atoms, and preferably less than one branch per 300 carbon atoms; a branch or side chain or chain branch usually containing at least 10 carbon atoms. The linear polyethylene may further contain up to 5 mol % of one or more comonomers, such as alkenes like propylene, butene, pentene, 4-methylpentene or octene.
Fibre A in the context of the present invention is the base fibre meaning that fibre A represent the main, constituting, principal fibre type of the yarn construction. Preferably the yarn construction comprises at least 60% by weight fibres A, more preferably at least 80% by weight, most preferably at least 90% by weight. Consequently is the indicator fibre in the context of the present invention a minor component of the yarn construction. Preferably the yarn construction comprises at most 40% by weight indicator fibres, more preferably at most 20% by weight, most preferably at most 10% by weight, wherein all weight percentages are expressed as the weight of the respective fibre to the total weight of the yarn construction. The yarn construction may further comprise auxiliary components to further enhance performance or give it some additional properties, as would be known to a skilled person.
In a further preferred embodiment, the yarn construction has a weight ratio of indicator fibres to fibres A of less than 0.1, preferably less than 0.05, more preferably less than 0.02 and most preferably less than 0.01. It was identified that larger ratios of fibre A to indicator fibres results in increased life time of the yarn construction while maintaining the ability to reliably monitor the life time of the construction.
In a preferred embodiment, the yarn construction according to the present invention comprises at least one yarn A and at least one indicator yarn, wherein the yarn A comprises UHMWPE fibres A and the indicator yarn comprises at least one indicator fibre. Preferably the yarn A substantially consists of UHMWPE fibres A and/or the indicator yarn substantially consists of indicator fibres.
The indicator fibre and indicator yarn in the context of the present invention comprise UHMWPE fibres as described above of which the surface is at least partially coated with an elemental metal. Not limiting examples of coated UHMWPE fibres and yarns are described in EP 2499291, which is incorporated herein by reference. The yarns disclosed in EP 2499291 comprise an elemental metal forming a layer that adheres to the surface of the UHMWPE fibres and covers at least partly the surface of the UHMWPE fibres. The elemental metal is deposited to the outer surface of a UHMWPE fibres via plasma sputtering. The indicator fibres and indicator yarns comprise an elemental metal once deposited to the yarn or fibres forms a layer that covers partly or fully the surface of the fibre or yarn. By partly is meant that the surface of the fibre or yarn presents bare parts. The latter are parts of the surface of the fibre or yarn where elemental metal is not deposited to them. By fully, is meant that the surface of the fibre or yarn does not present bare parts (as defined herein above). Random and usually occurring localized layer surface defects such as pin holing, cratering, etc. may exist in either partly or fully covered surface of an UHMWPE fibre or yarn.
The UHMWPE fibres B may be of continuous or discontinuous length, i.e. filaments or staple fibres. Though for some yarn constructions an indicator yarn with staple fibres B may be advantageous, for example for yarn constructions wherein fibre A is also a staple fibre, the yarn construction preferably comprises indicator fibres with continuous filament fibre B. The inventors identified that such indicator fibres have a wider range of application and in general deliver a better life time monitoring performance compared to staple indicator fibres.
An essential feature of the yarn construction of the present invention is that the UHMWPE fibre A and B are different. Herein is understood that the fibre A and B are not the same, i.e. can be distinguished from one another by at least one measurable feature. Such difference may for example be the result of a different production process, such as using different UHMWPE, using different spin solvents, applying different draw ratio during the spinning process, adding ingredients during the production process, etc. The skilled person will be aware of how to produce fibres that differ from on to another.
In particular, such dissimilarity between the fibre A and B can be expressed by the difference of a measurable fibre property. Such property of a fibre can typically be expressed in a numerical value. Examples of fibre properties are filament titer, fibre tenacity, fibre elongation at break, fibre tensile modulus, intrinsic viscosity of the UHMWPE. Accordingly is a preferred embodiment of the present invention that the fibres A and B differ by at least one property, the property being selected from the group consisting of filament titer, fibre tenacity, fibre elongation at break, fibre tensile modulus and intrinsic viscosity of the UHMWPE.
