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WO2000024965A1 - Procede et dispositif d'essorage par impulsions - Google Patents

Procede et dispositif d'essorage par impulsions Download PDF

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Publication number
WO2000024965A1
WO2000024965A1 PCT/FI1999/000871 FI9900871W WO0024965A1 WO 2000024965 A1 WO2000024965 A1 WO 2000024965A1 FI 9900871 W FI9900871 W FI 9900871W WO 0024965 A1 WO0024965 A1 WO 0024965A1
Authority
WO
WIPO (PCT)
Prior art keywords
shoe
press
area
pressure
web
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.)
Ceased
Application number
PCT/FI1999/000871
Other languages
English (en)
Inventor
Antti Ilmarinen
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.)
Valmet Technologies Oy
Original Assignee
Metso Paper Oy
Valmet Oy
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Metso Paper Oy, Valmet Oy filed Critical Metso Paper Oy
Publication of WO2000024965A1 publication Critical patent/WO2000024965A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • 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
    • D21F3/0281—Wet presses in combination with a dryer roll

Definitions

  • the invention concerns a method for impulse dewatering of a paper or board web, in which method the web to be dewatered is passed on support of a press fabric through an extended press zone formed between a heatable backup roll and a press shoe, in which press zone pressing is applied to the web in a number of component stages directly following one after the other so that, in the first stage, the pressure is increased evenly in the first hydrodynamic area in the initial part of the press zone from the starting level to the nip pressure proper, in the second stage the web is pressed with a uniform pressure in the area of effect of the hydrostatic pressure chamber in the press shoe, and in the third stage the pressing is continued in the second, short hydrodynamic area following after the hydrostatic area by using a compression pressure which is at least equally high as the compression pressure used in the preceding second stage.
  • the invention comprises a device for impulse dewatering, which comprises a backup roll and means for heating the face of the backup roll, a press fabric for supporting the web, and a press shoe device, which comprises a press shoe and a glide belt, which belt has been fitted to glide over the lubricated front face of the press shoe, and the press shoe has been fitted to be pressed against the face of the heatable backup roll by means of at least two successive sets of loading members, by whose means at least two separate loading forces are produced, and between the heatable backup roll and the press shoe an extended press zone has been formed, which comprises, in the direction of progress of the web, first a first hydrodynamic area, then an area of effect of a hydrostatic pressure chamber, and after that a second short hydrodynamic area.
  • Impulse dewatering is employed in the press section of a paper machine to intensify the draining of water out of the web.
  • US Patent 4,324, 613 in which the paper web is passed on support of a press fabric between two press rolls, of which rolls the face of one roll has been heated to a high temperature.
  • heat is transferred from the heated roll face to the paper web, in which connection the water contained in the web starts vaporizing.
  • the pressure of the vapour that is formed forces water, which has been pressed into the intermediate spaces in the fibre mesh, into the press fabric placed at the opposite side of the web.
  • the high temperature lowers the viscosity and the surface tension of the water and alters the elastic properties of the fibre mesh and also thereby enhances the mechanical pressing of the water out of the web into the press fabric.
  • a temperature range of 150...300 °C is used, and the pressure is, as a rule, in a range 0.5...8 MPa.
  • the time of dwell of the web in the press nip is 15...100 ms.
  • the heat that is transferred from the heated backup roll to the paper web raises the temperature of the web, whereat water attempts to vaporize in particular in the surface layers of the web.
  • the high pressure present in the nip restricts the vaporization of the water.
  • the pressure is lowered rapidly to the level of the ambient pressure, the water of a temperature higher than 100 degrees vaporizes abruptly, and the vapour that is formed expands explosively. This tends to result in delamination of the web, i.e. in disruption of the structure as the fibre mesh expands without control.
  • the shoe in the press be arranged so that the compression pressure in the nip is lowered towards the end of the press zone, in which case the web is not subjected to an excessively rapid lowering of the pressure at the end of the pressing.
  • a method for impulse drying is described in which attempts are made to prevent delamination of the pressed web so that the position of the press shoe in relation to the heated backup roll is regulated and that the form of the pressure curve in the press zone is thereby affected.
  • the possibilities to control the form of the pressure curve are, however, limited, among other things, because the press shoe is loaded by means of one set of loading members only.
  • the press zone comprises at least two hydrostatic press stages.
  • a high compression pressure is used, in which connection the pores in the web are filled with water.
  • a pressure is used that is lower than the pressure of saturated vapour at the temperature concerned but higher than the ambient tempera- ture.
