EP4158098B1 - Method and machine for producing a fibrous web which can be elongated in the transverse direction - Google Patents

Description

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

To date, there is no tool for directly controlling or adjusting the cross-extension properties (CD elasticity) of paper. The shrinkage curve or CD shrinkage profile (CD = cross direction) resulting in the cross direction still determines these cross-extension properties as a result of paper drying. As a result, the papermaker has so far only had the option of influencing the CD elasticity or CD shrinkage profile at the expense of web stabilization using web stabilization boxes, which is not a satisfactory measure. The machine manufacturer can, of course, influence the CD shrinkage profile roughly via the drying concept, in particular a single-row or double-row drying section. However, compromises have to be made here too.

Reduced stretch properties or too little elasticity have a particularly negative effect on corrugated cardboard base paper. The corrugated cardboard can break when being creasing, making it unusable as waste. A brittle corrugated cardboard box will burst when subjected to impact because the impact energy cannot be absorbed. In addition, when the corrugation is made from the corrugated material web, the web can break when being corrugated with the corrugating roller if the elasticity is too low. Excessive brittleness is therefore counterproductive here too.

The well-known Clupak system is used to specifically adjust the paper's longitudinal stretch (MD elasticity; MD = machine direction) or to produce a longitudinal micro crepe. The still-moist web runs through a press nip together with a rubber blanket, stretching both. After the nip, the blanket shortens again and the desired micro crepe is created in the web. The state of the art includes the publications US 3 148 108 A , WO 2011/151705 A2 and WO99/32722 A1 .

The invention is based on the object of specifying a method and a machine of the type mentioned at the beginning, with which the disadvantages mentioned above are eliminated. In particular, the elasticity or transverse stretching properties resulting in the transverse direction and the work absorption of the fibrous web in the transverse direction should be able to be specifically controlled or adjusted or improved. In addition, a possibility should be created to counteract the increasingly declining quality of waste paper raw materials.

According to the invention, this object is achieved by a method having the features of claim 1 and a machine having the features of claim 12. Preferred embodiments of the method according to the invention and preferred embodiments of the machine according to the invention emerge from the subclaims, the present description and the drawing.

The method according to the invention for producing a transversely stretchable fibrous web, in particular a transversely stretchable paper or cardboard web, is characterized in that the fibrous web coming from a 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 circulating elastic band, is wound over a predetermined or predeterminable wrap angle between the elastic band and the heated cylinder, that is, the cylinder surface, is guided lying over the heated cylinder and pressed against it by the elastic band, the elastic band is subjected to a variably adjustable and/or controllable pre-tension in the transverse direction before being brought into contact with the fibrous web, and the pre-tension of the elastic band generated in the transverse direction is released again after a steam cushion has been formed between the fibrous web and the heated cylinder, so that the fibrous web shrinks in the transverse direction with the elastic band sliding over the steam cushion on the heated cylinder, in particular shrinks more strongly in a controlled manner.

With such an inventive design of the method, the elasticity or transverse stretching properties resulting in the transverse direction and the work absorption of the fibrous web in the transverse direction can now be specifically controlled, adjusted or improved. In addition, the possibility is created to counteract the increasingly declining quality of waste paper raw materials. The fibrous web coming from the pre-drying section runs onto the elastic belt pre-tensioned in the transverse direction. By reducing the pre-tension of the elastic belt after the steam cushion has formed between the fibrous web and the heated cylinder, the fibrous web can slide over the steam cushion on the heated cylinder and shrink with the elastic belt in the transverse direction to produce the microcrepe.

A steel cylinder, in particular a chrome-coated steel cylinder, is preferably used as the heated cylinder. With such a steel cylinder, in particular a chrome-coated steel cylinder, it is ensured that the fibrous web can slide optimally on it after the steam cushion has formed.

The elastic band is advantageously pre-tensioned in the transverse direction by at least one variably adjustable tensioning roller arranged within its loop.

With the transverse pre-tensioning that can be variably adjusted via the tensioning roller, the transverse shrinkage resulting after the pre-tensioning is reduced can be controlled or adjusted accordingly.

It is expedient for the pre-tension of the elastic band generated in the transverse direction to be reduced again in the direction of web travel between a variably adjustable tension roller arranged within the loop of the elastic band and a guide roller arranged within the loop of the elastic band.

After the elastic belt running over the guide roller is no longer subjected to minimal or no pre-tension in the area of this guide roller, its pre-tension between the tension roller and this guide roller can continuously decrease again.

