US20230103146A1

US20230103146A1 - Method and machine for producing a fibrous web which can be elongated in the transverse direction

Info

Publication number: US20230103146A1
Application number: US18/073,684
Authority: US
Inventors: Johann Moser
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2020-06-02
Filing date: 2022-12-02
Publication date: 2023-03-30
Also published as: DE102020114602A1; WO2021244780A1; CN115698424A; EP4158098C0; EP4158098A1; EP4158098B1

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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application no. PCT/EP2021/053810, entitled “METHOD AND MACHINE FOR PRODUCING A FIBROUS WEB WHICH CAN BE ELONGATED IN THE TRANSVERSE DIRECTION”, filed Feb. 17, 2021, which is incorporated herein by reference. PCT application no. PCT/EP2021/053810 claims priority to German patent application no. DE 10 2020 114 602.7, filed Jun. 2, 2020, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for the production of a fibrous web. It moreover relates in particular to a machine, suitable for the implementation of such a method for the production of a fibrous web.

2. Description of the Related Art

To date, no tool is available for direct control or adjustment of the transverse elongation characteristics (CD elasticity) of paper. The shrinkage curve resulting in the transverse direction, or CD shrinkage profile (CD=cross direction), still firmly specifies these transverse elongation characteristics as the result of paper drying. Thus, the papermaker so far only has the possibility to influence the CD elasticity or the CD shrinkage profile at the expense of the web stabilization via web stabilization boxes, which is not a satisfactory measure. The machine builder can somewhat influence the CD shrinkage profile via the drying concept, such as in particular a single-row or double-row dryer section. However, compromises also have to be made here.
Reduced elongation characteristics or insufficient elasticity have a particularly negative effect on corrugated raw material. For example, the corrugated cardboard can break during corrugating, rendering it unusable as scrap. A brittle corrugated cardboard box will burst under impact because the impact energy cannot be absorbed. In addition, when producing the corrugation from the corrugating medium, the web can break if the elasticity is too low when corrugating with the corrugating roll. Too much brittleness is therefore also counterproductive here.
The well-known Clupak system is used for the targeted adjustment of a longitudinal elongation of paper (MD elasticity, MD=machine direction, machine running direction) or for producing a longitudinally directed micro crepe. Therein, the still moist web runs together with a rubber blanket through a press nip, whereby both are stretched. After the nip, the cloth contracts again, and the desired micro-creping is achieved in the web.
What is needed in the art is a method and a machine of the type described at the beginning, with which the aforementioned disadvantages can be eliminated. What is needed in the art is in particular to be able to specifically control or adjust or to improve the resulting elasticity or the transverse elongation characteristic and the energy absorption of the fibrous web in the transverse direction. What is also needed in the art is to create a possibility of counteracting the increasingly declining quality of waste paper raw material.

