EP2052796B1 - Method and device for suppressing the rattling of work rollers on a roll stand - Google Patents

Abstract

The method involves generating a pressure change in a hydraulic medium which impinges a roller gap of the roll stand adjusting a hydraulic cylinder (6). The pressure change is directly produced in a pressure chamber (24) of the hydraulic cylinder adjacent to a piston (8) where volume of the pressure chamber is changed. The pressure change is produced after the concept of an active increase of the stiffness. An independent claim is included for a device for suppressing the vibration of the rollers of a roll stand.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for suppressing the chattering of rolls of a rolling stand having the features of the preamble of independent claim 1 and to an apparatus for suppressing the chattering of rolls of a rolling stand with the features of the preamble of independent claim 6.

The rattling of rolls of a rolling stand are vibrations of the rolls, which are also known as Chatter vibrations, z. B. 3rd octave chatter, 5th octave chatter. These vibrations, or non-circularity of the rollers, which in turn cause vibrations, lead to variations in the nip of the respective rolling stand, which are manifested in the form of chatter marks on the rolled material. The Chattermarken represent in any case a reduction in quality of the rolled material, in which it is z. B. can be aluminum or steel sheet down to the film thickness. If the Chatter marks on the rollers themselves are visible, they must be removed and reground, because then even by changing operating parameters of the rolling stand Chatter vibrations can not be suppressed. Such changed operating conditions for suppressing Chatter oscillations usually mean a significant reduction in production speed.

STATE OF THE ART

A method comprising the features of the preamble of independent claim 1 and an apparatus having the features of the preamble of independent claim 6 are known from US 5,724,846 known. Here, pressure pulsations are caused in the hydraulic medium, which is supplied to at least one of the nip of the roll stand adjusting hydraulic cylinder. These pressure pulsations are asynchronous to the chatter vibrations to be suppressed and are intended to disturb the accumulation of vibrational energy at the natural frequencies of the rolls or rolling stand on which the Chatter oscillations are based, due to the asynchronous excitation of the rolls starting from them. How the pressure pulsations are to be generated concretely is in the US 5,724,846 not specified.

From the EP 0 956 950 A1 it is for the active suppression of contact vibrations on roller assemblies, in particular on Papierstreichapparaten, with two parallel aligned, directly or indirectly adjacent rollers, of which in particular a roller without active suppression of contact vibrations shows an increasing periodic deformation of its surface known movements of at least one of To detect rollers and apply compensation forces depending on the measured movements. In this case, the rotation frequency of the roller is determined with the potentially particular deforming surface, and the compensating forces between the two rollers are applied with this rotational frequency and / or at least one of the rotational frequency generated integer multiples of the rotational frequency. However, it is not described how the balancing forces should be applied concretely. It is only mentioned by an actuator acting between the axes of the two rollers actuator.

From the DE 10 2005 026 907 A1 a bending compensating roll is known, which has a circumferential roll shell, a roll jacket axially passing through the rotatable yoke and at least one arranged between the yoke and the roll shell hydraulic support source. In this case, means for detecting the roll shell movement and means for controlling the hydraulic pressure under or on the support source in dependence on the detected roll shell movement are provided. The regulation of the hydraulic pressure is preferably carried out such that a static force which superimposes the static load-generating force and which dampens the mantle motion is generated. For the control of the hydraulic pressure with the desired dynamics is in the support source, a piezo-stack actuator provided, which acts via a membrane, the pressure chamber under or the pressure chamber on the support source to vary the prevailing hydraulic pressure therein.

From the DE 40 10 662 A1 a setting device for adjusting the roll spacing in rolling stands is known, which has two hydraulic adjusting cylinder, which work on both sides of a work roll to be set. The adjusting cylinders each have two or more piston surfaces, which can be acted upon independently of one another, and individually in an optional combination or all together with pressure medium. As a result, the rolling force control in the respective rolling force range can be improved with respect to the admission of only one piston surface per setting cylinder such that percentage rolling force fluctuations are minimized.

From the WO 01/00346 A1 is a passive vibration damper for rolling stands known, the absorber mass has the shape of a piston which is elastically supported against each other swinging parts of the rolling stand. He is at the lower part of the rolling mill, with respect to which he is movable by means of hydraulic medium in a bore, soft elastic supported, while it is supported against a top of the roll stand to which it is pressed by means of the hydraulic medium with a higher spring stiffness is.

