EP1371776A2 - Calender and method for operating a calender - Google Patents

Abstract

Calender (1), with a vertical stack of rollers (2-6), has a sensor assembly (25) which registers oscillation at least at one roller (5). At least one roller (3,4) has a controlled magnetic field generator (21,23) which develops a magnetic field at least at one neighboring roller according to the sensor signals. The magnetic forces are directed in the press direction.

Description

The invention relates to a calender with several a roll stack arranged and a sensor arrangement, the one vibration of at least one roller detected. The invention further relates to a method to operate a calender with multiple rolls, the pressed against each other in a roll stack, whereby vibrations are determined on at least one roller.

The invention is based on a calender explained, which is intended for treating a paper web is. When producing a paper web, the Paper web passed through the calender and in the nips, that are formed between adjacent calender rolls, with pressure and possibly with elevated temperature applied. In calenders of this type act in many ways so-called "soft" rollers together with "hard" rollers. In some positions there are also two "soft" Rolling together. The soft rollers are included a plastic covering, which is more flexible than the surface of the hard rollers.

It has now been found that after a certain period of operation such a calender a so-called barring can be observed. On the one hand, this barring causes an unwanted stripe pattern on the paper web, that from the time of visibility at Committee of the paper web leads. But the stripes are also as stripe-shaped markings on the elastic Rolls recognizable. The soft rollers, so to speak polygonal. As soon as such a form occurs must the roller or the rollers on which the covering has been reshaped to be revised. In this is usually done by turning or grinding connected to the roller.

The causes of barring formation are not yet completely cleared up. It is believed that barring formation is due to vibrations to which the Roll stack and thus the individual rolls exposed are.

It is in to reduce the appearance of barring DE 100 08 800 A1 has been proposed in the interior of a Roll an active vibration to generate that on the roller shell acts. Generated with these vibrations so to speak, counter-vibrations to the vibrations, who train in the calender in the company. Through this Counter-vibrations can be seen in the feedback behavior change in the calender. Ideally you can use the calender eliminate excited vibrations, at least but avoid that the resulting vibration becomes a Barring formation leads.

However, the control of the active vibration relatively expensive in the interior of the roller. The feedback on the roll shell also requires a certain amount Expenditure.

The invention has for its object the barring formation to diminish.

This task is performed on a calender of the type mentioned at the beginning Kind solved in that at least one roller has a controllable magnetic field generating device, which is a magnetic field acting on another roller depending on signals from the sensor arrangement generated.

A magnetic field that acts on another roller creates Forces between those with the magnetic field generating device provided roller and the other roller. These forces do not have to be excessive. It So is not absolutely necessary, these forces like that to make it big, like they are used to pressurize the web of material are necessary. With the magnetically conditioned However, vibrations can be exerted by the roller is affected. This influence can fundamentally amplify the vibrations of the roller or weaken. You can therefore see it as one Measure before that the magnetic field generating device as a function of signals from the sensor arrangement a vibration in the calender is detected, is controlled.

This way you can be relatively reliable the magnetic field generating device so operate that the vibrations in the calender are not increased, but only weakened or even completely eliminated become.

The application of a magnetic field to a roller is known per se from DE 195 07 828 C1. There the magnetic field generating device but used the Forces that exert pressure on the material web are required to generate. This is the case with the present Invention as stated above is not required. The pressurizing forces can be generated in a conventional manner, for example through hydraulic support elements, which in one or both end rolls of the roll stack are provided are. The magnetic field generating device is used only to influence the vibration of the rollers to make the barring formation is reduced or even prevented.

The magnetic field preferably acts on at least one Neighboring roller. The closer the rollers are to which the magnetic field generating device Exercises forces, the more effective the forces and the more less energy is used to generate of the magnetic field is required. If you have powers generated between adjacent rollers, then you can Let the magnetic field work through the nip. A Influencing rollers further away is then relatively weak. Influencing two adjacent rollers are usually sufficient, to change the vibration behavior of a calender that the barring formation is reduced.

