WO2002055770A1

WO2002055770A1 - Method and device for cutting fibres

Info

Publication number: WO2002055770A1
Application number: PCT/NL2001/000763
Authority: WO
Inventors: Willem Frans Van Der Mast
Original assignee: Willem Frans Van Der Mast
Priority date: 2001-01-12
Filing date: 2001-10-16
Publication date: 2002-07-18
Also published as: NL1017098C2

Abstract

A method and a device for cutting glass fibres into pieces, wherein the fibres are passed between a knife roller and a pressure roller, which knife roller and which pressure roller rotate in opposite directions at substantially the same peripheral velocity, wherein the knives of the knife roller press the fibres into recesses in the pressure roller so as to break the fibres whilst the fibres are held in position between the pressure roller and pressure ribs disposed between said knives.

Description

METHOD AND DEVICE FOR CUTTING FIBRES
The invention relates to a method and a device for cutting glass fibres into pieces, wherein the fibres are passed between a knife roller and a pressure roller, which knife roller and which pressure roller rotate in opposite directions at substantially the same peripheral velocity, wherein the knives of the knife roller press the fibres into recesses in the pressure roller so as to break the fibres whilst the fibres are held in position between the pressure roller and pressure ribs disposed between said knives.

Glass fibres, hereinafter simply called fibres, can be divided into pieces of a specific length in this manner, which can subsequently be worked into a plastic, for example, for the purpose of reinforcing said plastic.

The fibres are supplied in long, more or less coherent bundles. The bundles are fed into a cutting device, in which the bundles are cut between the knife roller and the pressure roller, after which the pieces of fibre, which have a specific length, leave the cutting device.

Although the term cutting is used herein, the fibres are in fact broken as a result of being bent over the cutting edge of a cutting knife. The fibres are bent so strongly at the cutting edge that they break at that location. The cutting edge of the knife is not pressed against a surface which delivers a counterpressure, therefore, nor is the cutting edge moved along an edge so that a scissor-like (or cutting) operation is carried out as a result of shearing of the material.

In order to effect a sufficiently small radius at the location of the cutting edge of the knife so as to break the fibres, it is important that the fibres be properly stretched over the outer circumference of the pressure roller, whilst the knife moves into the recess in the pressure roller. The pressure ribs, which are disposed on either side of each knife on the knife roller, are capable of pressing the fibres against the pressure roller before and behind the knife (seen in the direction of movement of the knife). But especially if the knife roller and/or the pressure roller has (have) a small diameter, of if the bundle of fibres is relatively thick, there is a chance that the cutting edge of the knife will touch the fibres already before the pressure rib that is disposed behind the knife clamps the fibres against the pressure roller to a sufficient degree.

Such a situation will have a negative effect on the cutting operation, especially if not all the fibres extend fully in the longitudinal direction of the bundle.

The object of the invention is to improve the manner of processing the fibres, so that the fibres will be cut to the correct length in a more reliable manner.

Preferably, a stretching roller is provided for that purpose, which stretching roller mates with the pressure roller and which rotates in opposite direction at substantially the same peripheral velocity, wherein the fibres are first led between the stretching roller and the pressure roller and subsequently between the knife roller and the pressure roller. As a result, the bundle of fibres butts against the circumferential surface of the pressure roller already before the pressure rib that is disposed behind the knife in question clamps the bundle of fibres down.

As a result, the bundle is on the one hand correctly engaged by the pressure rib at all times, whilst on the other hand the bundle is prevented from sliding over the circumferential surface of the pressure roller in case the cutting edge of the knife should touch the bundle before the pressure rib that is disposed behind the knife clamps down the bundle to a sufficient degree.

In one preferred embodiment, the stretching roller is driven by the pressure roller, so that no special provisions for driving the stretching roller are required.

In one preferred embodiment, the dimensions of the rollers and the parts thereof are selected so that a knife of the knife roller will touch the fibres before the pressure rib that is disposed behind said knife makes contact with the pressure roller. In that case it is possible to use a limited number of knives, for example, because a relatively small diameter can be used for the knife roller. The fibres are thereby stretched between the pressure roller/stretching roller gap and the pressure rib disposed before the knife before the pressure rib disposed behind the knife clamps down the bundle of fibres to a sufficient degree.

Although it is possible to use a steel stretching roller having a smooth surface, for example, in particular if the counterpressure roller has a slightly elastic circumferential surface, the circumferential surface of the stretching roller is preferably elastic. The desired degree of elasticity can be obtained by forming the circumferential surface of the stretching roller from a sufficiently elastic material, but it is also possible to provide the material with recesses.

In one preferred embodiment, the hardness of the circumferential surface of the stretching roller ranges between 30 degrees and 120 degrees Shore A, preferably between 40 degrees and 100 degrees Shore A, more preferably between 60 and 80 degrees Shore A. In practice, satisfactory results have been obtained with therewith.

In one preferred embodiment, the circumferential surface of the stretching roller is provided with slots, preferably slots whose depth is greater than their width. This enhances the flexibility of the circumferential surface of the stretching roller.

