EP0496965B1 - Press section - Google Patents

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Publication number
EP0496965B1
EP0496965B1 EP91119700A EP91119700A EP0496965B1 EP 0496965 B1 EP0496965 B1 EP 0496965B1 EP 91119700 A EP91119700 A EP 91119700A EP 91119700 A EP91119700 A EP 91119700A EP 0496965 B1 EP0496965 B1 EP 0496965B1
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EP
European Patent Office
Prior art keywords
press
nip
web
roll
belt
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP91119700A
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German (de)
French (fr)
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EP0496965A1 (en
Inventor
Christian Schiel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JM Voith GmbH
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JM Voith GmbH
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Publication of EP0496965A1 publication Critical patent/EP0496965A1/en
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Publication of EP0496965B1 publication Critical patent/EP0496965B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F3/00—Press section of machines for making continuous webs of paper
    • D21F3/02—Wet presses
    • D21F3/0209—Wet presses with extended press nip
    • D21F3/0218—Shoe presses
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F3/00—Press section of machines for making continuous webs of paper
    • D21F3/02—Wet presses
    • D21F3/0209—Wet presses with extended press nip
    • D21F3/0218—Shoe presses
    • D21F3/0227—Belts or sleeves therefor
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F3/00—Press section of machines for making continuous webs of paper
    • D21F3/02—Wet presses
    • D21F3/04—Arrangements thereof
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F3/00—Press section of machines for making continuous webs of paper
    • D21F3/02—Wet presses
    • D21F3/04—Arrangements thereof
    • D21F3/045—Arrangements thereof including at least one extended press nip

Definitions

  • the invention relates to a press section of a machine for producing a fibrous web, in particular paper web, with the features a) to d) of claim 1, which are known from US Pat. No. 4,359,827.
  • the known press section is formed from a roll set of four (or five) rolls with a central roll 50 which forms a first and a second press nip 14 and 17 with two (or three) pressure rolls.
  • a press belt 15 runs through these two press nips, where it runs onto the central roll 50 in front of the first press nip 14 and runs behind the second press nip 17 from the central roll.
  • a first endless felt belt 12 guides the web W to be dewatered from the wire section first through a pre-press nip 13 and from this into the first press nip 14. Immediately behind this first press nip 14, the first felt belt 12 is separated from the web W. From this point, the press belt 15 guides the web W around the central roller 50 (with an additional press nip 16 possibly being passed) into the second press nip 17 and behind it to a take-off point at which a dryer fabric 19 takes over the web with the help of a take-off suction roll 18 transferred to a dryer section.
  • the author of the US-PS pursues, among other things, the goal of creating a paper machine in which there is nowhere a free paper draw between the wire section and dryer section, in particular also in the press section. This is to avoid weakening the web (which is still wet and therefore has little strength) in a free paper draw.
  • the author of the US-PS thus expects that higher working speeds, fewer paper breaks and the use of cheaper raw materials will be possible.
  • a disadvantage of the known press section according to US Pat. No. 4,359,827 is that it is difficult to detach the web behind the second press nip 17 from the press belt and to transfer it safely to the dryer fabric 19.
  • US Pat. No. 4,483,745 also describes various press sections in which a non-porous, water-impermeable and smooth surface press belt runs together with the web to be dewatered through one or two press nips.
  • a non-porous, water-impermeable and smooth surface press belt runs together with the web to be dewatered through one or two press nips.
  • U.S. Patent 4,359,827 the same problems arise with detachment of the web from the press belt as with the subject of U.S. Patent 4,359,827.
  • the risk of paper web tears is to be reduced and the economy of paper production is thereby improved.
  • dryer fabric usually: dryer fabric
  • the distance from the second press nip to the point where the web is removed from the substantially water-impermeable press belt is to be increased considerably compared to heretofore. (For preferred dimensions, see claim 2.)
  • the visco-elastic and previously flat-pressed fibers can partially straighten up again; this reduces the proportion of contact between the fibers and the smooth surface of the press belt.
  • the resistance to removal also decreases, so that the web can now be removed from the smooth surface of the press belt with a substantially lower tensile stress, that is to say much more gently than before.
  • the considerably increased distance from the second press nip to the removal point is combined with the feature that the two pressure rollers (or at least the first pressure roller) are designed as long-nip pressure rollers known per se.
  • This combination is based on the knowledge that the considerable distance of the take-off point from the second press nip makes it possible to let the press belt serving as the web conveyor belt run in succession through two so-called extended press nips. After an extended press nip through which the web runs in contact with a press belt, it is particularly difficult to detach the web from the press belt because the web comes into particularly intimate contact with the press belt due to the long dwell time in the press nip.
  • the so-called recovery time becomes longer; this is the time in which (after the web has emerged from the press nip) the previously flat-pressed fibers (as explained above) partially straighten up again, so that the joint proportion of contact between the press belt and the web becomes smaller.
  • the press nip length is, for example, three times larger than in a press nip formed by two normal rollers, a triple recovery time is also necessary in order to be able to detach the web sufficiently easily from the press belt. It has now been shown, however, that the above-described effect of the prolonged dwell time of the web on the press belt (behind the last press nip) also enables the web to be removed from the press belt flawlessly when it comes to extended press nips.
  • rollers have a flexible, tubular and hermetically sealed (and thus inflatable) press jacket at both ends. This is pressed against the central roller by means of a non-rotating press shoe which can be moved in the radial direction and which has a concave sliding surface.
  • a roller is therefore self-pressing, ie its bearing blocks and the bearing blocks of the cooperating roller (namely the central roller) do not have to be displaced radially to one another.
  • shoe press rolls allow a considerable increase in the working speed, because the extended press nips and the thus extended press time considerably increase the dewatering capacity of the press section.
  • the paper web thus leaves the press section with a relatively high dry content, so that less water has to be evaporated in the subsequent dryer section.
  • Another advantage of the extended press nips is that relatively thin and finely woven felt belts can be used in the press section; this contributes to improving the quality of the finished paper web.
  • Figure 1 shows schematically a press section according to the invention in side view.
  • FIG. 2 shows details of FIG. 1 on an enlarged scale.
  • FIG. 3 shows schematically the cross-sectional shapes of the press shoes of the long-nip press rolls.
  • FIG. 4 is a partial section through the press belt along line IV of FIG. 3.
  • the main part of the press section shown in FIG. 1 is a roller set with a central roller O, which forms two press nips I and II with a first pressure roller 11 and with a second pressure roller 12.
  • An essentially water-impermeable endless press belt 8 runs over the central roller O and thus successively through the two press nips I and II, and also over belt guide rollers 15, 15 '.
  • the press belt runs in front of the first press nip I on the central roll O and leaves it again behind the second press nip II.