OBJECT OF THE INVENTION

The invention has for its object to provide a method having the features of the preamble of independent claim 1 and an apparatus having the features of the preamble of independent claim 6, with which Chatter vibrations can be effectively suppressed on a rolling stand, without requiring extensive changes would have to be made on the rolling mill.

SOLUTION

The object of the invention is achieved by a method having the features of independent claim 1 and a device having the features of independent claim 6. Preferred embodiments of the new method are in the dependent claims 2 to 5 described while the dependent claims 7 to 15 describe preferred embodiments of the new device.

DESCRIPTION OF THE INVENTION

In the new method, pressure changes in a hydraulic medium, which acts on at least one of the nip of the roll stand adjusting hydraulic cylinder, directly generated in an adjacent to its piston pressure chamber of the hydraulic cylinder by the volume of the pressure chamber is changed. That is, no pressure pulsations are supplied to the hydraulic cylinder from the outside, depending on the switching position of valves leading to the hydraulic cylinder have different effects on the pressure in the hydraulic cylinder itself. In particular, delays between the generation of the pressure changes and their action on the piston of the hydraulic cylinder and any damping of the pressure changes until they act on the piston are avoided. In this way, the pressure changes can be highly dynamically intervened in the roll stand and reduced to Chatter vibrations or already acting on these possibly causing suggestions.

In concrete terms, the pressure changes in the pressure chamber can be generated as a function of the amplitude, frequency and phase of movements of one or more of the rolls of the roll stand. These movements are then detected on at least one working or support roller of the roll stand, preferably in the direction of the nip. By detecting motions is meant here optionally the detection of accelerations and / or the detection of velocities and / or the detection of positions or distances, it being understood that these three motion variables are temporal integrals or temporal derivatives of one another.

The control concept with which in the new method the pressure changes are generated as a function of amplitude, frequency and phase of the detected movements of the rolls of the roll stand can aim to virtually increase the stiffness at the considered point of the respective roll, ie all accelerations, which act on this point, countering with antiphase forces that keep the point at rest.

Alternatively, the control concept in the new method can be aimed at a virtual increase in the attenuation of occurring movements of the considered point. In this concept, as much movement of the rollers as possible is withdrawn. Both of the above concepts can also be combined with each other.

The movements of the rolls of the roll stand can be detected in the new process not only on the rolls themselves, but also in or at their camps. This is particularly useful if the movements of the work rolls or back-up rolls of the roll stand are to be detected, which directly or indirectly affect the constancy of the roll gap and thus directly affect the quality of the rolled material with their occurrence. In principle, these movements can also be detected directly, for example by sensors integrated in the roller. However, it should be noted that the work rolls of a rolling mill are replaced to be over-ground, even if no chatter marks occur. Sensors in the rollers would therefore greatly increase the total cost of implementing the new method, which is not the case with detecting the movements of the rollers by measuring accelerations of their bearings.

The movements of the support rollers of a rolling stand in the direction of the nip can be detected on their sides facing away from the work rolls also with a distance sensor. Since this can not be arranged absolutely fixed, but also experiences changes in position in vibrations of the roll stand, such a distance sensor is preferably to be combined with an acceleration sensor which provides a correction signal for proper movements of the distance sensor.

The novel device for suppressing the rattle of rolls of a rolling stand has electrically controllable linear actuators as parts of the means for generating pressure changes in the hydraulic medium acting on the hydraulic cylinder for adjusting the nip. These linear actuators change with their length changes directly the volume of the pressure chamber adjacent to the piston of the hydraulic cylinder.

Specifically, the linear actuators can support linearly movable regions of a wall of the pressure chamber. They are under the pressure prevailing in the pressure chamber set a bias. However, this is by no means disadvantageous, but for different linear actuators even a prerequisite for a highly dynamic response. The linearly movable regions of the wall of the pressure chamber supported by the linear actuators may be small pistons, ie pistons with a much smaller piston area than the piston of the hydraulic cylinder.

Specifically, the linear actuators can be arranged in the piston of the hydraulic cylinder and support with their small piston linearly movable areas within the piston surface of the piston of the hydraulic cylinder. By integrating the linear actuators in the pistons of the hydraulic cylinder, essentially only the piston needs to be replaced for retrofitting the new device to an existing rolling stand.

Preferably, the linear actuators of the new device are piezo stack actuators, i. H. to actuators in which a plurality of piezocrystal elements, in particular piezoceramic discs, stacked to increase the achievable length change. Piezo-stack actuators are highly dynamically controllable when they are under a compressive bias. In this case, the optimum pressure bias on the linear actuators can easily be adjusted by varying the diameter of the small pistons supported by them relative to the diameter of the piezo-stack actuators, taking into account the pressure prevailing in the pressure chamber of the hydraulic cylinder.