Preferably, the slots extend at an angle with respect to the axial direction, preferably an angle of more than 5 degrees, more preferably an angle of more than 10 degrees. As a result, the slots extend more or less helically over the circumferential surface of the stretching roller.

In one preferred embodiment, the depth direction of the slots extends at an angle to the radial direction of the stretching roller, preferably an angle of more than 5 degrees, more preferably an angle of more than 20 degrees and even more preferably an angle of more than 30 degrees. As a result, the slot extends obliquely into the material of the stretching roller with respect to the local surface of the stretching roller, so that the circumferential surface can be compressed more easily.

In practice it has become apparent that the movement of the stretching roller surface in radial direction and in tangential direction that is caused by said slots prevents the roller from becoming fouled or, at any rate, prevents fibres from adhering to the surface.

The knives of the knife roller and the corresponding recesses in the pressure roller may extend at an angle with respect to the axial direction. Preferably, the slots in the circumferential surface of the stretching roller extend at a different angle in that case, with the angles differing from each other by more than 5 degrees, preferably by more than 10 degrees, more preferably by more than 20 degrees.

The shape of the pressure ribs of elastic material that are disposed between the knives on the knife roller is of importance in connection with obtaining a reliable cutting operation.

In one preferred embodiment, the pressure ribs are shaped in such a manner that the deformation of the elastic material upon being compressed substantially comprises the bending of a radially outwardly extending part of the pressure rib. As a result, the material is loaded in flexion more than in compression, which enables a greater movement at a substantially constant pressure force.

The aforesaid radially outwardly extending part of the pressure rib is understood to be the part that is located on the outside of the knife roller, which part need not extend in radial direction. Preferably, the pressure rib includes a radially outwardly extending part which is zigzaged in shape, seen in crosssectional view of the pressure rib. Said part may comprise a portion which has a substantially constant thickness, seen in cross-sectional view ofthe pressure rib. Preferably, said portion takes up more than half the length of said part.

A first portion of said zigzag shape of said outwardly extending part extends at an angle with respect to the radial direction, and a portion that is located further outwards extends obliquely in the other direction. As a result, the pressure rib can be compressed over a relatively large distance, whilst the pressure force does not increase significantly during said compression.

Furthermore, said part is swung slightly outwards as a result of the centrifugal action, which helps to keep the pressure rib clean.

In another preferred embodiment, the part of the pressure ribs that extends radially outwards over at least the larger part of its length has a crosssectional dimension that decreases in outward direction.

The pressure rib preferably has a saddle-shaped or spherical end adjacent to two conically extending side faces, which preferably extend as far as the knives. The deformation that is caused by the pressure roller is mainly the result of compression in this embodiment. A relatively small degree of compression produces a large force, which increases more than proportionally to the degree of compression. When rollers having a larger diameter or a stretching roller is (are) used, this shape leads to a long life of the pressure ribs.

The above-describe shapes of the pressure ribs can be used advantageously in combination with the other aspects described herein, but the independent use of said shapes, that is, without the aforesaid said aspects being implemented as well, is advantageous in itself already, so that said shapes can be considered to constitute separate inventions.

The shape of the knives on the knife roller and in particular the manner of fixing the knives to the knife roller has been improved. This has been done in particular in order to make the device with which the cutting operation is carried out more reliable and/or more efficient and/or cheaper.

The plane of a knife is substantially axially and radially oriented with respect to the knife roller. A slight deviation of the plane of the knife both from the axial direction and from the radial direction is possible thereby.

In one preferred embodiment, each knife is provided with a recess at one end and with a projection at the other end, and the knife is retained in the knife roller by a first fixing element which extends into said recess, wherein said projection extends into a recess of a second fixing element. Since the knives are fixed in position in a different manner at each end, incorrect fitting of the knives is not possible.

The two ends of the knife are those parts of the knife that are located at the ends of the cutting edge. If the knife is substantially rectangular, seen in side view, and the cutting edge extends in the direction of the long side of the rectangle, the short sides of the rectangle form the ends of the knife.

In one preferred embodiment, the first fixing element is a ring which is disposed co-axially with the knife roller, which ring extends at least partially into the recesses of the knifes. The ring shape may be so selected that the ring fills said recesses entirely and hardly extends outside the recesses, if at all. As a result, the fitting of the knives does not lead to an increased axial dimension of the knife roller. This will be explained in more detail yet by means of an exemplary embodiment.

Preferably, the second fixing element is a gear which is fitted co-axially with the knife roller, which gear is provided with an annular co-axial groove on one side, which forms the aforesaid recess into which the projections of the knives can extend. The gear thus functions as a fixing element as well.

Preferably, the recess and the projection of the knife have corresponding shapes. If the two have corresponding shapes, for example a rectangular or trapezoidal shape, the knifes can be made from a strip of material, whereby the material from the recess of one knife forms the projection of another knife. The knives can thus be formed from one strip without any loss of material.

