EP1749930A1 - Apparatus for treating a fibrous web - Google Patents

Abstract

The device has a calender (1), which comprises a nip through which a fibrous web (2) rolls. A sensor arrangement has a black glazing sensor (28), which is arranged in the rolling direction of the web behind the nip. The sensor has several charge coupled camera (CCD) sensors and a light source, which emits light with a specific wavelength using which the CCD sensors exhibit their largest sensitivity.

Description

The invention relates to an apparatus for treating a web of pulp, in particular a paper or board web, with a calender having at least one nip through which the web passes, and with a sensor arrangement.

The invention will be described below with reference to a paper web as an example of a web of fibrous material. However, it is also applicable to other webs which are treated in a comparable way, for example a board web.

If the paper web is passed through the nip, it is subjected to elevated pressure there and usually also to an elevated temperature. In many cases, the web in front of the nip is also moistened to improve, for example, the smoothness of the moistened surface as it passes through the nip. The sensor arrangement determines after passing through the nip, possibly also only after passing through the calender or another device, whether the desired parameters have been achieved. In particular, it is desirable to achieve a uniform profile of the parameter in the transverse direction of the web, ie in a direction perpendicular to the direction of travel.

If the web is overstressed, for example at a pressure that is too high in relation to other parameters, such as humidity or temperature, there is a risk that a so-called "black satin" will occur. "Black satin" refers to a quality defect that occurs especially in heavily calendered graphic papers, such as SC paper, especially SC (A) paper, or LWC paper. According to one theory, the black satin is due to the fact that individual fibers are stressed too much during the smoothing and thereby collapse, so that the incident light is transmitted rather than largely reflected. If there is a dark object behind the web or a dark printed area on the back of the web after printing, this spot appears black, which gives the effect its name.

Black sating usually occurs in an unpredictable manner.

Black sation is known to have a negative concomitant effect of increasing the surface quality of the paper web, for example PPS roughness or gloss, and correlating with it. However, the degree of correlation is low, as further boundary conditions affect it. However, as the PPS roughness is reduced or the gloss is increased, the degree of calendering work increases, so to speak. Papers with too high a black satin are committee or sell only with significantly lower proceeds.

The invention has for its object to improve the web treatment.

This object is achieved in a device of the type mentioned above in that the sensor arrangement comprises a Schwarzsatinagesensor.

With this configuration, it is possible to capture the black satin online, ie during production. This gives you the opportunity to intervene relatively early in the production process and to adjust certain parameters. You can check immediately after adjusting whether the black satin has changed.

Preferably, the black satin sensor is arranged in the direction of the web behind the nip. There is a risk in the nip that a black satin is produced. The black sateen sensor can then detect the "error" immediately after its occurrence. Although this is a certain area of the railway with the error of the black satin afflicted. If necessary, this area must also be discarded later. However, the signal from the black-level sensor can already be used to tell a production control which area of the web is affected by errors. This facilitates later processing. On the other hand, one has the opportunity in good time to intervene in the production process, so that the area in which a black satin occurs, can be kept small.

Preferably, the black-satin sensor is designed as an optical sensor. With an optical sensor, the black satin can be determined without contact. An optical sensor is particularly well adapted to the phenomenon of black satin because it is the relationship between the orbit and the incident light.

Preferably, the black-satin sensor has a plurality of photosensitive elements and a light source. The light source shines on the web. The photosensitive elements can be used to determine how much light they capture from the light source. If one uses several photosensitive elements, then one can evaluate each photosensitive element individually, whereby a relatively high resolution is possible.

It is preferred that the light source emit light at a wavelength at which the photosensitive elements have their greatest sensitivity. This is, for example, light in the near infrared spectrum, for example 830 nm, ie the spectral line of semiconductor lasers, it being possible to use CCD sensors which have the highest sensitivity in this spectrum.

Preferably, the light source and the photosensitive elements are disposed on the same side of the web. In this case it is determined how much light is reflected from the surface of the web. In one area, where black sation has occurred, however, the light from the surface of the web is not reflected so well, but the light can pass through the web to a greater degree.

It is preferred here that a dark object is arranged on the side of the web opposite the photosensitive elements. A dark object reflects incident light rays much worse than the top of the orbit, to which the light source is directed. This increases the sensitivity of the black satin sensor.

It is preferred that the dark object is formed as a roller around which the web is guided. So you do not need a separate dark object. Rather, you can use an already existing dark roller, such as a guide roller, which is provided on its surface with CFRP (carbon fiber reinforced plastic). This results in a design with very few components.

