Patent Publication Number: US-10780465-B2

Title: Apparatus for cleaning a felt in a system for producing a paper web

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. § 119, of Austrian patent application A 320/2016, filed Jul. 7, 2016; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an apparatus for cleaning a felt in a system for producing a paper web. The apparatus has a device for introducing a cleaning liquid into the felt and at least one following suction device in the direction of movement of the felt and a vacuum duct, through which the cleaning liquid is suctioned out of the felt. The suction device between the vacuum duct and the felt is formed with suction ducts, through which the cleaning liquid in the felt is suctioned away. 
     Systems for producing paper webs contain a first area with at least one wire, to which a stock mixture for forming a paper web is applied, the wire being assigned suction boxes formed with foils, by which water is suctioned away out of the stock mixture, by which means the paper web is produced. These systems also contain a second area with felts, in which the paper web and at least one felt are led through between press rolls, by which means moisture in the paper web is picked up by the felts, and in addition a third area, in which the paper web is dried by way of drying cylinders. Further on, the dried paper web is wound onto spools, subdivided into sheets and packed in cartons. 
     Since the felts not only pick up moisture contained in the paper web but constituents of the stock mixture, i.e., pulp, in particular fiber material, also get into the same, as a result of which the effectiveness of the felts is impaired, there is the requirement to provide apparatuses for cleaning the felts in the movement path of the same. These apparatuses comprise at least one device for introducing a cleaning liquid into the felts and at least one following suction device in the direction of movement of the felts, by way of which the cleaning liquid in the felts is suctioned away at the same time as the foreign materials located in the latter. The suction device comprises a vacuum duct and a suction plate, on which the felt rests and over which the felt is guided. The suction plate is formed with suction ducts. The ducts are formed, for example, by multiple slots extending transversely with respect to the felt and located beside one another in the direction of movement of the felt or by a plurality or a multiplicity of openings in the suction plate, in particular bore holes. 
     During the operation of such a suction device, however, it happens that the felts cannot be cleaned completely of the foreign materials located in the same, as a result of which, over the course of the operating time, they contain more and more foreign materials. As a consequence, they become increasingly non-permeable for the extraction of the cleaning liquid. A felt that is new and thus contains no foreign materials is so permeable that the required minimum vacuum in the vacuum duct can be produced only when only a few suction ducts are provided in the suction plate for the extraction of the liquid, or the total cross section of the suction ducts is low. 
     With increasing operating time of the felt and therefore increasing loading of the felt by foreign materials, however, the permeability of the felt is reduced, for which reason that region of the felt on which the suction force acts must be enlarged. This is effected by the total cross section of the effective suction ducts being enlarged. 
     According to the known prior art, the suction plates are formed with suction ducts of which the total cross section is so large that, even in the case of a felt that is highly loaded with foreign materials, the necessary suction force acts on the felt. However, in order to be able to maintain the vacuum in the vacuum duct required for the operation with a felt that is new and therefore free of foreign materials, the suction ducts in the suction plate are initially partly closed and, with the increasing loading of the felt and therefore decreasing permeability of the felt, the initially closed suction ducts are successively opened. 
     For this purpose, it is known to assign sealing strips to some of the suction ducts located in the suction plate, by which sealing strips the suction ducts are initially partly closed, the sealing strips being removed successively with increasing operating time. Known felts have a width of up to 12 m. Suction ducts in suction plates have a width of, for example, 10 mm to 18 mm. Sealing strips which consist of polyethylene, for example, have a length, for example, of up to 12 m and a cross section of 10 mm to 18 mm×20 mm. 
     However, there is the difficulty that, during the operation of the system, it is therefore not possible to remove these sealing strips since, because of the vacuum prevailing in the suction device, they are pressed against the suction plate with very great pressure and since they are stuck to the suction plate by the foreign materials removed from the felt by means of the cleaning liquid. 