  • the paper web formed in a wire section 3 (indicated by a dotted line) is fed with the aid of a first endless felt belt 1 via a take-off suction roll 4 and fed to the first press nip I via suction guide rolls 5 and 6.
  • the suction guide roller 6 lying at a distance in front of the first press nip I is arranged such that first the felt belt 1 guiding the web and then the press belt 8 run up. From here, the web runs between felt belt 1 and press belt 8 to the first press nip I.
  • the first felt belt 1 separates from the web and from the press belt 8 and runs via felt guide rollers 7 back to the take-off suction roll 4.
  • the web sticks to the press belt 8 and runs with it around the central roller O into the second press nip II In many (but not all) applications, this runs through a second endless felt belt 2, which separates from the web and from the pressing belt 8 behind the second press nip II.
  • the felt belt 2 and the press belt 8 form an acute angle, which in most cases is less than 10 °. Outside the press nip II, the second felt belt 2 runs over felt guide rollers 18 and 18 '.
  • the hardness of the roll shell of the second pressure roller 12 should be lower than the hardness of the web side of the press belt 8, so that the web continues to run behind the second press nip II with the press belt 8. In order to achieve the highest possible dry content of the web and the highest possible running speeds, however, it will generally not be possible to do without the second felt belt.
  • the belt guide rollers 15 and 15 'of the press belt 8 are arranged such that the press belt 8 bridges a relatively large distance from the central roller O to the area of the first drying cylinder 14 of the dryer section following the press section.
  • the press belt 8 leads the web from the second press nip II to a take-off point 9; there it is transferred to a drying wire 13 by means of a take-off suction roll 10 and then runs with it in a known manner over the drying cylinders 14 and over further suction guide rolls 10 '.
  • the length of the path of the press belt 8 from the second press nip II to the take-off point 9 is at least equal to the circumference of the central roller O; however, this length is preferably 2 to 3 times, sometimes even 3 to 5 times the circumference of the central roller O.
  • the suction guide roll 5 can (in a reinforced form) together with a (preferably grooved) press roll 17 form a pre-press nip V through which an additional felt belt 16 runs, guided by felt guide rolls 19.
  • a double felt press preceding the press nips I and II the dewatering capacity of the press section can be increased even further.
  • a heating device 25 e.g. with heat radiators and / or warm air nozzles
  • a heating device 25 can be provided in order to heat and pre-dry the web.
  • the axes of the central roller O and the pressure rollers 11 and 12 lie in a vertically arranged press plane E.
  • the press plane E could also be inclined by up to 10 °, namely to the right in FIG. 1.
  • the two suction guide rollers 5 and 6 could be combined into a single roller.
  • the running direction of the press belt 8 through the first press nip I is opposite to the general machine direction; because on the way from the first to the second press nip the direction of the press belt 8 is reversed and then corresponds to the general machine direction.
  • the first press nip I below the second press nip II This arrangement is preferred because it causes the web on the subsequent path to the take-off point 9 on the upper side of the press belt 8. The reverse arrangement is also conceivable.
  • the press belt 8 can be guided on the way from the second press nip II to the take-off point 9 via an articulated roller 15 'which deflects the press belt 8 from a predominantly horizontal direction into a downward inclined direction.
  • FIGS. 2 and 3 again show the central roller O and the two pressure rollers 11 and 12.
  • the latter are designed as long-nip pressure rollers; that is, they have a flexible tubular press jacket 26, 27, the ends of which are hermetically sealed in a known manner by means of a rotating disk, not shown. This means that lubricant cannot escape and compressed air can be applied to the interior.
  • a stationary support body 28 or 29 extends through the interior of each extended-nip press roll.
  • a press shoe 30 or 31 which extends over the entire width of the web, has a concave sliding surface and is hydraulically displaceable in the radial direction . As a result, he can press the press jacket 26 or 27 against the central roller O.
  • the two press shoes 30 and 31 are shaped differently; ie the effective width b1 of the pressure shoe 30 of the first pressure roller 11 during pressing is greater than the effective width b2 of the pressure shoe 31 of the second pressure roller 12 during pressing.
  • the width B of the piston part of the two pressure shoes 30 and 31 is the same; thus the two support bodies 28 and 29 are shaped substantially the same.
  • the pressure chambers used to actuate the pressure shoes 30, 31 are preferably also subjected to approximately the same pressures.
  • largely identical line pressures are generated in both press nips I and II, so that they are on the central roller O at least approximately cancel out the acting line forces (apart from their own weight).
  • the central roller O can thereby be designed as a simple roller stored in normal bearings; ie it need not be designed as a roller with adjustable deflection. Nevertheless, the pressing pressure generated per unit area is lower in the first press nip I than in the second press nip II. A relatively gentle, but long-lasting dewatering of the paper web is achieved in the first press nip I, in contrast, in the second press nip II, more intensive dewatering, but of shorter duration. (Alternative: support body and press shoe, e.g. 29 and 31, could be replaced by a rotatable roller body).
  • the bearing housing 35 and the two bearing blocks 36 and 37 are positively connected, that is to say completely rigidly connected to one another. During normal operation, therefore, none of the bearing housings 35 or bearing blocks 36, 37 are moved. To apply the pressing forces, the radial displacement of the press shoes 30 and 31 is sufficient.
  • the two columns 41 and 42 can be removed to replace the felt belts 1 and 2, the press belt 8 or the press sleeves 26, 27. To replace the press sleeves 26, 27, the intermediate piece 38 or the tension elements 39 must also be removed.
  • the columns 41, 42 can also be connected to the stationary machine frame 40, as is indicated by way of example at 43.
  • the press belt 8 runs together with the felt belt 1 (and together with the paper web in between) at a point W on the Central roller O, which is located at a certain distance before entering the first press nip I. This causes the press belt 8 and felt 1 to lie snugly against the central roller O before the press jacket 26 comes into contact with the felt 1. Behind the first press nip I, the first felt belt 1 leaves the central roller O at a point X which lies at a certain distance behind the outlet from the press nip I.
  • the contact point Y of the second felt belt 2 on the central roll O is also at a certain distance from the entry into the second press nip II.
  • the press belt 8 runs from the central roll O at a point Z which is at a distance behind the second press nip II.
  • the second felt belt 2 forms an angle a of between 5 and 15 ° with the press belt 8. This angle depends, among other things. of the paper type and can be varied by vertically adjusting the guide roller 18 '(Fig. 1).
  • the press belt 8 is preferably made of a pourable and hardened plastic (for example polyurethane) with a reinforcement, for example in the form of a fabric or in accordance with FIG. 4 in the form of threads 44, for example in accordance with WO 88/08897 (file P 4378).
  • the hardness of the plastic (at least in the area of the web-side surface 45) is normally in the range between 80 and 95 Shore A.
  • the press belt 8 has a smooth and water-impermeable web-side surface 45 and a thickness of approximately 2.5 to 5 mm.
  • the surface 46 of the press belt facing the central roller O can also be smooth; however, it is preferably provided with recesses 47 for the temporary storage of water.
  • the recesses 47 can be designed as blind bores or as circumferential grooves or can be formed by a reinforcing fabric that partially protrudes from the plastic material.

