CN115698424A

CN115698424A - Method and machine for producing a fibrous web that can be stretched in the cross direction

Info

Publication number: CN115698424A
Application number: CN202180039696.7A
Authority: CN
Inventors: J.莫瑟
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2020-06-02
Filing date: 2021-02-17
Publication date: 2023-02-03
Also published as: US20230103146A1; EP4158098A1; EP4158098B1; EP4158098C0; WO2021244780A1; DE102020114602A1

Abstract

In a method for producing a fibrous web that can be stretched in the cross direction, in particular a paper or cardboard web that can be stretched in the cross direction, the fibrous web coming from a predrying section of an associated production machine is brought into contact with a heated, water-vapor-impermeable and smooth rotating cylinder and, together with a water-vapor-impermeable encircling elastic belt, is guided past the heated cylinder in a lying manner at a predetermined or predeterminable wrap angle between the elastic belt and the heated cylinder and is pressed by the elastic belt onto the heated cylinder, the elastic belt being acted upon in the cross direction by a variably adjustable and/or controllable pretensioning force before being brought into contact with the fibrous web. After the steam cushion is formed between the fibrous web and the heated cylinder, the pre-tension of the elastic belt in the cross direction is reduced again, so that the fibrous web shrinks in the cross direction with the elastic belt by the steam cushion sliding on the heated cylinder. A machine for performing the method is also presented.

Description

Method and machine for producing a fibrous web that can be stretched in the cross direction

The invention relates to a method for producing a fibrous web that can be stretched in the cross direction. The invention further relates to a machine for producing a fiber web that can be stretched in the cross direction, which is particularly suitable for carrying out such a method.

No tool exists to date for directly controlling or adjusting the cross direction strain characteristics (CD elasticity) of paper. Shrinkage curves or CD shrinkage characteristics (CD = cross direction) produced in the cross direction have hitherto unequivocally ascribed these cross direction strain characteristics to the sheet drying results. Therefore, paper makers have hitherto been able to influence the CD elasticity or CD shrinkage characteristic curve only at the expense of stabilizing the web by means of a web stabilizing box, which is not a satisfactory measure. In particular, the machine manufacturer can roughly influence the CD shrinkage characteristic curve by means of a drying program, for example, in particular a single-row or double-row dryer section. However, a compromise must also be made here.

Reduced strain characteristics or too low elasticity have a particularly negative effect on the corrugated cardboard base paper. Therefore, the corrugated cardboard may be broken at the flutes, so that it cannot be used as a defective product. Brittle corrugated cardboard boxes fracture under the effect of an impact because the impact energy cannot be absorbed. Furthermore, when the corrugation is produced from a corrugated web, the web can break when the elasticity is too low, when the grooving occurs by the grooved roll. I.e. too high brittleness, is also disadvantageous here.

For the targeted adjustment of the sheet longitudinal tension (MD elasticity; MD = machine direction) or for the production of longitudinally oriented micro-folds (Mikrokrepp), the known Clupak system is used. The still moist web is thereby passed through the nip together with the rubber blanket, whereby the web and the rubber blanket are stretched. After the nip, the blanket is shortened again and the desired micro-folds are produced in the web.

The object of the invention is to provide a method and a machine of the type mentioned in the introduction, by means of which the aforementioned disadvantages can be overcome. In this case, it should be particularly achieved that the elasticity or cross-direction strain characteristics of the fibrous web occurring in the cross direction and the energy consumption in the cross direction can be controlled or regulated or improved in a targeted manner. Furthermore, a possible solution should be created which is resistant to the decreasing quality of the waste paper raw material.

According to the invention, the object is achieved by a method having the features of claim 1 and a machine having the features of claim 13. Preferred embodiments of the method according to the invention and of the machine according to the invention result from the dependent claims, the description and the drawings.

The method according to the invention for producing a fibrous web that can be stretched in the cross direction, in particular a paper or cardboard web that can be stretched in the cross direction, is characterized in that the fibrous web coming from the pre-drying section of the relevant production machine is brought into contact with a heated, water-vapor-impermeable and smooth rotating cylinder and, together with a water-vapor-impermeable encircling elastic belt, is guided laterally through the heated cylinder at a predetermined or predeterminable wrap angle between the elastic belt and the heated cylinder, i.e. the cylinder surface, and is pressed onto the heated cylinder by the elastic belt, the elastic belt being acted upon in the cross direction by a variably adjustable and/or controllable pretensioning force before contact with the fibrous web, the cylinder elastic belt being subjected to a renewed reduction of the pretensioning force in the cross direction after the formation of a vapor cushion between the fibrous web and the heated cylinder, so that the fibers shrink in the cross direction, in particular are reinforced in a controlled manner, by the vapor cushion sliding on the heated cylinder together with the elastic belt.

