EP0035447A1 - Process and apparatus for the treatment of textile threads or fibres - Google Patents

Abstract

To treat a textile yarn (10) and in particular to increase its dyeing ability, it is passed through a location between two electrodes (11) and (12) and a cut arc is burst at this location. For this, an arc voltage is created using a generator (13) in series with an impedance (17).

Description

In the textile industry, it is often necessary to treat the yarns, in particular to increase their wettability with respect to dye baths or other chemical substances.

The term "yarn" should be understood in a broad sense, covering in particular natural fibers, for example cotton, and synthetic fibers, in the form of hair and multifilaments.

A known treatment method consists in subjecting the wire to an electric discharge. More specifically, the wire is passed through an alternative discharge created between a cylinder covered with a dielectric and a metal plate. This type of discharge has drawbacks. It requires significant electrical power. The residence time of the fiber in this type of discharge must be at least 5 seconds if a change in the fiber is to be observed. This duration is incompatible with online wire processing.

There is also known a process in which the wire is subjected to an electric arc which is rotated so that the wire is subjected to the arc repeatedly, but each time for a short time (patent _GB 1,300,088) .

The invention aims to provide a process that better meets those previously known to the requirements of practice, in particular in that it requires less energy consumption and allows high speed movement of the wire.

To this end, the invention proposes in particular a method according to which the wire is passed through a location where a cut arc is established, at high frequency, by an impedance placed in the electric circuit for creating the arc.

The effect of the cut arc, which can be compared to a spark, is very different from that of an arc maintained; we can probably attribute this difference to the fact that the cut arc starts at a much higher tension (at least an order of magnitude) than the permanent tension of a maintained arc, which results in the communication of much greater energy to particles. The excitation spectrum (spark spectrum) is much richer and the energy levels higher than in a maintained arc. In addition, the use of a cut arc eliminates a problem created by the use of a maintained arc: because of the suffocation of the arc, there is no "hooking" at a point on the moving wire.

It will generally be necessary for the average current to be at least 400 μA for a wire circulating at 5 m / min and to be higher the higher the speed of the wire. The intensity of the average arc current can moreover be regulated as a function of the speed of circulation of the wire.

The risk of burning and cutting the wire is avoided since each discharge is extremely brief; however, the high repetition frequency of the arcs makes it possible to process the wire over its entire length. Each discharge has a high peak power, but involves a low energy.

The process will generally be carried out in air when the only desired result is the improvement in wettability. This solution has the advantage of simplicity. The arc can be supplied: with rectified direct or alternating current, this second solution having the advantage of guaranteeing the extinction on each return to zero of the voltage.

The invention also provides a treatment device comprising at least one module consisting of a first electrode and a second electrode placed face to face and at a determined distance, an electrical circuit for applying voltage between the electrodes, and means for circulating the wire between the electrodes at an arcing location, characterized in that said circuit includes a generator capable of establishing between the two electrodes an arc voltage in the absence of current flow in the circuit, the power of the generator and the impedance of the circuit being such that the arc is cut, after ignition, in a short time compared to the duration of rise to arcing voltage.

In practice, the arc repetition period will be several orders of magnitude greater than the arc duration.

Avoid the arc from exploding anywhere other than the location of the wire. For this, in a first embodiment, the wire is surrounded by a dielectric forcing the arc to burst between the electrodes in line with the wire. However, this precaution has generally proven to be superfluous.

In another mode, the electrodes are formed by blades parallel to the same direction and forming an angle between them so as to be closest to the location of passage of the wire.

When it is desired to work at high speed of the wire, it is advantageous to subject the latter to several successive arcs. For this, the device can comprise several modules arranged successively on the path of the wire and corresponding to several different arc paths relative to the wire. Instead of providing several modules, the wire can be circulated so that it constitutes a wound winding, the adjacent turns of which are contiguous or very close together, which passes under the same electrode in the form of a blade.