     It is also further known to provide two suction devices following each other. Only one of the same is initially connected. Once the wire becomes highly loaded with foreign materials, the second suction device is also connected. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a device for cleaning a felt in a paper-web making facility which overcomes the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and to provide a suction device in which, during the operation of the system, individual suction ducts which are initially closed can be opened and also closed during the operation without difficulty. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for cleaning a felt in a system for producing a paper web, the apparatus comprising: 
     a device for introducing a cleaning liquid into the felt; 
     at least one suction device disposed downstream of said device in a direction of movement of the felt, said suction device having a vacuum duct, through which the cleaning liquid is suctioned out of the felt; 
     said suction device having suction ducts formed therein between said vacuum duct and the felt for suctioning the cleaning liquid away from the felt; and 
     an inflatable valve element assigned to at least one of said suction ducts, said inflatable valve element having an inflated state wherein said at least one suction duct is closed and a ventilated state wherein said at least one suction duct is opened. 
     In other words, the objects of the invention are achieved in that at least one of the suction ducts is assigned at least one inflatable valve element, in the inflated state of which the suction duct is closed and by the ventilated, or deflated, state of which the suction duct is opened. 
     Preferably, the suction duct is formed as a slot oriented transversely with respect to the felt, and the valve element is formed as an inflatable hose, the suction duct extending over the width of the felt. 
     The suction duct can also be formed by at least two slots oriented transversely with respect to the felt and adjoining one another, or by openings, in particular drilled holes. 
     According to a preferred embodiment, at least one suction plate which is formed with suction ducts and which extends transversely with respect to the felt is fixed to the suction device. Furthermore, the at least one valve element, which in particular is formed as a hose, is preferably formed with a projecting strip, by means of which it is clamped between the housing of the vacuum duct and the suction plate. 
     Furthermore, between the housing of the vacuum duct and the suction plate, it is possible to provide at least one supporting strip for the at least one valve element, which in particular is formed as a hose, to which supporting strip the valve element is fixed. The valve element can be fixed to the supporting strip by adhesive bonding. 
     According to a further embodiment, at least one valve plate, to which a valve element, in particular a hose, is fixed, is supported on the supporting strip and is adjustable by the valve element, wherein said valve plate can be pivoted by the inflatable valve element into the position closing the associated suction opening. Furthermore, the supporting strip can be screwed to the housing of the vacuum duct. Furthermore, the suction plate and the supporting strips can be formed with tongues and grooves assigned to one another, by means of which they are fixed to each other. The tongues and grooves are preferably oriented transversely with respect to the felt, by which means the suction plate is displaceable transversely with respect to the felt. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in an apparatus for cleaning a felt in a system for producing a paper web, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a schematic illustration of a system for producing a paper web; 
         FIG. 2  shows a device, located in the system according to  FIG. 1 , for introducing a cleaning liquid into felts and a suction device, on a scale enlarged with respect to  FIG. 1  and in cross section; 
         FIG. 2A  shows the suction device according to  FIG. 2  on a scale enlarged with respect to  FIG. 2  and having a control system assigned thereto; 
         FIG. 3 ,  FIG. 3A ,  FIG. 3B  show vertical sections taken through a first embodiment of the suction device according to  FIG. 2A  on a scale reduced with respect to  FIG. 2A  and in three different operating positions; 
         FIG. 4 ,  FIG. 4A ,  FIG. 4B  show vertical sections taken through a second embodiment of the suction device according to  FIG. 2A  on a scale reduced with respect to  FIG. 2A  and in three different operating positions; 
         FIG. 5 ,  FIG. 5A ,  FIG. 5B  show vertical sections taken through a third embodiment of the suction device according to  FIG. 2A  on a scale reduced with respect to  FIG. 2A  and in three different operating positions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown system for producing a paper web. The apparatus has a first system part  1 , in which an intrinsically closed wire  11  is guided over deflection rolls  12  and suction boxes  13  that are assigned to the wire  11 . On the wire  11  there is a stock material, or pulp, for producing a paper web  10 . Water is extracted from the stock material through the suction boxes  13 . 
     Since the system part  1  is not critical for the present invention, only its end region is illustrated in the drawing. The first system part  1  is adjoined by a second system part  2 ,  2   a ,  2   b , to which the paper web  10  is transferred. 
