EP2383387B1 - Method and device for cleaning a circulating fabric in a paper or board machine - Google Patents

Description

The invention relates to a method for cleaning a continuous fabric web in a paper or board machine. Moreover, the invention relates to a screen belt for such a paper or board machine, a device for cleaning the circulating web in a paper or board machine and a paper or board machine.

In paper or board machines circulating fabric webs are used to transport the raw paper web. A base paper web is understood to mean a web of the raw materials for the paper. In the course of the production process, more and more water is removed from the raw paper web by dehydration, so that at the end of the production process, a paper web has emerged from the raw paper web. For drying fabric webs are used, which consist of so-called sieve belts. A sieve belt thus makes it possible to transport the base paper web while simultaneously drying the base paper web, since sufficient air passes through the holes of the sieve belt in order to ensure drying. For the various drying stages within the paper or board machine, screen belts with different sized meshes or holes are used. The larger the mesh or holes, the more water can evaporate or vaporize. In order to avoid irregular drying of the base paper web, narrow meshes are used at the beginning of the production process, whereby a uniform drying of the base paper web takes place. The drier the base paper web becomes, the larger the holes or mesh of the screen belt become.

In the course of operation deposits are deposited in the mesh or holes of the fabric webs. These deposits may consist of paper fibers, glue, other constituents of the base paper web or other contaminants, for example. A particularly big problem in production are so-called stickies. These glue lumps clog the meshes or holes of the screen belt and thus prevent a uniform drying of the base paper web.

Therefore, a regular cleaning of the fabric web is required. For this purpose, for example brushes, water, compressed air or dry ice are used in the prior art. The DE 44 19 540 A1 For example, suggests cleaning a circulating fabric web with compressed air, water, steam or chemicals. DE 10 2008 049 337 A1 suggests cleaning the fabric web with dry ice.

DE 195 39 015 A1 discloses a device for cleaning a circulating Conveyor belt in a papermaking machine, for example, a dry or wet screen belt or a felt belt, with at least one directable against the conveyor belt nozzle for applying the tissue tape with a liquid or gaseous medium. The device is designed such that a suction chamber (18) cooperating with the cleaning nozzle (8) is provided, which is assigned to the cleaning nozzle (8) in such a way that dirt and / or dirt removed by the jet (27) from the conveyor belt (4) or water mist or residual water can be sucked into the suction chamber (18) and removed. To DE 195 39 015 A1 It is also conceivable to use laser and ultrasound sources to remove contaminants from the strip surface.

EP 1 520 928 A1 discloses an apparatus for cleaning tissue, particularly dry tissue for the paper industry. The dry tissue is thereby cleaned by a dry cleaning device with a laser head, which moves in a direction perpendicular to the direction of movement of the tissue.

The object of the invention is to provide an improved method for cleaning a circulating fabric web, an improved wire belt for a paper or board machine, an improved device for cleaning a circulating fabric web in a paper or board machine and an improved paper or board machine.

These objects are achieved by the objects specified in the independent patent claims. Embodiments of the invention are indicated in the dependent claims.

According to the invention, a method for cleaning a circulating fabric web in a paper or board machine is provided, wherein the fabric web is cleaned by irradiation with a laser beam.

The cleaning by irradiation by a laser beam is advantageous because in the cleaning method of the prior art by a complicated mechanism, a high mechanical wear occurs and makes regular maintenance of the cleaning device necessary. By a cleaning process by means of a Laser beam so low wear and lower maintenance intervals are achieved. This reduces the costs necessary for the production process. In addition, a cleaning process using a laser beam burdens the environment to a much lesser extent because no water is needed for the cleaning process.

Cleaning with the aid of the laser beam is effected by the laser beam being at least partially absorbed by the dirt particles, so that the dirt particles heat up and evaporate due to the energy of the laser beam.

According to one embodiment of the invention, the fabric web is made of a plastic or a metal. The laser beam also has a laser beam wavelength for which the plastic of the fabric web is transparent. By transparent is meant here that more than 95% of the energy of the laser beam is transmitted by the plastic, ie not absorbed. Preferably, this value is more than 99.5%.

This is advantageous to prevent heating of the fabric web by the laser beam. Heating the fabric web could result in its destruction. In the case of a fabric web made of a metal, this aspect is negligible since a metal better distributes the heat over the entire fabric web and thus does not cause any punctual heating of the fabric web. In addition, a metal is usually more resistant to high temperatures than a plastic.