The magnetic field preferably generates forces between the rollers, the resultant of which is essentially in Press direction is directed. The press direction is the direction in which the rollers are pressed against each other become. But it is also possible that the rollers in relation to a plane in which the axes of rotation of the two End rollers are, are slightly offset. Out for this reason it is not necessary that the of Magnetic field generated forces exactly parallel to this Level. Small deviations are quite possible possible. Due to the mentioned orientation avoided the rollers from additional vibration is imprinted, which is an essential component perpendicular to the plane. This keeps the burden on the bearing arrangement in the stand of the calender small. Nevertheless, adequate vibration damping possible.

Preferably, at least two rollers each have a magnetic field generating device. With it result there are other possibilities, vibrations that occur in the Calenders occur to dampen.

It is particularly preferred here that the magnetic field generating devices can be controlled depending on each other are. One can use the magnetic field generating devices for example, control so that they simultaneously to have an attractive effect on one another to cause a correspondingly strong vibration excitation. However, it is also possible to use the two magnetic field generating devices to be controlled so that the Repel magnetic fields. During the first mode of operation to a slight increase in the compressive stress in the Nip leads between the two rollers, the latter leads Operating mode to a slight lowering the pressure in the nip. Both measures influence the treatment the material web in the nip practically not or not worth mentioning. But they are well suited to that Vibration behavior of the calender positive to influence that barring formation diminishes becomes.

The magnetic field generating device preferably has a magnetic path that is a component has in the axial direction of the roller. The magnetic field can therefore close in the axial direction of the roller. This keeps magnetic losses through one larger air gap in the "return path" of the magnetic path could arise, small.

The magnetic field generating device preferably acts to a predetermined length of the roller that is shorter than is the axial length of the roller. For vibration damping Magnetic fields in the axial direction are also sufficient are relatively short. If necessary, one can the axial length of the roller distributes several relatively provide short magnetic field generating devices that can be operated in the same or different ways. A force application or a force impact on you Area of the roller that is on a relatively short limited axial length, but still influences the vibration of the entire roller and thus one Influencing the vibration in the calender. Indeed requires a shorter magnetic field generating device even less electrical energy.

The magnetic field generating device is preferably arranged in or on an intermediate roller. intermediate rolls usually have enough inside Space for accommodating the magnetic field generating device unlike finish rolls, which are due to hydraulic Support elements usually do not have enough space for a magnetic field generating device put.

The magnetic field generating device preferably acts between roll neck. There is usually enough there Space available, so that the magnetic field generating device can be positioned without the Functionality of the rollers or the calender otherwise to hinder.

It is particularly preferred here that the magnetic field generating device arranged axially within bearings in which the roller is stored. This training has the advantage that the magnetic field generating device caused on the rollers Forces cannot be dampened by the bearing. The forces rather act within a bounded by the camp Space directly on the rollers, so that possible Fights vibrations directly at the place where they originate can be.

The magnetic field generating device is preferably arranged within a hollow roll shell. In order to the magnetic field generating device can be arranged there be where it works best. Magnetic losses are kept short. The magnetic field generating device, which are usually designed as an electromagnet can be supplied easily because of a rotating union generally known for electrical supply lines is.

The magnetic field generating device preferably has their influencing maximum at at least one position on which a natural vibration of the roller has an antinode. The natural vibrations the roller for normal calender operation usually calculate in advance. In any case, this applies for the waveforms. From such a calculation you can see the position of an antinode (= Determine the location of the greatest deflection). If you do that Influence maximum of the magnetic field generating device to the position of such an antinode then the fight against training Vibration by the magnetic field generating device optimal. It is not necessary that this Position is hit exactly. However, the effect is the better, the better the forces exerted by the magnetic field generating device generated nearby of the antinode can attack.

A magnetic field generating device is preferred for each antinode intended. Leave with it achieve the best damping effects.

The task is in a method of the aforementioned Kind solved by using a magnetic field Additional forces between rollers depending generated by the determined vibrations.

