Suction roll in a machine for producing a fibrous web

Abstract

The present invention provides a suction roll system in a drying section of a machine for manufacturing a fibrous web, the suction roll system including a suction roll having an outer circumferential surface. The circumferential surface defines holes configured for attracting the fibrous web by suction and includes regions, more than two of the regions including the holes, at least two of the regions relative to one another having different numbers of the holes per unit area or having the holes with different diameters per unit area. The circumferential surface has strips which extend in a circumferential direction, at least one strip which extends in a helical shape over the circumferential surface, or strips which extend either substantially in a direction of a longitudinal axis of the suction roll or diagonally relative to the longitudinal axis. The regions include the strips. The strips have an increased number of the holes per unit area in comparison with the remaining regions between the strips or have the holes with greater diameters in comparison with the remaining regions.

1 . A suction roll system in a drying section of a machine for manufacturing a fibrous web, said suction roll system comprising a suction roll including an outer circumferential surface including a plurality of holes for attracting the fibrous web by suction, said circumferential surface divided into more than two regions having one of a different number of said holes per unit area and having said holes with different diameters per unit area, said circumferential surface having one of a plurality of strips which extends in a circumferential direction, at least one strip which extends in a helical shape over said circumferential surface, and a plurality of strips which extends one of substantially in a direction of a longitudinal axis of said suction roll and diagonally, said plurality of strips one of having an increased number of said plurality of holes per unit area in comparison with said plurality of regions between said plurality of strips and having said plurality of holes with greater diameters.  
   
   
       2 . The suction roll system of  claim 1 , wherein said circumferential surface includes a plurality of end-side edges and a central region, at least one of said plurality of end-side edges including one of said plurality of regions one of having an increased number of said plurality of holes per unit area in comparison with a number of said plurality of holes per unit area in said central region and having said plurality of holes with greater diameters.  
   
   
       3 . The suction roll system of  claim 1 , wherein each of said plurality of strips has a width of at least 70 mm.  
   
   
       4 . The suction roll system of  claim 1 , wherein each of said plurality of strips has a width from 100 mm to 1000 mm.  
   
   
       5 . The suction roll system of  claim 1 , wherein each of said plurality of strips is at a spacing from one another of at least 100 mm.  
   
   
       6 . The suction roll system of  claim 1 , wherein each of said plurality of strips is at a spacing from one another of more than 200 mm.  
   
   
       7 . The suction roll system of  claim 1 , wherein said circumferential surface includes a plurality of groove-shaped depressions.  
   
   
       8 . The suction roll system of  claim 7 , wherein each of said plurality of depressions has a depth of from 1 to 10 mm.  
   
   
       9 . The suction roll system of  claim 7 , wherein each of said plurality of depressions has a width between 1 and 10 mm.  
   
   
       10 . The suction roll system of  claim 7 , wherein each of said plurality of depressions is at a spacing from one another of from 5 to 30 mm.  
   
   
       11 . The suction roll system of  claim 1 , wherein said suction roll has a diameter of at least 3 m.  
   
   
       12 . The suction roll system of  claim 1 , further comprising a dryer fabric and an impingement dryer, wherein said suction roll is wrapped around by said dryer fabric and the fibrous web lying on said dryer fabric, said impingement dryer being set against said suction roll in order to dry the fibrous web.  
   
   
       13 . The suction roll system of  claim 1 , further comprising a vacuum source, wherein said suction roll includes a rotary leadthrough and a shaft, said suction roll being connected to said vacuum source via said rotary leadthrough in said shaft.  
   
   
       14 . The suction roll system of  claim 1 , further comprising a suction box which applies a vacuum to said suction roll and which bears sealingly against said circumferential surface.  
   
   
       15 . The suction roll system of  claim 1 , wherein said suction roll comprises an inner gastight cover and an outer cover, said outer cover including said plurality of holes, said inner gastight cover and said outer cover defining an annular vacuum space therebetween.  
   
   
       16 . The suction roll system of  claim 1 , wherein a proportion of said circumferential surface which is occupied by said plurality of holes in said plurality of regions on said circumferential surface which have one of a lower number of said plurality of holes and said plurality of holes with a smaller diameter is between 0.2 and 2.5%.  
   
   
       17 . The suction roll system of  claim 1 , wherein a proportion of said circumferential surface which is occupied by said plurality of holes in said plurality of regions on said circumferential surface which have one of a lower number of said plurality of holes and said plurality of holes with a smaller diameter is between 1 and 1.5%.  
   
   
       18 . The suction roll system of  claim 1 , wherein a proportion of said circumferential surface which is occupied by said plurality of holes of one of said plurality of regions and said plurality of strips which have a higher number of said plurality of holes than remaining said plurality of regions of said circumferential surface is at least  1 . 5  times that of said circumferential surface which is occupied by said plurality of holes in remaining said plurality of regions.