EP1783252A1 - Device and Method for spreading a carbon fibres tow - Google Patents

Abstract

Device for spreading a carbon fiber tow (2) to form a carbon fiber tape (3) comprises comprises a heater (14) and a spreader (9), where the heater comprises a series of electrodes (15-17) that are contacted by the tow as it moves towards the spreader and are connected to a voltage source. An independent claim is also included for spreading a carbon fiber tow to form a carbon fiber tape by heating and then widening the tow, where heating is effected by generating a current flow in a predetermined length of the tow.

Description

The invention relates to a device for spreading a carbon fiber strand to a carbon fiber tape with a heating device and arranged in the direction of the carbon fiber strand behind the heater widening device. Furthermore, the invention relates to a method for spreading a carbon fiber strand to a carbon fiber tape, in which the carbon fiber strand is heated and then widened.

Carbon fibers, which may also be referred to as carbon fibers, are widely used to make fiber reinforced plastic materials. Carbon fibers have a relatively low mass at a relatively high tensile strength in their longitudinal direction. The carbon fibers are often embedded in a plastic matrix. If in such a matrix there are several layers of carbon fibers that are in different Directions, then the increased tensile strength and thus the improved load can be given in several directions.

Carbon fibers are usually supplied by the manufacturer in the form of carbon fiber strands. These carbon fiber strands are often wound on spools. Occasionally, they are also stored in containers. The carbon fiber strands are usually far too thick to produce a composite material. In the production of a carbon fiber reinforced composite material one would usually like to have the individual carbon fibers next to one another and in a few layers one above the other. Thus, a carbon fiber strand is first widened and the carbon fiber strip thus obtained is fed to a machine with a weft insertion or laying device, for example a warp knitting machine with weft insertion or a multi-axial machine which forms a surface material from a plurality of adjacent carbon fiber ribbons , As a rule, several groups of carbon fiber ribbons are arranged one above the other in different orientations, for example in the form of a 0 ° layer, a 90 ° layer, a + 45 ° layer and a -45 ° layer. Spreading and depositing the carbon fiber ribbons is known per se.

It is also known that the spreading of a carbon fiber strand to a carbon fiber ribbon is much better accomplished by heating the carbon fiber strand prior to spreading. For carbon fibers, which are already provided with a size or an adhesive, the heating of the carbon fibers also leads to a Heating the sizing or adhesive so that the lateral adhesion of the individual carbon fibers is weakened and the carbon fibers are better spread under pressure acting on the carbon fiber strand.

There are several possibilities for heating. One known possibility is to pressurize the carbon fiber strand with heated air. However, if the flow conditions are unfavorable, heating with heated air may cause the carbon fibers in the carbon fiber strand to become confused, which in turn hinders the spreading or spreading effect.

Another possibility is to guide the carbon fiber strand over heated rolls. The heat is then transferred from the heated rollers to the carbon fiber strand. This embodiment has proven itself in principle. However, it requires a relatively large amount of energy because not only the carbon fiber strand, but also the entire heating rollers must be heated. Most of the heat radiates from the heating rollers unused into the environment. Moreover, due to the thermal inertia of the heat rollers, it is relatively difficult to respond quickly to changes, for example, to changes in the speed of movement of the carbon fiber strands. This can cause the carbon fiber strands to overheat or not heat sufficiently.

The invention has for its object to enable a simple propagation of carbon fiber strands.

This object is achieved in a device of the type mentioned above in that the heating device has at least two spaced-apart electrodes against which the carbon fiber strand abuts in its movement to the widening device, wherein the electrodes are connected to a voltage source.

