WO2005056921A1

WO2005056921A1 - A method for controlling the running parameters in an apparatus for processing a fibrous web and a device for applying the said method

Info

Publication number: WO2005056921A1
Application number: PCT/FI2004/050180
Authority: WO
Inventors: Tapio MÄENPÄÄ; Kari Hasanen; Reijo PIETIKÄINEN
Original assignee: Metso Paper, Inc.
Priority date: 2003-12-10
Filing date: 2004-12-08
Publication date: 2005-06-23
Also published as: JP2007514067A; DE112004002418T5; JP4718482B2

Abstract

The present invention relates to a method for controlling the running parameters in an apparatus (1) for processing a fibrous web (W). The apparatus (1) comprises an endless metal belt (2) arranged to rotate around guide means (3), and at least one counter-element (5) forming a contact surface with the metal belt (2). Between which metal belt (2) and the counter- element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed is passed. In the method, thickness measurement of the metal belt (2) is carried out during running by eddy-current measurement. According to a second aspect of the invention, the temperature of the belt (2) is measured during running in a noncontacting manner from the opposite side of the belt (2) with respect to the fibrous web (W). According to a third aspect of the invention, the metal belt (2) is cooled with cooling medium at a point outside the area in which it is in contact with the tail threading cord, in order to obtain an essentially even temperature profile for the metal belt (2). The invention also relates to devices for applying the methods.

Description

A method for controlling the running parameters in an apparatus for processing a fibrous web and a device for applying the said method

The present invention relates to a method for controlling the running parameters in an apparatus for processing a fibrous web, the processing apparatus comprising an endless metal belt arranged to rotate around guide means, and at least one counter-element forming a contact surface with the metal belt, between which metal belt and counter element is formed a processing zone for the fibrous web, through which the fibrous web to be processed is passed.

The present invention also relates to a device for controlling the running parameters in an apparatus for processing a fibrous web, the processing apparatus comprising an endless metal belt arranged to rotate around guide means and at least one counter-element forming a contact surface with the metal belt, between which the metal belt and counter-element is formed a processing zone for the fibrous web, through which the fibrous web to be processed can be passed.

The present invention further relates to a method for measuring the temperature of the belt and for controlling the process in the apparatus for processing the fibrous web, the processing apparatus comprising an endless belt arranged to rotate around at least one guide means, and at least one counter-element forming a contact surface with the belt, wherein between the belt and the counter-element is formed a processing zone for the fibrous web, through which the fibrous web to be processed is passed.

The present invention also relates to a device for measuring the temperature of the belt and for controlling the process in an apparatus for processing the fibrous web, the processing apparatus comprising at least one endless belt arranged to rotate around at least one guide means and at least one counter-element forming a contact surface with the belt, between which metal belt and counter-element is formed a processing zone for the fibrous web, through which the fibrous web to be processed is passed. Furthermore, the present invention relates to a method for controlling the temperature profile and tensile stresses of the belt of the metal belt calender intended for processing a fibrous web during the threading of the fibrous web, whereby a narrow tail threading cord is moved into contact with the metal belt having a higher temperature than the web, thus bringing about a cooling effect on the metal belt. The invention further relates to a device for applying the method.

Devices of this type for processing fibrous webs are previously known, for example, from the applicant's patent applications PCT/FI03/00066, PCT/FI03/00067, PCT/FI03/00068. The devices for processing a fibrous web disclosed in these applications are applied to calendering very different types of fibrous webs, such as different paper and board grades, as well as to coating, film transfer, drying and/or printing. Furthermore, the belt used in devices for processing fibrous webs disclosed in the said patent applications is most preferably a metal belt, or metal wire, but it may also be a polymer or composite wire or cord, or the like. The specification of the present patent application refers to a metal belt by way of an example without, however, being limited to it.

The effects of processing by the device referred to above for processing a fibrous web, which applies a belt cycle, on the end properties of the fibrous web are controlled by adjusting the processing conditions in the processing zone, such as the compression effective in the processing zone, the processing moisture of the fibrous web and the effective time of contact. In practice, these adjustment measures are carried out by adjusting the actuators affecting the fibrous web, for example, the temperature of the belt and/or counter-element, or the length of the processing zone and/or the processing time or belt tightness.

The adjustment measures carried out to control the process may be based on, for example, experimentally determined target values of the actuators' controlled variables. By means of pilot test runs, for instance, the optimal roll and web temperature, as well as the effective zone pressure and effective time are determined for each fibrous web grade. When the process is in a standard state, the aim is to adjust the controlled variables of the actuators to preferred values and to maintain them at these target values. In order for the actuator adjustments to function accurately and for the set values to remain at the target values, the operation of the actuators must, however, be controlled. For example, belt temperature and tightness must be measured either directly or indirectly and, where necessary, be adjusted for the process to function continuously in the same manner.