According to a preferred practical embodiment of the method according to the invention, which is particularly intended for relatively low machine or web speeds, preferably for machine or web speeds < 1000 m/min, the steam cushion between the fibrous web and the heated cylinder is generated in a press nip provided in the initial area of the zone of the heated cylinder wrapped around the fibrous web and the elastic band, viewed in the web running direction, which is formed between the heated cylinder in a press roller arranged within the loop of the elastic band, which is simultaneously designed as a variably adjustable tension roller, by means of which the elastic band is pre-tensioned in the transverse direction.

By using the initial press roll, which is designed to form a steam cushion between the fibrous web and the heated cylinder, as a variable adjustable tension roller, the elastic band can be pre-tensioned to the desired extent in the transverse direction.

It is particularly advantageous if, in the rear area of the zone of the heated cylinder wrapped by the fibrous web and the elastic band, as viewed in the direction of web travel, a guide roller is provided within the loop of the elastic band to hold the elastic band and the fibrous web on the heated cylinder, so that the pre-tension of the elastic band generated in the transverse direction is already reduced between the press nip provided in the initial area of the zone of the heated cylinder wrapped by the fibrous web and the elastic band, as viewed in the direction of web travel, and the guide roller provided in the rear area of the zone of the heated cylinder wrapped by the fibrous web and the elastic band, as viewed in the direction of web travel, to generate the transverse shrinkage of the fibrous web.

In this case, the elastic band is expediently removed from the heated cylinder via the guide roller provided in the rear area of the zone of the heated cylinder wrapped around the fibrous web and the elastic band, as viewed in the direction of web travel, and the fibrous web is separated again from the elastic band.

According to a preferred practical embodiment of the method according to the invention, which is particularly intended for relatively high machine or web speeds, preferably for machine or web speeds > 1000 m/min, the fibrous web is first guided along a conditioning or warming-up zone over the heated cylinder together with the pre-tensioned elastic band to form the steam cushion between the fibrous web and the heated cylinder with the elastic band kept pre-tensioned.

In this case, the steam cushion is formed in the conditioning or warming zone.

It is particularly advantageous if the elastic band of the fibrous web brought into contact with the heated cylinder is fed via a variably adjustable tensioning roller that pre-tensions the fibrous web, and at the end of the conditioning or warming-up zone, a press nip is provided to increase the adhesion of the fibrous web to the elastic band, which is formed between the heated cylinder and a press roller arranged within the loop of the elastic band, which is simultaneously designed as a variably adjustable tensioning roller to maintain the pre-tension of the elastic band within the preceding conditioning or warming-up zone, and the fibrous web, following the press nip provided at the end of the conditioning or warming-up zone, is guided further over the heated cylinder together with the elastic band along a shrinking zone, along which the pre-tension of the elastic band is reduced again to produce the transverse shrinkage of the fibrous web.

The press nip provided at the end of the conditioning or warming-up zone thus creates good adhesion between the fibrous web and the pre-tensioned elastic band. While the fibrous web now adheres securely to the elastic band, the existing steam cushion ensures that the fibrous web continues to have full mobility relative to the heated cylinder.

In this case, the fibrous web together with the elastic band is advantageously fed to a guide roller after the shrinking zone, via which the fibrous web and the elastic band are removed from the heated cylinder and separated from each other.

The elastic band can be subjected to a basic tension that is smaller than the pre-tension by a defined amount by a respective guide roller.

Preferably, the transversely shrunk fibrous web is fed to a post-drying section of the production machine, where the transverse shrinkage is fixed.

The machine according to the invention, which is particularly suitable for carrying out the method according to the invention for producing a fibrous web that can be stretched in the transverse direction, in particular a paper or cardboard web that can be stretched in the transverse direction, is characterized in that it comprises a heated, water vapor-impermeable and smooth rotating cylinder and a water vapor-impermeable circumferential elastic band, wherein the fibrous web together with the elastic band is guided over the heated cylinder over a predetermined or predeterminable wrap angle between the elastic band and the heated cylinder and is pressed against it by the elastic band, the elastic band can be subjected to a variably adjustable and/or controllable pre-tension in the transverse direction before being brought into contact with the fibrous web, and the pre-tension of the elastic band generated in the transverse 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 shrinks in the transverse direction with the elastic band as it slides over the steam cushion onto the heated cylinder.

Preferably, a steel cylinder, in particular a chrome-coated steel cylinder, is provided as the heated cylinder.

The elastic band can expediently be pre-tensioned in the transverse direction by at least one variably adjustable tensioning roller arranged within its loop.

It is particularly advantageous if the pre-tension of the elastic band generated in the transverse direction can be removed again when viewed in the web running direction between a variably adjustable tension roller arranged within the loop of the elastic band and a guide roller arranged within the loop of the elastic band.

