EP2205792B1 - Twin-wire former - Google Patents

Abstract

Disclosed is a twin-wire former of a machine for producing a fiber web, particularly a paper or cardboard web, from a fiber suspension. Said twin-wire former comprises a revolving continuous bottom wire and a revolving continuous top wire that are brought together to form a twin wire zone into which the fiber suspension is introduced. In the region in which the wires are brought together, at least one of the two wires is resiliently pressed against the other wire by means of pressing strips that generally extend transverse to the direction of travel of the machine. The twin-wire former according to the invention is characterized in that the width of a respective pressing strip amounts to = 30 mm and preferably ranges from about 45 to about 180 mm, said width being measured relative to the direction of travel of the machine. Furthermore, the product of the width of a respective pressing strip in mm and the travel speed of the machine in m/min amounts to = 25,000, preferably = 30,000, and the pressing strips that generally extend transverse to the direction of travel of the machine can be individually and resiliently pressed against the other wire.

Description

The invention relates to a twin-wire former of a machine for producing a fibrous web, in particular paper or board web, from a pulp suspension, according to the preamble of claim 1. Such twin-wire formers are made EP 0438685 A bzes. EP 1 770 206 A known. Twin-wire formers of this type are still from the documents DE 10 2005 041 554 A1 and DE 44 02 274 A1 known. In this case, the pressure strips, for example in the form of a drainage shoe forming shoe segments ( DE 10 2005 41 554 A1 ) or at a distance from each other ( DE 44 02 274 A1 ) be provided.

In older twin wire formers, the lower wire and the upper wire were brought together by means of pneumatically pressed strips. The strips had a width measured in the machine direction of 5 to 25 mm and usually a width of 15 mm. The contact pressure varied between 50 to 250 mbar and was usually between 80 and 120 mbar. The distance between the bars is currently 120 mm by default. The last surface is usually a flat surface without foil angle or curvature.

Through the strip width and the machine speed results in a certain time in which from the pulp suspension white water can be transported through the upper wire.

The contact pressure of the strips, the wire tension, the strip width and the strip shape define the drainage pressure.

In view of today's higher machine speeds and / or harder to dewater raw materials, the amount of water that is discharged in the area of the strips through the upper wire decreases continuously. The limiting factor here is the time available to the dewatering system in this area.

Another way to increase the drainage performance through the top wire in this area, consists in an increase of the drainage pressure or contact pressure of the strips. However, with the given last width of usually 15 mm, this leads to leaf disturbances.

The invention has for its object to provide an improved twin-wire former of the type mentioned, in which the aforementioned disadvantages are eliminated. In particular, the dewatering performance in the area of screen consolidation should be increased, without the dewatering pressure having to be excessively increased or even destroyed.

This object is achieved according to the invention by the characterizing features of claim 1.

Due to the wider Anpressleisten results in the field of Siebzusammenführung a correspondingly longer drainage time, which brings a higher dewatering capacity with it, without that the dewatering pressure must be increased excessively or until the leaf destruction.

By shaping the strip surface or the appropriate choice of the radii of curvature of this surface, a corresponding contact pressure of the strips in the wires and a corresponding choice of the wire tension of the desired dewatering pressure can be built. At the same time it can be ensured that the screen merge follows a defined line to avoid unwanted screen flutter, wrinkling, screen separation, etc. The soft or soft contact pressure of the one screen to the other can be fully retained, so that the screens, for example, dodge material bats and other disturbances "soft" can compensate.

Preferably, the pressing strips are each assigned at least one pneumatic contact pressure.

It is also particularly advantageous if at least one tilting pressure bar, in particular about an axis extending transversely to the machine direction, is provided. In this case, a respective tiltable pressure strip is preferably provided with at least two in particular in the machine direction a distance from each other having contact pressures. Expediently, at least one contact pressure is provided in each case in the front and rear regions of a respective tiltable pressure bar which are viewed in the machine direction.

Due to the respective surface contour of the contact strips in combination with, for example, two strip press-ons, which enable tilting of the strip, in particular adjustment of the pressure profile is possible.

