EP2042654B1 - Band calender and method for operating a band calender - Google Patents

Abstract

The method involves examining characteristics of a set of circular calendar bands (8) with respect to feasibility of break, cracks, thickness, surface structure, surface condition and surface defects of the calendar bands during operation of a band calendar device (1). An alarm is issued during exceeding of predetermined threshold values. The device is stopped during exceeding of the values. The characteristics of the calendar bands are checked by path measurement and acceleration measurement in region of cylinder (2) and acceleration measuring sensor (14) of the bands.

Description

The invention relates to a method for operating a belt calender device with a circulating calender belt for at least one-sided support of a material web to be calendered in a nip of the belt calender device, in which the properties of the calender belt are checked during operation of the belt calender device. Furthermore, the invention relates to a belt calender device with a circulating calender belt for at least one-sided support of a material web to be calendered in a nip of the belt calender device with at least one property checking device which checks the properties of the calender belt during operation of the belt calender device.

Such a method and apparatus are out WO 2005/056921 A1 known.

In the production and processing of sheet-like products, such as in the production and processing of films and in particular in the paper industry in the manufacture and processing of cardboard and paper, the corresponding sheet materials go through a variety of different machines.

For the smoothing and surface treatment of flat materials, so-called calenders have prevailed. In such calenders, the material web to be processed is passed through a gap located between two rollers, a so-called nip. In the nip, the material web to be processed experiences a corresponding force acting on it from the outside. The force acting on the material web causes in particular a compaction and surface smoothing of the corresponding material web.

Other parameters which influence the strength of the compaction or the quality of the resulting surface are the temperature and (residual) moisture of the material web to be processed.

In order to achieve a sufficient compaction or quality of the surface of the paper tube web, for example, in paper, a single nip a roll calender is usually not enough. Accordingly, the paper web is passed through a plurality of calender nips. Since calenders are costly systems which moreover require a not inconsiderable set-up area, attempts have already been made to achieve the required smoothing or densification of the material web in a different way. Thus, for example, so-called multinip calenders have been proposed (also known as supercalenders or Janus calenders) in which several rolls are arranged one above the other, with two rolls each having a nip. However, such a stacking of multiple rolls does not reduce the costs to the desired extent. In addition, a multinip calender also presents problems, in particular to the effect that the individual roll masses and thus the pressure forces prevailing in the nip add up from top to bottom. To compensate for this, complex pressure compensation devices are necessary.

Another way to reduce the required number of nips is to increase the dwell time of the paper web in a single nip. This accomplish so-called Breitnipkalander. In these, one of the calender rolls is provided with an elastic surface. As a result, the corresponding roll surface is concavely deformed by the corresponding calender roll in the nip region, so that a nip with a greater processing length is formed. A disadvantage of such Breitnipkalander is that with respect to the roll surface certain There are restrictions on material selection. In addition, the elastic deformability of a calender roll sets the speed of the rollers certain limits.

In order to eliminate the restrictions on the material properties of the calender roll surfaces, it has already been proposed to support the paper web to be calendered, at least on the side which faces the elastically deformable roll, with a thin-walled metallic endless belt. This endless belt serves as a substitute for a metallic roller surface.

Another proposal to increase the processing length of a calender, is that instead of an elastically deformable roller, a concave shaped Andruckschuh is provided, which is pressed against a corresponding roller surface. Between the counter shoe and the paper web to be calendered is a thin-walled metal endless belt, which supports the paper web to be calendered in the region of the counter shoe and moves at the same speed as the paper web. Such devices are for example in WO 03/064761 A1 disclosed.

Despite the great advantages of such tape calenders, they still have problems in practical use.

One problem is based on the use of a thin-walled metal strip as such. The thin-walled metal strip is sensitive due to its only small thickness to wear due to abrasion of the surface. In addition, the thin-walled metal strip is bent back and forth several times in the course of a pass through the belt calender. This also leads to a corresponding wear of the thin-walled Metal bands and can ultimately lead to a brittle fracture of the metal strip.

Such a breakage of the thin-walled, metallic calendered tape is undesirable. Regardless of the cost of a new metal strip, an uncontrolled, unforeseen breakage of the thin-walled calendered strip can lead to untimely delivery problems. A precautionary replacement of the thin-walled calender belt after a certain period of operation is also not desirable, since this may cause unnecessary costs, because a still useful band is changed unnecessarily early.

An even bigger problem, however, is the potential for harm inherent in such breakage of the calender belt.

Thus, it can easily lead to a bearing damage to a roller at a tearing of the calender belt. Because the metal or composite tape could after a tear of the band - similar to the paper web - form so-called batzen, which, when pulled through the nip, can damage the bearings of the roller, the rollers themselves, or the roll surfaces. This results in corresponding downtime and costs.