The voltage source generates a potential difference between the electrodes. The carbon fiber strand contains electrically conductive carbon fibers. The electrical conductivity, combined with the potential difference or voltage between the electrodes, leads to a flow of current through the carbon fibers. The electric current in turn causes due to the ohmic resistance of the carbon fibers electrical power loss in the carbon fibers, which in turn converts into heat and thus leads to the desired elevated temperature of the carbon fiber strand. The energy input is relatively low, because you only need to generate the necessary for the heating current flow. It is not necessary to heat other machine parts. By heating the carbon fibers, the sizing adhered to carbon fibers is also heated. This can be targeted counteracted a major obstacle to a carbon fiber strand spreading or spreading. By choosing the current in the carbon fiber strand, a specific temperature level can be set relatively accurately. With changes in ambient or operating conditions, the current can be changed relatively quickly, so that you can respond quickly to changes. The thermal inertia is relatively low. Since the carbon fiber strand is continuously pulled off during normal operation, you can neglect the thermal inertia in practice. Since only a small portion of the carbon fiber ribbon is heated, only a relatively small mass needs to be heated. This in turn leads, as stated above, to a low energy consumption during operation.

Preferably, the electrodes are alternately arranged on different sides of the carbon fiber strand. This has several advantages. First, you can lead the carbon fiber strand S-shaped between the electrodes. This in turn means that the carbon fiber strand is applied to the electrodes with a certain mechanical stress, so that the contact resistance is improved and the flow of current is facilitated. On the other hand, the mechanical tension acting on the carbon fiber strand can contribute to initial spreading of the carbon fiber strand. This in turn means that a larger area of the carbon fiber strand is applied to the electrodes and thus the transition of the current is facilitated.

Preferably, at least one electrode is designed as a deflection device. A baffle is designed to change the direction of the carbon fiber strand. The deflection angle must not be great here. But it should be sufficient to allow the application of sufficient mechanical stress on the carbon fiber strand.

Preferably, the electrodes have a cylinder shell shape at least in a contact region with the carbon fiber strand. Depending on the radius of the corresponding cylinder is ensured in a simple manner, that the mechanical stress of the carbon fiber strand and the carbon fibers contained therein remains small. The carbon fiber strand is therefore not kinked.

Preferably, the carbon fiber strand abuts more than two electrodes, wherein a first electrode in the direction of travel and a last electrode in the direction of travel are at the same electrical potential. This is an easy way to ensure that the carbon fiber strand outside the heater has the same electrical potential.

This is particularly advantageous if the potential corresponds to an ambient potential. It is thus ensured that electrical current can flow only within the heater. The ambient potential is, for example, the potential on which the subsequent strip contacts lie, ie the contact points of the carbon fiber strip with the frame of a multi-axial machine or a warp knitting machine with weft insertion. Also, the coil frame, from which the carbon fiber tape is peeled off, has the same potential, namely usually the so-called "ground or ground" potential. If you make sure that the first and the last electrode is at the ground or ground potential, then there is no additional current flow to the outside.

Preferably, the carbon fiber strand is frictionally passed over the electrode. This has the advantage that the electrode is cleaned by the carbon fiber tape itself. Fluff formation is thus counteracted. This can be almost synonymous with a longer operation achieve unchanged contact resistance between the carbon fiber tape and the electrode. The electrode can stand still. She can also turn. In the latter case, however, it should be braked or driven in order to be able to generate a relative speed between the carbon fiber strand and the electrode.

Preferably, the voltage source is designed as a constant current source whose current is adjustable. It is thus ensured that always a constant current with a set strength flows through the carbon fibers of the carbon fiber strand. Thus, the registered in the carbon fiber strand heat and the consequent increase in temperature can be set with a relatively high accuracy. Smaller disturbances, which could occur due to different contact resistances between the carbon fiber strand and the electrode, are eliminated in a simple, yet effective way. For example, if there is an increased contact resistance, then the voltage source must increase its voltage for a short time to ensure constant current flow. Constant current sources are commercially available at reasonable cost.

Preferably, the voltage source is connected to a sensor arrangement which detects at least one predetermined actual parameter of the carbon fiber strand and / or the carbon fiber ribbon, wherein the voltage source is controlled so that this actual parameter coincides with a predetermined desired parameter. For a passive control of the spreading process is possible.

