Abstract:
The invention relates to an apparatus for assessing the condition of at least one circulating band, in particular of a water-absorbing dewatering band and/or a transfer band in a papermaking machine, having a device for measuring the permeability of the at least one circulating band. The invention reliably and accuractly assesses the condition of the at least one circulating band. The apparatus according to the invention is additionally equipped with a device for measuring the moisture contained in the at least one circulating band.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an apparatus for assessing the condition of at least one circulating band, in particular of a water-absorbing dewatering band and/or a transfer band in a papermaking machine.  
         [0003]     2. Description of the Related Art  
         [0004]     In general, the prior art discloses apparatuses which permit a permeability measurement on the circulating dewatering band. However, such apparatuses have a disadvantage in that they measure a high permeability at holes, cracks or the like, a high permeability being an indication of a satisfactory quality of the dewatering band. Thus, those apparatuses, which measure only the permeability, supply erroneous information about the condition of the quality of the dewatering band, in particular at holes, cracks or the like.  
         [0005]     In addition, the prior art discloses handheld devices for measuring the permeability and handheld devices for measuring the moisture of a dewatering band in a papermaking machine. In using these handheld devices, it is not possible for any continuous monitoring of the permeability and of the moisture of the dewatering band to be carried out during operation. In addition, such handheld devices have only a limited accuracy, with which frequently no satisfactory statements can be made about the condition of the dewatering band. However, in order to be able to ensure a satisfactory quality of a fibrous web to be produced, it is necessary to be able to measure the permeability and the moisture of the dewatering band during operation, the quality of the fibrous web to be produced also depends on the quality of the permeability measurement and the moisture measurement.  
       SUMMARY OF THE INVENTION  
       [0006]     The object of the present invention is to improve the reliability and accuracy in assessing the condition of the at least one circulating band by way of an apparatus that measures the permeability of at least one circulating band.  
         [0007]     The present invention achieves the objective by way of an apparatus having a device for measuring the moisture contained in the at least one band. Thus, the apparatus according to the invention supplies further information about the state of the at least one circulating band. If, therefore, a high permeability is measured at a hole, at a crack or the like, a moisture level which is very low will be detected at the hole, at the crack or the like. From the simultaneous presence of a high permeability and a very low moisture, it is then possible to conclude that there is a hole, a crack or the like. Since the apparatus, according to the present invention, permits the measurement of the permeability and of the presence of moisture during operation, it is able to continuously supply accurate information about the instantaneous state of the at least one circulating band. Since continuous monitoring of the condition of the at least one circulating band is possible, the production of a high quality fibrous web is ensured.  
         [0008]     It is possible to carry out the moisture measurement simultaneously or with a time offset in relation to the measurement of the permeability. However, the time interval between the permeability measurement and the moisture measurement should be no more than five hours, since the at least one circulating band changes over time. If the time interval between the permeability measurement and the moisture measurement is too great, soiling on the at least one circulating band or wear of the at least one circulating band can distort the information obtained.  
         [0009]     If the moisture measurement and the measurement of the permeability are carried out at the same point on the at least one circulating band, very accurate information, with regard to the condition of the at least one circulating band, can be obtained. For this purpose, the measurement points for the permeability and moisture measurement are located one after another as viewed in the band running direction. The distances between the two measurement points are expediently relatively short so that, taking the high band speeds into account, a virtually simultaneous measurement of the two measured values can be carried out.  
         [0010]     However, it is also possible to carry out the moisture measurement and the measurement of the permeability at different points of the at least one circulating band. Then, for example, the two measuring points can be arranged transversely with respect to the band running direction; in this case, too, the distances between the two measurement points should be relatively short, in order to obtain the most reliable information possible about the condition of the at least one circulating band. If the moisture and the permeability are measured at different points of the at least one circulating band and the distances between the two measuring points are relatively short, it is possible, by computation, to associate one measuring point, for example, the measuring point at which the moisture is measured, with the other measuring point, for example, the measuring point at which the permeability is measured.  
         [0011]     The apparatus, according to the present invention can advantageously also have a device for measuring the band temperature. Thus, during operation, the temperature of the at least one circulating band can be measured. The band temperature likewise supplies information about the condition of the at least one circulating band. For example, the band temperature at soiled points, holes, cracks and the like differs from the band temperature at clean or fault-free points of the band. In addition, the measured band temperature can be useful for controlling the temperature of a measuring fluid needed for the permeability measurement.  
         [0012]     In a development of the present invention, the apparatus, on a reel-up, has a device for the measurement of moisture of a material web, in particular a fibrous web. It is likewise possible for the apparatus, according to the present invention, to have, after a press section, a moisture measurement device of the material web, in particular the fibrous web. If the at least one circulating band is a dewatering band, its condition directly affects the moisture of the material web to be produced. Thus, the measured moisture of the material web, at the reel-up and/or in the press section, provides information about the condition of the at least one circulating band.  