Adjustment may also be based on feedback on-line process measurement, in which case the on-line measurement values of the fibrous web are used as a basis for the adjustment. Should the processing effect observed not correspond to the target state, the adjustment system will change the actuator settings, for example, the temperature of the belt or web or belt tightness so that the target level will be reached. Furthermore, if it is desirable to maximise the output meeting the quality criteria during the transient change in the process, it must be possible to control the state of the actuators accurately and without delay. Also in this case, measurements can be used for controlling the state of the actuator itself, such as belt temperature, and as a basis for adjustment measures. As an example can be mentioned a situation where variations originating in earlier process stages cause disturbances in the treatment process, to compensate for which the actuators have to be adjusted, while it is, however, desirable to standardise the final quality produced. One problem is presented by the edge zones of the metal belt, where especially thickness varies as a result of possible temperature variations. This may have a deteriorating effect on the quality of the fibrous web. In addition, with increasing service life, particularly the thickness of the belt edges will not necessarily remain the same with the same initial values, due to the wearing of (fatigue of metal) and damage to the belt material.

By observing the above-mentioned properties, no information is obtained on the wearing of the metal belt, and thus no direct information is gained on its effect on the quality of the web. There do not exist any reliable, and especially no essentially continuously operating arrangements for measuring the thickness of the metal belt. Measuring methods making contact with the surface are unsuitable for measuring thickness and optical devices are susceptible to being soiled in an unclean environment. Methods using radiation sources, such as those emitting x-radiation, can under no circumstances be used for continuous monitoring of belt thickness due to their hazardousness (radioactivity).

Also the measurement of temperature on the surface of a moving belt having a glossy surface cannot at present be carried out in a very reliable manner in normal production conditions. In principle, numerous different temperature measuring techniques are known. The temperature of a moving belt could conceivably be measured, for example, by means of a contacting (dragging) temperature sensor or a non-contacting technique, such as a thermographic camera (IR measurement).

The problem with non-contacting infrared measurement is that the surface of the thermo roll or belt in contact with the fibrous web is polished and finished to produce good fibrous web quality. From the viewpoint of thermographic camera measurement, the low emission coefficient of the polished surface and reflections from the surroundings are problematic. Even the slightest soiling of the surface will affect the emission coefficient considerably and cause measurement errors. Even in testing facility environments, thermographic cameras must, in practice, be calibrated daily and this type of solution is not, therefore, applicable to industrial plant type conditions requiring high reliability and low maintenance. On the other hand, it is in principle possible to use contacting (dragging) temperature measurement also in production conditions. With high speeds, the result of contacting measurement is, however, unreliable and the measuring devices require constant maintenance and repeated calibration. Surplus heat from sliding friction also impedes measurement.

Furthermore, for example in metal belt calenders, where the counter-element is a heated thermo roll, one problem is that the metal belt of steel and the thermo roll come into mutual contact when no fibrous web is being processed in the processing zone between them. Thus, when the thermo roll is heated, and for instance during web breaks, heat is able to transfer from the hot thermo roll to the belt even if the guide rolls of the belt have liquid circulation, for example, water or heating oil, for cooling the belt and maintaining the temperature profile of the belt straight. The temperature of the heating oil used inside the thermo roll may be, for example, of the order of about 300°C, whereby the surface of the thermo roll is approximately at 250°C and the belt coming into contact with it may then heat up to a temperature of about 200°C, when there is no web being processed between them. Once the web has been taken to the processing zone and travels normally between the thermo roll and the belt, the surface temperature of the thermo roll will fall within the range from about 150 to 200°C, depending on properties and temperature of the incoming web. If the metal belt is not heated, it will reach essentially the temperature of the web in operating conditions.

When leading the web to the processing zone of the metal belt calender, a narrow tail threading cord cut, from the fibrous web, having a width of, for example, 100- 300 mm, is brought first to the calendering zone. This will cool the metal belt considerably at the cord. When the belt cools down over a narrow zone on one edge it shortens, and this zone begins to bear the tensioning force of the belt, whereby high tensile stress forms on the said edge. This asymmetry will probably also affect the controllability of the belt. As a result, fatigue durability of the belt is reduced. In addition, in solutions where no cooling liquid circulation is arranged in the guide rolls of the belt cycle, both the belt and the leading rolls of the belt heat up close to the temperature of the thermo roll, whereby it will take a considerably long time, for example, more than 10 minutes, after the spreading of the web before the temperature of the belt has fallen essentially to the temperature of the web and the hot belt no longer affects the bulk.

The object of the present invention is to eliminate, or substantially reduce, the above-mentioned disadvantages and to thus better control the running parameters in an apparatus for processing a fibrous web.