Furthermore, with a crack of the metal strip at today's usual machine speeds in the range of 100 m / min to 3000 m / min there is a risk that pieces of the thin-walled calendered tape are sheared off and thrown through the air. However, such flying material parts pose a significant threat to the operating personnel.

In WO 03/064761 A1 is therefore mentioned that one can enclose the belt calender with a hood that can serve as a protective shield in case of failure. This reduces the risk potential for the operating personnel. The risk potential for the machine and the other problems are not addressed by such a hood.

DE 10 2005 007 833 A1 shows a smoothing arrangement in the form of a so-called shoe calender. A shoe roll with a circumferential roll shell forms a nip with a counter roll. The jacket is pressed by a support shoe against the counter roll. Between the support shoe and the jacket, a lubricant in the form of a hydraulic fluid is fed. This hydraulic fluid can also be used to operate the support shoe. If the jacket is damaged, this hydraulic fluid could get onto the hot backing roll, resulting in dangerous situations. To prevent this, an impermeable sealing sheet is wrapped around the shoe roll upon the occurrence of a leak. The occurrence of a leak is detected by sensors that can be designed as vibration sensors, acoustic sensors or as air pressure sensors.

EP 0 978 589 A2 describes a device for actively weakening unwanted vibrations of a rotating roller, a device for treating a material web and a roller. The material web is guided through a nip between two rollers. In one of the rollers, a vibration can be detected with the aid of an acceleration sensor, which is arranged on the roll neck of the roller. An active weakening device comprises a force device, which acts with an actuator on the bearing journal of the roller and that in opposite phase to the unwanted vibrations of the roller to eliminate these unwanted vibrations.

DE 20 2007 007 404 U1 describes a fiber web treatment apparatus equipped with a metal belt circulation of a paper / board machine and / or aftertreatment machine. The metal strip passes over a measuring head which has a roller which is brought into contact with the belt by means of a force. Thereafter, a force is applied to the measuring head, which deflects the metal strip. With a transmitter, the deflection of the metal strip caused by this force is measured.

EP 1 693 509 A1 describes a press roll monitoring with several monitoring units. A monitoring unit records temperature changes. Another monitoring unit observes the surface of the roll mantle. A third monitoring unit monitors discoloration of the fibrous web which is being treated in a nip of the press roll assembly.

EP 1 484 442 A1 describes a method for treating a web, in particular a paper web, which is designed as a shoe calender. The shoe calender has a shoe roll and a counter roll. The coat of the shoe roll is monitored for damage. If damage occurs to the shell of the shoe roll, the nip is opened. The treated web is then wrapped around the sheath of the shoe roll. The monitoring can be carried out by checking a change in pressure in the space bounded by the roll shell of the shoe roll. You can also visually monitor the shoe roll.

US 2002/0152630 A1 shows a tissue manufacturing system using two metal bands to dry the web. Several

Sensors are provided to monitor the metal bands or the web itself. For example, one can monitor the uniformity of the temperature, the sheet structure or the topography. Furthermore, voltage sensors are used to determine the voltage with the aid of ultrasonic signals, and the flatness of the bands can be determined.

The object of the invention is to propose a method for operating a belt calender, in which a lower risk of unforeseen belt damage occurs. In addition, the object of the invention is to propose a tape calender suitable for this purpose.

A method of operating a band calendering device according to claim 1 and a band calendering device according to claim 14 solves this problem.

It is proposed that in a method according to the above type, the properties of the calendering belt be checked during operation of the band calendering device.

By such a continuous review of the properties of the calender belt, it can usually no longer come to an unexpected breakage of the calender belt. Nevertheless, it can be ensured that the calendered belt is optimally utilized before it is exchanged. It can therefore be avoided, for example, that a calender belt, which could still be used for a few operating hours, has to be replaced because a maintenance interval defined independently of the actual wear has been achieved. This not only reduces costs for the new procurement of calender belts In particular, machine downtimes can also be avoided. Since the inspection can be carried out continuously during operation of the belt calendering device, it is also not necessary to interrupt the production process in the short term in order to carry out a (manual) inspection of the calender belt. Under a continuous review during operation can of course also be understood that the review is carried out at regular intervals. In particular, it is possible that certain areas of the calendered band are only examined at certain times. In particular, in this context, systems are to be considered, which are moved along the width of the calender belt, and in this way examine at periodic intervals the corresponding area of the calender belt.

