Abstract:
The invention relates to a device ( 12 ) which is used to press a pressure shoe ( 10 ) against a counter surface, comprising at least one at least partially flexible pressure body ( 16 ) which is supported on the bearing body ( 14 ), said pressure body comprising at least one cavity ( 18 ) which can be impinged upon by pressure fluid in order to produce a predetermined pressing force over a corresponding pressure body volume.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a device for pressing a pressure shoe against a backing surface. 
   2. Background Description 
   A pressure shoe of this type can, in particular, be part of a shoe press unit, in particular of a shoe roll, and serve to press a flexible belt or flexible press cover for forming a press nip which is extended in the web running direction against a backing surface which is formed, for example, by a backing roll. A corresponding shoe press unit can be provided, for example, for manufacturing and/or treating a fibrous web, in particular a paper or paperboard web. Here, the fibrous web can be guided through the relevant press nip together with at least one felt or fabric. 
   Up to now, the pressure shoe was pressed on either by an oil pressure bed or separate pressing pistons. However, an oil pressure bed causes problems, in particular, with regard to sealing. The use of separate pressing pistons is associated with the disadvantage of a deviation in the transverse pressure profile which is caused by the individual pistons. 
   SUMMARY OF THE INVENTION 
   The invention is based on the aim of providing an improved pressing device of the type which is mentioned in the introduction, in which the abovementioned problems are eliminated. Here, in particular, a relatively uniform pressure distribution in the machine running direction and in the transverse direction is to be made possible, in order to achieve a pressure profile which is as planar as possible. The occurrence of reaction forces in the machine running direction and transverse direction is to be reduced to a minimum. 
   According to the invention, this aim is achieved by the fact that the device comprises at least one pressure element which is supported on a supporting body, is flexible at least in regions and has at least one hollow space which can be acted on with pressure fluid, in order to produce a predefinable pressing force via a corresponding pressure element volume. Here, the pressure element is preferably configured to be leakfree. 
   On account of this embodiment, a relatively uniform pressure distribution is possible in the machine running direction and transverse direction, with the result that pressure profiles which are as planar as possible can be produced. This therefore results in a relatively large pressing surface which faces the pressure shoe or its lower part, which results in the pressure which is required to achieve the necessary line force can be kept relatively low. In comparison with pressing using individual pistons, lower pressure levels of the pressure fluid are possible. 
   The risk of leakage of the pressure fluid is practically precluded. Moreover, reduced manufacturing expenditure and simple assembly result. 
   The pressure element can be configured, in particular, as a lifting cushion or pressure cushion or as a pressure tube. 
   In one preferred practical embodiment of the pressing device according to the invention, the pressure element is configured in the form of a folding bellows. Here, the folding bellows can have a plurality of, for example three, outer folds which are preferably circumferential, by which a relatively small initial height is achieved. 
   The pressure element can have, in particular, a generally cuboidal design. 
   However, the pressure element can also be formed by a pressure tube which extends preferably axially. 
   That pressing surface of the pressure element which acts on the pressure shoe or its lower part preferably corresponds at least substantially to the maximum pressure element cross section. This results in a pressing surface which is as large as possible, as a result of which the pressure which is required to achieve the necessary line force can be kept as small as possible. 
   A plurality of pressure elements which follow one another in the machine running direction and/or a plurality of pressure elements which follow one another in the transverse direction are advantageously provided. 
   In one expedient practical embodiment having a plurality of pressure elements which follow one another in the machine running direction, in order to vary the line force profile and/or pressure longitudinal profile in the press nip which is formed with the backing surface, the pressure elements can be acted on with pressure fluid at least partially independently of one another. 
   In one expedient practical embodiment having a plurality of pressure elements which follow one another in the transverse direction, in order to vary the line force profile and/or transverse pressure profile in the press nip which is formed with the backing surface, the pressure elements which follow one another in the transverse direction can be acted on with pressure fluid at least partially independently of one another. 
   At least three pressure elements which follow one another in the transverse direction are advantageously provided, as a result of which, for example, control in the edge zones is also made possible. 
   Pressure elements having different lengths can be provided for adaptation to the respective working width. 
   In one preferred practical embodiment of the pressing device according to the invention having at least three pressure elements which follow one another in the transverse direction, the two pressure elements on the edges have a smaller length, measured in the transverse direction, than the central pressure element or elements. 