To achieve the above objects, the method according to the first aspect of the present invention is characterised in that in the method, thickness measurement of the metal belt during running is carried out by eddy-current measurement.

In addition, the device applying the method according to the first aspect of the present invention is characterised in that the device comprises means by which the thickness of the metal belt can be measured by eddy-current measurement during running. The method according to the first aspect of the present invention is further characterised in that in the method, measurement of the properties of the fibrous web is carried out during running with measuring means, that information on the properties of the fibrous web is incorporated in the system controlling the quality of the fibrous web, and that the information on the properties of the fibrous web is used as feedback and/or positive feedback information for other running parameters controlling the quality of the fibrous web.

The device applying the method according to the invention is characterised in that the device comprises measuring means by means of which the properties of the fibrous web can be measured during running, and that the measuring means are incorporated in the system controlling the quality of the fibrous web, where the information on the properties of the fibrous web can be used as feedback and/or positive feedback information for other running parameters controlling the quality of the fibrous web.

One method according to the invention is characterised in that in the method, the temperature of the belt is measured during running in a non-contacting manner from the opposite side of the belt with respect to the fibrous web. Furthermore, the device applying the method according to a second aspect of the present invention is characterised in that the device comprises measuring means by means of which the temperature of the belt surface can be measured during running in a non-contacting manner from the opposite side of the belt with respect to the fibrous belt.

A further method according to the invention is characterised in that in the method, the metal belt is cooled with a cooling medium at a point outside the area in which it is in contact with the tail threading cord, in order to obtain an essentially even temperature profile for the metal belt. The device according to the invention, on the other hand, is characterised in that the device comprises means for cooling the metal belt with a cooling medium outside the area in which it is in contact with the tail threading cord in order to obtain an essentially even temperature profile for the metal belt.

Preferred embodiments of the invention are disclosed in the dependent claims. The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic side view of an example implementation of a part of an apparatus according to the invention,

Figure 2 shows a diagrammatic side view of another example implementation of the device according to the invention,

Figure 3 shows a diagrammatic side view of a third example implementation of the device according to the invention, and

Figure 4 shows the arrangement of Figure 3 as a top view.

Figure 1 thus shows a part of an apparatus applying the method according to the invention. The part of the apparatus, indicated here by reference numeral 1, is in this case a belt calender used for processing a fibrous web W, such as paper or board, to obtain the desired quality. The apparatus is, for example, a paper or board machine.

T e calender 1 comprises an endless belt which is preferably made of electro- conductive material, such as metal or a metal alloy. The metal belt 2 rotates on its track around guide means, such as guide rolls 3, of which guide rolls at least one is movable for adjusting the tightness of the belt 2. The tightness of the metal belt 2 is one of the running parameters of the apparatus by means of which the processing of the fibrous web W on the calender 1 is controlled.

Outside the loop-like track formed by the belt 2 is arranged a counter-element 5 which includes a counter-surface that can be placed against the metal belt. The counter-element 5 is preferably a backing roll, around the mantle of which the belt 1 is arranged to run. The belt 1 is in contact with the mantle preferably over a distance corresponding to less than half of the overall length of the circumference of the mantle. Between the belt 1 and the mantle is formed a processing zone A, in this case the calendering zone, through which the fibrous web W is passed. The desired pressure impulse and thermal effect (running parameters) as a function of time are then exerted on the fibrous web. The possibilities for adjusting these are disclosed in greater detail in the applicant's earlier patent applications PCT/FI03/00066, PCT/FI03/00067, PCT/FI03/00068. To put it briefly, pressure can be adjusted, for example, by means of a nip roll 4 forming the nip with a backing roll, and the thermal effect can be adjusted by heating and cooling the metal belt 1 with heating and cooling devices 6 profiling in the lateral direction of the metal belt 1. The adjustment of belt 1 temperature also affects the transverse distribution (stress distribution) of the machine-direction tightness of the belt. Temperature changes and pressure changes in processing zone A change the thickness profile of the metal belt in the lateral direction. Changes in the lateral thickness profile, on the other hand, cause changes to take place in the properties of the fibrous web (for example in thickness and gloss).

In accordance with the present invention, for monitoring changes in the thickness of the metal belt 2, the device 1 comprises means 7a, 7b for measuring metal belt thickness, by which means the longitudinal thickness profile of the metal belt 2 and/or the lateral thickness profile of the metal belt is measured. The measuring means 7a, 7b include measuring devices applying the eddy-current method known as such. In this case, at least one such measuring device is located in the vicinity of the surface of the metal belt 2, for example in the area between two guide rolls 3. The measuring means 7a, 7b comprises at least one electromagnetic transmitter, such as a coil 7a, and on the opposite side of the metal belt 2 a receiver, such as a measuring coil 7b, the metal belt 2 running between them. The measuring device 7a, 7b can also be located in such a way that the fibrous web will travel with the metal belt 2 between the transmitter coil 7a and the measuring coil 7b (measuring device depicted in broken line). As it is non-conductive, the fibrous web W will not affect the thickness measurement of the metal belt 2 carried out by the eddy- current measuring method.