  • the hot water contained in the pores in the web vaporizes in a controlled way, at the same time as the press zone restricts the expansion of the vapour and of the web.
  • the object of the present invention is to provide a method and a device suited for impulse dewatering of a paper or board web by whose means it is possible to avoid delamination of the web and, at the same time, to control the properties of the web efficiently.
  • compression is applied to the web in a number of component stages directly following each other, of which stages the first and the third stage are hydrodynamic, and the second stage is hydrostatic.
  • the invention is characterized in that in the fourth component stage of pressing, which follows after the three component stages of pressing mentioned above, in the hydrodynamic area in the final part of the press shoe, the compression pressure is lowered to a level, which is lower than the nip pressure proper but higher than the pressure in the environment, and the com- pression pressure is maintained at this level and substantially invariable to the end of the third hydrodynamic area, the duration in time of said last pressing stage being at least one third of the total duration in time of the whole pressing.
  • the device for impulse dewatering in accordance with the present invention com- prises a press shoe whose press zone includes a hydrostatic area which is preceded and followed by short hydrodynamic areas.
  • the invention is characterized in that the three areas of the press zone mentioned above are followed by a third hydrodynamic area, which forms the final part of the press shoe and whose length is at least one third of the total length of the press zone and whose shape and/or loading has/have been fitted such that, in this last area of the press zone, the pressure is initially lowered to a level that is lower than the nip pressure proper but higher than the pressure in the environment, and the pressure is then maintained at this level substantially invariable substantially to the end of the area.
  • the device in accordance with the invention it is also possible to affect the properties of the impulse-dewatered web in a versatile way by means of regulation of the loading of the press shoe.
  • the initial part of the shoe is loaded with two successive loading forces, and by means of alteration of the relative magnitudes of these forces, it is possible to affect the tilt of the shoe and, thereby, the maximal compression pressure which is effective in the hydrodynamic area following after the hydrostatic area.
  • Figure 1 is a general view of an impulse dewatering device in accordance with the invention.
  • Figure 2A is a sectional view in an enlarged scale of the press zone of the impulse dewatering device.
  • Figure 2B illustrates an alternative embodiment of the geometry of the press shoe.
  • Figure 3 illustrates the distribution of the pressure in the press zone of a press shoe as shown in Fig. 2A.
  • Figure 4 shows an alternative embodiment of the invention, in which the final part of the press shoe is connected with the initial part of the shoe by means of an articulated zone.
  • Figure 5 shows an alternative embodiment, in which the final part of the press shoe is resilient.
  • Figure 6 shows an alternative embodiment of the invention, in which the position of the press shoe is regulated by means of a screw member or equivalent.
  • Figure 7 shows an alternative embodiment of the invention in which the shoe consists of two separate parts fitted one after the other.
  • Figure 8 shows an alternative embodiment of the invention, in which the shape of the final part of the press shoe differs from that shown in Fig. 2A.
  • the impulse dewatering device comprises a heatable backup roll 20 and a press shoe device 16, between which an extended press zone is formed.
  • the web 10 is passed through the press zone on support of a press fabric 12, which press fabric also receives and carries away the water that was pressed out of the web in the nip.
  • the face of the backup roll 20 is heated by means of an induction heater 22 to a temperature higher than 150 °C. For heating the roll, it is also possible to use other heating methods in themselves known.
  • the press shoe device 16 comprises a press shoe, i.e. an extended-nip shoe 18, whose curved front face 25 is pressed, in the way illustrated in Fig. 2A, by means of loading members against the heated face of the backup roll 20.
  • the loading members that are used are two successive rows of hydraulic cylinders 23a, 23b, by whose means forces F A and F B that load the press shoe 18 are pro- quizd.
  • the distribution of the compression pressure between different parts of the shoe can be affected by regulating the tilt of the shoe, i.e. the relative magnitude of the forces F A and F B . Also, regulation of the pressure profile in the cross direction of the web is possible so that the loading of the individual cylinders in the rows of cylinders 23a, 23b is regulated.
  • An endless glide belt 14 made of a resilient and non-permeable material has been fitted to run over the press shoe 18.
  • lubrication has been arranged in order to minimize the glide friction.
  • the press shoe device consists of a belt mantle roll 16, in which a hose-like glide belt mantle 14 has been fitted to revolve around a stationary roll axle.
  • the press shoe device it is also possible to use other solutions in themselves known so as to support the press shoe and the glide belt.