SUMMARY OF THE INVENTION

The present invention relates to a method for the production of a fibrous web which can be elongated in transverse direction. It moreover relates in particular to a machine, suitable for the implementation of such a method for the production of a fibrous web that can be elongated in the transverse direction.
The present invention provides a method for producing a fibrous web which can be elongated in the transverse direction, in particular a paper or cardboard web which can be elongated in the transverse direction, is characterized in that the fibrous web exiting a pre-drying section of the particular production machine is brought into contact with a heated rotating cylinder which is smooth and impermeable to steam, and the fibrous web is guided over the heated cylinder together with a circulating elastic belt which is impermeable to steam over a specified or specifiable angle of wrap so as to be positioned between the elastic belt and the heated cylinder—that is, the cylinder surface, —and is pressed against the cylinder by the elastic belt; the elastic belt is subjected to a variably adjustable and/or controllable pre-tensioning in the transverse direction before being brought into contact with the fibrous web, and the pre-tensioning of the elastic belt generated in transverse direction is relieved again after formation of a steam cushion between the fibrous web and the heated cylinder, so that the fibrous web is shrunk with the elastic belt in the transverse direction in a sliding manner over the steam cushion on the heated cylinder.
With such an embodiment of the method according to the present invention, the elasticity or respectively the transverse elongation characteristic resulting in transverse direction and the energy absorption of the fibrous web in the transverse direction can now be controlled or adjusted or improved in a targeted manner. Moreover, the possibility is created to counteract the increasingly declining waste paper raw material quality. The fibrous web coming from the pre-dryer section runs onto the elastic belt which is pre-tensioned in the transverse direction. By relieving the pre-tension of the elastic belt after the formation of the steam cushion between the fibrous web and the heated cylinder, the fibrous web can shrink in the transverse direction over the steam cushion on the heated cylinder, sliding with the elastic belt to produce the micro-crepe.
A steel cylinder, in particular a chrome-plated steel cylinder, is optionally used as the heated cylinder. Such a steel cylinder, in particular a chrome-plated steel cylinder, ensures that the fibrous web can slide optimally on it after formation of the steam cushion.
The elastic belt is advantageously pre-tensioned in transverse direction by at least one variably adjustable tension roller arranged inside its loop.
With the pre-tensioning in transverse direction being variably adjustable via the tension roll, the transverse shrinkage resulting after a reduction in the pre-tension can be controlled or adjusted accordingly.
The pre-tensioning of the elastic belt which is generated in transverse direction is advantageously relieved again between a variably adjustable tension roll arranged inside the loop of the elastic belt and a guide roll arranged inside the loop of the elastic belt, viewed in direction of web travel.
Since, the elastic belt traveling over the guide roll is subjected to minimal or no pretension in the region of this guide roll, its pretension between the tension roll and this guide roll can again decrease continuously.
According to an optional practical embodiment of the method according to the invention—in particular for relatively lower machine or web speeds, optionally for machine or web speeds of <1000 m/min—the steam cushion between the fibrous web and the heated cylinder is generated in a press nip which is provided in the initial area of the zone of the heated cylinder around which the fibrous web and the elastic belt viewed in direction of web travel are looped; said press nip is formed between the heated cylinder and a press roll arranged inside the loop of the elastic belt, which is designed at the same time as a variably adjustable tension roller by way of which the elastic belt is pre-tensioned in transverse direction.
Since the initial press roll provided for forming a steam cushion between the fibrous web and the heated cylinder is at the same time designed as a variable adjustable tension roll, the respective desired pretension in transverse direction can be imposed on the elastic belt.
It is herein especially advantageous if—viewed in direction of web travel—a guide roll holding the elastic belt and the fibrous web on the heated cylinder is provided inside the loop of the elastic belt in the rear area of the zone of the heated cylinder around which the fibrous web and the elastic belt are wrapped, so that the pre-tensioning of the elastic belt that was generated in transverse direction is already relieved between the press nip provided in the initial region of the zone of the heated cylinder around which the fibrous web and the elastic belt are wrapped —when viewed in direction of web travel—and the guide roll provided in the rear region of the zone of the heated cylinder around which, viewed in direction of web travel, the fibrous web and the elastic belt are wrapped for generating transverse shrinkage of the fibrous web.
The elastic belt is herein again removed advantageously from the heated cylinder via the guide roll provided in the rear area of the zone of the heated cylinder around which the fibrous web and the elastic belt are wrapped, as viewed in direction of web travel, and the fibrous web is separated again from the elastic belt.
According to an optional practical embodiment of the method according to the invention, in particular for relatively higher machine or web speeds, optionally for machine or web speeds of >1000 m/min, the fibrous web together with the pretensioned elastic belt is guided—for the purpose of forming the steam cushion between the fibrous web and the heated cylinder—along a conditioning or warm-up zone over the heated cylinder with the elastic belt maintained in pretensioned condition.
Thus, in this case, the steam cushion is formed in the region of the conditioning and warm-up zone.
It is therein particularly advantageous if the elastic belt is fed to the fibrous web that is brought into contact with the heated cylinder via a variably adjustable tensioning roll which pretensions the fibrous web, and if in order to increase the adhesion of the fibrous web to the elastic belt at the end of the conditioning or warm-up zone a press nip is provided which is formed between the heated cylinder and a press roll arranged within the loop of the elastic belt, which, for maintaining the pretension of the elastic belt within the preceding conditioning or warm-up zone, is at the same time designed as a variably adjustable tension roll; and the fibrous web, following the press nip provided at the end of the conditioning or warm-up zone, is guided together with the elastic belt along a shrinkage zone further over the heated cylinder, along which the pretension of the elastic belt is again relieved for producing the transverse shrinkage of the fibrous web.
The press nip provided at the end of the conditioning or warm-up zone thus ensures good adhesion between the fibrous web and the pretensioned elastic belt. While the fibrous web now adheres securely to the elastic belt, the existing steam cushion continues to ensure full mobility of the fibrous web relative to the heated cylinder.