This embodiment of the method according to the invention enables the elasticity or cross-direction strain characteristics of the fibrous web occurring in the cross direction and the energy absorption in the cross direction to be controlled or regulated or improved in a targeted manner. Moreover, a feasible scheme capable of resisting the gradual reduction of the quality of waste paper raw materials is created. The fibrous web coming from the pre-drying section is brought into contact with an elastic belt which is pre-tensioned in the cross direction. By reducing the pretensioning force of the elastic belt again after the steam cushion is formed between the fibrous web and the heated cylinder, the fibrous web can be shrunk in the cross direction together with the elastic belt by the steam cushion sliding on the heated cylinder to produce the micro-folds.

Steel cylinders, in particular chromium-plated steel cylinders, are preferably used as the heated cylinders. This, in particular, chrome-plated steel cylinder ensures that the fibrous web can slide optimally on the steel cylinder after the steam cushion has been formed.

The elastic belt is advantageously pretensioned in the transverse direction by at least one variably adjustable tensioning roller arranged within its loop.

The transverse pretensioning force, which can be variably adjusted by the tensioning roller, enables the transverse contraction that occurs after the pretensioning force reduction to be controlled or adjusted accordingly.

The transversely occurring pretensioning force of the elastic belt is thereby advantageously reduced again, as viewed in the web running direction, between a variably adjustable tensioning roller arranged within the loop of the elastic belt and a guide roller arranged within the loop of the elastic belt.

After the elastic belt running through the guide roller is subjected to minimal or no pretensioning in the region of the guide roller, the pretensioning of the elastic belt between the tensioning roller and the guide roller can be continuously reduced.

According to a preferred practical embodiment of the method according to the invention for determining a relatively low machine or web running speed, preferably for a machine or web running speed of <1000m/min, a steam cushion between the fibrous web and the heated cylinder is generated in a nip which is arranged in a starting region, viewed in the web running direction, of a region of the heated cylinder which is enclosed by the fibrous web and the elastic belt, the nip being formed between the heated cylinder and a pressure roller which is arranged within the loop of the elastic belt and which is at the same time designed as a variably adjustable tensioning roller by means of which the elastic belt is prestressed in the transverse direction.

By designing the initial pressure roller, which is provided for forming the steam cushion between the fibrous web and the heated cylinder, at the same time as a variably adjustable tensioning roller, the elastic belt can be subjected to the respectively desired pretensioning in the transverse direction.

It is particularly advantageous here if, in the region of the heated cylinder which is surrounded by the fibrous web and the elastic band and which is located at the rear, viewed in the web direction of travel, a guide roller is provided within the loop of the elastic band, which guide roller holds the elastic band and the fibrous web on the heated cylinder, so that the transverse-direction-generating pretensioning force of the elastic band is already reduced again between a nip, which is provided in the initial region of the heated cylinder which is surrounded by the fibrous web and the elastic band, viewed in the web direction of travel, and a guide roller for generating transverse shrinkage of the fibrous web, which guide roller is provided in the region of the heated cylinder which is surrounded by the fibrous web and the elastic band and which is located at the rear, viewed in the web direction of travel.

The elastic belt is expediently removed again from the heated cylinder by a guide roller, which is arranged in the rear region of the heated cylinder enclosed by the fibrous web and the elastic belt, viewed in the web running direction, and the fibrous web is separated again from the elastic belt.

According to a preferred embodiment of the method according to the invention for determining a relatively high machine or web running speed, preferably for machine or web running speeds of >1000m/min, the fibrous web together with the prestressed elastic belt is first guided along a pretreatment or heating zone through a heated cylinder, so that a vapor cushion is formed between the fibrous web and the heated cylinder when the elastic belt is held prestressed.

In this case, a vapor mat is formed in the pretreatment or heating zone.

It is particularly advantageous here if an elastic band is supplied to the fibrous web which is brought into contact with the heated cylinder by means of a variably adjustable tensioning roller which pretensions the fibrous web and a nip is provided at the end of the pretreatment or heating zone to improve the adhesion of the fibrous web to the elastic band, which nip is formed between the heated cylinder and a pressure roller arranged within the ring of the elastic band, which pressure roller is at the same time designed as a variably adjustable tensioning roller for maintaining the pretensioning of the elastic band in the preceding pretreatment or heating zone, and the fibrous web is guided past the heated cylinder along a constriction zone after the nip provided at the end of the pretreatment or heating zone together with the elastic band, along which constriction zone the pretensioning of the elastic band for generating a transverse constriction of the fibrous web is reduced again.