It is preferred if the properties of the calendering belt are checked with regard to the probability of breakage of the calendering belt. In this way, a particularly effective protection of machine and machine operators can be achieved. It should be noted that in the case of brittleness fractures, which can occur as a result of the wear and the deflection of the calender belt, usually only statistical statements can be made about the occurrence of breakage or tearing of the calender belt. However, such a probability-based statement based on measurements is generally more sensible than a probability statement for the occurrence of a break of the calender belt, which is measured, for example, exclusively on the operating time of the calender belt.

Preferably, the properties of the calendering tape are checked for the presence of cracks and voids in the calendering tape. Such cracks and defects are usually a special one Indication that it can soon come to a break of the calendering tape. This applies at least from a certain size or frequency of cracks (eg macroscopic cracks). In addition, it should be noted that cracks and defects in the calendering belt can not only announce a coming break of the calendering belt. Rather, such cracks and defects in the calender belt can also lead to corresponding patterns and defects in the processed material web. Also in this regard, a continuous review of the properties, in particular the surface properties of the calender belt during operation of the belt calender prove to be particularly useful.

Furthermore, it is advantageous if the properties of the calendered tape are checked with regard to its thickness and its surface structure. Also, particularly large fluctuations in the thickness or in the surface structure of the calender belt can indicate an approaching breakage of the calender belt. In addition, such larger variations in calender belt thickness or in the calender belt surface texture can cause corresponding variations in the processed paper web, which can lead to scrap. Even changes in thickness of the calender belt can also lead to (unwanted) vibrations of the belt calender or its calender rolls. Of course, the thickness as such can also be an indication of an approaching breakage of the calender belt. If, for example, the calendering belt has become very thin due to wear during operation, it may be advisable to replace the calendering belt.

Another advantageous method results when the properties of the calendered belt are checked with respect to its surface condition. In this context, in particular to discoloration and / or dirt adherence on the surface of the calender belt think. Also, such effects can indicate wear of the calender belt, and thus also a coming breakage of the calender belt. In addition, such contamination or discoloration can also adversely affect the processed material web. Optionally, it is also conceivable that a cleaning operation of the calender belt is performed with an automatic cleaning device when contamination of the surface of the calender belt is detected. As a cleaning device, for example, a Bürsteinrichtung, a dry ice blasting, sandblasting, glass bead blasting, the use of a rotating grindstone, a diamond wheel, etc. could be used. The corresponding cleaning device can either take place across the entire width of the calender belt, or it can be a targeted use in the corresponding surface area or in the corresponding width range of the calender belt depending on the measurement result of Kalanderbandeigenschaftsmessung.

In principle, it is possible that the result of the property check is output continuously. It is preferable if a warning message is output when certain limit values are exceeded. For example, it could be a warning message that a critical state has been reached or a remaining operating time of, for example, 10 hours remains before such a critical state is reached. In the latter case, the production can be scheduled accordingly. It would be conceivable, for example, that a change of the product to be produced or processed, in any case, takes place in the near future, so that a change of the calendered band can also take place in the event of an already necessary changeover phase. The warning message can of course also include a warning signal. Here, for example, optical warning signals (warning lights, flashing lights, etc.) or audible warning signals (alarm bell, horn, etc.) to think.

It can also be particularly advantageous if the band calendering device is stopped when certain limit values are exceeded. In particular, when a critical limit is detected, such as the imminent breakage of a calender belt, such automatic protection shutdown can effectively prevent accidents. An incorrect operation of the corresponding system can be prevented as far as possible.

The verification of the properties of the calendering belt takes place by means of an acceleration measurement in the region of at least one bearing point of the calendering belt. In particular, macroscopic cracks or defects in the calender belt can be reliably detected by means of an acceleration measurement (oscillation measurement) in the region of the respective bearing points of the rollers over which the calender belt is guided. Such an acceleration measurement can also damage bearings, but also the speed of the rollers - and thus the machine speed - capture.

It is also possible that the verification of the properties of the calendering belt is additionally carried out by means of a travel measurement, in particular in the region of at least one bearing point of the calendering belt. If, for example, by a movable. Bearing roll or guide roll of the calender belt, the tension of the calender belt is kept substantially constant, the strain of the calender belt due to the operation can be detected via a travel measurement of the corresponding bearing roller. However, (excessive) elongation of the calendered belt may be an indication of the properties of the calendered belt and, in particular, an imminent breakage of it.

Furthermore, it may be advantageous if the review of the properties of the calendering belt is additionally carried out by an acoustic measurement. For example, microphones can detect the sound behavior of a calendering tape in the area of the nip or in the area of a bending point (e.g. evaluate in terms of the acoustic spectrum. With the help of such a sound image, a conclusion can be drawn on the properties of the calender belt.