The fibrous web together with the elastic belt is thereby advantageously fed to a guide roll following the shrinkage zone, via which the fibrous web and the elastic belt are again removed from the heated cylinder and separated from each other.
By way of a respective guide roll, the elastic belt can still be subjected to a basic tension that, compared to the pretension, is lower by a defined amount.
The fibrous web which was shrunk in transverse direction is optionally fed to an after-drying section of the production machine, where the transverse-shrinkage is set.
The machine according to the invention, which is particularly suitable for implementation of the method according to the invention, for producing a fibrous web which can be elongated in the transverse direction, in particular a paper or cardboard web which can be elongated in transverse direction, is characterized in that it includes a heated steam impermeable, smooth rotating cylinder and an elastic belt which is impermeable to steam, wherein the fibrous web is guided together with the elastic belt over a specified or specifiable wrapping angle between the elastic belt and the heated cylinder, positioned above the heated cylinder, and pressed against the latter by the elastic belt; the elastic belt can be subjected to a variably adjustable and/or controllable pretension in transverse direction before being brought into contact with the fibrous web, and the pretension of the elastic belt generated in transverse direction can be relieved after formation of a steam cushion between the fibrous web and the heated cylinder, so that the fibrous web shrinks with the elastic belt in the transverse direction in a sliding manner over the steam cushion on the heated cylinder.
A steel cylinder, in particular a chrome-plated steel cylinder, is optionally used as the heated cylinder.
The elastic belt can advantageously be pre-tensioned in transverse direction by at least one variably adjustable tension roller arranged inside its loop.
It is thereby particularly advantageous if the pre-tensioning of the elastic belt which is generated in transverse direction is relieved again between a variably adjustable tension roll arranged inside the loop of the elastic belt and a guide roll arranged inside the loop of the elastic belt, viewed in direction of web travel.
According to an optional practical embodiment of the machine according to the invention—in particular for relatively lower machine or web speeds, optionally for machine or web speeds of <1000 m/min—the steam cushion between the fibrous web and the heated cylinder is generated in a press nip which is provided in the initial area of the zone of the heated cylinder around which the fibrous web and the elastic belt viewed in direction of web travel are looped; said press nip is formed between the heated cylinder and a press roll arranged inside the loop of the elastic belt, which is designed at the same time as a variably adjustable tension roller by way of which the elastic belt is pre-tensioned in transverse direction.
It is herein especially advantageous if—viewed in direction of web travel—a guide roll holding the elastic belt and the fibrous web on the heated cylinder is provided inside the loop of the elastic belt in the rear area of the zone of the heated cylinder around which the fibrous web and the elastic belt are wrapped, so that the generated transverse directional pretension of the elastic belt is already relieved between the press nip provided in the initial region of the zone of the heated cylinder around which the fibrous web and the elastic belt are wrapped—when viewed in direction of web travel—and the guide roll provided in the rear region of the zone of the heated cylinder around which, viewed in direction of web travel, the fibrous web and the elastic belt are wrapped for generating transverse shrinkage of the fibrous web.
The elastic belt is herein again removed advantageously from the heated cylinder via the guide roll provided in the rear area of the zone of the heated cylinder around which the fibrous web and the elastic belt are wrapped, as viewed in direction of web travel, and the fibrous web is separated again from the elastic belt.
According to an optional practical embodiment of the machine according to the invention, in particular for relatively higher machine or web speeds, optionally for machine or web speeds of >1000 m/min, the fibrous web together with the pretensioned elastic belt is guided—for the purpose of forming the steam cushion between the fibrous web and the heated cylinder—along a conditioning or warm-up zone over the heated cylinder with the elastic belt maintained in pretensioned condition.
It is therein particularly advantageous if the elastic belt can be fed to the fibrous web that is brought into contact with the heated cylinder via a variably adjustable tensioning roll which pretensions the fibrous web, and if in order to increase the adhesion of the fibrous web to the elastic belt at the end of the conditioning or warm-up zone a press nip is provided which is formed between the heated cylinder and a press roll arranged within the loop of the elastic belt, which, for maintaining the pretension of the elastic belt within the preceding conditioning or warm-up zone, is at the same time designed as a variably adjustable tension roll; and the fibrous web, following the press nip provided at the end of the conditioning or warm-up zone, is guided together with the elastic belt along a shrinkage zone further over the heated cylinder, along which the pretension of the elastic belt can again be relieved for producing the transverse shrinkage of the fibrous web.
The fibrous web together with the elastic belt is thereby advantageously fed to a guide roll following the shrinkage zone, via which the fibrous web and the elastic belt are again removed from the heated cylinder and separated from each other.
By way of a respective guide roll, the elastic belt can still be subjected to a basic tension that, compared to the pretension, is lower by a defined amount.
Advantageously, the pre-tensioning of the elastic belt can be adjusted via tensioning devices provided laterally on the roll body of a respective tensioning roll and variably adjustable in transverse machine direction relative to the roll body.
According to an optional practical embodiment of the machine according to the invention, the elastic belt—for the purpose of targeted manipulation of the elongation of the fibrous web in the transverse direction—is provided symmetrically to its central longitudinal axis parallel to the machine direction with reinforcing threads extending at least substantially in transverse direction with correspondingly adapted elasticity moduli or with a laid scrim correspondingly adapted in particular with regard to its thread density.
It is thereby also particularly advantageous if the elasticity moduli of the reinforcing threads extending in transverse direction or the laid scrim of the elastic belt are or is correspondingly adapted to compensate for the trough-shaped shrinkage curve normally occurring in transverse direction during drying of the fibrous web.
The elastic belt may moreover also be provided with reinforcing threads extending at least substantially in the machine direction.
The elastic belt consists advantageously at least substantially of rubber.
The elastic belt has optionally a hardness of 55+/−10 Shore (107 P&J).
It is also advantageous if the elastic belt has a density in the range of approximately 1.2 kg/dm³to approximately 1.5 kg/dm³.
The elastic belt has optionally a thickness in the range of approximately 20 mm to approximately 30 mm, whereby a thickness of approximately 25 mm is optional.
Additional advantageous embodiments of the machine according to the invention are characterized in that