A good adhesion between the fibrous web and the pretensioned elastic belt is thereby established by the nip arranged at the end of the pretreatment or heating zone. The presence of the steam cushion further ensures complete movability of the fibrous web relative to the heated cylinder while the fibrous web is reliably attached to the elastic belt.

The fibrous web is advantageously fed after the shrinkage zone together with the elastic band to a guide roller, by means of which the fibrous web and the elastic band are removed again from the heated cylinder and separated from each other.

The elastic band can still be loaded by the corresponding guide roller with a base stress which is smaller than the pretension by a defined amount.

The fibrous web that shrinks in the cross direction is preferably supplied to a re-drying section of the manufacturing machine, where the cross direction shrinkage is fixed.

The machine according to the invention for producing a fibrous web that can be stretched in the cross direction, in particular a paper or cardboard web that can be stretched in the cross direction, which is particularly suitable for carrying out the method according to the invention, is characterized in that the machine comprises a heated, water-vapor-impermeable and smooth rotating cylinder and a water-vapor-impermeable encircling elastic belt, wherein the fibrous web together with the elastic belt is guided laterally past the heated cylinder at a predetermined or predeterminable wrap angle between the elastic belt and the heated cylinder and is pressed onto the heated cylinder by the elastic belt, wherein the elastic belt can be acted on by a variably adjustable and/or controllable pretension in the cross direction before contact with the fibrous web, and wherein the pretension of the elastic belt generated in the cross direction can be reduced again after a steam cushion has been formed between the fibrous web and the heated cylinder, so that the fibrous web is shrunk in the cross direction by the steam cushion sliding on the heated cylinder together with the elastic belt.

A steel cylinder, in particular a chrome-plated steel cylinder, is preferably provided as the heating cylinder.

The elastic belt can expediently be pretensioned in the transverse direction by at least one variably adjustable tensioning roller arranged within its loop.

In this case, it is particularly advantageous if the transversely occurring pretensioning force of the elastic belt, as seen in the web running direction, can be reduced again between a variably adjustable tensioning roller arranged within the loop of the elastic belt and a guide roller arranged within the loop of the elastic belt.

According to a preferred embodiment of the machine according to the invention, which is determined for relatively low machine or web running speeds, preferably machine or web running speeds of <1000m/min, a steam cushion between the fibrous web and the heated cylinder is generated in a nip which is arranged in a starting region, viewed in the web running direction, of a region of the heated cylinder which is enclosed by the fibrous web and the elastic belt, the nip being formed between the heated cylinder and a pressure roller which is arranged within the loop of the elastic belt and which is at the same time designed as a variably adjustable tensioning roller by means of which the elastic belt is pretensioned in the transverse direction.

In this case, it is preferred that in the region of the heated cylinder which is surrounded by the fibrous web and the elastic belt and which is located at the rear, viewed in the web direction of travel, a guide roller is provided within the loop of the elastic belt which holds the elastic belt and the fibrous web on the heated cylinder, so that the transversely occurring pretensioning force of the elastic belt is already reduced again between a nip which is provided in the initial region of the heated cylinder which is surrounded by the fibrous web and the elastic belt, viewed in the web direction of travel, and a guide roller for generating a transverse contraction of the fibrous web, which guide roller is provided in the region of the heated cylinder which is surrounded by the fibrous web and the elastic belt and which guide roller is located at the rear, viewed in the web direction of travel.

The elastic belt is advantageously removed again from the heated cylinder by means of guide rollers which are arranged in the region of the heated cylinder enclosed by the fibrous web and the elastic belt which is located at the rear, as viewed in the web running direction, and is separated again from the elastic belt.

According to a preferred embodiment of the machine according to the invention for determining a relatively high machine or web running speed, preferably for machine or web running speeds >1000m/min, the fibrous web together with the pretensioned elastic belt is first guided along a pretreatment or heating zone past the heated cylinder, so that a vapor cushion is formed between the fibrous web and the heated cylinder when the elastic belt is held pretensioned.

It is particularly advantageous here if an elastic band can be supplied to the fibrous web which is brought into contact with the heated cylinder by means of a variably adjustable tensioning roller which pretensions the fibrous web and a nip is provided at the end of the pretreatment or heating zone to improve the adhesion of the fibrous web to the elastic band, which nip is formed between the heated cylinder and a pressure roller arranged within the loop of the elastic band, which pressure roller is in turn designed as a variably adjustable tensioning roller for maintaining the pretensioning of the elastic band in the preceding pretreatment or heating zone, and the fibrous web is guided past the heated cylinder along a constriction zone together with the elastic band after the nip provided at the end of the pretreatment or heating zone, along which constriction zone the pretensioning of the elastic band for generating a transverse constriction of the fibrous web can be reduced again.