  • Fig. 2 A is a more detailed illustration of the construction of the press shoe 18 and of the press zone I... IV.
  • the press shoe is loaded by means of two rows of loading cylinders 23a,23b.
  • a support member 27 At the outlet side of the shoe, there is a support member 27, which receives the horizontal forces applied by the rotation of the backup roll 20 to the press shoe 18.
  • the curve form of the front face 25 of the shoe is close to the curve form of the face of the backup roll 20, but the curve radii are, however, not equal.
  • a capillary duct 26 In the bottom of each chamber 26, there is a capillary duct 26, through which hydraulic fluid is passed into the chamber.
  • the press zone in the impulse dewatering device in accordance with the invention can be divided into four operationally different areas I... IV. In the following, these areas will be described with reference to Figs. 2A and 3, the distribution of the compression pressure in the different operational zones of the shoe being illustrated in the latter one of said figures.
  • a hydrodynamic area I in which the compression pressure rises along a rather linear path from the starting level to the nip pressure pi proper.
  • the web 10 is compressed by the effect of the pressure, its pores are filled with water, and water starts flowing out of the web into the press fabric 12.
  • the web 10 reaches contact with the heated face of the backup roll 20, and transfer of heat from the backup, roll to the web starts.
  • the nip area proper is formed in the hydrostatic area II of the press shoe 18, which area includes a hydrostatic pressure chamber 24.
  • the hydrostatic area II is followed by a short hydrodynamic area III, whose length is at the maximum 30 mm and in which the shape of the pressure curve can, if necessary, still be affected by varying the tilt of the shoe, i.e. the relative proportion of the loading forces F A and F B .
  • a pressure peak p t can be produced in the hydrodynamic area III, in which connection the pressing efficiency is increased.
  • an extended-nip shoe In wet pressing of a web, as a rule, an extended-nip shoe is employed whose press zone ends with an abrupt pressure drop at the end of the area II or III. In such a case, the pressure must be lowered as rapidly as possible in order that rewetting of the web could be avoided at the outlet side of the shoe.
  • rewetting of the web is not a problem, but delamination of the web, which follows from an excessively rapid loss of pressure at the end of the press zone.
  • the risk of delamination of the web is reduced by, after the high-pressure press area I... Ill proper, providing a further, relatively long hydrodynamic area IV, in which the compression pressure is initially allowed to go down to a level p 2 lower than the nip pressure pi proper, and the pressure is then kept at this level substantially invariable up to the end of the area IV.
  • the pressure is not allowed to go down to the level of the pressure in the environment, but in the end of the press zone there is a part in which a low compression pressure is maintained.
  • the pressure p 2 is somewhat higher than the pressure in the environment, but, however, to such an extent low that the water at a temperature higher than 100 degrees vaporizes readily. Expansion of the web as a result of sudden formation of vapour is restricted by the almost parallel arcuate faces of the backup roll 20 and of the press shoe 18.
  • a conventional extended-nip shoe comprises the operational areas I... Ill only, by whose means the principal compression effect is produced while employing relatively high compression pressures.
  • a considerable proportion of the evaporation of water takes place in the last press stage IV, whose length is 1/3...2/3 of the entire length of the shoe and in which the pressure is lower than the vaporizing pressure of water at the temperature concerned but higher than the pressure in the environment.
  • the press shoe 18 is shaped so that the curve radius R ⁇ of its front face 25 is larger than the sum of the curve radius Ry of the backup roll 20, of the thickness of the press fabric 12 and of the thickness of the glide belt 14.
  • the distance between the front face 25 of the press shoe and the face of the backup roll 20 is shortest in the area of the middle portion of the shoe, and the gap becomes just a little wider towards the edges of the shoe.
  • the operation of the press shoe in the area IV is based on hydrodynamic lubrication.
  • a hydrodynamic system of lubrication the shape and the relative movement of the glide faces produces a fluid film, whose pressure is sufficient to keep the moving faces apart from one another.
  • the hydrodynamic pressure becomes higher in wedge shape.
  • the hydrodynamic pressure becomes lower and is finally converted to a vacuum.
  • the thickness of the fluid film and the shape of the shoe i.e. its curve radius in relation to the curve form of the backup roll, have been set appropriately, the desired pressure curve is obtained in the area IV.
  • the thickness of the fluid film on a face with hydrodynamic lubrication is also affected by the speed of movement of the face and by the viscosity of the fluid.
  • the thickness of the fluid film in the hydrodynamic area I can be, for example, 0.3...0.6 mm, and in the area III similarly 0.1...0.3 mm.
  • the thickness of the fluid film can be, for example, 0.2 mm and, when the radius R ⁇ of the shoe is larger than the radius of the backup roll Ry, the thickness of the film at the final point of the area IV is larger than 0.2 mm, favourably, for example, 0.4 mm.