         [0013]     In addition, the apparatus can be provided with a device for determining the grammage of the material web, in particular the fibrous web. If the at least one circulating band is a dewatering band, its quality also directly affects the grammage of the material web to be produced. Thus, the grammage of the material web also provides information about the condition of the at least one circulating band.  
         [0014]     Since the at least one circulating band discharges heat to the machine house surroundings during operation, the distribution of the machine house temperature along its width supplies information about its condition. At the points at which the at least one circulating band is highly soiled or has holes, cracks or the like, the heat emission varies. In addition, by using the device for measuring the machine house temperature and the device for measuring the band temperature, the difference between the two temperatures, along the width of the at the least one circulating band, can be determined. From this information statements about the condition of the band can be made. The device for measuring the machine house temperature can expediently be arranged on a cleaning assembly for cleaning the at least one circulating band.  
         [0015]     Since the thickness of the at least one circulating band additionally permits a statement about its condition, the apparatus can have a device for measuring the thickness of the at least one circulating band. Deposits increase its thickness, whereas band abrasion reduces its thickness.  
         [0016]     The condition of the at least one circulating band is also directly related to the tensile stress prevailing in it. It is therefore expedient to equip the apparatus with a device for measuring the tensile stress prevailing in the at least one circulating band. High band abrasion, soiling on the at least one circulating band and other influences can increase the tensile stress.  
         [0017]     In one embodiment of the present invention, the apparatus is equipped with a device for measuring the filler content of the material web. The fillers contained in the material web can block up the pores of the at least one circulating band. Thus, from the filler content of the material web, it is possible to draw conclusions about a level of soiling and/or about an increase in the soiling of the at least one circulating band.  
         [0018]     In a further embodiment of the present invention, the apparatus has a device for measuring a pressure, which prevails in a nip between two rolls, and/or a device for measuring the thickness of the material web. Since at least one circulating band, as a dewatering band, also affects the thickness of the material web to be produced, the level of the pressure, which prevails in the nip between two rolls, also depends on its condition. Thus, the pressure in the nip between two rolls supplies information about the condition of the at least one circulating band. The measurement of the thickness of the material web can advantageously be made by measuring the web suction which prevails in the material web.  
         [0019]     In a further embodiment of the present invention, the apparatus has a device for measuring at least one surface property of the material web, in particular the roughness, the soiling (pigments, stock) and the like.  
         [0020]     In yet another embodiment of the present invention, the apparatus has a steam blower box and/or a moistener. The steam outlet volume and/or moisture volume is regulated as a function of the condition of the at least one circulating band along the material web width. Thus, by using the steam blower box and/or the moistener, the quality of the material web to be produced can be evened out if this has been impaired by a worsening of the state of the at least one band. However, by using the steam blower box and/or the moistener, it is also possible to affect the condition of the at least one band.  
         [0021]     In addition, the mixture ratio of a fiber and filler suspension and a dilution stream at a flow box, along the width of an outlet opening of a nozzle from which the mixture emerges, can be regulated as a function of the condition of the at least one circulating band along the material web width. Since the fibers and fillers contained in the material web to be produced can soil the at least one circulating band, the mixture ratio can be changed by increasing the dilution stream in such a way that the soiling of the at least one circulating band is reduced.  
         [0022]     In addition, the present invention relates to a method for assessing the condition of the at least one circulating band. In particular of the water-absorbing dewatering band and/or transfer band in the papermaking machine. The permeability of the at least one circulating band is measured, and the moisture contained in the at least one circulating band is also measured. In addition, it is possible to measure the band temperature with the method according to the present invention.  
         [0023]     Furthermore, by using the method according to the present invention, the moisture of the material web at the reel-up, and/or the moisture of the material web after the press section, and/or the grammage of the material web, and/or the pressure in the nip between two rolls, and/or the machine house temperature prevailing along the material web width, and/or the thickness of the at least one circulating band, and/or the tensile stress prevailing in the at least one circulating band and/or the filler content of the material web, and/or the thickness of the material web can be measured.  
         [0024]     By using the method according to the present invention, the steam outlet volume, emerging from the steamer blower box, can also be regulated as a function of the condition of the at least one circulating band along the material web width.  
         [0025]     It is likewise possible, by using the method of the present invention, for the moisture volume, emerging from the moistener, to be regulated as a function of the condition of the at least one band along the material web width. Furthermore, the mixture ratio of the fiber and filler suspension and the dilution stream at the flow box, along the width of the outlet opening of the nozzle from which the mixture emerges, can be regulated as a function of the condition of the at least one band along the material web width. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0027]      FIG. 1  is shows a schematical side view of an embodiment of a papermaking machine of the present invention; and  
         [0028]      FIG. 2  is shows a schematical side view of a press section of the papermaking machine of  FIG. 1 . 