The fibrous web is expediently supplied after the nip together with the elastic band to a guide roller, by means of which the fibrous web and the elastic band are removed again from the heated cylinder and separated from one another.

The pretensioning force of the elastic belt can advantageously be adjusted by means of tensioning bodies which are arranged laterally on the roller bodies of the respective tensioning roller and can be variably adjusted relative to the roller bodies in the cross-machine direction.

According to a preferred practical embodiment of the machine according to the invention, the elastic belt is provided with reinforcing threads extending at least substantially in the transverse direction with a correspondingly adapted modulus of elasticity or, in particular, a correspondingly adapted thread layer with respect to its thread density, in order to influence the transverse strain of the fibrous web symmetrically with respect to a central longitudinal axis of the elastic belt parallel to the machine running direction.

It is also particularly advantageous here if the reinforcing threads or thread layers of the elastic band extending in the transverse direction are adapted accordingly to compensate for the basin-like shrinkage curve which usually occurs in the transverse direction when drying the fibrous web.

Furthermore, the elastic belt may also be provided with reinforcing threads extending at least substantially in the machine running direction.

The elastic band suitably consists at least substantially of rubber.

The elastic band preferably has a hardness in the range of 55+/-10 Shore hardness (107P and J).

It is also advantageous that the elastic belt has a thickness of about 1.2kg/dm ³ To about 1.5kg/dm ³ Density in the range of (1).

The elastic band advantageously has a thickness in the range of about 20mm to about 30mm, wherein the elastic band preferably has a thickness of about 25 mm.

A further advantageous embodiment of the machine according to the invention is characterized in that,

-the dry weight content of the fibrous web supplied to the heated cylinder is in the range of about 50% to about 65% and/or

The heatable cylinder has a diameter in the range of about 900mm to about 1500mm and/or

-the surface temperature of the heated cylinder is >110 ℃ and especially in the range of 110 ° to about 125 °, and/or

The pre-treatment or heating zone extends over about 30 DEG and/or

The constriction region extends over about 20 °, and/or

The average linear force in a nip, which is arranged in the starting region of the heated cylinder enclosed by the fibrous material web and the elastic band, viewed in the web running direction, is at most 50kN/m, and/or

The dwell time of the fibrous web in a nip, which is arranged in a starting region of a region of the heated cylinder enclosed by the fibrous web and the elastic belt, viewed in the web running direction, is about 0.1 second, and/or

-the average linear force in the nip arranged at the end of the pretreatment or heating zone is at most 50kN/m.

The invention is explained in more detail below with reference to embodiments and with reference to the drawings; in the drawings:

figure 1 shows a schematic view of an exemplary embodiment of the machine according to the invention which is suitable in particular for relatively low machine or web running speeds, preferably for machine or web running speeds <1000m/sec,

figure 2 shows a schematic view of another exemplary embodiment of the machine according to the invention, which is suitable in particular for relatively high machine or web running speeds, preferably for machine or web running speeds >1000m/sec,

figure 3 shows a schematic partial view in cross section of an exemplary tensioning roller of the machine according to the invention,

figure 4 shows a schematic partial view of an exemplary guide roll of the machine according to the invention in cross section,

fig. 5 shows a schematic partial view of an exemplary design of an elastic band of a machine according to the invention, with reinforcing threads extending in the transverse direction and reinforcing threads extending in the longitudinal direction,

figure 6 shows an exemplary course of the modulus of elasticity of reinforcing threads running in the transverse direction respectively, arranged symmetrically with respect to the central longitudinal axis of the belt according to figure 5,

figure 7 shows a schematic partial view of an exemplary design of an elastic belt with a thread layer of a machine according to the invention,

fig. 8 shows a schematic course of the transverse-direction-occurring basin-like shrinkage curve of the fibrous web in solid lines and an exemplary schematic course of the transverse-direction-occurring stress or strain behavior of the elastic band according to fig. 5 or 7 in dashed lines, and

fig. 9 shows a schematic representation of the shrinkage curve or strain behavior of the finished dried fiber or paper or cardboard web in the cross direction as produced by fig. 5 or 7.

Fig. 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 stretched in the cross direction, which can be, in particular, a paper or cardboard web that can be stretched in the cross direction.