The dimensions of dynamically operated (in particular cylindrical or rectangular) piezo stack actuators perpendicular to their stacking direction are limited, typically less than 20 mm, so that the heat input into the actuators does not lead to internal overheating due to hysteresis effects of the piezo material , The small dimensions make it easier to dissipate the heat generated inside the piezo material to the outside. The limitation of the dimensions of the individual piezo stack actuators also results in limitations for the force which can be applied to the piston via the hydraulic medium with each of these actuators. However, in the case of the present invention, this limitation is easily compensated for by connecting a multiplicity of piezo-stack actuators in parallel and each acting on the pressure chamber via a small piston. The space required for this purpose is readily available because hydraulic cylinders with which the nip of a roll stand is adjusted, typically have a very large piston area of a few square decimeters. About this piston surface, the individual piezo stack actuators can be distributed.

The limitation of the base area of piezoactuators in cylindrical or rectangular actuators due to the mentioned risk of overheating, which is typically below about 400 mm ² , can be overcome by the use of annular actuators. The wall thickness of the ring is then typically, for example, less than 20 mm. The Piezoaktuatorgrundfläche is defined here by the outer diameter of the annular actuator. For example, with an outside diameter of 60 mm and a wall thickness of 16 mm, a base area of 2,200 mm ^{2 is} achieved.

In order to reliably avert the already mentioned risk of overheating of the piezo stack actuators in the new device, the piezo stack actuators can be cooled with the hydraulic medium flowing through capillary lines leading from the pressure chamber. The capillary lines are to be dimensioned so that they can pass limited amounts of hydraulic medium to the piezo-stack actuators as a cooling medium and the pressure in the pressure chamber over its length completely drops. Thus, the hydraulic medium is no longer at the pressure in the pressure chamber on exiting the capillary, but at ambient pressure or an ambient pressure. From the piezo stack actuators, the heated hydraulic medium returns via a radiator in the circulation of the hydraulic fluid. However, such cooling of the piezo-stack actuators presupposes that hydraulic medium is continuously supplied to the pressure chamber in order to maintain the static pressure prevailing in it, which sets the nip.

At least one sensor is provided on the new device, which detects movements in the direction of the nip on at least one working or support roller of the rolling stand. Furthermore, a signal generator is provided, which drives the linear actuators with a drive signal which is dependent on the amplitude, frequency and phase of the detected movements. The applicable control concepts have already been discussed above in connection with the new procedure.

The sensor for detecting the movements of the roller may be an acceleration sensor provided on a bearing of a roller. The movements of a support roller in the direction of the nip can also be used with a distance sensor for a distance to a shell of Back-up roller to be detected. As already mentioned, such a distance sensor is to be combined with an acceleration sensor which supplies a correction signal for proper movements of the distance sensor. The distance sensor itself may be, for example, a capacitive distance sensor or also have a rolling on the jacket of the support roller Tastrad.

The hydraulic cylinder, in which the pressure changes are generated directly in a pressure chamber adjacent to its piston by changing the volume of the pressure chamber, may be a setting cylinder of the respective rolling stand, which specifies the nip or the force between the work rolls. It is preferred if the invention is implemented in all of the usually two Anstellzylinder. However, the present invention can also be implemented in any other hydraulic cylinder, which is provided in the respective rolling mill and the application of hydraulic medium acts on the nip, in particular in any bending cylinder, with the deflection of the work rolls or the parallelism of the nip between the work rolls is adjusted.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and of combinations of several features mentioned in the introduction to the description are merely exemplary and can come into effect alternatively or cumulatively, without the advantages having to be achieved by embodiments according to the invention. Further features are the drawings - in particular the illustrated geometries and the relative dimensions of several components to each other and their relative arrangement and operative connection - refer. The combination of features of different embodiments of the invention or of features of different claims is also possible deviating from the chosen relationships of the claims and is hereby stimulated. This also applies to those features which are shown in separate drawings or are mentioned in their description. These features can also be combined with features of different claims. Likewise, in the claims listed features for further embodiments of the invention can be omitted.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

zeigt ein Walzgerüst mit einer erfindungsgemäßen Vorrichtung zum Unterdrücken des Ratterns von Walzen des Walzgerüsts mit Blickrichtung auf die Achsen des Walzgerüsts, wobei die Darstellung von Fig. 1 im Bereich von Hydraulikzylindern zum Einstellen des Walzenspalts des Walzgerüsts geschnitten ist.