- The dry content of the fibrous web fed to the heated cylinder is in the range of approximately 50% to approximately 65%, and/or
- the heated cylinder has a diameter in the range of approximately 900 mm to approximately 1500 mm, and/or
- the surface temperature of the heated cylinder is >1100 and in particular in the range between 1100 and approximately 125°, and/or
- the conditioning or warm-up zone extends over approximately 30°, and/or
- the shrinkage zone extends over approximately 20°, and/or
- viewed in direction of web travel, the average line force of the press nip provided in the initial region of the zone of the heated cylinder wrapped by the fibrous web and the elastic belt is a maximum of 50 kN/m, and/or
- viewed in direction of web travel, the dwell time of the fibrous web in the press nip in the initial region of the zone of the heated cylinder wrapped by the fibrous web and the elastic belt is approximately 0.1 sec, and/or
- the average line force in the press nip provided at the end of the conditioning or warm-up zone is a maximum of 50 kN/m.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic representation of an exemplary embodiment of a machine according to the invention suitable in particular for relatively lower machine or web speeds, optionally for machine or web speeds of <1000 m/min;

FIG. 2 is a schematic representation of an exemplary embodiment of a machine according to the invention suitable in particular for relatively higher machine or web speeds, optionally for machine or web speeds of >1000 m/min;

FIG. 3 is a cross-sectional schematic partial representation of an exemplary tension roll of the machine according to the invention;

FIG. 4 is cross-sectional schematic partial representation of an exemplary guide roll of the machine according to the invention;

FIG. 5 is a schematic partial representation of an exemplary embodiment of the elastic belt of a machine according to the invention with reinforcing threads extending in transverse direction and reinforcing threads extending in longitudinal direction;

FIG. 6 is an exemplary progression of the moduli of elasticity of the reinforcing threads provided symmetrically relative to the central longitudinal axis of the belt according to FIG. 5 , each extending in transverse direction;

FIG. 7 is a schematic partial representation of an exemplary embodiment of the elastic belt of a machine according to the invention with a laid scrim;

FIG. 8 , with the continuous line, shows the schematic progression of the trough-like shrinkage curve of the fibrous web which generally results in transverse direction, and the dashed lines show an exemplary schematic progression of the tension or elongation behavior of an elastic belt occurring in the transverse direction according to FIGS. 5 or 7 ; and

FIG. 9 is a schematic representation of a shrinkage curve or elongation behavior of the finished fibrous web or paper or cardboard web resulting in transverse direction in the example of an elastic belt according to FIG. 5 or 7 .

