Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders
  • D21F5/04—Drying on cylinders on two or more drying cylinders

Definitions

• the present invention relates to paper making machines and, more particularly, to an apparatus for controlling shrinkage of a fiber web, such as a paper or paperboard web, during a drying process, an associated method, and a fiber web produced according to the method.
• Uneven shrinkage of a paper web during drying can cause, for example, a paper curl, i.e. that a sheet of paper from the dried paper web will tend to roll itself up to a cylindrical form about an imagined axis.
• a reduced shrinkage promotes a final sheet of paper having a higher stiffness, no curl, and a smoother surface, wherein such characteristics are desirable for most paper and paperboard grades.
• the shrinkage is too little, the paper may, however, become too stiff for its intended purpose.
• the shrinkage in both the machine direction (MD) and the transverse direction (TD) influences the properties of the final paper.
• shrinkage in the machine direction can be controlled relatively well, e.g. by means of accurate control of the roll speeds and web tension through the drying section.
• U.S, Patent No. 5,864,965 discloses a solution which comprises holding the web edges to a drying fabric with suction boxes positioned between the drying cylinders in a drying section in order to counteract the shrinkage of the web in the transverse direction.
• a partial vacuum is maintained along the edge portions of the web across essentially the entire free draw, wherein the vacuum is applied from the side of the drying fabric, which is turned away from the web, As such, the web will be steadily sucked to the drying fabric with forces that are greater than the counteracting forces acting in the transverse direction, thereby counteracting web shrinkage
• the partial vacuum is stated as being set within the range 0.1 to 0,8 bar, preferably between 0.2 to 0.5 bar.
• U.S, Patent No. 4,680,873 describes an arrangement and a method of controlling or adjusting shrinkage and/or stretching of a paper web transverse to the transport direction in a drying section of a paper making machine, in which the drying section has the shape of a cylinder dryer and/or a fan dryer.
• the drying section has the shape of a cylinder dryer and/or a fan dryer.
• the paper is subjected to outward forces, which are forced to act at the edge portions of the web, The forces are brought to act upon adjacent, parallel edge portions of the paper web and are directed away from each other.
• the magnitude of these forces are stated to be chosen so that they are at the most 50% lower than the shrinkage forces which momentarily occur on the paper web at the specified dry solids content.
• U.S Patent Nos. 5,553,392 and 5,647,141 describe an apparatus and a method, respectively, for drying a wet sheet material, such as a paper web.
• the apparatus is equipped with an appropriate number of drying cylinders, which operate in cooperation with a plurality of steam openings provided adjacent to the drying cylinders,
• the apparatus incorporates one or more gas permeable material belts arranged to cooperate with the drying cylinders for transporting the sheet material.
• the material belt or belts is/are then looped about the different drying cylinders for urging the sheet material against their outer circumferential surfaces and holding the sheet material during the drying operation.
• U.S Patent No. 5.737,848 describes a drying section for a running paper web with consecutive drying groups, each having drying cylinders. Felts or wires support the running paper web and rest against the drying cylinders. Guide rolls guide the web and the felts/wires. The guide rolls are arranged so that the running web is guided in a meandering manner in the transfer region between two consecutive drying cylinders, each associated with different felts or wires.
• US 5,737,848 it is stated, among other things, that the guide rolls are positioned in such a manner and that the felts are supported by the guide rolls in such a manner, that the paper web can be supported substantially continuously through the transfer region. It is stated that the purpose of the arrangement described in US 5,737,848, among other things, is to reduce vibrations and to keep undesired shrinkage of the paper web to a minimum.
• U.S. Patent No, 5,787,603 describes a drying section in a machine for production of a paper web, wherein the drying section incorporates a plurality ofheatable drying cylinders, The drying section incorporates a support belt, which by use of guide rolls, encloses a portion of the circumference of each of the drying cylinders against which the paper web is urged.
• the drying section incorporates pressing devices which, via the support belt, press the paper web against the drying cylinders.
• the pressing devices can include press rolls which are urged against the support belt. e.g. by means of springs. It is stated that one of the purposes of the arrangement disclosed in US 5,787,603 is to be able to reduce the tension in the support belt without impairing the drying contact between the drying cylinders and the paper web,
• U.S. Patent No. 5,921,000 describes a drying section which utilizes top-felted and bottom-felted drying sections, each of which incorporates a single steam-heated drying cylinder.
