Method and machine for producing a fibrous web which can be elongated in the transverse direction

Abstract

A method for producing a web of fibrous material includes the steps of: bringing the web into contact with a heated cylinder, the web being able to be elongated in a transverse direction; guiding the web, together with an elastic belt, over the heated cylinder, the web being between the elastic belt and a cylinder surface; pressing the web against the heated cylinder by the elastic belt; subjecting the elastic belt to a pre-tensioning—which is at least one of variably adjustable and controllable—in the transverse direction before being brought into contact with the web; and relieving the pre-tensioning of the elastic belt generated in the transverse direction again after formation of a steam cushion between the web and the heated cylinder, such that the web is shrunk with the elastic belt in the transverse direction in a sliding manner over the steam cushion on the heated cylinder.

What is claimed is: 
     
         1 . A method for producing a web of fibrous material, the method comprising the steps of:
 bringing the web—which is exiting a pre-drying section of a machine configured for producing the web—into contact with a heated cylinder, which is smooth, impermeable to steam, and rotating, the web being able to be elongated in a transverse direction;   guiding the web, together with an elastic belt, which is impermeable to steam and is circulating, over the heated cylinder over a specified or specifiable angle of wrap, the web being between the elastic belt and a cylinder surface of the heated cylinder;   pressing the web against the heated cylinder by the elastic belt;   subjecting the elastic belt to a pre-tensioning—which is at least one of variably adjustable and controllable—in the transverse direction before being brought into contact with the web; and   relieving the pre-tensioning of the elastic belt generated in the transverse direction again after formation of a steam cushion between the web and the heated cylinder, such that the web is shrunk with the elastic belt in the transverse direction in a sliding manner over the steam cushion on the heated cylinder.   
     
     
         2 . The method according to  claim 1 , wherein a steel cylinder is used as the heated cylinder. 
     
     
         3 . The method according to  claim 1 , wherein the elastic belt is pre-tensioned in the transverse direction by at least one variably adjustable tension roller arranged inside a loop of the elastic belt. 
     
     
         4 . The method according to  claim 3 , wherein the pre-tensioning of the elastic belt which is generated in the transverse direction is relieved again between the variably adjustable tension roller arranged inside the loop of the elastic belt and a guide roll arranged inside the loop of the elastic belt, viewed in a direction of web travel. 
     
     
         5 . The method according to  claim 1 , further comprising a press roll which is configured for being a variably adjustable tension roll, wherein the heated cylinder and the press roll—which is arranged inside a loop of the elastic belt—form a press nip, wherein the machine is configured such that the steam cushion between the web and the heated cylinder is generated in the press nip which is provided in an initial area of a zone of the heated cylinder around which the web and the elastic belt—viewed in a direction of web travel—are looped. 
     
     
         6 . The method of  claim 5 , wherein a machine or web speed is less than 1,000 m/min. 
     
     
         7 . The method according to  claim 5 , wherein, viewed in the direction of web travel, a guide roll holding the elastic belt and the web on the heated cylinder is provided inside the loop of the elastic belt in a rear area of the zone of the heated cylinder around which the web and the elastic belt are wrapped, so that the pre-tensioning of the elastic belt that was generated in the transverse direction is already relieved between the press nip provided in the initial region of the zone of the heated cylinder around which the web and the elastic belt are wrapped—when viewed in the direction of web travel—and the guide roll provided in the rear area of the zone of the heated cylinder around which, viewed in the direction of web travel, the web and the elastic belt are wrapped for generating a transverse shrinkage of the web. 
     
     
         8 . The method according to  claim 7 , wherein the elastic belt is again removed from the heated cylinder via the guide roll provided in the rear area of the zone of the heated cylinder around which the web and the elastic belt are wrapped, as viewed in the direction of web travel, and the web is separated again from the elastic belt. 
     
     
         9 . The method according to  claim 1 , wherein the web together with the elastic belt, which is pretensioned, is guided—in order to form the steam cushion between the web and the heated cylinder—over the heated cylinder along a conditioning or warm-up zone of the heated cylinder with the elastic belt maintained in a pretensioned condition. 
     
     
         10 . The method of  claim 9 , wherein a machine or web speed is greater than 1,000 m/min. 
     
     
         11 . The method according to  claim 9 , wherein the machine includes a variably adjusting tension roll, and the elastic belt is fed to the web that is brought into contact with the heated cylinder via the variably adjustable tension roll which pretensions the web;
 wherein the machine further includes a press roll;   wherein the heated cylinder and the press roll—which is arranged within a loop of the elastic belt—form a press nip which is configured to increase an adhesion of the web to the elastic belt at an end of the conditioning or warm-up zone;   wherein the press roll, for maintaining a pretension of the elastic belt within the conditioning or warm-up zone preceding the press roll, is at the same time formed as another variably adjustable tension roll;   wherein the web, following the press nip provided at the end of the conditioning or warm-up zone, is guided together with the elastic belt further over the heated cylinder along a shrinkage zone of the heated cylinder, along which the pretension of the elastic belt is again relieved for producing a transverse shrinkage of the web.   
     
