EP0722381A1

EP0722381A1 - A process for adding reinforcement fibres to cast stuff, and a device for providing and adding such fibres

Info

Publication number: EP0722381A1
Application number: EP94929712A
Authority: EP
Inventors: Arne Nordin; Jukka Suomela
Original assignee: Confiber AB
Current assignee: Bekaert NV SA
Priority date: 1993-10-05
Filing date: 1994-10-05
Publication date: 1996-07-24
Also published as: WO1995009723A1; SE501862C2; CA2173501A1; JPH09503458A; SE9303254D0; SE9303254L

Abstract

A method and a device for producing reinforcement fibres and adding them to concrete stuff. The fibres are produced from a continuous wire (6) by means of wire pieces, which form the fibres, being detached consecutively from the wire and then, in turn, by virtue of their kinetic energy, being flung into a mixer in which the concrete stuff is undergoing mixing. A device which is suitable for implementing the method comprises a wire spool which is mounted on a balance and from which the wire (6) runs to a wire-impelling unit (4), after which a fibre-detaching unit (8) is arranged which engages with the wire which has been fed forward by the impelling unit and consecutively detaches wire pieces from the wire. The fibres which have thus been detached pass through a nozzle tube (46) which is arranged downstream of the detaching unit (8) and which guides the fibres into a subsequent mixer which contains concrete stuff. The wire-impelling unit (4) and the fibre-detaching unit (8) each comprise a driven wheel (10 and 28, respectively), which engages with the wire, and a guide roller (12 and 30, respectively) which interacts with this wheel.

Description

A process for adding reinforcement fibres to cast stuff, and a device for providing and adding such fibres.

The present invention relates firstly to a process and secondly to a device of the types specified in the preambles to Patent Claims 1 and 7, respectively.

State of the art

Concrete is being used to an ever increasing extent as a building and construction material. However, concrete which is not reinforced has a relatively limited ability to absorb and transmit tension loads; indeed, the tensile strength amounts to only about 10% of the com¬ pression strength. For this reason, it is necessary, in many i stances, to place strengthening reinforcement in the concrete to ensure that it will be able to absorb and transmit the tension loads in question. The reinforcement can consist of bars, gratings, nets, thin wires, wires and the like, which are normally manufactured from steel. Fibres made of metal or organic material can also be used as reinforcement. The concrete is then termed fibre- reinforced concrete.

In conventional concrete reinforcement tech¬ nology, the reinforcement in question is placed in the casting mould before the latter is filled with the concrete stuff; however, this method of installing the reinforcement involves manual work which is heavy and also time-consuming. Therefore, in all those instances where fibre-reinforced concrete can be used (taking into account the strength demands which are placed on the reinforced concrete construction which is to be cast) , substantial saving of time and costs can be made since the reinforcing elements, i.e. the fibres, can already be mixed into the concrete stuff at the concrete mixing plant, and consequently arrive automatically in the casting mould as the latter is filled with the concrete stuf f .

It is previously known to add reinforcement fibres to concrete stuff by supplying previously cut steel fibres gradually or batchwise to the concrete stuff. The addition of such steel fibres, which have been ready-cut in advance, to the concrete stuff is normally effected manually from sacks, boxes or other packaging which contains a large number of ready-cut fibres. The fibres are metered either directly into a concrete mixer at a concrete mixing plant or into the mixer on a con¬ crete lorry. The actual feeding of the fibres into the concrete stuff in the mixer can then be effected using, for example, a blowing device or a conveying belt which passes from a shaking table to the inlet of the mixer drum. The fibres are poured out manually onto the shaking table from a sack or another packaging.

The abovementioned, known procedures are, as has been stated, more or less manual and very inefficient, and do not permit any exact metering of the fibres, let alone any efficient distribution of the fibres in the concrete stuff. As a result, fibre-reinforced concrete has not hitherto been used to the extent which, per se, might be considered to be justified. The said disadvan¬ tages have thus inhibited the development of the fibre concrete technique.