According to a preferred embodiment of the machine according to the invention, which is particularly intended for relatively low machine or web speeds, preferably for machine or web speeds < 1000 m/min, the steam cushion between the fibrous web and the heated cylinder is generated in a press nip provided in the initial area of the zone of the heated cylinder wrapped around the fibrous web and the elastic band, viewed in the web running direction, which is formed between the heated cylinder and a press roller arranged within the loop of the elastic band, which is simultaneously designed as a variably adjustable tension roller, by means of which the elastic band can be pre-tensioned in the transverse direction.

Preferably, in the rear region of the zone of the heated cylinder surrounded by the fibrous web and the elastic band, as viewed in the direction of web travel, a guide roller is provided within the loop of the elastic band, which holds the elastic band and the fibrous web on the heated cylinder, so that the pre-tension of the elastic band generated in the transverse direction is already present between the press nip provided in the initial region of the zone of the heated cylinder surrounded by the fibrous web and the elastic band, as viewed in the direction of web travel, and the press nip provided in the initial region of the zone of the heated cylinder surrounded by the fibrous web and the elastic band, as viewed in the direction of web travel. the rear area of the heated cylinder's zone surrounded by the fibrous web and the elastic band is removed again by the guide roller intended to generate the transverse shrinkage of the fibrous web.

The elastic band is advantageously removed from the heated cylinder and separated again from the elastic band via the guide roller provided in the rear area of the zone of the heated cylinder wrapped around the fibrous web and the elastic band, as viewed in the direction of web travel.

According to a preferred embodiment of the machine according to the invention, which is particularly intended for relatively high machine or web speeds, preferably for machine or web speeds > 1000 m/min, the fibrous web is first guided along a conditioning or warming-up zone over the heated cylinder together with the pre-tensioned elastic band to form the steam cushion between the fibrous web and the heated cylinder with the elastic band kept pre-tensioned.

It is particularly advantageous if the elastic band of the fibrous web brought into contact with the heated cylinder can be fed via a variably adjustable tensioning roller that pre-tensions the fibrous web, and at the end of the conditioning or warming-up zone, a press nip is provided to increase the adhesion of the fibrous web to the elastic band, which is formed between the heated cylinder and a press roller arranged within the loop of the elastic band, which is simultaneously designed as a variably adjustable tensioning roller to maintain the pre-tension of the elastic band within the preceding conditioning or warming-up zone, and the fibrous web, following the press nip provided at the end of the conditioning or warming-up zone, is guided further over the heated cylinder together with the elastic band along a shrinking zone, along the pre-tension of the elastic band for producing the transverse shrinkage of the fibrous web can be released again.

Conveniently, the fibrous web together with the elastic band is fed to a guide roller after the shrink zone, via which the fibrous web and the elastic band are removed from the heated cylinder and separated from each other.

The elastic band can be subjected to a basic tension by a respective guide roller that is smaller than the pre-tension by a defined amount.

Advantageously, the pre-tension of the elastic band can be adjusted via tensioning heads provided on the side of the roller body of each tensioning roller and which can be variably adjusted in the transverse direction of the machine relative to the roller body.

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

It is particularly advantageous if the elastic moduli of the reinforcing threads extending in the transverse direction or the thread structure of the elastic band are adapted accordingly to compensate for the trough-shaped shrinkage curve that normally occurs in the transverse direction when the fibrous web is dried.

In addition, the elastic band can also be provided with reinforcing threads extending at least substantially in the machine direction.

Conveniently, the elastic band consists at least essentially of rubber.

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

It is also advantageous if the elastic band has a density in the range of about 1.2 kg/dm ³ to about 1.5 kg/dm ³ .

Advantageously, the elastic band has a thickness in the range of about 20 mm to about 30 mm, preferably having a thickness of about 25 mm.

• der Trockengehalt der dem beheizten Zylinder zugeführten Faserstoffbahn im Bereich von etwa 50% bis etwa 65% liegt, und/oder
• der beheizbare Zylinder einen Durchmesser im Bereich von etwa 900 mm bis etwa 1500 mm besitzt, und/oder
• die Oberflächentemperatur des beheizten Zylinders >110° ist und insbesondere in einem Bereich zwischen 110° und etwa 125° liegt, und/oder
• sich die Konditionier- oder Aufwärmzone über etwa 30° erstreckt und/oder
• sich die Schrumpfzone über etwa 20° erstreckt, und/oder
• die mittlere Linienkraft im in Bahnlaufrichtung betrachtet anfänglichen Bereich der von der Faserstoffbahn und dem elastischen Band umschlungenen Zone des beheizten Zylinders vorgesehenen Pressnip maximal 50 kN/m beträgt, und/oder
• die Verweilzeit der Faserstoffbahn im in Bahnlaufrichtung betrachtet anfänglichen Bereich der von der Faserstoffbahn und dem elastischen Band umschlungenen Zone des beheizten Zylinders vorgesehenen Pressnip etwa 0,1 sec beträgt, und/oder
• die mittlere Linienkraft im am Ende der Konditionier- oder Aufwärmzone vorgesehenen Pressnip maximal 50 kN/m beträgt.

