FI114162B - Procedure and Arrangements for Controlling Thickness of a Runway and Procedure for Following Calendering - Google Patents

Description

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A method and system for adjusting web thickness and a method for monitoring calendering

The invention relates to an on-line method for adjusting the thickness of a web in a roller of a paper-5 or board machine. It is a further object of the invention to provide a system for adjusting the thickness of a paper or board web in a track of a paper or board machine. The invention further relates to an on-line method for monitoring the calendering of a paper or board web in a nip between a calender roll.

The quality requirements for papermaking have increased as the 10 technologies using paper have evolved. New, faster copying and printing machines require very consistent paper quality for reliable, continuous operation. For example, paper thickness variations, both lengthwise and crosswise, can cause a production outage in a printing press.

Calendering 15 in paper machines and paper finishing devices utilizes rolls which form a nip with the counter roll. Multi-roll calendars have a plurality of successive nip formed by pairs of rolls through which the web is passed.

In order to control the process, it is important that the nip pressure, and in particular the line pressure distribution (profile) in the transverse direction of the web, i.e. in the axial direction of the rolls, is. . measurable and adjustable as needed.

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: ': 20 There are several ways to measure the pressure in the calender nip. In US

No. 5,383,371 discloses a method for measuring pressure in a nip in both longitudinal and transverse directions of the web. The method uses piezoelectric detectors which:. · * *. can be attached either to the roll body or between the roll coating layers. Detection. · · ', Preferably are made of polyvinylidene difluoride film (PVDF), which is a piezoelectric film. Detectors can also be attached between two layers of a roll coating.

US 5,562,027 discloses a variety of detectors such as piezoelectric detectors; rope and piezo-resistive sensors, optical fibers and stress strain sensors.

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The piezoelectric and piezo-resistive sensors are preferably made of thin films 30 and placed on a roll so as to measure radial pressure. For the stress - ,.; · * Implants provide indirect information on radial pressure. Optical Fibers: Sensors that utilize optical fibers can measure pressure in any direction.

The sensors shown may be located on the roll surface or between the roll layers.

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The piezoelectric detector disclosed in US 5,383,371 comprises the aforementioned PVDF film having a metallic pattern, for example an aluminum pattern, on both sides. A protective film is still provided on the metal pattern. Metallized areas form detectors that measure clamping force. The metal-5 patterns are joined by strip guides, which are also formed of metallized film strips. The measurement signals are applied to a display device which displays the compression force distribution. The measurement signals can also be fed to, for example, a calender adjustment system.

In US 5,383,371, for example, a radio transmitter, an optical transmitter, or any other technique known per se for transmitting a signal wirelessly to a receiver, a signal processing unit, may be used to transmit the signals. US 5,592,875 further discloses a wired signal transmission system using, for example, a slip ring or a rotating transformer when the entire roll is rotated and the signal processing unit is stationary. On the other hand, rolls of the type described above with a stationary core and a rotating housing can also be used, whereby the signals can be easily transmitted along the wires to the processing unit. The transfer of measurement signals from a rotating roll to fixed reception devices is also disclosed in FI 92 771.

Knowledge of the longitudinal and transverse pressures of the paper web on the paper machine roll nip is important to know and adjust the papermaking process.

• · • Y'i The aim may be to keep the pressure or pressure distribution constant or that this · '/ j distribution can be adjusted as desired, for example to control the thickness of the web across the web. The information provided by the pressure of the nip can determine the correct method for adjusting the thickness profile of the paper web. These adjustments • · t. · · '. 25 possibilities are known in many different ways. The most common procedure for observed web defects ···. to correct the evenness is to increase or decrease the clamping force on the paper web in the nip, preferably by selectively changing the pressure across the web. Other methods available include adjusting the thickness profile in the headbox • ;;; (lip duct adjustment) and heating or wetting the web.