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  • Paper (AREA)
  • Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Abstract

In the press section of a paper making machine, there is a central roll, a first press roll beneath and a second press roll above the central roll defining respective first and second press nips. The first press nip or both nips may be extended nip presses. A water impervious press belt travels through the first press nip around the central roll and through the second press nip, meeting the central roll before the first nip and leaving the central roll after the second nip. A felt belt conducts the web to be dewatered into the first nip along with the press belt. The felt belt separates from the web after the first nip. Following the second press nip, the press belt carries the web to a place of removal where a dryer wire picks up the web. The distance from the second press nip to the place of removal is at least equal to the circumference of and is preferably greater than the circumference of the central roll. The path of the press belt from the second nip to the removal place may be bent by a deflection roll.

Description

Die Erfindung betrifft eine Pressenpartie einer Maschine zur Herstellung einer Faserstoff-Bahn, insbesondere Papierbahn, mit den Merkmalen a) bis d) des Anspruches 1, die aus der US-PS 4,359,827 bekannt sind. Die bekannte Pressenpartie ist gebildet aus einem Walzensatz von vier (oder fünf) Walzen mit einer Zentralwalze 50, die mit zwei (oder drei) Anpreßwalzen einen ersten und einen Zweiten Preßspalt 14 und 17 bildet. Ein Preßband 15 läuft durch diese beiden Preßspalte, wobei es vor dem ersten Preßspalt 14 auf die Zentralwalze 50 aufläuft und hinter dem zweiten Preßspalt 17 von der Zentralwalze abläuft. Ein erstes endloses Filzband 12 führt die zu entwässernde Bahn W von der Siebpartie zunächst durch einen Vor-Preßspalt 13 und von diesem in den ersten Preßspalt 14. Unmittelbar hinter diesem ersten Preßspalt 14 wird das erste Filzband 12 von der Bahn W getrennt. Von dieser Stelle führt das Preßband 15 die Bahn W um die Zentralwalze 50 herum (wobei eventuell ein zusätzlicher Preßspalt 16 passiert wird) in den zweiten Preßspalt 17 und dahinter zu einer Abnahmestelle, an der ein Trockensieb 19 mit Hilfe einer Abnahmesaugwalze 18 die Bahn übernimmt und in eine Trockenpartie überführt.The invention relates to a press section of a machine for producing a fibrous web, in particular paper web, with the features a) to d) of claim 1, which are known from US Pat. No. 4,359,827. The known press section is formed from a roll set of four (or five) rolls with a central roll 50 which forms a first and a second press nip 14 and 17 with two (or three) pressure rolls. A press belt 15 runs through these two press nips, where it runs onto the central roll 50 in front of the first press nip 14 and runs behind the second press nip 17 from the central roll. A first endless felt belt 12 guides the web W to be dewatered from the wire section first through a pre-press nip 13 and from this into the first press nip 14. Immediately behind this first press nip 14, the first felt belt 12 is separated from the web W. From this point, the press belt 15 guides the web W around the central roller 50 (with an additional press nip 16 possibly being passed) into the second press nip 17 and behind it to a take-off point at which a dryer fabric 19 takes over the web with the help of a take-off suction roll 18 transferred to a dryer section.

Der Urheber der US-PS verfolgt u.a. das Ziel der Schaffung einer Papiermaschine, in der zwischen Siebpartie und Trockenpartie, also insbesondere auch in der Pressenpartie, nirgends ein freier Papierzug vorhanden ist. Hierdurch soll vermieden werden, daß die Bahn (die noch naß ist und deshalb eine nur geringe Festigkeit aufweist) in einem freien Papierzug geschwächt wird. Der Urheber der US-PS erwartet somit, daß höhere Arbeitsgeschwindigkeiten, weniger Papier-Abrisse und die Verwendung billigerer Rohstoffe möglich werden.The author of the US-PS pursues, among other things, the goal of creating a paper machine in which there is nowhere a free paper draw between the wire section and dryer section, in particular also in the press section. This is to avoid weakening the web (which is still wet and therefore has little strength) in a free paper draw. The author of the US-PS thus expects that higher working speeds, fewer paper breaks and the use of cheaper raw materials will be possible.

Zum Preßband 15 offenbart die US-PS, Durchlässigkeit und Porosität seien gering (gemeint ist wohl, im Vergleich zu einem Filzband). Nähere Angaben fehlen jedoch in der US-PS.For the press belt 15, the US patent discloses that permeability and porosity are low (this is probably what is meant in comparison to a felt belt). However, more details are missing in the US PS.

Ein Nachteil der bekannten Pressenpartie gemäß US-PS 4,359,827 besteht darin, daß es schwierig ist, die Bahn hinter dem zweiten Preßspalt 17 von dem Preßband abzulösen und sicher auf das Trockensieb 19 zu überführen. Man versucht zwar, diese Schwierigkeiten durch Erhöhen des in der Abnahmesaugwalze 18 herrschenden Unterdruckes zu beseitigen, jedoch mit nur geringem Erfolg. Erschwerend kommt hinzu, daß das Ablösen der Bahn vom Preßband umso schwieriger wird, je höher die Arbeitsgeschwindigkeit der Papiermaschine ist.A disadvantage of the known press section according to US Pat. No. 4,359,827 is that it is difficult to detach the web behind the second press nip 17 from the press belt and to transfer it safely to the dryer fabric 19. One tries to overcome these difficulties by increasing the negative pressure prevailing in the take-off suction roll 18, but with little success. To make matters worse, the higher the operating speed of the paper machine, the more difficult it is to detach the web from the press belt.

Die US-PS 4,483,745 beschreibt ebenfalls verschiedene Pressenpartien, worin ein nicht-poröses, wasser-undurchlässiges und ein glatte Oberfläche aufweisendes Preßband zusammen mit der zu entwässernden Bahn durch einen oder durch zwei Preßspalte läuft. Bei einigen der Ausführungsbeispiele dieser US-PS ist wieder dafür gesorgt, daß an keiner Stelle ein unerwünschter offener Papierzug vorhanden ist. Jedoch treten mit dem Ablösen der Bahn vom Preßband die gleichen Probleme auf wie beim Gegenstand der US-PS 4,359,827.US Pat. No. 4,483,745 also describes various press sections in which a non-porous, water-impermeable and smooth surface press belt runs together with the web to be dewatered through one or two press nips. In some of the embodiments of this US-PS it is again ensured that there is no undesired open paper pull at any point. However, the same problems arise with detachment of the web from the press belt as with the subject of U.S. Patent 4,359,827.

Es ist Aufgabe der vorliegenden Erfindung, die bekannten Pressenpartien dahingehend weiter zu entwickeln, daß die Arbeitsgeschwindigkeit der Papiermaschine noch weiter gesteigert werden kann, nämlich bis in die Größenordnung zwischen 1400 und 2000 m/min. Gleichzeitig soll es möglich werden, einen höheren Prozentsatz als bisher an geringwertigen Rohstoffen (insbesondere Altpapier) einzusetzen. Ferner soll das Risiko von Papierbahn-Abrissen reduziert und hierdurch die Wirtschaftlichkeit der Papierherstellung verbessert werden. Dies verlangt insbesondere, daß die Bahn mit höherer Zuverlässigkeit als bisher von dem im wesentlichen wasserundurchlässigen Preßband auf das nachfolgende Transportband (in der Regel: Trockensieb) überwechselt. Speziell bei der Herstellung von Tiefdruckpapier soll auch noch eine Steigerung des Füllstoffanteils ermöglicht werden, zwecks weiterer Verbesserung der Bedruckbarkeit des fertigen Papiers.It is an object of the present invention to further develop the known press sections in such a way that the working speed of the paper machine can be increased even further, namely to the order of magnitude between 1400 and 2000 m / min. At the same time, it should be possible to use a higher percentage of low-value raw materials (especially waste paper) than before. Furthermore, the risk of paper web tears is to be reduced and the economy of paper production is thereby improved. This requires, in particular, that the web be more reliable than before from the substantially water-tight press belt the following conveyor belt (usually: dryer fabric) is changed. Especially in the production of rotogravure paper, an increase in the filler content should also be made possible in order to further improve the printability of the finished paper.

Nach dem Hauptgedanken der Erfindung ist vorgesehen, die Entfernung vom zweiten Preßspalt bis zu der Stelle, wo die Bahn von dem im wesentlichen wasserundurchlässigen Preßband abgenommen wird, gegenüber bisher beträchtlich zu vergrößern. (Bevorzugte Abmessungen siehe Anspruch 2.) Hierdurch wird eine wesentliche Verlängerung der Verweilzeit der Papierbahn zwischen dem letzten Preßspalt und der Abnahmestelle erreicht. In dieser verlängerten Verweilzeit können sich die visko-elastischen und zuvor flach gepreßten Fasern wieder teilweise aufrichten; hierdurch sinkt der Kontakt-Anteil zwischen den Fasern und der glatten Oberfläche des Preßbandes. Mit diesem kleiner werdenden Kontakt-Anteil sinkt auch der Abnahmewiderstand, so daß die Bahn nunmehr mit wesentlich geringerer Zugspannung, also wesentlich schonender als bisher von der glatten Fläche des Preßbandes abgenommen werden kann. Die Folge ist, daß die Arbeitsgeschwindigkeit gesteigert und insgesamt die Wirtschaftlichkeit der Papierherstellung verbessert werden kann. Dies gelingt dadurch, daß die Anzahl der Papierbahn-Abrisse, insbesondere an der genannten Abnahmestelle, wesentlich geringer wird, außerdem dadurch, daß ein höherer Anteil geringwertiger Rohstoffe, z.B. Altpapier, verwendet werden kann.According to the main idea of the invention, the distance from the second press nip to the point where the web is removed from the substantially water-impermeable press belt is to be increased considerably compared to heretofore. (For preferred dimensions, see claim 2.) This results in a substantial increase in the dwell time of the paper web between the last press nip and the removal point. During this extended dwell time, the visco-elastic and previously flat-pressed fibers can partially straighten up again; this reduces the proportion of contact between the fibers and the smooth surface of the press belt. With this proportion of contact becoming smaller, the resistance to removal also decreases, so that the web can now be removed from the smooth surface of the press belt with a substantially lower tensile stress, that is to say much more gently than before. The result is that the speed of work can be increased and the overall economy of paper production can be improved. This is achieved by the fact that the number of paper web tears, in particular at the said take-off point, is significantly lower, and also by the fact that a higher proportion of low-quality raw materials, e.g. Waste paper that can be used.

