FI115073B - Controlling running parameters in apparatus for processing fibrous web involves measuring thickness of metal belt during running by eddy-current measurement and using the information as positive feedback for other running parameters - Google Patents

Abstract

Controlling running parameters in an apparatus for processing a fibrous web involves measuring the thickness of a metal belt during running by eddy-current measurement and incorporating the information in a system controlling the quality of the fibrous web. The information 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. The processing apparatus comprises the metal belt rotating around a guide unit and at least one counter element forming a contact surface with the metal belt. Between the metal belt and the counter element, a processing zone is formed for the fibrous web. Independent claims are included for the following: (1) a device for controlling the running parameters in the apparatus for processing the fibrous web; and (2) a method and device for measuring the temperature of the belt in the apparatus.

Description

115073

A method for measuring the temperature of a belt and an apparatus for applying the method

The present invention relates to a method for measuring and controlling a belt temperature in a fibrous web processing apparatus comprising an endless belt which is rotated around at least one guide member and at least one matching member forming a contact surface with the belt.

The present invention further relates to an apparatus for measuring belt temperature and controlling a process in a fiber web processing apparatus having an endless belt arranged to rotate around at least one guide member and at least one matching member forming a contact surface with the belt. .

Such devices for handling fibrous webs are known in the prior art, for example from the applicant's patent applications PCT / FI03 / 00066, PCT / FI03 / 00067, PCT / FI03 / 00068. The fibrous web processing devices disclosed in these applications are applicable to the calendering of a wide variety of fiber types such as different paper and board grades, as well as to coating, film transfer, drying and / or printing. Further, the belt used in the fibrous web processing devices disclosed in said patent applications. -. n is particularly preferably a metal belt, wire, but it may also be polymeric or * ·. composite wire or ribbon, or the like. The 'description of this patent application refers, by way of example, to, but not limited to, a metal belt! 25 to it.

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The process effects of the fibrous web processing apparatus such as those referred to above, on the final properties of the fibrous web, are controlled by adjusting the process conditions in the treatment area, such as processing pressure, process temperature, contact moisture, and contact time. These adjusting measures are implemented in practice by adjusting the actuators acting on the fiber web, '; groups; for example, by adjusting the temperature of the belt and / or counterpart or the length and / or the duration of the treatment zone or the tension of the belt.

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The control measures to control the process may be based on predetermined target values for actuator control variables, for example experimentally. For example, pilot runs have determined the optimum roll and belt temperature for each type of fiber web, as well as the pressure and action time of the impact zone. When the process is in constant 5 mode, the actuator control values are set to advantageous values and maintained at those target values. However, in order for actuator controls to work accurately and set values to remain within target values, actuator performance must be monitored. For example, the temperature and tension of the belt must be measured either directly or indirectly and, if necessary, adjusted so that the process operates consistently.

10 Adjustment can also be based on feedback on-line process measurement, whereby the on-line measurement values of the fiber are used as a basis for the adjustment. If the observed treatment effect does not match the target state, the control system will adjust the actuator settings, such as belt or roll temperature or belt tension, so that the target level is reached. Further, in order to maximize the amount of production meeting the quality criteria during the process transient change, actuators must be able to accurately control the state and delay. Here too, measurements can be used to monitor the status of the actuator itself, such as the belt temperature, and as a basis for adjustments. By way of example, a situation in which variations from earlier stages of the process cause interference in the processing process, to compensate for the need to adjust the actuators, however, if it is desired to standardize the final quality produced.

• * · • · Measuring the temperature of a moving belt with a shiny surface is currently not very reliable under normal conditions of production. Numerous different temperature measurement techniques are known in Peri-25. In principle, the temperature of a moving belt may be measured by, for example, a tactile (drag) heat sensor, or by a non-contact technique such as a thermal camera (IR measurement).

• 30 The difficulty of non-contact infrared measurement is that of a thermal roller or belt; The surface in contact with the nanofiber web has been polished and finished to:. . good quality of the fibrous web is achieved. From the point of view of thermal camera measurement, the low emission coefficient of the shiny belt surface as well as reflections from the environment are problematic. Even a small surface contamination greatly affects the emission factor and causes 35 measurement errors. Even in a test facility environment, thermal cameras need to be calibrated 3 115073 daily, and thus such a solution is not suited to factory conditions where high reliability and low maintenance are required. On the other hand, it is also possible in principle to use a tactile (flat-wound) temperature measurement under production conditions. At high speeds, however, the result of the touch measurement is uncertain and the gauges require constant maintenance and repeated calibration. The excess heat from the slip friction also impairs the measurement.

The object of the present invention is to solve the above problems. To achieve said object, the method 10 of the present invention is characterized in that the method measures the temperature of the belt while driving in contact with the fibrous web on the opposite side of the belt. Further, the apparatus employing the method of the present invention is characterized in that the apparatus comprises measuring means for measuring the surface temperature of the belt during driving, in contact with the fibrous web, on the opposite side of the belt. Preferred embodiments of the invention are set forth in the dependent claims.