It is preferred that the actual parameter is the width of the carbon fiber ribbon in the running direction behind the broadening device. The width of the carbon fiber tape depends on the temperature. The temperature in turn depends on the current flow and the electrical heat loss generated thereby. The determination of the width of the carbon fiber tape can be performed contactless and relatively easy. The width is ultimately the target size by which to align the process. If you can capture the width immediately and use it as a control parameter, then no further conversions are required.

Preferably, the voltage source is connected to a machine control, which is also connected to a tape insertion device, wherein the machine control controls the voltage source in dependence on the operation of the tape insertion device. Thus, the spread of the carbon fiber strand to a carbon fiber ribbon can be actively designed by taking over process data. For example, offer significant advantages in legers, which provide for a discontinuous web entry. For example, a liner deposits a carbon fiber tape between two transport chains, the deposit taking place only in one movement direction of the liner. When returning the Leger no carbon fiber tape is consumed. You can now adjust the heating of the carbon fiber strand relatively easy to the activity of the Legers, because only generates a current flow when the carbon fiber ribbon is actually deducted. "Stand rows" or band marks can at least be reduced. Of course you will in such a case, the heating under Take into account the guidance of the carbon fiber tapes and, in particular, take into account the carbon fiber tape runs between the heater and the leger when heating the carbon fiber strand.

Preferably, the carbon fiber strand is engaged with a belt tension control. Thus, the contact resistance between the carbon fiber strand and the electrode can be influenced and kept substantially constant.

Preferably, the electrodes are provided with a cleaning device. This cleaning device may additionally or alternatively be provided for cleaning the electrodes by the carbon fiber strand itself. It is thus ensured that the contact resistance between the electrodes and the carbon fiber strand can be kept substantially constant.

Preferably, the voltage source between two electrodes generates a DC voltage of at most 60V, in particular a voltage in the range of 12V to 20V. A DC voltage can be regulated relatively easily. Using a maximum voltage of 60V is a SELV (Safety Extra Low Voltage) or PELV (Protective Extra Low Voltage), which has a relatively low safety burden. There is no danger potential for operators.

The problem is solved by a method of the type mentioned, one for heating a Current flow generated in a predetermined length of the carbon fiber strand.

It is therefore used that the carbon fibers in the carbon fiber strand are electrically conductive, because the carbon fibers simultaneously represent an ohmic resistance. When a current flow through the carbon fibers is generated, then, at the same time, a loss of electrical energy is produced, resulting in an elevated temperature of the carbon fibers themselves and the surface coatings adhered thereto, for example, a sizing agent or an adhesive. With this heating, the adhesion between adjacent carbon fibers is reduced, thus creating a condition that facilitates the spreading or spreading of the carbon fiber strand. The fact that the heat is generated in the carbon fibers themselves, only relatively small masses must be heated. The electric current can be changed relatively quickly. A thermal inertia is therefore relatively small or almost nonexistent. The method can therefore be adapted relatively quickly to changes in the operation of a machine connected to the spreading device, for example a multiaxial machine or a warp knitting machine with weft insertion. It is given relatively little heat in the environment, because you do not mitbeheizen additional machine elements. At best, there is a low power loss in the machine elements used for the supply of electrical energy to the carbon fiber strand. However, this power loss is much lower than that of a heat roller.

Preferably, starting from one position, current flow is generated to two positions distant in different directions from the position. Thus, from the "feeding" position, one generates a current flow in the direction of travel and a current flow counter to the direction of travel of the carbon fiber strand. This can ensure that carbon fiber strand sections, which lie in the direction before or behind the last electrode, are electrically virtually free of stress. In these sections so no current flow is generated, so that the loading of the carbon fiber strand with electrical energy can be limited to clearly defined sections.

Preferably, the carbon fiber strand is mechanically stressed by at least two electrodes. This has the advantage that the contact resistance between the carbon fiber strand and the electrodes is improved. At the same time, the mechanical stress already contributes to a certain spread, which in turn increases the contact area between the carbon fiber strand and the electrode. This, in turn, improves the electrical continuity between the electrodes and the carbon fiber strand, so that the electrical power dissipation is generated almost exclusively in the carbon fibers of the carbon fiber strand, but not in other machine elements.