In one preferred embodiment, the knives have two cutting edges located opposite each other, one extending radially inwards and the other extending radially outwards when the knife is present on the knife roller, wherein each cutting edge can be given an outward orientation by turning the knife through 180 degrees.

Each knife can thus be used twice.

The above-described shape of the knives can be used advantageously in combination with the other aspects described herein, but the independent use of said shape, that is, without the aforesaid said aspects being implemented as well, is advantageous in itself already, so that said shape can be considered to constitute a separate invention.

The length to which the fibres are to be cut may be larger than the spacing between the knives of the knife roller that is desirable for constructional reasons.

Said constructional reasons may be connected to the manner in which the pressure ribs are provided between the knives, or to the position of the pressure rib on the knife roller, that is, the distance between a pressure rib and a knife.

In one preferred embodiment, the knife roller comprises knives as well as dummies whose shape corresponds to that of the knives, with this difference that a cutting edge is missing, as is a portion of the knife adjacent to the cutting edge. If knives and dummies are alternately disposed on the knife roller between respective pressure ribs, the cut fibre will be twice as long in comparison with the situation in which the knife roller only comprises knives. The use of dummies makes it possible to cut fibres to different lengths by means of the same device.

In one preferred embodiment, the transverse dimension of the dummy is larger near the ends than near the centre.

The transverse dimension is the distance between the cutting edge and the knife edge opposite said cutting edge. As a result, the ends of the dummy extend further outwards in radial direction than the central portion thereof. In practice this has appeared to lead to an improved operation of the device, in particular if not all the fibres in the bundle extend parallel to each other, as a result of which a number of fibres are not stretched when the bundle is being stretched over the circumferential surface of the pressure roller and move out in lateral direction. Said fibres will be additionally stretched in that case by the portion of the dummies that extends further outwards.

The above-described dummies can be used advantageously in combination with the other aspects described herein, but the independent use of said dummies, that is, without the aforesaid said aspects being implemented as well, is advantageous in itself already, so that the use of said dummies can be considered to constitute a separate invention.

The bundle of fibres may contain knots or other accumulations of fibres. The ends of the bundles may be knotted together manually or mechanically, for example, in order to enable continuous operation. The local accumulation of fibres may affect the cutting operation or it may even cause the cutting device to break down.

In one preferred embodiment, in order to prevent this, the fibres, or the bundle of fibres, can be passed between the pressure roller and a cutting element comprising a plurality of substantially parallel cutting edges arranged in side-by-side relationship, which lie in radial planes with respect to the pressure roller. It has become apparent in practice that this arrangement makes it possible to cut knots and other local accumulations of fibres through in such a manner that sufficient cohesion among the fibres remains to enable transport of the fibres to the knives, where they can be subjected to the cutting operation without any problems, however.

Preferably, the spacing between the cutting edges of the cutting element and the surface of the pressure roller is less than 1 mm, more preferably said spacing ranges between 0.1 mm and 0.7 mm, and even more preferably between 0.3 mm and 0.5 mm.

Preferably, the spacing between the respective cutting edges of the cutting element is less than 3 mm, more preferably said spacing ranges between 0.5 mm and 2 mm, and even more preferably it is about 1.5 mm.

The above-described cutting element can be used advantageously in combination with the other aspects described herein, but the independent use of said cutting element, that is, without the aforesaid said aspects being implemented as well, is advantageous in itself already, so that the use of said cutting element can be considered to constitute a separate invention.

Although satisfactory results have been obtained with the above-described method, whereby the method was carried out smoothly for a relatively long period of time, there is always a chance that trouble will occur.

If said trouble manifests itself in the form the cutting device seizing up, this can be easily detected. It would be advantageous, however, to be able to detect also that the cutting device is functioning less well.

In one preferred embodiment, the energy consumption involved in the cutting operation is measured for that purpose, which has appeared to be a good measure of the manner in which the cutting device is functioning and/or of the state of the cutting operation and/or the means that are being used. Preferably, the energy consumption involved in the cutting operation is measured, whereby a warning signal is delivered when a predetermined energy consumption value is exceeded.

In practice it has become apparent that the energy consumption of the cutting device is a good measure of the manner in which the cutting operation is proceeding.

It is important thereby that the cutting device be so designed that all the moving parts require relatively little driving energy, so that the necessary constructional measures may have to be taken to achieve this.

In one preferred embodiment, the energy consumption of the cutting operation is measured and a warning signal is delivered if the energy consumption falls below a predetermined value. In practice it has become apparent that it is readily possible in this manner to detect whether or not a bundle of glass fibres is being processed. If several bundles are being processed at the same time, it is even readily possible to establish the number of bundles being processed on the basis of the energy consumption.

The above-described method of detecting the operation of the cutting device can be used advantageously in combination with the other aspects described herein, but the independent use of said method of detection, that is, without the aforesaid said aspects being implemented as well, is advantageous in itself already, so that said method of detection can be considered to constitute a separate invention.