Fig. 2

zeigt einen der bereits in Fig. 1 geschnitten dargestellten Hydraulikzylinder des Walzgerüsts in gegenüber Fig. 1 vergrößerter Querschnittsansicht.

Fig. 3

zeigt eine andere Ausführungsform eines Walzgerüsts mit einer erfindungsgemäßen Vorrichtung in einer Seitenansicht mit Blickrichtung längs der Achsen der Walzen des Walzgerüsts, wobei auch hier ein Hydraulikzylinder zum Einstellen des Walzenspalts des Walzgerüsts geschnitten dargestellt ist.

Fig. 4

zeigt eine Draufsicht auf die Kolbenfläche des Kolbens des Hydraulikzylinders gemäß Fig. 3.

Fig. 5

zeigt einen Schnitt durch ein Detail des Kolbens gemäß Fig. 4.

Fig. 6

zeigt einen Schnitt durch ein Detail des Kolbens gemäß Fig. 4 und einen separaten Piezostapel-Ringaktuator als Alternative zu der Ausführungsform gemäß Fig. 5.

Fig. 7

zeigt ein Walzgerüst, wobei zusätzlich zu Fig. 1 zwischen Lagern von Arbeitswalzen wirkende Biegezylinder wiedergegeben sind.

The invention is explained in more detail below with reference to embodiments with reference to the accompanying drawings and described.

Fig. 1

shows a rolling stand with a device according to the invention for suppressing the rattling of rolls of the rolling stand with a view towards the axes of the roll stand, the illustration of Fig. 1 is cut in the range of hydraulic cylinders for adjusting the nip of the rolling stand.

Fig. 2

shows one of the already in Fig. 1 Cut illustrated hydraulic cylinder of the rolling mill in opposite Fig. 1 enlarged cross-sectional view.

Fig. 3

shows another embodiment of a rolling stand with a device according to the invention in a side view looking along the axes of the rolls of the rolling stand, wherein also here a hydraulic cylinder for adjusting the roll gap of the roll stand is shown in section.

Fig. 4

shows a plan view of the piston surface of the piston of the hydraulic cylinder according to Fig. 3 ,

Fig. 5

shows a section through a detail of the piston according to Fig. 4 ,

Fig. 6

shows a section through a detail of the piston according to Fig. 4 and a separate piezo stack ring actuator as an alternative to the embodiment of FIG Fig. 5 ,

Fig. 7

shows a rolling stand, in addition to Fig. 1 between bearings of work rolls acting bending cylinder are shown.

DESCRIPTION OF THE FIGURES

This in Fig. 1 Roll stand 15 shown comprises four rolls 1 to 4, of which the two middle rolls 2 and 3 serve as work rolls and the two outer rolls 1 and 4 as support rolls. Between the work rolls 2 and 3, a nip 16 is formed, through which passes the rolled with the roll stand 5 material. The rollers 1 to 4 are mounted with their shafts 17 to 20 in a rolling mill 5, which is based on a base 21. In this case, the nip 16 is adjusted by means of hydraulic cylinders 6, which act on bearings for the shaft 20 of the lower support roller 4. The bearings of the work rolls 2 and 3 are guided in the direction of the nip 16 slidably on the rolling mill. The bearings for the shaft 17 of the upper back-up roll are supported upwardly at a bar of the rolling mill seating. Movements of the rollers 1 to 4 in the direction of the nip 16 are detected by acceleration sensors 13 at the bearings for the shaft 17 of the upper support roller 1. A controller 14 controls linear actuators 11 in the hydraulic cylinders 6 in response to the detected movements of the rollers 1 to 4 to actively suppress these movements. The controller 14 is additionally supplied with a speed signal 23, which tells her the current speed of the work rolls 2 and 3 and / or the current speed of the support rollers 1 and 4, because it is particularly effective at the frequencies corresponding to these speeds or their harmonics, to counteract the movements of the rollers 1 to 4.