  • the vapour pressure is, at the same time, increased at the opposite side of the glide belt 14 in the web 10 and in the press fabric 12, in which case the compression pressure p 2 as a whole remains substantially invariable in the area IV, as is illustrated in Fig. 3.
  • Fig. 2B shows an alternative solution for the geometry of the front face of the press shoe.
  • the curve radius R K1 of the front face of the shoe in the initial part of the shoe in the areas I... Ill is smaller than the corresponding curve radius R K2 in the final part of the shoe in the area IV.
  • Both curve radii R ⁇ > R ⁇ 2 are still larger than the curve radius R v of the backup roll.
  • the faces 25a, 25b with different curve forms in the initial part and final part of the shoe have a common tangent t at the point P, at which the area III is converted to the area IV.
  • Figs. 4...8 illustrate further alternative solutions for formation of the low-pressure zone IV in accordance with the invention and for regulation of the compression pressure in this zone.
  • the illustrations have been simplified by omitting the web, the drying fabric, and the glide belt in the illustrations.
  • the press shoe 18 is composed of two parts 18a and 18b interconnected by means of an articulated zone, of which parts the first part 18a comprises the areas I... Ill with high compression pressure, and the second part 18b comprises the area IV with low pressure.
  • the articulation point 28 between the parts 18a and 18b can be accomplished, besides by means of an articulated joint proper, also by means of appropriate design of the shoe (e.g. a thinner portion) or by using a resilient material in the shoe.
  • the initial part 18a of the shoe is loaded with the forces F A and F B , and a separate loading force F is applied to the final part 18b of the shoe.
  • the force F c is produced, for example, by means of hydraulic cylinders (not shown), but other loading members can also be used, such as a screw (cf. Fig. 6).
  • a screw cf. Fig. 6
  • the final part 18c of the press shoe has been made into a resilient construction by making it thinner at the bottom side over the entire length of the area IV. Also in this case, a loading force F c is applied to the final part 18c of the shoe, which force makes the final part 18c of the shoe to be bent to the desired distance from the face of the backup roll 20.
  • the distance between the final part of the press shoe 18 and the face of the backup roll 20 is regulated by means of a force F c applied to the final part of the shoe. Since the construction of the shoe is rigid in this case, the loading force F also acts upon the loading of the initial part of the shoe at the same time, and, thus, the pressure in the areas I... Ill with high compression pressure depends on the resultant of all the loading forces F A , F B and F c applied to the shoe. In the case of Fig.
  • a screw 30 operates as a loading member, which screw has been attached to a hole fitted in a bracket 29 of the support member 27 and provided with inside threading, and the tightening force of the screw can be adjusted from outside the belt mantle roll. Since the construction of the shoe is not resilient, in view of obtaining the desired pressure profile it is particularly important that the ratio of the curve radius R ⁇ of the press shoe 18 to the curve radius R v of the backup roll has been chosen appropriately so that R ⁇ > R v .
  • the press shoe comprises two separate parts 18d' and 18d" fitted one after the other, of which parts the first part 18d' comprises the areas I... Ill with high pressure, and the second part 18d" comprises the area IV of low pressure.
  • the first part 18d' is loaded in the customary way with the forces F A and F B
  • the second part 18d" is again loaded, independently from the first part, with the forces F C1 and F C2 .
  • This solution provides versatile possibilities for regula- tion of the pressure profile in the area of the final part 18d" of the shoe.
  • Fig. 8 shows an alternative solution in which, in the area of the final part of the press shoe, the shape of the front face 25" is different from that in the area (25') of the initial part of the shoe. Also by means of this shoe construction, it is possible to achieve the objective of the invention, i.e. a long area IV of low and relatively invariable pressure after the areas I... Ill with high compression pressure.
  • the press shoe has been shaped so that in its final part, in the beginning of the area IV of low pressure, the distance between the backup roll 20 and the press shoe 18 becomes stepwise wider from what this gap is in the end of the area III. Towards the end of the area IV, the gap becomes slightly narrower and, at the same time, the thickness of the fluid film between the glide faces becomes thinner.
  • pressurized lubrication fluid is fed through a duct 26 into the hydrostatic pressure chamber 24 so as to produce a hydrostatic pressure in the area II of the press zone and in order to lubricate the hydrodynamic glide faces.
  • low- pressure additional fluid is fed through the duct 32.
  • the shoe is loaded in the customary way with the forces F A and F B .
  • the thickness of the fluid film present between the press shoe 18 and the glide belt 14 can vary, for example, as follows: in the area I, i.e. in the beginning of the press zone, 0.5 mm; in the hydrodynamic area III following after the hydrostatic area II, 0.15 mm, in the beginning of the area IV of low pressure, 0.6...2.0 mm, and in the end of the same area IV, 0.3...0.5 mm.

