Abstract:
The present invention relates to a method for removing water from a movable roll jacket surface in a wet section of a paper-making machine, which roll jacket surface preferably belongs to a flexible roll jacket in a shoe press, said method comprising the following steps: arranging a spray device next to the roll jacket surface, making available a collecting device which is provided with an opening and collects liquid, moving said roll jacket surface past said spray device, applying a medium onto said roll jacket surface with the aid of said spray device, and collecting liquid in said liquid-collecting device. The invention is characterized in that said medium is sprayed with high kinetic energy onto said roll jacket surface to follow a fluid stream rebounding from the roll jacket surface, so that the liquid is conveyed to said liquid-collecting device.

Description:
This application claims the benefit of Provisional application Ser. No. 60/273,367, filed Nov. 5, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for removing water from a movable roll jacket surface in a wet section of a paper-making machine, which roll jacket surface preferably belongs to a flexible roll jacket in a shoe press, said method comprising the following steps:
         arranging a spray device next to the roll jacket surface,   setting up a collecting device which is provided with an opening and collects liquid,   moving said roll jacket surface past said spray device,   applying a medium onto said roll jacket surface with the aid of said spray device, and   collecting liquid in said liquid-collecting device or liquid-receiving device.       

     2. Description of Related Art 
     In a wet section of a paper-making machine, large quantities of water have to be removed from the fiber web. This is done with, inter alia, the aid of pairs of rolls which form a nip for pressing/sucking water out of the fiber web. A certain amount of water remains behind on the roll jacket surface after the nip. In many situations it is desirable to remove at least the majority of the remaining water before that part of the roll jacket surface passes through the nip again. 
     It is already known, for example from U.S. Pat. Nos. 4,852,209 and 5,810,974, to set up spray devices which can clean (and/or cool) a roll jacket surface. However, this known technique does not deal with the problem of how to remove water from the roll jacket surface. 
     A press device in a wet section is already known from EP 771,903, where the roll jacket surface of one of the roll pairs is sprayed with water, after which a special scraping device (called a doctor blade) removes water from the roll jacket surface. DE 19860735 shows that it is also already known to arrange a scraping device/doctor blade solely for the purpose of removing water, i.e. without first spraying the roll jacket surface. Similar cleaning and dewatering devices are also already known from U.S. Pat. No. 5,520,782, DE 19841637, DE 19860735 and DE 19810800. 
     However, it is not always desirable to use a scraping member which is in direct contact with the roll jacket surface. In the case of a shoe press roll, where a flexible roll jacket is used, it may be particularly undesirable because the flexible roll jacket is often relatively sensitive and expensive. 
     There is a risk that such a scraping member may destroy the flexible roll jacket or at least accelerate its wear, in the same way that it can also cause damage on another type of roll surface. 
     A further disadvantage of known dewatering devices according to the above is that they have a very limited effect if the roll jacket surface from which water is to be removed is patterned, i.e. provided with grooves, for example of the type described in U.S. Pat. No. 4,559,258. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to eliminate or at least minimize the above-mentioned problems, and this is done by a method according to the above which is characterized in that a liquid medium is sprayed with high kinetic energy onto said roll jacket surface, in that the high-kinetic fluid thus forces liquid present on the roll jacket surface to follow a fluid stream rebounding from the roll jacket surface, so that the liquid is conveyed to said liquid-collecting device. 
     By virtue of the solution according to the invention, a method is obtained which eliminates or at least minimizes the risk of the roll jacket surface, from which water is to be removed, becoming damaged or worn, since there is no direct physical contact between the roll jacket surface and the dewatering device. In addition, the dewatering and cleaning (if required) are combined in one and the same step. A further important advantage is that it has a good dewatering effect (or cleaning effect) irrespective of whether the roll jacket surface is smooth or patterned. 
     According to another aspect of the invention, said medium is water. 
     By using water as the medium, high kinetic energy is obtained in a favorable manner in the stream of medium used for removing water from the roll jacket surface. Tests have shown that a surprisingly good effect can be obtained using this medium. 
     According to another aspect of the invention, said medium is sprayed onto the roll jacket surface at a certain spray angle (α) in relation to the normal (N) o£ the roll jacket surface, so that an oriented and rebounding fluid stream is created, where α is between 5 and 85° and is a function of the speed (ν) of the roll jacket surface, the spray angle (α) increasing as the speed increases. By virtue of using an acute angle in relation to the roll jacket surface when applying the medium, it is possible to obtain a controlled rebound of the water which is removed from the roll jacket surface. 
     According to another aspect of the invention, the liquid-collecting device is provided with a lip element which is positioned in the rebounding fluid stream in order to convey the liquid onwards towards the liquid-collecting device. By virtue of the arrangement of a lip element, the rebounding stream of medium can be collected in a simple and flexible manner and conveyed to the collecting device. 