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 each show an exemplary embodiment of a machine 10 according to the invention for producing a fibrous web 12 that can be elongated in the transverse direction, which in particular can be a paper or board web that can be elongated in the transverse direction.
Machines 10 always include a heated, steam-impermeable and smooth rotating cylinder 14, and a steam-impermeable circulating elastic belt 16.
In each case, fibrous web 12 is guided over heated cylinder 14 together with elastic belt 16 at a specified or specifiable wrap angle between elastic belt 16 and heated cylinder 14 and is pressed against the latter by elastic belt 16.
Elastic belt 16 can be subjected to a variably adjustable and/or controllable pretension in transverse direction before being brought into contact with fibrous web 12. The pretension of elastic belt 16 generated in transverse direction can be relieved again after formation of a steam cushion between fibrous web 12 and heated cylinder 14, so that fibrous web 12 shrinks with the elastic belt in transverse direction in a sliding manner over the steam cushion on heated cylinder 14.
In machine 10, illustrated in FIG. 1 , intended in particular for relatively lower machine or web speeds, optionally for machine or web speeds of <1000 m/min, the steam cushion between fibrous web 12 and heated cylinder 14 is generated in a press nip 18 which is provided in the initial area of the zone of heated cylinder 14 around which fibrous web 12 and elastic belt 16 viewed in direction of web travel are wrapped; said press nip 18 is formed between heated cylinder 14 and a press roll 20 arranged inside the loop of elastic belt 16, which is designed at the same time as a variably adjustable tension roller by way of which elastic belt 16 can be pre-tensioned in transverse direction.
Viewed in direction of web travel I, a guide roll 22 holding elastic belt 16 and fibrous web 12 on heated cylinder 14 is provided inside the loop of elastic belt 16 in the rear area of the zone of heated cylinder 14 around which fibrous web 12 and elastic belt 16 are wrapped, so that the generated pretension generated in the transverse direction of elastic belt 16 is already relieved between press nip 18 provided in the initial region of the zone of heated cylinder 14 around which fibrous web 12 and elastic belt 16 are looped—when viewed in direction of web travel I—and guide roll 22 provided in the rear region of the zone of heated cylinder 14 around which, viewed in direction of web travel I, fibrous web 12 and elastic belt 16 are wrapped for generating transverse shrinkage of fibrous web 12.
Elastic belt 16 is again removed from heated cylinder 14 via guide roll 22 provided in the rear area of the zone of heated cylinder 14 around which fibrous web 12 and elastic belt 16 are wrapped, as viewed in direction of web travel I, and fibrous web 12 is separated again from elastic belt 16.
In contrast, in machine 10 according to FIG. 2 which is intended in particular for relatively higher machine or web speeds, optionally for machine or web speeds of >1000 m/min, fibrous web 12 together with pre-tensioned elastic belt 16 is guided—for the purpose of forming the steam cushion between fibrous web 12 and heated cylinder 14—along a conditioning or warm-up zone α over heated cylinder 14 with elastic belt 16 maintained in prestressed condition.
Elastic belt 16 of fibrous web 12 that is brought into contact with heated cylinder 14 is fed via a variably adjustable tensioning roll 24 which pretensions fibrous web 12. In order to increase the adhesion of fibrous web 12 to elastic belt 16 at the end of the conditioning or warm-up zone α, a press nip 26 is provided which is formed between the cylinder 16 and a press roll 28 arranged within the loop of elastic belt 16, which, for maintaining the pretension of elastic belt 16 within the preceding conditioning or warm-up zone α, is at the same time designed as a variably adjustable tension roll. Fibrous web 12 following press nip 26 provided at the end of conditioning or warm-up zone α, is guided together with elastic belt 16 along a shrinkage zone β further over heated cylinder 14, along which the pretension of elastic belt 16 can again be relieved for producing the transverse shrinkage of fibrous web 12.
Following shrinkage zone β, fibrous web 12 together with elastic belt 16 is fed to a guide roll 30, via which fibrous web 12 and elastic belt 16 are again removed from heated cylinder 14 and separated from each other.
In the two embodiment examples according to FIGS. 1 and 2 , elastic belt 16 can still be subjected to a basic tensioning by way of a respective guide roll 22, 30 that, compared to the pre-tension, is lower by a defined amount.