Preferably, one generates an adjustable constant current flow. About the current flow, the electrical power loss and thus the temperature increase can be set relatively accurately.

Preferably, the width of the carbon fiber tape is determined after widening and adjusts the current intensity as a function of the width achieved. The current through the carbon fiber strand is thus regulated as a function of the width of the carbon fiber strip.

Fig. 1

eine schematische perspektivische Darstellung einer Vorrichtung zum Ausbreiten eines Karbonfaserstrangs,

Fig. 2

eine vergrößerte Darstellung einer Verbreiterungseinrichtung und

Fig. 3

eine schematische Darstellung der Einbettung der Ausbreitvorrichtung in eine Verarbeitungsmaschine.

The invention will be described below with reference to a preferred embodiment in conjunction with the drawings. Herein show:

Fig. 1

a schematic perspective view of an apparatus for spreading a carbon fiber strand,

Fig. 2

an enlarged view of a broadening device and

Fig. 3

a schematic representation of the embedding of the spreading device in a processing machine.

Fig. 1 shows a device 1 for spreading a carbon fiber strand 2 to a carbon fiber tape 3. The carbon fiber strand 2 is wound on a coil 4 which is rotatably mounted in a gate frame 5 on a shaft 6 fixed there. In a manner not shown, but known per se, the coil 4 may be braked in the gate frame 5. On the coil 4 acts a pressing device 7, which can additionally fulfill the function of a "level indicator".

A carbon fiber strand contains several thousand individual carbon fibers, for example 12,000 (12 K) or 24,000 (24 K) carbon fibers, which are grouped together in the manner of a bundle. In general, the carbon fibers are provided with a surface coating, such as a size. This surface coating leads to a sticking of the individual carbon fibers together.

For further processing, one would now like to spread a carbon fiber strand 2 transversely to its running direction 8. For this purpose, a broadening device 9 is provided, which is shown enlarged in Fig. 2.

The widening device 9 has a plate 10 with an opening 11. The width of the opening 10 transversely to the running direction 8 basically defines the maximum later width of the carbon fiber tape 3.

In the running direction 8, the opening 11 is bounded by a first deflecting device 12 and a second deflecting device 13. The carbon fiber strand 2 is now alternately guided once below the first deflecting device 12 and above the second deflecting device 13, wherein it by a train on the carbon fiber tape 3 under a certain tension is maintained. The two deflection devices 12, 13 have in the direction of 8 a relatively small distance, so that even with a comparatively small thickness of the plate 10 can achieve sufficient spreading or spreading of the carbon fiber strand 2 to the carbon fiber tape 3.

It should be noted at this point that in a manner not shown a plurality of carbon fiber strands 2 can be processed, which are deducted from a corresponding number of coils 4. For each carbon fiber strand 2 a corresponding broadening device 9 is then provided, wherein adjacent broadening devices 9 are arranged side by side so that their openings 11 adjoin one another.

In order to facilitate the spreading or spreading of the carbon fiber strand 2, the widening device 9 is preceded by a heater 14 in the running direction 8. The heater 14 has in the present embodiment, three electrodes 15-17 over which the carbon fiber strand 2 is guided S-shaped. In the embodiment according to FIG. 1, the carbon fiber strand 2 is guided under the first electrode 15 in the running direction 8, then via the second electrode 16 and again under the third electrode 17. The carbon fiber strand 2 is kept under a certain tension. In Fig. 3 for this purpose a strand tension control device 18 is shown schematically, which is part of an unwinding device 19, to which the gate frame 5 and the coil 4 belongs.

The electrodes 15-17 are formed as cylinder rods. So they have a cylindrical peripheral surface on which the carbon fiber strand 2 rests in each case. However, the electrodes 15-17 are not made to rotate, so that the carbon fiber strand is passed over the electrodes 15-17 with some friction. It is also possible that the carbon fiber strand 2 is displaced during unwinding of the coil 4 perpendicular to the direction 8, so iridescent over the electrodes 15 to 17 runs.