F. US 4,791,863 discloses a system for adjusting the pressure profile of a nip across the web by means of zone adjusting rollers. The system comprises a zone adjustment roll and its counter element, such as a counter roll, which together form a nip through which the web to be processed passes. The zone adjustment roller is deflection compensated te, which comprises a stationary part, i.e. a massive central axis, and a cylindrical roller sheath about 35 rows round it. Sliding 11416 against the smooth inner surface of the roll shell; 3 shoes grouped into pressure loading zones, each of which is loaded with pressure cylinders.

US 4,903,517 also discloses a calender in which at least one nip is formed of a roll having a deformable, cylindrical-5-shaped shell around its rigid, bearing core, and a counter member thereof. Further, the rigid core may be stationary, with the shell rotating about it. The deformable casing is divided into sections that can be independently adjusted without affecting the other sections. The control units are arranged in at least one row parallel to the axis of the roll.

Further, the pressure profile of the nip can be adjusted by varying the temperature of the roll either inside or outside the roll 10, whereby the adjustment is based on thermal expansion within the roll.

The adjustment of the nip pressure and, through it, the thickness profile of the web is based on measurement data, which is usually collected by a transverse web thickness sensor mounted after the nip and fixed to the measuring bar. However, in this case, the measuring bar is often 15 away from the control arrangement, and in addition, the sensor moves transversely, resulting in a large adjustment delay. In addition, information is only available on the final paper thickness. On the other hand, the actual pressure in the nip is influenced by many factors, such as running speed, the characteristics of the incoming paper, and the temperature, for which there is no precise information. In this case, the operation of the nip, in particular the pressure therein and the resulting thickness,. There is no precise understanding of the 20 profile changes.

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It is an object of the invention to provide a method for monitoring web calendering and a method and system for rapidly and accurately adjusting the thickness profile of a web. *. for.

These objects have now been achieved as set forth in the appended claims.

The on-line method for adjusting the web thickness in accordance with the invention is characterized in that the roller of a paper or board machine is characterized in that: > ·. - the thickness of the web is measured in the machine with at least one thickness measuring member before the nip between the rolls,; : - the compressive pressure exerted on the web is measured by at least one pressure measuring member at a nip,. - the thickness of the web is re-measured after the nip by at least one thickness measurement. means, - the thickness profile of the web and the distribution of compression pressure in the nip are measured in the transverse direction, and the thickness of the web is selectively adjusted to influence the thickness profile, and 11416: 7 4 - data obtained from thickness measurements before and after the nip and compression pressure.

Thus, in the method according to the invention, measurement data is collected on the properties of the paper web in the transverse direction just before, at and just after the nip, wherein the thickness of the paper web is measured just before and just after the nip. This data is combined in a data processing and control unit to determine the relationship between the pressure applied to the nip and the resulting thickness change. Based on this information, the roll load can be further corrected for either a relative change target or a direct Ιοί 0 roll change target to selectively control the web thickness.

Preferably, the pressure applied to the web in the nip is controlled by the pressure medium or roll surface temperature affecting the roll dimensions. The surface temperature of the roll causes thermal expansion or contraction of the roll, which changes the roll dimensions. The surface temperature of the roll can be influenced, for example, by changing the temperature of the roll mantle or by externally heating the roll surface, for example by infrared rays or inductively.

Further, the thickness profile of the web can be adjusted by selectively changing the roll profile in the longitudinal direction of the roll in one of the ways described above. In addition, the profile of the paper web can be influenced by some secondary adjusting action, such as wetting the web.

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The method according to the invention can be used, for example, in a multi-roll calender and in a press section of a paper or board machine. When using the method in a multi-roll calender, compression pressure and web thickness changes can be monitored simultaneously in double ···, or more nipples. This is advantageous when the adjustment measures following the measurements 25 are optionally applied to the various nipples of the calender.

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The multi-roll calender may be, for example, as described in FI 96 334 or WO 98/50 628. Further, the rolls in the multi-roll calender are preferably deflection compensated * * * * rolls.

When using the above method in a multi-roll calender, measurements are preferably made in at least one nip, particularly preferably in the first nip, wherein the thickness of the web is preferably adjusted by varying the compression pressure applied to the web in at least one nip different from the measuring nip, particularly • · 11416: 5 preferably the thickness of the web is adjusted in the second nip of the multi-roll calender. Further, the method can be used in a multi-roll calender in a plurality of nips simultaneously.

