Forming screen for use in a paper machine

Abstract

The invention relates to a forming screen for use in the forming section of a paper machine, comprising a paper and a machine side as well as longitudinal threads extending in the intended running direction and binding cross threads extending transversely thereto, wherein the longitudinal threads are divided in the ratio of the number of threads of 1:1 in a longitudinal thread layer on the machine side and a longitudinal thread layer on the paper side, and the binding cross threads bind in both longitudinal thread layers, which is characterized in that the forming screen has a fiber support index (FSI) which is in the range of 230 to 250 and has an air permeability which is in the range of 5700 to 10600 m 3 /m 2 /h.

1 . A forming screen ( 1 ) for use in the forming section of a paper machine, comprising a paper and a machine side as well as longitudinal threads ( 4 ,  5 ) extending in the intended running direction and binding cross threads ( 10 ,  11 ) extending transversely thereto, wherein the longitudinal threads ( 4 ,  5 ) are divided in the ratio of the number of threads of 1:1 in a longitudinal thread layer ( 3 ) on the machine side and a longitudinal thread layer ( 2 ) on the paper side, and the binding cross threads ( 10 ,  11 ) bind in both longitudinal thread layers ( 2 ,  3 ), characterized in that the forming screen ( 1 ) has a fiber support index (FSI) which is in the range of 230 to 250 and an air permeability which is in the range of 5700 to 10600 m 3 /m 2 /h. 
   
   
       2 . The forming screen according to  claim 1 , characterized in that the air permeability is in the range of 6500 to 8200 m 3 /m 2 /h. 
   
   
       3 . The forming screen according to  claim 1 , characterized in that the forming screen ( 1 ) on the paper side has 1200 to 1600 flow-through openings per cm 2  surface of the forming screen ( 1 ). 
   
   
       4 . The forming screen according to  claim 1 , characterized in that the flow-through openings are rectangular in shape with a ratio of the extension in running direction to the extension in transverse direction of 1:1,8 to 1:3,4. 
   
   
       5 . The forming screen according to  claim 1 , characterized in that the fill degree of the longitudinal threads ( 4 ) in the longitudinal thread layer ( 2 ) on the paper side is maximum 32%. 
   
   
       6 . The forming screen according to  claim 1 , characterized in that the total fill degree of all longitudinal threads ( 4 ,  5 ) is maximum 90%, preferably maximum 85%. 
   
   
       7 . The forming screen according to  claim 1 , characterized in that the diameter of the longitudinal threads ( 4 ,  5 ), at least in the longitudinal thread layer ( 2 ) on the paper side, is in the range of 0.08 to 0.12 mm. 
   
   
       8 . The forming screen according to  claim 1 , characterized in that the diameter of the longitudinal threads ( 5 ) in the longitudinal thread layer ( 3 ) on the machine side is in the range of 0.15 to 0.25 mm. 
   
   
       9 . The forming screen according to  claim 1 , characterized in that at least a part of the longitudinal threads ( 4 ,  5 ) consist of PET with an intrinsic viscosity of at least 0.8 dl/g and an elasticity module of at least 10 N/mm 2 . 
   
   
       10 . The forming screen according to  claim 1 , characterized in that at least a part of the longitudinal threads ( 4 ,  5 ) consist of PEN. 
   
   
       11 . The forming screen according to  claim 1 , characterized in that the number of longitudinal threads ( 4 ,  5 ) are in the range of 50 to 66 threads per cm in transverse direction. 
   
   
       12 . The forming screen according to  claim 1 , characterized in that the number of cross threads ( 6 ,  7 ,  9 ,  10 ,  11 ) are in the range of 100 to 110 threads per cm in longitudinal direction. 
   
   
       13 . The forming screen according to  claim 1 , characterized in that there are second cross threads ( 6 ,  7 ) which are only bound in the longitudinal thread layer ( 2 ) on the paper side. 
   
   
       14 . The forming screen according to  claim 13 , characterized in that the second cross threads ( 6 ,  7 ), taken alone, form a plain weave with the longitudinal thread layer ( 2 ) on the paper side. 
   
   
       15 . The forming screen according to  claim 1 , characterized in that the binding cross threads ( 10 ,  11 ) are arranged adjacent to one another to form groups of at least two binding cross threads ( 10 ,  11 ) each, whereby one of the binding cross threads ( 10 ,  11 ) binds in the longitudinal thread layer on the machine side when the other binding cross thread ( 11 ,  10 ) or the other binding cross threads bind in the longitudinal thread layer ( 2 ) on the paper side. 
   
   
       16 . The forming screen according to  claim 15 , characterized in that the respectively adjacent binding cross threads ( 10 ,  11 ) bind in the longitudinal thread layer ( 2 ) on the paper side with their repeating staggered vis-à-vis one another in such a way that their binding patterns complement one another in transverse direction without a gap. 
   
   
       17 . The forming screen according to  claim 15 , characterized in that the binding cross threads ( 10 ,  11 ) bind in the longitudinal thread layer ( 3 ) on the machine side within a repeating with less longitudinal threads ( 5 ) than in the longitudinal thread layer ( 2 ) on the paper side. 
   
   
       18 . The forming screen according to  claim 17 , characterized in that the binding cross threads ( 10 ,  11 ) bind in the longitudinal thread layer ( 3 ) on the machine side within a repeating with not more than two longitudinal threads ( 5 ). 
   
   
       19 . The forming screen according to  claim 1 , characterized in that there are third cross threads ( 8 ) which only bind in the longitudinal thread layer ( 3 ) on the machine side. 
   
   
       20 . The forming screen according to  claim 19 , characterized in that the third cross threads ( 8 ) float on the outer side of the longitudinal thread layer ( 3 ) on the machine side over several longitudinal threads ( 5 ), wherein the number of these longitudinal threads ( 5 ) is always greater than the number of the longitudinal threads ( 5 ) with which the third cross threads ( 8 ) bind between two floatings ( 9 ). 
   
   
       21 . The forming screen according to  claim 20 , characterized in that the third cross threads ( 8 ) float over more than three longitudinal threads ( 5 ) on the outside and, in between, only bind with one longitudinal thread ( 5 ).