The object of the invention

The object of the present invention is to remove the abovementioned disadvantages which are inherent in the known technique and to make available a more advanced and appreciably improved technique (both process and device) for producing reinforcement fibres and, directly thereafter, adding the fibres to cast stuff, preferably concrete stuff.

Description of the invention That which is novel and distinctive about the process according to the invention is that the fibres, which are to be mixed into the cast stuff, are produced, using a wire which is unwound continuously from a storage spool, by means of wire pieces, which form the reinforce¬ ment fibres and have a predetermined length, being detached continuously and consecutively from the wire in the region of its free end, and by means of these detached wire pieces being fed continuously one after the other, and with high kinetic energy, directly into a mixer which is in operation and in which the cast stuff is undergoing mixing. By virtue of the fact that the reinforcement fibres (the wire pieces) which are produced from the con¬ tinuously supplied wire are flung in a "jet" directly into the mixer in question, very good distribution of the individual fibres is achieved in the cast stuff. This procedure also renders it possible to use an appreciably higher proportion of reinforcement fibres in the cast stuff than was possible using previously known processes. The novel process according to the invention also effec¬ tive!-- avoids the risk of so-called bolus formation, i.e. a clumping together of a relatively large number of individual fibres such as is more or less unavoidable when adding ready-cut fibres batchwise from a sack or another packaging.

The novel technique is suitable for producing reinforcement fibres (preferably steel fibres) which have a length/diameter ratio of up to at least 200, and for mixing fibres into cast stuff (preferably concrete stuff) . In order to ensure the necessary adhesion between fibre (wire piece) and concrete stuff, the length of the fibre should be as great as possible. In practice, it can be appropriate to have fibre lengths which are between, for example, 40 and 100 times as great as the wire diameter. In this context, appropriate wire diameters can be between, for example, 0.4 mm and 1.0 mm. Fibre lengths within the range 30 mm - 80 mm can be appropriate. Increased adhesive capacity can also be achieved by using embossed wire.

The very good distribution of the fibres in the cast stuff (the concrete stuff) which is achieved using the process according to the invention ensures that the fibres fulfil their function very adequately and bring about an efficient reinforcing effect in the concrete.

The process according to the invention is not restricted to metallic fibres, and, instead, it is also possible to conceive of using fibres made of organic material with the proviso that the latter material exhibits an E modulus which is appropriate with regard to the properties of the concrete. In general, when the cast s.tuff is concrete stuff, it is likely to be appropriate for the reinforcement fibres to consist of steel fibres which are produced from a steel wire which is unwound from the storage spool. Under these circumstances, the cast stuff is a concrete stuff which is present in the mixer and which is prepared, or compounded, from cement, ballast, water, and additives where appropriate.

The wire which is unwound from the storage spool is expediently supplied continuously, using a wire-impel¬ ling unit which impels the wire forwards, to a fibre- detaching unit which detaches the wire pieces. This impelling unit is preferably arranged immediately prior to, i.e. upstream of, the fibre-detaching unit, with the impelling unit and the detaching unit being operated in such a manner that they impart to the fibre pieces which are detached continuously and consecutively from the wire a kinetic energy which flings the fibres directly into the mixer, which is arranged downstream of the detaching unit and in which the fibres are mixed into the cast stuff. The wire from which the fibres (the wire pieces) are detached is thus a wire which is unwound continuously from a storage spool and from whose free end region the fibres are continuously detached in the fibre-detaching unit, from which the fibres, due to their high kinetic energy, are flung into the mixer.

Since, for example, floor casting using fibre concrete normally requires an admixture of 20-40 kg of fibres per cubic metre of concrete stuff, it is obvious that the reinforcing wire must pass through the impelling unit and the detaching unit at a relatively high speed so as to ensure that the admixing does not take an unreason¬ able length of time. The impelling unit and the detaching unit are therefore expediently operated in such a manner that the fibre pieces which are detached from the wire leave the detaching unit with a translational velocity of the order of size of 40-60 m/s. In order to avoid over- frequent changes of storage spools and wire, it is appropriate to use wire spools containing a relatively large amount of wire, with appropriate spool sizes being spools containing 90 kg or 500 kg of wire.