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Abstract

L'invention concerne un procédé et un dispositif d'essorage par impulsions. Une bande de papier ou de carton (10) est pressée dans une zone de presse étendue (I IV) formée entre un cylindre d'appui chauffant (20) et un support de presse (18). Dans le sens de défilement de la bande (10), la zone de presse (I IV) comprend d'abord une première partie hydrodynamique (I) suivie d'une partie hydrostatique (II) et d'une seconde partie hydrodynamique courte (III). Ces trois parties haute pression (I III) sont suivies d'une troisième partie hydrodynamique (IV) qui forme la partie finale du support de presse (18). La longueur de la dernière partie (IV) correspond à au moins un tiers de la longueur totale de la zone de presse (I IV) et sa forme et/ou sa charge est(sont) telle(s) que la pression dans cette partie (IV) de la zone de presse est d'abord abaissée à un niveau (p2) inférieur à celui de la pression de contact (p1) correcte mais supérieur à celui de la pression présente dans l'environnement. La pression reste ensuite à son niveau sensiblement invariable jusqu'à la fin de la partie (IV).
PCT/FI1999/000871 1998-10-23 1999-10-20 Procede et dispositif d'essorage par impulsions Ceased WO2000024965A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI982293 1998-10-23
FI982293A FI105050B (fi) 1998-10-23 1998-10-23 Impulssikuivatusmenetelmä ja -laite

Publications (1)

Publication Number Publication Date
WO2000024965A1 true WO2000024965A1 (fr) 2000-05-04

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI1999/000871 Ceased WO2000024965A1 (fr) 1998-10-23 1999-10-20 Procede et dispositif d'essorage par impulsions

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WO (1) WO2000024965A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0949376A3 (fr) * 1998-03-26 2000-12-06 Beloit Technologies, Inc. Presse à zone de pressage prolongée
US6936139B2 (en) 2002-02-06 2005-08-30 Ichikawa Co., Ltd. Shoe press apparatus of a papermaking machine
WO2008068381A1 (fr) * 2006-12-04 2008-06-12 Metso Paper, Inc. Elément de chargement pour une machine à bande fibreuse
WO2022126817A1 (fr) * 2020-12-17 2022-06-23 淄博泰鼎机械科技有限公司 Presse à sabot

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5047122A (en) * 1989-06-23 1991-09-10 Beloit Corporation Method for heated extended nip pressing
US5071513A (en) * 1986-12-24 1991-12-10 Sulzer-Escher Wyss Gmbh Method for the mechanical-thermal dewatering of a fiber stock web

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5071513A (en) * 1986-12-24 1991-12-10 Sulzer-Escher Wyss Gmbh Method for the mechanical-thermal dewatering of a fiber stock web
US5047122A (en) * 1989-06-23 1991-09-10 Beloit Corporation Method for heated extended nip pressing

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0949376A3 (fr) * 1998-03-26 2000-12-06 Beloit Technologies, Inc. Presse à zone de pressage prolongée
US6936139B2 (en) 2002-02-06 2005-08-30 Ichikawa Co., Ltd. Shoe press apparatus of a papermaking machine
WO2008068381A1 (fr) * 2006-12-04 2008-06-12 Metso Paper, Inc. Elément de chargement pour une machine à bande fibreuse
WO2022126817A1 (fr) * 2020-12-17 2022-06-23 淄博泰鼎机械科技有限公司 Presse à sabot

Also Published As

Publication number Publication date
FI982293A0 (fi) 1998-10-23
FI982293A7 (fi) 2000-04-24
FI105050B (fi) 2000-05-31

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