• - la figure 1 est un schéma de principe d'un dispositif de mise en oeuvre de l'invention,
• - la figure 2 est une vue de dessus du module de la figure 1,
• - la figure 3 montre un module constituant une variante de celui des figures 1 et 2,
• la figure 4 montre une répartition possible de modules successifs le long d'un fil à traiter,
• - la figure 5 montre l'allure de la variation de la tension entre les électrodes en fonction du temps dans le cas d'un générateur continu,
• - la figure 6 illustré les résultats d'essais effectués sur un même fil, traité et non traité,
• - la figure 7 est un schéma de principe montrant les éléments principaux d'un dispositif constituant une autre variante ;
• - la figure 8 montre l'allure de la variation du champ électrique en fonction du temps dans le dispositif de la figure 7, relevée à l'oscillographe,
• - la figure 9, similaire à la figure 1, montre une autre variante encore.

The invention will be better understood on reading the following description of devices which constitute particular embodiments thereof given by way of nonlimiting examples. The description refers to the accompanying drawings, in which:

• FIG. 1 is a block diagram of a device for implementing the invention,
• FIG. 2 is a top view of the module of FIG. 1,
• FIG. 3 shows a module constituting a variant of that of FIGS. 1 and 2,
• FIG. 4 shows a possible distribution of successive modules along a wire to be treated,
• FIG. 5 shows the shape of the variation of the voltage between the electrodes as a function of time in the case of a continuous generator,
• FIG. 6 illustrates the results of tests carried out on the same wire, treated and untreated,
• - Figure 7 is a block diagram showing the main elements of a device constituting another variant;
• FIG. 8 shows the shape of the variation of the electric field as a function of time in the device of FIG. 7, measured with the oscillograph,
• - Figure 9, similar to Figure 1, shows yet another variant.

The device shown diagrammatically in FIGS. 1 and 2 is intended to subject the wire 10 to be treated to an arc produced in a single location. It comprises a conductive support 11, such as a plate or a wire drive drum 10, constituting a first electrode, and a blade 12 constituting a second electrode. An electric generator 13 makes it possible to establish a sufficient voltage between the electrodes 11 and 12 to create an arc between the electrodes. To locate the arc at the location of the wire 10, it can be framed by plates of dielectric material 14, made of polished beryllium oxide for example, delimiting a path for circulation of the wire and which can serve as a support for the blade 12. This should be as close as possible to the wire 10. Experience has shown, however, that the plates are frequently unnecessary and that the wire channels the discharge.

The generator 13 must be capable of establishing an arc voltage, but provided with means which suffocate this arc from its birth. It can be provided to apply a polarity voltage te or alternative advantageous. high frequency, of the order of at least kHz.

The use of a determined polarity voltage is of particular interest when the nature of the charges transported influences the transformations of the wire. For example, the egrets (also called darts or "streamers") which appear when the electrode plate 12 is positive, are made up of particles charged with sufficient kinetic energy to open bonds.

In all cases, the arc breaking means can be constituted by a series impedance, of sufficient value. This impedance will be a resistance in the case of direct voltage, an inductance in the event of alternating or pulsed voltage, this latter solution making it possible to reduce the Joule losses.

In the embodiment shown in FIG. 1, the generator 13 includes a step-up transformer 15 to which an alternating voltage is applied, either from the distribution network, or from a chopper or oscillator supplying a high frequency. A bridge of rectifiers 16 makes it possible to apply alternations all of the same polarity to the electrode 12 by means of an inductor 17. The electrode 11 is maintained at ground.

The generator 13 must be capable. supply the starting voltage V (Figure 5) which will be at least 2 kV and generally between 5 and 20 kV.

