Long nip press for machines transporting fibre webs

Abstract

A long nip press for machines transporting fibre webs, which press drains water from the fibre web and comprises two hydrostatic bearings opposite each other, both comprising a pressure shoe comprising a pressure chamber, the pressure shoe having a sealing element in the form of a flexible pressure-balancing diaphragm, and a press belt to press the fibre web against a fabric, the pressure-balancing diaphragm protruding on its edge-zone without support from the inner rim of the pressure shoe towards the pressure chamber. So as to make the long nip press very simple in structure and to enable self-adjusting, even and efficient lubrication in the nip, the protruding edge-zones comprise pinholes for transporting hydraulic fluid. The invention also relates to a pressure-balancing diaphragm.

1 . A long nip press for machines transporting fibre webs, such as paper and board machines, which press drains water from the fibre web ( 8 ) and comprises a hydrostatic bearing and a press belt ( 6 ) sliding on the bearing to press the fibre web ( 8 ) against a press roll ( 1 ) in such a manner that the fibre web ( 8 ) when moving presses against at least one fabric ( 13 ,  14 ), the bearing comprising a pressure shoe ( 3 ) comprising at least one pressure chamber ( 10 ), and on the surface of the pressure shoe that is towards the press belt ( 6 ), there is a sealing element in the form of a flexible pressure balancing diaphragm ( 20 ) and comprising an outer rim ( 26 ), an inner rim ( 22 ) and an opening ( 27 ) defined by the inner rim, the pressure balancing diaphragm ( 20 ) being supported by the pressure shoe, but protruding from the inner rim ( 17 ) of the pressure shoe towards the pressure chamber ( 10 ) in such a manner that on its protruding edge-zone ( 21 ), it is at least mainly unsupported, whereby its inner edge ( 22 ) is free, and the pressure balancing diaphragm ( 20 ) being made of a material, the rigidity of which enables it to bend during use according to hydraulic pressure changes occurring in the area of the pressure shoe ( 3 ) away from the press roll ( 1 ) and correspondingly towards the press roll in such a manner that hydraulic fluid can flow away from the nip ( 2 ) from the area between the press roll ( 1 ) and the pressure shoe, and when the hydraulic fluid flow exceeds a certain value, the pressure balancing diaphragm ( 20 ) is adapted to bend towards the press roll ( 1 ) to reduce the hydraulic fluid flow, characterized in that the protruding edge-zone ( 21 ) of the pressure balancing diaphragm ( 20 ) comprises pinholes ( 25 ) for transporting hydraulic fluid in the pressure chamber ( 10 ) from the pressure chamber to the press belt ( 6 ) to lubricate the press belt.  
     
     
         2 . A long nip press for machines transporting fibre webs, such as paper and board machines, which press drains water from the fibre web ( 8 ) and comprises two hydrostatic bearings located opposite each other, both comprising a pressure shoe ( 3   a  and  3   b ) comprising at least one pressure chamber ( 10   a ,  10   b ), the pressure shoe having on its surface a sealing element in the form of a flexible pressure balancing diaphragm ( 20   a ,  20   b ) and comprising an outer rim, an inner rim ( 22   a ,  22   b ) and an opening defined by the inner rim, and a press belt ( 6   a  and  6   b ) sliding on a bearing to press the fibre web ( 8 ), when it moves, against at least one fabric ( 13   a ,  13   b ), the pressure balancing diaphragm ( 20   a ,  20   b ) being supported by the pressure shoe, but protruding from the inner rim ( 17   a ,  17   b ) of the pressure shoe towards the pressure chamber ( 10   a  and  10   b ) in such a manner that on its protruding edge-zone ( 21   a ,  21   b ), it is at least mainly unsupported, whereby its inner edge ( 22   a ,  22   b ) is free, and the pressure balancing diaphragm ( 20   a  and  20   b ) being made of a material, the rigidity of which enables it to bend during use according to hydraulic pressure changes occurring in the area of the pressure shoe ( 3   a ,  3   b ) towards the opposing pressure shoe ( 3   b ,  3   a ) and correspondingly away from it so that hydraulic fluid can flow away from the nip from the area between the pressure shoe ( 3   a ,  3   b ) and the surface of the pressure shoe, and when hydraulic fluid flow exceeds a certain value, the pressure balancing diaphragm ( 20   a ,  20   b ) is adapted to bend towards the pressure shoe ( 3   a ,  3   b ) to reduce the hydraulic fluid flow, characterized in that the protruding edge-zone ( 21   a ,  21   b ) of the pressure balancing diaphragm ( 20   a ,  20   b ) of both pressure shoes ( 3   a ,  3   b ) comprises pinholes ( 25 ) for transporting hydraulic fluid in the pressure chamber ( 10   a ,  10   b ) from the pressure chamber to the press belt ( 6   a ,  6   b ) to lubricate the press belt.  
     
     
         3 . A press as claimed in  claim 1  or  2 , characterized in that the diameter of the pinholes ( 25 ) is 0.01 to 10 micrometers.  
     
     
         4 . A press as claimed in  claim 3 , characterized in that the diameter of the pinholes ( 25 ) is 1 to 10 micrometers.  
     
     
         5 . A press as claimed in  claim 1  or  2 , characterized in that the pressure-balancing diaphragm ( 20 ;  20   a ,  20   b ) is made of a uniform rectangular element.  
     
     
         6 . A press as claimed in  claim 5 , characterized in that the pressure balancing diaphragm ( 20 ;  20   a ,  20   b ) is made of a 0.2 to 3-mm thick stainless steel plate and protrudes in its edge-zone ( 21 ) towards the pressure chamber ( 10 ) at least mainly unsupported a distance of L=20 to 40 mm.  
     
     
         7 . A press as claimed in  claim 6 , characterized in that the inner rim of the pressure balancing diaphragm ( 20 ;  20   a ,  20   b ) is at its outermost section bent towards the pressure shoe body ( 18 ) to form a wedge-like inlet slot to the press belt ( 6 ).  
     
     
         8 . A press as claimed in  claim 1  or  2 , characterized in that the surface of the pressure shoe that is towards the press belt ( 6 ;  6   a ,  6   b ) is bevelled towards the outer rim ( 28 ;  28   a ,  28   b ) of the pressure shoe in such a manner that the bevelled section ( 15 ) forms a 5 to 10-degree angle with respect to the top level of the pressure shoe.  
     
     
         9 . A press as claimed in  claim 8 , characterized in that the pressure balancing diaphragm ( 20 ;  20   a ,  20   b ) is fastened to the bevelled surface ( 15 ) of the pressure shoe by a weld joint ( 16 ) running along the rim of the pressure balancing diaphragm.  
     
     
         10 . A press as claimed in any one of the preceding claims, characterized in that the pressure-balancing diaphragm ( 20 ;  20   a ,  20   b ) is made of stainless steel.  
     
     
         11 . A pressure-balancing diaphragm ( 20 ) comprising an outer rim ( 26 ), an inner rim ( 22 ) and an opening ( 27 ) defined by the inner rim, characterized in that the diaphragm comprises pinholes ( 25 ) in an edge-zone ( 21 ) close to the inner rim ( 22 ).