To put it briefly, measurement is preferably carried out by using a pulsed eddy- current measuring technique. In it, the transmitter coil 7a is used to form a three- phase magnetic field in the electro-conductive belt 2, whereby eddy currents are also induced to the belt 2 in three different phases. From each successive phase, voltages characteristic of each phase are induced to the measuring coil 7b. From them can, in turn, be determined the distance of the measuring coil 7b from the surface of the metal belt 2 to be measured, the electrical resistance of the material being measured, and the thickness of the metal belt 2.

The above-mentioned measuring device 7a, 7b, or several measuring devices 7a, 7b, can be fitted to move in a transverse direction with respect to the direction of travel of the belt 2. Alternatively, a sufficient number of measuring devices 7a, 7b can be fitted in a transverse row with respect to the direction of travel of the belt 2, whereby more detailed measuring results are obtained compared with moving measuring devices. Measurement can be carried out while the metal belt 2 moves and essentially continuously.

The measurement data obtained on the thickness of the metal belt 2 can be used for several purposes. This data can be incorporated into the system 10 controlling the quality of the fibrous web W, to which belong, among others, the control devices 6 and 4 of the running parameters, such as belt 2 temperature and the processing area A pressure impulse. The information on the thickness of the belt 2 and the changes taking place in it is obtained in real time from the measuring coil 7b, for example, along the transmission path 8 between the system 10 and the measuring coil 7b, to the system controlling the quality of the fibrous web W. Thus, for example, changes in the thickness profile of the edge zones of the belt can be monitored in connection with different load and temperature changes.

The measurement data can be used in a system 10 controlling the quality of a fibrous web W, for example, in such a way that changes in the quality of the fibrous web W, which are due to changes in the thickness of the belt 2, are compensated for by using the thickness data on the belt 2 as positive feedback for the other parameters controlling the quality of the fibrous web W. For example, from the controlling system 10 can be given control commands along transmission paths 9 to the profiling heating and cooling devices 6 of the belt 2. Profiling heating or cooling can be controlled so that the thickness profile of the belt 2 will be of the desired type, for example even. It is also conceivable to control the tightness profile of the belt 2 by controlling the thickness profile. The quality control system 10 is obviously connected to other parts of the apparatus 1 (here, of a paper machine) in addition to the calender, and thus the thickness data may obviously also be used as positive feedback data for the running parameters of other parts of the apparatus 1 controlling the quality of the fibrous web W.

A model can also be made of the effects of the changes in the thickness of the belt 2 on the quality of the web W, on the basis of which model, the quality control system 10 will make the necessary compensating adjustments to the parameters controlling quality.

Measurement data can be used for monitoring the quality of the belt 2 itself. For example, before its actual commissioning, the belt 2 is ground to appropriate thickness. The measurement data on measurements preceding grinding can be used for setting the grinder so as to obtain the correct thickness profile for belt 2. Furthermore, for example, changes in the tensions and temperatures of the belt 2 will before long cause damage to the belt, especially in the edge zones of the belt 2. These defects are observed in good time, taking into account the other parameters of the quality control system. On the basis of observations, the belt 2 may, for example, be changed at the optimal time.

Figure 2 thus shows an apparatus 1 applying the method according to a second aspect of the invention. Here, the apparatus is a metal belt calender used for processing the fibrous web W to provide the desired processing effects. The apparatus could also be some other processing apparatus, such as a drying apparatus, a film transfer apparatus, a printing apparatus, etc. The belt calender 1 is installed, for example, in a paper or board production line as an on-line device, or it operates independently as an off-line device. The apparatus 1 comprises an endless belt 2 made of metal which rotates around guide rolls 3, of which guide rolls at least one is movable for adjusting the tightness of the belt 2. Outside the loop- like track formed by the belt 2 is arranged a counter-element 5 which includes a counter-surface that can be placed against the belt. The counter-element 5 is preferably a backing roll, around the mantle of which the belt 1 is arranged to run. The backing roll 5 may preferably be a thermo roll. Between the belt 2 and the roll 5 mantle is formed a processing zone A, through which the fibrous web W to be processed is led. The desired pressure impulse and thermal effect are then exerted on the fibrous web W as a function of time. The possibilities for adjusting the process parameters effective in processing zone A are disclosed in greater detail in the applicant's earlier patent applications

PCT/FI03/00066, PCT/FI03/00067, PCT/FI03/00068, and will not be described in greater detail in this connection.