In den Unteransprüchen sind zahlreiche flankierende Maßnahmen angegeben, die der weiteren Verbesserung des Ergebnisses dienen.Numerous accompanying measures are specified in the subclaims, which serve to further improve the result.

Gemäß einem besonders wichtigen weiterführenden Erfindungsgedanken wird die beträchtlich vergrößerte Entfernung vom zweiten Preßspalt bis zur Abnahmestelle kombiniert mit dem Merkmal, daß die zwei Anpreßwalzen (oder zumindest die erste Anpreßwalze) als an sich bekannte Langspalt-Preßwalzen ausgebildet sind. Diese Kombination beruht auf der Erkenntnis, daß es durch die beträchtliche Entfernung der Abnahmestelle vom zweiten Preßspalt möglich wird, das als Bahn-Transportband dienende Preßband nacheinander durch zwei sogenannte verlängerte Preßspalte laufen zu lassen. Hinter einem verlängerten Preßspalt, durch den die Bahn in Kontakt mit einem Preßband läuft, ist es nämlich besonders schwierig, die Bahn von dem Preßband abzulösen, weil die Bahn infolge der langen Verweilzeit im Preßspalt zu besonders innigem Kontakt mit dem Preßband kommt. Entsprechend wird auch die sogenannte Erholungszeit länger; dies ist die Zeit, in der sich (nach Austritt der Bahn aus dem Preßspalt) die zuvor flach gepreßten Fasern (wie oben erläutert) wieder teilweise aufrichten, so daß der gemeinsame Kontakt-Anteil zwischen dem Preßband und der Bahn kleiner wird. Wenn die Preßspalt-Länge beispielsweise dreimal größer ist als in einem von zwei normalen Walzen gebildeten Preßspalt, so ist auch etwa eine 3-fache Erholungszeit nötig, um die Bahn wieder genügend leicht vom Preßband ablösen zu können. Es hat sich nun aber gezeigt, daß die oben beschriebene Wirkung der verlängerten Verweilzeit der Bahn auf dem Preßband (hinter dem letzten Preßspalt) auch dann das einwandfreie Abnehmen der Bahn vom Preßband ermöglicht, wenn es sich um verlängerte Preßspalte handelt.According to a particularly important further inventive concept, the considerably increased distance from the second press nip to the removal point is combined with the feature that the two pressure rollers (or at least the first pressure roller) are designed as long-nip pressure rollers known per se. This combination is based on the knowledge that the considerable distance of the take-off point from the second press nip makes it possible to let the press belt serving as the web conveyor belt run in succession through two so-called extended press nips. After an extended press nip through which the web runs in contact with a press belt, it is particularly difficult to detach the web from the press belt because the web comes into particularly intimate contact with the press belt due to the long dwell time in the press nip. Accordingly, the so-called recovery time becomes longer; this is the time in which (after the web has emerged from the press nip) the previously flat-pressed fibers (as explained above) partially straighten up again, so that the joint proportion of contact between the press belt and the web becomes smaller. If the press nip length is, for example, three times larger than in a press nip formed by two normal rollers, a triple recovery time is also necessary in order to be able to detach the web sufficiently easily from the press belt. It has now been shown, however, that the above-described effect of the prolonged dwell time of the web on the press belt (behind the last press nip) also enables the web to be removed from the press belt flawlessly when it comes to extended press nips.

Im übrigen kann man, durch die Verwendung der genannten Langspalt-Preßwalzen, deren an sich schon bekannte Vorteile nutzen, insbesondere wenn sie als sogenannte Schuh-Preßwalzen ausgebildet sind. Diese Walzen besitzen einen flexiblen, schlauchförmigen und an seinen beiden Enden hermetisch abgeschlossenen (und somit aufblasbaren) Preßmantel. Dieser wird mittels eines nicht-rotierenden und in radialer Richtung verschiebbaren Preßschuhes, der eine konkave Gleitfläche hat, gegen die Zentralwalze gepreßt. Eine derartige Walze ist somit selbstanpressend, d.h. ihre Lagerböcke und die Lagerböcke der kooperierenden Walze (nämlich der Zentralwalze) müssen nicht radial zueinander verschoben werden.For the rest, by using the long nip press rolls mentioned, the advantages known per se can be used, in particular if they are designed as so-called shoe press rolls. These rollers have a flexible, tubular and hermetically sealed (and thus inflatable) press jacket at both ends. This is pressed against the central roller by means of a non-rotating press shoe which can be moved in the radial direction and which has a concave sliding surface. Such a roller is therefore self-pressing, ie its bearing blocks and the bearing blocks of the cooperating roller (namely the central roller) do not have to be displaced radially to one another.

Die Verwendung von Schuh-Preßwalzen erlaubt eine erhebliche Steigerung der Arbeitsgeschwindigkeit, weil die verlängerten Preßspalte und die somit verlängerte Preßzeit die Entwässerungskapazität der Pressenpartie erheblich steigern. Die Papierbahn verläßt somit die Pressenpartie mit einem relativ hohen Trockengehalt, so daß in der nachfolgenden Trockenpartie weniger Wasser verdampft werden muß. Ein weiterer Vorteil der verlängerten Preßspalte besteht darin, daß in der Pressenpartie relativ dünne und fein-gewobene Filzbänder verwendet werden können; dies trägt zur Qualitätsverbesserung der fertigen Papierbahn bei.The use of shoe press rolls allows a considerable increase in the working speed, because the extended press nips and the thus extended press time considerably increase the dewatering capacity of the press section. The paper web thus leaves the press section with a relatively high dry content, so that less water has to be evaporated in the subsequent dryer section. Another advantage of the extended press nips is that relatively thin and finely woven felt belts can be used in the press section; this contributes to improving the quality of the finished paper web.

Ein ebenfalls wichtiger weiterführender Erfindungsgedanke ist im Anspruch 4 angegeben. Durch diese Maßnahme gelingt es, zuströmende Luft in relativ großer Entfernung vor dem ersten Preßspalt daran zu hindern, zwischen die Papierbahn und das Preßband einzudringen. Mit anderen Worten: Es wird auch bei sehr hohen Arbeitsgeschwindigkeiten vermieden, daß Lufteinschlüsse zwischen der Papierbahn und dem Preßband den einwandfreien Betrieb der Pressenpartie stören.An equally important further inventive idea is specified in claim 4. This measure makes it possible to prevent inflowing air at a relatively large distance from the first press nip from penetrating between the paper web and the press belt. In other words, even at very high working speeds, it is avoided that air pockets between the paper web and the press belt interfere with the proper operation of the press section.