In an alternative embodiment it can be provided that the dark object is displaceable together with the photosensitive elements transversely to the running direction of the web. The dark object should be at least as large as the area of the web surface detected by the photosensitive elements. With such a configuration, the black satin sensor can be kept relatively small.

In an alternative embodiment it can be provided that the light source and the photosensitive elements are arranged on different sides of the web. In this case, the responsiveness is virtually the opposite, i. a photosensitive element is then exposed to light when a black satin has occurred. In the remaining areas, the photosensitive elements are shaded by the web.

Preferably, the photosensitive elements are arranged side by side transversely to the direction of travel of the web in a row. The photosensitive elements thus form a kind of line scan camera. One can then divide the surface of the web into individual "strips" which can be individually examined for the appearance of a black satin. When the photosensitive elements, optionally together with the light source, are displaced transversely to the direction of travel of the web, the stripes run diagonally across the web. The train can be checked randomly in this way. If the photosensitive elements are arranged side by side transversely to the running direction of the web in a row, then there are also relatively few output signals, which would have to be evaluated by an evaluation device. This simplifies the evaluation.

In an alternative embodiment it can be provided that the photosensitive elements are arranged in a plurality of rows arranged one behind the other in the direction of travel of the web, the rows being transverse to the direction of travel the course are aligned. With such a configuration, one detects, so to speak, a surface area of the web. Thus, the monitoring of the black satin can be extended to a larger area, which is particularly advantageous for a traversierenden Schwarzsatinagesensor. However, the amount of data to be evaluated increases, so that an increased computing power is required.

Preferably, the light source is designed as a flash or strobe light. With such a configuration avoids motion blur. The movement of the web is frozen with a flash or strobe light, so to speak. This is particularly advantageous when a planar arrangement of photosensitive elements is used.

Alternatively, an aperture arrangement can be provided between the light source and the photosensitive elements, which only releases the illumination for short periods of time. The diaphragm arrangement can, for example, have one or more slotted or perforated diaphragms which can be closed. This procedure is particularly suitable for laser light, because this is only with great effort pulsatile.

The sensor arrangement preferably has a traversing black satin sensor and a black satin sensor which can be fixed at a predeterminable position transversely to the direction of travel of the web. The fixable black sateen sensor is then attached to the Position of the highest black satin positioned when the black satin has different values in the transverse direction. This position is then determined beforehand by means of a traversing measurement. Thus, at the position (in the transverse direction) at which the largest black sating occurs, a continuous monitoring can be carried out and, moreover, the web can only be randomly checked by the traversing black sation sensor for the occurrence of black sation. This has the advantage that it can be relatively quickly determined whether countermeasures against the occurrence of black satin have had the desired results or not.

It is also advantageous if, in the case of several nips through which the web runs, a plurality of black-satin sensors are provided, which are arranged one behind the other in the running direction of the web. This can be used to check with several nips whether a black satin has occurred, i. one is not limited to determining black satin only after the last nip. This results in improved intervention options. In particular, one can intervene earlier in other production parameters to influence the occurrence of black satin.

• Feuchtigkeitsauftrag
• Druck
• Temperatur.

Preferably, the black sation sensor is connected to a calender control which influences at least one of the following parameters in the calender:

• humidity order
• print
• Temperature.

In this case, it may well be useful to influence the moisture application, the pressure and / or the temperature across the direction of travel of the web zone by zone. This is especially true when the black satin is limited to individual sections in the transverse direction.

• Stoffzusammensetzung
• Mahlung
• Sortierung
• Entwässerung im Former
• Druck in der Pressenpartie
• Heizkurve in der Trockenpartie
• bei gestrichenen oder geleimten Bahnen Menge, Verdünnung, Art oder Zusammensetzung des Auftragsmediums.

Die Schwarzsatinage kann durchaus auch durch Parameter beeinflußt sein, die außerhalb des Kalanders liegen. Es kann dabei sinnvoll sein, die Einflußnahme des Schwarzsatinagesensors gestuft ablaufen zu lassen, so daß zunächst die Parameter im Kalander beeinflußt werden und dann die weiteren Produktionsparameter.It is also advantageous if the black-satin-sensor is connected to a process control device which influences at least one of the following parameters during the production of the web:

• composition
• grinding
• Sorting
• Drainage in the shaper
• Pressure in the press section
• Heating curve in the dryer section
• for coated or glued webs amount, dilution, type or composition of the application medium.