The electrodes 15-17 are, as shown in FIGS. 1 and 3, at different electrical potentials. The middle electrode 16 is at a positive potential and the two outer electrodes 16, 17 in the running direction 8 are at a negative potential, which may also be referred to as the ground or ground potential 20. On this ground potential 20 are electrically also the other components of Fig. 3 schematically illustrated means 21 for processing the carbon fiber tape 3, which are described in more detail below.

To generate the individual electrical potentials and thus the potential difference between the electrode 16 and the electrode 15 on the one hand and the electrode 16 and the electrode 17 on the other hand, a voltage source 22 is provided, which is connected on the one hand to the electrode 16 and on the other hand to the ground potential 20 is, so that it is connected via the ground potential 20 with the two electrodes 15, 17. The voltage source 22 generates an electrical voltage between the electrodes 16, 15 and 16, 17, which is in the range of 12V to 20V. It is preferred that this electrical voltage is a maximum of 42V, because it is then a safety extra-low voltage, mean in the more extensive protective measures against contact by an operator only a relatively small effort.

Between the electrodes 15, 16 is a first section 23 of the carbon fiber strand and between the electrodes 16, 17 is a second section 24 of the carbon fiber strand arranged. Both sections 23, 24 are traversed by an electric current when the carbon fiber strand 2 is applied to the electrodes 15-17. However, the current flow is actually limited to these sections 23, 24, because the two outer electrodes 15, 17 are at the same electrical potential as other contact points of the carbon fiber strand 2 or the carbon fiber strip 3.

The flow of current between the electrodes 15, 16 and 16, 17 is possible because the carbon fibers of the carbon fiber strand 2 are electrically conductive per se. They also have an ohmic resistance, so that between the electrodes 15, 16; 16, 17 flowing current leads to an electrical power loss, which manifests itself in a heat generation. The heat generation leads to an elevated temperature of the carbon fiber strand, which affects the surface coating of the carbon or carbon fibers and thus favors the spreading of the carbon fiber strand 2.

The electrical properties, in particular the ohmic resistance of the carbon fibers in the carbon fiber strand is known or can be previously determined by measurement. About the amount of current flow can thus be relatively easily calculate the amount of electrical power loss and thus the temperature increase, which results at a certain current. By controlling the amperage can thus very targeted also achieve an adjustment of the carbon fiber strand 2 to a predetermined temperature. This temperature setting can be virtually inertia-free done because the voltage source 22 can be set very quickly to predetermined currents. In order to reduce a negative influence of electrical contact resistance between the electrodes 15-17 and the carbon fiber strand 2, the voltage source 22 is formed as a constant current source with an adjustable current. As the contact resistances increase, the voltage source 22 must increase its output voltage to ensure constant current flow.

The fact that the carbon fiber strand 2 is guided with a certain friction on the electrodes 15-17, one can ensure that the electrical contact resistance during operation remains largely constant. The settling of lint is thus selectively prevented or adhering fluff are removed. In addition, a cleaning device 25-27, shown schematically in FIG. 3, can be provided for each electrode 15-17, which cleans the surface of the electrodes 15-17, for example, by means of a targeted air flow.

Fig. 3 shows schematically the embedding of the device 1 in a device 21 for processing carbon fiber ribbons 3. The device comprises, for example, a separator 28, which may also be referred to as a belt insertion device, a multiaxial machine or a warp knitting machine with weft insertion. In a multiaxial machine, a plurality of carbon fiber ribbons 3 are placed side by side in one layer. Several layers are superimposed. In each layer, the carbon fiber ribbons have a predetermined orientation to the longitudinal extent of the path formed by the depositing. For example, the orientations of the carbon fiber ribbons 3 in the individual layers can be 0 °, 90 °, + 45 ° and -45 °. The Leger 28 is controlled by a machine control 29 shown schematically. The Leger 28 detects a portion of a carbon fiber tape 3 and places it between two transport chains. When returning the Legers 28 no carbon fiber ribbon 3 is promoted. During these rest periods, the heating of the carbon fiber strand 2 can be omitted or reduced. The machine controller 29 is thus connected to the voltage source 22 in order to control the voltage source 22 as a function of the operation of the jig 28. Tape marks or "stand rows" that currently occur when using heat rollers can be reduced.

