Patent Application
20140245577
The present invention refers to a method for the manufacturing of a semi-finished product starting from recycled carbon fibers, in particular a semi-finished product suitable for the subsequent obtainment of a yarn or of a so-called “tow”.
The high ratio between mechanical properties and weight causes Carbon Fiber-Reinforced Plastics (CFRPs) to be ever more successful, in terms both of variety of applications and of volumes of sale.
However, though it is true that composite materials using reinforcement carbon fibers and the related technical fabrics are increasingly considered as the materials of the future, the problem of disposal of components manufactured therewith at the end of their service life has not yet been posed nor addressed adequately.
For instance, to date CFRP and CF yarn manufacturing waste disposal occurred in a dump or by incineration. However, such solutions are very onerous, from both an economical standpoint and an ecological one.
Moreover, a few CFRP recycling techniques have been devised, some with the aim of separating the resin from the fibers, leaving the latter as intact as possible. An example in that sense is provided by WO 2003/089212, describing a CFRP incineration method aimed to remove the plastic matrix and recover fibers contained therein. With said process the recycled fibers obtained as output retain about the 80% of the mechanical properties of original fibers present in the composites treated. In general, fibers recovered with this method, taken individually, retain a fair part of the starting physical properties, but appear entangled and possibly contaminated by other materials and dusty residues. In addition, since waste undergoes a grinding treatment before being processed, fiber length is extremely variable.
Moreover, the problem of the effective re-use of recycled fibers in an industrial field, i.e. of the manufacturing of semi-finished products directly usable in a primary production chain, remains anyhow open. In this connection, besides the afore-mentioned drawbacks there should also be considered:
Therefore, the technical problem set and solved by the present invention is to provide a method for the manufacturing of semi-finished products starting from recycled carbon fibers, overcoming the drawbacks mentioned above with reference to the known art.
Such a problem is solved by a method according to claim 1 and by an apparatus according to claim 15.
Preferred features of the present invention are the subject of the dependent claims.
It will be understood that, in the present context, by “recycled” carbon fibers are meant fibers recovered from other applications, in particular both pre-treated at the end of the service life of a finished product, and virgin fibers discarded from other processings.
The invention allows to obtain, starting from recovered carbon fibers, semi-finished products suitable for the manufacturing of new finished quality products. In particular, the method and the apparatus of the invention make the recovered fibers, with a particularly reduced length, suitable for spinning processes, overcoming the workability problems mentioned above with reference to the known art and enabling the manufacturing of finished textile manufacts of various kinds, thereby fostering recovered fibers reintroduction on the market.
In the semi-finished products obtained with the invention, carbon fibers are in a shape substantially aligned, or anyhow have a main direction of orientation, and discontinuous, i.e. there are various fiber segments, aligned with ends overlapped. Thanks to the method and apparatus of the invention, the fibers in the semi-finished product have a degree of alignment comparable with that of virgin fibers. As is known, fiber alignment along the direction of the stress enables to enhance the performance contribution of the fibrous phase itself.
An example of privileged industrial application of the semi-finished products obtained with the invention is the manufacturing of reinforcement members of composite materials.
In particular, reinforcement fabrics can be manufactured which are able to optimally adjust to complex-shape molds, giving to the composite an adequate resistance even in zones with a very strong radius of curvature.
In the known art, such complex shapes are obtained starting from yarns of virgin and continuous carbon fiber, which are subjected to a lengthening process until attaining a yarn comprised of randomly broken filaments, referred to as SBCF (Short Broken Carbon Fiber). Thus, relative motions among the filaments themselves are allowed. This technology, however, entails the limitation of a scarce predictability in fibers lengths, and of the increase in production expenses, due to the remarkable cost of yarns of virgin carbon fiber.
Instead, as mentioned above, in the semi-finished product of the invention the fibers are already in discontinuous form. Therefore, the resulting fabric exhibits a “pseudo-ductility”, similar to that of metals, which greatly facilitates the formability of complex-shape components, by accelerating lay-up operations and remarkably reducing wrinkling in the reinforcement of the composite material.
Therefore, the method of the invention allows to attain substantially the same features of discontinuity and alignment of the known virgin fiber yarns, but at a remarkably reduced cost and with a good control of fiber length.