In order to facilitate metering of the correct amount of fibre to the concrete stuff, it is desirable for it to be possible continuously to monitor the summed weight of all the fibres which, at a given instant, have already been added to the concrete stuff. This can be effected, for examplen by the total weight of the rein¬ forcement fibres supplied to the cast stuff being deter¬ mined by preferably continuous weighing of the storage spool from which the wire is unwound during formation of the fibres. For this purpose, the wire storage spool is expediently mounted or a balance which shows, for example digitally, how much wire has, at any moment, already been unwound from the spool in question. The balance then operates with so-called negative weighing, i.e. all the time indicates the decrease in weight which the spool has undergone from the time at which the fibre detachment commenced.

In view of the fact that the wire is fed forwards at high velocity (of the order of size of 50 m/s) , it is appropriate to provide for guidance of the wire in the area between the storage spool and the wire-impelling unit, on the one hand, and in that between the wire- impelling unit and the fibre-detaching unit on the other. This can be effected, for example, as specified in Claim 5.

According to the invention, a device having the features specified in Patent Claim 7 is proposed for producing reinforcement fibres and adding the fibres to cast stuff, for example concrete stuff, which is under¬ going mixing in a mixer.

Such a device comprises, firstly, at least one storage spool, on which wire, for example metal wire, is wound and which is mounted on a balance, secondly a wire- impelling unit, through which the wire which can be unwound from the storage spool passes and which is in driving engagement with the wire, and, thirdly, a fibre- detaching unit which is arranged adjacent to the impel- ling unit. This detaching unit is in engagement with the wire supplied from the impelling unit and is used for continuously and consecutively detaching from the wire the wire pieces which form the fibres. Due to the kinetic energy which the impelling unit and the detaching unit impart to the fibres, the latter are flung into the rotating mixer, which is mounted downstream and in which the fibres are mixed into the cast stuff.

In order to ensure that the equipment for adding reinforcement fibres to cast stuff has a large capacity, it is appropriate for the equipment to operate with two or more (for example four) wire supply tracks which run simultaneously.

It is appropriate, therefore, that at least two storage spools, from which two separate wires are sup- plied to the wire-impelling unit and the fibre-detaching unit, are mounted on the balance. The wire-impelling unit then comprises a driving wheel which interacts with a rotatably mounted guide roller and which has a cylin¬ drical wire engagement surface which, together with the peripheral surface of the guide roller, forms a driving nip for the wires which run in parallel through it. The detaching unit then comprises a driven cutting wheel which interacts with a rotatably mounted guide roller, engages with the wires supplied from the driving wheel and, on its cylindrical peripheral surface, is provided with two parallel rims of cutting steel which, when the wheel rotates, effect piece-by-piece detachment of one wire fibre piece at a time from each wire during its passage through the driving nip between the cutting wheel and its guide roller.

The wire engagement surface of the driving wheel is appropriately designed in order to obtain a high degree of friction against the wire. In order to guide the wires and drive the driving wheel and cutting wheel, the device according to the invention may appropriately display the features speci¬ fied in Claim 9.

Stainless steel tubes having a diameter of, for example, 10 mm are appropriately arranged between each storage spool and the driving nip of the driving wheel as guiding tubes for the wires.

The cutting wheel of the detaching unit possesses cutting element rims which include cutting elements whose number depends on the outer diameter of the cutting wheel and on the desired fibre length. These cutting elements are expediently cutti j teeth with cutting edges made of a very hard material.

Using equipment which supplies two parallel fibre wires and which detaches fibres of 60 mm in length, it is easy to achieve a "fibre flow" of the order of size of 1500 fibres per second. The detached fibres continue into the rotating drum of the concrete mixer at a velocity equivalent to the peripheral velocity of the cutting wheel, which velocity can, for example, be 50 m/s.