The difference in the at least one feature may thus be the result of a difference in the production process and is hence an intended difference of the fibres or yarns. By difference is herein not understood the differences that typically occur due to process fluctuations during a production process. Such differences resulting for example from a fluctuation during the manufacturing process are in principle small and would fall within the specifications of a commercial material. In contrast are the fibres or yarns according to the present invention different to a point to be fibres or yarns that can be identified as individual, separate products. Accordingly is it a preferred embodiment of the present invention that at least one ratio of a property of fibre B to the corresponding property of fibre A is at most 0.95, preferably at most 0.9, even more preferably 0.8.
Alternatively the difference of at least one fibre property may be expressed as a percentage difference. Such percentage difference is calculated by dividing the difference between property of fibre A and the corresponding property of fibre B by said property of fibre A, expressed in percent, herein referred to fractional difference or percentage differences. The concerned properties for the fibres are measured in the same way and expressed in the same units.
By different property as used herein is meant that the value of the relevant property of fibre B is at least 5% lower than the value of the fibre A, more preferably at least 10%, even more preferably at least 15%, most preferably at least 20%.
In one embodiment, the at least one difference between fibre A and fibre B may be the presence of fillers in fibre A and/or fibre B. Filler comprising fibres are for example known from EP2074248 and EP2815006 which are herewith included by reference. In a specific embodiment of the invention, the difference in fibre property is that the fibre B comprises more weight of filler than the fibre A. Preferably the fibre B comprises at least 2 wt %, more preferably at least 3 wt % and most preferably at least 4 wt % more filler than fibre A. All weight percentages are expressed as at the weight of filler present in the fibre divided by the total weight of the respective fibre, including the filler. It will be clear to the skilled person that the presence of filler in the fibre may affect further properties of the fibre and hence more than one difference in fibre property can potentially be identified. In a preferred embodiment, fibre A comprises less than 1 wt % of a filler, preferably fibre A comprises less than 0.5 wt % of filler.
By filler is herein understood particles present in the fibre different from UHMWPE, in a preferred embodiment the filler particles have a high hardness. Accordingly is a preferred embodiment of the present invention a yarn construction wherein the fibres B comprises filler with a hardness higher than the hardness of the fibre measured in the absence of the filler. The hardness as expressed herein can be measured by known methods, preferably the harnesses are expressed and compared to one another in Moh's hardness.
Preferably the filler has a Moh's hardness of at least 2.5, more preferably at least 4, most preferably at least 6. Typical fillers include, but are not limited to, metals, metal oxides, such as aluminum oxide, metal carbides, such as tungsten carbide, metal nitrides, metal sulfides, metal silicates, metal silicides, metal sulfates, metal phosphates, and metal borides. Other examples include silicon dioxide and silicon carbide. Other ceramic materials and combination of the above materials may also be used.
The particle size, particle size distribution, particle diameter and the quantity of the filler are suitable to affect mechanical properties of the fibre. The filler particles may be of substantially spherical shape, with an average particle size substantially equal to the average particle diameter. For particles of substantially oblong shape, such as needles or fibres, the particle size may refer to the length dimension, along the long axis of the particle, whereas the average particle diameter, or in short the diameter, refers to the average diameter of the cross-section which is perpendicular to the length direction of said oblong shape.
In a preferred embodiment of the invention, at least part of the filler particles has an aspect ratio of at least 3, more preferably the filler substantially consists of particles having an aspect ratio of at least 3. Such oblong filler particle shape showed to improve the responsiveness of the indicator yarn to mechanical stress of the yarn construction. The aspect ratio of a filler particles is the ratio between the length and the diameter of the hard fibre. The diameter and the aspect ratio of the hard fibres may easily be determined as reported in EP2815006.
Preferably the fillers of the fibres are produced out of glass, a mineral or a metal or are carbon fibres.
In one embodiment carbon fibres are used as the filler. Most preferably carbon fibres are used having a diameter of between 3 and 10 microns, more preferably between 4 and 6 microns. Molded articles containing the carbon fibres have increased electrical conductivity, and are particularly suitable as the fibre for the indicator yarn for rope constructions with lengths of more than 100, 500 or even 1000 meter.
