WO2001000926A1 - Dispositif et procede de calandrage - Google Patents

Dispositif et procede de calandrage Download PDF

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Publication number
WO2001000926A1
WO2001000926A1 PCT/FI2000/000517 FI0000517W WO0100926A1 WO 2001000926 A1 WO2001000926 A1 WO 2001000926A1 FI 0000517 W FI0000517 W FI 0000517W WO 0100926 A1 WO0100926 A1 WO 0100926A1
Authority
WO
WIPO (PCT)
Prior art keywords
calender
web
roll
air
paper web
Prior art date
Application number
PCT/FI2000/000517
Other languages
English (en)
Inventor
Reijo PIETIKÄINEN
Original Assignee
Metso Paper, Inc.
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, Inc. filed Critical Metso Paper, Inc.
Priority to DE10084664T priority Critical patent/DE10084664T1/de
Priority to AU50808/00A priority patent/AU5080800A/en
Publication of WO2001000926A1 publication Critical patent/WO2001000926A1/fr

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
    • D21G1/00—Calenders; Smoothing apparatus

Definitions

  • the present invention relates to a method in calendering, in which a paper web to be calendered is led through successive calender nips.
  • the invention also relates to a device in calendering.
  • Calendering is a step after drying of paper to make the surface structure of the paper as desired.
  • the paper web is passed through calender roll nips formed between rotating calender rolls.
  • the temperature of some of the calender rolls is adjustable.
  • the press of the rolls i.e. the nip pressure (linear load), the temperature, and the moisture of the paper web, it is possible to achieve a suitable surface smoothness and other desirable surface qualities, as well as a desired thickness for the paper.
  • a common cal- ender type to be used in calendering is a multi-nip calender which comprises several successive nips between calender rolls, each exerting a specific nip pressure on the web passing through the nip.
  • calenders of more than 4 nips are generally used.
  • the paper web is passed through a set of calender rolls, in which successive calender nips are formed between calender rolls placed on top of each other as a stack.
  • This principle is presented e.g. in the applicant's international publication WO 95/14813, to which corresponds US patent 5,438,920.
  • the calender rolls and the paper web are open to the environment, i.e. flows of ambient air affect the heat loss from the rolls and the moisture evaporating from the paper web.
  • a boundary layer is formed between the running paper web and the ambient air, i.e. an area of change in flow rates, temperatures and moisture concentration. With high running speeds, for example 1 ,000 to 2,000 m/min, the boundary layer has a thickness of only a few millimetres. Thus, the moisture and heat discharged from the surface of the roll or the paper quickly pass through the boundary layer, resulting in a relatively high heat loss and drying of the paper web.
  • Convective heat transfer from temperature-adjusted rolls, so-called thermal rolls, into the air makes up about 25 to 30 % of the heating effect of the roll in a multi-nip calender, even 40 to 50 % in a soft calender, and radiation energy makes up about 1 to 2 % of the heating effect of the roll.
  • the calender dries the paper so much that the moisture of the paper will drop even 2 to 5 percentage units. With present calenders, this means a water quantity of 2,000 to 3,000 kg/h, which loss must be compensated by supplemental wetting.
  • the method according to the invention is characterized in that air flows developing at the calender in connection with the mantle of a calender roll and/or the paper web are controlled.
  • the device according to the invention is, in turn, characterized in that it is arranged to control air flows developing at the above-mentioned locations at the calender.
  • the method of the invention provides a simpler process, e.g. the need for rewetting is decreased and energy is saved, wherein the invention is also economically significant.
  • the con- trol is performed at locations in which the mantle of a calender roll or the web running in the calender is open to the environment, i.e. heat or moisture has a chance to escape from the surface of the roll or from the surface of the web directly to the mass of air surrounding the calender.
  • the control can be implemented actively by additional flows produced at these locations or by static, passive means, such as guide plates or foils.
  • the plates or the like protect the paper web, and they can be provided with other actuators, such as wetting means, wherein the air guidance and wetting can be performed with the same device.
  • the calender is a soft calender or a multi-nip calender in which the successive nips are formed between rolls on top of each other in a stack of calender rolls.
  • the construction of the calender can be any one used in multi-nip calenders; it comprises preferably more than 4 nips. It is also possible to use calenders with a different number of rolls and nips.
  • the calender comprises, in a way known per se, rolls with metal and polymer surfaces. The paper web passed through the calender, having normally a width of several metres, is reeled up into a machine reel in a reel-up.
  • the calendering can take place as an on-line process in connection with the paper manufacturing process, wherein the calendering takes place in a continuous manner for a paper web coming from the drying section of a paper machine at a production rate.
  • the calendering can also be a separate off-machine process, wherein the paper web has first been reeled up into a reel. In the calendering process, the web is unwound from the reel into the calender.
  • the invention can be applied in either process.
  • Fig. 1 shows, in a side view, a typical calender structure and the principle of the propagation of air flows at a roll
  • Fig. 2a shows, in a side view, the control of air flows by passive guidance in the area of one web loop and a calender roll by the loop,
  • Fig. 2b shows, in a side view, a second possible device for passive guidance of air flows
  • Fig. 3 shows, in a side view, the control of air flows by active guidance in the area of a web loop passing through successive calender nips.
  • Figure 1 shows a calender of 6 rolls and 5 nips, in which a web W is passed in a winding manner through successive nips N between calender rolls 1.
  • the web W is taken out from the surface of the calender roll following the nip N, to cool it down and to stabilize its run, by means of a take-out leader roll 2.
  • take-out leader rolls 2 or corresponding devices guiding the path of the web W web loops are formed on both sides of the stack of rolls, running away from the calender rolls 1.
  • the web W is reeled up in a reel-up which is not shown in the figure.
  • Figure 1 also shows the principle of propagation of air flows at one roll 1 when the flow streams freely, without guidance.
  • the direction of the air flow is indicated with arrows in the figure.
  • On the surface of the roll and the paper web there is a layer whose rate in relation to a moving piece is zero, that is, also the air layer moves with the running paper web and the rotating roll.