• the paper web to be dried is transferred between the drying cylinders by means of a vacuum roll transfer without any open draw.
• the wrap of the machine fabric over the drying cylinders is over 270 degrees, which is considered to give a high drying capacity per drying cylinder.
• Each drying cylinder might have its own stretching means and guide means for the machine fabric. It is stated that the paper web can be restrained during about 96 % of the period of its passage through the drying section.
• the earlier known arrangements for controlling the shrinkage or other dimensional change of a paper or paperboard web during the drying operation have certain shortcomings.
• earlier systems having belt-like members, extending through the drying section for exerting forces upon the edges of the web may not be capable of delivering a sufficient, continuous holding force for holding the web rigidly through the entire drying section to thereby prevent or control the shrinkage of the web in transverse direction.
• earlier known arrangements where the web is supported or to some extent is firmly secured by aid of suction rolls, machine fabrics, guide rolls, sometimes in cooperation with drying cylinders may also be incapable of ensuring a sufficiently large, continuous holding force throughout the entire drying section.
• such types of earlier known arrangements are not capable of controlling the width of the web.
• some machine configurations may include an arrangement of pressure rolls, which directly or via V- belts, hold the edges of the films or foils therebetween in draws between the stretching rolls.
• Such an arrangement is described in DE-B 1 1 1 1 811.
• a drying section for drying and controlling shrinkage of a moist fiber web, the web having a predetermined width and opposed transverse ends, in a paper making machine.
• a drying section comprises a plurality of drying section members configured to receive and forward the web in a machine direction, Each drying section member has opposed ends in a transverse direction.
• the drying section members further comprise a first drying section member and a second drying section member, with the second drying section member being separated from the first drying section member so as to define an intermediate zone therebetween.
• the drying section further comprises a primary belt set having a belt member wrapping about each of the opposed ends of each of the drying section members.
• Each belt member is configured in an endless loop and has a width less than half of the width of the web.
• the drying section also comprises a first web-contacting element opposing the primary belt set, at least substantially through the intermediate zone, such that the web is disposed therebetween.
• the first web- contacting element cooperates with the primary belt set so as to at least partially constrain the web about the opposed transverse ends thereof to thereby control at least transverse shrinkage of the web.
• Another advantageous aspect of the present invention comprises a method of drying and controlling shrinkage of a moist fiber web, wherein the web has a predetermined width and opposed transverse ends, in a drying section of a paper making machine.
• First, the web is forwarded about a plurality of drying section members configured to receive and forward the web in a machine direction.
• Each drying section member has opposed ends in a transverse direction.
• the drying section members further comprise a first drying section member and a second drying section member, with the second drying section member being separated from the first drying section member so as to define an intermediate zone therebetween.
• the web is at least partially constrained in at least the transverse direction, and at least substantially through the intermediate zone, with a first belt set disposed opposite to the web from a web- contacting element, wherein both the first belt set and the web-contacting element operably engaging the web.
• the first belt set comprises a belt member wrapping about each of the opposed ends of each of the drying section members, wherein each belt member is configured in an endless loop and has a width less than half of the width of the web, The first belt set cooperates with the web-contacting element to at least partially constrain the web about the opposed transverse ends thereof so as to control shrinkage of the web.
• a fiber web produced according to a method such as described herein would exhibit increased stiffness due to the shrinkage control experienced during the drying process. Consequently, for example, less papermaking fibers may be required in order to produce the paper grades having the same stiffness than in corresponding paper grades produced according to a process where shrinkage is not controlled,
• embodiments of a drying section in a paper making machine according to the present invention are capable of controlling shrinkage in a fiber web during the drying process and producing an advantageous product thereby.
• Fig. 1 is a schematic diagram of the resulting forces when one edge of a paper or paperboard web is held between belt members in a drying section according to prior art apparatuses and methods.
• Fig. 2 is a schematic side view of a two-tier drying section in accordance with one embodiment of the invention,
• Fig. 3 is a schematic cross-sectional view in the machine direction corresponding to a portion of a roll forming part of the drying section shown in Fig. 2.
• Fig. 4 is a schematic perspective view of the drying section illustrated in Figs. 2 and 3, showing the extension of the intermediate zone in the machine direction.
• Fig. 5 is a schematic side view of a two-tier drying section in accordance with an alternative embodiment of the invention.