The machine 10 comprises a heated, water-vapour impermeable and smooth rotating cylinder 14 and a water-vapour impermeable, circumferential elastic belt 16, respectively.

The fibrous web 12 is guided in each case together with the elastic band 16 across the heated cylinder 14 at a predetermined or predefinable wrap angle between the elastic band 16 and the heated cylinder 14 and is pressed onto the latter by the elastic band 16.

The elastic bands 16 can be acted upon in the cross direction by a variably adjustable and/or controllable pretensioning force before they come into contact with the fibrous web 12. After the steam cushion has been formed between the fibrous web 12 and the heated cylinder 14, the transverse pretension of the elastic belt 16 can be reduced again, so that the fibrous web 12 is shrunk in the transverse direction together with the elastic belt by the steam cushion sliding on the heated cylinder 14.

In the machine 10 shown in fig. 1, which is intended in particular for relatively low machine or web running speeds, preferably machine or web running speeds of <1000m/min, a steam cushion between the fibrous web 12 and the heated cylinder 14 is produced in a nip 18, which is arranged in a starting region, viewed in the web running direction I, of the region of the heated cylinder 14 enclosed by the fibrous web 12 and the elastic belt 16, said nip being formed between the heated cylinder 14 and a pressure roller 20 arranged within the loop of the elastic belt 16, which pressure roller is at the same time designed as a variably adjustable tensioning roller, by means of which the elastic belt 16 can be pretensioned in the transverse direction.

In the rear region of the heated cylinder 14 enclosed by the fibrous web 12 and the elastic belt 16, viewed in the web running direction I, a guide roller 22 is arranged within the loop of the elastic belt 16, which holds the elastic belt 16 and the fibrous web 12 on the heated cylinder 14, so that the transversely occurring pretensioning force of the elastic belt 16, which is arranged in the initial region of the heated cylinder 14 enclosed by the fibrous web 12 and the elastic belt 16, viewed in the web running direction I, is already reduced again between the nip 18, which is arranged in the rear region of the heated cylinder 14 enclosed by the fibrous web 12 and the elastic belt 16, viewed in the web running direction I, and the guide roller 22 for generating a transverse contraction of the fibrous web.

The elastic belt 16 is removed again from the heated cylinder 14 by means of guide rollers 22, which are arranged in the rear region of the heated cylinder 14 enclosed by the fibrous web 12 and the elastic belt 16, viewed in the web running direction I, and are separated again from the elastic belt 16.

In the machine 10 according to the fig. 2 determination for relatively high machine or web running speeds, preferably machine or web running speeds >1000m/min, the fibrous web 12 together with the prestressed elastic belt 16 is first guided through the heated cylinder 14 along the pretreatment or heating zone α, so that a vapor cushion is formed between the fibrous web 12 and the heated cylinder 14 when the elastic belt 16 is held prestressed.

The elastic belt 16 is supplied here to the fibrous web 12 which is brought into contact with the heated cylinder 14 by a variably adjustable tensioning roller 24 which pretensions the fibrous web 12. At the end of the pretreatment or heating zone α, a nip 26 is provided to improve the adhesion of the fibrous web 12 to the elastic belt 16, which nip is formed between the heated cylinder 14 and a pressure roller 28 arranged within the loop of the elastic belt 16, which pressure roller is at the same time designed as a variably adjustable tension roller in order to maintain the pretension of the elastic belt 16 in the previous pretreatment or heating zone α. After the nip 26 provided at the end of the pretreatment or heating zone α, the fibrous web 12 is guided together with the elastic belt 16 along the contraction zone β past the heated cylinder 14, along which the pretensioning force of the elastic belt 16 for generating the transverse contraction of the fibrous web 12 is reduced again.

After the contraction zone β, the fibrous web 12 is fed together with the elastic band 16 to the guide roller 30, by means of which the fibrous web 12 and the elastic band 16 are removed again from the heated cylinder 14 and separated from one another.

In both exemplary embodiments according to fig. 1 and 2, the elastic belt 16 can still be loaded by the

respective guide roller

22, 30 with a base stress that is smaller than the pretension by a defined amount.

Fig. 3 shows an exemplary embodiment of a tensioning roller a in a schematic partial view, which can also be used, for example, for the roller 20, which is simultaneously designed as a press roller, according to fig. 1, the tensioning roller 24, and the press roller 28, which is also simultaneously designed as a tensioning roller, according to fig. 2.