     According to another aspect of the invention, said roll jacket surface has irregularities in the form of grooves or cavities in which liquid can gather. By virtue of the invention, it has been found that it is also possible to remove water from patterned roll jacket surfaces in an extremely effective way, something which could not be done satisfactorily by previously known methods, especially not without the risk of damage or undesired wear. 
     The invention also relates to a device having the same features and advantages as the method. This, along with further advantages of the invention, is set out in the description below. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The invention is explained in more detail below with reference to the attached figures, of which: 
         FIG. 1  is a schematic view of a shoe press with a device for removing water according to the invention, 
         FIG. 2  shows a side view of a preferred embodiment of a device for removing water according to the invention, 
         FIG. 3  shows a front view of the device according to  FIG. 2 , and 
         FIG. 4  shows a preferred principle for how sprays according to the invention are directed towards a roll jacket surface. 
         FIG. 5  shows a shoe press device included in a press section in which the device and the method according to the invention are used. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic representation of a shoe press roll S which is included in a paper-making machine and which cooperates with a counter roll M so that an extended nip for a fiber web W and press felt P is formed between them. A flexible roll jacket  1  is arranged in a known manner so that it encloses the shoe press roll S. A device for removing water according to the invention, with a spray device  2  and a liquid-collecting container  21 , is arranged to remove water from the flexible roll jacket  1 . 
       FIG. 2  is a side view of a preferred embodiment of a device for removing water according to the invention. It will be seen that the device for removing water is arranged close to the roll jacket surface  1 A of a flexible roll jacket  1  which moves upwards at a defined speed (ν) past the device for removing water. The liquid-collecting device or liquid-receiving device  21  comprises an elongate container  22  (see also  FIG. 3 ) with an axially elongate opening  24  directed towards the roll jacket surface  1 A. The opening  24  thus extends parallel to the axial extent of the shoe press roll S around which the flexible, roll jacket  1  rotates. With the aid of clamp connections  18 A,  18 B, the collecting container  22  is adjustably mounted on a circular support part  20  which in turn is connected securely to a support  17  which is fixed in relation to the paper-making machine. With the aid of screw connections  19 , the clamp connections  18 A,  18 B can be released/secured in order to obtain the desired positioning of the container  22  in relation to the support part  17 ,  20 . 
     On top of the container  22  there are bracket elements  16  on which a first adjustable fastening device  8  for the spray device  2  is arranged. This first fastening device  8  makes it possible, on the one hand, to adjust the angle β and on the other hand to adjust the distance between the spray device  2  and the roll jacket surface  1 A. In order to change the angle β, there is a clamp connection  13 A,  13 B which is fixed on said bracket  16 . This clamp connection  13 A,  13 B cooperates with a sleeve  15  which can be locked at a certain angular position inside the clamp connection by means of screw connection  14 . Welded onto said sleeve  15  there is an outer pipe-shaped part  10  which cooperates in a telescopic manner with a rod  9 . With the aid of a locking screw  11 , the rod  9  can be locked in different positions, i.e. displaced to different positions inside the outer pipe-shaped part  10 . A plate  7  is arranged at one end of the rod  9 . This plate  7  constitutes a rear support for a spray pipe  3 . The spray pipe  3  is clamped securely against the support plate  7  with the aid of a conventional pipe clamp  6  which is locked on the plate  7  with the aid of nuts  6 A,  6 B. Arranged on the spray pipe  3  there are a number of spray nozzles  4  which each have a mouth  4 A directed towards the roll jacket surface  1 A. 
     Arranged near the lower edge of the opening  24  of the collecting container  22  there is a lip element  26  which projects in the direction towards the roll jacket surface  1 A. With the aid of a screw connection  27 , the lip element  26  is mounted adjustably on the container  22  so that the gap between the roll jacket surface  1 A and the front edge of the lip can be adjusted. At the upper edge of the opening too, and secured by means of a screw connection  29 , there is an adjustable lip-like device  28 . The purpose of this last-mentioned device is to vary the size of the opening  24  in order to be able to obtain approximately the same vacuum, which is thus produced by varying the opening vertically along the container. The container  22  is connected at one end to an outlet  23  (see  FIG. 3 ) connected to an outlet which is under vacuum or communicates with a vacuum source so that liquid can be actively sucked in through the opening  24  of the container  22 . By means of the fact that the size of the opening can be varied along the container, an identical vacuum can be obtained along the container opening  24 . 
       FIG. 3  shows the device according to the invention in a front view, i.e. seen from the direction where the roll jacket surface  1 A is placed. Most of the details shown in  FIG. 3  are already clear from FIG.  2  and from the above description. However,  FIG. 3  shows that the spray pipe  3  is elongate and that a large number of spray nozzles  4  are arranged alongside each other along the spray pipe  3 . It will also be seen that each spray nozzle  4  has a mouth  4 A, which in one direction emits a diverging jet (see FIG.  4 ). It will also be seen that the outlet  23  is arranged at one end of the collecting device  21 , which is the reason for the arrangement of an adjustable upper lip  28 , so that the distance between the lower edge of this lip  28  and the lower surface  26  of the mouth  24  can be varied in the vertical direction along the container. In this way, an identical vacuum can be obtained along the whole mouth  24 . 