In a device which has two storage spools, and, as a result, two parallel wires entering the wire-impelling unit and the fibre-detaching unit, it is appropriate for the cutting wheel to have a rim of cutting elements for each wire, at each circumferential margin of the cylin¬ drical peripheral surface of the cutting wheel. In this case, the cutting elements in each such rim are expedi¬ ently arranged at regular distances along each circum ferential margin, and the cutting elements in one of the rims are then offset in the circumferential direction in relation to the cutting elements in the other rim. The cutting elements, which are preferably provided with cut¬ ting edges made of a hard material, can be fixed in recesses which are directed outwards towards the cylindrical peripheral surface of the cutting wheel at each circumferential margin of the cutting wheel.

The cutting wheel is preferably dimensioned and/or driven in relation to the driving wheel such that the peripheral velocity of the wire at the cutting wheel nip is somewhat greater than the peripheral velocity of the wire at the driving wheel nip. This ensures that detachment of the fibre pieces at the cutting wheel nip is effected, in reality, by the wire pieces which form the fibres being torn off from each wire by the cutting elements of the cutting wheel when these elements engage with, and virtually cut through, each wire in its radial direction in the cutting wheel nip.

The technique according to the invention makes it possible to achieve a high concentration of steel fibres in a concrete stuff without there being any risk of the formation of a so-called bolus of fibres which have clumped together. The equipment may advantageously be wholly or partially automated and coordinated with an existing control system and equipment for producing concrete stuff, for example in a concrete mixer in a concrete mixing plant. The equipment according to the invention may also be sited entirely separately from such a concrete mixer and, instead, be arranged for the direct metering of the fibres into a concrete lorry's rotating transport vessel for ready-mixed concrete stuff.

Equipment constructed according to the principles of the present invention can be readily provided with an electrical control system including automatic gentle start and stop.

Brief description of the figures

The invention will now be described and elucida¬ ted in more detail below with reference to an exemplary embodiment, which is shown on the attached drawing, of a device according to the invention. In this context: Fig. 1 shows, in side view, a wire-feeding and fibre- generating device according to the invention for producing reinforcement fibres and adding these fibres to, for example, concrete stuff;

Fig. 2 shows, in perspective, a cutting wheel belonging to a fibre-detaching unit according to Fig. 1; Fig. 3 shows a side view of the cutting wheel according to Fig. 2;

Fig. 4 shows an enlarged detail of the margin section of the cutting wheel according to Fig. 3;

Fig. 5 shows an edge view of the cutting wheel according to Fig. 3;

Fig. 6 shows an enlarged detail view of the margin section of the cutting wheel according to Fig. 5; and Fig. 7 shows, in perspective, how a device according to the invention can be mounted.

Description of an exemplary embodiment

Fig. 1 shows, in diagrammatic form, a side view of the primary parts of a device according to the inven¬ tion. The device is intended for producing reinforcement fibres and adding these fibres to cast stuff which is undergoing mixing in a stationary mixer or in a rotatable transport vessel on a vehicle for transporting the cast stuff in question. In the subsequent description of the invention, it is assumed that the cast stuff is concrete stuff and that the wire which is used for producing the reinforcement fibres is metal wire, such as steel wire. The equipment shown in Fig. 1 is mounted on a supporting plate 2 which is supported by a stand which is not shown here in any detail.

Apart from the equipment shown in Fig. 1, the device according to the invention also includes two storage spools on which metal wire is wound. These storage spools can be of a standard type and are each expediently placed in its own cylindrical or conical container 3 (see Fig. 7) , which has a conical lid 5 at the centre of which there is an exit hole for the steel wire which is wound off from the spool in the wire con¬ tainer. The storage spools are mounted vertically in the wire containers 3, which are likewise vertical. The wire containers, which thus contain the storage spools, are mounted on a stand 7, which functions as a balance, by means of which it is easy to determine the weight of the wires which have been unwound from the storage spools. The equipment which pertains to the device according to the invention and which is shown in Fig. 1 will now be described in more detail.

