Dry forming plant and method for dry forming a fibrous tissue using such dry forming plant

Abstract

A dry forming plant is described which comprises at least one distribution unit having a fibre and air inlet. Such distribution unit is placed above a forming wire opposite to at least one vacuum box which is connected to a suction unit. The distribution unit has an open bottom for release of the fibre material onto the forming wire below the distribution unit. More rotating rollers having protruding spikes are provided in the distribution unit for covering the cross sectional area of the open bottom. The vacuum box is divided into at least three longitudinal zones in a direction transversal to the advance direction of the forming wire. Said longitudinal zones have upwardly orientated intakes arranged below the forming wire. The longitudinal zones are connected with the suction unit via an outlet. The outlet comprises first shut-off means for partly or totally closing the outlet. The first shut-off means are independently operable.

1 . A dry forming plant for dry forming of a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, the dry forming plant comprises;
 a forming wire;   at least one distribution unit having a fibre and air inlet, and the at least one distribution unit positioned above the forming wire,   a suction unit;   at least one vacuum box connected to the suction unit, the at least one vacuum box positioned below the forming wire;   wherein the at least one distribution unit includes an open bottom configured and arranged to release the fibre material onto the forming wire which is configured and arranged to be advanced below the distribution unit; and   one or more rotating rollers having protruding spikes are provided in the distribution unit, the one or more rotating rollers are configured and arranged to cover the cross sectional area of the open bottom,   wherein each of the at least one vacuum box is divided into at least three longitudinal zones in a direction transverse to an advance direction of the forming wire, and   wherein the at least three longitudinal zones have upwardly orientated intakes arranged below the forming wire, and wherein each of the at least three longitudinal zones are connected with the suction unit via an outlet, each of the outlets include first shut-off means configured and arranged to partly or totally close the respective outlet independent of the other outlets.   
     
     
         2 . The dry forming plant according to  claim 1 , wherein the at least three longitudinal zones are divided into a number of transverse zones, wherein at least one of the transverse zones includes a second shut-off means, the second shut-off means are configured to partly or totally close the respective intake to that transverse zone independent of the other intakes at least in the advance direction. 
     
     
         3 . The dry forming plant according to  claim 2 , wherein the longitudinal zones and transverse zones are formed by partition plates provided with cut-outs configured and arranged for joining the partition plates. 
     
     
         4 . The dry forming plant according to  claim 1 , wherein the outlet of the longitudinal zones are further connected with the suction unit via suction tubes directed in the advance direction. 
     
     
         5 . The dry forming plant according to  claim 1 , wherein the at least one distribution unit includes two or more independent distribution units arranged side by side in a direction transverse to the advance direction, 
     
     
         6 . The dry forming plant according to  claim 5 , wherein the at least one vacuum box comprises a longitudinal zone in an area where adjacent sides of the two or more independent distribution units are joined, the longitudinal zone is a central zone and at least one side zone is provided on each side of the central zone. 
     
     
         7 . The dry forming plant according to  claim 1 , wherein the at least one vacuum box includes two or more independent vacuum boxes arranged side by side in a direction transverse to the advance direction. 
     
     
         8 . The dry forming plant according to  claim 1 , wherein the at least one vacuum box unit comprises an outermost side zone, the outermost side zone having a local width being smaller than a local width of another longitudinal zone of the at least one vacuum box. 
     
     
         9 . The dry forming plant according to  claim 1 , wherein at least two of the distribution units and/or the vacuum boxes are either identical or symmetrical. 
     
     
         10 . The dry forming plant according to  claim 1 , wherein the first shut-off means for each of the longitudinal zones are slide valves connected with independently operable first operation units. 
     
     
         11 . The dry forming plant according to  claim 2 , wherein the second shut-off means for the at least one transverse zone are rotary dampers mounted on a common pivotally mounted shaft connected with independently operable second operation units. 
     
     
         12 . A method of dry forming a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, using a dry forming plant according to  claim 1 , wherein the method includes the steps of:
 feeding at least one fibrous material into at least one distribution unit,   establishing a suction through a forming wire via at least one vacuum box,   distributing the at least one fibrous material from the at least one distribution unit onto the forming wire, and   advancing the forming wire in an advance direction during the distribution of the fibrous material to form the fibrous tissue.   
     
     
         13 . The method according to  claim 12 , wherein the at least one fibrous material is fed to at least two distribution units arranged side by side in a direction transverse to the advance direction, where a first local suction is provided in a central zone where adjacent sides of the two distribution units are joined, and where the first local suction is independently controlled in relation to a second local suction provided in at least one side zone arranged on each side of the central zone. 
     
     
         14 . The method according to  claim 12 , wherein a first local suction is provided in an outermost side zone arranged at a side edge of the at least one vacuum box, and where the first local suction is independently controlled in relation to a second local suction provided in at least one side zone arranged adjacent to the outermost side zone.