The present invention relates to a device for cutting a bundle of fibres, in particular a bundle of bard fibres, such as Kevlar fibres or Twaron fibres, into fibres. Such bundles of so-called hard fibres are very difficult to process to give separate, small fibres. The reason for this lies in the very great hardness of the fibre material. Very small fibres of such a material, where "very small" is understood to mean in particular fibres with a length of up to 20 mm, in particular less than 10 mm, are used in practice as a substitute for asbestos, in brake blocks, in clutch plates etc. Common practice is that such small fibres are obtained by laying the bundle of fibres on a substrate, such as a bench or some other worktop, and chopping the bundle into small fibres using a chopping blade by chopping with the chopping blade onto said substrate, perpendicularly to the plane of the substrate. The substrate then serves as an anvil. With the installations known in practice it is virtually impossible to obtain fibres with a length significantly shorter than 6 mm. Shorter than 6 mm is found to be unachievable,

Incidentally, it is pointed out that longer small fibres are also obtained from bundles of hard fibres. In, for example, bulletproof vests, Kevlai/Twaron fibres with a length of

10 cm or more, such as 20 to 40 cm, are used. Such lengths are also still understood as

"small" according to the invention. The point at issue is that such hard fibres are subdivided into "smaller" fibres.

The aim of the present invention is to provide a device of the type indicated in the preamble by means of which a bundle of so-called hard fibres can be cut in an efficient, reliable manner to give fibres, hereinafter also referred to as smaller fibres.

According to the invention said aim is achieved by providing a device for cutting a bundle of fibres, in particular a bundle of hard fibres, such as Kevlar fibres or Twaron fibres, into fibres, wherein the device comprises:

• a cutting plate with a cutting side and an opposing feed side as well as at least one hole for feeding the bundle from the feed side through the hole to the cutting side;

• a blade head that has at least one blade, wherein the blade head is provided on the cutting side of the plate and is equipped to move the at least one blade along the cutting side of the cutting plate over the at least one hole such that the blade, on passing over the hole, in interaction with the part of the cutting plate surrounding the hole, cuts off a portion of the bundle protruding from said hole for making the fibres;

_• feed means provided on the feed side of the cutting plate for feeding the bundle through the hole from the feed side,

Such a device makes it possible to feed the bundle containing fibres to be cut to the cutting location in a reliable manner, specifically by feeding this bundle through a hole in the cutting plate and then cutting it off when it emerges from the hole on the cutting side.

With this arrangement the hole holds the bundle of fibres in place. Furthermore, a very high production speed is possible with these devices and also very small fibres can be produced while maintaining said high production speed. The production speed as such is determined by the frequency with which the blade passes over the cutting hole. This frequency can be increased by using multiple blades. With this arrangement the fibre length of the cut-off fibres is determined by the feed speed of the bundle in combination with the cutting frequency.

With the device according to the invention it is advantageous if this device furthermore comprises pressure means engaging on the cutting plates or the cutting head, or at least the blade, and equipped to press the blade and the cutting side of the cutting plate against one another when the blade moves along the cutting side, or at least past the hole. By ensuring mat the blade and the cutting plate are pressed against one another during cutting, a sharp cut can be achieved and at the same time trapping of the very hard fibre material between the blade and the cutting side of the cutting plate is counteracted. Ih this context it is particularly advantageous according to the invention if said pressure means are equipped to press said cutting side and the cutting head, or at least said blade, against one another with a pressure of at least 3 bar. According to the invention this pressure is in particular 5 to 10 bar. The Applicant has found mat a pressure higher than 30 bar gives no noticeable improvement in the cutting result. It is furthermore advantageous according to the invention if the cutting edge of the blade facing in the cutting direction during cutting is blunt. The Applicant has found that the tool life of the blade can be appreciably increased by deliberately making the blade blunt or at least the effective cutting edge thereof. This is extremely important in the case of such so-called hard fibres because the wear on the cutting materials is very high here. Moreover, it is surprising that a deliberately blunt blade leads, on the one hand, to a good cutting result and, on the other hand, to a significantly longer tool life. Here "blunt" is understood to mean that the blade is at an angle of more than 45° to the part of the cutting side of the cutting plate facing away from the cutting direction, as well as angles that are to

be considered equivalent in the technical sense below. It will therefore be in particular the so-called cutting surface that is concerned here, On production engineering grounds it is preferable if such a cutting surface is a flat surface. However, the cutting surface can also be a curved surface. In this context it is in particular advantageous according to the invention if the cutting surface is a flat surface that with the part of the cutting surface of the cutting plate facing away from the cutting direction encloses an angle B that is greater than 70°. This is an essentially fairly blunt angle.