According to a further advantageous embodiment, at least one flexible pressing bar is provided in the machine direction. In this case, a respective flexible pressure strip is preferably simultaneously tiltable about an axis extending in particular transversely to the machine direction.

According to a preferred practical embodiment of the twin-wire former according to the invention, at least three contact pressures are associated with a respective flexible and preferably tiltable contact pressure bar, preferably at least one contact pressure being provided in the front and rear region viewed in the machine direction by at least one contact pressure in the central area of the contact pressure bar.

By a corresponding tilting and / or bending of a respective pressure strip thus an adjustment of the pressure profile and an adjustment of the strip surface contour such. the radius, the inlet angle and / or the outlet angle, etc. possible.

Appropriately, the tiltable and / or flexible Anpressleisten each pneumatic pressures are assigned.

Advantageously, at least one contact strip has a smooth or closed or open, in particular a grooved, a blind drilled and / or a perforated surface facing the sieves.

It is particularly advantageous if at least one pressure bar is provided with a change covering on its surface facing the screens.

The successive in the machine direction direction Anpressleisten conveniently have the same measured width in the machine direction, wherein the measured distance in the machine direction between the contact strips is preferably less than or equal to the measured width of a respective pressure strip in the machine direction.

The distance measured in the machine direction between the contact pressure strips can advantageously amount to 0.15 times to 0.35 times the width of a respective pressure strip.

The twin-wire former can advantageously be designed as a hybrid former or as a gap former. In the latter case, the Anpressleisten can be provided in particular as a kind of shoe of the Gapformers. With such a shoe, there is the possibility of using rolls of smaller diameter and the advantage of a defined and adjustable impingement zone and a shortening of the free jet length. An appropriate combination of these Characteristics leads to a lasting improvement in the beam quality and the layer purity of multilayer headboxes.

According to the invention, the dewatering time in the area of the screen consolidation is therefore realized by means of particularly wide pressure strips. The drainage time is significantly extended by the wider pressure strips. With the increased drainage time, the drainage performance of the subsequent upper suction zone can be correspondingly increased. In addition, higher machine speeds can be realized. Moreover, the dewatering pulses in this area can be optimally controlled.

By means of an appropriate choice of the contour of the strip surface and of the strip spacing, a reduction of the pulse peaks is achieved. Damage to the leaf structure is avoided. As a result of the gentle contact pressure results in a stronger upper sieve drainage.

Fig. 1

eine schematische Teildarstellung eines Hybridformers mit beispielsweise zwei im Bereich der Siebzusammenführung angeordneten Anpressleisten, durch die im vorliegenden Fall beispielsweise das Untersieb gegen das Obersieb gepresst wird;

Fig. 2

eine schematische Teildarstellung eines Gapformers mit beispielsweise zwei im Bereich der Siebzusammenführung angeordneten Anpressleisten, durch die im vorliegenden Fall beispielsweise wieder das Untersieb gegen das Obersieb gepresst wird;

Fig. 3

eine mit der Fig. 2 vergleichbare Darstellung eines Gap- formers, wobei im vorliegenden Fall durch die Anpressleisten jedoch das Obersieb gegen das Untersieb gepresst wird;

Fig. 4

eine schematische Darstellung einer kippbaren Anpressleiste mit beispielsweise zwei zugeordneten, in Maschinenlauf- richtung einen Abstand voneinander aufweisenden Anpres- sungen; und

Fig. 5

eine schematische Darstellung einer in Maschinenlaufrich- tung biegsamen Anpressleiste mit beispielsweise drei zuge- ordneten, in Maschinenlaufrichtung einen Abstand vonein- ander aufweisenden Anpressungen.