As can be seen from fig. 3, with such a tensioning roller a, the pretensioning force of the elastic belt 16 can be adjusted by means of tensioning bodies which are arranged laterally on the roller bodies and can be variably adjusted in the cross-machine direction relative to the roller bodies 32.

Fig. 4 shows a schematic embodiment of the guide roller B in a schematic partial view, which can be considered for example for the guide roller 22 according to fig. 1 and the guide roller 30 according to fig. 2. As can be seen from fig. 4, the elastic band 16 can still be loaded with a base stress smaller than the pretension by a defined amount Δ L for such a guide roller B.

The respective bearing structure 36 of the respective roller a or B can also be seen in fig. 3 and 4.

Fig. 5 shows in a schematic partial view an exemplary embodiment of an elastic band 16 of the machine according to the invention with reinforcing threads 38 running in the cross direction CD and reinforcing threads 40 running in the machine direction MD. The reinforcing threads 38 extending in the cross direction CD and arranged symmetrically with respect to the central longitudinal axis L are provided with a correspondingly adapted modulus of elasticity E in order to influence the cross-direction strain of the fibrous web 12 in a targeted manner. The reinforcing threads 38 of the elastic band 16 extending in the cross direction CD can be adapted accordingly in this case in order, in particular, to compensate for the basin-like shrinkage curve 42 (see solid line in fig. 8) which usually occurs in the cross direction when drying the fibrous web 12.

Fig. 6 shows a schematic extension of the modulus of elasticity E of the reinforcing threads running in the transverse direction, respectively, arranged relative to the central longitudinal axis L of the elastic band 16 according to fig. 5.

Fig. 7 shows, in a schematic partial view, an exemplary embodiment of the elastic belt 16 of the machine according to the invention with a thread layer 44, in which a desired shaping contour can be achieved by means of a variable thread density in order to influence the transverse strain of the fibrous web in a targeted manner. The thread density is for example higher in the left part of fig. 7, in the middle range and relatively lower in the right part of fig. 7. Such a thread layer 44 can also be adapted accordingly to compensate for the basin-like shrinkage curve 42 that usually occurs in the cross direction when drying the fibrous web 12, which in the present case is achieved in particular by a variable thread density.

As already mentioned, fig. 8 shows a schematic course of the basin-like contraction curve 42 of the fibrous web 12, which is generally produced in the cross direction CD, in solid lines. Fig. 8 shows in dash-dot lines an exemplary schematic course of the stress or strain behavior in the cross direction CD of the elastic band according to fig. 5 and 7. In particular, the course of the transverse strain epsilon of the fibrous web 12 dried in a conventional manner (see solid line 42) and the course of the transverse strain epsilon of the elastic band 16 according to fig. 5 and fig. 7 (dash-dot line 46) are shown.

Fig. 9 shows the compensated shrinkage curve 48 or strain characteristic of the finished dried fibrous or paper or cardboard web 12 that can be achieved by the elastic band 16 according to fig. 5 and 7. The hitherto customary basin-like structure is avoided here.

List of reference numerals

10. Machine with a rotatable shaft

12. Fibrous web

14. Heated cylinder

16. Elastic band

18. Nip area

20. Squeeze roll

22. Guide roller

24. Tension roller

26. Nip area

28. Squeeze roll

30. Guide roller

32. Roller body

34. Tensioning head

36. Supporting structure

38. Reinforcing threads extending in transverse direction

40. Reinforcing threads extending in longitudinal direction

42. Shrinkage curve

44. Silk thread layer

46. CD strain of elastic band

48. Shrinkage curve

Direction of travel of the I web

A tensioning roller

B guide roller

CD transverse direction

E modulus of elasticity

MD machine direction

L central longitudinal axis

Delta stress difference

Alpha pre-treatment or heating zone

Beta-constriction region

Epsilon transverse strain

Claims

1. Method for producing a fibrous web (12) that can be stretched in the cross direction, in particular a paper or cardboard web that can be stretched in the cross direction, in which method the fibrous web (12) coming from a pre-drying section of an associated production machine (10) is brought into contact with a heated, water-vapor-impermeable and smooth rotating cylinder (14) and, together with a water-vapor-impermeable encircling elastic belt (16), is guided laterally past the heated cylinder (14) over a predetermined or predeterminable wrap angle between the elastic belt (16) and the heated cylinder (14) and is pressed onto the heated cylinder by the elastic belt (16), the elastic belt (16) being subjected to a variably adjustable and/or controllable pretension in the cross direction before being brought into contact with the fibrous web (12), the pretension of the elastic belt (16) occurring in the cross direction being reduced again after a steam cushion has formed between the fibrous web (12) and the heated cylinder (14), so that the fibrous web (12) is shrunk together with the elastic belt (16) by the steam cushion sliding over the heated cylinder (14) in the cross direction.