• Fig. 6 is a schematic side view of a single-tier drying section in accordance with one embodiment of the invention.
• Fig. 7 is a schematic side view of a single-tier drying section in accordance with an alternative embodiment of the invention.
• Fig. 8 is a schematic view from below the drying section arrangement shown in Fig. 7,
• Fig. 9 is a schematic side view of a two-tier drying section in accordance with an alternative embodiment of the invention.
• Fig. 30 is a schematic side view of a single-tier drying section in accordance with an alternative embodiment of the invention.
• Fig. 11 is a schematic side view of the drying section shown in Fig. 10 in accordance with one embodiment of the invention.
• Fig. 12 is a schematic side view of a linear type drying section in accordance with a further alternative embodiment of the invention.
• Fig. 1 illustrates conditions which may occur when securing the edge of a paper or paperboard web running through a drying section in order to eliminate or control shrinkage of the web in transverse direction according to one embodiment of the present invention.
• the web 1 runs through the drying section in the machine direction MD.
• al least the width of a running, moist paper or paperboard web 101 ; 201 ; 301; 401 ; 501 ; 601; 701 is controlled, while during the drying process in a drying section 100; 200; 300; 400; 500; 600; 700, wherein the drying section includes at least one body 103, 103', 103"; 203, 203', 203 "; 303, 303'; 403, 403'; 503, 503', 503"; 603, 603 '; 703, 703' capable of emitting heat that is transferred to the web 101 ; 201; 301 ; 401; 501; 601; 701 so as to evaporate residual water therein.
• the drying section 100; 200; 300; 400; 500; 600; 700 thereby has a machine direction MD and a transverse direction TD, perpendicular to the machine direction, and, in the transverse direction TD, a tender side and a drive side.
• at least one belt member 102, 102', 102"; 202, 202', 202"; 302, 302'; 402, 402'; 502, 502'; 602, 602'; 702, 702' is arranged in an endless loop.
• the belt members 102, 102', 102"; 202, 202', 202"; 302, 302'; 402, 02'; 502, 502'; 602, 602'; 702, 702' each have a belt width 105' which is less than half the width of the web 101, wherein the belt members 102, 102', 102"; 202, 202', 202" ; 302, 302'; 402, 402'; 502, 502'; 602, 602'; 702, 702' are arranged through the drying section so as to secure opposed side edges of the web 101; 201 ; 301; 401; 501; 601 ; 701 at least through an intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706 between two drying section members which are spaced apart in the machine direction MD.
• intermediate zone refers, as can be seen by the arrow 106' in Fig. 4, in principle to the free draw present in corresponding prior art drying sections.
• the beginning and the end of the intermediate zone i.e. the points where the belt members begin and cease, respectively, to secure of the web therethrough, are typically defined by drying section members.
• the intermediate zone may extend between the external circumferences of the two drying cylinders in a drying section but also along the entire drying section, as illustrated in Fig. 12.
• the belt members 102, 102', 102"; 202, 202', 202"; 302, 302'; 402, 402'; 502, 502'; 602, 602'; 702, 702' are in direct or indirect contact with at least one preferably cylindrical counter element 107, 107', 107", 107'"; 207, 207', 207", 207'"; 307, 307', 307"; 407; 507, 507', 507", 507'"; 607; 707, 707' while accompanying the web while the web is secured therebetween through the intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706.
• the width of the web is thereby controlled in that the edges of the web 101; 201; 301 ; 401 ; 501; 601; 701 are at least substantially continuously secured in their intended transverse positions during drying of the web. Accordingly, it will be understood by one skilled in the art that the number of intermediate zones could be one or several, depending on the configuration of the drying section,
• a desired width of the web is maintained in the intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706 by the belt members and the counter elements accompanying the web and opposing the shrinkage forces generated during the drying operation.
• the width of the web may be gradually reduced by the belt members and the counter elements being configured to allow web shrinkage, though to a lesser extent than if the edges of the web were not constrained.
• the web width in the intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706 may gradually be increased by the belt members and the counter elements accompanying the web.
• expansion of the width of the web may be achieved by providing grooves 110', similar to what is shown in Fig. 3, at each end of the drying cylinders and in the counter elements, and at an increased distance from each other for successive drying cylinders and in the counter elements through the drying section.
• the belt members will gradually diverge from each other during passage through the drying section and will thereby generate forces on the web directed outwards in the transverse direction TD.