     Felts  21 ,  21   a ,  21   b  are located in the second system part  2 ,  2   a ,  2   b . The felts  21 ,  21   a ,  21   b  are guided over deflection rolls  22 ,  22   a ,  22   b  in the direction of the arrows. Each of the felts is intrinsically closed, or endless. In addition, press rolls  23 ,  23   a ,  23   b ,  23   c , which are each assigned to one another in pairs, are provided in the system part  2 ,  2   a ,  2   b . Also provided are tensioning rolls  24 ,  24   a ,  24   b , over which the felts  21 ,  21   a ,  21   b  are guided and by means of which the felts can be tensioned. 
     From the first system part, the paper web  10  is transferred to the felt  21  in the second system part  2 ,  2   a ,  2   b . Next, the paper web  10  arrives between the felts  21 ,  21   a , with which it is pressed by means of the press rolls  23 ,  23   a , as a result of which moisture in the paper web  10  is given up to the felts  21 ,  21   a . Thereupon, the paper web  10  with the felt  21  passes between the press rolls  23 ,  23   b , by means of which it is pressed with the felt  21 . Furthermore, the paper web  10  with the felt  21   b  passes between the two press rolls  23   b ,  23   c . Thus, moisture from the paper web  10  is given up to the felts  21 ,  21   a ,  21   b.    
     The second system part  2 ,  2   a  and  2   b  is followed by a third system part  3 , in which there is a plurality of drying rolls  31 , over which the paper web  10  is led, by means of which it is dried further. 
     The paper web  10  located on the wire  11  has a dryness of about 20% at the end of the first system part  1 . At the end of the second system part  2 ,  2   a ,  2   b , the paper web  10  has a dryness of about 50% to 55%. In the third system part  3 , the paper web  10  is brought to a dryness of about 93%. 
     Since it is not only moisture but also foreign materials found in the paper web  10 , such as pulp fibers and other paper constituents such as fillers, resins, ash, printer&#39;s ink, that are transferred from the paper web  10  into the felts  21 ,  21   a ,  21   b , there is the need to assign the felts  21 ,  21   a ,  21   b  apparatuses  4 ,  5  for cleaning the same. The structure and functionality of the cleaning apparatuses  4  and  5  is explained in the following. 
     As illustrated in  FIG. 2 , an apparatus of this type for cleaning a felt  21 ,  21   a ,  21   b  has at least one spraying device  4 ,  4   a  for introducing a cleaning liquid into the felt  21 ,  21   a ,  21   b  and, following in the direction of movement of the felt  21 ,  21   a ,  21   b , at least one suction device  5 . In  FIG. 2 , a first spraying device  4 , by means of which a wide jet  41   a  is applied to the felt  21 ,  21   a ,  21   b , and a second spraying device  4   a , by means of which a narrow jet  41   a  is applied to the felt  21 ,  21   a ,  21   b , are illustrated. The application to the felt  21 ,  21   a ,  21   b  is carried out in each case over the entire width of the felt  21 ,  21   a ,  21   b . The cleaning liquid is composed of water, which is possibly provided with additives such as solvents. 
     The suction device  5  has a housing  51  with a vacuum duct  52 , in which a negative pressure of −200 millibar to −600 millibar is produced. An opening  53  is provided on the top of the housing  51  which is enclosed by a frame  60  and which is sealed off by a suction plate  54  formed with suction ducts  55 ,  56 ,  57 . The felt  21 ,  21   a ,  21   b  is moved along the top of the suction plate  54 . The suction ducts  56 ,  57  are assigned valve elements  58 ,  59 , by means of which these two suction ducts  56 ,  57  can be closed. 