As explained above in connection with the calender the vibrations are first determined, to which the calender is exposed. Here it is enough in in most cases, the vibrations on a single Determine roller. From these vibrations can you then derive control signals that are used for control the magnetic field generating device is used become. The magnetic field generating device generates then a magnetic field, which in turn forces the rollers exercises. These forces can now be controlled that they are the previously determined vibration in the calender counteract.

The additional forces are preferably left on immediately the rollers work. So the additional forces are not introduced into the rollers via one or more bearings. For example, rolling bearings allow vibrations to be initiated only up to a frequency of about 200 to 250 Hz. Vibrations that exceed the frequency are made by a roller bearing heavily subdued. If, on the other hand, you see the additional forces under Bypass the bearings by acting directly on the rollers leaves because the additional forces, so to speak, on the roll side Side of the bearings can then be generated one can also apply higher-frequency forces to the rollers and accordingly also higher-frequency vibrations fight.

It is preferred that the additional forces between adjacent rollers can act. Between neighboring Rolling is the distance and therefore the magnetic one Air gap is the smallest, so with this approach the energy consumption is small. Can at the same time Relatively large forces can easily be generated. These forces only have to be so great that they are Counteract vibrations in the calender. The smaller the air gap to be overcome by the magnetic field, the more the mode of operation is cheaper.

The additional forces are preferably left in a press plane Act. The vibrations are then mainly eliminated in the press plane. This will Position loads kept small perpendicular to the press plane.

The additional forces are preferably left in dependence of the vibrations increasing or decreasing pressure act in a nip. So you don't need to an attraction due to the magnetic field or magnetic fields to exercise on adjacent rollers. The neighboring ones Rollers can also repel each other if this is for damping of the vibrations is favorable.

The additional forces are preferably generated where an antinode of natural vibration of the roller is expected. As mentioned above, at least the position of the antinodes of the natural vibrations the roller with a relatively high reliability determine in advance. If you look at the additional forces there lets act where the vibration amplitude of the natural vibration is greater, then the dampening effect the strongest.

Fig. 1

einen schematischen Querschnitt durch einen Kalander,

Fig. 2

eine schematische Seitenansicht eines Kalanders,

Fig. 3

einen schematischen Querschnitt durch eine zweite Ausführungsform eines Kalanders und

Fig. 4

eine schematische Seitenansicht des Kalanders nach Fig. 3.

The invention is described below with reference to a preferred embodiment in connection with the drawing. Show here:

Fig. 1

1 shows a schematic cross section through a calender,

Fig. 2

a schematic side view of a calender,

Fig. 3

a schematic cross section through a second embodiment of a calender and

Fig. 4

3 shows a schematic side view of the calender according to FIG. 3.

A calender 1 shown only schematically has one Roll stack of five rolls 2-6, of which at least one roller carries an elastic cover. in the In the present case, the rollers 2, 4, 6 are elastic Rolling, i.e. as rollers with an elastic coating educated. However, this is not shown in more detail.

The two end rollers 2, 6 are as deflection adjustment rollers trained, i.e. they point out schematically shown hydrostatic or hydrodynamic support elements 7, 8 on, the facing forces produce. These forces in turn lead to pressures in the nips 9-12, through which a not shown Material web, for example a paper web, guided can be applied to there with increased pressures to become.

The calender 1 can also be provided with heating rollers be, but are not shown in detail.

The two upper center rolls 3, 4 are hollow rolls trained, i.e. the roller 3 has a roller shell 13, which is supported on a carrier 19 via bearings 15, 16 is. The roller 4 has a roller jacket 14 on which is supported on a carrier 20 via bearings 17, 18 is.

Between the carrier 19 and the roll shell 13 is one Magnetic field generating device 21 in the form of an electromagnet intended. As can be seen from Fig. 2, the magnetic field generating device 21 has a first one Electromagnet 21a and a second electromagnet 21b on the axial (based on the axial direction the roller 3) are offset from one another and opposite be excited to each other. This results in a magnetic indicated by arrows 22 Path in which a magnetic field is formed. It's closed recognize that the magnetic path 22 through the carrier 19 and the two electromagnets 21a, 21b. in the Carrier 19 and in the roll shell 13 can not in more detail measures shown can be provided to a prevent magnetic short circuit. It can e.g. around "air gap" inserts made of magnetic not act conductive material.