2. Method according to claim 1, characterized in that a steel cylinder, in particular a chrome-plated steel cylinder, is used as the heated cylinder (14).

3. Method according to claim 1 or 2, characterized in that the elastic belt (16) is pretensioned in the transverse direction by means of at least one variably adjustable tensioning roller (a, 20, 24, 28) arranged inside the loop of the elastic belt.

4. A method as claimed in claim 3, characterized in that the cross-direction-generated pretension of the elastic belt (16) is reduced again, viewed in the web running direction (I), between a variably adjustable tensioning roller (a, 20, 28) arranged inside the loop of the elastic belt (16) and a guide roller (B, 22, 30) arranged inside the loop of the elastic belt (16).

5. Method according to one of the preceding claims, characterized in that a steam cushion between the fibrous web (12) and the heated cylinder (14) is generated in a nip (18) which is provided in a starting region of a region of the heated cylinder (14) enclosed by the fibrous web (12) and the elastic belt (16) as seen in the web running direction (I), in particular for relatively low machine or web running speeds, preferably for machine or web running speeds <1000m/min, which nip is formed between the heated cylinder (14) and a squeeze roller (20) arranged inside a loop of the elastic belt (16) which is at the same time designed as a variably adjustable tension roller by means of which the elastic belt (16) is pretensioned in the transverse direction.

6. A method according to claim 5, characterized in that guide rollers (B, 22) holding the elastic belt (16) and the fibrous web (12) on the heated cylinder (14) are provided within the loop of the elastic belt (16) in the rear region, viewed in the web running direction (I), of the region of the heated cylinder (14) surrounded by the fibrous web (12) and the elastic belt (16), so that the cross-direction-generated pretensioning of the elastic belt (16) has been lowered again between a nip (18), which is provided in the initial region, viewed in the web running direction (I), of the region of the heated cylinder (14) surrounded by the fibrous web (12) and the elastic belt (16), and a guide roller (B, 22) for generating a cross-direction contraction of the fibrous web (12), which is provided in the rear region, viewed in the web running direction (I), of the region of the heated cylinder (14) surrounded by the fibrous web (12) and the elastic belt (16).

7. The method according to claim 6, characterized in that the elastic belt (16) is removed again from the heated cylinder (14) by means of guide rollers (B, 22) which are arranged in the rear region of the heated cylinder (14) enclosed by the fibrous web (12) and the elastic belt (16) as viewed in the web running direction (I) and the fibrous web (12) is separated again from the elastic belt (16).

8. Method according to one of claims 1 to 4, characterized in that, in particular for relatively high machine or web running speeds, preferably machine or web running speeds >1000m/min, the fibrous web (12) together with the pretensioned elastic belt (16) is first guided through the heated cylinder (14) along a pretreatment or heating zone (α) so that a vapour cushion is formed between the fibrous web (12) and the heated cylinder (14) when the elastic belt (16) is held pretensioned.

9. The method according to claim 8, characterized in that the elastic belt (16) is supplied to the fibrous web (12) which is brought into contact with the heated cylinder (14) by variably adjustable tensioning rollers (A, 24) which pretension the fibrous web (12) and which provide a nip (26) at the end of the pretreatment or heating zone (a) to improve the adhesion of the fibrous web (12) on the elastic belt (16), the nip being formed between the heated cylinder (14) and a pressing roller (28) arranged inside the loop of the elastic belt (16), which pressing roller is at the same time designed as a variably adjustable tensioning roller (A) for maintaining the pretension of the elastic belt (16) in the preceding pretreatment or heating zone (a), and the fibrous web (12) after the nip (26) provided at the end of the pretreatment or heating zone (a) continues with the elastic belt (16) through the heated cylinder (14) along a contraction zone (β), the contraction of the elastic belt (16) for generating a transverse reduction of the contraction of the fibrous web (12).

10. The method according to claim 9, characterized in that the fibrous web (12) is supplied after the constriction zone (β) together with the elastic belt (16) to a guide roller (B, 30), by means of which the fibrous web (12) and the elastic belt (16) are removed again from the heated cylinder (14) and separated from each other.

11. Method according to one of the preceding claims, characterized in that the elastic belt (16) is still loaded by the respective guide roller (B, 22, 30) with a base stress smaller than the pretension by a defined amount (Δ L).