The operation of the device is as follows:

The voltage applied by the generator 13 to the electrodes 11 and 12 increases until reaching the ignition voltage of an arc. This arc goes around the wire and penetrates it. The arc current causes an almost instantaneous voltage drop, indicated at 18 in FIG. 5. As soon as the intensity of the current falls below a value of the order of 1 A, the arc is cut off. The voltage then having practically dropped to zero, it rises according to an approximately exponential law as indicated in 19 in FIG. 5. As soon as the voltage again reaches the value V, corresponding to priming, the cycle is repeated.

The duration of a cycle is extremely short, so that there is no risk of burning and cutting of the wire, without it being necessary to coat the support 11 with a dielectric, as in the case of alternative discharge treatment devices, mentioned above.

The average current which passes, for wires of current diameter, must be at least 400 µA for a running speed of a few meters per minute. This average current must obviously increase with speed. An average current of the order of a milliampere can be envisaged for a speed of 50 m per minute.

In the alternative embodiment shown in FIG. 3, the wire 10a passes through a module, the electrodes of which consist of two blades 11a and 12a. These two blades are flat with a beveled end. They are parallel to the same direction but form an angle between them, typically greater than 10 °. Thus, the distance between their bevels is variable and has a minimum at a location which is where the wire 10a is passed.

The operation of such a device is the same as that already described with reference to Figures 1 and; 2.

It will often be desirable to subject the wire to several successive discharges. For this, in the case of Figure 1, we can constitute the support 11 by a drum on which the wire rests and which circulates in front of electrode blades regularly distributed in the circumferential direction.

In the case of the embodiment shown in FIG. 3, it is possible to use several identical successive modules 20, 21, 22, ... distributed along the path followed by the wire 10a. The successive modules advantageously have different orientations around the wire so that the latter is treated in a homogeneous manner.

As an example, we can indicate that we have compared the effects of the treatment according to the invention and of the treatment by conventional alternative discharge on a cotton thread.

For this, we measured the shrinkage of the wire dipped in a sodium hydroxide solution at 23% by weight and containing 3 cm ³ of a wetting agent type "Mercerol" per liter. The variation in length ΔL, as a function of time T, is indicated in FIG. 6. Curve 23 shows the variation for an untreated wire. Curve 24, in solid lines, shows the variation in the case of a wire treated by twenty modules of the kind shown in FIG. 3, with a running speed of 5 m per minute and an average current of 400 μA for each module. This curve 24 is substantially the same as that which is obtained for a conventional machine. It can be seen that the invention makes it possible to obtain substantially the same result as the previous method, but with a much shorter treatment time.

In the embodiments shown in FIGS. 1 to 4, each electrode allows only one wire to be treated once.

This drawback is eliminated in the embodiment shown in FIG. 7 where the wire to be treated 10b is put in the form of a winding with contiguous turns or slightly spaced by a set of two rollers 25 and 26 whose axes are generally parallel and a guide comb 27. The cut arc is then formed between the wire where it is carried by the roller 25 and a blade-shaped electrode 12b, similar to that shown in FIG. 1, located in a plane passing through the axis of the roller. This multiplies the number of thread passages under the same electrode.

It was feared that the arc would preferentially burst on certain passageways. Experience has shown that this is not the case, and even that the location struck by a spark eliminates the next spark. Presumably, the fact that the wire has become conductive where it has been reached by the arc and that it flows the charges which cannot accumulate means that the next ignition must take place elsewhere. We can also check the good distribution of the discharges visually: because of the persistence of the luminous impressions, one must see appearing a curtain of discharges interesting all the "package" of son.

This same visual test makes it possible to verify that one is in a spark regime, which results in a whiter appearance; moreover, it is often possible to switch from the maintained arc regime to the cut arc regime by reducing the power of the generator or by increasing the speed of travel.

The generator 13b shown in FIG. 7 comprises, like that of FIG. 1, a step-up transformer 15b whose primary receives an alternating voltage, advantageously at high frequency, greater than that of the distribution network, at which the parasitic capacity distributed 28 of transformer is generally no longer negligible.