     
         12 . The method according to  claim 11 , wherein the web together with the elastic belt is fed to a guide roll following the shrinkage zone via which the web and the elastic belt are again removed from the heated cylinder and separated from each other. 
     
     
         13 . The method according to  claim 1 , wherein the elastic belt is still subjected to a basic tensioning by way of a respective guide roll that, compared to the pre-tensioning, is lower by a defined amount. 
     
     
         14 . A machine for producing a web of fibrous material, the machine comprising:
 a heated cylinder which is smooth, steam-impermeable, and configured for rotating; and   an elastic belt which is impermeable to steam and configured for circulating, the machine being configured such that the web—which is able to be elongated in a transverse direction—is guided together with the elastic belt at a specified or specifiable angle of wrap between the elastic belt and the heated cylinder, is positioned above the heated cylinder, and is pressed against the heated cylinder by the elastic belt, the elastic belt being configured for being subjected to a pretension—which is at least one of variably adjustable and controllable—in the transverse direction before being brought into contact with the web, the machine being further configured such that the pretension of the elastic belt generated in the transverse direction is relievable after formation of a steam cushion between the web and the heated cylinder, such that the web shrinks with the elastic belt in the transverse direction in a sliding manner over the steam cushion on the heated cylinder.   
     
     
         15 . The machine according to  claim 14 , further comprising a press roll which is configured for being a variably adjustable tension roll, wherein the heated cylinder and the press roll—which is arranged inside a loop of the elastic belt—form a press nip, wherein the machine is configured such that the steam cushion between the web and the heated cylinder is generated in the press nip which is provided in an initial area of a zone of the heated cylinder around which the web and the elastic belt—viewed in a direction of web travel—are looped. 
     
     
         16 . The machine according to  claim 14 , wherein the machine is configured such that at least one of:
 (a) the web together with the elastic belt, which is pretensioned, is guided—in order to form the steam cushion between the web and the heated cylinder—over the heated cylinder along a conditioning or warm-up zone of the heated cylinder with the elastic belt maintained in a pretensioned condition, and   (b) the machine includes a variably adjusting tensioning roll, and the elastic belt is fed to the web that is brought into contact with the heated cylinder via the variably adjustable tensioning roll which pretensions the web;   wherein the machine further includes a press roll;   wherein the heated cylinder and the press roll—which is arranged within a loop of the elastic belt—form a press nip which is configured to increase an adhesion of the web to the elastic belt at an end of the conditioning or warm-up zone;   wherein the press roll, for maintaining the pretension of the elastic belt within the conditioning or warm-up zone preceding the press roll, is at the same time formed as a variably adjustable tension roll;   wherein the web, following the press nip provided at the end of the conditioning or warm-up zone, is guided together with the elastic belt further over the heated cylinder along a shrinkage zone of the heated cylinder, along which the pretension of the elastic belt is again relieved for producing a transverse shrinkage of the web.   
     
     
         17 . The machine according to  claim 14 , wherein the elastic belt defines a central longitudinal axis parallel to a machine direction, wherein, for the purpose of a targeted manipulation of a transverse elongation of the web, the elastic belt is provided, symmetrically to the central longitudinal axis, with a plurality of reinforcing threads extending at least substantially in the transverse direction with correspondingly adapted elasticity moduli or with a laid scrim correspondingly adapted with regard to a thread density of the laid scrim. 
     
     
         18 . The machine according to  claim 14 , wherein at least one of:
 a dry content of the web fed to the heated cylinder is in a range of approximately 50% to approximately 65%;   the heated cylinder has a diameter in a range of approximately 900 mm to approximately 1500 mm;   a surface temperature of the heated cylinder is >110°;   a conditioning or warm-up zone of the heated cylinder extends over approximately 30°;   a shrinkage zone of the heated cylinder extends over approximately 20°;   viewed in a direction of web travel, an average line force of a press nip of the machine provided in an initial region of a zone of the heated cylinder wrapped by the web and the elastic belt is a maximum of 50 kN/m;   viewed in the direction of web travel, a dwell time of the web in the press nip in the initial region of the zone of the heated cylinder wrapped by the web and the elastic belt is approximately 0.1 sec; and   an average line force in a press nip of the machine provided at an end of the conditioning or warm-up zone is a maximum of 50 kN/m.