EP2128337A1 - Method for operating a calender and same - Google Patents

Abstract

The method involves using two rollers (2, 3) of a calender (1) as nip forming elements. The roller (2) is designed as a soft roller, and the roller (3) is designed as a hard roller. A nip (4) is limited by the rollers, such that the nip is closed and a surface of the rollers is offset in a circulating motion. The circulating motion of the rollers in the nip superimposes an oscillatory motion. One of the rollers is offset in oscillation parallel to a running direction of a web e.g. paper web, by the nip. A synchronous motor is used for generation of the oscillatory motion. An independent claim is also included for a calender comprising a frequency converter.

Description

The invention relates to a method for operating a calender with at least one nip, which is bounded by two nip-forming elements, in which one closes the nip and the surface of the nip-forming elements in a circulating movement.

Furthermore, the invention relates to a calender with at least one nip, which is bounded by two nip-forming elements, of which at least one has a circulation generating drive.

The invention will be described below in connection with a calender used to treat a paper web. But it is also applicable when other webs are treated in the calender, such as cardboard sheets.

The nip-forming elements are often formed as cylindrical rollers. But they can also be designed as shoe rollers or as a metal band. For the sake of simplicity, the following explanation will be given using the example of rolls for the nip-forming elements.

Regardless of the type of calender you can usually observe after a certain operating time that results in a barring formation. Barrings are strips that run transversely to the direction of travel of the web. As soon as These streaks become visible, is the paper or cardboard board committee, which is no longer salable and must be disposed of. The formation mechanism of this barring formation has not yet been finally clarified, it is often assumed that it is the effect of vibrations that make the soft or elastic rollers of the calender over time "polygonal". In simple terms, this results in a wave pattern on the surface of an elastic roller.

Various solutions have been proposed to avoid barring. That's the way it is EP 0 949 378 B1 it is known to drive at least two rollers in a calender with several nips and to vary the drive torque distribution of the driven rollers.

DE 102 38 949 B3 suggests to generate a relative speed between the web and the surface during the passage of a portion of the web and dispose of the portion of the web.

DE 198 21 854 C1 suggests the use of an actuator which counteracts contact vibrations between adjacent rollers by generating a corresponding counter-vibration.

DE 100 08 800 A1 describes a roller in the interior of an active vibration is generated, which acts on the roll shell. For this purpose, an actuator is arranged in the interior.

All of the suggestions, in one way or another, bring an improvement in operation, as shown by the fact that barring is delayed. However, in many cases, it is still observed that barring formation necessitates reworking of the rolls, particularly soft-surfaced rolls, before the roll has reached its life. A reworking of the roller usually means that the roller must be removed, abraded and installed. At least during the removal and installation of the roller, the calender is not available for processing a web.

The invention has for its object to reduce effects of barrings.

This object is achieved in a method of the type mentioned in that one superimposes a vibration movement at least in the nip of the circumferential movement of a nip-forming element.

As a result of this oscillatory movement, a reciprocating relative movement arises between the two nip-forming elements, which results in the two nip-forming elements, so to speak, mutually grinding one another in this operation. Assuming that one of the nip-forming elements has a "hard" surface and the other nip-forming element has a "soft" surface, then the grinding process will essentially be confined to the soft surface.

But this is also the surface on which the barring formation usually occurs. Thus, there is a grinding process across the width of the calender, that is, the axial length of the nip-forming elements, without the corresponding nip-forming elements must be removed. Although the removal that can be achieved in such a grinding process, extremely low. However, this has the advantage that the relevant roller (or another nip-forming element) is not stressed too much by the grinding process. The grinding process is sufficient if it eliminates the wave pattern causing the barring on the surface of the nip-forming element. Since even at relatively small amplitudes of this wave pattern the risk of barring formation arises, even relatively small material removal by the grinding process to put the nip-forming element back into a "trouble-free" state. Although it takes a certain amount of time for the machine-wide grinding process. However, this time is usually not longer than the time that would be required to remove and install a roller or other nip-forming element. You can perform the machine-wide grinding process by the two nip-forming elements can create directly to each other. In this case, the abrasion during grinding is effected by a relative movement between the two surfaces of the nip-forming elements. You can also close the nip when a train goes through. In this case, the web causes the removal of material, so that also realized with a web in the nip a machine-wide grinding process can be. However, the web must then be disposed of as a rule.