The invention further relates to a system for applying the above described method to a paper or board machine roll system characterized in that it comprises - at least one thickness gauge sensor located in front of a nip formed by the first and second rolls relative to the direction of web travel, 10 - at least one thickness gauge sensor arranged behind the nip formed by the first and second rolls relative to the direction of travel of the web, - means for transmitting and processing information collected by the aforementioned devices, and - means for adjusting the thickness of the web based on the collected and processed information. .

The paper thickness measurement can be carried out in any manner known to those skilled in the art, for example, a high speed laser meter, an IR spectroscopy sensor, or one of the methods described above. According to a preferred embodiment of the invention, the thickness measurement is performed with a non-contact measuring device. When used in a press section of a paper or board machine, 20 non-contact measuring devices can be used with a dry solids content of 35-50%.

It is particularly advantageous to place the thickness measuring transducers side by side in the transverse direction of the paper web so that rapid measurement of the transverse profile over the entire width of the web is possible. In addition, the measuring device is preferably so small that it can be placed as close as possible to the nip. Thickness of front and rear nipple • · ;;; Furthermore, the gauges are preferably identical. Further, the thickness measuring transducers may be placed, for example, in a measuring beam.

· · Measurement of compression pressure at the roll nip can also be accomplished by any measuring method known to those skilled in the art, for example piezoelectric or electromagnetic film sensors (EMF). The EMF film is a flexible plastic film with a permanent electrical charge of about 0.05 mm thick. Further, the measurement of the compression pressure may be accomplished by any of the other methods described above. The sensors may be located. · · ·. the roll in any manner known to the person skilled in the art, for example in strings or in some uniform pattern, unevenly distributed over the entire surface area of the roll, or as a helix pattern. Preferably, the sensors are located parallel to the roll 11416; 6, at least one, particularly preferably, two opposed, flat, longitudinal patterns throughout the width of the roll. When using polymer rolls, the sensors can be integrated between the coating layers.

5 When positioning the pressure sensors, it should be taken into account that at each revolution of the roll, or at sufficiently frequent intervals, the compression pressure on the roll surface, and hence on the paper web, must be recorded.

The connection between the pressure sensors and the data processing and control units may be accomplished by any wireless communication method or wiring known to those skilled in the art. If the communication is arranged along the wires, the rotating parts of the roll may be slidingly in contact with the stationary receiving part of the signal. The connection between the thickness gauges and the data processing and control units may likewise be effected by any wireless communication method known per se or by means of wires. The data processing and control unit collects data from the first 15 thickness gauges, the pressure gauge and the second thickness gauge, combines, processes, and uses the data to control the process.

According to one embodiment of the invention, in multi-roll calendering, a pair of calender rolls comprises a polymer roll and a hard roll, wherein the pressure sensors are arranged on or between the flexible surface layer of the polymer roll.

; ; The method and system of the invention provide accurate and rapid • «· *; management of the paper web profile in the paper machine track. The method is capable of controlling both the transverse and longitudinal profile of the web. The method provides a particular advantage of I I f in paper machines which are frequently changed quality. The process according to the invention provides a precise process control and reduces production losses.

The invention further relates to an on-line method for monitoring the fishterization of a paper or board web in a nip between a pair of calender rolls, characterized in that the method is characterized in that the thickness of the web is measured across the web with one or more nip: * \: with a positioned thickness transducer and again with one or more nipples: "': 30 with a positioned thickness transducer, and that: - the compression pressure on the web in the nip is measured across the web by one ;;; or by the coefficient of change in thickness and compression of the web.

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The method provides the advantage that the effect of the nip compression pressure on the change in web thickness is precisely known, so that the consequences of a quantitative change in the compression pressure are predictable. The procedure allows for faster and more reliable regulation of the web thickness by means of a controlled compression pressure which selects 5 in the nip. In addition, the web continuously provides thickness information that can be utilized in any other process control measures.