Ein ebenfalls wichtiger weiterführender Erfindungsgedanke ist im Anspruch 13 angegeben. Danach wird die relativ lange Verweilzeit der Bahn zwischen Pressung und Abnahme zu einem zusätzlichen vorteilhaften Zweck genutzt, nämlich zur Vortrocknung der Bahn mittels einer Heizeinrichtung. Hierdurch kommt die Bahn mit einem noch zusätzlich gesteigerten Trockengehalt und folglich mit erhöhter Festigkeit an den kritischen Abnahmepunkt. Außerdem wird durch die Erwärmung die Viskosität des in der Bahn noch vorhandenen Wassers reduziert, insbesondere an der Kontaktfläche zwischen der Papierbahn und dem Preßband, so daß der Abnahmewiderstand der Papierbahn vom Preßband noch weiter reduziert wird.Another important further inventive idea is specified in claim 13. Thereafter, the relatively long dwell time of the web between pressing and acceptance is used for an additional advantageous purpose, namely for pre-drying the web by means of a heating device. As a result, the web comes to the critical point of take-off with an additional increase in dry content and consequently with increased strength. In addition, the viscosity of the water still present in the web is reduced by the heating, in particular at the contact surface between the paper web and the press belt, so that the removal resistance of the paper web from the press belt is reduced even further.

Weitere Ausgestaltungen und Vorteile der Erfindung sind in der nachfolgenden Beispielsbeschreibung erläutert.Further refinements and advantages of the invention are explained in the example description below.

Die Figur 1 zeigt schematisch eine erfindungsgemäße Pressenpartie in Seitenansicht.Figure 1 shows schematically a press section according to the invention in side view.

Die Figur 2 zeigt Einzelheiten der Fig. 1 in vergrößertem Maßstab.FIG. 2 shows details of FIG. 1 on an enlarged scale.

Die Figur 3 zeigt schematisch die Querschnittsformen der Preßschuhe der Langspalt-Preßwalzen.FIG. 3 shows schematically the cross-sectional shapes of the press shoes of the long-nip press rolls.

Die Figur 4 ist ein Teilschnitt durch das Preßband entlang der Linie IV der Fig. 3.FIG. 4 is a partial section through the press belt along line IV of FIG. 3.

Der Hauptteil der in Fig. 1 dargestellten Pressenpartie ist ein Walzensatz mit einer Zentralwalze O, die mit einer ersten Anpreßwalze 11 und mit einer zweiten Anpreßwalze 12 zwei Preßspalte I und II bildet. Ein im wesentlichen wasserundurchlässiges endloses Preßband 8 läuft über die Zentralwalze O und somit nacheinander durch die beiden Preßspalte I und II, außerdem über Bandleitwalzen 15, 15'. Das Preßband läuft vor dem ersten Preßspalt I auf die Zentralwalze O auf und verläßt diese wieder hinter dem zweiten Preßspalt II. Die in einer Siebpartie 3 gebildete Papierbahn (angedeutet durch eine gepunktete Linie) wird mit Hilfe eines ersten endlosen Filzbandes 1 über eine Abnahmesaugwalze 4 und über Saugleitwalzen 5 und 6 dem ersten Preßspalt I zugeführt. Die in einem Abstand vor dem ersten Preßspalt I liegende Saugleitwalze 6 ist derart angeordnet, daß zunächst das die Bahn führende Filzband 1 und sodann das Preßband 8 auflaufen. Von hier ab läuft also die Bahn zwischen Filzband 1 und Preßband 8 zum ersten Preßspalt I.The main part of the press section shown in FIG. 1 is a roller set with a central roller O, which forms two press nips I and II with a first pressure roller 11 and with a second pressure roller 12. An essentially water-impermeable endless press belt 8 runs over the central roller O and thus successively through the two press nips I and II, and also over belt guide rollers 15, 15 '. The press belt runs in front of the first press nip I on the central roll O and leaves it again behind the second press nip II. The paper web formed in a wire section 3 (indicated by a dotted line) is fed with the aid of a first endless felt belt 1 via a take-off suction roll 4 and fed to the first press nip I via suction guide rolls 5 and 6. The suction guide roller 6 lying at a distance in front of the first press nip I is arranged such that first the felt belt 1 guiding the web and then the press belt 8 run up. From here, the web runs between felt belt 1 and press belt 8 to the first press nip I.

Hinter dem ersten Preßspalt I trennt sich das erste Filzband 1 von der Bahn und vom Preßband 8 und läuft über Filzleitwalzen 7 zurück zur Abnahmesaugwalze 4. Die Bahn bleibt dagegen am Preßband 8 haften und läuft mit diesem um die Zentralwalze O herum in den zweiten Preßspalt II. Durch diesen läuft in vielen (aber nicht in allen) Anwendungsfällen ein zweites endloses Filzband 2, das sich hinter dem zweiten Preßspalt II von der Bahn und vom Preßband 8 trennt. Dabei bilden das Filzband 2 und das Preßband 8 einen spitzen Winkel, der in den meisten Fällen kleiner als 10° ist. Außerhalb des Preßspaltes II läuft das zweite Filzband 2 über Filzleitwalzen 18 und 18'. Falls das zweite Filzband 2 weggelassen wird, soll die Härte des Walzenmantels der zweiten Anpreßwalze 12 geringer sein als die Härte der Bahnseite des Preßbandes 8, damit die Bahn hinter dem zweiten Preßsspalt II mit dem Preßband 8 weiterläuft. Zur Erzielung eines möglichst hohen Trockengehaltes der Bahn und möglichst hoher Laufgeschwindigkeiten wird man aber in der Regel auf das zweite Filzband nicht verzichten können.Behind the first press nip I, the first felt belt 1 separates from the web and from the press belt 8 and runs via felt guide rollers 7 back to the take-off suction roll 4. The web, on the other hand, sticks to the press belt 8 and runs with it around the central roller O into the second press nip II In many (but not all) applications, this runs through a second endless felt belt 2, which separates from the web and from the pressing belt 8 behind the second press nip II. The felt belt 2 and the press belt 8 form an acute angle, which in most cases is less than 10 °. Outside the press nip II, the second felt belt 2 runs over felt guide rollers 18 and 18 '. If the second felt belt 2 is omitted, the hardness of the roll shell of the second pressure roller 12 should be lower than the hardness of the web side of the press belt 8, so that the web continues to run behind the second press nip II with the press belt 8. In order to achieve the highest possible dry content of the web and the highest possible running speeds, however, it will generally not be possible to do without the second felt belt.

Wesentlich ist, daß die Bandleitwalzen 15 und 15' des Preßbandes 8 derart angeordnet sind, daß das Preßband 8 eine relativ große Entfernung überbrückt von der Zentralwalze O bis in den Bereich des ersten Trockenzylinders 14 der auf die Pressenpartie folgenden Trockenpartie. Das Preßband 8 führt hierbei die Bahn vom zweiten Preßspalt II bis zu einer Abnahmestelle 9; sie wird dort mittels einer Abnahmesaugwalze 10 auf ein Trockensieb 13 überführt und läuft sodann mit diesem in bekannter Weise über die Trockenzylinder 14 und über weitere Saugleitwalzen 10'.It is essential that the belt guide rollers 15 and 15 'of the press belt 8 are arranged such that the press belt 8 bridges a relatively large distance from the central roller O to the area of the first drying cylinder 14 of the dryer section following the press section. The press belt 8 leads the web from the second press nip II to a take-off point 9; there it is transferred to a drying wire 13 by means of a take-off suction roll 10 and then runs with it in a known manner over the drying cylinders 14 and over further suction guide rolls 10 '.