In order to explain the invention more fully, a few exemplary embodiments will now be described with reference to the drawing.

Figure 1 is a schematic representation of a device for cutting glass fibres;
Figure 2 is an exploded view of a knife roller;
Figure 3 is a view of part of the knife roller;
Figures 4A and 4B are cross-sectional views of pressure ribs;
Figures 5 and 6 show a dummy;
Figures 7 and 8 show a knife;
Figures 9 and 10 show a stretching roller;
Figures 11 and 12 show a cutting element; and
Figures 13 and 14 are a front view and a side view, respectively, of an embodiment of the device.

The figures are merely schematic representations of exemplary embodiments, from which parts that do not contribute towards a better understanding of the device have been left out.

Figure 1 shows a knife roller 1, a pressure roller 2 and a stretching roller 3. The direction of rotation of the three rollers 1,2,3, all three of which are shown in cross-sectional view, is indicated by arrows. The diameters of the rollers range between 50 mm and 100 mm, for example.

Knives 4 are present on the periphery of knife roller 1, which knives extend radially outwards in axial direction. The knives may also lie in planes which do not extend exactly in radial and axial direction, but at a slight angle thereto.

The core 5 of the knife roller may be made of a metal or a plastic, and the knives 4 may be made of a hard material, for example tungsten carbide or a hardened metal.

Pressure ribs 6 are disposed between the knives 4 on the knife roller 1, which pressure ribs are made of an elastic material. In unloaded condition, the pressure ribs 6 extend in radial direction beyond the cutting edges 7 of the knives 4, and a pressure rib 6 can be compressed so that it will be positioned between the knives 4 in its entirety.

Pressure roller 2 is made of a hard material, for example a metal or a plastic, with recesses 8 being present in its circumferential surface, which recesses are so positioned that a knife 4 will extend into a respective recess 8 during rotation of the knife roller 1 and the pressure roller 2, and that approximately centrally between the side walls 9 of the recess.

The circumferential surface of the pressure roller 2 is slightly concave between the recesses 8, which enables that part of the circumferential surface to mate more easily with the pressure ribs 6.

If the knives 4 and the pressure ribs 6 extend from the core 5 of the knife roller 1 in a direction which deviates slightly from the axial direction, the recesses 8 are arranged at a corresponding angle with respect to the axial direction. The knife roller 1 and the pressure roller 2 are furthermore interconnected by means of gears, so that they rotate in opposite directions at the same circumferential speed.

The stretching roller 3 is not driven directly, but it rotates because it abuts against pressure roller 2 with a force equal to its own weight or with a predetermined force, which force may or may not be adjustable. The circumferential surface 10 of stretching roller 3 is preferably elastic.

Figure 1 shows a bundle 11 of glass fibres being led into the gap between the pressure roller 2 and the stretching roller 3. Then the bundle 11, which lies on the surface of pressure roller 2, is carried to the gap between the knife roller 1 and the pressure roller 2. In said gap, the glass fibres are pressed against the pressure roller 2 by the pressure ribs 6, whereby the pressure ribs 6 exert a force on the fibres which suffices to retain the fibres in position.

In the gap between the knife roller 1 and the pressure roller 2, the knife 4 moves into the recess 8, so that the bundle 11 is stretched over the cutting edge 7 of the knife 4 in question, whereupon it will break at that location. Not all the fibres of bundle 11 break at the same time thereby, because not all the fibres are fully stretched and not all the fibres extend in longitudinal direction in the bundle 11. Consequently, the knife must move a particular distance into the recess. This is different from a pure cutting operation with a knife or with scissors. With such a cutting operation, a small movement suffices to place the knife fully into contact with or past the counter element that is present thereby and thus effect a separation of fibres.

As is apparent from Figure 1, the knife 4 already comes into contact with the bundle 11 when the pressure rib 6 disposed behind the knife 4 does not clamp down the bundle 11 on the circumferential surface of the pressure roller 2 yet, or at least not to a sufficient degree.

Nevertheless, the cutting operation can start at that moment already, because the bundle is also clamped down by stretching roller 3, so that the bundle 11 will not shift on the surface of the pressure roller upon being pressed into recess 8 by the knife 4 in question. To that end the stretching roller 3 must be pressed against the pressure roller 2 with sufficient force.

After the cutting operation, the cut fibres 12 fall downwards, where they are caught (not shown in Figure 1).

Figure 2 shows a number of parts of the knife roller 1.

In the centre, the core 5 of the knife roller 1 is shown in sectional view. The gear 13 that is shown to the right of said core can be fixed to the core 5 by means of bolts which can be passed through the holes 14 in the core 5 and the gear 13. During the cutting operation, the gear 13 is in engagement with a gear (not shown in the figures) which is fixed to the pressure roller 2.

The gear 13 is preferably made of a plastic material, such as Delrin TI. This reduces wear on the gear of the pressure roller 2, which is preferably made of a metal, so that frequent replacement of said gear is not necessary. The plastic gear 13 can be replaced at the same time as the knives 4, for example, and an important advantage of this construction is the fact that all the parts that are to be replaced regularly are fitted on or to the knife roller 1.

