EP1275774A1 - Process for operating a calender and calender - Google Patents

Abstract

The invention relates to a method for operating a calender and a calender with a roll stack (2-6) which has two end rolls (2, 3) and in between a plurality of middle rolls (4-5) which abut one another in a press direction (7). wherein at least one roller (2, 3, 5) has an elastic surface (9). One would like to extend the service life of the rollers with an elastic surface. For this purpose, a vibration is continuously determined in at least one roller (5) and a roller offset transversely to the press direction (7) is carried out as a function of the vibration. For this purpose, a controller is provided, to which vibration absorption devices (20, 21) are connected and which in turn is connected to an actuator (26) on at least one roller. <IMAGE>

Description

The invention relates to a method for operating a Calender with a roll stack, the two end rolls and having a plurality of intermediate rolls therebetween abut each other in a press direction, whereby at least one roller has an elastic surface. The invention also relates to a calender a roll stack, the two end rolls and in between has a plurality of center rollers, at least one Roller has an elastic surface.

Calenders of this type are used in particular for calendering used by paper or cardboard webs. The invention is based on the treatment of a paper web described. But it is in the same way other material webs applicable, where similar Problems occur.

When satinizing a paper web, the paper web becomes passed through the calender and into nips between a hard and a soft roller, i.e. a roller with elastic surface, are formed, with increased Pressure and possibly also at elevated temperature applied. For newer calenders, for example the "Janus" calenders, rollers are used, which are covered with a plastic covering. One can now observe that in many cases there is a certain Operating time for horizontal stripes on the paper web comes. As soon as these stripes become visible, the Paper web unusable and forms rejects. The reasons this so-called barring formation are currently not yet fully clarified. But one assumes that it concerns the effects of a vibration phenomenon is. Vibrations are in a calender though practically inevitable.

When the barring is formed, the soft roller is changed on their elastic surface. It is still did not finally clarify exactly how this change looks. The following options are currently accepted: The roller gets a ripple on the surface, i.e. a mountain and valley structure, the roller becomes polygonal or the roller gets alternately in the circumferential direction Zones of different surface quality, for example different roughness. Independently the concrete nature of the change is evident the periodic barring formation, running in the axial direction Strip on the circumference of the roller. Appropriate Stripes then appear on the paper web, at the latest from the time the strips become visible the paper web is to be regarded as a committee.

If a barring phenomenon occurs, the roller, which causes, develops and grinds the barring formation or be turned off. The service life of one such roller is therefore limited.

The object of the invention is the service life to increase such a roller.

This task is carried out in a method of the type mentioned at the beginning Art solved in that at least one Roll continuously determines a vibration and one Roll offset depending on the direction of the press of the vibration.

So one uses a scheme to train To prevent barring patterns. As a rule, a barring pattern on the surface of a roller already notice before this barring pattern takes shape of horizontal stripes into the paper web. If So take timely action to get the stronger one Disturbing expression of the barring pattern, then lets the service life of the roller increases. Here you go based on the following considerations:

A stack of rolls made up of several rolls has a variety of natural frequencies. Here are not the natural frequencies of the individual rollers for itself, such as natural bending frequencies, but the natural vibration forms that result from the vibrating Roll masses on the spring and damper systems of the interposed plastic coverings of the "soft" Rolls result. A running calender creates excitation forces, whose frequencies are multiples of Assemble roller speeds. These excitation forces can inhomogeneities, anisotropies or geometry errors (Out of roundness). You can also Paper thickness fluctuations in the calender Excite the paper web the stack of rollers. One in the Calender incoming paper web is before the smoothing process still very rough. In addition, a paper web is never free of Surface weight or thickness fluctuations. analyzed these fluctuations with the help of an FFT analysis their frequencies, so you usually put a broadband Noise in which all frequencies are included. Strikes one of these excitation frequencies to a natural frequency, so the vibration system answers of the calender with increased vibrations. Because of the large number of possible pathogens and the multitude of possible natural vibrations these resonance points cannot be avoided constructively. The vibration system is usually the same strongly damped and the excitation forces are so small that the resulting vibratory movements are not immediate are disturbing. Over a more or less long period however, these oscillating movements are characterized in the Plastic coverings of the elastic rollers.