Preferably, a torque oscillation is generated in addition to a drive torque. The drive torque generates the circumferential movement of the surface of the nip-forming element. If one superposes a torque oscillation on this revolving movement, then the surface of the nip-forming element in the nip briefly moves faster and for a short time slower than the average speed. This results in a relative movement between the surface of the nip-forming element and the surface of the adjacent nip-forming element or the continuous web, which causes the machine-wide grinding.

Preferably, one of the nip forming elements is vibrated parallel to a direction of travel of a web through the nip. Relative to a roller, this means that you create a tangential movement in the nip. This movement can be generated, for example, by a suitable excitation of a torque support or a bearing.

Preferably, one chooses the frequency of the oscillatory motion at least twice as large as the rotational frequency of the nip-forming element. In this case, a sufficient relative movement is generated in order to achieve the desired removal on the nip-forming element.

Preferably, a synchronous motor is used to generate the oscillatory motion. A synchronous motor, which is controlled by a frequency converter, can be controlled with a relatively high frequency, so that you can generate the desired vibrations using the synchronous motor.

In a particularly preferred embodiment, it is provided that one adjusts the phase position of the oscillatory motion to a determined by a measurement barring pattern, wherein a relative movement between the two nip-forming elements in the region of a wave crest of the barring pattern is greater than in the region of a wave trough. This ensures that the wave crest of the wave pattern is abraded by the relative movement. In the wave trough, on the other hand, no or only a small amount of material is removed. In this way, it is relatively quickly possible to eliminate the barring pattern. However, it is necessary to determine the vibrations of the nip-forming elements or of the roll package in the calender. However, since such a measurement is already performed many times now, basically no additional elements are required.

A drive torque with a size in the range of 1 to 50% of the drive torque of the nip-forming element is preferably used to generate the oscillatory motion. This ensures that the nip-forming element can still perform a circulating movement, ie can rotate in the case of a roller. This in addition to generating the oscillatory motion However, the drive torque generated has a size sufficient to produce the relative movement on the surface of the nip-forming element.

Preferably, a vibrational motion is generated at a frequency in the range of 30 Hz to 2000 Hz. This is a relatively high frequency, which is significantly higher than the rotational frequency of the nip-forming element. The greater one chooses the distance of the corresponding frequencies, the lower the risk that these frequencies influence each other negatively.

Preferably, a frequency is used at which the nip-forming element still performs a rigid body movement. In the case of rollers, at higher frequencies there is the risk that individual vibration nodes are formed across the machine width at the corresponding roller. In the area of the vibration nodes, a reliable grinding movement and thus a desired material removal will not be possible with the required reliability. In a rigid body movement, however, the additionally eingepulste torque leads to a slightly higher overall wear at a significantly extended roller life.
Preferably, the oscillatory motion is generated before a barring pattern on the nip-forming element reaches a depth of 5 μm. Even with smaller barring patterns with a depth of 1 to 2 microns on the surface of the nip-forming element shows a significant noise on the calender. When the barring pattern is impressed with more than 10 to 20 microns in the elastic cover of a roll, then the barring strips are detectable in the web. If, on the other hand, you intervene relatively early and reduce or remove the barring pattern due to machine-wide grinding, then you can significantly increase the service life of the nip-forming elements. If you have to grind a barring pattern on the nip-forming element to a depth of 1 to 2 μm, then you do not need too much time to perform this sanding process. The material removal is correspondingly low, which has a positive effect on the life of the roller or another nip-forming element.

The object is achieved in a calender of the type mentioned above in that the nip-forming element has an additional drive which is controlled at a higher frequency than the drive and generates a vibrational movement in the nip transversely to the nip direction. However, the auxiliary drive is only put into operation if you actually want to eliminate the barring pattern. In "normal" production, the auxiliary drive is out of action. In contrast, if a grinding operation is required to eliminate the barring pattern on the nip-forming element, then a vibrational movement of the nip-forming element is generated, which is anyway directed in the nip parallel to the direction of rotation. Since the other nip-forming element or the continuous web does not have this oscillatory motion, a relative movement is created with which Help one can effect a machine-wide grinding of the nip-forming element.

Preferably, the auxiliary drive has a synchronous motor which is connected to a frequency converter. The frequency converter drives the synchronous motor at the desired higher frequency to produce the oscillatory motion.

It is preferred that the frequency converter is connected to at least one vibration sensor which determines a vibration of the nip-forming element and / or in the calender. It is thus possible to control the frequency converter in order to achieve optimum grinding of the barring pattern on the nip-forming element.

The auxiliary drive preferably has a driven torque support. Even with this, the desired additional movement can be generated in the form of a vibration.