Similarly, the roller 4 has a magnetic field generating device 23 on, the two axially to each other has offset electromagnets 23a, 23b, which also flow in opposite directions and a magnetic circuit 24 form, which closes by the carrier 20.

There are vibration sensors on the lower intermediate roller 5 25 arranged, which is connected to a control device 26 are. The control device 26 now controls on the basis the signals of the vibration sensors 25, the magnetic field generating devices 21, 23 so that this Magnetic field generating devices 21, 23 magnetic fields and associated forces between the rollers 3, 4 generate that lead to a weakening or even to a Elimination of vibrations in the calender. Here, the magnetic field generating devices 21, 23 are both operated so that the two rollers 3, 4 are tightened together. In this case the line load in the Nip 10 is increased slightly. The Magnetic field generating devices 21, 23 can, however also be operated so that the rollers 3, 4 repel each other. In this case, the line load in the Nip 10 slightly lowered.

The magnetic field generating devices 21, 23 are from the control device 26 with electric currents fed. By controlling the currents you are in the Able to generate changing magnetic fields, the Magnetic fields in higher-frequency areas can swing. This "higher frequency" refers however to the operating frequency of the calender 1 or the speeds of the rollers 2-6. The frequencies of the Magnetic fields can range from 100 to 3,000 Hz are still quite manageable.

Instead of the stationary magnetic field generating devices 21, 23 can also magnetic field generating devices provide that in not shown Rotate way together with the rollers 3, 4. In this The magnetic field generating devices in FIG Circumferential direction distributes several electromagnets, which then not only depends on the vibrations, which are determined via the vibration sensors 25, can be controlled, but also depending from their instantaneous angular position in relation to the neighboring roller. Nevertheless, these magnetic field generating devices should also then be controlled that the magnetic fields and the forces generated with them act essentially in the direction of the press, i.e. parallel to a plane that is the axis of rotation of the two End rollers 2, 6 connects together.

By the magnetic field generating devices 21, 23 forces are exerted on the jackets 13, 14 of the rollers 3, 4 act, which lead to an oscillation in the calender 1 would. This vibration is superimposed on a vibration in the calender 1 by the rotation of the rolls 2-6 is caused. With an appropriate control can then the from these two vibrations Strongly dampen the resulting vibration.

In principle, it is also possible to use the magnetic field generating devices to be arranged outside the rollers 3, 4. The arrangement within the rollers 3, 4, i.e. within the hollow roll shell 13, 14, however the advantage that the energy consumption of the magnetic field generating devices 21, 23 is kept small.

3 and 4 show a further embodiment of a calender in which a magnetic field generating device between rollers 3, 4 21 is arranged. This Embodiment can be used both alone and in combination with the magnetic field generating device shown in FIGS. 1 and 2 be used.

3 and 4, the magnetic field generating device acts 21 on roll neck 30, 31 of the intermediate rolls 3, 4, the roll journals 30, 31 mounted in bearings 34, 35 via roller bearings 32, 33 are. The carriers 34, 35 can be but in a known manner via lever in the chair of a calender.

The magnetic field generating device 21 now acts axially within the roller bearings 32, 33 on the rollers 3, 4. The Magnetic field generating device 21 can with the carrier 34 of the upper intermediate roller 3 via a holder 36 be connected. So it remains when lowering the lower roller 4 in relative proximity to the roll neck 30 the upper roller 3 and then takes a distance to Roll neck 31 of the lower roller 4.

The magnetic field generating device 21 is in FIG. 3 only shown schematically. Your magnetic field is 37 passed through a schematically illustrated yoke 38, that with pole shoes 39, 40 up to the immediate Extends near the pin 30, 31.

If now the magnetic field generating device 21 with Power is supplied, then it creates a magnetic field, that either attracts the roller journals 30, 31 to one another or repels each other. By a correspondingly high Frequency of this application of force can be an additional Vibration exposure of the rollers 3, 4 realize that can be controlled so that vibrations, that are trained in the calender are fought. The vibration sensors required for this are 3 and 4 not shown in detail.