Further 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 about 50% to about 65%, and/or
• the heatable cylinder has a diameter in the range of about 900 mm to about 1500 mm, and/or
• the surface temperature of the heated cylinder is >110° and in particular lies in a range between 110° and about 125°, and/or
• the conditioning or warm-up zone extends over approximately 30° and/or
• the shrinkage zone extends over approximately 20°, and/or
• the mean line force in the initial area of the fibrous web and the elastic band viewed in the direction of web travel the press nip provided for in the wrapped zone of the heated cylinder is a maximum of 50 kN/m, and/or
• the residence time of the fibrous web in the initial area of the zone of the heated cylinder surrounded by the fibrous web and the elastic band, viewed in the direction of web travel, 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.

Fig. 1

eine schematische Darstellung einer insbesondere für relativ niedrigere Maschinen- oder Bahnlaufgeschwindigkeiten, vorzugsweise für Maschinen- bzw. Bahnlaufgeschwindigkeiten < 1000 m/sec geeigneten beispielhaften Ausführungsform einer erfindungsgemäßen Maschine,

Fig. 2

eine schematische Darstellung einer insbesondere für relativ höhere Maschinen- oder Bahnlaufgeschwindigkeiten, vorzugsweise für Maschinen- bzw. Bahnlaufgeschwindigkeiten > 1000 m/sec geeigneten weiteren beispielhaften Ausführungsform einer erfindungsgemäßen Maschine,

Fig. 3

eine schematische Teildarstellung einer beispielhaften Spannwalze der erfindungsgemäßen Maschine im Querschnitt,

Fig. 4

eine schematische Teildarstellung einer beispielhaften Leitwalze der erfindungsgemäßen Maschine im Querschnitt,

Fig. 5

eine schematische Teildarstellung einer beispielhaften Ausführung des elastischen Bandes einer erfindungsgemäßen Maschine mit sich in Querrichtung erstreckenden Verstärkungsfäden und sich in Längsrichtung erstreckenden Verstärkungsfäden,

Fig. 6

einen beispielhaften Verlauf der Elastizitätsmodule der symmetrisch zur Mittenlängsachse des Bandes gemäß Fig. 5 vorgesehenen, sich jeweils in Querrichtung erstreckenden Verstärkungsfäden,

Fig. 7

eine schematische Teildarstellung einer beispielhaften Ausführung des elastischen Bandes einer erfindungsgemäßen Maschine mit einem Fadengelege,

Fig. 8

mit der durchgehenden Linie den schematischen Verlauf der sich in Querrichtung üblicherweise ergebenden wannenartigen Schrumpfkurve der Faserstoffbahn und mit der gestrichelten Linien einen beispielhaften schematischen Verlauf des sich in Querrichtung ergebenden Spannungs- oder Dehnungsverhaltens eines elastischen Bandes gemäß den Fig. 5 oder 7, und

Fig. 9

eine schematische Darstellung einer sich in Querrichtung mit einem elastischen Band gemäß den Fig. 5 oder 7 ergebenden Schrumpfkurve oder Dehnungsverhalten der fertig getrockneten Faserstoff- bzw. Papier- oder Kartonbahn.

The invention is explained in more detail below using exemplary embodiments with reference to the drawing, in which:

Fig.1

a schematic representation of an exemplary embodiment of a machine according to the invention, particularly suitable for relatively low machine or web speeds, preferably for machine or web speeds < 1000 m/sec,

Fig.2

a schematic representation of a further exemplary embodiment of a machine according to the invention, particularly suitable for relatively higher machine or web speeds, preferably for machine or web speeds > 1000 m/sec,

Fig.3

a schematic partial representation of an exemplary tension roller of the machine according to the invention in cross section,

Fig.4

a schematic partial representation of an exemplary guide roller of the machine according to the invention in cross section,

Fig.5

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

Fig.6

an exemplary course of the elastic moduli symmetrical to the central longitudinal axis of the band according to Fig.5 provided reinforcing threads extending in the transverse direction,

Fig.7

a schematic partial representation of an exemplary embodiment of the elastic belt of a machine according to the invention with a thread layer,

Fig.8

with the solid line the schematic course of the trough-like shrinkage curve of the fibrous web that usually occurs in the transverse direction and with the dashed line an exemplary schematic course of the tension or elongation behavior of an elastic band in the transverse direction according to the Fig. 5 or 7 , and

Fig.9

a schematic representation of a transversely arranged elastic band according to the Fig. 5 or 7 resulting shrinkage curve or expansion behaviour of the dried fibre, paper or cardboard web.