Moreover, pre-forms obtained starting from the method of the invention can effectively be dimensionally stabilized by organic or inorganic yarns.
Furthermore, association with suitable thermoplastic yarns allows to enhance some properties of the CFRPs manufactured with such pre-forms, such as, e.g., tenacity and flame-retardant aptitude.
As mentioned above, the fibers recovered and made workable with the method of the invention are usable at a cost remarkably lower than with the use of virgin carbon fiber, though providing comparable performances.
The invention enables a remarkable cost reduction, both on the economical and the environmental sides, also since it avoids having to dispose of in a dump, or send to incineration, CFRP products or waste, or waste from the processing of yarns and manufacts of virgin carbon fiber.
In a preferred variant embodiment, the semi-finished product of the invention is subjected to a spinning processing with discontinuous cutting.
In another preferred variant embodiment, the semi-finished product of the invention is hot-cohesioned by application of additives, or cohesioning materials in general, to obtain as output a web or tow.
The yarn, web or tow obtained downstream of such processings has physical-mechanical performances adequate to a use in the field of functional textile manufacts, which may also be utilized as reinforcement for composite materials having a polymeric matrix. Moreover, as already mentioned above, the textile manufacts, being manufactured from aligned and discontinuous carbon fibers, exhibit interesting features in term of drapeability.
Other advantages, features and operation steps of the present invention will be made apparent in the following detailed description of some embodiments thereof, given by way of example and not for limitative purposes.
Reference will be made to the figures of the annexed drawings, wherein:
Referring initially to
Correspondingly,
In the present embodiment of method and of apparatus, these work on carbon fibers as provided as output by the method of which at the aforecited WO 2003/089212, incorporated herein by this reference. In particular, in the present example recovered carbon fibers, initially in the form of tuft or cloth, are considered.
In general, as mentioned hereto, the method and the apparatus of the invention are suitable to the treatment of carbon fibers recovered from the recycle of composite materials or waste from the processing of virgin carbon fibers.
Thus, referring to
Preferably, the pitch of the blades of the cutter 102, their cutting rate and/or the fiber feed rate are adjustable so as to allow a corresponding adjustment of the length of the cut fibers being output.
The minimum length of the carbon fibers that can be treated with the method and the apparatus considered herein is, downstream of the cutting step, of about 30 mm. Accordingly, there is a considerable increase in the amount of carbon fibers that can be spun.
In general terms, the fibers being output from said cutting step have a length comprised in a range of about 30-60 mm.
Cut fibers are then collected, preferably always by an automatic extraction system 103 and, e.g., of conveyor belt type, and fed to an opening unit 104 for opening the tufts/cloths, so as to blend the fibrous blanket for a first time. To this end, the device 104 is typically a rag-grinding machine or carding willow.
Thus the fibrous mass is refined, obtaining also a first step of partial parallelizing of the fibers.
In a subsequent enzyming step, the fibrous mass is inlet—preferably by mechanical and/or pneumatic transport means and/or—into a hopper 105 of an enzyming unit 106. In the latter, the fibrous mass is sprayed by nozzles, which nebulize a (typically water-emulsified) product having a twin power: the product fosters fiber sliding and abates electrostatic charge. In this step, there may also be envisaged the applying of a substance which improves the adhesive properties of the carbon fiber, as is the case for virgin fibers on which a substance, generally of epoxy type, referred to as “sizing” is deposited.
The enzyming step is of remarkable significance, as it provides fibers more mechanically protected, more slidable and less electrostatic for the subsequent treatment and processing steps.
The fibrous mass is then subjected to a step of blending with auxiliary fibers in a suitable unit 107. In this case as well, the fibrous mass can be automatically fed to the blending unit 107, by a conveyor belt or an equivalent means.
The percentage of auxiliary fibers added to the mass of carbon fibers being input can be variable and adjustable, depending on the processing specifications and in particular on the textile manufact that is to be obtained as output, so as to obtain a homogeneous material able to guarantee even distribution of reinforcement carbon fibers in the semi-finished end product.
Auxiliary fibers may be of organic nature, as well as of inorganic nature. By way of a non-limiting example there are reported as auxiliary fibers, e.g.: thermoplastic fibers of polyester, PEEK, co-PES, co-PA, PP, PE, PS, PVA type; natural fibers of cotton, hemp, linen type; metallic fibers, glass fibers and aramid fibers.