• the belt members during passage through the drying section, may be alternatingly allowed to diverge from each other and then converge towards each other, or vice versa. Still other embodiments may combine alternating convergence/divergence or convergence/divergence with belt members running in parallel with the machine direction MD in certain areas of the drying section.
• the web may be stretched, or at least prevented from shrinking freely in the machine direction MD. This can be achieved by adjustment of the rotational speeds of the different drying cylinders and/or the line speeds of the drying units.
• Such a method combined with the control of the width of the web in the transverse direction, thus gives significant control over the dimensional changes of the web in the machine direction MD as well as in the transverse direction TD, and it therefore provides many possibilities of influencing or improving the physical properties of the final paper or the finished paperboard.
• the drying section includes at least one drying unit 100; 200; 300; 400; 500; 60Q; 700 having at least one drying section member 103, 103', 103"; 203, 203', 203"; 303, 303'; 403, 403'; 503, 503', 503 "; 603, 603'; 703, 703' capable of emitting heat that can be transferred to the web 101; 201; 301 ; 401 ; 501; 601 ; 701 so as to evaporate residual water therein.
• drying unit shall be understood as.
• a drying section of a paper or paperboard making machine usually includes a plurality of such drying units. Drying units of different types and with different methods of operation can also form a drying section.. Within the scope of the invention, other drying sections may also be implemented, which may include, for instance, cylinder drying units or basically linear drying units (e.g. of the Valmct OptiDry type), or combinations thereof.
• a drying unit within a drying section defines ⁇ machine direction MD and a transverse direction TD, perpendicular to the machine direction, and, in the transverse direction, a tender side and a drive side.
• at least one belt member 102, 102', 102" ; 202, 202', 202"; 302, 302'; 402, 402'; 502, 502'; 602, 602'; 702, 702' is arranged in an endless loop.
• the belt members have a belt width 105' which is less than half the width of the web 101.
• the belt members are arranged so as to help to firmly secure opposite side edges of the web 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706, at least through the intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706 in the machine direction MD,
• the belt members, the support counter elements and the main counter elements are arranged to maintain a desired width of the web in the intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706, regardless of the shrinkage forces arising during drying.
• the belt members, the support counter elements and the main counter elements are arranged to gradually reduce the width of the web in the intermediate zone 106, 106'; 206, 206'; 306; 406; 506, 506'; 606; 706 by permitting at least some web shrinkage, though to a lesser extent than if the web were not constrained.
• the belt members, the support counter elements and the main counter elements may be arranged to gradually increase the width of the web in the intennediate zone 106, 106'; 206, 206' 306; 406; 506, 506'; 606; 706 by, for example, stretching.
• the drying unit or drying units 100; 200; 300; 400; 500; 600; 700 are arranged to stretch the web, or at least to prevent it from shrinking freely in the machine direction MD, during the drying,
• the drying unit 700 (or the drying units) comprises a linear dryer for drying a web, wherein the heat-emitting body or bodies include at least one blowing-on element 703, 703' for blowing hot air against the web.
• the heat-emitting body or bodies further extend over the width of the web 701 and spaced at a substantially constant distance from the web.
• the heat emitting bodies may comprise appropriate members for drying the web such as, for example, by IR drying, induction drying or other types of drying.
• the drying unit 100; 200; 300; 400; 600' (or the drying units) is a multicylinder drying group with at least two heat-emitting bodies comprising drying cylinders 103, 103', 103"; 203, 203', 203" ; 303, 303'; 403, 4Q3' extending over the width of the web 101; 201 ; 301; 401, with each having a circumference 104, 104', 104" and spaces between the circumferences, which form at least one of said intermediate zones 106, 106'; 206, 206'; 306, 406,
• the web rests against the drying cylinders during a pail of the drying process, and at least one machine fabric, such as a drying fabric 108, 108'; 208, 208'; 308; 408; 608 runs about at least a portion of the circumference 104, 104', 104" of at least
• the belt members may include a first belt member 102; 202; 302 arranged in a first endless loop, and a second belt member 102'; 202'; 302' arranged in a second endless loop, wherein the first and the second loops accompany each other only in the intermediate zone 106; 206; 306.
• the belt members include a third belt member
• the third and fourth loops accompany each other over the drying cylinders 403, 403', wherein the intermediate zone 406 is fo ⁇ ned about at least one of the support members 407.
