Title of Invention

PROCESS AND APPARATUS FOR MANUFACTURING CHOPPED THERMOPLASTIC FIBRES

Abstract

Process for manufacturing chopped thermoplastic fibres, in particular chopped glass fibres in an apparatus disposed downstream of a manufacturing plant, the apparatus comprising atleast one blade-holder wheel having blades on its periphery, a feed roller, an anvil wheel having a coating, and an abrasive means, the blade-holder wheel and the anvil wheel in the rotating phase simultaneously contact each other to constitute a chopping area, characterized in that atleast part of the peripheral surface of the anvil wheel in contact with the blade-holder wheel is directly machined on the abrasive means to compensate the wear, and in that the machining comprises in reducing the thickness of the anvil wheel.

Full Text

PROCESS AND APPARATUS FOR MANUFACTURING CHOPPED THERMOPLASTIC FIBRES The present invention relates to a process for manufacturing chopped thermoplastic fibres, especially chopped glass fibres, in which the thermoplastic fibres are chopped in a region where at least an anvil wheel and a blade-holder wheel, rotating simultaneously, are in contact with each other. Although not limited to such an application, the invention will more particularly be described with reference to the manufacture of chopped glass fibres made directly beneath bushings. For this type of application, it is well known to cut the glass fibres continuously by using a chopping assembly consisting of two contacting wheels, one called the anvil wheel and the other the blade-holder wheel. This chopping assembly must both: - draw several continuous glass fibres coming from bushings at a high rate of about one or more tens of metres per second; - chop each glass fibre into fragments of predetermined length. A major problem encountered during the aforementioned manufacture is associated with the phenomenon of relative wear of the contacting wheels, this being greater the higher their speed of rotation and the higher the contact pressure between them. In particular, wear occurs rapidly and progressively, on the one hand, of the cutting edge of the blades, and, on the other hand of the external peripheral surface of the anvil wheel made of an elastomer of the polyurethane type. Such wear means that the contact between the two wheels becomes less and less suited to drawing the glass fibres correctly and that the deformation applied by each of the blades to the external peripheral surface of the anvil wheel no longer allows the fibres - 2 - to be broken cleanly. Consequently, the quality of the chopped fibres produced deteriorates progressively. Hitherto, this difficulty has been overcome firstly by accepting a somewhat degraded quality of chopped fibre and then, when this degradation is excessive, by stopping the production so as to carry out a wheel change quite frequently. Quite obviously, this change is detrimental to the production yield. The object of the invention is therefore to improve the production yield of chopped fibres of the type mentioned above without thereby degrading the quality set. To do this, the subject of the invention is a process for manufacturing chopped thermoplastic fibres, especially chopped glass fibres, in which the thermoplastic fibres are chopped in a region where at least an anvil wheel and a blade-holder wheel, rotating simultaneously, are in contact with each other, characterized in that at least part of the peripheral surface of the said rotating anvil wheel in contact with the blade-holder wheel is machined so as to compensate for its wear. The machining consists in reducing the thickness of the anvil wheel and, advantageously, by grinding the peripheral surface of the wheel. The direct in-production machining proposed by the invention is a simple and effective solution to the problem posed. To achieve this solution, the inventors have been able to demonstrate that the wheel change mentioned in the preamble was above all necessitated only for the anvil wheel, the wear of the material (polyurethane) of which its external peripheral surface is composed being unacceptable, while the potential of the cutting edge of the blades was not used to its maximum extent. They have therefore discarded the solution consisting in formulating a more wear-resistant material, this solution being tricky to - 3 -develop and difficult to apply under industrial conditions. There are many advantages provided by the invention. First of all, because of the direct machining, the frequency of wheel changes is considerably reduced, hence a significant increase in production time. Moreover, this increase is all the greater since the production is not interrupted during