  • an overpressure is developed which collides with the paper web W at the same side of the stack of rolls at a location when the web W comes out from a lower nip N.
  • the collision causes a disturbance in the boundary layer of the flow, increasing evaporation from the web.
  • a negative pres- sure is developed due to the movements of the web and the roll, wherein air tends to flow towards the opening nip N.
  • air flows developing in the vicinity of the open mantle surface of the calender web or in the vicinity of the web are guided. These air flows develop in the way shown in Fig. 1 , and they are characterized by flows developing in directions transverse to the shafts of the rolls, extending parallel to the surfaces of the web or the roll or towards them or away from them.
  • Figure 2 shows the control of air flows by passive guidance.
  • Passive guidance means that the air flows are influenced by the location and shape of a structure remaining substantially stationary during the calendering.
  • a guide plate or foil 3 is placed as such a structure in the vicinity of the paper web W or a calender roll 1.
  • the guide foil refers in this context to a plate or blade designed in a suitable manner in a cross-section perpendicular to the shaft or the calender roll.
  • the guide plate or foil 3 can have an integrated structure, as shown in Fig. 2a, or it can constitute e.g. a lamellar structure, as shown in Fig. 2b. It is particularly advantageous to place guide plates or foils in connection with calender rolls with adjusted temperatures, i.e.
  • thermal rolls 1 at a small distance from the outer surface of the roll, or close to the outer surface of the paper web W running freely from the surface of the roll in a loop formed by a take-out leader roll 2, i.e. the surface running outermost in the loop, at a small distance from it.
  • the distance is selected so that the flow technical boundary layer can be influenced by said guide plates or foils. Thanks to the guide plates or foils, the state of the air between them and the calender rolls and/or the paper web is in balance, where e.g. considerable evaporation does not take place. The transfer of heat and mass from the surface of the calender rolls and/or the paper web is thus at a minimum.
  • the guide plates or foils are advantageously placed at a distance of less than 100 mm from the thermal roll 1 or the paper web W. Said distance is preferably 0 to 50 mm, but such that the plate or foil is off the roll or web.
  • FIG. 1 shows how a guide plate or foil 3 follows the path of the web loop formed by a take-out leader roll 2 at the length where the web runs from an opening nip N to the take-out leader roll 2, by the take-out leader roll 2, and at the length where it runs from the roll 2 to a closing nip N.
  • a curved guide plate or foil 3 placed in the vicinity of the open mantle surface of the roll 1 in the area outside the web loops, following the same.
  • said guide plate or foil is placed close to a thermal roll with a polymer coating, but it can be used in connection with thermal rolls with other types of coatings as well.
  • the guide plate or foil 3 placed close to the paper web W can also be connected with a wetting device.
  • the wetting device can be for example a device feeding aqueous vapour, or a device in which a mixture of pressurized air and water is driven through a nozzle, forming very small atomized drops of water.
  • Figure 2b shows how the guide plate 3 has a lamellar structure and comprises horizontal lamellas 3a following each other close to the open mantle surface of the calender roll 1 and partially overlapping each other on the periphery of the roll.
  • the action of the guide plates and foils is primarily based on the control of the convective transfer of heat or moisture carried away by an air flow, by controlling and guiding the direction, quantity and turbulence of the air flow. Furthermore, the guide plates and foils act as minor protective shields for radiation heat.
  • Figure 3 shows the control of air flows by active guidance. Towards point A, at which a negative pressure has been developed (after an opening nip N), air is blown from a nozzle 4 located right after the nip N in the running direction of the web.
  • the blowing or suction rate corresponds to the running speed of the paper web, wherein a speed difference as small as possible is achieved between the boundary layer and the surface of the paper web.
  • the suction and blowing nozzles 4 are placed as close as possible to the respective nip N.
  • the blowing nozzles 4 are placed outside the web loop so that orifices, openings or the like in the nozzle are directed substantially in the run- ning direction of the web so that they produce a flow outside the web loop, close to the outer surface of the web, which extends in the running direction of the web between the opening nip N and the take-out leader roll 2.
  • To feed an additional air mass means increasing the thickness of the flow technical boundary layer, wherein the transfer of mass and heat across this boundary layer will become more difficult.
  • the quantity of supplied air can also be selected so that the additional air mass will only replace the air that is carried away in connection with the calendering, and the feeding of air thereby prevents the development of a negative pressure.
  • the suction nozzle 4 outside the web loop is used to suck air before the closing nip N, wherein the development of an overpressure is prevented, and the flow produced by the suction is parallel to the running direction between the take-out leader roll 2 and the closing nip N.
  • the boundary layer can also be increased during suction of air towards the closing nip N, because a greater quantity of the air flow can thus be directed towards the running direction of the web.
  • the devices whether passive or active, extend their effect on the whole or part of the width of the web W to be calendered.
  • Passive structures following the surface of the web or the roll such as guide plates or foils 3, are located substantially on the whole running width of the web, or they can be located only on a part of the width of the web.
  • the nozzles producing a suction or a blow close to the different nips N are devices extending substantially on the whole width of the web, e.g. suction and blowing nozzles 4 which produce a suction and, respectively, a blow as a front over the width of the web W or as a front extending over a part of the width of the web W only.
  • the devices can be used to act over the whole width of the web W in the same way or in a profiled manner, wherein a desired part of the width of the web W is affect in a desired manner, i.e. in different zones in the width direction, the suction or blowing effect can be arranged independently, irrespective of the suction or blow of the adjacent zones.
  • Passive guides can be constructed in several different shapes. Active guides can be varied in several ways, for example by modifying the shape of the nozzles.