• the circumference 104' is defined by an outer envelope surface 109' of one of the drying cylinders 103'.
• the outer envelope surface 109' is provided with a groove 110' adapted to house a longitudinal portion of one of the belt members 102'.
• the counter elements include one or more rotatable, belt-guiding members 107'" over and/or between which said belt members run.
• the rotatable, belt-guiding members 107'" are constituted by axially short rolls, wheels or pulleys, which are provided, in the circumferential surfaces thereof with one or more grooves 111 " for housing longitudinal portions of one or more of the belt members 102".
• belt-guiding members 107' may take many different forms consistent with the spirit and scope of the present invention,
• belt-guiding members 107'" may comprise a V-belt pulley having a shallow groove for the belt member such that only the belt member engages the paper web, or a camber-faced pulley configured to correspond to ⁇ flat belt.
• the above-mentioned rotatable, belt-guidmg members comprise chain wheels, wherein the belt members comprise corresponding chain belts.
• the drying cylinders are a ⁇ 'anged in one single row in at least one drying unit 300; 400; 600; 600' of the drying section so as to form a single-tier dryer.
• Such embodiments are illustrated in Figs. 6 - 8 and 10 - 11 ,
• the drying cylinders are arranged in two rows in at least one drying unit 100; 200; 500 of the drying section so as to form a two- tier dryer.
• Such embodiments are illustrated in Figs. 2, 5 and 9,
• the above-mentioned belt members are preferably comprised of a rigid material with a rough surface which, in the intermediate zone, faces the fibrous web.
• the belt members may have a cross-section shaped as a rectangle, a parallel trapezoid, or other quadrilateral, as shown in Fig. 3.
• the belt members may comprise, for example, a strip of a paper machine fabric, a V-belt, a steel belt, or a plastic strip, It will also be understood by one skilled in the art that the belt members may have many different forms and dimensions as required for the particular machine configuration and/or the product to be formed thereby consistent with the spirit and scope of the present invention.
• the belt members may be relatively narrow, such as, for instance, on the order of about 20mm wide, and thin, such as, for instance, on the order of about 0,5mm thick, though such dimensions do not constrain the myriad of other possible configurations.
• At least one heating device 212 is arranged for heating the fibrous web 201, specifically at a position and over a width in the transverse direction corresponding to the intermediate zone or zones 206, 206' ⁇ n ⁇ Vor for heating one or more of the belt members.
• Embodiments of the present invention thus permit controlled shrinkage/stretching of a paper or paperboard web through the drying section of a paper making machine, in both the machine direction as well as in the transverse direction.
• This control can be utilized, e.g. for obtaining a higher and more even quality of the final paper or the finished paperboard after drying, for controlling the physical properties of the paper or the paperboard, or for an improved runnability.
• the present invention may also be advantageously used for "tail threading" in connection with the start-up of a paper o ⁇ paperboard-making machine, for instance, after a web break or after a shut down.
• the securing of the web by the belt members, in cooperation with support counter elements, the main counter elements, and possibly drying cylinders and machine clothings, enables the machine to be started with a full web width of the paper or paperboard web instead of the less advantageous conventional tail threading, wherein only a narrow strip of the web is conducted through the drying section, with the assistance of manual handling by on attendant, before full web width drying can be resumed.
• Fig. 11 thus shows an alternative embodiment 600' of a drying unit 600 as shown in Fig. 10.
• a drying fabric 608 which firmly secures the width of the web 601 during passage over the drying cylinders 603, 603', is substituted for the belt members 602, which, as shown in Fig. 10, secure the edges of the web during passage over the drying cylinders 603, 603', whereas the remaining belt members 602' secure the edges of the web 601 during passage through the intermediate zone 606,
• a fiber web produced according to a method such as described herein would exhibit increased stiffness due to the shrinkage control experienced during the drying process.
• the stiffness of paper or paperboard may be controlled so as to produce intermediate products such as paper sheets or paperboard blanks, or final products such as a paperboard box, having desirable stiffness characteristics corresponding to the particular application.
• many other paper grades such as copying paper, newsprint, and journal paper may be made suffer.

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• 2000
  • 2000-11-24 EP EP00982015A patent/EP1285122A1/de not_active Withdrawn
  • 2000-11-24 WO PCT/SE2000/002334 patent/WO2001038634A1/en not_active Application Discontinuation

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