The nip compression pressure may be adjusted in any manner known to those skilled in the art, such as that disclosed in WO 98/50628.

In the method, the thickness profile of the web is preferably measured using a plurality of thickness sensors arranged side by side across the web. Similarly, the pressure distribution is preferably measured in the transverse direction of the web by pressure sensors arranged adjacent to the web. Particularly preferably, the pressure distribution is measured over the entire length of the roll. Measurements allow selective adjustment operations in the transverse direction of the web, for example, to keep the thickness of the web constant.

The invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 shows a pair of rolls of the system according to the invention, Figure 2 shows closer measurements of the web in the system according to the invention; Fig. 4 shows one way of positioning the pressure transducer on a polymer roll.

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Figure 2 shows the measurements on the paper web in the apparatus according to the invention. The pressure sensors 30, 31, 32 provide information on the pressure applied to the nipple both in the transverse direction (curve 14, pressure P) and in the longitudinal or machine direction (curve 15, pressure P). On the other hand, the thickness measuring element 4 provides information on the thickness profile of the pa-5 web in both machine and transverse directions (curve 16, paper web thickness h). This information is combined in a data processing and control unit 10.

Figure 3 shows an example of the application of the invention in a multi-roll calender. The picture has been simplified for the sake of clarity by omitting part of the reference numerals and lines representing data transmission. The calender comprises three soft-surface polymer rolls 17, 18, 19 and two hard rolls 20, 21 alternating therewith, pressure measuring means 8, 9 are provided on the polymer rolls 17, 18, and thickness measuring means 3, 4 are arranged in front and behind the roll nipples. 1 and 2. It will be apparent to one skilled in the art that said measuring means may also be disposed other than as shown in the figure.

The data collected from the pressure sensors and the thickness sensors is led to a data processing unit 22 from which the combined data is transmitted to the control unit 23. From the control unit 23, the control signal is transmitted to a calender control system comprising a roller 24 for changing nip pressure and two heating devices 25, 26. by means of which the surface profile of the hard rollers 20, 21 can be changed.

Figure 4 shows one way of positioning the pressure transducer on a polymer roll. Pressure Sensor 8 • ·. 1.: is arranged between the elastic coating 27 of the roll and the intermediate layer 28. The roll comprises: 1, furthermore a base layer 29.

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Claims (18)