Usually the closest to the natural frequency integer multiples of the roll rotation frequency embossed as a pattern on the rollers. This is done a feedback of the vibration. The vibration rashes then increase exponentially. You express yourself on the one hand in an increased sound level (up to more than 120 dB (A)) and on the other hand in periodic fluctuations in thickness the continuous paper web. In practice different periods are observed in who are experiencing these feedback phenomena express in barrings, train. Most of them pass Days or weeks until this phenomenon grew so much is that it disrupts the production process.

You can take action relatively early which the formation of barring patterns on the elastic Prevent or interfere with rollers. This will only be Vibrations determined. With some experience or with measures specified below are, you can now the feedback behavior of the roll stack or even change the whole calender, so that there is an ongoing formation of barring patterns at least not further enlarged. Usually will one with a targeted regulation based on the vibrations responds, a regression of the barring pattern reachable. Here you accept that Barring patterns are formed again with different frequencies. But since the regulation works continuously, can the roll offset also at several points in time Carry out one after the other, the time intervals between two adjustments of the roll offset by the Vibration condition of the calender are determined.

The roll offset is preferably carried out when the Vibration contains a frequency that is one of several Preset frequencies corresponds. The vibration that one usually finds a broad spectrum contain frequencies that have different causes to have. Not to be neglected here Influence of paper web after leaving the paper machine has a certain surface roughness and thus providing an excitation for the vibrations. Of However, the frequencies are only a few frequencies critical. So it is enough if you do a frequency analysis makes the vibration and "checks" whether the critical frequencies are included. Because these are critical Frequencies are given as "Specification frequencies" referred to.

An offset is preferably made when the portion with the frequency exceeds a predetermined amplitude. Even critical frequencies are not in everyone Case disturbing from the start. They are when with small amplitude occur, only a warning signal. You can now provide a certain tolerance threshold and make an offset only when a predetermined one Amplitude is exceeded. You risk it that barring patterns are starting to develop. The operation of the calender then becomes less frequent changed, making further malfunctions small being held.

There is preferably one for each default frequency Wavelength that is an integer fraction of the circumference corresponds to a roller. If you look at the barring pattern analyzed on the surface of a roller, one finds that this is a wave pattern where the wavelength is an integer Fraction of the roll circumference corresponds. Barring pattern you will not observe at other wavelengths can because of these other barring patterns should constantly result in a transformation, the one final formation of such a barring pattern prevented. For barring patterns where an integer Multiples of the wavelength exactly the scope of the Roller results, there is no such extinction. you but each of these barring patterns can have a specific one Assign frequency that also from the peripheral speed depends on the roller in question. To this Way it is relatively easy to set the default frequencies calculate.

It is preferable to determine at least on each center roll the vibration and limits the default frequencies at wavelengths that are on the corresponding roller occur. This approach has several advantages. First, the vibration that occurs on a roller with much lower damping immediately removable on this roller than on other rollers. The Information about the roller vibration is therefore more immediate to disposal. On the other hand, one has to be essential Note the lower number of default frequencies. This is especially true when the rollers of the Roll stack have different sizes. This However, situation usually occurs, especially then when one or more rollers with elastic coverings have already been revised once. In this In this case, the processing effort is reduced because less information needs to be evaluated. The regulation can then take place more quickly.

Preferably, you move the roller a distance, which depends on the wavelength of the frequency. Over there the frequency determined is the wavelength of the barring pattern is known, you can now get this information evaluate and the roller across the press direction by one Offset amount in which this wavelength information flows. You can achieve that with certain Offset stretches a formation of the barring pattern undone. In the case of deviating offset distances may further develop the barring pattern at least be inhibited.

It is particularly preferred that the roller offset a route where there is a path length difference between two nips, the one in the range quarter to half a wavelength. You would make a roll offset in which the path length difference one wavelength would certainly be no positive effect. With longer path length differences you would have to continue the roller accordingly move, taking the risk, an unfavorable change in the geometry of the roll stack to obtain. However, if you set the offset on relatively short path length differences between one limited to a quarter and a half wavelength, then you also have a correspondingly small offset of the Roll across the press direction and still receives the advantageous effect that the barring patterns recede or at least not further.