The invention will now be explained in more detail with reference to the accompanying drawing, in which Figure 1 is a schematic side view of an exemplary embodiment of the device of the invention.

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Figure 1 thus shows an apparatus applying the method according to the invention; '; 1. The apparatus herein is a metal belt calender used to process a fiber web W to obtain the desired processing effects. The device may also be another processing device. Such as a drying device, a film transfer device, a printing device, etc. The belt calender 1 is mounted, for example, on a paper or board manufacturing line as an on-line device or functions as an independent off-line device. 1 includes an endless metal belt 2 which rotates about guide rollers 3, at least one of which is movable to adjust the tension of belt 2. Outside the loop forming the belt 2, a counter member 5 is provided which includes a counter surface that can be placed against the belt. Preferably, the stop member 5 is a counter roll, the belt 2 of which is provided with a strap 2. The counter roll 5 may in particular be a thermal roll.

f »• 1: A treatment area A is formed between the belt 2 and the mantle of the roll 5, through which the product to be treated _. '; the fibrous web W is exported. The fibrous web W is then subjected to the desired pressure pulse and the heat *! *. 35 dust effect as a function of time. The control options for process parameters affecting processing area A »4115073 are described in more detail in the applicant's previous patent applications PCT / FI03 / 00066, PCT / FI03 / 00067, PCT / FI03 / 00068 and are not described in more detail herein.

In addition to the belt tension, the pressure / pressure impulse of the treatment area in the treatment area can be adjusted, for example, with the counter roll 5 by means of the nip roll 4 forming the nip N. The thermal effect in the treatment area can be adjusted by heating and cooling the belt 2 by means of its heating and heating means 6a, which can be profiled in width. Likewise, heat can be introduced into or removed from the metal belt by means of control elements 3. At the same time, the temperature adjustments of the belt 2 also affect the transverse distribution of the belt tension MD (tension distribution).

In accordance with the present invention, for measuring the temperature of the belt 2, the apparatus 1 comprises means 7 for measuring the temperature of the belt 2 to indicate its length-15 and / or width-directional temperature profile. The measuring means 7 include temperature sensors employing contactless measuring techniques known per se, for example infrared technology, which may be either spot-measuring or so-called. cloud-scanning sensors. In this case, at least one such temperature sensor is located near the surface of the belt 2, for example in the region 20 between two guide rollers 3. The temperature sensors 7 can also advantageously be located before and / or after the treatment area A. Further, if the belt 2 is cooled and / or heated. . ·. the cooling / heating devices 6a, 6b are used for measuring, the measuring devices 7 · · can be placed before and / or after the cooling / heating devices 6a.

/ '; * 25 The surface of the strap 2 in contact with the fiber web W is finished and polished to achieve •:: quality, making it unsuitable for thermal camera measurement. In the method according to the invention, the problem is solved so that the temperature is preferably measured from the inside of the belt cycle, i.e. from the "sticky" side to the fiber web W. Because the metal belt 2 is remarkably thin; i * 30 (normally on the order of about 1 mm or less), the average belt temperature is obtained with good accuracy by measuring on one side of the belt.

> '. This side of the belt 2 can be traced to an emissivity such that infrared heat measurement is successful. For example, the belt can be sanded to a matte finish. Is ' ·; · 'It has been found that the surface of the belt 2 does not polish in contact with the metal roll 3: 35 but remains "rough".

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According to one embodiment of the invention, the temperature measurement is carried out over the entire width of the belt so as to obtain a transverse temperature profile of the belt.

According to a further embodiment of the invention, the measurement can be carried out using synchronization so that the measurement is always made at the same point of the belt rotation 2 in its longitudinal direction, whereby the temperature of the belt 2 at its desired longitudinal position can be accurately determined.

The method according to the invention is also suitable for measuring the temperature 10 of the metal belt 2 when polymeric coatings or the like are used on the belt 2, in particular on the surface facing the fiber web W thereof. Further, the method according to the invention works reliably even when dirt is adhered to the fibrous web side of the belt or the surface roughness changes as a result of wear.

15 The belt temperature measurement data obtained by the method can be used for many purposes. The measurement data obtained can be used, for example, to control the process of treating the fibrous web W (by controlling belt heating or profiling) or to control the flow of the belt cycle. The information may also be transmitted to the fiber web W quality adjusting rigid system 9, which may include, for example, belt temperature 20 humidity adjusting members 6a, fiber web temperature or humidity adjusting members 6b, back roll temperature adjusting members 5, clamping force adjusting members 4, or tension rolls. adjusting means 3. Further, the system may include a fiber web condition • * · (temperature, humidity, caliber, gloss, etc.) monitoring means 8a and 8b. Information: ,,; * the temperature of the belt 2 and changes therein can be transmitted to the fluid; 25 in real time along the transmission path 11 between the system 9 and the measuring device 7.