To avoid the appearance of a maintained arc, the circuit includes an impedance constituted by a capacitor 29 placed as close as possible to the electrode 12b and which spaces the arcs cut over time, due to the time necessary for its recharging: the intervals thus provided avoid maintenance by ionization residue. The maintained arc starts more easily on a negative half-wave, the rectifiers 30 are mounted so as not to; allow the application of positive alternations. The presence of the capacitor 31 avoids a corresponding consumption.

A device made for treating polyester material yarns included a transformer supplied at a frequency of 2 kHz and supplying a circuit having capacitors 29 and 31 of 70 and 500 pF, respectively. The transformer was supplied at 2 kHz, that is to say at a value close to its tuning frequency of 2.5 kHz, and supplied a peak voltage of 15 kV.

The voltage across the arc (between electrodes 12b and 25) then had the form shown in Figure 8: we see that the duration t, determined by the recharge time of the capacity 31 through the rectifiers 30, was significantly longer than the duration t between arcs. The latter was around 50 µs while the duration of each arc was a few ns.

The very nature of the circuit in FIG. 7 means that only one spark can burst at a time, which limits the number of sparks hitting the wire during processing. This limitation can be removed by dividing the electrode connected to the generator into several decoupled blades. The embodiment of FIG. 9 comprises two blades 12c each placed opposite a respective zone of the drum 25c. Each blade 12c is supplied by the transformer 15c through a choking impedance, which may consist of an impedance 32 of a few µH, due to the operation of alternating current, and is decoupled by a capacitor 33. There can thus be simultaneous application of two arcs to wire 10c.

Claims (10)

1. A method of treating textile threads (10, 10a, 10b) by electrical discharge in which the thread is passed through a location where an arc is established, characterized in that the arc is cut at high frequency, the repetition period being at least an order of magnitude greater than the duration of an arc. 2. Method according to claim 1, characterized in that the same wire carried by several drafts is circulated by a conductive surface under a blade-shaped electrode (12b) placed in the immediate vicinity of the wire, and in that the '' the blade is brought to a voltage at least equal to 2 kV in the absence of an arc current. 3. Method according to claim 1 or 2, characterized in that the frequency and the intensity of the arcs are determined, so that the average current is at least 400 uA for a wire circulating at 5 m / min and the higher the higher the wire speed. 4. Device for treating textile threads by electrical discharge, comprising at least one module consisting of a first electrode (12) and a second electrode (11) placed face to face and at a determined distance, an electrical application circuit voltage between the electrodes and means for circulating the wire between the electrodes at an arcing location, characterized in that said circuit comprises a generator (13) capable of establishing a voltage between the two electrodes arc in the absence of current flow in the circuit, the power of the generator and the impedance of the circuit being such that the arc is cut after ignition in a short time compared to the duration of rise to the arc voltage . 5. Device according to claim 4, characterized in that one of the electrodes is connected to a power transformer (15b) via a capacitor (31) and mounted in parallel with a rectifier (29). 6. Device according to claim 4, characterized in that one of the electrodes is connected to a supply transformer (15c) via an inductive impedance (32) and is in parallel with a capacitor (33) . 7. Device according to claim 4, 5 or 6, characterized in that the electrodes are constituted by blades (lla, 12a) parallel to the same direction and forming between them an angle so as to be closest to the location thread passage. 8. Device according to claim 4, 5 or 6, characterized in that the electrodes are formed one by a rotary drum (11, 25, 25c) carrying the wire and the other, by a blade (12, 12b , 12c) arranged in a plane passing through the axis of the drum. 9. Device according to claim 8, characterized in that it is intended to circulate the wire (10b, 10c) according to several successive turns-on the drum (25, 25c) facing the blade (12b, 12c). 10. Device according to claims 6 and 9, characterized in that the blade (12c) is in several fractions each of which is opposite a fraction of the drum (25c) and is connected to the transformer (15c) via 'a separate impedance (32), each fraction cooperating with several turns of the wire (10c).

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