Furthermore, for the yarn construction UHMWPE fibre A with very good performance properties under stress can be used. Such performance property can for example be creep, dynamic reverse bending capacity, elongation at break, abrasion resistance or tension-tension fatigue. The UHMWPE fibre B comprised in the indicator fibre and/or the indicator yarn will have a respective performance property under stress inferior to that of the fibre A. The skilled person dealing with yarn constructions for specific applications will be knowledgeable about dominant stress and failure mechanisms and will opt for a fibre A with high performance in said application. Accordingly will the skilled person also be aware of fibres with inferior performance to be employed as fibre B for the indicator fibre. Accordingly is another embodiment of the present invention a yarn construction wherein the fibre B is inferior to the fibre A in terms of withstanding a stress.
In a yet preferred embodiment the inferiority of fibre B to fibre A is expressed in that the flexural fatigue strength of the fibres B is inferior to the flexural fatigue strength of the fibres A, in that the elongation at break of the fibres B is inferior to the elongation at break of the fibres A, in that the resistance to abrasion of the fibres B is inferior to the resistance to abrasion of the fibres A, in that the tension-tension fatigue of the fibres B is inferior to the tension-tension fatigue of the fibres A or in that the creep rupture of the fibres B is inferior to the creep rupture of the fibres A. It was observed that flexural fatigue, yarn elongation, abrasion and creep rupture are dominant failure mechanisms of yarn constructions comprising high strength UHMWPE fibres. Especially ropes or related constructions are subject to fatigue due to repeated bending of the construction or to extension break due to high loads or prolonged operation under load. Failure of a yarn construction due to abrasion can be observed in yarn constructions for protective covers but also in outer layers of load bearing yarn constructions such as ropes and slings. Failure of yarn construction due to creep can be observed when the yarn construction is installed under a permanent tension. The present invention may provide a monitoring system for timely identifying the need for replacing a yarn construction before substantial damage occurs.
In the present invention withstanding a stress is expressed as a property of a fibre. It will be clear to the person skilled in the art that in some cases a stress can only be applied and the resistance to said stress only be measured on a fibre present in a yarn or even in a yarn construction such as a rope. By the expression that fibre B is inferior to fibre A in terms of withstanding a stress is hence understood that fibre A and B will be compared to one another as fibres, as yarns consisting of the respective fibres or in yarn constructions of said yarns of fibres.
The yarn construction may comprise other synthetic fibres next to the indicator fibres comprising fibre B and the fibre A. It was observed by the inventors that the performance of withstanding a stress and/or the properties of such other synthetic fibres is less critical for the functioning of the indicator yarn. In a preferred embodiment, the indicator yarn may comprise next to the elemental metal coated UHMWPE fibre B other synthetic fibres. Preferably the other synthetic fibres have a respective property at least equal to the property of fibre B and/or a performance of withstanding a stress at least equal to the performance of fibre B. Preferably the other synthetic fibre that may be present in the indicator yarn is fibre A or fibre B. Such yarn constructions have proven to be less complex and may have increased reliability of the service life indication of the yarn construction.
In a yet preferred embodiment of the invention the at least one indicator fibre or indicator yarn is twisted, laid or braided to form an assembled yarn of the yarn construction. Said assembled yarn may substantially consist of indicator fibres or may be combined with other synthetic fibres as described above to form the assembled yarn. In a further preferred embodiment the indicator fibre or indicator yarn is twisted, laid or braided with fibre A, with fibre B or with fibre A and fibre B to form an assembled yarn. By assembled yarn is herein understood an intermediate product comprising at least one yarn, the at least one yarn has been processed alone or in combination with other yarns.
In a further preferred embodiment, the yarn construction comprises a load carrying core which comprises at least one indicator fibre or indicator yarn. It is considered that especially the load carrying cores of yarn constructions, such as synthetic or hybrid ropes, slings or synthetic chain links, are subject to damages occurring through wear of the yarn construction. Said cores are substantially buried within the yarn construction, covered by further yarn layers, metal wires, resinous coatings etc. making a non-destructive, visible inspection utmost difficult. The present invention is thus especially suitable for monitoring life-time of such yarn construction comprising a load carrying core.