FIG. 3 shows a schematic partial representation of an exemplary design of a tension roll A, as is possible, for example, for roll 20 according to FIG. 1 , which is also designed as a press roll, and for tension roll 24 and press roll 28 according to FIG. 2 , which at the same time is also designed as a tension roll.
As can be seen from FIG. 3 , in the case of such a tensioning roll A, the pre-tension of elastic belt 16 can be adjusted via tensioning devices 34 provided on the side of roll body 32 and can be variably adjustable in the transverse direction of the machine relative to roll body 32.
In contrast, FIG. 4 shows a schematic partial representation of an exemplary embodiment of a guide roller B, such as is conceivable for the guide roll 22 according to FIG. 1 and guide roll 30 according to FIG. 2 . As can be seen from FIG. 4 , also with such a guide roll B, elastic belt 16 can still be subjected to a basic tensioning that is lower by a defined amount ΔL than the pretension.
In both FIGS. 3 and 4 , the respective mounting 36 of respective roll A and B can also be seen.
FIG. 5 shows in schematic partial representation an exemplary embodiment of elastic belt 16 of a machine according to the invention with reinforcing threads 38 extending in cross direction CD and reinforcing threads 40 extending in longitudinal direction MD (machine direction). Reinforcing threads 38 extending in cross direction CD and arranged symmetrically relative to the central longitudinal axis L are provided with correspondingly adapted elasticity moduli E for targeted influencing of the cross-directional elongation of fibrous web 12. Thereby, elastic moduli E of reinforcing threads 38 of elastic belt 16 extending in cross direction CD can be adapted accordingly, in particular to compensate for trough-shaped shrinkage curve 42 (compare to continuous line in FIG. 8 ) normally occurring in cross direction during drying of fibrous web 12.
An exemplary progression of elasticity moduli E of the reinforcing threads provided symmetrically relative to central longitudinal axis L of elastic belt 16 according to FIG. 5 , each extending in transverse direction, is shown in FIG. 6 .
FIG. 7 shows a schematic partial representation of an exemplary embodiment of elastic belt 16 of a machine 10 according to the invention with a laid scrim 44, in which the desired profiling for targeted influencing of the elongation of the fibrous web in the transverse direction can be achieved via a variable thread density. For example, in the left part of FIG. 7 , the thread density is high, in the center it is in the medium range, and in the right part of FIG. 7 , the thread density is relatively low. Again, such a laid scrim 44 can be suitably adapted to compensate for trough-shaped shrinkage curve 42 normally occurring in transverse direction during drying of fibrous web 12, which in the present case is possible in particular by way of a variable thread density.
As already mentioned, the continuous line in FIG. 8 shows the schematic progression of trough-shaped shrinkage curve 42 of fibrous web 12 that generally occurs in cross direction CD. In contrast, the dashed line in FIG. 8 shows a schematic example of the tensioning or elongation behavior of an elastic belt in cross direction CD as shown in FIGS. 5 and 7 . In particular, the progression of the cross-directional elongation F of fibrous web 12 dried in the conventional manner is shown (see solid line 42), as is the progression of the cross-directional elongation F of an elastic belt 16 according to FIGS. 5 and 7 according to the present invention (dashed line 46).
FIG. 9 shows a balanced shrinkage curve 48 or elongation behavior of the finished dried fibrous web or paper or cardboard web 12 that can be achieved with an elastic belt 16 as shown in FIGS. 5 and 7 , avoiding the formation of troughs that has been common up to now.

COMPONENT IDENTIFICATION LIST

10 Machine
12 Fibrous web
14 heated cylinder
16 elastic belt
18 press nip
20 press roll
22 guide roll
24 tension roll
26 press nip
28 press roll
30 guide roll
32 roll body
34 tensioning device
36 mounting
38 reinforcement thread, extending in transverse direction
40 reinforcement thread, extending in longitudinal direction
42 shrinkage curve
44 laid scrim
46 CD elongation of elastic belt
48 shrinkage curve
I direction of web travel
A tension roll
B guide roll
CD cross direction (transverse direction)
E elasticity module
MD longitudinal direction
L center longitudinal axis
Δ differential tension
α conditioning or warm-up zone
β shrinkage zone
ε cross elasticity

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

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 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;

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.