12. A machine (10) for producing a fibrous web (12) that can be stretched in the cross direction, in particular a paper or cardboard web that can be stretched in the cross direction, in particular for carrying out the method according to one of the preceding claims, comprising a heated, water-vapor-impermeable and smooth rotating cylinder (14) and a water-vapor-impermeable encircling elastic belt (16), wherein the fibrous web (12) together with the elastic belt (16) is guided laterally over the heated cylinder (14) at a preset or presettable wrap angle between the elastic belt (16) and the heated cylinder (14) and is pressed onto the heated cylinder (14) by the elastic belt (16), the elastic belt (16) being loadable in the cross direction by a variably adjustable and/or controllable pretension before contact with the fibrous web (12), and after forming a steam cushion between the fibrous web (12) and the heated cylinder (14), the pretension of the elastic belt (16) in the cross direction being reducible again so that the fibrous web (12) slides together with the heated cylinder (14) in the cross direction by the heating of the elastic belt (16).

13. The machine according to claim 12, characterized in that a steam cushion between the fibrous web (12) and the heated cylinder (14) is generated in a nip (18) which is provided in a starting region of a region of the heated cylinder (14) enclosed by the fibrous web (12) and the elastic belt (16) as viewed in the web running direction (I), in particular for relatively low machine or web running speeds, preferably <1000m/min, which nip is formed between the heated cylinder (14) and a pressure roller (20) arranged inside the loop of the elastic belt (16) and which is at the same time designed as a variably adjustable tensioning roller (a) by means of which the elastic belt (16) can be pretensioned in the transverse direction.

14. The machine according to claim 12 or 13, characterized in that, in particular for relatively high machine or web running speeds, preferably for machine or web running speeds >1000m/min, the fibrous web (12) together with a pretensioned elastic belt (16) is first guided past the heated cylinder (14) along a pretreatment or heating zone (a) so that a vapor cushion is formed between the fibrous web (12) and the heated cylinder (14) when the elastic belt (16) is held pretensioned, and/or the elastic belt (16) can be supplied by pretensioning variably adjustable tensioning rollers (a, 24) of the fibrous web (12) to a fibrous web (12) which is in contact with the heated cylinder (14) and a nip (26) is provided at the end of the pretreatment or heating zone (a) to improve the adhesion of the fibrous web (12) on the elastic belt (16), which nip is formed between the heated cylinder (14) and a pressing roller (28) arranged inside a loop of the elastic belt (16), and the nip (16) is designed to be adjusted again after the pretreatment or heating zone (16) is held with the nip (16) in front of the elastic belt (16) and the nip (16) is held with the pretreatment or pressing roller (a nip (28) in front of the elastic belt (16), and the nip (16) and the nip (a nip is adjusted again with the nip (16) and the nip (16) is designed to maintain the nip (a) in front of the nip (a nip of the nip or the nip of the elastic belt The pretension of the elastic belt (16) for producing the transverse contraction of the fibrous web (12) is reduced again along the contraction zone (β) as the heated cylinder (14) is passed further along the contraction zone.

15. The machine according to one of the preceding claims 12 to 14, characterized in that the elastic belt (16) is provided with reinforcing threads (38) having a correspondingly adapted modulus of elasticity (E) or, in particular, a correspondingly adapted thread layer (44) in terms of its thread density, extending at least substantially in the Cross Direction (CD), so that the cross-direction stretching of the fibrous web (12) is effected symmetrically with respect to a central longitudinal axis (L) of the elastic belt (16) parallel to the machine running direction (MD).

16. The machine according to one of the preceding claims 12 to 15, characterized in that the dry weight content of the fibrous web (12) supplied to the heated cylinder (14) is in the range of about 50% to about 65%, and/or

The heatable cylinder (14) has a diameter in the range of about 900mm to about 1500mm, and/or

The surface temperature of the heated cylinder (14) is greater than 110 ℃ and especially in the range of 110 DEG to about 125 DEG, and/or

The pre-treatment or heating zone (alpha) extends over about 30 DEG and/or

The constriction zone (β) extends over a range of about 20 °, and/or

The average linear force in the press nip (18) is at most 50kN/m, the press nip is arranged in a starting region of a region of the heated cylinder (14) enclosed by the fibrous material web (12) and the elastic belt (16) as viewed in a web running direction (I), and/or

The dwell time of the fibrous material web (12) in a nip (18) which is arranged in a starting region of a region of the heated cylinder (14) enclosed by the fibrous material web (12) and the elastic band (16) as viewed in a web running direction (I) and/or in which the dwell time is about 0.1 seconds

The average linear force in the nip (26) arranged at the end of the pre-treatment or heating zone (a) is at most 50kN/m.