The pressure of the processing zone/the pressure impulse in the processing zone can, in addition to belt tightness, be adjusted, for example, by means of the nip roll 4 forming a nip N with the backing roll 5. The thermal effect in the processing zone can be adjusted by heating and cooling the belt 2 with its heating and cooling devices 6a, which may be profiling in the lateral direction. Similarly, heat may be supplied to or removed from the metal belt by guide means 3. By controlling the temperature of the belt 2, also the transverse distribution (stress distribution) of the machine-direction (MD) tightness of the belt is affected.

According to the present invention, to measure the temperature of the belt 2, the apparatus 1 comprises means 70, by which means the temperature of the belt 2 can be measured to indicate its longitudinal and/or lateral temperature profile. The measuring means 70 include temperature sensors applying non-contacting measuring techniques known as such, for example, the infrared technique, which may be either point measuring or so-called line scanning sensors. In this case, at least one such temperature sensor is located in the vicinity of the belt 2 surface, for example, in the area between two guide rolls 3. The temperature sensors 70 may also preferably be located before the processing zone A and/or after the processing zone. Furthermore, if cooling/heating devices 6a, 6b are used for cooling and/or heating the belt 2, the measuring devices 70 may be located before and/or after the cooling/heating devices 6a.

The belt 2 surface in contact with the fibrous web W is finished and polished in order to achieve the qualitative properties of the fibrous web, which means that it is unsuitable as an object of measurement by thermographic camera. In the method according to the invention this problem is solved by measuring the temperature preferably on the inside of the belt cycle, that is, on the "reverse" side with respect to the fibrous web W. As the metal belt 2 is remarkably thin (normally of the order of about 1 mm or less), the average temperature of the belt is obtained with good accuracy by carrying out the measurement on the other side of the belt. The emissivity of this side of the belt 2 can be arranged to be such that infrared thermal measurement can be successfully carried out. The belt may, for example, be polished so as to have a matt finish. It has been found that in contact with the metal roll 3, the surface of the belt 2 is not polished but remains "rough".

According to one embodiment of the invention, temperature measurement is carried out over the total width of the belt so that a temperature profile transverse to the belt is obtained.

According to a further embodiment of the invention, measurement can be carried out by applying synchronisation in such a way that measurement is always carried out at the same point on the belt cycle 2 in its longitudinal direction, whereby the temperature of the belt 2 can be determined accurately in its desired longitudinal position.

The method according to the invention is applicable to measuring the temperature of the metal belt 2 also when polymer coatings or the like are used in the belt 2, especially on the surface on the fibrous web W side. Furthermore, the method according to the invention is also reliable is cases where dirt adheres on the fibrous web side of the belt or when the roughness of the surface changes as a result of wear.

The measurement data obtained by means of the invention can be used for several purposes. The measurement data obtained can be used, for example, for controlling the treatment process of the fibrous web W (by controlling the heating or profiling of the belt) or for controlling the running of the belt cycle. Data may also be transmitted to the system 10 controlling the quality of the fibrous web W which comprise, for example, belt temperature control means 6a, control means 6b for controlling the temperature or moisture of the fibrous web, backing roll temperature control means 5, compressive force control means 4 or control means 3 for controlling the position of the guide rolls (belt tightness. The system may further include measuring means 13a and 13b for monitoring the state or the fibrous web (temperature, moisture, calibre, gloss, etc.). Information on the temperature of the belt 2 and the changes taking place in it can be transmitted to the system 10 in real time along a transmission path 12 between the system 10 and the measuring device 70.

The most common application of the measurement 70 of belt temperature is to use the measurement as a part of the feedback control of the belt temperature. In this case, the real temperature of the belt is monitored with measuring sensors 70, and if this temperature deviates from the given target temperature, the controller 10 will control the actuator 6a on the basis of the measuring signal received until the target temperature is reached. The target temperature may be predetermined, for example, by means of pilot tests. The target temperature of the belt may also be obtained from the on-line quality control system in real time, whereby the controller will determine a preferable process temperature (belt temperature) on the basis of quality measurements (13a and 13b) of the fibrous web. Thus, the controlling of the belt temperature acts as a part of a more extensive control system.

An essential application for controlling the running of the belt cycle is the use of a measuring signal 70 in controlling the belt. The temperature profile of the belt inevitably produces a tightness profile through thermal expansion, this profile having a significant effect on the running of the belt cycle. From the measured temperature profile can be estimated the cross-direction (CD) profile of the machine-direction tightness of the belt. The running of the belt cycle is controlled mainly by adjusting the position of the guide rolls 3, and this adjustment may thus be based on temperature measurement.