A wire-impelling unit 4, through which the wires 6, 6' pass which are unwound from the storage spools, and a fibre-detaching unit 8, which is arranged alongside the impelling unit 4, are both mounted on the supporting plate 2. The wire-impelling unit 4 comprises a motor- driven driving wheel 10 and a guide roller 12, which interacts with this driving wheel and is rotatably mounted in a roller holder 14 which, in turn, is adjust¬ ably mounted on the supporting plate 2 and in relation to an anchor plate 16 which is connected thereto. At its periphery, the driving wheel 10 has a cylindrical wire- engagement surface 18 which, together with the peripheral surface of the guide roller 12, forms a driving nip 20 for the wires 6, 6' which run in parallel through it. The wire-engagement surface 18 of the driving wheel 10 is expediently provided with a friction-generating surface coating, for example an electroplated surface layer con- taining diamond grains. From the driving nip 20, the two wires 6, 6' run onwards through two horizontally direc¬ ted, straight guiding tubes 22, 22', which are arranged in parallel and which are mounted on the supporting plate 2 by means of a holder 24. The wires 6, 6' continue from the outlet ends of the guiding tubes 22, 22' into a driving nip 26 belonging to the fibre-detaching unit 8.

The fibre-detaching unit 8 comprises a motor- driven cutting wheel 28 and a guide roller 30, which interacts with the cutting wheel 28 and which is rota- tably mounted in a holder 32 which, like the roller holder 14, is adjustably mounted on the supporting plate 2. The holders 14 and 32 are adjustable in the direction towards the wheel axles 58 and 60. The roller holder 14 is adjustable in relation to its attachment 38 by means of a screw mechanism comprising an adjustment screw 19 having a locking nut 21 and a turning nut 23. The holder 14 (and thus the guide roller 12) is elasti- cally pretensioned in the direction towards the driving wheel 10 by means of a rubber buffer 36. The roller holder 32 is adjustable in the vertical direction in the same way as the holder 14 and, for this, has a screw mechanism of the same type as that of the holder 14. However, the holder 32 does not have any elastic preten- sioning element.

The cutting wheel 28, which engages with the wires 6, 6' which are supplied by the wire-impelling unit 4, has, on its cylindrical peripheral surface 40, two parallel rims of cutting elements 42 and 44, respec- tively, as is also evident from Fig. 2. When the cutting wheel 28 rotates, these cutting elements 42, 44 effect a piece-by-piece detachment of one wire fibre piece at a time from the wire 6 and 6' , respectively, during passage of the latter through the driving nip 26 between the cut- ting wheel 28 and the guide roller 30. Thus, the cutting wheel 28, with its cutting elements 42 and 44, respec¬ tively, effects, in the fibre-detaching unit 8, a c tinuous and consecutive detachment of wire pieces fr^m the wires 6, 6' . These detached wire pieces constitute reinforcement fibres which, by virtue of their kinetic energy obtained from the impelling unit 4 and the detach¬ ing unit 8, are flung onwards into a nozzle tube 46 whose inlet end is shaped such that it projec* s inwards to a point directly downstream of the driving nip 26. The fibres which are flung into the nozzle tube 46 continue, from the opposite end, which is not shown here, of the tube 46, into a mixer which is placed downstream of t._^e nozzle tube 46.

As is evident from Fig. 1, the driving wheel 10 and the cutting wheel 28 are, in this instance, driven by a common motor 48 which is arranged on the reverse side of the supporting plate 2. The driving force from the driving wheel 50 of the motor is expediently transmitted to the driving wheel 10 and the cutting wheel 28 by means of a driving chain or a cog belt 52. The drives 54 and 56 of the wheels 10, 28, which drives interact with the belt/chain 52, are, of course, placed on the wheel axles 58 and 60, respectively, on the reverse side, which is not shown in Fig. 1, of the supporting plate 2.

The wires 6, 6' are each conducted, from the two wire containers, which are not shown here and which are mounted on a balance, to the driving nip 20 between the driving wheel 10 and its guide roller 12 through their own conducting-in tubes 62 and 62', respectively, arranged between each respective wire container and the nip. In practice, it is probably preferable for these two conducting-in tubes to be each divided, by means of a pair of quick couplings 64 and 64', into two parts, namely a first conducting part which is connected to a respective wire container, and a second conducting part, which can be coupled to the latter by means of a respec¬ tive quick coupling and which is fixed to the supporting plate 2 by means of two holders 66 and 68 which are attached to the supporting plate.