• einzige Figur: eine schematische Darstellung eines Kalanders

The invention will be described below with reference to a preferred embodiment in conjunction with a drawing. Herein show:

• single figure: a schematic representation of a calender

A calender 1 has two rollers 2, 3 as nip-forming elements. The roller 2 is designed as a "soft roll", ie it has an elastic cover their surface. The other roller 3 is formed as a hard roller having a peripheral surface of steel or cast, which is substantially harder than the surface of the soft roll. 2

Between the two rollers 2, 3, a nip 4 is formed, which is closed in the drawing. In a production operation of the calender 1, a web is guided by the closed nip 4, for example a paper or board web. The calender 1 is then used to satinize this web.

For the operation described below, however, it does not depend on the calendering of the web. Accordingly, the nip 4 can be closed so that the two rollers 2, 3 lie directly against each other. But it is also possible to lead a path through the nip 4.

In the production operation of the calender 1, in which the web is calendered, it can be observed after a certain operating time that results in a barring formation. The barrings are strips that run transversely to the direction of the web. Once these streaks become visible, the web is broke, which must be disposed of. In some cases, there is already a quality deficiency before the streaks become visible.

It is believed that the barrings are formed by vibrations that imprint a pattern in the surface of the soft roll 2. Usually there is a significant noise on the calender 1 when the barring pattern has a depth of 1 to 2 microns. If the barring pattern is imprinted more than 10 to 20 microns in the elastic cover, then the variations in thickness with visible streaks in the web are detectable.

A sensor 5 is provided to inspect the surface of the soft roll continuously or from time to time. At the latest when the barring pattern has a depth of 5 μm, a signal indicating that condition is generated. One can then initiate by an operator or automatically a machine-wide grinding process.

The roller 2 has a rotary drive 6. The roller 3 has a rotary drive 7. The two rotary drives 6, 7 are coordinated so that the two rollers 2, 3 in the normal production, ie in the calendering of the web, which is guided by the nip 4, rotate at the same peripheral speed. The two rotary drives 6, 7 act on roll cams 8, 9 or otherwise on the rollers 2, 3rd

The soft roller 2 has at its other end an auxiliary drive 10, which is shown here for explanation smaller. The auxiliary drive 10 is designed as a synchronous motor which provides a drive torque which corresponds to approximately 1 to 50% of the rated motor of the rotary drive 6 of the soft roller 2. The auxiliary drive 10 acts on the roll pin 11 at the other End, ie the end facing away from the rotary drive, on the roller. 2

The auxiliary drive 10 is connected to a frequency converter 12, which forms part of a control device 13. The sensor 5, which determines the barring pattern, is connected to the control device 13. Also connected to the control device 13 is a vibration sensor 14 which detects a vibration of the soft roller 2. In a manner not shown further vibration sensors 14 may be provided.

The auxiliary drive 10 is driven by the frequency converter with a relatively high frequency. The frequency can be in the range of 30 to 2000 Hz. In rolls, however, it is advantageous to choose the frequency so that the roller 2 still performs a vibration in the form of a rigid body movement. In this case, the frequency is for example 30 to 150 Hz. The rotational frequency of the roller, however, is in the range of 5 to 15 Hz.

By the action of the auxiliary drive 10 now lead the two rollers 2, 3 in the nip 4 at a constant circumferential speed in the circumferential direction reciprocating motion relative to each other, which causes the soft roller 2 through the hard roller 3 or the guided through the nip 4 track is sanded. If you start grinding enough early enough, for example at the depth of the barring pattern of the order of 1 to 2 μm, then only a relatively small material thickness must be removed. This can be achieved in a reasonable time, for example, has an order of 15 to 120 minutes.

When passing a web through the nip 4, the time required for machine-wide grinding of the soft roll 2 by means of the web is somewhat shorter. For example, a paper web has a coefficient of friction with respect to the plastic cover of the soft roll in the range of 0.2 to 0.4. The coefficient of friction of a steel roller against a plastic roller is about half. Accordingly, if you pass a web through the nip 4 for grinding, you only need half the time that would be required if the two rolls 2, 3 are in direct contact with each other.