The yarn construction may comprise a plurality of yarn layers or strand layers. Each layer of the construction may include at least one indicator fibre or yarn so that progressive degradation of the yarn construction can be monitored and replacement of the yarn construction can be estimated. Accordingly is a specific embodiment of the invention a yarn construction comprising at least 2 indicator fibres or yarns asymmetrically positioned within the yarn construction. By asymmetrical positions is herein understood that the indicator fibres or yarns are located at positions that undergo a different stress under operation of the yarn construction. In the case the yarn construction is a rope, asymmetrically defines positions within the cross-section of the rope that ore not equidistant from the center of the rope. In the case the yarn construction is a fabric, asymmetrically defines positions within the fabric that are not equidistant from a reference surface of said fabric.
In a further embodiment, the yarn construction may comprise at least 2 distinct indicator fibres or yarns. The 2 distinct indicator fibres have distinct responsiveness to the stress applied to the yarn construction. Such distinct responsiveness may be achieved by indicator fibres comprising different UHMWPE fibres B wherein the difference is expressed by a measurable fibre property as yet described for the fibres B. The different responsiveness of the indicator yarn may also be achieved by assembling the indicator fibres alone or in combination with further synthetic fibres through twisting or braiding.
The invention will be further explained with the help of the following example and comparative experiment.
Preparation of silver coated fibres and indicator yarns
Two types of silver coated fibres have been prepared according to the method described in example 3 of EP 2499291. Silver coated fibres have been prepared starting respectively from the commercial UHMWPE yarn grades 3G12 1760 dtex and SK78 1760 dtex sourced from DSM Dyneema. The silver treatment was performed on a 220 dtex filament bundle resulting in silver coated filament bundle 1 (3G12) and 2 (SK78).
With these 2 silver coated filament bundles, 3 indicator yarns were assembled:
Indicator yarn 1: the silver coated filament bundle 1 was assembled with 20 tz from 8×220 dtex 3G12 80 tz to form a 1760 dtex silver coated indicator yarn.
Indicator yarn 2: the indicator yarn 1 was further assembled (4 st/cm, braided) with 3 3G12 1760 dtex yarns.
Indicator yarn 3: the silver coated filament bundle 2 was assembled with 20 tz from 8×220 dtex SK78 80 tz to form a 1760 dtex silver coated indicator yarn which was further assembled (4 st/cm, braided) with 3 3G12 1760 dtex yarns.
A rope with a diameter of 21 mm has been prepared comprising the above three indicator yarns. The rope construction was 12×1×7×15×1760 dtex SK78. To avoid the three indicator yarns contacting each other, the indicator yarns were inserted in the S-strands, with an indicator free S-strand between every indicator comprising S-strand. At the ends of the evaluated rope section, the indicator yarns have been exited from the rope construction and connected through copper wires to an adjustable power supply and LED indicator lights.
The rope with a maximum break load of 400 kN was subjected to a cyclic bending over sheave test until complete rupture with a stainless steel sheave of with a D/d of 20, a cycle frequency of 12 seconds and a bend zone of 420 mm under dry conditions. Cyclic Bending Over Sheave test machine sourced from Lucassen Metaalbewerking b.v., NL.
During the test, the load applied to the rope was ramped up (100 cycles at 10% MBL, 25 cycles at 15% MBL, 25 cycles at 20% MBL) to 25% of its MBL. The rope failed after a total of 1907 cycles.
The degradation of the rope was monitored by the 3 LED connected to the 3 indicator yarns. After 925 cycles the conductivity of indicator yarn 1 dropped, indicating failure of said indicator yarn at 49% of rope lifetime. Indicator yarns 2 and 3 failed after 1876 and 1899 cycles, i.e. 98 and 99% of the rope lifetime respectively, unacceptably late as an indicator for premature replacement of the rope in a real life application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15157133.8 | Mar 2015 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/054200 | 2/29/2016 | WO | 00 |