The auxiliary fibers may have a supporting function for the subsequent steps, in particular a spinning step which will be introduced below, and/or also give specific functional properties to the semi-finished product that is output and to the fabric or manufact manufactured therewith.
The blended fibrous mass is then subjected to a parallelizing operation in a suitable unit 108. In a particularly preferred embodiment, such parallelizing step is a (preferably double) carding step, carried out in a suitable carding machine, at the output of which just a carded material, definable as film or web, is obtained.
A preferred embodiment of said carding unit 108 is shown in
A drum 4 rotates clockwise and has clothing points (with a special profile ensuring maximum holding of the fibers) tilted in the same sense of the motion (i.e., the points work in the positive sense of the motion). To be able to make fibers elementary, in order to have them set for carding and therefore for a further parallelizing, disentangling the same from tangles or thickenings yet unopened or compact, it is necessary that the clothing be particularly thick (about 600 points/in2) and have a working angle of about 25°.
A carding segment 5—interchangeable according to the grade of the material treated (processing scraps or fibers recovered from CFRP)—has the purpose of parallelizing the fibers even more, reducing their mass, uniformly distributing them on the drum 4, thereby facilitating the task of the actual carding.
The carding action, enabling the feed and the partial parallelizing of the fibers, is increasingly ensured by the further carding sectors 6, 8, 10 and 12 set at an adjustable distance from the drum 4; such a distance or adjustment will be all the more narrow the more the fiber output zone is approached (as an indication, 25 to 12 thousandths of inch). The drum 4, thanks to its large diameter and its rate, creates a centrifugal force that enables fibers, on the one hand, to be held by the clothing, and, on the other hand, to be carded by the carding sectors themselves. The clothings exhibit a point thickness progression toward the outlet, carrying out a gradually more marked parallelizing of the fibers.
Each carding sector, therefore, has a more intense action depending on the number of points per square inch and on the tilt of the same points with respect to those of the drum 4. Between one sector and the other one there are open slits 7, 9 and 11, preferably of 10-20 mm of width, each of which—by a special profile called “presser or tegolino”—is able to separate the fraction of short fibers (or broken fibers) and the carbon dust generated during the carding step, dust which would prove damaging for the subsequent processings. A suction system guarantees removal of these particles, making more compact and even the material on the drum.
Another carding system 13, of a typology analogous to the segment 5, but with a clothing with thinner and thicker-populated points, set at the outlet of the drum 4, enables a further parallelizing of the fibers, by disentangling the last possible fibrous thickenings. As to fiber transit, fibers held on the clothing of the clockwise-rotating drum 4 pass on an unloading cylinder 14. The latter rotates counterclockwise, and has points which grab the fibers, holding them by friction, condensing them thereon due to the big difference in peripheral velocities of the two bodies.
Unloading of carded material occurs thanks to a film-detaching device 15 working synergistically with the unloading cylinder 14. When being output from the device 15, the semi-finished product is in the form of a compact film of fibers.
The film thus obtained could be collected and set aside for a new carding step utilizing the same process, thereby obtaining the above-mentioned double carding. Such operation might be carried out by a “tandem card” carding system, known per se and shown by way of example in
The film being output from the single or double carding step is comprised of fibers by now well-parallelized, and could be forwarded to intermediate finishings in the form in which it is manufactured.
The carding by carding segments or plates is specifically suitable to be able to process short fibers having a high ultimate strength, but fragile like carbon ones are, even when blended with other fibers, be them natural, organic and inorganic.
In a variant embodiment, said film is entrained to a very simple and reduced drawing system 16, thereby undergoing a drawing step. The drawing system 16 operates a reduction, or condensation, of the fibrous bundle in order to obtain as output of the same drawing system a fibrous web. Being output from such a drawing system 16, the semi-finished product is in the form of a web.
The use of a large-diameter cylinder 4 with clothings of special rubbers, or equivalent means apt to guarantee the abatement of electrostatic charges, fosters drawing.
The preparation to the spinning is carried out in a unit 109, through the use of a very simple and reduced drawing system which preferably enables the fibers to be drawn by a twisting system, forming a thin web, or wick.