The invention will be explained in more detail below with reference to exemplary embodiments with reference to the drawing. In this show:

Fig. 1

a schematic partial view of a hybrid former with, for example, two arranged in the region of Siebzusammenführung pressure bars through which in the present case, for example, the lower wire is pressed against the upper wire;

Fig. 2

a schematic partial view of a Gapformers with, for example, two arranged in the field of Siebzusammenführung pressure bars through which in the present case, for example, the lower wire is pressed against the upper wire again;

Fig. 3

one with the Fig. 2 comparable representation of a gap former, wherein in the present case, however, the top wire is pressed against the bottom wire by the pressure bars;

Fig. 4

a schematic representation of a tiltable pressure bar with, for example, two associated Anpres- sungen in Maschinenlauf- direction spaced from each other Anpres- sungen; and

Fig. 5

a schematic representation of a bendable in the machine direction pressing bar with, for example, three assigned, in the machine direction a distance from each other having contact pressures.

The Fig. 1 to 3 show in schematic representation in each case a twin-wire former of a machine for producing a fibrous web, in particular paper or board web, from a pulp suspension.

In this case, these twin-wire formers each comprise a continuous endless lower wire 10 and a continuous endless upper wire 12, which are brought together to form a twin-wire zone 14, into which the pulp suspension delivered by a headbox 16 is finally introduced. In each case one of the two screens 10, 12 is pressed against the other screen in the area of the screen merge by pressing bars 18, 20 extending generally transversely to the machine direction MD. In the in the Fig. 1 to 3 In the region of the screen merge, for example, two pressing bars 18, 20 are provided, which preferably describe a radius R in the range of 400 to 10,000 mm. In addition, the incoming and outgoing tangent points of the respective pressure strip 18, 20 may be wrapped in a range of 0.1 to 5.0 ° of the at least one sieve 10, 12. In principle, however, any other number of pressure bars is conceivable. In addition, the contact strips 18, 20 can extend in the transverse direction, for example, at least substantially over the entire machine width or be divided in the direction of the width in several sub-strips.

The pressure strips 18, 20 can be used, for example, as a kind of shoe of the gap former 28.

The pressing strips 18, 20 are each viewed in the machine direction MD one or more successive contact pressures 22 (see Fig. 1 to 3 ) or 22 ', 22 "(see. Fig. 4 ) or 22 'to 22 "' (cf. Fig. 5 ). The contact pressures can be divided in the transverse direction, for example, in several Teilanpressungen.

The measured in the machine direction MD width of the pressure bars 18, 20 is ≥ 30 mm and is preferably in a range of about 45 to about 180 mm.

The value of the product of the width of a respective pressure bar 18, 20 in mm and the machine speed in m / min is desirably ≥ 25,000, preferably ≥ 30,000.

The sieve 10, 12 facing surface of a respective pressure bar 18, 20 may viewed in the machine direction MD have a constant radius of curvature or different radii of curvature. The constant radius of curvature or the first radius of curvature of the surface of a respective pressure strip 18, 20 is expediently chosen such that the sieve pressed against the other sieve by the pressure strip 18, 20 is almost or at least essentially tangential to the front strip section runs in the area of the front edge of the groin or at least slightly wraps around the front edge of the groin.

In the pressing strips 18, 20 associated contact pressures 22; 22 ', 22 ", 22' to 22"'may, for example, be pneumatic contact pressures. The contact strips 18, 20 may each have a sieve 10, 12 facing smooth or closed surface. In principle, however, such embodiments are also conceivable in which the pressure strips 18, 20 each have a sieve 10, 12 facing open surface. In this case, the relevant surface of the pressure bars 18, 20 in particular grooved, blind drilled, perforated and / or the like.

In principle, for example, such embodiments are conceivable in which the pressure bars 18, 20 are provided on their the screens 10, 12 facing surface in each case with a removable covering.

The pressing bars 18, 20 following one another in the machine direction MD can in particular have the same width measured in the machine direction MD. In this case, the distance between the contact pressure bars 18, 20 measured in the machine direction MD is preferably less than or equal to the width of a respective pressure strip 18, 20 measured in the machine direction MD. The distance between the pressure bars 18, 20 measured in the machine direction MD is preferably 0.15-. times up to 0.35 times the width of a respective pressure strip 18, 20.