According to embodiments of the invention, the plastic at least partially scatters the laser beam. This is advantageous because it also prevents punctual heating of the fabric web. As a result of the scattering, only a small proportion of the energy of the laser beam is transmitted to the plastic. In addition, due to the scattering, there is little heating of the fabric web over a larger area, since the laser beam is not directed by the scattering to a point on the fabric web.

Preferably, the plastic for the laser beam of a CO ₂ laser or for a YAG laser is transparent or at least partially scatters its wavelength. These lasers are preferably used according to the invention for cleaning the fabric web or the wire belt.

According to embodiments of the invention, the laser beam has a laser beam energy and the plastic absorbs less than 5% of this laser beam energy. This value is preferably below 5 parts per thousand. This is also advantageous for low heating of the plastic.

According to the invention, the fabric web is guided in a first direction over at least two deflection rollers in the paper or board machine. In other words, the fabric web circulates in a first direction over at least two guide rollers in the paper or board machine. The laser beam is guided in a second direction over the fabric web. The first and second Direction include an angle. This is equivalent to intersecting direction vectors of the first and second directions, with the result that the first direction is not equal to the second direction. The laser beam is therefore not guided in the direction over the fabric web, in which the fabric web moves itself, but at an angle, in particular perpendicular to the direction of movement of the fabric web.

The fabric web is used on a first path in the first direction for transporting a raw paper web. On a second path in the first direction, the fabric web is returned to the starting point of the first path. Preferably, the first path in the first direction is above the second path in the first direction. At the end of the first path, the stock paper web is transferred to another web or other device within the paper or board machine. The fabric web has at the end of the first path to a guide roller, which changes the direction of circulation of the fabric web. This changed direction can be a third direction or continue to be the first direction. If it remains the first direction, the second path is opposite to the first way. In other words, the first path is a positive path in the first direction and the second path is a negative path in the first direction. When the diverting roller deflects the fabric web in a third direction, the third direction is not equal to the first and second directions. The third direction thus includes an angle with the first and with the second direction. Direction vectors of the third direction thus intersect with direction vectors of the first and the second direction.

In the second way, the fabric web is irradiated with the laser at a deflection roller. This need not necessarily be the guide roller at the end of the first path, but may also be any other guide roller of the plurality of guide rollers in circulation of the fabric web. The only condition is that the guide roller is on the second path, since the base paper web is no longer allowed to be on the fabric web. The irradiation with the laser beam on a guide roller is advantageous because the tissue of the fabric web on a guide roller is widened, so that the dirt can be better solved by the fabric web. The irradiation of the fabric web with the laser beam takes place in the region of the deflecting roll in which the fabric web has a curvature.

The movement of the laser beam in the second direction is carried out by the laser beam is directed onto a mirror, which in turn deflects the laser beam on the fabric web. The mirror is then moved in the second direction over the fabric web, thereby also moving the laser beam in the second direction across the fabric web.

According to embodiments of the invention, the cleaning of the revolving fabric web takes place in that impurities on the fabric web at least partially absorb and vaporize the energy of the laser beam.

According to embodiments of the invention, the circulating fabric web is a wire belt of the paper or board machine.

According to the invention, the laser beam is guided through a pipeline system with mirrors to the fabric web. The laser beam is thus not disturbed by dust or other impurities. In addition, it is possible to position the laser to generate the laser beam at a sufficiently great distance from the rest of the paper or board machine. This is advantageous to avoid damage to the sensitive laser technology. The laser is preferably stored in a secure cabinet, such as provided for computer servers or similar electronic devices. This prevents soiling and possible damage to the laser.

The laser beam from the laser is directed from this safe location through a pipeline system to the fabric web. The piping system contains mirrors for redirecting the laser beam. The piping system can thus have several curves, corners or deflections. At the end of the piping system, the laser beam exits the piping system onto a final mirror, which directs the laser beam onto the fabric web. The laser beam therefore emerges from the pipeline system in a direction parallel to the plane of the fabric web and is only directed onto the fabric web by the last mirror. This last mirror is preferably continuously supplied with compressed air, whereby contamination of the mirror with dust or other particles is prevented. The last mirror is movable in the second direction, thereby allowing movement of the laser beam in the second direction on the web.