Figure 2 furthermore shows in side elevation a knife 4 having a tapered cutting edge 7. The knife 4 is provided with a recess 15 and a projection 16. When the knife 4 is present in knife roller 1, projection 16'extends into an annular recess 17 in the gear 13. Furthermore, a fixing element in the form of a ring 18 is present in recesses 15 of the knives 4 in the knife roller 1. The ring 18 is disposed in an annular groove 19 in the core 5.

As a result of this manner of fitting the knives 4 to the knife roller 1, the knives can only take up one position, so that the risk of incorrect fitting is excluded. In addition, the fixing element 18 as shown in
Figure 2 does not extend outside the core 5, which enables a compact construction.

The knife 4 that is shown in Figure 2 can be made advantageously from a strip-shaped material by means of a cutting operation, such as laser cutting or wire sparking, wherein the knives 4 can be cut out with one cut. In the embodiment of the knife 4 that is shown in
Figure 2, the projection 16 is slightly smaller than the recess 15, because it has been formed by means of a cutting operation with a particular width of the cut.

The shape of recess 15 and the projection 16 may differ from the shape that is shown in the Figure, for example a trapezoidal shape, so that they can be brought into engagement with the fixing element in question more easily.

Figure 3 shows the core 5 and the knife 4 in axial view.

The knives 4 are moved into slots 21 of the core 5 after the pressure ribs 6 (Figure 4) have been placed on the fixing cams 22. Figures 4A and 4B show the pressure rib 6 cross-sectional view, from which it appears that recess 24 is shaped to fit over the cam 22 and that the pressure ribs 6 are fixed in position on the cams 22 after the knives 4 have been fitted.

According to Figure 4A, the radially outwardly extending part 25 extends in a zigzag fashion. A first portion 26 extends obliquely upwards to the left and a second portion 27 extends obliquely upwards to the right. As a result, the part 25 of the pressure rib 6 can be depressed, whereby said part 25 is loaded in flexion, which is an advantageous manner of loading that allows a large degree of compression. In addition, any dirt that may be present can easily leave pressure rib 6 during rotation of the knife roller 1. Figure 4B shows a pressure rib 6 which is less flexible, which may have the advantages described in the introduction in comparison with a flexible pressure rib 6 as shown in
Figure 4A.

Figure 5 shows a so-called dummy 31, which can be placed on knife roller 1 instead of a knife 4. This makes it possible to increase the spacing between the knives 4 without increasing the distance between a knife 4 and the pressure ribs 6 adjacent thereto.

Like the knife of Figure 2, the dummy that is shown in
Figures 5 and 6 is provided with a recess 32 and a projection 33 for being fitted in the knife roller 1.

The recess 32 and the projection 33 are trapezoidal, which facilitates the assembly of knife roller 1.

As appears from Figure 5, the dummy 31 comprises a radially outwardly extending part, which comprises portions 34 near its ends which extend further outwards than central portion 35. In practice it has become apparent that fibres or-if several bundles 11 are being supplied simultaneously, the bundles that move away from the centre of knife roller 1 too much-are being moved towards the centre.

Figures 7 and 8 show a knife 37 having two cutting edges 38,39, which makes it possible to use the knife 37 twice. Since each cutting edge 38,39 is formed by bevelling off the edge on different sides of the knife 37, the recess 15 and the projection 16 prevent incorrect fitting of the knife 37 in the knife roller 1.

Figures 9 and 10 are views of a stretching roller 3 in axial and radial directions. In order to enhance the flexibility of the circumferential surface 10 of stretching roller 3, slots 41 are formed in said surface. As appears from the figures, the slots are slightly helical, and the depth direction deviates from the radial direction, that is, the slots 41 extend obliquely into the material or the stretching roller 3 from the circumferential surface 10 of the stretching roller 3.

Figures 11 and 12 show a cutting element 42 which can be disposed near the pressure roller 2 for the purpose of removing knots and other accumulations of fibres in the bundle 11 or, at any rate, to work said knots and accumulations in such a manner that the fibres can be cut into pieces without any problem.

The cutting element consists of a frame 43, in which a number of knives 44, seven knives 44 in this embodiment, are mounted. The number of knives 44 is selected so that the knives extend across the entire width of the bundle or bundles 11 of glass fibres that is (are) being supplied. The knives 44 extend parallel to each other, they have a thickness of 1 mm, for example, and they are spaced 1 mm apart. The frame 43 is disposed in such a manner relative to pressure roller 2 that the knives 44 almost reach the circumferential surface of the pressure roller 2. When the bundle 11 passes the knives 44, fibres which do not extend in the longitudinal direction of the bundle 11 are cut through.

In practice it has become apparent that sufficient cohesion remains among the fibres in the bundle 11 to enable efficient cutting of the fibres, whilst the cutting device is prevented from seizing up.