The Fig. 1 and 2 each show an exemplary embodiment of a machine 10 according to the invention for producing a transversely stretchable fibrous web 12, which can in particular be a transversely stretchable paper or cardboard web.

The machines 10 each comprise a heated, water vapor impermeable and smooth rotating cylinder 14 and a water vapor impermeable circumferential elastic belt 16.

In this case, the fibrous web 12 is guided together with the elastic band 16 over a predetermined or predeterminable wrap angle between the elastic band 16 and the heated cylinder 14 over the heated cylinder 14 and pressed against it by the elastic band 16.

The elastic band 16 can be subjected to a variably adjustable and/or controllable pre-tension in the transverse direction before it is brought into contact with the fibrous web 12. The pre-tension of the elastic band 16 generated in the transverse direction can be removed again after a steam cushion has been formed between the fibrous web 12 and the heated cylinder 14, so that the fibrous web 12 shrinks in the transverse direction with the elastic band, sliding over the steam cushion on the heated cylinder 14.

At the Fig.1 In the machine 10 shown, which is designed in particular for relatively low machine or web speeds, preferably for machine or web speeds < 1000 m/min, the steam cushion between the fibrous web 12 and the heated cylinder 14 is generated in a press nip 18 provided in the initial region of the zone of the heated cylinder 14 wrapped around by the fibrous web 12 and the elastic band 16, viewed in the web running direction I, which is formed between the heated cylinder 14 and a press roller 20 arranged within the loop of the elastic band 16, which is simultaneously designed as a variably adjustable tension roller, by means of which the elastic band 16 can be pre-tensioned in the transverse direction.

In the rear area of the zone of the heated cylinder 14 wrapped by the fibrous web 12 and the elastic band 16, as viewed in the web travel direction I, a guide roller 22 is provided within the loop of the elastic band 16 to hold the elastic band 16 and the fibrous web 12 on the heated cylinder 14, so that the pre-tension of the elastic band 16 generated in the transverse direction is already reduced between the press nip 18 provided in the initial area of the zone of the heated cylinder 14 wrapped by the fibrous web 12 and the elastic band 16, as viewed in the web travel direction I, and the guide roller 22 provided in the rear area of the zone of the heated cylinder 14 wrapped by the fibrous web 12 and the elastic band 16, as viewed in the web travel direction I, to generate the transverse shrinkage of the fibrous web 12.

The elastic band 16 is removed from the heated cylinder 14 again via the guide roller 22 provided in the rear area of the zone of the heated cylinder 14 wrapped around by the fibrous web 12 and the elastic band 16, as viewed in the web travel direction I, and is separated again from the elastic band 16.

In contrast, in the case of the machine 10 designed in particular for relatively higher machine or web speeds, preferably for machine or web speeds > 1000 m/min, according to Fig.2 the fibrous web 12 together with the pre-tensioned elastic band 16 is initially guided along a conditioning or warming-up zone α over the heated cylinder 14 to form the steam cushion between the fibrous web 12 and the heated cylinder 14 with the elastic band 16 kept pre-tensioned.

The elastic band 16 is fed to the fibrous web 12 brought into contact with the heated cylinder 14 via a variably adjustable tensioning roller 24 which pre-tensions the fibrous web 12. At the end of the conditioning or In the heating zone α, a press nip 26 is provided to increase the adhesion of the fibrous web 12 to the elastic band 16. This press nip is formed between the heated cylinder 14 and a press roller 28 arranged within the loop of the elastic band 16, which is simultaneously designed as a variably adjustable tension roller to maintain the pre-tension of the elastic band 16 within the preceding conditioning or heating zone α. Following the press nip 26 provided at the end of the conditioning or heating zone α, the fibrous web 12 is guided along a shrink zone β over the heated cylinder 14 together with the elastic band 16, along which the pre-tension of the elastic band 16 can be reduced again to produce the transverse shrinkage of the fibrous web 12.

Following the shrinking zone β, the fibrous web 12 is fed together with the elastic band 16 to a guide roller 30, via which the fibrous web 12 and the elastic band 16 are again removed from the heated cylinder 14 and separated from each other.