Furthermore, it may prove to be advantageous if the review of the properties of the calendering belt is additionally carried out by at least one tension measurement. In particular, the tension measurement can be carried out on the guide rollers of the calender belt in front of and behind the nip on the driver's side and / or on the drive side. In particular, the calender belt run can be detected by means of such a tension measurement and, in particular, a slanted position of the calender belt can be detected (with). Furthermore, cracks and defects can also be easily detected by means of this measuring method. In any case, a conclusion on the properties of the calendered tape is possible.

A further advantageous method results if the verification of the properties of the calendering belt additionally takes place by means of a measurement using radioactive radiation. Such a measurement can be done for example by means of a Geiger counter and a radioactive isotope or an X-ray tube. It is advantageous in such measuring methods that they can be carried out without contact with the calender belt, and such methods are particularly suitable for metallic materials in particular. In particular, cracks and defects, but also the thickness of the calendered band can be detected.

A further advantageous method may be obtained if the checking of the properties of the calendering belt additionally takes place by means of an electromagnetic, in particular an inductive measurement. Such a method is particularly suitable for metallic calender bands or for composite calender bands which have at least a certain amount of metal. As a result, cracks and defects as well as, for example, the thickness of the calendered strip can be determined particularly effectively. In this way, a conclusion on the properties of the calendered tape is possible.

A further advantageous method may result if the checking of the properties of the calendering belt is additionally effected by at least one optical measuring method. Optical measuring methods are now well developed and can also be largely automated. Again, there is a great advantage in that such optical measuring methods can be performed contactless. Optical measuring methods are particularly suitable for checking the surface structure and surface quality of the calendered belt. In particular, by interferometric methods but also thickness and possibly also cracks and defects and other properties of the calendered tape can be measured.

The optical measuring method can be carried out with the aid of a camera device, in particular an area camera and / or a cell camera. Such systems are available relatively inexpensively. If necessary, they can also be provided with a suitable lighting unit. Likewise, a corresponding optics may be provided, for example a telecentric optics. Such a telecentric optics can be used to set a true-to-length image of the error, but also a magnification that is independent of the distance between optics and calendering tape is. The optical signal thus obtained can be processed, for example, by image processing equipment or else by digital computing devices.

It can also prove to be advantageous if the optical measuring method is carried out by means of a laser measuring device. Especially for the measurement of cracks, changes in thickness, but also surface quality and surface structure of the calender belt, light sources can make it useful as a laser. In addition, due to the large coherence wavelength of laser light interferometric methods are particularly well to perform. In particular, laser triangulation systems should be considered in this context.

It is particularly advantageous if at least one measurement, which is used to check the properties of the calendering belt, is carried out using error compensation. Here, for example, to think of active and / or passive damping systems that compensate for temperature-related changes (eg deflection) of the fastening device for a corresponding measuring sensor. Of course, this may also apply to any source (light source, radioactive source, etc.) that may be required. Active and / or passive systems for damping vibrations for the corresponding sensors or sources can also be provided. Here, for example, temperature scanners for a mounting bar of a sensor or else strain gauges that are located on a mounting bar of the sensor, can explicitly measure the change in length of the bar and then take it into account during the measurement. As active vibration damping systems, for example, piezo-actuated vibration cancellation systems can be used.

It is particularly advantageous if the checking of the properties of the calendering belt is carried out using an averaging of measured values. An averaging of measured values can refer to a plurality of time-spaced measured values of a single measuring method or a single measuring sensor. Such temporal averaging can smooth out short-term, statistically occurring fluctuations ("spikes"), which can lead to an improved measurement result. However, it is also possible to average the measured values of different sensors or different measuring methods. In this way, the properties of the calendered belt can be determined particularly accurately. Of course, should a particular measurement method be received by a plurality of measurement sensors (e.g., vibration measurement on each bearing roller), it is also possible for the majority of these measurement values to be averaged (weighted).

A further solution of the problem results if, in a band calendering device of the type described above, at least one property checking device which checks the properties of the calender band during operation of the band calendering device is provided.

Such a band calender device has the advantages already described above in an analogous manner. Such a band calender device can moreover be defined in the sense of the corresponding subclaims and / or in the sense of the method refinements described above be formed. Such further developed band calender devices have the advantages and properties already described in an analogous manner.

Fig. 1

einen Bandkalander mit mehreren Messvorrichtungen in schematischer Ansicht;

Fig. 2

eine optische Detektorvorrichtung;

Fig. 3

eine Detektorvorrichtung, die radioaktive Strahlung nutzt;

Fig. 4

eine Zellenkamera zur Oberflächeninspektion in schematischer Ansicht; und

Fig. 5

ein Lasertriangulationssystem in schematischer Ansicht.