According to the invention it is particularly advantageous if the cutting surface is a flat surface that with the part of the cutting side of the cutting plate facing away from the cutting direction encloses an obtuse angle β of greater than or equal to 90°. Ih other words, it is preferable if the blunting is an obtuse angle in the mathematical sense. According to the invention it is particularly advantageous here if the obtuse angle β is approximately 90° to 120°, such as approximately 95° to 105°. According to the invention it is furthermore advantageous if the at least one blade has a flat section running parallel to the cutting plate on the side of the blade facing away rrom the cutting direction, which flat section, at least during cutting, is in contact with the cutting side of the cutting plate. This is particularly advantageous in order to maintain the contact pressure between blade and cutting plate and, at the same time, to spare the cutting edge of the blade because this entire flat portion takes the pressure. According to the invention it is particularly advantageous if this flat portion, viewed in the direction of the relative movement of the blade with respect to the hole, has a length of at least 2 mm, preferably 2 to 4 mm.

According to the invention feeding of the bundle of fibres can be achieved in a very efficient manner if the feed means comprise gas injection means and a tube with one end that can be joined onto the at least one hole, the opposing, other end of which tube widens, preferably continuously, such as conically, for introducing the bundle of fibres into the tube, the gas injection means being equipped for injecting a gas into the tube in the direction of the cutting plate, such that injected gas carries the bundle along towards the hole. In this way, on the one hand, a very reliable feed of the bundle of fibres to the cutting location is achieved and, on the other hand, the gas can be used to influence the temperature at the cutting location.

With this arrangement the gas injection means comprise an injection nozzle that according to the invention advantageously opens into the widened end of the tube.

It is furthermore advantageous according to the invention if the cutting side of the cutting plate and/or the blade, in particular the portion facing the cutting plate and the cutting portion of the blade oriented towards the bundle to be cut, are polished.

Li order to counteract wear of the hole in the drilled plate under the influence of the bundle of fibres passing through, it is advantageous according to the invention if the inside wall of the hole is covered with a diamond-like material, such as boron nitrite, hi order to counteract wear of the cutting plate during cutting, it is advantageous according to the invention if the orifice of the hole on the cutting side of the cutting plate is covered with a diamond-like material, such as boron nitrite.

With this arrangement it is particularly advantageous according to the invention if the covering is implemented by means of one or more tube sections of said diamond-like material, or at least tube sections covered on the inside with said diamond-like material, placed in the hole. This has the advantage that said tube sections can easily and quickly be replaced by other tube sections in the event of wear.

With a view to a rapid and efficient cutting process it is advantageous according to the invention if the cutting head can be rotated about an axis of rotation by means of a drive. Ih order to increase the cutting efficiency it is advantageous according to the invention if the cutting plate has several such holes, wherein said holes are provided at a specific radius with respect to the axis of rotation, and if the cutting head has one or more blades, preferably at least as many blades as there are holes. Ih this way it is possible to cut at several holes with one blade. By providing at least one blade per hole it is furthermore possible to cut at high frequency.

According to the invention it is furthermore advantageous if the cutting plate is provided with cooling channels which are connected to a cooling system for feeding a cooling medium through the cooling channels. As a consequence of the very hard fibre material heat will be generated during cutting. In order to prolong the tool life of the cutting plate and the blade it is then advantageous to cool, for which purpose the cutting plate is extremely suitable.

According to a further aspect the invention relates to the use of a device according to the invention for cutting a bundle of fibres, in particular a bundle of hard fibres, such as

Kevlar fibres or Twaron fibres, into fibres. As far as the advantages of such a use are concerned reference can be made to the previously explained advantages with regard to the device according to the invention.

In this context it is furthermore advantageous according to the invention if, on the one hand, the cutting side of the cutting plate and, on the other hand, the cutting head, or at least the at least one blade, are pressed against one another with a pressure of at least 3 bar during cutting. Preferably this pressure will be at most 30 bar. Ih particular the pressure will be approximately 5 to 10 bar.

In the case of the use according to the invention it is advantageous if the bundle of fibres is fed to the hole in the cutting plate by blowing this bundle by means of a gas through a channel that emerges at said hole. With this arrangement it is advantageous if ambient air, in particular ambient air at room temperature (15 to 20 ⁰ C) is used for said gas.

Ordinary ambient air is inexpensive and is found to function adequately.

The invention can be applied in particular to fibre bundles consisting of polyarylamide fibres, in particular comprising poly-p-phenyleneterephthalamides, which include Twaron and Kevlar. However, the invention can also be applied for cutting glass fibre, such as glass fibre sheathed in polyurethane. However, the invention can also be applied for cutting strands of a material that is less hard or not hard into smaller pieces.

The present invention will be explained in more detail below with reference to an example shown diagrammatically in the drawing. In the drawing:

Figure 1 shows a highly diagrammatic and perspective complete view of an assembly of which the device according to the invention forms part;

Figure 2 shows a diagrammatic side view in section of the device according to the invention; Figure 3 shows a view of a cutting plate of the device according to the invention;

Figure 4 shows a highly diagrammatic detail, partially in section, partially in front view, of the cutting plate and blade at the cutting location, which detail corresponds to the section indicated as IV-IV in Figure 3.

