Triple papermaking fabric

Abstract

A papermaking fabric has a fabric repeating unit that comprises eight top MD yarns and eight bottom MD yarns that extend in machine direction; three top CMD yarns interwoven only with the top MD yarns; three bottom CMD yarns interwoven only with the bottom MD yarns; and two pairs of binding yarns interwoven with both the top MD yarns and the bottom MD yarns; the binding yarns of each pair cross each other under respective transition yarns; the binding yarns of each pair, together, leave exposed on a top surface of the fabric only single isolated transition yarns, all separated from each other in cross machine direction by a plurality of adjacent top MD yarns.

1 . A triple papermaking fabric ( 100 ), having at least one fabric repeating unit ( 104 ) that comprises:
 a set of warp yarns or machine direction (MD) yarns ( 1 - 16 ), that extend in machine direction (MD) and subdivide in eight top MD yarns ( 1 - 8 ) and eight bottom MD yarns ( 9 - 16 );   a set of weft yarns or cross machine direction (CMD) yarns (P 6 ,P 10 ,P 14 ; MC 5 ,MC 9 ,MC 13 ; L 7 ,L 8 ,L 11 ,L 12 ), that extend in cross machine direction and specifically comprise: three top CMD yarns (P 6 ,P 10 ,P 14 ), three bottom CMD yarns (MC 5 ,MC 9 ,MC 13 ) and two pairs of binding yarns (L 7 ,L 8 ,L 11 ,L 12 ) comprising respective support portions ( 115 ) and respective binding portions ( 116 );   
       wherein:
 the top CMD yarns (P 6 ,P 10 ,P 14 ) are interwoven only with the top MD yarns ( 1 - 8 ) to form a top fabric layer ( 101 ); 
 the bottom CMD yarns (MC 5 ,MC 9 ,MC 13 ) are interwoven only with the bottom MD yarns ( 9 - 16 ) to form a bottom fabric layer ( 102 ); 
 the binding yarns (L 7 ,L 8 ,L 11 ,L 12 ) are interwoven with both the top MD yarns ( 1 - 8 ) and the bottom MD yarns ( 9 - 16 ) so as to bind the top layer ( 101 ) with the bottom layer ( 102 ); 
 the binding yarns (L 7 ,L 8 ,L 11 ,L 12 ) are arranged in pairs between pairs of adjacent top CMD yarns (P 6 ,P 10 ,P 14 ); and the binding yarns (L 7 ,L 8 ,L 11 ,L 12 ) of each pair intersect with each other under respective transition yarns (T), which pass over both the binding yarns of the pair; 
 
       the fabric being characterized in that:
 the binding yarns (L 7 ,L 8 ; L 11 ,L 12 ) of each pair, together, leave exposed on a top surface of the fabric ( 100 ) only single isolated transition yarns (T), all separated from each other in cross machine direction by a plurality of adjacent top MD yarns ( 1 - 8 ); and 
 the transition yarns (T) defined by a first pair of binding yarns (L 7 ,L 8 ) are offset by one top MD yarn with respect to the transition yarns (T) defined by a second pair of binding yarns (L 11 ,L 12 ). 
 
     
     
         2 . The fabric according to  claim 1 , wherein the transition yarns (T) of each pair of binding yarns (L 7 ,L 8 ,L 11 ,L 12 ) are separated from each other by terns of adjacent top MD yarns ( 1 - 8 ). 
     
     
         3 . The fabric according to  claim 1  or  2 , wherein the sequence of the two binding yarns (L 7 ,L 8 ; L 11 ,L 12 ) of each pair, together, with respect to the top MD yarns ( 1 - 8 ) is the same as the sequence of the top CMD yarns (P 6 ,P 10 ,P 14 ) with respect to the top MD yarns ( 1 - 8 ). 
     
     
         4 . The fabric according to  claim 1 , wherein the two binding yarns (L 7 ,L 8 ; L 11 ,L 12 ) of each pair, together, pass over three adjacent top MD yarns ( 1 - 8 ) and under the following top MD yarn, and so on. 
     