The invention will be explained in more detail below by the description of exemplified embodiments and with reference to the accompanying figures. Show it:

Fig. 1

a tape calender with several measuring devices in a schematic view;

Fig. 2

an optical detection device;

Fig. 3

a detector device that uses radioactive radiation;

Fig. 4

a cell camera for surface inspection in a schematic view; and

Fig. 5

a laser triangulation system in schematic view.

In Fig. 1 schematically a Breitnip-Bandkalander 1 is shown. The wide-nip belt calender has two opposing rollers 2, 3. The top of the in Fig. 1 shown rollers is a metallic cylinder roller 2. The lower of the in Fig. 1 Rolls shown is a hollow cylinder roller 3. The hollow cylinder roller 3 has a cylinder jacket 4, which is supported on a support bar 5. The cylinder jacket 4 can slide on corresponding sliding elements of the Abstützbalkens 5, which are not shown in detail here for reasons of clarity.

While the cylindrical roller 2 is rigidly made of metal, the cylinder barrel 4 of the hollow cylinder roller 3 is elastically formed. As a result, the nip 6 is a so-called broad nip. The force curve 7 of the nip 6 is in Fig. 1 indicated schematically.

Furthermore, the wide-nip belt calender 1 has a calender belt 8, which is passed through the nip 6. In addition, guide rollers 9 are provided which guide the calender belt 8 accordingly.

The calender belt 8 supports the paper web 10 to be calendered during the passage through the wide-nip belt calender 1. In particular, the calendering belt 8 supports the paper web 10 to be calendered in the area of the nip 6 toward the cylinder jacket 4.

The calender belt 8 may in particular be a thin-walled metal band, but also a composite band. The calender belt 8 is loaded in a different manner during the circulation by the wide-nip belt calender 1. For example, bending in the area of the deflection rollers 9 and in the area of the rollers 2, 3 results in repeated bending of the calender belt 8 in different directions. In addition, there is a wear of the calender belt 8 by friction. Another effect can occur when a bearing of the guide rollers 9 and / or the rollers 2, 3 has a damage or is slightly warped. Such a defect can lead to warping of the calender belt 8, which can very quickly lead to tearing of the calender belt 8.

In order to prevent an unexpected tearing of the calender belt 8 and to be able to estimate the remaining remaining operating time of the calender belt 8 without having to interrupt the ongoing production process, a continuous check of the properties (quality) of the calender belt 8 is made during operation of the wide-nip belt calender 1 carried out.

According to the embodiment Fig. 1 There are five different measuring devices provided. Of course, the number of measuring devices can be increased or decreased depending on the application. Also, certain measuring devices may be provided twice or more frequently. An electronic controller 11 receives the measurement signals of the individual sensor devices and averages them both in terms of time as well as with respect to the source. It can also be a weighted average. For example, the measuring signal of a measuring device 20 that uses radioactive rays can be weighted higher than the vibration signals of a bearing bushing 9.

Based on these averaged sensor signals, information about the operating time that can still be achieved with the calender belt 8 is output to the user. For example, an in Fig. 1 only schematically illustrated screen 12. Exceeds the wear of the calender belt 8 a certain limit, so on the screen 12 additionally issued a warning that the useful life of the calender belt is approaching its end and therefore appropriate measures are taken. This information can be used to properly control the production flow. If, for example, a residual life of the calendered belt 8 is specified as ten hours, but production must be interrupted in any case in five hours, since, for example, a product change is being carried out, it is worth considering to replace the calender belt 8 already "prematurely" in order to avoid a repeated interruption of the production process.

When the controller 11 determines that certain critical limits have been exceeded, the wide-nip band calendering device is stopped fully automatically, so that an accident caused by carelessness or misoperation is avoided.

At the in Fig. 1 illustrated embodiment of a wide-nip tape calender 1 is carried out, among other measuring methods to be described, an acceleration measurement. For this purpose, a presently not shown accelerometer 14 is shown at the bearing point 13 of the cylinder roller 2. The acceleration measuring sensor 14 measures vibrations of the cylinder roller 2 in the region of the bearing axis 13. Such vibrations can be caused, for example, by different thicknesses or (macroscopic) cracks in the calender belt 8. Of course, such vibrations can also be caused by a defective bearing.

The characteristic of the resulting vibrations is usually somewhat different, so that a distinction can be made with regard to the type of error due to the vibration spectrum recorded by the acceleration measuring sensor 14.

That the acceleration sensor 14 can detect not only irregularities of the calender belt 8 but also defective bearings and similar defects is not disadvantageous but on the contrary advantageous. For such errors can also have a negative impact on the safety of the wide-nip strip calender 1 or on the quality of the paper web 10 processed by it.