According to embodiments of the invention, the region of the fabric web in which the irradiation with the laser beam takes place is surrounded by a housing. The housing has an opening for the Rahrleitungssystem. The laser beam is thus passed through the pipe system through the opening of the housing on the fabric web, where then takes place by the energy of the laser beam, the evaporation of the contaminants. The gases occurring during the evaporation are sucked off by a suction device, so that the environment is not polluted with these gases. In addition, such a housing is advantageous to comply with fire safety guidelines.

According to embodiments of the invention, the laser beam is widened before impacting the fabric web. This can happen, for example, with an optical lens. An adaptive optical lens may be configured such that various Expansions of the laser beam are made possible. An expansion of the laser beam is advantageous in order to clean a larger area of the fabric web and to avoid pointy large heat. The expansion can be done either directly in front of the fabric web, so after the last mirror, or after exiting the piping system before hitting the last mirror. Alternatively, the expansion can also be done in the piping system.

• der Modus des Lasers;
• die Intensität oder Energie des Laserstrahls;
• der Grad der Aufweitung des Laserstrahls;
• die Geschwindigkeit des Laserstrahls in der zweiten Richtung; und
• der Winkel zwischen Laserstrahl und Gewebebahn.

According to embodiments of the invention, the laser generates a continuous laser beam in a first mode and a pulsed laser beam in a second mode. This results in a laser with several parameters that are adjustable depending on the fabric web and the contamination occurring on the fabric web. These parameters are:

• the mode of the laser;
• the intensity or energy of the laser beam;
• the degree of expansion of the laser beam;
• the speed of the laser beam in the second direction; and
• the angle between laser beam and fabric web.

For example, if stubborn stains are a problem, the energy of the laser beam can be increased. The degree of expansion may be used to clean up a larger area or to more thoroughly clean a smaller area as the expansion is reduced. The speed of the laser beam can be increased if a large-area cleaning of the fabric web is desired. A reduction in speed results in a more thorough cleaning. The angle between the laser beam and the web can also be varied to respond to the nature of the contaminants. For contaminants such as glue lumps, for example, another angle of incidence of the laser beam can be advantageous than for impurities with paper fibers. The angle can be reached by the inclination angle of the last mirror or by the inclination of the fiber optic cable end.

The fact that the laser beam moves in a second direction and the fabric web in a first direction creates a zigzag line on the fabric web. When the laser beam is moved from a first position at one end of the web in the second direction to the other end of the web, the web moves in that first direction in that time, causing the laser beam to skew on the web. When the laser beam has now reached the other end of the fabric web, it will again travel in the second direction but with a negative distance back to the starting point. Since during this path, the fabric web continues to move in the first direction, the laser beam again describes an oblique line on the fabric web. This creates the mentioned zigzag pattern.

In a further aspect, the invention relates to a device for cleaning a fabric web circulating in a first direction in a paper or board machine with a laser for generating a laser beam and means for directing the laser beam onto the circulating fabric web. The steering of the laser beam is done with the piping system written above.

According to embodiments of the invention, the device also has a controller. The steering of the laser beam is controllable by the controller and the laser beam can be moved by the controller in a second direction on the web. The controller is configured to move the laser beam across the web in the second direction such that each point of the web has been irradiated by the laser beam after a plurality of passes of the web.

In yet another aspect, the invention relates to a paper or board machine having a device according to embodiments of the invention and a screen belt according to embodiments of the invention.

Fig. 1

eine Kunststoffgewebebahn, die in einem mittleren Bereich mit Hilfe eines Laserstrahls gereinigt wurde;

Fig. 2

eine Kunststoffgewebebahn, die am Randbereich mit Hilfe eines Laserstrahls gereinigt wurde; und

Fig. 3

eine Kunststoffgewebebahn, die mit Hilfe eines gepulsten Laserstrahls gereinigt wurde.

In addition, to clarify embodiments of the invention with a laser beam cleaned fabric webs are shown. Show it:

Fig. 1

a plastic web which has been cleaned in a central area by means of a laser beam;

Fig. 2

a plastic web, which was cleaned at the edge area with the help of a laser beam; and

Fig. 3

a plastic web, which was cleaned with the help of a pulsed laser beam.

FIG. 1 shows a soiled plastic fabric web 100, which has been cleaned in a central region 102 by means of a laser beam. In the middle region 102, the cleaned area 104 can clearly be seen, which differs by its color from the remaining plastic fabric of the plastic fabric web 100.

FIG. 2 shows a soiled plastic fabric web 200, which has a cleaned area 202 in the edge region.