     The modes of action of the spraying devices  4 ,  4   a  and of the suction device  5  are as follows: 
     The felt  21 ,  21   a ,  21   b  is moved past the spraying devices  4 ,  4   a  and then past the suction device  5 . By means of the spraying devices  4 ,  4   a , a cleaning liquid, which penetrates into the felt  21 ,  21   a ,  21   b , is applied to the felt  21 ,  21   a ,  21   b . By means of the at least one suction device  5 , this cleaning liquid is drawn out of the felt  21 ,  21   a ,  21   b  to thereby remove foreign materials from the felt  21 ,  21   a ,  21   b . However, as the operating time increases, more and more proportions of foreign materials remain in the felt  21 ,  21   a ,  21   b , as a result of which the latter becomes less and less permeable. For this reason, the area of the felt  21 ,  21   a ,  21   b  on which a suction force is exerted by the suction device  5  must be enlarged, in order to be able to carry out effective cleaning of the felt  21 ,  21   a ,  21   b  by means of the cleaning liquid. 
     This need is met in that, for the cleaning of a new and thus still very permeable felt  21 ,  21   a ,  21   b , the suction ducts  56 ,  57  are closed by means of the valve elements  58 ,  59 , as illustrated in  FIG. 2 . This ensures that the vacuum which is produced in the vacuum duct  52  and which is required to achieve the necessary suction force can be maintained. However, as soon as the permeability of the felt  21 ,  21   a ,  21   b  decreases on account of the foreign materials remaining in the same, which means that the cleaning force affected by the extracted cleaning liquid is reduced, the area of the suction force acting on the felt  21 ,  21   a ,  21   b  must be enlarged. For this purpose, the valve elements  58 ,  59  assigned to the suction ducts  56 ,  57  are brought into the open position thereof, by which means that area of the felt  21 ,  21   a ,  21   b  on which a suction force is exerted is enlarged. 
     In the following, by using  FIG. 2A , the formation of the suction device  5  and its mode of action are explained further. 
     The housing  51  of the suction device  5  is formed on its upper side with the frame  60 , which encloses the opening  53 . Provided on this frame  60  are supporting strips  61 ,  62  located at the side of the opening  53 , which are fixed to the frame  60  by means of bolts  63 . The suction plate  54  and the supporting strips  61 ,  62  are formed with grooves  54   a  and tongues  61   a ,  62   a  assigned to one another. 
     The valve elements  58 ,  59  are each formed by an inflatable hose, which is rectangular in cross section and which is respectively formed with a laterally projecting flap  58   a ,  59   a , which is located between the frame  60  and the strips  61 ,  62 , by which means the hoses  58 ,  59  are fixed. The inflatable hoses consist of a rubber or synthetic material, such as ethylene-propylene-diene rubber (EPDM) or of nitrile butadiene rubber (NBR). 
     A vacuum pump applies a vacuum to the vacuum duct  52  which is measured by a measuring device  64 . The output from the measuring device  64  is led to a control device  65 . The hoses  58 ,  59  can be connected via lines  70 ,  71  either to a pressurized air pump +P, by which means they are inflatable, or they can be connected to a vacuum pump −P, by means of which they can be vented. For this purpose, two lines  70   a ,  70   b  are connected to the line  70 , and two lines  71   a ,  71   b  are connected to the line  71 , the lines  70   a ,  71   a  being connected to the compressed air pump and the lines  70   b ,  71   b  being connected to the vacuum pump. In the lines  70   a ,  70   b  and  71   a ,  71   b  there are valves  72   a ,  72   b  and  73   a ,  73   b , which are controlled by the control device  65 . As soon as the valves  72   a ,  73   a  are opened, compressed air is applied to the hoses  58 ,  59  assigned to the suction ducts  56 ,  52 . As a result, they are inflated, by which means the suction ducts  56 ,  57  are closed. This is necessary when the permeability of the felt  21 ,  21   a ,  21   b  is still so high that only the suction ducts  55  should be opened to maintain the vacuum in the vacuum duct  52 , whereas the suction ducts  56 ,  57  must be closed. 
     However, as soon as the permeability of the felt  21 ,  21   a ,  21   b  to the cleaning liquid has been reduced as a result of the fact that foreign materials are increasingly located in the latter, for which reason that area of the felt  21 ,  21   a ,  21   b  on which the suction force is exerted must be enlarged, the valves  72   b ,  73   b  are opened, by which means the hoses  58 ,  59  are vented. In this way, the suction ducts  56 ,  57  are opened, by which means suction force is also applied to the felt  21 ,  21   a ,  21   b  through the suction ducts  56 ,  57 . 