In the execution according to Fig. 1 For example, the twin-wire former is designed as a hybrid former 26. The pulp suspension delivered by the head box 16 is first applied to the lower wire 10 before the two wires 10, 12 are brought together. About the lower wire 10, the pulp suspension finally enters the twin-wire zone, in which, as shown in the Fig. 1 it can be seen, a Obersiebsaugkasten 24 may be provided, which is provided in the machine direction MD according to the provided in the field of Siebzusammenführung Anpressleisten 18, 20.

While in the present embodiment the pressure bars 18, 20 press the lower wire 10 against the upper wire 12 and are arranged correspondingly in the loop of the lower wire 10, these pressure bars 18, 20 may in principle be arranged in the loop of the upper wire 12 to this upper wire 12 against to press the lower wire 10.

In the embodiment according to Fig. 2 the twin-wire former is designed as a gap former 28. In this case, the pulp suspension delivered by the head box 16 is introduced directly into the region of the entry gap 30 of the twin-wire zone 14 formed by the two screens 10, 12.

The pressing strips 18, 20 provided in the region of the screen consolidation are arranged in the present case, for example, within the loop of the lower wire 10, so that the lower wire 10 is pressed against the upper wire 12 by these strips. Following the pressure strips 18, 20, i. in the machine direction MD behind these bars, the two wires 10, 12 are guided around a forming roller 32.

Fig. 3 shows one with the Fig. 2 comparable representation of the Gapformers 28, wherein in the present case by the Anpressleisten 18, 20, however, the upper wire 12 is pressed against the lower wire 10. The contact strips 18, 20 are thus arranged here within the loop of the upper wire.

Incidentally, this version has according to Fig. 3 at least essentially the same structure as that of Fig. 2 , wherein like reference numerals are assigned to corresponding parts.

Fig. 4 shows a schematic representation of a tiltable pressure bar 18, 20 with, for example, two associated, in the machine direction MD a distance from each other having contact pressures 22 ', 22 "by an appropriate action on the Anpressungen 22', 22", the respective pressure bar 18, 20, for example a transversely to the machine direction MD extending axis are tilted. For this purpose, as shown, for example, the contact pressure 22 "can be subjected to greater force than the contact pressure 22 'or vice versa Fig. 4 indicated by arrows.

As based on the Fig. 4 can be seen, in the machine direction MD viewed front and rear portion of the tiltable pressure bar 18, 20 are each provided at least one contact pressure 22 'and 22 ", in the present embodiment .in the two areas each such a pressing 22' or 22 "is provided.

The contact pressures 22 ', 22 "may, in particular, again be pneumatic contact pressures, for example, they may each comprise at least one pressure hose or the like, for example, a double-row pressure system may be provided in the present case.

Fig. 5 shows a schematic representation of a flexible in the machine direction MD pressing bar 18, 20 with, for example, three associated, in the machine direction MD a distance from each other having contact pressures 22 '- 22 "'.

In this case, in the present case, for example, in each case a contact pressure 22 'or 22 "in the machine direction MD considered front and rear and for example a contact pressure 22" in the central region of the pressure bar 18, 20 are provided.

The contact pressures 22 '- 22 "may in particular be pneumatic contact pressures, wherein the various contact pressures 22' - 22" 'may each comprise at least one pressure hose. In the present embodiment, each of the three contact pressures 22 '- 22 "' in each case such a pressure hose.

As based on the Fig. 5 can be seen, the flexible pressure bar 18, 20, for example, thereby deformable in the desired manner that the average contact pressure 22 "'is applied more than the other two contact pressures 22', 22". In principle, any other different loading of the various contact pressures 22 '- 22 "' possible.

Basically, for example, such embodiments are conceivable in which a respective flexible pressure bar 18, 20 at the same time about an in particular transverse to the machine direction MD extending axis is tilted. In this case, tilting can in particular also take place via corresponding contact pressures, here for example the two outer contact pressures 22 'and 22 " In this case, the contact pressures 22 '- 22 "' in particular be provided again as a pneumatic contact pressures and, for example, each comprise at least one pressure hose.