The black satin may well be influenced by parameters that lie outside the calender. It may be useful to let the influence of the Schwarzsatinagesensors run stepped, so that first the parameters are affected in the calender and then the other production parameters.

Preferably, the black sation sensor is connected to a database in the predetermined parameter combinations of the web production process and output values of the black satin sensor are stored. One can then access the combination of these parameters and shorten the control, for example by means of fuzzy logic. So you have a self-learning system available, in which after a certain period of operation, the times can be drastically shorten, which elapse after the occurrence of a black satin until the controlled disappearance of the black satin.

Advantageously, a calibration location is provided, to which the black-satin sensor moves from time to time. There, the sensor calibrates itself independently, for example by comparing and comparing the measured value with surfaces having defined brightness values (white or black cards).

Fig. 1

eine Vorrichtung zum Behandeln einer Bahn,

Fig. 2

eine erste Ausgestaltung eines Schwarzsatinagesensors,

Fig. 3

eine zweite Ausgestaltung eines Schwarzsatinagesensors,

Fig. 4

eine dritte Ausgestaltung eines Schwarzsatinagesensors,

Fig. 5

eine erste Anordnung von lichtempfindlichen Elementen und

Fig. 6

eine zweite Anordnung von lichtempfindlichen Elementen.

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

Fig. 1

a device for treating a web,

Fig. 2

a first embodiment of a black-satin sensor,

Fig. 3

a second embodiment of a black-satin sensor,

Fig. 4

a third embodiment of a black-satin sensor,

Fig. 5

a first arrangement of photosensitive elements and

Fig. 6

a second arrangement of photosensitive elements.

1 shows a calender 1 for treating a web 2, in the present case a paper web, which is supplied from a paper machine 3.

The calender 1 has two end rollers 4, 5, which are formed as deflection adjustment rollers. Each end roll 4, 5 has a support shoe arrangement 6, 7, which is divided transversely to the running direction 8 of the web 2 into individual zones. The support shoe assemblies 6, 7 act in one direction against each other.

Between the two end rollers 4, 5 more intermediate rollers 9-14 are arranged. The rollers 4, 5, 9-14 form between each nips 15-21, through which the web 2 is guided.

The two end rollers 4, 5 and the intermediate rollers 10, 12, 13 are formed as so-called soft rolls, ie, they have on their periphery a lining 22 made of a plastic. The rollers 9, 11, 14 are formed as so-called hard rollers. Their scope is unyielding. The hard rollers 9, 11, 14 are heated. As examples of a heater peripheral bores 23 are shown, through which a heat transfer medium can be passed.

A control device 24 has a calendering control 25, with which the pressures in the nips 15-21 can be adjusted via the support shoe arrangements 6, 7 (or other pressurizing devices) and the temperatures in the nips 15-21 can be set via the heating devices 23. In addition, the calender control 25 also acts on humidifying devices 26, which are shown schematically here. The moistening devices 26 can also be divided transversely into individual zones.

Furthermore, the control device 24 has a process control device 27, which acts on the paper machine 3 and influences, for example, parameters that are important for the production of the web 2, in particular composition, grinding, sorting, dewatering in the former, pressure in the press section, heating curve in the drying section and, in the case of coated or glued webs, the amount, the dilution, the type or composition of the application medium.

In order for the control device 24 to operate the calender control 25 and the process control device 27 with the desired results, the control device 24 requires a multiplicity of parameters which are determined by sensors known per se and therefore not further described, for example moisture sensors, gloss sensors, smoothness sensors, thickness sensors, etc ,

In the present embodiment, black satin sensors 28 are added to the sensors mentioned, two of which are shown. Both black-satin sensors 28 are connected to the controller 24. They are each behind a nip 16, 21 arranged. However, it is also possible to arrange such a black sation sensor 28 behind other nips or even behind each nip. When using two black-satin sensors, it is convenient to place them after the last nip in which the web rests against a hard roller.

Such a black satin sensor 28 is designed as an optical sensor. It detects the black sateen, which may have formed during the treatment of web 2, directly, ie not via secondary indicators such as smoothness or PPS roughness. The recording takes place online, that is during operation.

Exemplary embodiments of black-satin sensors are explained with reference to FIGS. 2 to 4.

2 shows a first embodiment of a black-satin sensor 28. The black-satin sensor 28 has a light source 29, for example a semiconductor laser emitting light in the near-infrared spectrum, for example 830 nm. The light source 29 can have a reflector 30 to direct light onto the surface to train 2.

The light reflected from the web 2 is received by photosensitive elements 31. Examples of an arrangement of photosensitive elements 31 are given in FIGS. 5 and 6.