On a more general level, other measured process variables relating to the said more extensive control system and changes in them can be rapidly transmitted to the system 10. Accordingly, the quality control of the web will consist of positive feedback and/or feedback control, including, in addition to the belt 2 temperature measuring device 70, means 13a and 13b for measuring the state of the fibrous web, actuators 3, 4, 5, 6a, 6b and the quality control system 10 (controller). Thus each actuator operating under quality control will be rapidly controlled by the controller based on quality measurements, such as belt temperature measurement. The control may be based, for example, on a model. Controllable actuators are listed above and the controlled variables, or running parameters, controlled by them may be, for example, the following: input temperature and moisture of the web, belt tightness, belt temperature, belt moisture, overlap angle and length of the belt, additional load (nip roll 4), temperature of the thermo roll (i.e. roll 5).

Naturally, the above-mentioned adjustments may relate either to average target values in the transverse direction or measurement and adjustment may take into account variations in measurement and controlled variables, that is, profiles are measured and adjusted.

Furthermore, by means of the method according to the invention may especially be observed temperature variations in the belt 2, in the longitudinal direction (MD) of the belt. By synchronising the taking of the measurement suitably with the cycle length of the belt, the measuring position can be varied controllably to the desired point on the belt in the machine direction. In this way can be discovered cyclic process failures in belt temperature, such as local soiling of the belt or heat transfer roll, which decreases the heat transfer coefficient.

The measurement data of the machine-direction temperature profile can also be used to control a rapid heating actuator, such as an induction heater (for example in position 6a), to adjust the machine-direction temperature profile of the belt.

One conceivable application of the invention could be the measurement of heating/cooling effect transmitted through the belt. By positioning temperature sensors on both sides of the pressing zone, from the temperature difference can easily be calculated the thermal energy transmitted between the belt and the fibrous web. The measurement data can be used to aid process control, to adjust the cooling/heating effects on the belt, 2 and thus to adjust especially the processing temperature of processing zone A. Measured data can also be used in systems monitoring energy use. Furthermore, according to the embodiment shown in Figure 3, the metal belt calender 1 comprises a metal belt 2 arranged to rotate around guide rolls 3. Outside the belt is arranged a thermo roll acting as a counter-element 5, whereby the calendering zone is formed between the belt 2 and the roll 5. At least some of the guide rolls 3 are preferably arranged to be movable for the purpose of adjusting the belt 2 to the desired tightness and for adjusting the length of the contact area between the belt 2 and the counter- element 5 if necessary, for example, by changing the overlap angle between the roll 5 and the belt 2. Inside the belt cycle 2 may optionally be arranged a nip roll 4 acting as a pressing means pressing the belt 2 against the roll 5, thus generating the highest pressure within the calendering zone of the nip zone.

According to the present invention, in the metal belt calender 1 is arranged a metal belt cooling device 6a which is comprised of cooling medium spreading means 6a, by means of which the cooling medium, for example, air or water, can be directed at desired points on the metal belt 2. The cooling medium spreading means 6a are preferably arranged to be movable in the transverse direction of the metal belt, as shown in Figure 4, but they may also be comprised of several spray nozzles or similar means extending across the width of the metal belt 2, by means of which the supply of cooling medium may be directed in the desired manner at different points over the width of the metal belt 2. The cooling medium spreading means 6a are preferably arranged outside the metal belt cycle 2, at a point before the calendering zone, as shown in Figures 1 and 2, but they may conceivably also be located at a point following the calendering zone and also inside the metal belt cycle, at a point before or after the calendering zone.

The basic idea of the invention is to cool the metal belt in the area outside the tail threading cord Wi in order to render the temperature profile as straight as possible and to even out the prevailing tensile stresses at different points of the transverse direction of the belt to increase the fatigue durability of the belt. When using, for example, water as the cooling medium, and when belt temperature exceeds 100 °C, the water sprayed on the belt surface vaporises essentially immediately and it may be recovered with air conditioning in the same way as the moisture evaporating from the web after the nip. This type of directing of the cooling medium at the metal belt will help to achieve a more even quality for the paper or board grade being processed, especially when the normal operating temperature of the belt is significantly lower than that of the thermo roll. If this type of cooling is not used, and no cooling medium cycle is arranged, both the belt and the belt's guide rolls will heat up close to the temperature of the thermo roll, whereby after the spreading of the web, a considerably long time will be taken before the belt temperature has fallen to essentially the temperature of the web.

The spraying of the cooling medium is preferably arranged to be profiling, for example, so that cooling medium spraying is directed only at the hottest points on the metal belt in order to render the heat profile essentially straight.

Claims

1. A method for controlling the running parameters in an apparatus (1) for processing a fibrous web (W), the processing apparatus (1) comprising an endless metal belt (2) arranged to rotate around guide means (3), and at least one counter- element (5) forming a contact surface with the metal belt (2), between which metal belt (2) and counter- element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed is passed, characterised in that in the method, thickness measurement of the metal belt (2) is carried out during running by eddy-current measurement.