   In order to form a modular system, in accordance with a further refinement of the invention, pressure elements can be provided which have a length which corresponds to a fraction of a working width. Depending on the working width, more or less pressure elements of this type can be arranged behind one another or next to one another. If required, compensation pressure elements having a smaller length are used, in order to fill a remaining part of the working width. 
   The pressure element preferably has one or more connections to the pressure fluid supply mechanism. Here, ventilation and/or cooling and/or heating of the pressure element is also advantageously possible via the least one connection. 
   Water, gas, air and/or oil can be provided as pressure fluid, for example. 
   In one expedient practical embodiment of the pressing device according to the invention, the pressure element is mounted in a pressure bed of the supporting body. This is possible in all vertical and horizontal directions. Here, the pressure element can be fixed, in particular, by a corresponding design of the pressure bed and of the pressure shoe lower part. 
   The pressure shoe is advantageously assigned at least one return element, by which it can be moved away from the backing surface. Relatively sensitive transverse profiling is possible as a result of a suitable combination of pressure element or pressure elements and return element or return elements. 
   A respective return element can comprise, in particular, at least one spring element and/or at least one cylinder/piston element. 
   The length and shape of the pressure element are expediently defined at least partially by stops. 
   A stop bar can be provided in the center of the working width, for example. As a result, movements of the pressure shoe unit in the working width direction can advantageously be suppressed, and at the same time the deformation-free thermal expansion of the pressure shoe lower part can be permitted. A plurality of stop bars can also be provided, for example in each case on the outer sides of the pressure shoe. 
   The stop bar can also be provided with sliding strips which can preferably be exchanged, in order to reduce the friction between the stop bars and the bellows or the supporting body. 
   The stop bar in the center of the working width is preferably configured to be longer than the other stops. Moreover, the stop bar is preferably guided in a U-shaped stop in the center of the working width. 
   The brackets which serve to connect with the pressure fluid supply mechanism are expediently arranged on that side of the pressure element which faces away from the pressure shoe. 
   Moreover, it is advantageous for the connections to the pressure fluid supply mechanism to be arranged diagonally relative to the pressure element. In the case of adjacent pressure elements, the brackets are preferably connected to one another in pairs, in particular in an alternating manner on the inlet/outlet side. This results in short connecting paths. 
   It is also preferred for the connection to be provided below the supporting body upper belt, that is to say its horizontal part, and/or next to the web of the supporting body, that is to say its vertical part. The connections can be accommodated here in a protected manner and do not require any additional space. 
   The pressure element is preferably composed at least partially of fiber reinforced plastic. 
   According to a further refinement of the invention, the pressure shoe can be mounted rotatably in the machine running direction, to be precise, in particular, centrally. Moreover, the pressure shoe can also be mounted in the machine transverse direction, in particular in a multiple manner. This has the advantage that a defined position of the pressure shoe results, without stop bars being required. As a result, the pressure shoe is given a position which can be calculated exactly, and the pressure profile can also be calculated exactly. Furthermore, the rotatable mounting can for its part be mounted so as to move freely in the horizontal direction. 
   According to the invention, two or more pressure elements can also be arranged one above another. Here, one or more dividing plates are preferably arranged between the pressure elements. Pressure pistons can also be provided instead of the lower pressure elements, at least partially. In this way, further variation possibilities and setting possibilities can be realized. 
   The solution according to the invention is used, in particular, in dewatering devices in machines for manufacturing and/or finishing paper webs, paperboard webs, tissue webs or other fibrous webs. Here, the fibrous web is guided, together with at least one dewatering belt, through a press nip which is formed with the aid of the pressing device. The line force in the press nip preferably lies between 50 and 980 KN and, in particular, between 60 and 210 KN. The use is therefore particularly suitable for the manufacture of tissue webs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in greater detail in the following text using exemplary embodiments with reference to the drawing, in which: 
       FIG. 1  shows a diagrammatic cross-sectional illustration of a pressure shoe having an associated pressing device, 
       FIG. 2  shows a diagrammatic illustration of the pressure element which is shown in  FIG. 1 , in a view from below, 
       FIG. 3  shows a diagrammatic illustration of a further embodiment of the pressing device having two pressure elements which follow one another in the machine running direction and restoring elements which are assigned to the pressure shoe, 
       FIG. 4  shows a diagrammatic illustration of a further embodiment of the pressing device having only one pressure element, as viewed in the machine running direction, the pressure shoe also being assigned restoring elements in this case again, 
       FIG. 5  shows a diagrammatic illustration of an embodiment of the pressing device having three pressure elements which follow one another in the transverse direction, 
       FIG. 6  shows a diagrammatic illustration of an embodiment having a pressure tube, 
       FIG. 7  shows an illustration, corresponding to  FIG. 1 , of a further variant of the invention, and 
       FIG. 8  shows an illustration according to  FIG. 1  of yet another variant of the invention. 