direct machining. Next, the costs associated with equipment consumption are also considerably reduced. In fact, according to the prior art, the cost of consumables associated with frequently reconditioning the wheels was far from being negligible, especially by frequently putting the anvil wheel on a conventional machining device, such as a lathe, etc. Furthermore, the quality of the chopped fibre obtained is much more constant. In addition, direct machining makes it possible to ensure that there is always perfect coaxiality between the external peripheral surface of the anvil wheel and the rotation spindle which supports it, something which might not be the case according to the prior art insofar as, especially when refitting the anvil wheel whose wear had been compensated for on a conventional machining device, there was always a risk of the axis of symmetry of this wheel not being coincident with the aforementioned rotation spindle. Finally, regenerating as it were the external peripheral surface of the anvil wheel results in a reduction in the wear of the blades, this wear being much less since they no longer suffer abrasion due to the thermoplastic particles resulting from the chopping, which particles are no longer able to become embedded in this same surface. According to an advantageous characteristic of the invention, the fibres are drawn using the assembly formed by the anvil wheel and the blade-holder wheel. _ 4 - Preferably, prior to chopping, the thermoplastic fibres are arranged in such a way that they bear on part of the peripheral surface of one of the wheels, preferably the anvil wheel. Such an arrangement helps in the frictional drawing and entrainment of the fibres on the anvil wheel. Preferably still, the thermoplastic fibres are obtained by a direct fiberizing process. The invention also relates to an apparatus for implementing the process that has just been described. This apparatus is noteworthy in that it comprises: - at least an anvil wheel and a blade-holder wheel in contact with each other; - means for machining at least part of the external peripheral surface of the anvil wheel. Advantageously, the apparatus furthermore comprises means for arranging the fibres such that they bear on part of the peripheral surface of one of the wheels, preferably the anvil wheel. According to another characteristic of the invention, the anvil wheel consists of a roll covered over at least part of its circumference with a covering made of a polymer material, especially an elastomer of the polyurethane type. Advantageously, the means for carrying out the machining of the aforementioned apparatus comprise at least one abrasive wheel. Of course, the means for carrying out the machining may comprise a cutting tool such as a blade. However, the abrasive wheel is perfectly suited to the machining according to the invention insofar as it constitutes a simple and compact tool capable of "regenerating", that is to say making uniform again, the external peripheral surface of the anvil wheel running with a high peripheral velocity. According to an additional characteristic, the said abrasive wheel consists of a cylinder, preferably made of metal, the peripheral surface of which is covered with a multitude of grit par tides, of the - 5 -diamond type. This particular grinding-wheel structure makes it possible to abrade without the risk of slip between the surfaces in question. According to another characteristic, the means for carrying out the machining furthermore comprise means for moving the said abrasive wheel. These means must specially allow the grinding wheel to machine over the entire peripheral surface simultaneously, working in so-called plunge-grinding mode. In order to further optimize the work of the machining means, the operation and, where necessary, the movement of the means for carrying out the machining is (are) slaved to means for checking the external peripheral surface finish of the anvil wheel, such as an optical sensor or a roughness measurement sensor, or to means for checking the quality of the chopped fibres. In order to avoid any risk of the particles resulting from the machining fouling the various surrounding elements and, as the case may be, getting mixed up with the end-product, it is preferable for the apparatus to furthermore comprise means for collecting them. These particles may either be "chips" coming from particles of elastomer or may be abrasive particles liberated from the abrasive wheel. These recovery means may preferably consist of at least one suction nozzle, preferably located immediately downstream of the means for carrying out the machining. The term "downstream" should be understood to mean here