       FIG. 4  shows that the configuration of the mouth  4 A is such that the spray jets follow a diverging pattern, by which means they are sprayed along a line L 3 . The mouth  4 A of each spray nozzle  4  is set in such a way that this spray line L 3  is at an acute angle in relation to the centre line C of the spray pipe  3 . In this way, an overlapping of the spray jets on the roll jacket surface  1 A is obtained, without two adjacent spray jets being able to interfere with one another. 
     Referring to FIG.  1  and  FIG. 5 , a shoe press roll S is shown with a shoe which is enclosed by a flexible rotatable roll jacket, which roll jacket has a roll jacket surface  1 A. Together with a counter roll M, the shoe press roll S forms a shoe press unit with an extended nip. A press felt P forms a loop around the shoe press roll S, so that the shoe press roll S is located within the felt loop. A spray device  2  is arranged inside the felt loop and close to the roll jacket surface  1 A, which spray device is directed towards the roll jacket surface  1 A in order to be able to spray a medium onto the roll jacket surface  1 A. 
     Before the device for removing water is started up, the various components involved are adjusted so as to obtain optimum positions and angles. This is preferably done by first adjusting the angle of the whole dewatering device with the aid of clamp connections  18 A,  18 B around the support part  20 . As is shown in the figure, it is preferably adjusted in such a way that the lip device  26  is arranged substantially horizontally. Alternatively, it can be given a certain rearward inclination in order to increase the removal capacity with the aid of gravity. Thereafter, the lip device  26  can be moved so that an optimum gap is formed between the roll jacket surface  1 A and the front edge of the lip element  26 . This is preferably followed by adjusting the angle α at which the spray is directed towards the roll jacket surface  1 A in relation to the normal N of the roll jacket surface. This angle α must be such that the medium which is conveyed with the aid of the spray removes as much liquid as possible from the roll jacket surface  1 A and so that the rebounding fluid stream with liquid L 2  impacts the lip element  26  in the desired manner. It will be appreciated that this angle α must be able to be adapted because different liquids can have different optimum angles of incidence. In the same way, the nature of the roll jacket surface  1 A is also of course important as regards the optimum angle of incidence α, especially if, as in the preferred case, it is a question of removing water from a patterned roll jacket surface  1 A. 
     The angle of incidence α can be adjusted with the aid of the upper clamp connection  13 A,  13 B by locking the sleeve  15  in the desired angle position β. Preferably however, or as a complement to this, the direction L 1  of the spray mouth  4 A in relation to the support plate  7  is also adjusted by locking the spray pipe  3  in a different angle position by means of the pipe clamp  6 . This is preferably followed by adjusting the distance between the spray mouth  4 A and the roll jacket surface  1 A by locking the rod  9  in the desired position with the locking screw  11 , so that the optimum spray distance is obtained. The distance that is optimum will to a large extent depend on how the spray mouths  4  dispense the medium onto the roll jacket surface  1 A. Finally, the height of the mouth gap is adapted to the prevailing vacuum by setting the upper lip-shaped element  26  to a suitable position. 
     The device for removing water functions in such a way that a medium, for example water, is sprayed via the nozzles  4  at a certain angle of incidence α and at high pressure onto the roll jacket surface  1 A, the medium being given a component of movement which is directed counter to the movement of the roll jacket surface  1 A. The liquid, usually water, present on the roll jacket surface  1 A will then combine with the water which is being conveyed at high kinetic energy, after which they jointly rebound from the flexible roll jacket surface towards the lip element  26 . From the lip element  26 , the water is conveyed towards the mouth  24  of the container device  22  by means of the latter being under vacuum. The water is then led off from the container via its outlet  23 . The arrangement thus permits rapid and effective removal of water from the roll jacket surface  1 A, and at the same time, if necessary, cleaning thereof. The method is particularly effective in connection with patterned roll jacket surfaces which cannot always be dewatered (or cleaned) sufficiently well by current methods. In addition, the method has the great advantage that there does not need to be any direct physical contact between the roll jacket surface and the device for removing water, which fact minimizes the risks of wear and risks of damage which exist when a flexible roll jacket is in direct contact with any device. Given that these flexible roll jackets are expensive, this is a not inconsiderable advantage. 
     By means of the device according to the invention, a press section is also obtained which includes the device according to the invention. 
     The invention is not limited by what has been described above, and instead it can be varied within the scope of the attached patent claims. It will be appreciated that, among other things, the lip element  26  can advantageously be made of a resilient/flexible material which, in some applications, can advantageously be arranged in direct contact with the roll jacket surface  1 A.