Fig. 5 shows a series of photosensitive elements 31 in which a plurality of photocells 32 or CCD elements are arranged in a row next to each other. This arrangement is preferably parallel to the transverse direction of the web 2, that is perpendicular to the running direction 8 of the web 2. The photosensitive elements 31 form a kind of line scan camera.

The web 2 is guided around a guide roller 33. This guide roller is a CFK guide roller, so a guide roller made of a carbon fiber reinforced plastic. This guide roller 33 has a black or at least dark surface. This dark surface of the guide roll 33 appears to pass through the web 2 in the region of a mottling or a black satin.

Now, when the web 2 passes the light source 29, the light in front of the light source 29 is reflected by the web 2 in the defect-free areas and can be detected by the photosensitive elements 31. Where a black satin has occurred, the surface of the guide roll 33 through the paper web 2 by. At this point, the light from the light source 29 is not reflected by the bright surface of the web 2. Accordingly, one or more photocells 32 does not contain the same luminous flux as one Photocell 32, which receives light that has been reflected from the surface of the web 2. Such a lack of light output is a clear indication of the appearance of a black satin.

Although the reflected amounts of light will also differ from one another on the surface of the web 2. But such a difference can be calculated. When a black satin has occurred, there is such a significant difference that one can clearly deduce black satin.

Today's standard production speeds are up to 1800 m / min, i. 30 m / s. If you want to achieve a resolution of 20 microns in the direction 8, then you need a line rate of 1 / (30 m / s x 20 microns) = 1.67 kHz. Since line sensors, that is to say rows of photosensitive elements 31, are currently available at a line rate of 73 kHz, the desired resolution can thus be achieved without problems.

The transversely attainable resolution is a function of the optics placed in front of the photosensitive elements 31 and their distance to the paper surface.

Of course you can increase the spatial resolution in the machine direction by increasing the data rate. However, this also requires the use of a lighting stronger by the same factor.

On the other hand, one can also increase the number of pixels and thus the resolution in the transverse direction or the area observed in the transverse direction.

A sensor with 4096 pixels, with which one can e.g. at 20 microns per pixel could detect a width of 80 mm, has e.g. a line rate of 23 kHz. The computing power required for the further evaluation of the data is hardly a problem. Even a computer with a standard processor and a currently possible clock frequency of 4 GHz still provides 4 GHz / (4096 pixels × 23 kHz) = approx. 40 at the maximum pixel number and data rate Calculation steps per detected data point for the signal processing available. In terms of computing power, faster systems are also possible. On the other hand, there is hardly any need for the maximum acquisition rate. Based on only 512 pixels and 2 kHz data rate, it is possible to handle approx. 4,000 arithmetic steps per detected data point.

One can form the black satin sensor 28 so that it can detect the entire width of the web 2 at once. This allows a quasi-continuous detection of black satin.

But you can also form the Schwarzsatinagesensor so that it traverses across the web transversely to the direction 8. In theory, there is the risk that a black sation that has occurred may go undetected. This risk is relatively low.

Fig. 3 shows a modified embodiment of a black satin sensor 28, in which the same parts as in Fig. 2 are provided with the same reference numerals. Instead of a guide roller 33, another dark object 34 is now arranged on the side of the web 2 facing away from the light source 29. This dark object 34, for example a blackened plate, performs the same function as the dark guide roller 33.

For a black-satin traversing sensor 28, it is recommended that the dark object 34 traverse the web 2 along with the light source 29 and photosensitive elements 31.

In the embodiments of FIGS. 2 and 3, the black-satin sensor 28 operates, as it were, with "incident light".

In an embodiment shown in Fig. 4, the black satin sensor operates with transmitted light. The same elements are provided with the same reference numerals as in Fig. 2. The light source 29 is disposed on one side of the web 2 and the photosensitive elements 31 on the opposite side of the web. In this case, the evaluation must be changed. Here, the light-sensitive elements 31 receive more light where a black sateen has occurred than in defect-free regions of the web 2.

Instead of a single row of photosensitive elements, as shown in FIG. 5, it is also possible to use a matrix 35 with photocells 36 or others photosensitive elements, such as CCD sensors use.

In this case, i. when using a surface sensor as a black-satin sensor 28, it may be useful to avoid motion blur to freeze the movement of the web with a flash or strobe light.

