Process and a device for the formation of fiberboard

Abstract

A process for the formation of fiberboard where the fiber stock suspension is dewatered on two sides between wires or felts, a top wire being provided in the main dewatering zone.

What is claimed is:  
     
         1 . Process for the formation of wood fiber board wherein a wood fiber stock suspension is dewatered on two sides between wires or felts forming a wood fiberboard having a basic weight of at least 1200 g/m 2 .  
     
     
         2 . Process according to  claim 1  wherein dilution water is added locally to regulate the board thickness across the web running direction.  
     
     
         3 . Process according to  claim 1  wherein headbox lips are set locally to regulate the board thickness across the web running direction.  
     
     
         4 . Process according to  claim 1  wherein pre-dewatering takes place in a wedge zone.  
     
     
         5 . Process according to  claim 1  wherein the stock is distributed over the working width by means of a cross-flow distributor and part of the wood fiber stock suspension flow is recirculated to the headbox.  
     
     
         6 . Process according to  claim 1  wherein the wood fiber stock suspension is dewatered to a dry content of more than 40%.  
     
     
         7 . Process according to  claim 1  wherein a top layer is applied after pre-dewatering.  
     
     
         8 . Process according to  claim 7  wherein vacuum extraction is provided in the area where the top layer is applied.  
     
     
         9 . Process according to  claim 7  wherein the wood fiber stock is further dewatered in a wedge zone after the top layer has been applied.  
     
     
         10 . Process according to  claim 1  wherein several points are provided with line pressure.  
     
     
         11 . Process according to  claim 10  wherein two to six points are provided with line pressure.  
     
     
         12 . Process according to  claim 10  wherein three to five points are provided with line pressure.  
     
     
         13 . Process according to  claim 1 , wherein the wood fiber stock suspension is dewatered to a dry content of more than 45%.  
     
     
         14 . Device for forming wood fiber board having a basic weight of 1200 to 8000 g/m 2  from a wood fiber stock suspension, the device comprising a first headbox and a main dewatering zone having a first top wire or felt and a bottom wire or felt.  
     
     
         15 . Device according to  claim 14  wherein the first top wire and the bottom wire form a first wedge zone.  
     
     
         16 . Device according to  claim 15  wherein the first wedge zone is adjustable.  
     
     
         17 . Device according to  claim 14  wherein the bottom wire runs essentially horizontally.  
     
     
         18 . Device according to  claim 15  further comprising support means for supporting the wire or felt in the first wedge zone said support means comprising perforated plastic, steel plates, foil strips or table rolls.  
     
     
         19 . Device according to  claim 14  further comprising a second headbox for applying a top layer.  
     
     
         20 . Device according to  claim 19  further comprising a second dewatering zone having a second top wire or felt and the bottom wire or felt forming a second wedge zone.  
     
     
         21 . Device according to  claim 20  wherein the wedge zones are suitable for pressure loading at an end.  
     
     
         22 . Device according to  claim 14  further comprising several press nips, each of the press nips including opposed press rolls.  
     
     
         23 . Device according to  claim 22  wherein the press rolls are arranged substantially vertically above one another.  
     
     
         24 . Device according to  claim 22  wherein the press rolls in the press nips are suitable for individual pressure loading.  
     
     
         25 . Device according to  claim 14  wherein the machine frame is suitable for cantilevering.  
     
     
         26 . Device according to  claim 14  further including two to six press nips.  
     
     
         27 . Device according to  claim 14  further including three to five press nips.  
     
     
         28 . Device for forming wood fiber board comprising a closed and pressurized first headbox and a main dewatering zone having a first top wire or felt and a bottom wire or felt.