LIST OF REFERENCE NUMBERS

10

bottom wire

12

top wire

14

twin

16

headbox

18

pressure bar

20

pressure bar

22

pressing

22 '

pressing

22 "

pressing

22 " '

pressing

24

top wire suction

26

hybrid former

28

Gapformer

30

entrance slit

32

forming roll

MD

Machine direction

R

radius

Claims (12)

1. Twin-wire former of a machine for producing a fibrous web, in particular a paper or board web, from a fibrous suspension, comprising a circulating endless bottom wire (10) and a circulating endless top wire (12), which are brought together to form a twin-wire zone (14) into which the fibrous suspension is introduced, in the region in which the wires are brought together at least one of the two wires being pressed resiliently against the other wire by pressure foils (18, 20) extending generally transversely with respect to the machine running direction (MD), the width measured in the machine running direction (MD) of a respective pressure foil (18, 20) being ≥ 30 mm and preferably lying in a range from about 45 to about 180 mm, the value of the product of the width of a respective pressure foil (18, 20) in mm and the machine running speed in m/min being ≥ 25 000, preferably ≥ 30 000, and it being possible for the pressure foils (18, 20) extending generally transversely with respect to the machine running direction (MD) to be pressed individually and resiliently against the other wire,
   characterized in that,
   viewed in the machine running direction (MD), the surface of a respective pressure foil (18, 20) that faces the wires (10, 12) has a constant radius of curvature, and in that the constant radius of curvature of the surface of a respective pressure foil (18, 20) is chosen such that the wire pressed against the other wire by the pressure foil (18, 20) runs virtually or at least substantially tangentially onto the front section of the foil in the region of the front foil edge or at most wraps slightly around the front foil edge.
2. Twin-wire former according to Claim 1,
   characterized in that
   the pressure foils (18, 20) are in each case assigned at least one pneumatic pressing means (22; 22', 22"; 22'-22"') .
3. Twin-wire former according to one of the preceding claims,
   characterized in that
   at least one pressure foil (18, 20) which can in particular be tilted about an axis extending transversely with respect to the machine running direction is provided.
4. Twin-wire former according to Claim 3,
   characterized in that
   a respective tiltable pressure foil (18, 20) is provided with at least two pressing means (22', 22") that are at a distance from one another, in particular in the machine running direction (MD).
5. Twin-wire former according to Claim 4,
   characterized in that
   viewed in the machine running direction (MD), in each case at least one pressing means (22', 22") is provided in the front and rear region of a respective tiltable pressure foil (18, 20).
6. Twin-wire former according to one of the preceding claims,
   characterized in that
   at least one pressure foil (18, 20) that is flexible in the machine running direction (MD) is provided.
7. Twin-wire former according to one of the preceding claims,
   characterized in that
   a respective flexible pressure foil (18, 20) can be tilted simultaneously about an axis extending in particular transversely with respect to the machine running direction (MD).
8. Twin-wire former according to one of the preceding claims,
   characterized in that
   a respective flexible and preferably tiltable pressure foil (18, 20) is assigned at least three pressing means (22'-22"'), preferably in each case at least one pressing means (22', 22") being provided in the front and rear region of the pressure foil (18, 20), viewed in the machine running direction (MD), and at least one pressing means (22"') being provided in the central region thereof.
9. Twin-wire former according to one of the preceding claims,
   characterized in that
   the tiltable and/or flexible pressure foils (18, 20) are each assigned pneumatic pressing means (22'-22"').
10. Twin-wire former according to one of the preceding claims,
    characterized in that
    the pressure foils (18, 20) following one another in the machine running direction (MD) have the same width measured in the machine running direction (MD).
11. Twin-wire former according to Claim 10,
    characterized in that
    the distance between the pressure foils (18, 20) measured in the machine running direction (MD) is less than or equal to the width of a respective pressure foil (18, 20) measured in the machine running direction (MD).
12. Twin-wire former according to Claim 11,
    characterized in that
    the distance between the pressure foils (18, 20) measured in the machine running direction (MD) is 0.15 to 0.35 times the width of a respective pressure foil (18, 20).

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