Aus den oben erläuterten Gründen ist die Länge des Laufweges des Preßbandes 8 vom zweiten Preßspalt II bis zur Abnahmestelle 9 mindestens gleich dem Umfang der Zentralwalze O; vorzugsweise beträgt diese Länge jedoch das 2- bis 3-fache, manchmal sogar das 3- bis 5-fache des Umfanges der Zentralwalze O.For the reasons explained above, the length of the path of the press belt 8 from the second press nip II to the take-off point 9 is at least equal to the circumference of the central roller O; however, this length is preferably 2 to 3 times, sometimes even 3 to 5 times the circumference of the central roller O.

Die Saugleitwalze 5 kann (in einer verstärkten Form) zusammen mit einer (vorzugsweise gerillten) Preßwalze 17 einen Vor-Preßspalt V bilden, durch den ein zusätzliches Filzband 16 läuft, geführt durch Filzleitwalzen 19. Durch eine derartige, den Preßspalten I und II vorgeschaltete Doppelfilzpresse kann die Entwässerungskapazität der Pressenpartie noch weiter gesteigert werden.The suction guide roll 5 can (in a reinforced form) together with a (preferably grooved) press roll 17 form a pre-press nip V through which an additional felt belt 16 runs, guided by felt guide rolls 19. Through such a double felt press preceding the press nips I and II the dewatering capacity of the press section can be increased even further.

Zur Reinigung der Filzbänder 1, 2 und 16 sind in der üblichen Weise Spritzrohre 21 und Rohrsauger 20 vorgesehen. Zur Reinigung des Preßbandes 8 ist ein Schaber 22, ein Spritzrohr 24 und eine Bürstwalze 23 vorgesehen. Zur Reinigung der Zentralwalze O und der Leitwalzen 7, 15, 18 und 19 können ebenfalls Schaber vorgesehen werden, die in der Zeichnung weggelassen sind.For cleaning the felt tapes 1, 2 and 16, spray pipes 21 and pipe suction devices 20 are provided in the usual way. A scraper 22, a spray tube 24 and a brush roller 23 are provided for cleaning the press belt 8. For cleaning the central roller O and the guide rollers 7, 15, 18 and 19, scrapers can also be provided, which are omitted in the drawing.

In der Zone, wo die Bahn zusammen mit dem Preßband vom zweiten Preßspalt II zur Abnahmestelle 9 läuft, kann eine Heizeinrichtung 25 (z.B. mit Wärmestrahlern und/oder Warmluftdüsen) vorgesehen werden, um die Bahn anzuwärmen und vorzutrocknen.In the zone where the web runs together with the press belt from the second press nip II to the take-off point 9, a heating device 25 (e.g. with heat radiators and / or warm air nozzles) can be provided in order to heat and pre-dry the web.

Beim dargestellten Ausführungsbeispiel liegen die Achsen der Zentralwalze O und der Anpreßwalzen 11 und 12 in einer senkrecht angeordneten Preßebene E. Die Preßebene E könnte jedoch auch um bis zu 10° geneigt sein, nämlich in Fig. 1 oben nach rechts. In diesem Falle könnten die beiden Saugleitwalzen 5 und 6 zu einer einzigen Walze zusammengefaßt werden.In the illustrated embodiment, the axes of the central roller O and the pressure rollers 11 and 12 lie in a vertically arranged press plane E. However, the press plane E could also be inclined by up to 10 °, namely to the right in FIG. 1. In this case, the two suction guide rollers 5 and 6 could be combined into a single roller.

Wichtig ist, daß die Laufrichtung des Preßbandes 8 durch den ersten Preßspalt I der allgemeinen Maschinenlaufrichtung entgegengesetzt ist; denn auf dem Weg vom ersten zum zweiten Preßspalt kehrt sich die Laufrichtung des Preßbandes 8 um und entspricht dann der allgemeinen Maschinenlaufrichtung. Beim dargestellten Ausführungsbeispiel liegt der erste Preßspalt I unterhalb des zweiten Preßspaltes II. Diese Anordnung wird bevorzugt, weil hierdurch die Bahn auf dem nachfolgenden Weg zur Abnahmestelle 9 auf der Oberseite des Preßbandes 8 liegt. Die umgekehrte Anordnung ist allerdings ebenso denkbar.It is important that the running direction of the press belt 8 through the first press nip I is opposite to the general machine direction; because on the way from the first to the second press nip the direction of the press belt 8 is reversed and then corresponds to the general machine direction. In the illustrated embodiment, the first press nip I below the second press nip II. This arrangement is preferred because it causes the web on the subsequent path to the take-off point 9 on the upper side of the press belt 8. The reverse arrangement is also conceivable.

Aus Gründen der Platzersparnis kann das Preßband 8 auf dem Weg vom zweiten Preßspalt II zur Abnahmestelle 9 über eine Knickwalze 15' geführt werden, die das Preßband 8 aus einer überwiegend horizontalen Richtung in eine nach unten geneigte Richtung umlenkt.To save space, the press belt 8 can be guided on the way from the second press nip II to the take-off point 9 via an articulated roller 15 'which deflects the press belt 8 from a predominantly horizontal direction into a downward inclined direction.

In den Figuren 2 und 3 erkennt man wieder die Zentralwalze O und die beiden Anpreßwalzen 11 und 12. Die letzteren sind als Langspalt-Preßwalzen ausgebildet; d.h. sie haben einen flexiblen schlauchförmigen Preßmantel 26, 27, dessen Enden in bekannter Weise mittels einer nicht dargestellten rotierenden Scheibe hermetisch abgeschlossen sind. Somit kann Schmiermittel nicht nach außen dringen und der Innenraum kann mit Druckluft beaufschlagt werden. Durch das Innere jeder Langspalt-Preßwalze erstreckt sich ein stationärer Tragkörper 28 bzw. 29. In diesem ist in bekannter Weise ein Preßschuh 30 bzw. 31 gelagert, der sich über die gesamte Bahnbreite erstreckt, eine konkave Gleitfläche aufweist und hydraulisch in radialer Richtung verschiebbar ist. Hierdurch kann er den Preßmantel 26 bzw. 27 an die Zentralwalze O anpressen. Die beiden Preßschuhe 30 und 31 sind unterschiedlich geformt; d.h. die beim Pressen wirksame Breite b1 des Preßschuhes 30 der ersten Anpreßwalze 11 ist größer als die beim Pressen wirksame Breite b2 des Preßschuhes 31 der zweiten Anpreßwalze 12. Dagegen ist die Breite B des Kolbenteiles der beiden Preßschuhe 30 und 31 gleich; somit sind die beiden Tragkörper 28 und 29 im wesentlichen gleich geformt. Vorzugsweise werden auch die zum Betätigen der Preßschuhe 30, 31 dienenden Druckkammern mit annähernd gleichen Drücken beaufschlagt. Somit werden in beiden Preßspalte I und II weitgehend gleiche Liniendrücke erzeugt, so daß sich die auf die Zentralwalze O wirkenden Linienkräfte (abgesehen vom Eigengewicht) gegenseitig wenigstens angenähert aufheben. Die Zentralwalze O kann hierdurch als einfache, in normalen Lagern gelagerte Walze ausgebildet werden; d.h. sie braucht nicht als Walze mit einstellbarer Durchbiegung ausgebildet zu sein. Trotzdem ist der je Flächeneinheit erzeugte Preßdruck im ersten Preßspalt I kleiner als im zweiten Preßspalt II. Man erzielt also im ersten Preßspalt I eine relativ sanfte, aber lange andauernde Entwässerung der Papierbahn, im zweiten Preßspalt II dagegen eine intensivere Entwässerung, jedoch von kürzerer Zeitdauer. (Alternative: Tragkörper und Preßschuh, z.B. 29 und 31, könnten ersetzt werden durch einen drehbaren Walzenkörper).FIGS. 2 and 3 again show the central roller O and the two pressure rollers 11 and 12. The latter are designed as long-nip pressure rollers; that is, they have a flexible tubular press jacket 26, 27, the ends of which are hermetically sealed in a known manner by means of a rotating disk, not shown. This means that lubricant cannot escape and compressed air can be applied to the interior. A stationary support body 28 or 29 extends through the interior of each extended-nip press roll. A press shoe 30 or 31, which extends over the entire width of the web, has a concave sliding surface and is hydraulically displaceable in the radial direction . As a result, he can press the press jacket 26 or 27 against the central roller O. The two press shoes 30 and 31 are shaped differently; ie the effective width b1 of the pressure shoe 30 of the first pressure roller 11 during pressing is greater than the effective width b2 of the pressure shoe 31 of the second pressure roller 12 during pressing. In contrast, the width B of the piston part of the two pressure shoes 30 and 31 is the same; thus the two support bodies 28 and 29 are shaped substantially the same. The pressure chambers used to actuate the pressure shoes 30, 31 are preferably also subjected to approximately the same pressures. Thus, largely identical line pressures are generated in both press nips I and II, so that they are on the central roller O at least approximately cancel out the acting line forces (apart from their own weight). The central roller O can thereby be designed as a simple roller stored in normal bearings; ie it need not be designed as a roller with adjustable deflection. Nevertheless, the pressing pressure generated per unit area is lower in the first press nip I than in the second press nip II. A relatively gentle, but long-lasting dewatering of the paper web is achieved in the first press nip I, in contrast, in the second press nip II, more intensive dewatering, but of shorter duration. (Alternative: support body and press shoe, e.g. 29 and 31, could be replaced by a rotatable roller body).