Preferably, you move the roller a distance, that are in the range of one eighth to one quarter wavelength lies. This applies to center rolls where the roll surface two nips in one revolution passes. By a path length difference on the surface between two nips of a quarter or one half wavelength, it is then only required, the roller by half the path length difference to move. Then on one side of the roller the path length difference by twice the Roll misalignment increased while on the other Side of the roller reduced by twice the offset distance becomes. So if you look at the path length difference want to change by a quarter wavelength is just an offset movement of an eighth wavelength is required. The offset movement is therefore limited to a length of the order of 10 mm.

The task is with a calender of the aforementioned Art solved in that at least one Roller arranged a vibration pickup which is connected to a controller which is connected to a Adjustment drive is connected to at least one roller.

So you establish a control loop that a roller in Dependence on vibrations adjusted on this or another roller. So you are not more on a random adjustment according to the principle instructed to try. You also have to use the rollers do not adjust continuously to the vibration training prevent at any operating point. you rather controls whether vibrations are certain Train kind. If such vibrations develop, the controller intervenes and adjusts via the adjustment drive the roller.

It is preferred that the vibration pickup device connected to a frequency analysis device is. The frequency analysis device determines which Frequencies contained in the vibration. As above not all frequencies are critical. you So can the activity of the controller on certain frequencies restrict.

Preferably, the vibration pickup device several vibration sensors based on different Directions are aligned. You can do it condense the information to be evaluated. vibrations which, for example, their main vibration direction parallel for the axial direction of the rollers are for the Barring formation is less critical than vibrations are directed radially to the roller axis.

The vibration-absorbing device is preferably at least arranged on each center roll. One determines so the vibrations on each center roll. this has the advantage that you have the vibration of everyone Middle roller on the middle roller itself can determine so that it is not through a transmission path through others Rolling has been dampened or even falsified. On the other hand, you can rely on the evaluation limit critical frequencies at the particular Roller can occur. Finally, if the vibration on each roller, at least on each Center roll, determined individually, more targeted one Take action to form a barring pattern to prevent on each roller.

At least the middle rollers are preferably on levers arranged and the adjustment drive acts on the lever. This is a relatively simple measure to offset of the respective roller perpendicular to the direction of the press cause.

There is now one for the training of the adjustment drive Number of possibilities.

In a preferred embodiment, that the adjustment drive has an eccentric bush, in which a bearing point of the lever is arranged. By a twisting of the eccentric sleeve around an axis that A bearing point can be run parallel to the roller axis the lever, for example the fulcrum, relative change to press direction.

In an alternative embodiment it is provided that the lever is stored in a sliding block that one Has linear drive. The linear drive works first a translational shift of the sliding block, for example with the help of a threaded spindle. The sliding block takes the lever with it, so that the roller is finally perpendicular to the direction of the press can be relocated.

Finally, it can also be provided that the lever is designed to be variable in length. Such training can, for example, by a telescopic or implement a prismatic guide in which two components of the lever shifted relative to each other become.

In a further alternative embodiment, provision can be made be that between the lever and a bearing housing an articulated connection is provided with a tilt drive is. This makes it possible to offset movements relatively precisely adjust the roller.

Fig. 1

eine schematische Darstellung eines Kalanders von der Seite,

Fig. 2

einen Ausschnitt der Darstellung des Kalanders nach Fig. 1 von vorne,

Fig. 3

eine schematische Darstellung zur Erläuterung der Ausbildung eines Barring-Musters und

Fig. 4

verschiedene Möglichkeiten zum Versatz einer Walze.

The invention is described below on the basis of preferred exemplary embodiments in conjunction with the drawing. Show here:

Fig. 1

a schematic representation of a calender from the side,

Fig. 2

1 shows a section of the representation of the calender according to FIG. 1 from the front,

Fig. 3

a schematic representation for explaining the formation of a barring pattern and

Fig. 4

different ways to offset a roller.

Fig. 1 shows schematically a calender 1 with two end rolls 2, 3, which are designed as deflection rollers and three center rollers 4-6, which together form one Form the roll stack. The roll stack has a roll plane 7, in which the axes of all rollers 2 - 6 lie when the rollers 2 - 6 are arranged exactly one above the other are. In this roller plane 7 lies for the For the purpose of the following description also the press direction, i.e. the direction in which the reels 2-6 pressed against each other.

Further details of the calender are only schematic shown as a drive 8, or omitted entirely, like means for heating individual rollers. The two End rollers 2, 3 and the middle roller 5 have but an elastic covering 9, which is exaggerated is shown in bold.