Furthermore, in one of the guide rollers 9, a tension measuring box 15 is provided. The tensile load cell 15 is used to measure the force which is exerted on the corresponding deflection roller 9 by the cylindrical rollers 2, 3, mediated by the calender belt 8. The cylindrical roller 2 is actively driven, whereas the hollow cylinder roller 3 and the guide rollers 9 passively pass. Depending on whether the calender belt 8 has flaws or macroscopic fractures or not, a different signal is recorded by the Zugmessdose 15. The signal of the Zugmessdose 15, as well as the signal of the accelerometer 14, sent to the controller 11. This processes the signal together with the remaining signals, which are still to be explained.

Another measuring sensor is in the form of a microphone 16 in the region of one of the deflection rollers 9. The deflection (from straight to curved and curved back to straight) produces a characteristic acoustic signal picked up by the microphone 16. The corresponding acoustic spectrum generated by the calender belt 8 is an indication of the properties of the calender belt 8, in particular with respect to whether ma-microscopic cracks or defects are present in the calender belt 8.

Another sensor arrangement is in the form of a laser measuring system 17. The laser measuring system 17 has a laser 18 and an associated camera, which in the present case is in the form of a CCD camera 19. The laser 18 emits a laser beam 41 in the direction of the calender belt 8. In order to accommodate a larger area of the calender belt 8, the laser beam 41 can be expanded, for example, with the aid of beam splitters, beam expanders and similar optical devices.

The light 41 reflected by the calender belt 8 has a corresponding interference pattern (e.g., speckle interferometry) from which information about surface imperfections, macroscopic cracks and soiling of the calender belt 8, as well as other information, can be obtained. The reflected, interfered laser light 41 is picked up by the CCD camera 19, and the digital signals thus obtained are relayed to the controller 11. In the controller 11, these can be evaluated with a suitable image recognition software or in a similar manner.

Finally, the broad-nip tape calender 1 is still a radioactive fluoroscopy device 20 is provided. The radioactive transilluminator 20 has a source 21 of radioactive radiation 20. For this purpose, for example, a radioactive isotope can be used. It is also possible that, as is the case, an X-ray tube 21 is used. The X-ray radiation 22 emanating from the X-ray tube 21 passes through the calendering belt 8 and is picked up by the X-ray detector 23. The signals obtained by the X-ray detector 23 are also forwarded to the controller 11 and evaluated by this suitable.

For some of the in Fig. 1 shown sensors, in particular the microphone 16, the laser measuring system 17 and the radioactive transillumination unit 20, the problem arises that they can only check a certain surface area of the calender belt 8 (based on the width of the calender belt 8). At today's usual widths of calenders 1, which are often in the range of up to 10 to 15 m, a single, fixed sensor is not sufficient to check the entire width of the calender belt 8.

Since the accuracy of the review is significantly increased when the properties of the calendered belt 8 are checked over its entire width, therefore, suitable methods or devices must be provided in order to check the entire width of the calender belt 8 despite a limited detection surface of the corresponding sensor , For this purpose, on the one hand offers to provide a correspondingly large number of individual sensors, which together cover the entire width of the calender belt 8. This possibility is related to Fig. 2 explained in more detail.

Another possibility is to arrange the corresponding sensor elements movable on a rail, so that they can also check the entire width of the calender belt 8 by a movement. This is related to the in Fig. 3 shown example explained in more detail.

In Fig. 2 an optical arrangement of several CCD line scan cameras 25 is shown. The CCD line scan cameras 25 are arranged on a carrier 26. The CCD line cameras 25 each have a sensor area 27 in which the optical signal (the image) is received. Furthermore, the CCD line scan cameras 25 have an integrated illumination unit 28, so that even in unfavorable lighting conditions or in a correspondingly problematic installation position of the CCD line scan cameras 25 sufficient for the sensors 27 of the CCD line scan-25 illumination can be ensured ,

As Fig. 2 can be removed, the individual CCD line scan cameras 25 are arranged offset from one another, so that in each case in the end regions 29 of the CCD line scan cameras 25 overlap areas 29 result. By means of these overlapping regions 29, a complete inspection of the calender belt 8 can be ensured. Of course, the size of the overlapping regions 29 is not too large to choose from economic considerations out. Incidentally, the CCD line scan cameras 25 can also be arranged at an angle to the direction of movement of the calender belt 8.

