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
  • D21F3/04—Arrangements thereof
  • D21F3/045—Arrangements thereof including at least one extended press nip

Definitions

• the present invention relates to a pressing apparatus for a paper- or board-making machine, but can be used also with pulp and tissue presses too, for removing fluids from a web by pressing, and relates to a method for treating a web in a paper- or board-making machine.
• dewatering paper or cardboard webs in a press section of a paper- or board-making machine to pass the web through a press nip defined by two rolls in opposed relationship with each other.
• One or two press fabrics are passed through the dewatering press nip in order to carry away the water pressed out of the web and they also function to transport the web to and from the press nip.
• Dewatering of the web in the press section has become a major factor to be improved.
• the press nips defined by a pair of rolls have a relatively short region of action in the web moving direction
• the time spent by the web in such press nips is relatively short at high web moving speeds.
• it requires a certain minimum time period to ensure that the water in the web may be transferred from the web towards a recessed surface of the press roll or rolls or to the press fabric (i.e. a felt or the like) .
• US 6 994 771 discloses an apparatus in a pressing section of a paper- making machine.
• the paper web guided through said pressing section is interposed between two felts or between one transfer belt made of metal and one felt or belt.
• the web is dewatered in elongated press nips by being pressed by shoe press rolls against respective backing rolls.
• a further arrangement of an elongated press nip is formed by a so-called shoe press arrangement shown in US 4 568 423.
• shoe press arrangement different treatment pressures for dewatering the web may be achieved along the web moving direction through the press nip, in which nip the web is interposed between two inner felts which are pressed by the treatment pressures of the shoe press arrangement applied to two outer belts.
• a press roll and a press shoe together form the extended press nip of the shoe press arrangement through which the web to be pressed is guided.
• the press shoe includes a pressure chamber isolated from the external environment by sealing members urged against one of the outer belt by means of springs and to which a pressure medium (i.e. fluid) is passed.
• a pressure medium i.e. fluid
• the pressure chamber of the press shoe comprises a hydrostatic pressure chamber which, when viewed in the moving direction of the web, is bounded at its front and rear by hydrodynamic press shoes which function both as sealing elements for the hydrostatic pressure chamber and, additionally, as press-shoe members which produce compression pressures on the press belt and on the web.
• the pressure chamber has a complex structural constitution .
• a belt press arrangement shown in US 3 974 026.
• This belt press arrangement has a rotating suction roll, a guide belt, a pressure member including a pressure chamber, and an adjusting means for adjusting the gap between the pressure member and the belt.
• the guide belt can be permeable to water (i.e. a felt or a fabric) or impermeable (i.e. a rubber fabric or belt) .
• a pressure fluid for pressing the guide belt and the web guided on the belt through the nip against the suction roll may be air or a liquid such as water.
• the pressure member can be so adjusted by the adjusting means in relation to the suction roll and the guide belt that a gap is formed between the end wall of the chamber and the guide belt. Thus, no additional sealing means at the end portions of the chamber are provided.
• the pressure of the pressure fluid urges the guide belt against the suction roll so that water is pressed out of the web. The water pressed out of the web passes through openings into the suction roll and is removed therefrom through a suction box and a suction pipe or thrown away from the roll surface after the nip.
• the gap is made larger in order to avoid such contact to improve the wear of the above mentioned components, a large part of the pressure medium escapes through the gap. This represents a high pressure loss in the pressure chamber. Therefore, the pressure in the pressure chamber is limited to low pressures, so that the dewatering of the web along the nip is insufficient.
• the object of the present invention is to provide an improved pressing apparatus for a paper- or board-making machine and an improved method for treating a web in a paper- or board-making machine for removing fluids from a web by pressing, wherein the dewatering efficiency is improved with a simple structural constitution of the pressing apparatus and simple control thereof.
• a pressing apparatus for a paper- or board-making machine for removing fluids from a web by pressing comprises at least one belt which guides the web, wherein the belt is impervious to fluids and forms an endless loop. At least one nip is provided which is formed between a press roll and a pressure means, and through which nip the guided web is arranged to pass.