2. A method as claimed in claim 1, characterised in that the metal belt (2) is measured essentially continuously in the longitudinal direction to determine the longitudinal thickness profile.

3. A method as claimed in claim 1 or 2, characterised in that the metal belt (2) is measured essentially continuously in the lateral direction to determine the lateral thickness profile.

4. A method as claimed in any of the claims 1 to 3, characterised in that the information on the thickness of the metal belt (2) is incorporated in the system (10) controlling the quality of the fibrous web (W), and that the information on the thickness of the metal belt (2) is used as positive feedback information for the other running parameters controlling the quality of the fibrous web and/or for monitoring the state of the metal belt (2).

5. A device for controlling the running parameters in an apparatus (1) for processing a fibrous web (W), the processing apparatus (1) comprising an endless metal belt (2) arranged to rotate around guide means (3), and at least one counter- element (5) forming a contact surface with the metal belt (2), between which metal belt (2) and counter- element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed can be passed, characterised in that the device comprises measuring means (7a, 7b) by means of which the thickness of the metal belt (2) can be measured during running by eddy- current measurement.

6. A device as claimed in claim 5, characterised in that one or more measuring means (7a, 7b) are fitted to move in a transverse direction with respect to the direction of travel of the metal belt (2) in order to determine the longitudinal and/or lateral thickness profile of the metal belt (2).

7. A device as claimed in claim 5 or 6, characterised in that several measuring means (7a, 7b) are fitted in a transverse row with respect to the direction of travel of the metal belt (2) in order to determine the longitudinal and/or lateral thickness profile of the metal belt (2).

8. A device as claimed in any of the claims 5 to 7, characterised in that the measuring means (7a, 7b) comprise an electromagnetic transmitter or coil (7a) by means of which can be formed a three-phase magnetic field for inducing eddy currents to the metal belt (2) in three different phases, and a receiver or measuring coil (7b), to which are induced the voltages corresponding to the eddy currents, which correlate with the thickness of the metal belt (2).

9. A device as claimed in any of the claims 5 to 8, characterised in that the measuring means (7a, 7b) are connected to the system (10) controlling the quality of the fibrous web (W), where the information on the thickness of the metal belt (2) is available for use as positive feedback information for the other running parameters controlling the quality of the fibrous web (W) and/or for monitoring the state of the metal belt (2).

10. A method for controlling the running parameters in an apparatus (1) for processing a fibrous web (W), the processing apparatus (1) comprising an endless metal belt (2) arranged to rotate around guide means (3), and at least one counter- element (5) forming a contact surface with the metal belt (2), between which metal belt (2) and counter- element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed is passed, characterised in that in the method, measurement of the properties of the fibrous web (W) is carried out during running with measuring means (13a, 13b), that the information on the properties of the fibrous web (W) is incorporated in the system (10) controlling the quality of the fibrous web (W), and that the information on the properties of the fibrous web is used as feedback and/or positive feedback information for the other running parameters controlling the quality of the fibrous web (W).

11. A method as claimed in claim 10, characterised in that the measuring means (13a, 13b) are used to measure at least the temperature, moisture, calibre, gloss, roughness, air permeability and/or flexural rigidity of the fibrous web.

12. A device for controlling the running parameters in an apparatus (1) for processing a fibrous web (W), the processing apparatus (1) comprising an endless metal belt (2) arranged to rotate around guide means (3), and at least one counter- element (5) forming a contact surface with the metal belt (2), between which metal belt (2) and counter- element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed can be passed, characterised in that the device comprises measuring means (13a, 13b), by means of which the properties of the fibrous web (W) can be measured during running, that the measuring means (13a, 13b) are connected to the system (10) controlling the quality of the fibrous web (W), where the information on the properties of the fibrous web is available for use as feedback and/or positive feedback information for the other running parameters controlling the quality of the fibrous web (W).

13. A device as claimed in claim 12, characterised in that measured properties of the fibrous web (W) include at least temperature, moisture, calibre, gloss, roughness, air permeability and/or flexural rigidity.

14. A method for measuring the temperature of the belt (2) in an apparatus (1) for processing the fibrous web (W), the processing apparatus (1) comprising an endless belt (2) arranged to rotate around at least one guide means (3), and at least one counter-element (5) forming a contact surface with the metal belt (2), between which belt (2) and counter-element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed is passed, characterised in that in the method, the temperature of the belt (2) is measured during running in a non-contacting manner from the opposite side of the belt (2) with respect to the fibrous web (W).

15. A method as claimed in claim 14, characterised in that the belt (2) is measured essentially continuously in its longitudinal direction to determine the longitudinal temperature profile.