   

   DETAILED DESCRIPTION 
   In a diagrammatic cross-sectional illustration,  FIG. 1  shows a pressure shoe  10  having an associated pressing device  12 . 
   The pressing device  12  comprises at least one pressure element  16  which is supported on a supporting body  14  and is flexible at least in regions. The pressure element  16  has at least one hollow space  18  which can be acted on with pressure fluid, in order to produce a predefinable pressing force via a corresponding pressure element volume. 
   In the present case, the pressure element  16  has only a single, continuous hollow space  18 . 
   A flexible belt, for example the flexible press cover of a shoe roll, can be guided over the pressure shoe  10 . Via the pressing unit which acts on the lower part  20  of the pressure shoe  10 , the pressure shoe  10  and thus the relevant flexible belt can be pressed against a backing surface which can be formed, for example, by a backing roll, in order to form an extended press nip. 
   The pressure element  16  which is configured as a lifting cushion or pressure cushion in the present case is configured to be practically leakfree. As can be seen from  FIG. 1 , it is configured in the present case in the form of a folding bellows having, for example, three outer folds  22  which are preferably circumferential. 
   The pressure element  16  is to have as large a pressing surface  24  as possible which acts on the pressure shoe  10  or its lower part  20 , in order to keep the pressure which is required to achieve the necessary line force as low as possible. This is achieved with the pressure element  16  according to the invention. 
   The pressure element  16  can, for example, have a generally cuboidal design. That pressing surface  24  of the pressure element  16  which acts on the pressure shoe  16  or its lower part  20  can correspond at least substantially to the maximum pressure element cross section. 
   Moreover, a connection  26  to the pressure fluid supply mechanism is to be seen in  FIG. 1 . 
   As results from  FIG. 2 , the pressure element  16  can in principle also have a plurality of connections  26  to the pressure fluid supply mechanism. In the present case, two connections  26  of this type are provided. As is to be seen from  FIG. 2 , the brackets which serve to connect with the pressure fluid supply mechanism are expediently arranged on that side of the pressure element  16  which faces away from the pressure shoe  10  (cf. also  FIG. 1 ). Here, a diagonal arrangement of these brackets can be provided for improved throughflow of the pressure fluid. 
   The pressure element  16  can expediently be acted on with the relevant pressure fluid in a variable manner, in order to produce a pressing force which can be set in a variable manner by a corresponding variation of the pressure element volume. 
   As results from  FIGS. 3 to 5 , a plurality of pressure elements  16  which follow one another in the machine running direction MD and/or a plurality of pressure elements  16  which follow one another in the transverse direction CD can be provided. 
     FIG. 3  shows a diagrammatic illustration of an embodiment of the pressing device  12  having two pressure elements  16  which follow one another in the machine running direction MD, and also having return or restoring elements  28  which are assigned to the pressure shoe  10 . 
   The pressure elements  16  which follow one another in the machine running direction MD are provided with separate connections  26  to the pressure fluid source  30 . Here, these pressure elements  16  which follow one another in the machine running direction MD can be acted on with pressure fluid, in particular independently of one another, in order to vary the line force profile and/or longitudinal pressure profile in the press nip which is formed with the backing surface. In the present case, although the pressure elements  16  are connected to the same pressure fluid source  30 , a pressure reducing valve  32  or the like, for example, can be provided in the feed line to one of the two pressure elements  16 , with the result that the two pressure elements  16  can be acted on with different pressures if required. 
   As is to be seen from  FIGS. 3 and 4 , return or restoring elements  28  can be provided both on the front side and on the rear side of the pressure shoe  10 , as viewed in the machine running direction, in order to move the pressure shoe  10  away from the backing surface. 
   A respective return element  28  can, for example, comprise at least one spring element and/or at least one cylinder/piston element. 
     FIG. 4  shows a diagrammatic illustration of an embodiment of the pressing device  12  having only one pressure element  16 , as viewed in the machine running direction MD. In this case, the pressure shoe  10  is also again assigned return elements  28 . In the present case, a respective return element  28  can also again comprise, for example, at least one spring element and/or at least one cylinder/piston element. 