An on-line method for controlling the transverse thickness (h) of a web (6) in the roll portion (1,2, 17, 18, 19, 20, 21, 24) of a paper or cardboard machine by -. 1 in the compression pressure (P) of a nip, characterized in that the thickness (h) of the web (6) is measured in the machine at least with a thickness measuring means (3) before the nip between the roll pair (1,2, 17, 18, 19, 20). 21, 24),: - the compression pressure (P) directed to the web (6) is measured at least with a pressure measuring means (8) in the nip; the thickness (h) of the web (6) is measured again after the nip with at least one thickness gauge - (4), - the thickness profile of the web (6) and the distribution of the compression pressure (P) in the nip are fed in the transverse direction of the web (6), and the thickness (h) of the web (6) is selectively adjusted to affect the thickness profile, and - the data about the thickness measurements before and after the nip, and whether the measurement of the pressure (P) is combined in a data processing and control unit (22, 23). Method according to claim 1, characterized in that the compression pressure (P) against the web (6) in the nip is controlled by means of a pressure medium which affects the dimensions of the roll (1, 17, 18, 19). Method according to any of the preceding claims, characterized in that the pressing pressure (P) which is directed towards the web (6) in the nip is controlled by means of thermal expansion or shrinkage of the roll (1, 17, 18, 19). Method according to claim 2 or 3, characterized in that the thickness profile of the web (6) is controlled by changing the profile of the roll selectively in the longitudinal direction of the roll. Method according to any of claims 2-4, characterized in that the measurements are carried out at least in one of the nips of a multiple-choice set (1, 2, 17, 18, 19, 20, 21, 24), preferably in the first nip, and that the thickness (h) of the web (6) is controlled by changing the compression pressure (P) directed against the web (6) in at least one nip of multiple rolls; ; The set (1,2, 17, 18, 19, 20, 21, 24), which is different from the measurement nip, preferably: the thickness (h) of the web (6) is controlled in a second nip by the multiple selection set. >. . Method according to any of the preceding claims, characterized in that it is. . a calendering process. 1 System for controlling the thickness (h) of a paper or cardboard web (6) in the roll portion (1, 2, 17, 18, 19, 20, 21, 24) of a paper or cardboard machine, characterized in that the system includes; - at least one thickness sensor (3) arranged before the nip (5) formed by the first and second rolls (1, 2), relative to the direction of movement (7) of the web (6), - at least one pressure sensor (8) in the first roll (1) for measuring the compressive pressure (P) in the nip (5); - at least one thickness sensor (4) arranged behind the nip (5) formed by the first and second rolls (1, 2) ), relative to the direction of movement (7) of the track (6), - means for transmitting and processing data collected by said devices, and 11416; means for controlling the thickness (h) of the web (6) on the basis of collected and processed data. System according to claim 7, characterized in that it comprises a number of parallel thickness sensors (3) in front of the nip, a number of parallel pressure sensors (8) in the roll (1, 5 17, 18, 19) and a number of parallel thickness sensors (4) after nip. System according to claim 7 or 8, characterized in that the thickness sensors (3) in front of and / or behind the nip are laser sensors or sensors based on IR spectroscopy. System according to claims 7-9, characterized in that the pressure transducer (8, 9) in the roller 10 (1, 17, 18, 19) is a piezoelectric measuring transducer, a magnetorrestrictive transducer or an electromechanical diaphragm transducer. System according to claims 7-10, characterized in that the transfer of data received from the pressure sensors (8, 9) from the roller (1, 17, 18, 19) to the data processing means (22) is arranged wirelessly. System according to claims 7-10, characterized in that the transmission of data received from the pressure sensors (8, 9) from the drum (1, 17, 18, 19) to the data processing means (22) is arranged Sng's lines, wherein the drum (1) , 17, 18, 19) rotating parts are in sliding contact with a stationary signal receiving part. System according to any of claims 7-12, characterized in that the pressure transducers (8, 9) are arranged in the elastic surface layers of the polymer roll (1, 17, 18, 19). > ·. (27) or between the layers (27, 28) of the polymer roll (1, 17, 18, 19), and that - the polymer roll (1, 17, 18, 19) forms a nip together with a hardening roll (2, 20, 21). 24). 14. On-line method for monitoring the calendering of a paper or carton web (6) in a nip between a calender roll pair (1, 2, 17, 18, 19, 20, 21, 24) , feel- • '*'. characterized by the • ·. The thickness (h) of the web (6) is measured in the transverse direction of the web (6) by one or more thicknesses. Sensor (3) arranged in front of the nip and reattached with one or more thickness sensors (4) • * '' arranged after the nip, and ·: · *: 30 - the compression pressure (P) directed against the web (6) in the nip is measured in the transverse direction of the web (6) with one or more pressure sensors (8, 9) arranged in the roll (1, 17, 18, 19) to correct the change in thickness in the web (6) and the pressing pressure (P). 114167 Method according to claim 14, characterized in that the thickness profile of the web (6) is measured in the thickness measurement by using several thickness sensors (3, 4) arranged next to each other in the transverse direction of the web (6). Method according to Claim 14 or 15, characterized in that in measuring 5 of the pressing pressure (P), the pressure distribution in the transverse direction of the web (6) is preferably measured over the entire width of the web (6). Method according to claim 16, characterized in that pressure sensors (8, 9) are used which are arranged in parallel throughout the entire length of the roller (1, 17, 18, 19) transverse to the web (6). 10 Method according to any of claims 14-17, characterized in that the pressure pressure (P) and the thickness changes of the web (6) are simultaneously monitored in two or more nips in the plurality scale. • 1 1 • t · • · · • t • f I • • · 1 • «• · I •« ♦ · • I • · »• 1 ·« M ♦ · • «• · * · · * ♦ 1 • t I • »My • i