Fig. 2 shows one of the hydraulic cylinders 6 according to Fig. 1 in an enlarged view. In the hydraulic cylinder 6, a pressure chamber 24 is provided, which is acted upon by hydraulic medium to adjust the nip. This is a lower piston chamber 10 of the hydraulic cylinder 6. The hydraulic cylinder 6 also has an upper piston chamber 9, which acts with a smaller effective area on the piston 8 of the hydraulic cylinder and which can be acted upon for clamping the hydraulic cylinder. The piston 8 supports with a piston rod 7 of one of the two end bearing for the shaft 20 according to Fig. 1 on the rolling mill 15 from. The forces acting on the piston via the piston rod 7, however, are determined not only by the introduced from the outside with the hydraulic medium in the two piston chambers 9 and 10 pressures. Rather, two linear actuators 11 are provided, with which the pressure in the pressure chamber 24, that is, the lower piston chamber 10, can be varied within the hydraulic cylinder 6. This makes it possible to vary the forces acting on the piston rod 7 in the highly dynamic, ie high-frequency range of several hundred to a thousand Hz, to that with the acceleration sensors 13 according to Fig. 1 counteract detected movements of the rollers 1 to 4. The linear actuators 11 are provided in the piston 8 and are supported at the rear on the piston 8. On their other side, they act on small pistons 12 whose piston surfaces 25 are movable regions 26 of a piston surface 27 of the piston 8. About the piston 12, the linear actuators 11 are also acted upon by the pressure in the pressure chamber 24. However, this is not a disadvantage in the preferred embodiment of the linear actuators as piezo stack actuators 28, but an advantage, because a highly dynamic control of piezo stack actuators already presupposes a pressure bias.

Fig. 3 shows another rolling mill from the side, which also has four rolls 1 to 4 consisting of two work rolls 2 and 3 and two back-up rolls 1 and 4. Differences to the structure of Fig. 1 do not insist that in Fig. 3 was omitted for convenience on the playback of the controller 14, but in the arrangement of the acceleration sensor 13 not on the bearing 29 for the shaft 17 of the upper support roller 1, which is supported on the latch 22, but on the bearing 31 for the shaft 19 of lower work roll 3. In addition, the hydraulic cylinder 6 is formed differently, as now based on the 4 and 5 will be explained in more detail.

Fig. 4 shows a plan view of the piston surface 27 of the piston 8 of the hydraulic cylinder 6 according to Fig. 3 , It can be seen a plurality of pistons 12 with piston surfaces 25, which are supported relative to the piston 8 each with a linear actuator not visible here, which is controlled by the controller for suppressing the rattling of the rollers of the rolling stand. The multiplicity of pistons 12 take into account the maximum diameter of piezo stack actuators, so that they are not so much heated in their interior under dynamic stress due to hysteresis effects that they die a "heat death". A maximum diameter of 20 mm or less ensures that the heat generated inside the piezo material can be dissipated to the surfaces of the piezo stack actuator.

To further dissipate the heat from the surfaces of the piezo-stack actuators 28, the pistons 12 according to Fig. 4 each two perpendicular to the piston surfaces 25 extending capillary 33, can flow through the hydraulic medium while reducing the pressure prevailing in front of the piston surface 27 pressure on the back of the piston 12 to cool the piezo-stack actuators 28 located there. This is closer Fig. 5 seen. Fig. 5 is a cut by a piston 12 and the underlying piezo stack actuator 28 as a linear actuator 11. Sketched Fig. 5 in that the diameter of the piston 12 can be greater than that of the piezo-stack actuator 28 in order to set a favorable pressure bias on the piezo-stack actuator 28 depending on the pressure on the piston surface 25. Further shows Fig. 5 in that the capillary conduits 33 lead to a bore 34 in which the piezo-stack actuator 28 is arranged. The free cross-section of the bore 34 to the piezo-stack actuator 28 is much larger than the diameter of the capillary 33. Also a line 35, which leads from the bore 34 to a manifold 36 for the through the capillary 33 passed through hydraulic medium has a much larger cross section than the capillary 33 on. Thus, the complete pressure reduction of the hydraulic medium via the capillary 33 can take place. The hydraulic medium flowing along the piezo-stack actuators 28 absorbs the heat generated by the latter and leads it to a cooler for the hydraulic medium, not shown here.

The piezo actuator 11 according to Fig. 5 can also be used as a piezo stack ring actuator 37 Fig. 6 be executed. As a result, the increase in the base area, while maintaining the good heat dissipation is given.

It is understood that the invention can also be used for several pairs of rolls for work rolls and / or back-up rolls or more than 4 rolls.

It is also understood that the present invention is not limited to the implementation of the large-sized hydraulic cylinders 6 of a roll stand 15, which are also referred to as adjusting cylinder. Fig. 7 outlines between the bearings 30 and 31 of the work rolls 2 and 3 acting, so-called bending cylinder 38 and 39, with which the parallelism of the nip 16 influence can be taken and the piston chambers 40 to 43 can also be used as pressure chambers 24, in which invention pressure changes are produced by changes in the volume of the respective pressure chamber 24, which affect the nip 16 and with which, accordingly, the rattling of the rollers 1 to 4 of the roll stand 15 influenced, ie in particular can be suppressed.