In Fig. 2 sieht man noch an einem der beiden Walzenenden das Lagergehäuse 35 der Zentralwalze O und die zweiteiligen Lagerböcke 36 bzw. 37, in denen die Tragkörper 28 bzw. 29 der Langspalt-Preßwalzen 11 und 12 ruhen. Der untere Lagerbock 36 ruht auf einem entfernbaren Zwischenstück 38 und dieses auf einem stationären Maschinengestell 40, Fundament od.dgl. Der obere Lagerbock 37 ist mittels zweier Zugelemente 39 an dem Maschinengestell 40 aufgehängt.In Fig. 2 you can still see at one of the two roller ends, the bearing housing 35 of the central roller O and the two-part bearing blocks 36 and 37, in which the support bodies 28 and 29 of the extended-nip press rollers 11 and 12 rest. The lower bracket 36 rests on a removable intermediate piece 38 and this on a stationary machine frame 40, foundation or the like. The upper bracket 37 is suspended from the machine frame 40 by means of two tension elements 39.

Mit Hilfe von zwei Säulen 41, 42 sind das Lagergehäuse 35 und die beiden Lagerböcke 36 und 37 formschlüssig, also vollkommen starr miteinander verbunden. Im normalen Betrieb wird also keines der Lagergehäuse 35 oder Lagerböcke 36, 37 bewegt. Zum Aufbringen der Preßkräfte genügt allein das radiale Verschieben der Preßschuhe 30 und 31. Die beiden Säulen 41 und 42 können zum Auswechseln der Filzbänder 1 und 2, des Preßbandes 8 oder der Preßmäntel 26, 27 entfernt werden. Zum Auswechseln der Preßmäntel 26, 27 sind zusätzlich das Zwischenstück 38 bzw. die Zugelemente 39 zu entfernen. Um Schwingungen zu vermeiden können die Säulen 41, 42 ebenfalls mit dem stationären Maschinengestell 40 verbunden sein, wie beispielhaft bei 43 angedeutet ist.With the help of two columns 41, 42, the bearing housing 35 and the two bearing blocks 36 and 37 are positively connected, that is to say completely rigidly connected to one another. During normal operation, therefore, none of the bearing housings 35 or bearing blocks 36, 37 are moved. To apply the pressing forces, the radial displacement of the press shoes 30 and 31 is sufficient. The two columns 41 and 42 can be removed to replace the felt belts 1 and 2, the press belt 8 or the press sleeves 26, 27. To replace the press sleeves 26, 27, the intermediate piece 38 or the tension elements 39 must also be removed. In order to avoid vibrations, the columns 41, 42 can also be connected to the stationary machine frame 40, as is indicated by way of example at 43.

Um in den Preßspalten I und II eine möglichst störungsfreie und über die Maschinenbreite gleichmäßige Entwässerung zu erzielen, ist gemäß Fig. 3 folgendes vorgesehen: Das Preßband 8 läuft zusammen mit dem Filzband 1 (und zusammen mit der dazwischenliegenden Papierbahn) an einer Stelle W auf die Zentralwalze O auf, die sich in einem gewissen Abstand vor dem Einlauf in den ersten Preßspalt I befindet. Dies bewirkt, daß Preßband 8 und Filz 1 satt an der Zentralwalze O anliegen, bevor der Preßmantel 26 mit dem Filz 1 in Kontakt kommt. Hinter dem ersten Preßspalt I verläßt das erste Filzband 1 die Zentralwalze O an einer Stelle X, die in einem gewissen Abstand hinter dem Auslauf aus dem Preßspalt I liegt. Dies ermöglicht, daß Luft von unten her - unmittelbar hinter dem Auslauf aus dem Preßspalt I - in den Filz 1 eindringen kann, so daß sich dieser leicht von der Bahn löst. Die Auflaufstelle Y des zweiten Filzbandes 2 auf die Zentralwalze O liegt ebenfalls in einem gewissen Abstand vor dem Einlauf in den zweiten Preßspalt II. Schließlich läuft das Preßband 8 an einer mit Abstand hinter dem zweiten Preßspalt II liegenden Stelle Z von der Zentralwalze O ab. Das zweite Filzband 2 bildet in diesem Bereich mit dem Preßband 8 einen Winkel a zwischen 5 und 15°. Dieser Winkel hängt ab u.a. von der Papiersorte und kann durch vertikales Verstellen der Leitwalze 18' (Fig. 1) variiert werden.In order to achieve the most trouble-free and uniform drainage in the press nips I and II, the following is provided according to FIG. 3: The press belt 8 runs together with the felt belt 1 (and together with the paper web in between) at a point W on the Central roller O, which is located at a certain distance before entering the first press nip I. This causes the press belt 8 and felt 1 to lie snugly against the central roller O before the press jacket 26 comes into contact with the felt 1. Behind the first press nip I, the first felt belt 1 leaves the central roller O at a point X which lies at a certain distance behind the outlet from the press nip I. This enables air to penetrate into the felt 1 from below - immediately behind the outlet from the press nip I - so that it easily detaches from the web. The contact point Y of the second felt belt 2 on the central roll O is also at a certain distance from the entry into the second press nip II. Finally, the press belt 8 runs from the central roll O at a point Z which is at a distance behind the second press nip II. In this area, the second felt belt 2 forms an angle a of between 5 and 15 ° with the press belt 8. This angle depends, among other things. of the paper type and can be varied by vertically adjusting the guide roller 18 '(Fig. 1).