• the pressure means comprises at least one pressure chamber containing a pressure medium and extending along the length of the nip in the web moving direction such that the pressure medium directly contacts the belt. Further, the pressure chamber has a pressure-operated sealing member which cooperates with the belt, and the sealing operating pressure is adjusted in accordance with the pressure acting in the pressure chamber.
• the sealing means of the pressure chamber is a pressure- operated sealing member, i.e. the sealing operating pressure is adjusted in accordance with the pressure acting in the pressure chamber.
• the sealing member is adapted to act in accordance with rising pressure of the pressure medium in the pressure chamber in order to increase the pressure acting on the belt. This improves the dewatering efficiency of the pressing apparatus arrangement .
• the pressure medium in the pressure chamber cooperates with the belt, i.e. directly contacts the belt.
• a predetermined pressing pressure is maintained only by the pressure in the chamber. Consequently, the structure of the whole pressing apparatus including the pressure chamber is simplified because no further means for pressing are required.
• sealing between the belt and the pressure chamber is carried out using an adjustable gap between the belt and the pressure means. This increases the range of pressure of the pressure from very low pressures to high pressures in order to avoid heavy leakage of the pressure medium. Simultaneously, lubrication between the belt and the pressure means may be achieved by the pressure medium in order to reduce wear of the corresponding contact portions between the belt and the pressure means (in particular, the pressure-operated sealing member) .
• the belt of the pressing apparatus consists of one of a metal, synthetic, and ceramic material or various different combinations of at least two of these materials.
• the belt material is made of metals, synthetics and/or ceramics, a corresponding hardness, durability, and heat transfer capacity of the belt is achieved.
• Such materials exhibit only small deterioration phenomenon during operations of the belt, so that the pressing apparatus has good performance characteristics throughout its durability. Further, the heat transfer capacity of the belt supports the dewatering effect of the web while pressing against the belt during passage of the web through the nip.
• the sealing member slidably contacts the belt on the rear side of the belt, on which rear side the web is not guided.
• This definition includes an arrangement that the pressure medium within the pressure chamber provides a finite lubrication film between the pressure-adjusted sealing member and the rear side of the belt (i.e. sliding occurs on a thin liquid film) .
• the rear side of the belt is opposite to the side on which the web is guided through the nip. This lubrication effect decreases the friction forces between the sealing and the belt, and therefore the wear resistance thereof is increased.
• the pressure means of the pressing apparatus comprises different pressure chambers which are successively arranged along the length of the nip in the web moving direction and in which different pressures and/or temperatures act.
• the respective pressures of at least part of the pressure chambers are adjusted by controlling sealing leakage flow from one pressure chamber to another pressure chamber having a different pressure/temperature. More preferably, in the one pressure chamber acts a higher pressure than in the another pressure chamber .
• the respective pressure chambers may be provided with sealing elements between the chambers. These sealing elements may also be adjustable by pressure acting in the respective chamber. Thus, sealing leakage flow from one pressure chamber to another pressure chamber may be controlled. This enables the use of a longer nip (an elongated nip) and therefore a better shape of the pressure curve over the nip. That is, the pressures in the chambers increase in the web moving direction such that a pressure impulse on the guided web may be adjusted smoothly.
• different temperatures may be provided with the pressure medium.
• a high temperature pressure medium is used which heats the belt, the web drying rate of the belt is improved such that a higher dryness and smoothness of the web can be achieved.
• the sealing operating pressure is set to lock the pressure-operated sealing member in a definite position. This further reduces the control effort but allows easy access to the belt when the press section is switched off.
• a felt is arranged to travel along the nip. More preferably, the felt is detached from the web immediately after the web has passed through the nip along the web moving direction in order to avoid rewetting of the web after passing through the nip. In particular, the detached felt may be guided downwards from the belt after passing through the nip so as to quickly remove any collected water from the vicinity of the nip.