Especially interferometric measuring methods, but also other measuring methods, can be sensitive to vibrations or (for example thermally induced) deflections of the carrier 26. In the case of oscillations, it may still be possible to improve the properties of the generated measurement signal by averaging the measured value over time. In deflections of the carrier 26, this is not possible. However, in paper machines in particular, not inconsiderable mass-caused deflections of the carrier 26 can occur. In addition, thermal deflections can also result since calender rolls, as already mentioned, are often also heated. A compensation of the occurring measurement errors is only possible if the extent of the deflection is known.

In order to obtain information about the deflection of the carrier 26, the in Fig. 2 illustrated embodiment, a strain gauge 30 is provided. The measured values obtained from this are likewise fed to the controller 11, which takes them into account accordingly in the evaluation of the signal of the CCD line scan cameras 25. Of course, other measuring methods are also possible here, such as an optical interferometric measurement, a temperature scanner with a vibrating mirror, a line scanner, etc.

It is also conceivable that active deflection damping systems and / or active vibration damping systems are provided.

The use of a larger number of sensors, as in the optical arrangement 24 according to FIG Fig. 2 the case is particularly appropriate when the individual sensors are relatively inexpensive. In this way can be dispensed with moving mechanical parts, which can result in a corresponding cost reduction. In particular, the maintenance costs of such an arrangement can be reduced. Furthermore, the properties of the calender belt 8 can be measured continuously over the entire width. Thus, after one revolution of the calender belt 8, complete information is available over the entire surface of the calender belt 8. As a result, for example, damage events can be registered much faster.

Another way to obtain information across the entire width of the calender belt 8 is in FIG Fig. 3 shown. Here is the sensor assembly 20 (for example, the radioactive transillumination unit off Fig. 1 ) slidably disposed on a support rail 31, 32.

Since the radioactive radioscopy unit 20 has two units formed separately from each other, namely an X-ray tube 21 and an X-ray detector 23, which are respectively arranged on opposite sides of the calender belt 8, two retaining rails 31, 32 are provided accordingly. The movement of the x-ray tube 21 and of the x-ray detector 23 (indicated by the double arrows) along the corresponding holding rail 31, 32 is coordinated with one another such that x-ray tube 21 and x-ray detector 23 move in synchronism with one another. As a result, the outgoing from the X-ray tube 21 X-ray radiation 22 are detected by the X-ray detector 23 at any time.

The structure with a movable arrangement is particularly suitable for detector arrangements in which the source and / or the sensor are expensive to purchase and / or in operation. This is usually the case with radioactive acceleration units 20.

Due to the displaceable arrangement of the corresponding detector unit 20, it is possible to detect the entire width of the calender belt 8 with a single detector unit 20. Since in each case only a certain width range of the calender belt 8 can be measured, a correspondingly large number of revolutions of the calender belt 8 is of course required for this until information about the entire surface of the calender belt 8 is present.

However, this time period is sufficiently small during normal operating times of calender bands 8, so that this is not a problem. If, in addition to the radioactive radioscopy unit 20, further detectors (such as the optical arrangement 24 according to FIGS Fig. 2 ) can be responded to quickly occurring, unforeseen events nevertheless very quickly.

Another way to reduce the amount of time required to measure the entire calender belt 8 is to have two radioactive transilluminators 20. The two detector units then each measure a partial area (in the case of two detector units, half) of the calender belt 8. The time required to measure the entire surface of the calender belt 8, decreases accordingly (with two detector units it halves).

In Fig. 4 is a particularly suitable for the realization of the invention sensor arrangement shown schematically. In Fig. 4 a cell camera 35 can be seen, which is arranged at a working distance d from the calender belt 8, and checks the surface of the calender belt 8.

The cell camera 35 is composed of a plurality of individual light-emitting diodes 34. The light emitted by the light-emitting diodes 34 is reflected by the surface of the calender belt 8. The reflected light enters one of the microlenses 33, which have a greater longitudinal extent ("perpendicular" to the plane of the drawing). The microlenses 33 are thus formed as a type of "cylindrical lens". The light focused by the microlenses 33 falls on a photodiode line 36 assigned to the respective microlenses 33.

Such a cell camera 35 is particularly suitable for interferometric methods. It is therefore particularly suitable for use in connection with a check of the calendering belt 8 of a wide-nip belt calender 1 (see Fig. 1 ) according to the present invention.

In Fig. 5 Finally, another advantageous sensor system is shown, which is particularly suitable for the realization of the invention. This is a laser triangulation system 37.

In the laser triangulation system 37, a laser beam 41 is emitted by a laser 38 to a certain surface point 40 on the surface of the calender belt 8. The surface point 40 reflects in dependence the surface texture and the surface structure and the position of the calender belt 8, the laser beam 41 incident in the surface point 40. The emitted light intensity is different depending on the emission direction.