     On account of the fact that the valve elements are inflatable, being formed in particular by inflatable hoses, those suction ducts which are assigned these valve elements can be opened at any time during the operation of the system for paper production, which means that the difficulties adhering to the known prior art during the opening of further suction ducts are avoided. 
     Since the suction plate  54  is formed with grooves  54   a  and the supporting strips  61 ,  62  are formed with tongues  61   a ,  62   a  assigned to the grooves  54   a , the suction plate  54  can be drawn out laterally, by which means the hoses  58 ,  59  can be mounted in a simple way. 
     In the following, by referring to  FIG. 3 ,  FIG. 3A ,  FIG. 3B , the mode of action of such a suction device  5  is explained by using a first embodiment. 
     According to  FIG. 3 , the two hoses  58 ,  59  have compressed air applied thereto, by which means they are inflated. In this way, the suction ducts  56 ,  57  are closed. This is necessary when the felt  21 ,  21   a ,  21   b  contains no or only few foreign materials, so it is very permeable for the extraction of the cleaning liquid. 
     However, as soon as the felt  21 ,  21   a ,  21   b  contains more and more foreign materials with increasing operating time, as a result of which its permeability to the cleaning liquid is reduced more and more, firstly the hose  58  is vented, which means the suction duct  56  is opened and a suction force is also exerted on the felt  21 ,  21   a ,  21   b  via said suction duct. This operating position is illustrated in  FIG. 3A . 
     Next, the hose  59  is also vented, by which means the suction duct  57  is also opened and a suction force is also exerted on the felt  21 ,  21   a ,  21   b  via the suction duct  57 . This operating position is illustrated in  FIG. 3B . 
     A second embodiment, changed with respect to  FIG. 3 ,  FIG. 3A ,  FIG. 3B , is illustrated in  FIG. 4 ,  FIG. 4A ,  FIG. 4B . Here, the supporting strips  61 ,  62  are formed with extensions  61   a ,  62   a , to which the hoses  58 ,  59  are fixed, for example by adhesive bonding with an adhesive. 
     The mode of action of the hoses  58 ,  59  and the modes of operation thereof are the same as explained by using  FIG. 3 ,  FIG. 3A ,  FIG. 3B . 
     In the following, by using  FIG. 5 ,  FIG. 5A ,  FIG. 5B , a third embodiment in the formation of the hoses acting as valve elements is explained. Here, between the suction plate  54  and the supporting strips  61 ,  62  there are hinge-like elements  80 ,  82 , each having two plates  81 ,  81   a  and  83 ,  83   a , which are mounted on axle bolts  81   b ,  83   b . The plates  81 ,  83  are located between the suction plate  54  and the supporting strips  61 ,  62  and are fixed in this way. The plates  81   a ,  83   a  are pivotable with respect to the plates  81 ,  83 . Between the plates  81   a ,  83   a  and the supporting strips  61 ,  62  there are hoses  58   a ,  59   a . If the hoses  58   a ,  59   a  are inflated, the plates  81   a ,  83   a  rest on the suction plate  55 , by which means the suction ducts  56 ,  57  are closed. As soon as the hoses  58   a ,  59   a  are vented, the plates  81   a ,  83   a  are lifted off the suction plate  55 , by which means the suction ducts  56 ,  57  are opened. 
     The suction ducts located in the suction plate  55  can be formed by slots extending over the widths of the felts, by a plurality of slots which, overall, extend over the widths of the felts, or by a plurality or a multiplicity of openings, in particular drilled holes, which are arranged over the widths of the felts. Some of these suction ducts are assigned inflatable valve elements, in particular in the form of hoses, by means of which individual suction ducts can be opened. 
     The particular advantage of such an apparatus consists in the fact that, on account of the inflatable and deflatable valve elements which are assigned to the suction ducts located in the suction plate, it is possible to open the suction ducts during the operation of the system, in order to be able to apply suction force to enlarged areas of the felts. In this way, it is not necessary to provide a further suction device which is connected as the loading of the felts with foreign materials rises.