     
    
       [0029]     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     Referring now to the drawings, and more particularly to  FIG. 1 , which shows a side view of a papermaking machine  10 , with which a material web  11  is produced. Material web  11  can be a paper, board or tissue or other fibrous web. Papermaking machine  10  has various circulating bands  12 ,  13 ,  14  and  15 . In the example illustrated, band  12  performs the function of a first top felt picking up material web  11 , band  13  the function of a first bottom felt, band  14  the function of a second top felt and band  15  the function of a second bottom felt. However, band  15  can also be a transfer band.  
         [0031]     Now, additionally referring to  FIG. 2 , bands  12 ,  13 ,  14  and  15  are provided with measuring devices  20 ,  21 ,  22  and  23 . Measuring devices  20 ,  21 ,  22  and  23  are equipped with devices, not shown specifically here, for measuring the permeability and/or the moisture of bands  12 ,  13 ,  14  and  15 . In this way, reliable information can be obtained about the condition of bands  12 ,  13 ,  14  and  15 . If a high permeability is measured, this can indicate bands  12 ,  13 ,  14  or  15  are clean. However, it is also possible for bands  12 ,  13 ,  14  or  15  to have a hole, a crack or the like, so that in this case, too, a high permeability is measured. In order to rule out misinterpretations, which can result from the permeability measurement, the moisture measurement is additionally carried out. In order that the measuring result supplies reliable information, it is expedient to carry out the moisture measurement and the permeability measurement at the same measuring point, or at measuring points located close beside one another, on circulating bands  12 ,  13 ,  14  or  15 . If a high permeability is measured in the permeability measurement and a very low moisture is measured in the moisture measurement, then these results allow the conclusion that there is a hole or a crack or the like in bands  12 ,  13 ,  14  or  15 . Thus, the moisture measurement is an expedient supplement to the permeability measurement in order to assess the condition of bands  12 ,  13 ,  14  or  15 . Apart from holes, cracks and the like, the soiling of bands  12 ,  13 ,  14  or  15  can also be detected by way of the combined permeability and moisture measurement. Then, by way of conditioning devices  25 ,  26 ,  27  and  28 , soiled bands  12 ,  13 ,  14  or  15  can be cleaned. For this purpose, measuring devices  20 ,  21 ,  22  and  23  are connected via measuring signal lines  19  to an evaluation unit  16 , which activates conditioning devices  25 ,  26 ,  27  or  28  as required in order to clean bands  12 ,  13 ,  14  or  15 . If band  15  is a transfer band, conditioning device  28  is omitted. In addition, a device for measuring the temperature of bands  12 ,  13 ,  14  and  15  is provided in measuring devices  20 ,  21 ,  22  and  23 .  
         [0032]     At the end of a press section  17 , papermaking machine  10  has a device  18  for measuring the moisture of material web  11  and, on a reel-up  100 , a measuring device  101  is positioned for measuring the moisture of material web  11 . The moisture measured with devices  18  and  101  provides information about the condition of bands  12 ,  13 ,  14  and  15 . The moisture value measured by devices  18  and  101  is transmitted to an evaluation unit  16  by way of measuring signal lines  19 .  
         [0033]     In evaluation unit  16 , all the measured values, including the measured values transmitted by measuring devices not specifically illustrated here, are evaluated and, if required, conditioning devices  25 ,  26 ,  27  and  28  are activated. In addition, a flow box  103  and a steam blower box  104  can be regulated by way of actuating signal lines  102  in accordance with the condition of bands  12 ,  13 ,  14  and  15 .  
         [0034]     In the case of the regulation of flow box  103 , the mixture ratio of a fiber and filler suspension and a dilution stream at flow box  103 , along the width of an outlet opening, not shown here, of a nozzle from which the mixture emerges, is regulated as a function of the condition of bands  12 ,  13 ,  14  and  15  along the width of material web  11 . In order to avoid soiling of bands  12 ,  13 ,  14  and  15  by the fibrous stock and fillers, the dilution stream is increased during this regulation procedure.  
         [0035]     In the case of the regulation of steam blower box  104 , the steam outlet volume is regulated as a function of the condition of bands  12 ,  13 ,  14  and  15 . In this way, with steam blower box  104 , the quality of the material web to be produced can be balanced out if the latter has been impaired by a worsening of the condition of bands  12 ,  13 ,  14  and  15 . In addition, the state of bands  12 ,  13 ,  14  and  15  can be acted on with steam blower box  104 .  
         [0036]     Thus, by way of the apparatus according to the present invention and by way of the method that can be carried out therewith, the measured values interacting with one another can be registered and evaluated, in order to be able to make appropriate changes in the process of the material web production and/or the conditioning of bands  12 ,  13 ,  14  and  15 . By way of these appropriate changes, bands  12 ,  13 ,  14  and  15  are kept in a state which ensures the production of a qualitatively satisfactory material web.  
         [0037]     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.