The wick thus obtained is set on special supports apt to the unwinding of the same wick. Such supports are an integral part of a feed system for the feeding of a cylinder spinning machine 110 or of an equivalent device.
Referring to
The yarn being output from the spinning machine 110 will be collected on suitable supports, apt to facilitate yarn unwinding for further processings. The operations subsequent to spinning require yarns with a good ultimate strength and a determined size (count). The yarn could then be subjected to two- or plural-strand coupling and be subjected to twisting, or be coupled and twisted with other typologies of yarns or filaments having specific properties selected depending on the purpose to which the end product will be intended for. The yarn thus obtained could in turn be twisted again in order to obtain a simple-twist thread or a cord (twist of plural twisted threads).
On the basis of a second variant, corresponding to the left-side branch of
As to the film-forming step, this is carried out in a relevant device 111 by using a cohesioning material, e.g. a thermoplastic material, a resin or a combination thereof, in the form of fibers or liquid or solid additives. Thus, it is obtained just a fiber film that is then continuously fed to an activation unit 112, suitable to activate the cohesioning material and therefore to bring about the actual cohesion of the web. E.g., when the cohesioning material is a thermoplastic, a heating unit will be resorted to.
Thus, a semi-finished product is obtained which, cut e.g. in a thread-shaped or web-shaped manner in a unit 113, represents a valid alternative to the twisted yarn obtained with the first variant embodiment described above.
The yarn, tow or web provided by the above-described apparatus and method can be managed as standard semi-finished products of continuous fiber, and therefore can undergo subsequent weaving processes with optional subsequent pre-impregnation.
Such semi-finished products allow the design and manufacturing of novel materials having selected properties of strength, ductility and/or tenacity, even with respect to the different directions, concomitantly optimizing the use of the single components, both in mechanical and quantitative terms. Therefore, it is evident that a composite thus manufactured, properties being equal, is also lighter in weight than a traditional material.
A particular application of the auxiliary fibers consists in the supporting of the spinning for the obtainment of 100% carbon fiber yarns; an example consists in the cotton that may be used as support fiber during the spinning step and after, when the manufact (thread or web) has been manufactured, it may be removed by acid attack, leaving the carbon fiber fabric unaltered. The same may hold true for the use of soluble or thermolabile auxiliary fibers. A particular application may be the use of thermoplastic-type auxiliary fibers soluble in the polymeric matrix of the end composite, enabling to increase the tenacity of the end manufact.
It will be understood that the devices and the units of the above-described apparatus 100 are equipped with means, per se known, suitable to prevent the carbon fiber, particularly conductive electrically and statically, from damaging related electrical parts, control systems and/or safety devices. Hoods, shields, protections, wirings and the like are the most common known precautions for performing this task.
Some experimental results attained on an end product (the yarn), containing 40% by weight of recovered carbon fibers are discussed hereinafter, purely by way of a non-limiting example.
Table 1 reports the average features of tensile strength of the carbon fibers recovered by the thermal treatment of which at WO 2003/089212 and utilized for the manufacturing of a yarn following the preferred embodiment of the method discussed above.
The characterizations of the individual filaments have been carried out on two test lengths (10 and 40 mm), with 20 test pieces per each length according to standard ISO11566:1996 (“Carbon fibre—Determination of the tensile properties of single-filament specimens”).
Recycled composites consisted of epoxy resin reinforced with carbon fibers of ToraycaT800s type (Intermediate modulus, high tensile strength fiber), with the following features declared: Tensile Modulus: 294 GPa; Tensile Stress: 5880 s MPa; Filament Diameter: 5 μm.
The diagram of
Determination of carbon fiber content of the obtained yarn was carried out by tests performed with differential scanning calorimetric analyses and with thermogravimetric analyses.
Always from
The present invention has been hereto described with reference to preferred embodiments thereof. It is understood that other embodiments might exist, all falling within the concept of the same invention, as defined by the protective scope of the claims hereinafter.
| Number | Date | Country | Kind |
|---|---|---|---|
| RM2011A000520 | Oct 2011 | IT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2012/055298 | 10/3/2012 | WO | 00 | 4/2/2014 |