Furthermore, a scraper 51 is disposed near the pressure roller 2. Said scraper 2 has a sharp scraping edge 52 and a discharge surface 53, which are capable of removing and discharging dirt that collects on pressure roller 2. Said dirt may consist, for example, of particles of the coating that is present on the glass fibres 11, which particles deposit on the pressure roller 2, where they may form a hard crust which may have an adverse effect on the operation of the device.

The scraping edge is preferably disposed at a distance of less than 0.1 mm from the outer circumferential surface of the pressure roller 2 without touching the pressure roller 2 thereby, so that the pressure roller 2 can rotate freely.

Figures 13 and 14 show an embodiment of a device for cutting glass fibres wherein the above-described parts are mounted in a frame 61. The device furthermore shows a motor 62, which drives the pressure roller 2, and a control knob 63 for starting the motor 62. The frame 61 is pivot-mounted on a cover 65 by means of a horizontal pivot, which cover 65 can be mounted on a container for receiving the cut glass fibres. The device can thus be swung down as a cover of the container, as is indicated by the arrow in Figure 13. In the raised position, the bundles 11 can be manually led between the rollers 1,2, 3 in the manner as described in the foregoing, after which the device is swung down and the device can be started.

In the swung-down position, the axes of the knife roller 1, the pressure roller 2 and the stretching roller 3 extend vertically and the motor 62 as well as the bearings and the gears are positioned above the place where the cutting operation is carried out, and the pieces of glass fibre can freely fall down under the influence of the force of gravity. This arrangement, wherein the axes of the rollers 1, 2 and 3 are preferably vertically oriented rather than horizontally, can be considered to constitute a separate invention. In this way parts that are sensitive to dirt are prevented from becoming clogged.

The cover 65 is provided with a recess 66, and the frame 61 is provided with a projecting part 67 of complementary shape, in which holes 68 are formed, through which holes the bundles 11 can be fed to the cutting device 1,2,3. In the raised position, the motor 62 is supported on a supporting block 69.

The device may furthermore comprise a control device, for example a computer provided with a processor unit, which automatically detects trouble and which turns off the device in such a case. Said control device measures the average power delivered by the motor 62 during a particular period of time. It is assumed that no trouble occurs during this period, which can be visually checked by an operator, for example. Said measured power is the typical power for the number of bundles 11 being processed at that point in time, which can be stored in a memory, for example, so. that the measurement for the number of bundles 11 in question needs to be carried out only once.

If the power exceeds a particular upper limit, for example the typical power plus 10%, during normal operation, it is assumed that an obstruction has occurred in the device, and the device is turned off by the control device, whilst also an alarm signal is triggered, if desired. If the power falls below a predetermined lower limit, for example the typical power minus 10%, it is assumed that one of the bundles 11 has broken and the device is likewise stopped and an alarm signal may be triggered. In either case the operator will be able to remedy the failure in a safe manner.

This manner of failure detection in a glass fibre cutting device can likewise be considered to constitute a separate invention.

Claims

CLAIMS 1. A method for cutting glass fibres into pieces, wherein the fibres (11) are passed between a knife roller (1) and a pressure roller (2), which knife roller (1) and which pressure roller (2) rotate in opposite directions at substantially the same peripheral velocity, wherein the knives (4) of the knife roller (1) press the fibres into recesses (8) in the pressure roller (2) so as to break the fibres whilst the fibres are held in position between the pressure roller (2) and pressure ribs disposed between said knives (4).

2. A method according to claim 1, characterized in that a stretching roller (3) is provided, which stretching roller (3) mates with the pressure roller (2) and which is capable of rotation in opposite direction at substantially the same peripheral velocity, wherein the fibres (11) are first led between the stretching roller (3) and the pressure roller (2) and subsequently between the knife roller (1) and the pressure roller (2).

3. A method according to claim 2, characterized in that the stretching roller (3) is driven by the pressure roller (2).

4. A method according to any one of the preceding claims, characterized in that a knife (4) of the knife roller (1) touches the fibres before the pressure rib (6) that is disposed behind said knife (4) makes contact with the pressure roller (2).

5. A method according to any one of the claims 2-4, characterized in that the stretching roller (3) is made of a metal, at least near its circumferential surface (10), and in that said circumferential surface (10) is smooth.

6. A method according to any one of the claims 2-5, characterized in that the circumferential surface (10) of the stretching roller (3) is elastic.

7. A method according to any one of the claims 2-6, characterized in that the hardness of the circumferential surface (10) of the stretching roller (3) ranges between 30 degrees and 120 degrees Shore A, preferably between 40 degrees and 100 degrees Shore A, more preferably between 60 and 80 degrees Shore A.

8. A method according to any one of the claims 2-7, characterized in that the circumferential surface (10) of the stretching roller (3) is provided with slots (41).

9. A method according to claim 8, characterized in that said the depth of said slots (41) is greater than their width.

10. A method according to claim 9, characterized in that the slots (41) extend at an angle with respect to the axial direction, preferably an angle of more than 5 degrees, more preferably an angle of more than 10 degrees.