The design of the cutting wheel 28 of the fibre- detaching unit 8 will now be described in more detail with reference to Figs. 2-6.

As is evident from Figs. 2, 5 and 6, the cutting wheel 28 has a rim of cutting elements 42, 44 at each circumferential margin of its cylindrical peripheral surface 40. The cutting elements 42 and 44, respectively, in each rim are arranged at regular distances along each respective circumferential margin. At the same time, the cutting elements (for example 42) in the one rim are offset by one half distance in the circumferential direction in relation to the cutting elements 44 in the other rim. As is clearly evident from Figs. 3 and 4, the cutting elements 42, 44 are fixed in recesses 70 which are directed outwards towards the cylindrical peripheral surface 40 at each respective circumferential margin of the cutting wheel 28. As is clearly evident from the enlarged detail, shown in Fig. 4, of one of the cutting elements 42, 44, the latter has a cutting edge 72 made of synthetic diamond at its bevelled functional margin.

An appropriate device for implementing the process according to the present invention has been described above. That which is distinctive for this process is thus that fibres, which are to be mixed into, for example, concrete stuff, are produced from wires 6, 6' which are unwound from storage spools which are not shown here and which are mounted inside wire containers which enclose them. Wire pieces which form the reinforce- ment fibres and have a predetermined length (equal to the length of the arc between two consecutive cutting elements in the same cutting element rim) are detached continuously and consecutively from each wire in the region of its free end immediately downstream of the outlet ends of the straight guiding tubes 22, 22' . By virtue of their kinetic energy, the wire pieces which are detached in this manner are then flung, in sequence one after the other, directly into a mixer which is in opera¬ tion and which is located downstream of the outlet end of the nozzle tube 46.

Claims

Patent claims 1. Process for adding reinforcement fibres to cast stuff which has already been finally prepared or to cast stuff which is undergoing admixture, characterized in that the fibres, which are to be mixed into the cast stuff, are produced, using a wire (6) which is unwound continuously from a storage spool, by means of wire pieces, which form the reinforcement fibres and have a predetermined length, being detached continuously and consecutively from the wire in the region of its free end, and by means of these detached wire pieces being fed continuously one after the other, and with high kinetic energy, directly into a mixer which is in operation and in which the cast stuff is undergoing mixing.

2. Process according to Claim 1, characterized in that the reinforcement fibres consist of steel fibres which are produced from a steel wire which is unwound from the storage spool and the cast stuff is a concrete stuff which is present in the mixer and which is pre- pared, or compounded, from cement, ballast, water, and additives where appropriate.

3. Process according to Claim 1 or 2, characterized in that the wire (6) which is unwound from the storage spool is supplied continuously to a fibre-detaching unit (8) , which detaches the wire pieces, with the aid of a wire-impelling unit (4) , which impels the wire forwards and which is arranged immediately prior to, i.e. upstream of, the fibre-detaching unit, and in that the impelling unit (4) and the detaching unit (8) are operated in such a manner that they impart to the fibres which are detached continuously and consecutively from the wire a kinetic energy which flings the fibres directly into the mixer, which is arranged downstream of the detaching unit and in which the fibres are mixed into the cast stuff.

4. Process according to any one of Claims 1-3, characterized in that the total weight of the reinforce¬ ment fibres which have been supplied to the cast stuff is determined by preferably continuous weighing of the storage spool from which the wire (6) is unwound during formation of the fibres.

5. Process according to Claim 3 or 4, characterized in that, a the region between the storage spool and the wire-impelling unit (4), the wire (6) is guided through a conducting-in tube which is curved at least in sec¬ tions, and, between the wire-impelling unit (4) and the fibre-detaching unit (8) , the wire is guided through a straight guiding tube (22) , and, downstream of the detaching unit, the detached wire pieces which form the fibres are flung in through the one end of a nozzle tube (46) , from whose other end the fibres are flung onwards into the mixer.