     
         5 . The fabric according to  claim 1 , wherein each binding yarn (L 7 ,L 8 ,L 11 ,L 12 ) passes over three adjacent top MD yarns ( 1 - 8 ) and under the following five adjacent top MD yarns ( 1 - 8 ), and so on; and under one bottom MD yarn ( 9 - 16 ) and over all the following bottom MD yarns ( 9 - 16 ), and so on. 
     
     
         6 . The fabric according to  claim 1 , wherein the pairs of binding yarns (L 7 ,L 8 ; L 11 ,L 12 ) are offset with respect to the adjacent top CMD yarns (P 6 ,P 10 ,P 14 ) so, as to pass over the top MD yarns ( 1 - 8 ) which are instead left exposed by the adjacent top CMD yarns (P 6 ,P 10 ,P 14 ). 
     
     
         7 . The fabric according to  claim 1 , wherein each binding yarn (L 7 ,L 8 ,L 11 ,L 12 ) binds, i.e. passes over, a tern of adjacent top MD yarns ( 1 - 8 ) and binds, i.e. passes under, one bottom MD yarn ( 9 - 16 ) which is offset in cross machine direction by an even number of positions with respect to said tern of top MD yarns. 
     
     
         8 . The fabric according to  claim 7 , wherein each binding yarn (L 7 ,L 8 ,L 11 ,L 12 ) binds a tern of adjacent top MD yarns ( 1 - 8 ) and one bottom MD yarn ( 9 - 16 ) which is offset by two or four positions in cross machine direction with respect to the third and last top MD yarn of the tern. 
     
     
         9 . The fabric according to  claim 1 , wherein each top CMD yarn (P 6 ,P 10 ,P 14 ) passes over three adjacent top MD yarns ( 1 - 8 ) and under the next top MD yarn ( 1 - 8 ), and so on. 
     
     
         10 . The fabric according to  claim 9 , wherein the top CMD yarns (P 6 ,P 10 ,P 14 ) are offset in cross machine direction by one or two top MD yarns ( 1 - 8 ). 
     
     
         11 . The fabric according to  claim 9 , wherein the fabric repeating unit ( 104 ) there is a first, a second and a third top CMD yarns (P 6 ,P 10 ,P 14 ); the second top CMD yarn (P 10 ) being offset by one top MD yarn with respect to the preceding first top CMD yarn (P 6 ) and the third top CMD yarn (P 14 ) being offset by two top MD yarns with respect to the preceding second top CMD yarn (P 10 ). 
     
     
         12 . The fabric according to  claim 1 , wherein the binding yarns (L 7 ,L 8 ,L 11 ,L 12 ) and the top CMD yarns (P 6 ,P 10 ,P 14 ) form a four harness satin structure with the top MD yarns ( 1 - 8 ). 
     
     
         13 . The fabric according to  claim 1 , wherein the bottom CMD yarns (MC 5 ,MC 9 ,MC 13 ) are interwoven with the bottom MD yarns ( 9 - 16 ) with an “over-2/under-6” sequence. 
     
     
         14 . The fabric according to  claim 13 , wherein each bottom CMD yarns (MC 5 ,MC 9 ,MC 13 ) is offset by one position in cross machine direction with respect to the preceding bottom CMD yarn. 
     
     
         15 . The fabric according to  claim 1 , wherein the fabric ( 100 ) has a ratio between weft and warp yarns of 4:1. 
     
     
         16 . The fabric according to  claim 1 , wherein the top layer ( 101 ) and the bottom layer ( 102 ) are also bound in machine direction, i.e. in the warp direction. 
     
     
         17 . The fabric according to  claim 16 , wherein in the fabric repeating unit ( 104 ) at least a pair of directly overlapped MD yarns (MD 6 ,MD 14 ), i.e. a top MD yarn and a bottom MD yarn directly overlapping one another, cross each other in machine direction, i.e. in the warp direction, so as to define a pair of binding warp yarns (MD 6 ,MD 14 ) maintaining the weaving patterns of both the top layer ( 101 ) and the bottom layer ( 102 ). 
     
     
         18 . Use of a fabric ( 100 ) according to  claim 1  in a papermaking machine for conveying a cellulose pulp and/or a paper material to be formed.