11. A method according to claim 9 or 10, characterized in that the depth direction of the slots (41) extends at an angle to the radial direction, preferably an angle of more than 5 degrees, more preferably an angle of more than 20 degrees and even more preferably an angle of more than 30 degrees.

12. A method according to any one of the claims 8-11, characterized in that said knives (4) extend at an angle with respect to the axial direction and in that said slots (41) extend at a different angle, with said angles differing from each other by more than 5 degrees, preferably by more than 10 degrees, more preferably by more than 20 degrees.

13. A method according to any one of the preceding claims, characterized in that the pressure ribs (6) are shaped in such a manner that the deformation of the elastic material upon being compressed substantially comprises the bending of a radially outwardly extending part (25) of the pressure rib (6).

14. A method according to claim 13, characterized in that the pressure rib (6) includes a radially outwardly extending part (25) which is zigzaged in shape, seen in cross-sectional view of the pressure rib (6).

15. A method according to claim 14, characterized in that said outwardly extending part (25) comprises a portion which has a substantially constant thickness, seen in cross-sectional view of the pressure rib (6), over a distance of more than half its length.

16. A method according to any one of the preceding claims, characterized in that each knife (4) is provided with a recess (15) at one end and with a projection (16) at the other end, and in that the knife (4) is retained in the knife roller (1) by a first fixing element (18) which extends into said recess (15), wherein said projection (16) extends into a recess (17) of a second fixing element (13).

17. A method according to claim 16, characterized in that said first fixing element is a ring (18) which is disposed co-axially with the knife roller (1).

18. A method according to claim 16 or 17, characterized in that said second fixing element is a gear (13) which is fitted co-axially with the knife roller (1), which gear is provided with an annular co axial groove (17) on one side, which forms the aforesaid recess.

19. A method according to any one of the claims 16 18, characterized in that said recess (15) and said projection (16) have substantially corresponding shapes.

20. A method according to any one of the preceding claims, characterized in that the knives (37) have two cutting edges (38,39), one extending radially inwards and the other extending radially outwards, wherein each cutting edge (38,39) can be given an outward orientation.

21. A method according to any one of the preceding claims, characterized in that the knife roller (1) comprises knives (4) as well as dummies (31) whose shape corresponds to that of the knives (4), with this difference that a cutting edge (7) is missing.

22. A method according to claim 21, characterized in that the transverse dimension of the dummy (31) is larger near the ends (34) than near the centre (35).

23. A method according to any one of the preceding claims, characterized in that the fibres (11) are passed between the pressure roller (2) and a cutting element (42) comprising a plurality of substantially parallel cutting edges arranged in side-by-side relationship, which lie in radial planes with respect to the pressure roller (2).

24. A method according to claim 23, characterized in that the spacing between the cutting edges of the cutting element and the surface of the pressure roller (2) is less than 1 mm, more preferably said spacing ranges between 0.1 mm and 0.7 mm, and even more preferably between 0.3 mm and 0.5 mm.

25. A method according to claim 23 or 24, characterized in that the spacing between the respective cutting edges of the cutting element (42) is less than 3 mm, preferably said spacing ranges between 0.5 mm and 2 mm.

26. A method according to any one of the preceding claims, characterized in that the energy consumption involved in the cutting operation is measured and in that the functioning and/or of the state of the cutting operation and/or the means that are being used is detected on the basis of said measurement.

27. A method according to any one of the preceding claims, characterized in that the energy consumption of the cutting operation is measured and a warning signal is delivered if the energy consumption exceeds a predetermined value.

28. A method according to any one of the preceding claims, characterized in that the energy consumption of the cutting operation is measured and a warning signal is delivered if the energy consumption falls below a predetermined value.

29. A device for cutting glass fibres (11) into pieces, comprising a knife roller (1) and a pressure roller (2), which knife roller (1) and pressure roller (2) are capable of rotation in opposite directions at substantially the same circumferential velocity, wherein the knife roller (1) is circumferentially provided with knives (4) and pressure ribs (6) which are disposed substantially in axial direction, and wherein the pressure roller (2) is provided with recesses (8) corresponding to said knives, wherein each knife (4) can move into a corresponding recess (8) during said rotation while remaining spaced from the side walls (9) of said recess (8), whilst the pressure ribs (6) disposed on either side of the knife (4) in question abut against the pressure roller (2).

30. A device according to claim 29, characterized in that a stretching roller (3) is provided, which stretching roller (3) mates with the pressure roller (2) and which is capable of rotation in opposite direction at substantially the same peripheral velocity, wherein the fibres (11) are first led between the stretching roller (3) and the pressure roller (2) and subsequently between the knife roller (1) and the pressure roller (2).

31. A device according to claim 30, characterized in that the stretching roller (3) is driven by the pressure roller (2).