The torque oscillations, which are generated by means of the auxiliary drive 10, are adapted with their phase position to the phase position of the barring pattern. The phase position of the barring pattern can be determined by the sensor 5. A relatively large relative movement is produced between the roller 2 and the roller 3 or between the roller 2 and the track guided by the nip 4 when a mountain of the barring pattern is in the nip 4, and a relatively small relative movement when a Valley of the Barring pattern located in nip 4. This results in an optimal grinding of the barring pattern of the soft roll. 2

The calender 1 is shown here with two rollers, wherein the soft roller is provided with the auxiliary drive 10. Alternatively, it is also possible to provide the hard roller 3 with the auxiliary drive 10 and then to initiate a grinding movement over the path guided by the nip onto the elastic surface of the soft roller 2.

It is also possible to provide both rollers 2, 3 with an additional drive 10.

Instead of the soft roll 2, one can also use a shoe roll. In principle, the same considerations apply here, whereby it should be taken into account that the shoe roll rests on the circumference of the hard roll 3 over a somewhat longer circumferential region.

In a metal belt calender, in which additionally a band of metal or other material passes through the nip 4, one can perform the grinding operation on the soft or elastic roller 2 with the aid of the belt.

The described procedure can be used not only for two rolls 2, 3, as shown, but also for a multi-nip calender, in which a soft roll is provided as a center roll. If a barring pattern with an even multiple of the rotational frequency, ie the vibration frequency measured by the sensor 14, forms on the soft roller, then a high-frequency torque pulsating at a higher frequency is introduced into the roller journal 11 and thus introduced into the roller 2. If it is an even multiple in a multi-nip calender, then vibrates the elastic roller against their relatively stationary rollers. As a result, the nip of the elastic roller is loaded on one side in contact with the counter-roller, while the other nip is relieved rather, which is formed with the underlying counter-roller. This results in the sum of an even barring pattern across the roll width with the elastic roll cover.

On the other hand, when a barring pattern having an odd multiple of the revolution frequency is formed on the elastic roller, the elastic roller is comparatively still, while the counter rollers mainly move synchronously against the elastic roller. As a result, both nips are loaded when passing through a wave crest of the elastic roller in contact with the counter-roller, while passing through a wave trough both nips of the elastic center roller are relieved.

It is therefore advantageous, in this case not only to arrange a sensor 14 on the soft roller, but also on one of the adjacent counter-rollers.

The line load used in machine-wide grinding of the soft roll 2 can be reduced in comparison with the conditions of calendering.

Of course, when the hard roll 3 is a heated roll, this roll 3 must be cooled to a suitable surface temperature before the soft roll 2 is ground.

Claims (14)

Method for operating a calender with at least one nip delimited by two nip-forming elements, in which one closes the nip and sets the surface of the nip-forming elements in a revolving movement, characterized in that the circumferential movement of a nip-forming element at least in the nip a vibrational motion superimposed. A method according to claim 1, characterized in that in addition to a drive torque generates a torque oscillation. A method according to claim 1 or 2, characterized in that one puts one of the nip-forming elements in a vibration parallel to a running direction of a web through the nip. Method according to one of claims 1 to 3, characterized in that one selects the frequency of the oscillatory motion at least twice as large as the rotational frequency of the nip-forming element. Method according to one of claims 1 to 4, characterized in that one uses a synchronous motor for generating the oscillatory motion. Method according to one of claims 1 to 5, characterized in that the phase position of the oscillatory motion adapted to a determined by a measurement barring pattern, wherein a relative movement between the two nip-forming elements in the region of a wave crest of the barring pattern is larger than in the region of a wave trough. Method according to one of claims 1 to 6, characterized in that one uses for generating the oscillatory motion, a drive torque having a size in the range of 1 to 50% of the drive torque of the nip-forming element. Method according to one of claims 1 to 7, characterized in that one generates a vibrational movement with a frequency in the range of 30 Hz to 2000 Hz. A method according to claim 8, characterized in that one uses a frequency at which the nip-forming element still performs a rigid body movement. Method according to one of claims 1 to 9, characterized in that one generates the oscillatory motion before a barring pattern from the nip-forming element reaches a depth of 5 microns. A calender having at least one nip delimited by two nip-forming elements, at least one of which is an orbiting element Drive has, characterized in that the nip-forming element (2) has an auxiliary drive (10) which is controllable at a higher frequency than the drive (6) and generates a vibrational movement in the nip (4) transversely to the nip direction. Calender according to claim 11, characterized in that the auxiliary drive (10) has a synchronous motor which is connected to a frequency converter (12). Calender according to claim 12, characterized in that the frequency converter (12) is connected to at least one vibration sensor (14) which determines a vibration of the nip-forming element (2) and / or in the calender (1). Calender according to one of claims 11 to 13, characterized in that the additional drive has a driven torque arm.

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