In the two exemplary embodiments according to the Fig. 1 and 2 the elastic band 16 can be subjected to a basic tension which is smaller than the pre-tension by a defined amount by a respective guide roller 22, 30.

Fig.3 shows a schematic partial representation of an exemplary embodiment of a tension roller A, as for example for the roller 20, which is also designed as a press roller, according to Fig.1 , the tension roller 24 and the press roller 28, which is also designed as a tension roller, according to Fig.2 is possible.

As shown by the Fig.3 As can be seen, in such a tension roller A the pre-tension of the elastic band 16 is via the side of the roller body 32 provided clamping heads 34 which are variably adjustable in the machine transverse direction relative to the roller body 32.

In contrast, Fig.4 in a schematic partial representation an exemplary embodiment of a guide roller B, as for example for the guide roller 22 according to Fig.1 and the guide roller 30 according to Fig.2 is conceivable. As can be seen from this Fig.4 As can be seen, even with such a guide roller B, the elastic band 16 can still be subjected to a basic tension which is smaller than the pre-tension by a defined amount ΔL.

In both Fig. 3 and 4 The respective bearing 36 of the respective roller A or B can also be seen.

Fig.5 shows a schematic partial representation of an exemplary embodiment of the elastic band 16 of a machine according to the invention with reinforcing threads 38 extending in the transverse direction CD and reinforcing threads 40 extending in the longitudinal direction MD. The reinforcing threads 38 extending in the transverse direction CD, arranged symmetrically to the central longitudinal axis L, are provided with appropriately adapted elasticity moduli E for the targeted influencing of the transverse expansion of the fibrous web 12. The elasticity moduli E of the reinforcing threads 38 of the elastic band 16 extending in the transverse direction CD can be used in particular to compensate for the trough-shaped shrinkage curve 42 that normally occurs in the transverse direction when drying the fibrous web 12 (cf. the solid line in Fig.8 ) must be adjusted accordingly.

An exemplary course of the elastic moduli E symmetrical to the central longitudinal axis L of the elastic band 16 according to Fig.5 The reinforcement threads provided, each extending in the transverse direction, are in Fig.6 reproduced.

Fig.7 shows a schematic partial representation of an exemplary embodiment of the elastic belt 16 of a machine 10 according to the invention with a thread layer 44, in which the desired profiling for the targeted influencing of the transverse stretch of the fibrous web can be achieved via a variable thread density. In the left part of this Fig.7 For example, the thread density is high, in the middle it is in the middle area, and in the right part of the Fig.7 the thread density is relatively low. Such a thread layer 44 can also be adapted accordingly to compensate for the trough-shaped shrinkage curve 42 that normally occurs in the transverse direction when the fibrous web 12 is dried, which in the present case is possible in particular by means of a variable thread density.

As already mentioned, Fig.8 with the solid line the schematic course of the trough-shaped shrinkage curve 42 of the fibrous web 12, which usually occurs in the transverse direction CD. In contrast, in this Fig.8 The dashed line shows an exemplary schematic progression of the stress or strain behaviour of an elastic band in the transverse direction CD according to the Fig. 5 and 7 In particular, the course of the transverse elongation ε of a conventionally dried fibrous web 12 (see the solid line 42) and the course of the transverse elongation ε of an elastic band 16 according to the Fig. 5 and 7 (dashed line 46).

Fig.9 shows a with an elastic band 16 according to the Fig. 5 and 7 achievable balanced shrinkage curve 48 or expansion behavior of the completely dried fiber or paper or cardboard web 12. The previously common trough formation is thereby avoided.

List of reference symbols

10

machine

12

Fibrous web

14

heated cylinder

16

elastic band

18

Press nip

20

Press roller

22

Guide roller

24

Tension roller

26

Press nip

28

Press roller

30

Guide roller

32

Roller body

34

Clamping head

36

storage

38

Reinforcing thread running in transverse direction

40

longitudinal reinforcing thread

42

Shrinkage curve

44

Scrim

46

CD stretch of the elastic band

48

Shrinkage curve

I

Web direction

A

Tension roller

B

Guide roller

CD

Transverse direction

E

modulus of elasticity

MD

Longitudinal direction

L

Central longitudinal axis

Δ

Differential voltage

α

Conditioning or warm-up zone

β

Shrinkage zone

ε

Transverse strain

Claims (16)