32. A device according to any one of the claims 29- 31, characterized in that the dimensions of the knife roller are such that a knife (4) of the knife roller (1) touches the fibres before the pressure rib (6) that is disposed behind said knife (4) makes contact with the pressure roller (2).

33. A device according to any one of the claims 30- 32, characterized in that the stretching roller (3) is made of a metal, at least near its circumferential surface (10), and in that said circumferential surface (10) is smooth.

34. A device according to any one of the claims 30- 33, characterized in that the circumferential surface (10) of the stretching roller (3) is elastic.

35. A device according to any one of the claims 30- 34, characterized in that the hardness of the circumferential surface (10) of the stretching roller (3) ranges between 30 degrees and 120 degrees Shore A, preferably between 40 degrees and 100 degrees Shore A, more preferably between 60 and 80 degrees Shore A.

36. A device according to any one of the claims 30 35, characterized in that the circumferential surface (10) of the stretching roller (3) is provided with slots (41).

37. A device according to claim 36, characterized in that said the depth of said slots (41) is greater than their width.

38. A device according to claim 37, characterized in that the slots (41) extend at an angle with respect to the axial direction, preferably an angle of more than 5 degrees, more preferably an angle of more than 10 degrees.

39. A device according to claim 37 or 38, characterized in that the depth direction of the slots (41) extends at an angle to the radial direction, preferably an angle of more than 5 degrees, more preferably an angle of more than 20 degrees and even more preferably an angle of more than 30 degrees.

40. A device according to any one of the claims 37 39, characterized in that said knives (4) extend at an angle with respect to the axial direction and in that said slots (41) extend at a different angle, with said angles differing from each other by more than 5 degrees, preferably by more than 10 degrees, more preferably by more than 20 degrees.

41. A device according to any one of the claims 29 40, characterized in that the pressure ribs (6) are shaped in such a manner that the deformation of the elastic material upon being compressed substantially comprises the bending of a radially outwardly extending part (25) of the pressure rib (6).

42. A device according to claim 41, characterized in that the pressure rib (6) includes a radially outwardly extending part (25) which is zigzaged in shape, seen in cross-sectional view of the pressure rib (6).

43. A device according to claim 42, characterized in that said outwardly extending part (25) comprises a portion which has a substantially constant thickness, seen in cross-sectional view of the pressure rib (6), over a distance of more than half its length.

44. A device according to any one of the preceding claims 29-43, characterized in that each knife (4) is provided with a recess (15) at one end and with a projection (16) at the other end, and in that the knife (4) is retained in the knife roller (1) by a first fixing element (18) which extends into said recess (15), wherein said projection (16) extends into a recess (17) of a second fixing element (13).

45. A device according to claim 44, characterized in that said first fixing element is a ring (18) which is disposed co-axially with the knife roller (1).

46. A device according to claim 44 or 45, characterized in that said second fixing element is a gear (13) which is fitted co-axially with the knife roller (1), which gear is provided with an annular co axial groove (17) on one side, which forms the aforesaid recess.

47. A device according to any one of the claims 44 46, characterized in that said recess (15) and said projection (16) have substantially corresponding shapes.

48. A device according to any one of the claims 29 47, characterized in that the knives (37) have two cutting edges (38,39), one extending radially inwards and the other extending radially outwards, wherein each cutting edge (38,39) can be given an outward orientation.

49. A device according to any one of the claims 29 48, characterized in that the knife roller (1) comprises knives (4) as well as dummies (31) whose shape corresponds to that of the knives (4), with this difference that a cutting edge (7) is missing.

50. A device according to claim 49, characterized in that the transverse dimension of the dummy (31) is larger near the ends (34) than near the centre (35).

51. A device according to any one of the claims 29 50, characterized in that a cutting element (42) is present near the pressure roller (2), so that the fibres (11) can be passed between the pressure roller (2) and the cutting element (42), which cutting element comprising a plurality of substantially parallel cutting edges arranged in side-by-side relationship, which lie in radial planes with respect to the pressure roller (2).

52. A device according to claim 51, characterized in that the spacing between the cutting edges of the cutting element and the surface of the pressure roller (2) is less than 1 mm, more preferably said spacing ranges between 0.1 mm and 0.7 mm, and even more preferably between 0.3 mm and 0.5 mm.

53. A device according to claim 51 or 52, characterized in that the spacing between the respective cutting edges of the cutting element (42) is less than 3 mm, preferably said spacing ranges between 0.5 mm and 2 mm.

54. A device according to any one of the claims 29 53, characterized in that means are present for measuring the energy consumption involved in the cutting operation so as to detect the functioning and/or of the state of the cutting operation and/or the means that are being used on the basis of said measurement.

55. A device according to any one of the claims 29 54, characterized in that means are present which measure the energy consumption of the cutting operation and which deliver a warning signal if the energy consumption exceeds a predetermined value.

56. A device according to any one of the claims 29 55, characterized in that means are present which measure the energy consumption of the cutting operation and which deliver a warning signal if the energy consumption falls below a predetermined value.