Good to see here is the expanded beam width of the laser beam. It corresponds to the width 204. The course of the laser beam on the plastic fabric web does not correspond to the movement of the laser beam within the paper or board machine, since the fabric web moves simultaneously in a different direction. As already described above, the fabric web moves in a first direction and the laser beam moves in a second direction. The first direction is in FIG. 2 indicated by arrow 206 and the second direction by arrow 208. Depending on the speeds of the movement of the fabric web and the laser in the first direction 206 and the second direction 208, the effective direction 210 of the laser beam on the fabric web 200 results.

FIG. 3 shows a soiled plastic web 300 which has been cleaned with a pulsed laser beam of width 302. The many partial cleanings 104 of the plastic web 300 are caused by the fact that the laser was always turned on only for a certain time and then switched off again, with no cleaning of the plastic web during an off laser. Therefore, between the cleaned areas 304, uncleaned areas 306 are located FIG. 3 is similar to in FIG. 2 , the laser beam has been effectively shifted to the fabric web in an effective 308 direction. This results from the fabric web being moved in the first direction 310 and the laser beam being moved in the second direction 312.

LIST OF REFERENCE NUMBERS

100

Plastic fabric web

102

middle area

104

cleaned area

200

Plastic fabric web

202

cleaned area

204

width

206

first direction

208

second direction

210

effective direction

300

Plastic fabric web

302

width

304

cleaned area

306

uncleaned area

308

effective direction

310

first direction

312

second direction

Claims (12)

1. A method for cleaning a fabric web in a paper or board machine, wherein a raw paper web is transported through the paper or board machine by the fabric web, the fabric web in a first direction revolving over at least two deflection rollers in the paper or board machine, the fabric web being cleaned by irradiation with a laser beam,
   characterized in that the laser beam is conducted through a conduit system having mirrors to the fabric web, at the end of the conduit system the laser beam exiting the conduit system onto a last mirror, which directs the laser beam to the fabric web, the last mirror being subjected to compressed air and movable in a second direction so that the laser beam is moved in the second direction on the fabric web, and the first and second directions enclosing an angle.
2. The method according to claim 1, wherein the laser beam has a laser beam wavelength, the fabric web being made of a plastic material or a metal, and the plastic material absorbing less than 5% of the energy of the laser beam.
3. The method according to claim 2, wherein the plastic material at least partially scatters the laser beam.
4. A method according to one of the preceding claims, wherein, on a first path, the fabric web transports a raw paper web in the first direction and on the second path is returned to the starting point of the first path, the fabric web being irradiated with the laser beam at a deflection roller on the second path.
5. A method according to one of the preceding claims, wherein the cleaning of the revolving fabric web is achieved in that impurities on the fabric web at least partially absorb the energy of the laser beam and evaporate.
6. A method according to one of claims 1 to 5, wherein the laser is conducted through an optical waveguide to the fabric web.
7. A method according to one of the preceding claims, wherein the laser beam is expanded in front of the fabric web.
8. The method according to claim 7, wherein the laser generates a continuous laser beam in a first mode and generates a pulsed laser beam in a second mode, the following parameters being adjustable as a function of the fabric web and the soiling of the fabric web:

   - the mode of the laser;

   - the intensity or energy of the laser beam;

   - the degree of expansion of the laser beam;

   - the velocity of the laser beam in the second direction; and

   - the angle between the laser beam and the fabric web.
9. A device for cleaning a fabric web revolving in a first direction in a paper or board machine using a laser for generating a laser beam, characterized by a conduit system having mirrors for conducting the laser beam to the fabric web, at the end of the conduit system the laser beam exiting the conduit system onto a last mirror, which directs the laser beam to the fabric web, and the last mirror being subjectable to compressed air and movable in a second direction enclosing an angle with the first direction so that the laser beam can be moved in the second direction on the fabric web.
10. The device according to claim 9, wherein the device further comprises a control unit, the directing of the laser beam being controllable by the control unit, and the laser beam being movable in the second direction on the fabric web by way of the control unit, the control unit being designed to move the laser beam in the second direction over the fabric web in such a way that each point of the fabric web has been irradiated by the laser beam after a plurality of revolutions of the fabric web.
11. The device according to claim 10, wherein the control unit controls at least one of the following parameters of the laser beam:

    - the mode of the laser;

    - the intensity or energy of the laser beam;

    - the degree of expansion of the laser beam;

    - the velocity of the laser beam in the second direction; and

    - the angle between the laser beam and the fabric web.
12. A paper or board machine, comprising a device according to one of claims 9 to 11.

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