Additionally or alternatively, behind the broadening device 9, a sensor 30 can be provided which, for example, determines the width of the carbon fiber tape 3 perpendicular to the running direction 8. It is possible to regulate the current flow generated by the voltage source 22 as a function of the width achieved, so that the determined actual width corresponds to a predetermined desired width. The width achieved with the widening device 9 depends on the magnitude of the current flowing through the sections 23, 24.

The heating device 14 with the electrodes 15-17 allows in a simple manner a rapid adaptation to different operating conditions, for example, different machine speeds of the leger 28 of a multi-axial machine. The spreading process can On the one hand passively controlled, for example, by detecting a measured variable such as the width of the carbon fiber tape 3 or the temperature of the carbon fiber tape 3. On the other hand, you can make the Ausspreizvorgang active by taking over process data from the multi-axial machine or other downstream machine.

Claims (19)

Apparatus for spreading a carbon fiber strand to a carbon fiber ribbon having a heater and a widening device arranged in the direction of the carbon fiber strand behind the heater, the heater (14) having at least two spaced-apart electrodes (15-17) against which the carbon fiber strand moves to the widening device (9) is applied, wherein the electrodes (15-17) are connected to a voltage source (22). Apparatus according to claim 1, characterized in that the electrodes (15-17) are arranged alternately on different sides of the carbon fiber strand (2). Apparatus according to claim 1 or 2, characterized in that at least one electrode (15-17) is designed as a deflection device. Device according to one of claims 1 to 3, characterized in that the electrodes (15-17) have a cylinder shell shape at least in a contact region with the carbon fiber strand. Device according to one of claims 1 to 4, characterized in that the carbon fiber strand (2) on more than two electrodes (15-17) is applied, wherein in the running direction (8) first electrode (15) and in the running direction (8) last Electrode (17) are at the same electrical potential (20). Apparatus according to claim 5, characterized in that the potential (20) corresponds to an ambient potential. Device according to one of claims 1 to 6, characterized in that the carbon fiber strand (2) is guided with friction over the electrodes (15-17). Device according to one of claims 1 to 7, characterized in that the voltage source (22) is designed as a constant current source whose current is adjustable. Device according to one of claims 1 to 8, characterized in that the voltage source (22) is connected to a sensor arrangement (30) which detects at least one predetermined actual parameter of the carbon fiber strand (2) and / or the carbon fiber ribbon (3) the voltage source (22) so is regulated that this actual parameter coincides with a predetermined target parameter. Apparatus according to claim 9, characterized in that the actual parameter is the width of the carbon fiber tape (3) in the running direction (8) behind the widening device (9). Device according to one of claims 1 to 10, characterized in that the voltage source (22) is connected to a machine control (29) which is also connected to a belt insertion device (28), wherein the machine control (29) the voltage source (22) in Dependence on the activity of the tape insertion device (28) controls. Device according to one of claims 1 to 11, characterized in that the carbon fiber strand (2) is in engagement with a belt tension control (18). Device according to one of claims 1 to 12, characterized in that the electrodes (15-17) are provided with a cleaning device (25-27). Device according to one of claims 1 to 13, characterized in that the voltage source between two electrodes (16, 15; 16, 17) generates a DC voltage of at most 60V. A method of spreading a carbon fiber strand into a carbon fiber strand, in which the carbon fiber strand is heated and then widened, characterized in that a current flow of a predetermined length (23, 24) of the carbon fiber strand (2) is generated for heating. Method according to claim 15, characterized in that, starting from one position, a current flow is generated to two positions in different directions from the position. A method according to claim 15 or 16, characterized in that the carbon fiber strand (2) is clamped mechanically via at least two electrodes (15-17). Method according to one of claims 15 to 17, characterized in that one generates an adjustable constant current flow. Method according to one of Claims 15 to 18, characterized in that the width of the carbon fiber strip (3) is determined after widening and the current intensity is set as a function of the width achieved.

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