1. Method for producing a web (12) which can be elongated in the cross direction, in particular a paper or cardboard web which can be elongated in the cross direction, in which the web (12) coming from a predrying section of the relevant production machine (10) is brought into contact with a heated, water vapour-impermeable and smooth rotating cylinder (14) and is guided together with a water vapour-impermeable circumferential elastic band (16) over a predetermined or predeterminable wrap angle lying between the elastic band (16) and the heated cylinder (14) above the heated cylinder (14) and is pushed by the elastic band (16) against the latter, characterized in that the elastic band (16) is subjected to a variably adjustable and/or controllable pretensioning in the cross direction before bringing it into contact with the web (12), and the pretensioning of the elastic band (16) generated in the cross direction is reduced again after the formation of a vapour cushion between the web (12) and the heated cylinder (14) so that the web (12) shrinks in the cross direction sliding over the vapour cushion on the heated cylinder (14) with the elastic band (16) .
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 band (16) is pretensioned in the cross direction by at least one variably adjustable tension roller (A, 20, 24, 28) arranged within its loop.
4. Method according to Claim 3, characterized in that the pretensioning of the elastic band (16) generated in the cross direction, viewed in the web travel direction (I), between a variably adjustable tension roller (A, 20, 28) arranged within the loop of the elastic band (16) and a guide roller (B, 22, 30) arranged within the loop of the elastic band (16) is reduced again.
5. Method according to any one of the preceding claims, characterized in that in particular for relatively lower machine or web travel speeds, preferably for machine or web travel speeds < 1000 m/min, the vapour cushion between the web (12) and the heated cylinder (14) is generated in a press nip (18) provided in an initial region, viewed in the web travel direction (I), of the zone of the heated cylinder (14) wrapped by the web (12) and the elastic band (16), which press nip is formed between the heated cylinder (14) and a press roller (16) arranged within the loop of the elastic band (16), which press roller (20) is at the same time embodied as a variably adjustable tension roller by which the elastic band (16) is pretensioned in the cross direction.
6. Method according to Claim 5, characterized in that a guide roller (B, 22) which holds the elastic band (16) and the web (12) on the heated cylinder (14) is provided in the rear region, viewed in the web travel direction (I), of the zone wrapped by the web (12) and the elastic band (16) of the heated cylinder (14) within the loop of the elastic band (16) so that the pretensioning generated in the cross direction of the elastic band (16) is already reduced again between the press nip (18) provided in an initial region, viewed in the web travel direction (I), of the zone of the heated cylinder (14) wrapped by the web (12) and the elastic band (16) and the guide roller (B, 22) provided in the rear region, viewed in the web travel direction (I), of the zone of the heated cylinder (14) wrapped by the web (12) and the elastic band (16) in order to generate the cross shrinkage of the web (12).
7. Method according to Claim 6, characterized in that the elastic band (16) is removed from the heated cylinder (14) again via the guide roller (B, 22) provided in the rear region, viewed in the web travel direction (I), of the zone of the heated cylinder (14) wrapped by the web and the elastic band (16) and the web (12) is separated again from the elastic band (16) .
8. Method according to any one of Claims 1 to 4, characterized in that, in particular for relatively higher machine or web travel speeds, preferably for machine or web travel speeds > 1000 m/min, the web (12) is guided together with the pretensioned elastic band (16) for the formation of the vapour cushion between the web (12) and the heated cylinder (14) in the case of an elastic band (16) which is held in a pretensioned state firstly along a conditioning or warm-up zone (α) over the heated cylinder (14).
9. Method according to Claim 8, characterized in that the elastic band (16) is fed to the web (12) brought into contact with the heated cylinder (14) via a variably adjustable tension roller (A, 24) which pretensions the web (12) and a press nip (26) is provided at the end of the conditioning or warm-up zone (α) in order to increase the adhesion of the web (12) to the elastic band (16), which press nip (26) is formed between the heated cylinder (14) and a press roller (28) arranged within the loop of the elastic band (16), which press roller (28) is embodied to maintain the pretensioning of the elastic band (16) within the previous conditioning or warm-up zone (α) simultaneously again as a variably adjustable tension roller (A), and the web (12) is guided subsequently to the press nip (26) provided at the end of the conditioning or warm-up zone (α) together with the elastic band (16) along a shrinkage zone (β) further over the heated cylinder (14), along which the pretensioning of the elastic band (16) is reduced again to generate the cross shrinkage of the web (12).
10. Method according to Claim 9, characterized in that the web (12) is fed together with the elastic band (16) subsequently to the shrinkage zone (β) to a guide roller (B, 30) via which the web (12) and the elastic band (16) are once again removed from the heated cylinder (14) and separated from one another.