The rollers 2 - 6 form during operation of the calender in known manner nips 10-13, through which one to be treated Material web is guided. All nips are here formed as so-called soft nips because they are from a hard and limited by a soft roller.

Vibration transducers 20, 21, 22 (Fig. 2) arranged which vibrates the center rollers Determine 4 - 6. The vibration sensors 20 - 22 are preferably on the bearing 23, more precisely on the bearing housing 24 arranged. The vibration sensors determine this 20 vibrations in the vertical direction, the vibration sensor 21 vibrations perpendicular to Roller plane, i.e. the plane through the central axes of the (non-offset) rollers 2 - 6, and the vibration sensor 22 vibrations in the axial direction. Generally can it is said that the vibration sensors 20 - 22 in the Can basically determine any direction of vibration, as long as the directions are orthogonal to each other.

The vibration sensors 20-22 are connected to one Regulator 25, which in turn is based on an adjustment drive 26 acts. The controller 25 also has a frequency analysis device 27 on that with a not shown Comparator and a threshold element coupled could be. The frequency analysis device 27 determined from the vibrations by the vibration sensors 20 - 22 are recorded, the amplitude Percentage of a frequency (or a narrow frequency range) can be assigned. When the amplitude of a frequency is a predetermined Limit or threshold and this frequency can be viewed as critical because with is related to a wavelength whose integer multiple of the scope of the corresponding Corresponds to the roller, then the adjustment drive 26 in Operation set to cross the appropriate roller To adjust the press direction. This is schematic in Fig. 1 shown for the middle roller 5. It but it is obvious that basically all rollers 2 - 6 can be adjusted.

One can now observe that after a roll misalignment around the distance X the vibration behavior of the rollers changes. Particularly favorable conditions result if you determined X in the offset movement Boundary conditions observed, which are based on Fig. 3 are to be explained.

3 shows the roller 5, the one above it Roller 4 and the roller 6 below. With exaggerated amplitudes there are different reference ripples shown and a ripple, in which seven shafts run around the circumference of the roller 5, one with eight waves and one with nine waves. The numbers n = 7, 8, 9 were for the sake of clarity selected. With real rollers, the Adjust the circumference of the roller accordingly more shafts, for example in the order of 30 to 50. At the number of waves around the circumference of the roller 5 in the first approximation, one can assume that with a small offset movement of the roller 5 opposite the roller plane 7, which is smaller than one Wavelength, the curvature of the roller 5 does not matter plays.

If the controller 25 has now determined that a critical Frequency that you either get beforehand from empirical values predetermined or determined in some other way has occurs with a predetermined amplitude, then it is to be expected that a certain frequency will also be associated with this frequency Wavelength λ belongs to the barring pattern on the surface of the roller. You move then the roller 5 opposite the roller plane 7, i.e. towards the nips 11, 12 so that the distance between the two nips 11, 12 on one side half a wavelength λ / 2 enlarged and on the other Side reduced by this half wavelength λ / 2 becomes. All that is required is an offset X, which corresponds to X = λ / 4 because the desired one Path length difference between the two nips 11, 12 results.

With a path length difference of λ / 2 arises at Points of the circumference of the roller 5, which was previously heavily loaded and where there are corresponding troughs have trained, no burden. This burden rather, arises from the wave crests on which so far the corresponding burden was missing. The burdens result from the vibrational movements of the three rollers 4, 5, 6 relative to each other. You can go through achieve a path length difference of λ / 2 that a barring pattern that has already been formed shaped and disappears over time. You risk while doing that there is a different barring pattern trains whose wavelength is close to the wavelength of the original Barring pattern. If so the original barring pattern is one wavelength U / n, where U is the circumference of the roller 5, then has the new barring pattern may be a wavelength of U / (n ± 1). Until such a new barring pattern but so far that it bothers some that passes Time.