Das Preßband 8 ist hergestellt vorzugsweise aus einem gießfähigen und ausgehärtetem Kunststoff (z.B. Polyurethan) mit einer Armierung, z.B. in Form eines Gewebes oder gemäß Figur 4 in Form eingelegter Fäden 44, z.B. entsprechend WO 88/08897 (Akte P 4378). Die Härte des Kunststoffes (zumindest im Bereich der bahnseitigen Oberfläche 45) liegt normalerweise im Bereich zwischen 80 und 95 Shore A. Das Preßband 8 hat eine glatte und nicht-wasserdurchlässige bahnseitige Oberfläche 45 und eine Dicke von etwa 2,5 bis 5 mm. Die der Zentralwalze O zugewandte Oberfläche 46 des Preßbandes kann ebenfalls glatt sein; vorzugsweise ist sie jedoch mit Ausnehmungen 47 versehen zum vorübergehenden Speichern von Wasser. Hierdurch wird Aquaplaning vermieden, das durch im Inneren der Preßbandschlaufe vagabundierendes Wasser verursacht werden kann. Hierdurch würde die Zugbeanspruchung des Preßbandes 8 in den Preßspalten I und II in unerwünschter Weise erhöht werden. Die Ausnehmungen 47 können (wie an sich bekannt) als Sackbohrungen oder als Umfangsrillen ausgebildet sein oder durch ein Armierungsgewebe gebildet sein, das teilweise aus dem Kunststoffmaterial herausragt.The press belt 8 is preferably made of a pourable and hardened plastic (for example polyurethane) with a reinforcement, for example in the form of a fabric or in accordance with FIG. 4 in the form of threads 44, for example in accordance with WO 88/08897 (file P 4378). The hardness of the plastic (at least in the area of the web-side surface 45) is normally in the range between 80 and 95 Shore A. The press belt 8 has a smooth and water-impermeable web-side surface 45 and a thickness of approximately 2.5 to 5 mm. The surface 46 of the press belt facing the central roller O can also be smooth; however, it is preferably provided with recesses 47 for the temporary storage of water. This prevents aquaplaning, which can be caused by water straying inside the press belt loop. This would undesirably increase the tensile stress on the press belt 8 in the press nips I and II. The recesses 47 (as is known per se) can be designed as blind bores or as circumferential grooves or can be formed by a reinforcing fabric that partially protrudes from the plastic material.

Claims (21)

  1. Press section of a machine for producing a fibrous material web, in particular, a paper web with the following features:
    a) a central roll (O) forms a first and a second press nip (I and II) with a first press roll (11) and a second press roll (12);
    b) a continuous essentially water-impervious press belt (8) runs through both press nips (I and II), whereby it runs onto the central roll (O) in front of the first press nip (I) and runs off the central roll behind the second press nip (II);
    c) an continuous felt band (1) guides the web to be dewatered into the first press nip (I) and is afterwards separated from the web;
    d) the press belt (8) guides the web behind the first press nip (I) around the central roll (O) into the second press nip (II) and behind to a receiving point (9) at which a another means of transport (10) takes the web;
    e) characterized in that the distance from the second press nip (II) to the said receiving point (9) is at least the same as the circumference of the central roll (O), whereby the second press nip (II) is the last press nip of the press section.
  2. The press section according to claim 1, characterized in that the distance from the second press nip (II) to the said receiving point (9) is 1.5 to 5 times, preferably 2 to 3 times the circumference of the central roll (O).
  3. The press section according to claim 1 or 2, characterized in that at least the first press roll (11), preferably both press rolls (11 and 12) are designed to be long-nip press rolls each with a hose-shaped press shell which can be pressed against the central roll (O) by means of a support member, preferably by means of a press shoe (30, 31).
  4. The press section according one of claims 1 to 3, characterized in that a suction roll (6) is provided spaced in front of the first press nip (I) onto which first the felt band (1) guiding the web and then the press belt (8) run.
  5. The press section according to claim 4, characterized in that in front of the first press nip (I) the felt band (1) guiding the web runs together with an additional felt band (16) through a pre-press nip (V).
  6. The press section according to one of claims 1 to 5, characterized in that the direction of travel of the web in the first press nip (I) is at least roughly opposite to the general direction of travel of the machine.
  7. The press section according to one of claims 1 to 6, characterized in that the axes of the central roll (O) and the press rolls (11 and 12) lie at least approximately in a single plane, the press plane (E), and that the press plane (E) is arranged to be roughly perpendicular or inclined to the perpendicular by 10° at the most.
  8. The press section according to one of claims 1 to 7, characterized in that the first press roll (11) is arranged beneath the central roll (O) and that the second press roll (12) is arranged above the central roll (O).
  9. The press section according to one of claims 1 to 8, characterized in that the press belt (8) together with the felt band (1) run onto the central roll (O) at a point (W) spaced in front of the first press nip (I) and that the felt band (1) runs off the central roll (O) at a point (X) spaced behind the first press nip (I).
  10. The press section according to one of claims 1 to 9, characterized in that the press belt (8) runs off the central roll (O) at a point (Z) spaced behind the second press nip (II).
  11. The press section according to one of claims 1 to 10, characterized in that a felt band (2) also runs through the second press nip (II) and that behind the second press nip (II) the second felt band (2) and the press belt (8) together form an acute angle a of 5 to 15°.
  12. The press section according to one of claims 1 to 11, characterized in that between the second press nip (II) and the receiving point (9) a bending roll (15') is provided for steering the press belt (8).
  13. The press section according to one of claims 1 to 12, characterized in that the press belt (8) - between the second press nip (II) and the receiving point (9) - guides the web past a heating device (25), e.g. past thermal radiators and/or hot air ducts.
  14. The press section according to one of claims 1 to 13, characterized in that at each roll end of the central roll (O) and the press rolls (11, and 12) the bearing blocks (36, 37) of the press rolls (11, 12) and the bearing housing (35) of the central roll (O) are positively connected with the aid of removable posts (41, 42).
  15. The press section according to one of claims 1 to 14, characterized in that cleaning devices are provided on the press belt (8), e.g. a scraper (22), spray pipe (24), brush roll (23) or the like.
  16. The press section according to one of claims 2 to 15, characterized in that the measured length of the press nip in the direction of travel of the web, i.e. the effective width b1 or b2, is greater in the first press nip (I) than in the second press nip (II).
  17. The press section according to claim 16, characterized in that the line forces, i.e. the pressing force per m of web width, in both press nips (I, II) are at least roughly the same, i.e. differ by 20% at the most.
  18. The press section according to one of claims 1 to 17, characterized in that the web side surface (45) of the press belt (8) is smooth and impervious to water.
  19. The press section according to claim 18, characterized in that surface (46) contacting the central roll (O) of the press belt (8) has recesses (47) for temporarily storing water.
  20. The press section according to claim 18 or 19, characterized in that the hardness of the web side (45) of the press belt (8) is in the region of 80 to 95 Shore.
  21. The press section according to claim 20, wherein the second press nip (II) is free of the felt band, characterized in that the roll shell, e.g. the press shell (27), of the second press roll (12) is less hard than the web side (45) of the press belt (8).
EP91119700A 1991-01-26 1991-11-19 Press section Expired - Lifetime EP0496965B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4102356A DE4102356C1 (en) 1991-01-26 1991-01-26
DE4102356 1991-01-26

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EP0496965A1 EP0496965A1 (en) 1992-08-05
EP0496965B1 true EP0496965B1 (en) 1995-04-19

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EP91119700A Expired - Lifetime EP0496965B1 (en) 1991-01-26 1991-11-19 Press section

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US (1) US5256257A (en)
EP (1) EP0496965B1 (en)
JP (1) JPH0544189A (en)
AT (1) ATE121475T1 (en)
CA (1) CA2059870C (en)
DE (2) DE4102356C1 (en)
ES (1) ES2071892T3 (en)
FI (1) FI920082A (en)

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Also Published As

Publication number Publication date
US5256257A (en) 1993-10-26
ES2071892T3 (en) 1995-07-01
CA2059870C (en) 1996-04-02
DE4102356C1 (en) 1992-01-23
FI920082A (en) 1992-07-27
DE59105267D1 (en) 1995-05-24
JPH0544189A (en) 1993-02-23
FI920082A0 (en) 1992-01-08
EP0496965A1 (en) 1992-08-05
ATE121475T1 (en) 1995-05-15

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