The light 41 emitted by the surface point 40 is received by a corresponding number of light receivers 39 as a function of the solid angle. Of course, it is not necessary that the entire half space above the calender belt 8 is detected. Usually, a number of three, four, five or six light receivers 39 proves to be sufficient to achieve a sufficient measurement accuracy.

The signals received by the light receivers 39 are appropriately correlated and evaluated. In this way, information about the properties of the calender belt 8 can be obtained.

Claims (27)

1. Method for operating a band calender (1) having a circulating calender band (8) for supporting at least one side of a material web (10) to be calendered in a nip (6) of the band calender (1), in which the properties of the calender band (8) are checked during continuous operation of the band calender (1),
   characterized in that the properties of the calender band (8) are checked by means of an acceleration measurement (14) in the region of at least one bearing point (13, 14) of a roll (2) over which the calender band (8) is led.
2. Method according to Claim 1,
   characterized in that the properties of the calender band (8) are checked with regard to the probability of breakage of the calender band (8).
3. Method according to Claim 1 or 2,
   characterized in that the properties of the calender band (8) are checked with regard to the presence of cracks and faults in the calender band (8).
4. Method according to one of Claims 1 to 3,
   characterized in that the properties of the calender band (8) are checked with regard to its thickness and its surface structure.
5. Method according to one of Claims 1 to 4, characterized in that the properties of the calender band (8) are checked with regard to its surface state.
6. Method according to one of Claims 1 to 5, characterized in that a warning message is output when specific limiting values are exceeded.
7. Method according to one of Claims 1 to 6, characterized in that the band calender (1) is stopped when specific limiting values are exceeded.
8. Method according to one of Claims 1 to 7, characterized in that the properties of the calender band (8) are additionally checked by means of a distance measurement (9), in particular in the region of at least one bearing point (15) of the calender band (8).
9. Method according to one of Claims 1 to 8, characterized in that the properties of the calender band (8) are additionally checked by means of an acoustic measurement (16).
10. Method according to one of Claims 1 to 9, characterized in that the properties of the calender band (8) are additionally checked by means of at least one tension measurement (9).
11. Method according to one of Claims 1 to 10, characterized in that the properties of the calender band (8) are additionally checked by means of a measurement (20) using radioactive radiation (22).
12. Method according to one of Claims 1 to 11, characterized in that the properties of the calender band (8) are additionally checked by means of an electromagnetic, in particular inductive, measurement.
13. Method according to one of Claims 1 to 12,
    characterized in that the properties of the calender band (8) are additionally checked by means of at least one optical measuring method (17).
14. Band calender (1) having a circulating calender band (8) for supporting at least one side of a material web (10) to be calendered in a nip (6) of the band calender (1), having at least one property checking device (14, 15, 16, 17, 20) which checks the properties of the calender band (8) during continuous operation of the band calender (1),
    characterized in that at least one property checking device has an accelerometer (14) in the region of at least one bearing point (13) of a roll (2) over which the calender band (8) is led.
15. Band calender according to Claim 14,
    characterized by at least one breakage probability assessment device (11).
16. Band calender according to Claim 14 or 15,
    characterized in that at least one property checking device (14, 15, 16, 17, 20) detects cracks and faults in the calender band (8).
17. Band calender according to one of Claims 14 to 16,
    characterized in that at least one property checking device (14, 15, 16, 17, 20) detects the thickness and/or surface structure of the calender band (8).
18. Band calender according to one of Claims 14 to 17, characterized in that at least one property checking device (14, 15, 16, 17, 20) detects the surface state of the calender band (8).
19. Band calender according to one of Claims 14 to 18, characterized in that at least one property checking device has an acoustic measuring device (16).
20. Band calender according to one of Claims 14 to 19, characterized in that at least one property checking device has a tension measuring device (15).
21. Band calender according to one of Claims 14 to 20, characterized in that at least one property checking device has a measuring device (20) using radioactive radiation (22).
22. Band calender according to one of Claims 14 to 21, characterized in that at least one property checking device has an electromagnetic detection device, in particular an eddy current measuring sensor.
23. Band calender according to one of Claims 14 to 22, characterized in that at least one property checking device has an optical measuring device (17).
24. Band calender according to Claim 23, characterized in that at least one optical measuring device (17) has a two-dimensional camera and/or line-scan camera (35).
25. Band calender according to Claim 23 or 24, characterized in that at least one optical measuring device (17) has a laser measuring device (18).
26. Band calender according to one of Claims 14 to 25,
    characterized in that at least one property checking device has at least one measuring error compensating device.
27. Band calender according to one of Claims 14 to 26,
    characterized by at least one averaging device.

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