A reduction in the feedback can already occur with one Phase shift between two nips 11, 12 of X = λ / 4 can be achieved. Because both for the feedback through the material web as well as for the feedback a reduction or extinction over the roller surface the fault should be reached, one should Displacement can be selected in which both the phase shift for the paper as well as the phase shift for the roller in the range from λ / 4 to λ / 2 lies. The aim here is a phase shift by the controller 25, which is closer to λ / 2. The danger, connected with a phase shift of λ / 2 is that after the initial pattern is canceled a new pattern is created by the Regulation counteracted. As soon as using the vibration measurement Imprint frequencies with predetermined Amplitudes can be seen, these amplitudes can also be relatively small, a new roller offset determined and set, which in turn a Extinction. The time intervals between two Adjustments to the roll offset are therefore through determines the vibration condition of the calender.

Fig. 4 now shows different ways to To cause roll misalignment. The explanation is given in all cases using the example of the center roller 5, which in one Bearing housing 30 is mounted, which is on the front End of a lever 31 is located.

4a, the lever is 31st stored with a bearing point 32 in an eccentric sleeve 33. If the eccentric bushing 33 is rotated, then the position of the roller 5 changes in horizontal Direction.

In the embodiment according to FIG. 4b, the lever 31 stored in a sliding block 34, which is in a housing 35 by a linear drive 36, which is only schematic is shown, can be moved in the housing 35. The linear drive can be used, for example, as a threaded spindle will be realized. Also with a threaded spindle relatively precise adjustment movements are possible.

In the exemplary embodiment according to FIG. 4c, the lever is 31 adjustable in length, which is indicated by a double arrow 37 is shown. The lever 31 can for example have a telescopic or a prismatic guide. The drive of the two movable against each other Parts of the lever can also be threaded (not shown).

4d is the bearing housing 30 connected to the lever 31 via a swivel joint 38. The swivel 38 is at the lower end of a mounting plate 39 arranged, which in turn on the lever 31 is attached. An attachment is at the top of course also possible. A schematically represented Tilt drive 40 is provided around the bearing housing 30 compared to the lever 31 by a defined amount to tip.

Claims (17)

Method for operating a calender with a roll stack, which has two end rolls and in between a plurality of middle rolls which abut one another in a press direction, at least one roll having an elastic surface, characterized in that vibration is continuously determined in at least one roll and roll offset transversely to the direction of the press depending on the vibration. Method according to Claim 1, characterized in that the roll offset is carried out when the oscillation contains a frequency which corresponds to one of a plurality of preset frequencies. A method according to claim 2, characterized in that a roll offset is carried out when the portion with the frequency exceeds a predetermined amplitude. Method according to claim 2 or 3, characterized in that for each preset frequency there is a wavelength which corresponds to an integer fraction of the circumference of a roller. Method according to one of claims 2 to 4, characterized in that the vibration is determined at least on each center roll and the preset frequencies are limited to wavelengths which occur on the corresponding roll. Method according to one of claims 1 to 5, characterized in that the roller is displaced by a distance which depends on the wavelength of the frequency. Method according to Claim 6, characterized in that the roller is displaced by a distance in which there is a path length difference between two nips which is in the range of a quarter to a half wavelength. Method according to Claim 7, characterized in that the roller is displaced by a distance which is in the range from one eighth to one quarter wavelength. Calender with a roll stack, which has two end rolls and several intermediate rolls in between, at least one roll having an elastic surface, characterized in that on at least one roll (4 - 6) a vibration absorbing device (20 - 22) is arranged, which is equipped with a controller (25) is connected, which is connected to an adjustment drive (26) of at least one roller (5). Calender according to claim 9, characterized in that the vibration recording device (20 - 22) is connected to a frequency analysis device (27). Calender according to claim 9 or 10, characterized in that the vibration pick-up device (20 - 22) has a plurality of vibration pickups which are aligned in different directions. Calender according to one of claims 9 to 11, characterized in that the vibration absorbing device is arranged at least on each central roller (3 - 5). Calender according to one of claims 9 to 12, characterized in that at least the middle rollers (3-5) are arranged on levers (31) and the adjustment drive (26) acts on the lever (31). Calender according to claim 13, characterized in that the adjustment drive has an eccentric bush (33) in which a bearing point (32) of the lever (31) is arranged. Calender according to claim 13, characterized in that the lever (31) is mounted in a sliding block (34) which has a linear drive (36). Calender according to claim 13, characterized in that the lever (31) is constructed to be variable in length. Calender according to one of claims 9 to 12, characterized in that an articulated connection (38) with a tilting drive (40) is provided between the lever (31) and a bearing housing (30).

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