By the arrangement of the magnetic field generating device 21 axially within the roller bearings 32, 33 it is no longer required any powers through to let the roller bearings 32, 33 act through them. such Forces would have a frequency of approximately values 200 to 250 Hz limited. Higher frequency forces would be damped too much by the bearings 32, 33. Since one but now the bearings 32, 33 in the power transmission is no longer required, but by the magnetic field generating device 21 generated forces immediately can act on the roll neck 30, 31, can also introduce higher-frequency forces into the rollers 3, 4.

In the embodiment shown in FIGS. 1 and 2 one can use the magnetic field generating devices Arrange 21, 23 so that their maximum effect is where Antinode of the natural frequencies of the rollers 3, 4 or one of the rollers 3, 4 are to be expected. There is then the damping effect of the magnetic field generating devices 21, 23 largest. Of course it is also possible for each antinode or for several Antinodes of natural vibrations such Provide magnetic field generating device 21, 23 or that from the magnetic field generating means 21, 23 generated magnetic field so that the Effective maximum at the location of at least one antinode the natural vibration is present or on several antinodes. The antinodes of the natural vibration the corresponding roller 3, 4 can be in advance with calculate the necessary accuracy or simply estimate.

Claims (19)

Calender with a plurality of rolls arranged in a roll stack and a sensor arrangement which detects a vibration of at least one roll, characterized in that at least one roll (3, 4) has a controllable magnetic field generating device (21, 23) which is applied to another roll (4, 3) acting magnetic field as a function of signals from the sensor arrangement (25). Calender according to claim 1, characterized in that the magnetic field acts on at least one neighboring roller (3, 4). Calender according to claim 1 or 2, characterized in that the magnetic field generates forces between the rolls (3, 4), the resultant of which is directed essentially in the direction of the press. Calender according to one of claims 1 to 3, characterized in that at least two rollers (3, 4) each have a magnetic field generating device (21, 23). Calender according to claim 4, characterized in that the magnetic field generating devices (21, 23) can be controlled as a function of one another. Calender according to one of claims 1 to 5, characterized in that the magnetic field generating device (21, 23) has a magnetic path (22, 24) which has a component in the axial direction of the roller (3, 4). Calender according to one of claims 1 to 6, characterized in that the magnetic field generating device (21, 23) acts on a predetermined length of the roller (3, 4) which is shorter than the axial length of the roller (3, 4). Calender according to one of claims 1 to 7, characterized in that the magnetic field generating device (21, 23) is arranged in or on an intermediate roller (3, 4). Calender according to one of claims 1 to 8, characterized in that the magnetic field generating device (21) acts between roller journals (30, 31). Calender according to claim 9, characterized in that the magnetic field generating device (21) is arranged axially within bearings (32, 33) in which the roller (3, 4) is mounted. Calender according to one of claims 1 to 8, characterized in that the magnetic field generating device (21, 23) is arranged within a hollow roll shell (13, 14). Calender according to one of claims 1 to 11, characterized in that the magnetic field generating device (21, 23) has its influencing maximum at at least one position at which a natural vibration of the roller (3, 4) has an antinode. Calender according to claim 12, characterized in that a magnetic field generating device (21, 23) is provided for each antinode. Method for operating a calender with a plurality of rollers which are pressed against one another in a roller stack, vibrations being determined on at least one roller, characterized in that additional forces are generated between rollers (3, 4) with the aid of a magnetic field as a function of the vibrations determined , A method according to claim 14, characterized in that the additional forces are allowed to act directly on the rollers (3, 4). A method according to claim 14 or 15, characterized in that the additional forces are allowed to act between adjacent rollers (3, 4). Process according to Claims 14 to 16, characterized in that the additional forces are allowed to act in a press plane. Method according to one of claims 14 to 17, characterized in that the additional forces are allowed to act in a nip (10) to increase or decrease pressure as a function of the vibrations. Method according to one of claims 14 to 18, characterized in that the additional forces are generated where an antinode of natural vibration of the roller (3, 4) is to be expected.

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