Figure 1 shows an assembly of which the device 1 according to the invention forms part. The assembly shown in Figure 1 comprises a stock system 30 with a number of spools 31 on which bundles 2 of fibres to be cut into smaller fibres have been wound as well as a number of guide members 32.

Figure 1 furthermore shows a frame unit 40 of which the cutting device 1 according to the invention foπns part. The frame unit 40 is provided with a drive 22 for driving the cutting head 7 (Figure 2) for rotation about the axis of rotation 23. Furthermore, pressure means 12 in the form of a hydraulic pressure system, by means of which the cutting head 7, or at least the blades 8 thereof, can be pressed against the cutting side 4 of the cutting plate 3 under pressure can also be seen in Figure 1. The cutting device 1 with cutting plate 3 and cutting head 7 will be described in more detail further below. One or more, in this case four bundles of fibres are fed to the cutting device 1. Each bundle is fed through a hole in the cutting plate and on emerging from said hole is in each case cut off in portions. On cutting off, the cut-off portion of the bundle falls apart into separate "smaller" fibres. These separate fibres are collected on a conveyor 42 and fed to a collection bin 43.

A third frame unit 50 is also shown on the left of Figure 1. This frame unit is provided with a polishing table by means of which the cutting plate, or at least the cutting side thereof, can be machined, in particular polished and smoothed. In this way it is possible, when the cutting plate has worn to a certain extent, to remove the cutting plate from the frame unit 40 and to place it in the frame unit 50, whilst in the interim another cutting plate can be installed in the frame unit 40. The cutting plate that has just been placed in the frame unit 50 is then re-machined so as to be ready for replacement in the cutting device 1 again. Figure 2 shows the cutting device 1 according to the invention in side view, diagrammatically, partially in section and partially in a front view. The cutting device 1 essentially comprises a cutting plate 3 with a cutting side 4. This can also be seen in the front view in Figure 3, where the cutting plate 3 is viewed from the cutting side. In Figure 3 in combination with Figure 2 it can clearly be seen that the cutting side 4 is a raised ring. Furthermore, holes 6 have been made in the cutting plate. These holes can have a diameter of, for example, approximately 20 mm. Bundles 2 of fibres are fed from the feed side 5 of the cutting plate 3 to each hole 6, in this case four holes. This feed can be effected in a wide variety of ways. For example, the bundle of fibres can be fed between two conveyor belts placed some distance apart and said conveyor belts can be made to run round. However, according to the invention it is much more effective to implement the feed means as tubes 10 that join onto the holes 6 at one end and widen conically at the other end. Bundle 2 of fibres is fed into said tubes at the widened end 17. An annular injection nozzle 11, which is located around the bundle 2, is also provided at the widened end 17. The injection nozzle

11 is connected to a gas feed line 12. The injection nozzle 11 has its injection openings oriented towards the cutting plate 3. By now blowing a gas via the feed line 12 and the injection nozzle 11 into the tube 10 the bundle 2 of fibres can be transported, or more accurately blown, in the direction of the cutting plate 3. On emerging from the cutting plate 3 on the cutting side 4, the bundle 2 will in each case be cut off as soon as a blade 8 passes by a hole 6. Since such so-called hard fibres are very difficult to cut, there will be substantial evolution of heat during this operation. For this reason the cutting plate is provided with cooling channels 24 and 25. However, according to the invention the gas blown in via the injection nozzle 11 primarily for transport purposes is also highly advantageous for cooling the bundle, the cutting plate 3 and the blade 8 at the cutting location. For this purpose it can even be advantageous to cool the gas additionally. However, good cooling is already achieved if ordinary ambient air at, for example, room temperature or even at 40 ⁰ C is used.

As indicated, hard fibres, such as, in particular, Kevlar and Twaron fibres, are very difficult to cut. However, according to the invention this becomes very readily possible by means of a number of measures that can be used independently of one another or in combination with one another. These measures are:

The blade 8 is pressed under a sufficiently high pressure, of at least 3 bar, against the cutting side of the cutting plate. - To prevent the blade 8 earing into the cutting side 4 of the cutting plate 3 during this operation, said blade 8 is advantageously provided with a flat surface 16 on the bottom.

The Applicant has found that in order to counteract wear at the cutting edge 14 of the blade 8 it is highly advantageous to make this cutting edge 14 blunt, in particular to provide this edge at an obtuse angle with respect to the flat surface 16.

In order to counteract wear on the cutting plate 3 it is advantageous according to the invention if the hole 6 is covered with a diamond-like material, for example a synthetic diamond-like material or a natural diamond-like material. This covering can preferably be produced by means of tube sections 20, 21. These tube sections 20, 21 enable simple replacement should a tube section be worn.

The feed of the bundle of fibres by blowing these forwards by means of a gas, said gas being able to serve as cooling agent