The most common application of belt temperature measurement 7 is the use of measurement as part of the feedback control of belt temperature:. In this case, the measuring sensors 7 monitor the actual belt temperature, and if this temperature deviates from the given target temperature, the regulator 9a controls the actuator 6a until the target has reached the measured measurement signal. the temperature has been reached. For example, the target temperature may be predetermined by pilot experiments. The target belt temperature can also be obtained from an on-line quality control system in real time, whereby, based on the fiber web quality measurements (8a and 8b), the controller 9 .. determines the preferred process temperature (belt temperature). Thus, the adjustment of the belt temperature 35 acts as part of a broader control system.

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An essential application for the control of the belt rotation is the use of a measuring signal 7 for controlling the belt. The temperature profile of the belt through thermal expansion will inevitably result in a tension profile which will have a significant effect on the course of the belt rotation. From the measured temperature profile, a cross-machine (CD) profile of the belt tension 5 can be estimated. The passage of the belt rotation is mainly controlled by adjusting the position of the guide rollers 3, and thus this adjustment can be based on a temperature measurement.

Naturally, the aforementioned adjustments may be directed either to the transverse average target values or the measurement and adjustment may take into account the variations in the measurement and adjustment quantities in the transverse direction of the machine, i.e. the profiles are measured and adjusted.

Furthermore, the method according to the invention can in particular detect the temperature variations of the belt 2 in the longitudinal direction (MD) of the belt. By synchronizing the sampling sample 15 appropriately to the belt rotation time, the measuring position is variably varied to the desired machine direction position on the belt. In this way, cyclic process disturbances in the belt temperature, such as local fouling of the belt or heat transfer roller, which reduces the heat transfer coefficient, can be detected.

Further, the measurement data of the machine temperature profile may be used to control a fast heating actuator, such as an induction heater (e.g., at position 6a),. for adjusting the machine temperature profile of the belt.

• <· *. ,; One embodiment of the invention is the measurement of heating 25 / cooling power transmitted through the belt. By placing the temperature sensors in the compression zone mo «* ·; : On the lemon side, the thermal energy transferred between the belt and the fibrous web can easily be calculated from the temperature difference. The measurement data can be used to assist in: process control to adjust the cooling / warming power of the belt 2, and thus specifically to control the processing temperature of treatment area A. Measured data can be *! · 30 also used in energy monitoring systems

Claims (13)

A method for measuring the temperature of a web (2) in a processing machine (1) of a fiber web (W), which consists of an endless web (2) running around an at least one guide means (3) and at least one with the web (2) a contact surface forming the motor member (5), between which web (2) and the motor member (5) forms a treatment zone (A) for the fiber web (W), through which the fiber web (W) zone is led, characterized in that in the method the temperature of the web (2) is measured during thread motionless in relation to the fiber web (W) from opposite sides of the web (2). 10 A method according to claim 1, characterized in that the web (2) is measured substantially continuously in its longitudinal direction to determine a longitudinal temperature profile. 15 Method according to claim 1, characterized in that the web (2) is measured substantially continuously in its width direction in order to determine a temperature profile in the width direction. Method according to Claim 1, characterized in that the temperature is measured in synchronization so that the temperature of the web (2) is obtained at some of its positions. The method according to claim 1, characterized in that the measured temperature is used in turn to control the temperature of the web (2). * * · • · j 25 Method according to the preceding claims 1 - 5, characterized in that the temperature data of the web (2) is connected to a process controlling system: “(9), and that the temperature data of the web (2) is used as coupling data for the second fiber web ( W) quality regulating driving parameters. "" 30 Method according to any of the preceding claims 1 - 5, characterized in that the temperature data of the web (2) is connected to the process controlling system (9), and that the temperature data of the web (2) is used for controlling the orbit of the web (2). , 'and / or for checking the condition of the web (2). 115073 ίο Method according to one of claims 1 to 7, characterized in that in the method a metal, polymer or sandwich web, wire, felt or the like is used as web (2). Apparatus for measuring the temperature of a web (2) in a fiber web (W) processing machine (1), which processing machine consists of an endless web (2) running around a Itminstone (3) and an Itminstone one having the web (2) a contact surface forming the motor member (5), between which web (2) and the motor member (5) forms a treatment zone (A) for the fiber web (W), through which the fiber web (W) zone is led, characterized in that the device has measuring means (7), with which the temperature of the web (2) can be measured under no movement in relation to the fiber web (W) from opposite sides of the web (2). 10. Device according to claim 9, characterized in that one or more measuring means (7) is arranged to be displaced substantially transversely relative to the running direction of the web (2) to determine the longitudinal and / or transverse temperature profile of the web (2). . Device according to claim 9, characterized in that one or more measuring means (7) is arranged one after the other in the running direction of the web (2) to measure the temperature difference between these positions. 12. Device according to claim 9-11, characterized in that: the measuring means (7) are connected to a quality control system (9) of a fiber web (W), where: the temperature data of the web (2) can be used as coupling data for other fiber: · quality of the web (W) controlling driving parameters and / or for checking the condition of the web (2). • 13th Device according to any of claims 9-12, characterized in that "1. The nano (2) is of metal, polymer or sandwich construction, wire, felt or equivalent. the. LII