   As is to be seen from  FIGS. 3 and 4 , the return elements  28  can be provided on that side of the supporting body  14  which faces away from the pressure shoe  10 , and can be connected to the pressure shoe  10  via pulling elements  34  which extend through the supporting body  14 . 
   As is to be seen from  FIG. 4 , the pressure element  16  is again provided with at least one connection  16  to the pressure fluid supply mechanism  30 . 
     FIG. 5  shows a diagrammatic illustration of an embodiment of the pressing device  12  having three pressure elements  16  which follow one another in the transverse direction CD. 
   In order to vary the line force profile and/or transverse pressure profile in the press nip which is formed with the backing surface, the pressure elements  16  which follow one another in the transverse direction CD can be acted on with pressure fluid, in particular again independently of one another. They are therefore again provided with separate connections  26  to the pressure fluid supply mechanism. 
   In the present case, for example, three pressure elements  16  are provided which follow one another in the transverse direction CD; however, more than three or only two pressure elements  16  can also follow one another in the transverse direction. 
   In particular, a combination of the embodiments according to  FIGS. 3 and 4  with the embodiment according to  FIG. 5  is also conceivable. 
   In  FIG. 6 , the pressure shoe  10  is pressed via two pressure elements  16  which lie next to one another in the pressure bed  36  in the direction of rotation, in the form of axially extending pressure tubes. The expansion of the pressure tube in the pressing direction is also set here via the pressure of the pressure fluid in the pressure tube. 
   Pressure elements  16  having different lengths can be provided for adaptation to the respective working width. 
   If at least three pressure elements  16  which follow one another in the transverse direction CD are provided, it is possible to control the edge zones, for example, via the pressure elements  16  at the edges. As is to be seen from  FIG. 5 , the pressure elements  16  at the edges can have, for example, a smaller length, measured in the transverse direction, than the central pressure element or elements  16 . 
   The length and shape of the pressure elements  16  can be limited, in particular, by stops. 
   That pressing surface of a respective pressure element  16  which faces the pressure shoe  10  is relatively great, with the result that the required oil pressure is kept correspondingly low. The brackets for connection to the pressure fluid supply means are arranged on the underside of a respective pressure element  16  (cf.  FIG. 2 ). Here, the brackets can be arranged diagonally for improved pressure fluid throughflow (cf., in particular,  FIG. 2  again). The respective displacement results from a change in volume by opening of the folds  22  (cf., in particular,  FIG. 1 ). The result is a correspondingly lower initial height with a limited number of outer folds  22  (cf. the embodiment according to  FIG. 1  having only three outer folds). The pressure elements  16  can, in particular, be composed of fiber reinforced plastic or the like. 
   A respective pressure element  16  can be mounted in a pressure bed  36  of the supporting body  14  (cf., in particular,  FIG. 1 ). Here, the pressure element  16  can be fixed by a corresponding design of the pressure bed  36  and of the pressure shoe lower part  20 . 
     FIG. 7  shows a pressure shoe  10  which is mounted rotatably via a bearing element  36  in the machine running direction MD, as indicated by arrow  38 . For its part, the mounting  36  is mounted so as to move freely in a horizontal bearing  40 . In this refinement, as shown, two pressure elements  16  are arranged one behind another in the machine running direction MD. In addition, there can also be provision for a rotatable mounting in the machine transverse direction CD, preferably in a multiple manner, which is not shown here. 
     FIG. 8  shows a variant, in which two pressure elements  16  are arranged one above another. A dividing plate  42  is provided between the two pressure elements  16 . Instead of the lower pressure element  16 , it is also possible for pressure pistons to be provided. Moreover, a plurality of pressure elements  16  can be arranged next to one another, in each case in the machine transverse direction CD, as has been described with respect to the previous exemplary embodiments. The same is true for the variant of  FIG. 7 . 
   LIST OF DESIGNATIONS 
   
       
         10  Pressure shoe 
         12  Pressing device 
         14  Supporting body 
         16  Pressure element 
         18  Hollow space 
         20  Lower part 
         22  Outer fold 
         24  Pressing surface 
         26  Connection 
         28  Return or restoring element 
         30  Pressure fluid source 
         32  Pressure reducing valve 
         34  Pulling element 
         36  Pressure bed 
         37  Mounting 
         38  Arrow 
         40  Horizontal bearing 
         42  Dividing plate 
       MD Machine running direction 
       CD Transverse direction