The data obtained with the black sation sensor 28 are immediately evaluated, in particular with the control device 24, and the black sation is determined. If this is above a permissible value, countermeasures are initiated immediately. In the case of variations in the black satin in the transverse direction, the countermeasures can also be designed in different zones. This includes adapting the amount of moisture applied by steaming or moistening before the calender nip or nips 15-21, adjusting the line load or the temperature in the calender 1, or also adapting the smoothing of previous process steps, such as composition, grinding or sorting of the raw material , Dilution of the suspension before the headbox, fiber orientation, dewatering in the former, pressure in the press section, heating curve of the dryer section and coated or glued varieties amount, dilution, type or composition of the organic or inorganic coating medium applied to the web.

Furthermore, it may be useful to summarize the deviations from the target values together with essential parameters of the papermaking process and the control parameters in a database in order to be able to access them during later control processes and thereby shorten them, e.g. using fuzzy logic.

In addition, the combination with other online measurements is useful and conceivable, e.g. thickness, humidity, gloss or roughness. Thickness and moisture are, on the one hand, parameters influencing black sation and, on the other, quality parameters of the end product to be observed. Gloss or roughness are quality properties that worsen with the desired decline in black satin. Here again one must remedy this by secondary measures.

The controller 24 may also log the occurrence of black satin so that a later user of the produced web 2 knows which black satin portions are damaged and which are not. This facilitates later processing of the web 2.

Claims (20)

Apparatus for treating a web of fibrous material, in particular a paper or board web, with a calender having at least one nip through which the web passes, and with a sensor assembly, characterized in that the sensor assembly comprises a black sateen sensor (28). Device according to Claim 1, characterized in that the black-satin-position sensor (28) is arranged in the running direction (8) of the web (2) behind the nip (15-21). Apparatus according to claim 1 or 2, characterized in that the black-satin sensor (28) is designed as an optical sensor. Apparatus according to claim 3, characterized in that the black-satin sensor (28) comprises a plurality of photosensitive elements (31) and a light source (29). Apparatus according to claim 4, characterized in that the light source (29) emits light of a wavelength at which the photosensitive elements (31) have their greatest sensitivity. Device according to one of claims 1 to 5, characterized in that the light source (29) and the photosensitive elements (31) are arranged on the same side of the web (2). Apparatus according to claim 6, characterized in that a dark object (33, 34) is arranged on the side of the web opposite the photosensitive elements (31). Apparatus according to claim 7, characterized in that the dark object (33) is formed as a roller around which the web (2) is guided. Apparatus according to claim 7, characterized in that the dark object (34) is displaceable together with the photosensitive elements (31) transversely to the running direction (8) of the web (2). Device according to one of claims 1 to 5, characterized in that the light source (29) and the photosensitive elements (31) are arranged on different sides of the web (2). Device according to one of claims 4 to 10, characterized in that the photosensitive elements (31) are arranged transversely to the running direction (8) of the web (2) in a row next to each other. Device according to one of Claims 4 to 10, characterized in that the photosensitive elements are arranged in a plurality of rows arranged one behind the other in the direction of travel of the web, the rows being aligned transversely to the running direction (8) of the web (2). Device according to one of claims 4 to 12, characterized in that the light source (29) is designed as a flash or strobe light. Device according to one of claims 4 to 12, characterized in that an aperture arrangement is provided between the light source (29) and the photosensitive elements (31). Device according to one of Claims 4 to 14, characterized in that the sensor arrangement has a traversing black-satin sensor (28) and a black-satin sensor which can be fixed at a predeterminable position transversely to the running direction (8) of the web (2). Device according to one of Claims 1 to 15, characterized in that, in the case of a plurality of nips (15-21) through which the web passes, a plurality of black-satin sensors (28) are provided which are arranged one behind the other in the running direction (8) of the web (2) , Device according to one of Claims 1 to 16, characterized in that the black-satin sensor (28) is connected to a calender control (25) which influences at least one of the following parameters in the calender (1): - Moisture application - Print - temperature. Device according to one of Claims 1 to 17, characterized in that the black-satin sensor (28) is connected to a process control device (27) which influences at least one of the following parameters in the production of the web (2): - Composition of the substance - Grinding - Sorting - Drainage in the former - Pressure in the press section - Heating curve in the dryer section - For coated or glued webs amount, dilution, type or composition of the application medium. Device according to one of Claims 1 to 18, characterized in that the black-satin-sensor (28) is connected to a database in which predetermined parameter combinations of the web-production process and output values of the black-and-satin sensor are stored. Device according to one of claims 1 to 19, characterized in that a calibration location is provided, to which the black-satin-sensor (28) moves from time to time.

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