the relative position with respect to the direction of rotation of the anvil wheel. In fact, the position of the suction nozzle will be advantageously chosen depending on the main direction of ejection of the particles resulting from the machining. This direction will, of course, depend on the direction of relative rotation of the grinding wheel with respect to that of the anvil wheel, as well as on the value of its relative velocity. - 6 - As mentioned previously, the invention is particularly applicable to the manufacture of chopped glass fibres made directly beneath bushings, especially those having a fibre diameter of between 5 and 24 µm and/or or those having a length of between 1.5 and 15 mm. Further details and advantageous characteristics will emerge from reading the detailed description of an illustrative but non-limiting example with reference to the figures which show: - Figure 1: a diagrammatic representation of a plant for manufacturing chopped glass fibres directly beneath bushings, comprising an apparatus according to the invention; - Figure 2: a diagrammatic representation of an apparatus according to the invention. Figure 1 is a diagrammatic view of a plant for manufacturing chopped glass fibres directly beneath bushings. This plant 1 comprises a series of bushings 2 from which are continuously drawn glass fibres 3, and a chopping assembly 4 lying downstream of the plant with respect to the fibre-drawing direction. Each bushing 2 supplied with molten glass by a feed device {not shown) is provided in its lower part with a multiplicity of orifices from which a large number of fibres 5 are gathered in the form of sheets. These fibres are then coated with a size, in a manner known per se, by means of a coating device 6, and finally are gathered in the form of fibres 3 with the aid of small combining rollers 7. The fibres 3 thus formed are brought, after passing over small deflection rollers 8, to a guiding device 9 and are introduced into a chopping machine 10 according to the invention, explained in detail below. The chopped fibres 11 are collected by a receiving device 12. Figure 2 is a. diagrammatic representation of the chopping machine 10 according to the invention. This chopping machine 10 first comprises a blade-holder - 7 -wheel 13 and an anvil wheel 14, and a small feed roller 15 which in particular allows the fibres 3 to bear on the peripheral surface of the anvi 1 wheel 14 over a great length and therefore to be drawn and entrained by-friction. The blade-holder wheel 13 is provided on its periphery with blades (not shown). The anvil wheel 14 is coated with an elastomer cover 17 having a thickness e0 moulded on a metal mandrel 18. The rotating wheels 13 and 14 are in contact with each other in such a way that the contact area is also the chopping area. According to the invention, this chopping machine 10 comprises, in its lower part, an abrasive device 19 in a region where there is no risk of disturbing the chopping of the fibres 3. This abrasive device 19 is capable of machining the external surface of the elastomer cover 17 of the anvil wheel 14 so as to smooth the surface, by reducing its thickness. This device comprises an abrasive wheel 2 0 in the form of a metal cylinder, the peripheral surface of which is covered with a multitude of diamond grit particles, placed in the terminal part of a lever arm 21, the movement of which allows the said grinding wheel to come into contact with the aforementioned elastomer cover 17. It also comprises a suction nozzle 22 placed in the immediate vicinity of the cover 17. The operation of the chopping machine 10 according to the invention will now be explained. It should straightaway be pointed out that it is not the manner in which the chopping is carried out that is described but rather the mode of action of the abrasive device 19. Placed downstream of the receiving device 12 are means allowing the density of the chopped fibres 11 to be checked and monitored over time. Reduction in the density is directly related to the degradation of the surface finish of the aforementioned elastomer cover 17. When the density falls below a predetermined minimum threshold, the operation of the abrasive wheel 20 is initiated, as well as the rotation of the lever - 8 -arm 21 so that the grinding wheel passes from its initial position Po away from the elastomer cover 17 to its final position P1 which brings it into contact with the said cover and allows it to perform plunge grinding. This contact lasts for a predefined period of time, long enough to remove from the periphery of the cover 17 an amount of elastomer such that the surface finish of the latter becomes uniform again, its thickness going from eo to ei. It goes without saying that many modifications may be made without thereby departing from the scope of the invention. 