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  • Paper (AREA)

Abstract

Cette invention concerne un procédé de calandrage d'une bande de papier selon lequel une bande de papier (W) à calandrer passe entre des rouleaux pinceurs (N) successifs. Afin d'empêcher les pertes de chaleur et l'évaporation de l'eau au niveau de la calandre, on règle les flux d'air qui apparaissent sur la surface libre du manteau du rouleau de calandrage (1) et/ou de la bande de papier (W) selon un sens qui est essentiellement perpendiculaire à l'axe du rouleau de calandrage.
PCT/FI2000/000517 1999-06-23 2000-06-09 Dispositif et procede de calandrage WO2001000926A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
DE10084664T DE10084664T1 (de) 1999-06-23 2000-06-09 Verfahren und Vorrichtung zum Kalandrieren
AU50808/00A AU5080800A (en) 1999-06-23 2000-06-09 A method and a device in calendering

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI991421A FI113790B (fi) 1999-06-23 1999-06-23 Menetelmä ja laite kalanteroinnissa
FI991421 1999-06-23

Publications (1)

Publication Number Publication Date
WO2001000926A1 true WO2001000926A1 (fr) 2001-01-04

Family

ID=8554931

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI2000/000517 WO2001000926A1 (fr) 1999-06-23 2000-06-09 Dispositif et procede de calandrage

Country Status (4)

Country Link
AU (1) AU5080800A (fr)
DE (1) DE10084664T1 (fr)
FI (1) FI113790B (fr)
WO (1) WO2001000926A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4029098A1 (de) * 1989-09-15 1991-04-11 Teollisuusmittaus Oy Kontakttrockenzylinder-haube
DE4105978A1 (de) * 1991-02-26 1992-08-27 Escher Wyss Gmbh Waermeschutzhaube
US5152076A (en) * 1989-12-01 1992-10-06 Valmet Paper Machinery Inc. Method and device in a paper machine
CA2181323A1 (fr) * 1995-08-18 1997-02-19 Abitibi-Price Inc. Capot pour calandre

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4029098A1 (de) * 1989-09-15 1991-04-11 Teollisuusmittaus Oy Kontakttrockenzylinder-haube
US5152076A (en) * 1989-12-01 1992-10-06 Valmet Paper Machinery Inc. Method and device in a paper machine
DE4105978A1 (de) * 1991-02-26 1992-08-27 Escher Wyss Gmbh Waermeschutzhaube
CA2181323A1 (fr) * 1995-08-18 1997-02-19 Abitibi-Price Inc. Capot pour calandre

Also Published As

Publication number Publication date
DE10084664T1 (de) 2002-06-06
FI991421A0 (fi) 1999-06-23
FI991421A (fi) 2000-12-24
AU5080800A (en) 2001-01-31
FI113790B (fi) 2004-06-15

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