LIST OF REFERENCE NUMBERS

1

supporting roll

2

Stripper

3

Stripper

4

supporting roll

5

Walzwerksstuhlung

6

hydraulic cylinders

7

piston rod

8th

piston

9

piston chamber

10

piston chamber

11

linear actuator

12

piston

13

accelerometer

14

control

15

rolling mill

16

nip

17

wave

18

wave

19

wave

20

wave

21

base

22

bars

23

Speed signal

24

pressure chamber

25

piston area

26

Area

27

piston area

28

Piezo-stack actuator

29

camp

30

camp

31

camp

32

camp

33

capillary

34

drilling

35

management

36

manifold

37

Piezo stack Ringaktuator

38

bending cylinders

39

bending cylinders

40

piston chamber

41

piston chamber

42

piston chamber

43

piston chamber

Claims (15)

1. Method of suppressing chatter of rollers of a roll stand (15) which comprises at least two working rollers (2, 3) opposing each other across a nip, two supporting rollers (1, 4) supporting the working rollers (2, 3), and two hydraulic cylinders (6) adjusting the nip (16), pressure variations in a hydraulic fluid, which charges at least one of the hydraulic cylinders (6) adjusting the nip (16) of the roll stand (15), being created, characterized in that the pressure variations are generated directly in a pressure chamber (24) of the hydraulic cylinder (6) adjacent to its piston (8) in that the volume of the pressure chamber (24) is varied.
2. Method of claim 1, characterized in that movements in the direction of the nip (16) are monitored at at least one roller (1 to 4) of the roll stand (15), and that the pressure variations in the pressure chamber (24) are generated depending on amplitude, frequency and phase of the movements.
3. Method of claim 2, characterized in that the pressure variations are generated according to the concept of actively increasing the stiffness.
4. Method of claim 2, characterized in that the pressure variations are generated according to the concept of actively increasing the attenuation.
5. Method of any of the claims 2 to 4, characterized in that the movements of the roller (1, 2, 3 or 4) are monitored by measuring accelerations of its bearings (29, 30, 31 or 32).
6. Apparatus for suppressing chatter of rollers of a roll stand (15) which comprises at least two working rollers (2, 3) opposing each other across a nip (16), two supporting rollers (1, 4) supporting the working rollers (2, 3), and two hydraulic cylinders (6) adjusting the nip (16), the apparatus having means for generating pressure variations in a hydraulic fluid charging at least one of the hydraulic cylinders (6), characterized in that the means for generating pressure variations comprise electrically controllable linear actuators (11) which vary the volume of a pressure chamber (24) of the hydraulic cylinder (6) directly adjacent to its piston (8) with their changes in length.
7. Apparatus of claim 6, characterized in that the linear actuators (11) support linearly movable areas (26) of a wall of the pressure chamber (24).
8. Apparatus of claim 7, characterized in that the linear actuators (11) are arranged in the piston (8) of the hydraulic cylinder (6) and support linearly movable areas (26) of the piston surface (27).
9. Apparatus of any of the claims 6 to 8, characterized in that the linear actuators are piezo stack actuators (28).
10. Apparatus of claim 9, characterized in that the piezo stack actuators are made as ring actuators (37).
11. Apparatus of claim 9 or 10, characterized in that the piezo stack actuators ((28) are cooled by the hydraulic fluid via capillary lines (33) leading out of the pressure chamber (24).
12. Apparatus of any of the claims 6 to 11, characterized in that at least one sensor is provided which monitors movements in the direction of the nip (16) in or at at least one roller (1 to 4) of the roll stand (15), and that a controller (14) is provided which controls the linear actuators (11) with a control signal which depends on amplitude, frequency and phase of the movements.
13. Apparatus of claim 12, characterized in that the sensor is an acceleration sensor (13) provided at a bearing (29, 30, 31 or 32) of a roller (1, 2, 3, or 4).
14. Apparatus of claim 12, characterized in that the sensor includes a distance sensor for a distance to an envelope of a supporting roller (1 or 4).
15. Apparatus of any of the claims 6 to 14, characterized in that the at least one hydraulic cylinder is an engaging cylinder (6) or a bending cylinder (38, 39) of the roll stand (15).

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