9 We Claim 1. Process for manufacturing chopped thermoplastic fibres, in particular chopped glass fibres in an apparatus disposed downstream of a manufacturing plant, the apparatus comprising atleast one blade-holder wheel having blades on its periphery, a feed roller, an anvil wheel having a coating, and an abrasive means, the blade-holder wheel and the anvil wheel in the rotating phase simultaneously contact each other to constitute a chopping area, characterized in that atleast part of the peripheral surface of the anvil wheel in contact with the blade-holder wheel is directly machined on the abrasive means to compensate the wear, and in that the machining comprises in reducing the thickness of the anvil wheel. 2. Process as claimed in Claim 1, wherein the machining comprises in grinding the peripheral surface of the anvil wheel. 3. Process as claimed in Claim 1, wherein the fibres are drawn using an assembly formed by the anvil wheel and the blade-holder wheel. 4. Process as claimed in Claim 1, wherein prior to chopping, the thermoplastic fibres are arranged in such a way that they rest on part of the peripheral surface of one of the wheels, preferably the anvil wheel. 5. Process as claimed in one of Claim 1 to 4, wherein the thermoplastic fibres are fibres obtained by a direct fiberizing process. 1. 10 6. Apparatus for implementing the process as claimed in any one of Claims 1 to 5, comprising: - at least one anvil wheel (14) and a blade-holder wheel (13) in contact with each other; - means (19) for machining at least part of the external peripheral surface of the anvil wheel. 7. Apparatus as claimed in Claim 6, comprising means (15) for arranging fibres (3) such that they rest on part of the peripheral surface of one of the wheels (13,14), preferably the anvil wheel (14). 8. Apparatus as claimed in Claim 6 or 7, wherein the anvil wheel (14) consists of a roll (18) covered over at least part of its circumference with a coating (17) made of a polymer material, especially an alastomer of the polyurethane type. 9. Apparatus as claimed one of Claims 6 to 8, wherein the means (19) for carrying out the machining comprise at least one abrasive wheel (20). 10.Apparatus as claimed in Claim 9, wherein said abrasive wheel (20) consists of a cylinder, preferably made of metal, the peripheral surface of which is covered with a multitude of grit particle, of the diamond type. 11.Apparatus as claimed in Claim 9 or 10, wherein the means (19) for carrying out the machining comprise means (21) for moving the said abrasive wheel. 11 12. Apparatus as claimed in any one of Claims 6 to 11, wherein the operation and, where necessary the movement of the means (19) for carrying out the machining is not clearly worded to means the external peripheral surface finish of the anvil wheel, such as an optical sensor or a roughness measurement sensor, or to means for checking the quality of the chopped fibres. 13. Apparatus as claimed one of in Claims 6 to 12, comprising means (12) for collecting the particles resulting from the machining. 14. Apparatus as claimed in Claim 13, wherein the collecting means (12) consist of at least one suction nozzle (22), preferably located immediately downstream of the means (19) for carrying out machining. 15. The process as claimed in claim 1 for manufacturing chopped glass fibres made directly beneath bushings, those having a fibre diameter between 5 and 24 mm and having a length between 1.5 and 15 mm. Process for manufacturing chopped thermoplastic fibres, in particular chopped glass fibres in an apparatus disposed downstream of a manufacturing plant, the apparatus comprising atleast one blade-holder wheel having blades on its periphery, a feed roller, an anvil wheel having a coating, and an abrasive means, the blade-holder wheel and the anvil wheel in the rotating phase simultaneously contact each other to constitute a chopping area, characterized in that atleast part of the peripheral surface of the anvil wheel in contact with the blade-holder wheel is directly machined on the abrasive means to compensate the wear, and in that the machining comprises in reducing the thickness of the anvil wheel.

Documents:

00662-cal-1999 abstract.pdf

00662-cal-1999 claims.pdf

00662-cal-1999 correspondence.pdf

00662-cal-1999 description(complete).pdf

00662-cal-1999 drawings.pdf

00662-cal-1999 form-1.pdf

00662-cal-1999 form-18.pdf

00662-cal-1999 form-2.pdf

00662-cal-1999 form-3.pdf

00662-cal-1999 form-5.pdf

00662-cal-1999 letters patent.pdf

00662-cal-1999 p.a.pdf

00662-cal-1999 priority document.pdf