11. Method according to any one of the preceding claims, characterized in that the elastic band (16) is still acted upon by a respective guide roller (B, 22, 30) with a base tension which is lower than the pretensioning by a defined amount (ΔI).
12. Machine (10) for producing a web (12) which can be elongated in the cross direction, in particular a paper or cardboard web which can be elongated in the cross direction, in particular for carrying out the method according to any one of the preceding claims, with a heated, water vapour-impermeable and smooth rotating cylinder (14) and a water vapour-impermeable circumferential elastic band (16), wherein the web (12) is guided together with the elastic band (16) over a predetermined or predeterminable wrap angle lying between the elastic band (16) and the heated cylinder (14) above the heated cylinder (14) and is pushed by the elastic band (16) against the latter, characterized in that the elastic band (16) is subjected to a variably adjustable and/or controllable pretensioning in the cross direction before bringing it into contact with the web (12), and the pretensioning of the elastic band (16) generated in the cross direction can be reduced again after the formation of a vapour cushion between the web (12) and the heated cylinder (14) so that the web (12) shrinks in the cross direction sliding over the vapour cushion on the heated cylinder (14) with the elastic band (16).
13. Machine according to Claim 12, characterized in that, in particular for relatively lower machine or web travel speeds, preferably for machine or web travel speeds < 1000 m/min, the vapour cushion between the web (12) and the heated cylinder (14) is generated in a press nip (18) provided in the initial region, viewed in the web travel direction (I), of the zone wrapped by the web (12) and the elastic band (16) of the heated cylinder (14), which press nip (18) is formed between the heated cylinder (14) and a press roller (20) arranged within the loop of the elastic band (16), which press roller (28) is embodied simultaneously as a variably adjustable tension roller (A) by which the elastic band (16) can be pretensioned in the cross direction.
14. Machine according to Claim 12 or 13, characterized in that, in particular for relatively higher machine or web travel speeds, preferably for machine or web travel speeds > 1000 m/min, the web (12) is guided together with the pretensioned elastic band (16) for the formation of the vapour cushion between the web (12) and the heated cylinder (14) in the case of an elastic band (16) which is held in a pretensioned state firstly along a conditioning or warm-up zone (α) over the heated cylinder (14) and/or that the elastic band (16) can be fed to the web (12) brought into contact with the heated cylinder (14) via a variably adjustable tension roller (A, 24) which pretensions the web (12) and a press nip (26) is provided at the end of the conditioning or heat-up zone (α) in order to increase the adhesion of the web (12) to the elastic band (16), which press nip (26) is formed between the heated cylinder (14) and a press roller (28) arranged within the loop of the elastic band (16), which press roller (28) is embodied to maintain the pretensioning of the elastic hand (16) within the previous conditioning or warm-up zone (α) simultaneously again as a variably adjustable tension roller (A), and the web (12) is guided subsequently to the press nip (26) provided at the end of the conditioning or warm-up zone (α) together with the elastic band (16) along a shrinkage zone (β) further over the heated cylinder (14), along which the pretensioning of the elastic band (16) can be reduced again to generate the cross shrinkage of the web (12).
15. Machine according to any one of preceding Claims 12 to 14, characterized in that, for the purpose of targeted influencing of the cross elongation of the web (12) symmetrically to its central longitudinal axis (L) parallel to the machine direction (MD), the elastic band (16) is provided with reinforcement threads (38) extending at least substantially in the cross direction (CD) with correspondingly adjusted moduli of elasticity (E) or with a laid scrim (44) which has been correspondingly adjusted in particular in terms of its thread density.
16. Machine according to any one of preceding Claims 12 to 15, characterized in that

    - the dry content of the web (12) fed to the heated cylinder (14) lies in the range from approximately 50% to approximately 65%, and/or

    - the heatable cylinder (14) has a diameter in the range from approximately 900 mm to approximately 1500 mm, and/or

    - the surface temperature of the heated cylinders (14) is > 110° and lies in particular in a range between 110° and approximately 125°, and/or

    - the conditioning or warm-up zone (α) extends over approximately 30°, and/or

    - the shrinkage zone (β) extends over approximately 20°, and/or

    - the average linear force in the press nip (18) provided in the initial region, viewed in the web travel direction (I), of the zone of the heated cylinder (14) wrapped by the web (12) and the elastic band (16) is at most 50 kN/m, and/or

    - the dwell time of the web (12) in the initial region, viewed in the web travel direction (I), of the zone of the heated cylinder (14) wrapped by the web (12) and the elastic band (16) is approximately 0.1 sec, and/or

    - the average linear force in the press nip (26) provided at the end of the conditioning or warm-up zone (α) is at most 50 kN/m.

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