6. Process according to any one of Claims 3-5, characterized in that the impelling unit (4) and the detaching unit (8) are operated in such a manner that the fibre pieces which are detached from the wire (6) leave the detaching unit with a translational velocity which amounts to between 40 m/s and 70 m/s.

7. Device for producing reinforcement fibres and adding the fibres to cast stuff, for example concrete stuff, which is undergoing mixing in a mixer, charac¬ terized in that the device comprises, firstly, at least one storage spool, on which wire (6) , for example metal wire, is wound and which is mounted on a balance, secondly a wire-impelling unit (4) , through which the wire (6) which can be unwound from the storage spool passes, and which impelling unit (4) is in driving engagement with the wire, and, thirdly, a fibre-detaching unit (8) which is arranged adjacent to the impelling unit, is in engagement with the wire supplied from the impelling unit and is used for continuously and conse¬ cutively detaching from the wire the wire pieces which form the fibres which, by virtue of the kinetic energy they have received from the impelling unit (4) and the detaching unit (8) , are flung into the mixer which is mounted downstream and in which the fibres are mixed into the cast stuff.

8. Device according to Claim 7, characterized in that at least two storage spools are mounted on the balance, from which spools two separate wires (6, 6') are supplied to the wire-impelling unit (4) and the fibre- detaching unit (8) , and in that the wire-impelling unit (4) comprises a driving wheel (10) which interacts with a rotatably mounted guide roller (12) and which has a cylindrical wire engagement surface (18) which, together with the peripheral surface of the guide roller (12) , forms a driving nip (20) for the wires (6, 6') which run in parallel through it, and in that the detaching unit (8) comprises a driven cutting wheel (28) , which inter¬ acts with a rotatably mounted guide roller (30) , engages with the wires (6, 6') supplied from the driving wheel (10) , and, on its cylindrical peripheral surface (40) , is provided with two parallel rims of cutting elements (42 and 44, respectively) which, when the wheel rotates, effect piece-by-piece detachment of one wire fibre piece at a time from each wire (6, 6') during its passage through the driving nip (26) between the cutting wheel (28) and its guide roller (30) .

9. Device according to Claim 8, characterized in that the driving wheel (10) and the cutting wheel (28) are connected for driving to a common driving motor (48) , in that each respective guide roller (12 and 30, respec¬ tively) for the driving wheel and the cutting wheel is mounted on a displaceably adjustable roller holder (14 and 32, respectively), and the guide roller (12) for the driving wheel (10) is, via its roller holder (14) , elastically pretensioned in the direction towards the driving wheel (10), in that the wires (6, 6') are each conducted from the storage spools to the driving nip (20) between the driving wheel (10) and its guide roller (12) through its own conducting-in tube (62, 62'), which is arranged between each respective storage spool and the nip (20) , in addition to which, in the region between this driving nip (20) and the nip (26) between the cutting wheel (28) and its guide roller (30) , there is arranged a straight guiding tube (22, 22') for each of the wires (6 and 6', respectively), and in that there is arranged, downstream of the detaching unit (8) and in line with the trajectory of the wire fibre pieces which are flung out, a nozzle tube (46) into one end of which the fibres are thrown and from the opposite end of which the fibres are guided onwards into the mixer which is located downstream of the nozzle tube.

10. Device according to Claim 9, characterized in that the cutting wheel (28) has a rim of cutting elements (42, 44) at each circumferential margin of its cylindri¬ cal peripheral surface (40) and the cutting elements in each rim are arranged at regular distances along each respective circumferential margin, with the cutting elements (42) in the one rim being offset in the circum¬ ferential direction in relation to the cutting elements (44) in the other rim, and in that the cutting elements (42, 44) are fixed in recesses (70), which are directed outwards towards the cylindrical peripheral surface, at each respective circumferential margin of the cutting wheel (28) and have a cutting edge (72) made of a hard material, for example synthetic diamond.