16. A method as claimed in claim 14, characterised in that the belt (2) is measured essentially continuously in its lateral direction to determine the lateral temperature profile.

17. A method as claimed in claim 14, characterised in that the temperature is measured in a synchronised manner so that the temperature of the belt (2) at a particular point is obtained.

18. A method as claimed in claim 14, characterised in that the measured temperature is used as feedback for adjusting the temperature of the belt (2).

19. A method as claimed in any of the claims 14 to 18, characterised in that the information on the temperature of the belt (2) is incorporated in the system (10) controlling the process (10), and that the information on the temperature of the belt (2) is used as positive feedback information for the other running parameters controlling the quality of the fibrous web (W).

20. A method as claimed in any of the claims 14 to 18, characterised in that the information on the temperature of the belt (2) is incorporated in the system (10) controlling the process (10), and that the information on the temperature of the belt (2) is used for controlling the running of the belt cycle (2) and/or for monitoring the state of the belt (2).

21. A method as claimed in any of the claims 14 to 20, characterised in that in the method, as a belt (2) is used a metal, polymer or sandwich-type belt, a wire, felt or the like.

22. A device for measuring the temperature of the belt (2) in an apparatus (1) for processing the fibrous web (W), the processing apparatus (1) comprising an endless belt (2) arranged to rotate around at least one guide means (3), and at least one counter-element (5) forming a contact surface with the metal belt (2), between which metal belt (2) and counter-element (5) is formed a processing zone (A) for the fibrous web (W), through which the fibrous web (W) to be processed is passed, characterised in that the device comprises means (70) for measuring the temperature of the belt (2) during running, in a non-contacting manner from the opposite side of the belt (2) with respect to the fibrous web (W).

23. A device as claimed in claim 22, characterised in that one or more measuring means (70) are arranged to be moveable in an essentially transverse direction with respect to the direction of travel of the belt (2) in order to determine the longitudinal and/or lateral temperature profile of the belt (2).

24. A device as claimed in claim 22, characterised in that one or more measuring means (70) are arranged in succession in the direction of travel of the belt (2) in order to measure the temperature difference between these positions.

25. A device as claimed in any of the claims 22 to 24, characterised in that the measuring means (70) are connected to the system (10) controlling the quality of the fibrous web (W), where the information on the temperature of the belt (2) is available for use as positive feedback information for the other running parameters controlling the quality of the fibrous web (W) and/or for monitoring the state of the belt (2).

26. A device as claimed in any of the claims 22 to 25, characterised in that the belt (2) is of a metal, polymer or sandwich type, a wire, felt or the like.

27. A method for controlling the temperature profile and tensile stresses of the belt of the metal belt calender intended for processing a fibrous web during the threading of the fibrous web, whereby a narrow tail threading cord (Wj) is moved into contact with the metal belt (2) having a higher temperature than the web, thus bringing about a cooling effect on the metal belt, characterised in that in the method, the metal belt (2) is cooled with a cooling medium at a point outside the area in which it is in contact with the tail threading cord, in order to obtain an essentially even temperature profile for the metal belt (2).

28. A method as claimed in claim 27, characterised in that in the method, as counter-element of the metal belt calender is used a heated thermo roll (5) when the metal belt (2) is unheated, whereby the metal belt will be heated when in contact with heated thermo roll without a fibrous web between them.

29. A method as claimed in claim 27 or 28, characterised in that the cooling medium is a liquid or a liquid mixture.

30. A method as claimed in claim 29, characterised in that the cooling medium is water.

31. A method as claimed in claim 27 or 28, characterised in that the cooling medium is a gas or a gas mixture.

32. A method as claimed in claim 31, characterised in that the cooling medium is air.

33. A method as claimed in any of the claims 27 to 32, characterised in that the cooling is arranged to be profiling so that cooling medium effect is directed only at the hottest points on the metal belt.

34. A device for controlling the temperature profile and tensile stresses of the belt (2) of the metal belt calender (1) intended for processing a fibrous web during the threading of the fibrous web, the metal belt calender (1) comprising a belt (2) arranged to rotate around at least one guide means (3), outside which belt is arranged at least one counter-element (5) forming a contact surface with the belt, so as to form a processing zone for the fibrous web between the metal belt and the counter-element, through which the web to be processed is passed, whereby when a narrow tail threading cord (Wj) is moved into contact with the metal belt (2) having a higher temperature than the web, the metal belt will cool at the cord, characterised in that the device comprises means for cooling the metal belt (2) with cooling medium at a point outside the area in which it is in contact with the tail threading cord, in order to obtain an essentially even temperature profile for the metal belt (2).

35. A device as claimed in claim 34, characterised in that the cooling means include cooling medium spraying means (6a) which can be directed at the desired point in the metal belt.