• the belt is immediately detached from the felt after the belt has passed through the nip. This is to minimise web rewetting after the nip.
• an opening gap i.e. a gap after the web has passed through the nip
• the belt and felt helps to lead water flow coming from the nip away from the belt because this opening gap creates a negative pressure.
• rewetting of the web guided on the felt is minimized.
• the nip is an extended nip between the press roll and the pressure means in the moving direction of the web .
• edge seals seal the pressure means against the belt at outer edges of the pressure means in order to avoid escape of the pressure medium to the ambient outside pressure means.
• the pressure means is adapted to press against the belt towards the press roll in arbitrary radial directions. And, the pressure medium in the pressure chambers is pressed against the belt such that the fluids in the web are transferred to the at least one felt and/or to the press roll.
• the belt may have a smooth surface and/or an embossed surface. Also, the belt may be heated by an auxiliary heating means which is located upstream of the nip in the web moving direction, or is heated by the pressure medium itself which is heated and directly contacts the belt in the pressure means.
• the nip is an extended nip which extends in the moving direction of the web up to 150 cm, more preferably, up to 70 cm.
• a method for treating a web in a paper- or board-making machine is provided.
• the method comprises the steps of: travelling at least one belt that is impervious to fluids, that forms an endless loop and that guides a web to pass through at least one nip, in which the guided web is arranged between a press roll and the belt, operating the press roll and a pressure means which comprises at least one pressure chamber containing pressure medium and extends along the length of the nip in the web moving direction, such that the pressure medium directly contacts and presses the belt hydraulically or pneumatically and the nip is formed between the press roll and the pressure means, adjusting a sealing operating pressure in accordance with the pressure in the pressure chamber, sealing the pressure chamber by the sealing operating pressure acting on a pressure-operated sealing member cooperating with the belt, and removing fluids from the web in the nip by pressing.
• Fig. 1 schematically shows a sectional view of a first embodiment of a pressing apparatus according to the invention along the cross-direction of the apparatus;
• Fig. 2 schematically shows a constitution of an edge portion of a pressure chamber of a pressure means of the pressing apparatus according to the first embodiment of the invention having a pressure-operated sealing member;
• Fig. 3 schematically shows a constitution of a pressure chamber of a pressure means of a pressing apparatus according to a second embodiment of the invention, wherein the pressure chamber has several chambers and pressure- operated sealing members;
• Fig. 4 shows a press section having a pressing apparatus according to the invention
• Fig. 5 shows another press section having two pressing apparatus according to the invention
• Fig. 6 shows another press section having a pressing apparatus according to the invention
• Fig. 7 shows another press section having a pressing apparatus according to the invention
• Fig. 8 shows another press section having a pressing apparatus according to the invention
• Fig. 9 shows another press section having a pressing apparatus according to the invention.
• Fig. 10 shows another press section having two pressing apparatus according to the invention
• Fig. 11 shows still another press section having two pressing apparatus according to the invention
• Fig. 12 schematically shows a preferred constitution for detaching the web after the web has passed through the pressing apparatus according to the invention
• Fig. 13 schematically shows another preferred constitution for detaching the web after the web has passed through the pressing apparatus according to the invention.
• Fig. 1 shows a sectional view of a first embodiment of a pressing apparatus according to the present invention along the cross-direction of the apparatus.
• the pressing apparatus is used in paper- or board-making machines for removing fluids from a web by pressing.
• a nip is formed between a loading means (pressure means) 1 and a press roll 2.
• the loading means 1 comprises at least one pressure chamber 30 (see Fig. 2) containing a pressure fluid (medium) such as water, water with additives, oil or air for pressing against a metal belt (see Fig. 2) 20 which is impervious to fluids and forms an endless loop.
• the loading means 1 extends along the length of the nip in a web moving direction, i.e. from the left side to the right side in Figs . 1 and 2.
• the press roll 2 has a support element 3 inside the roll 2 in order to transmit and carry the load applied by the pressure fluid in the loading means 1 for dewatering the web guided on the belt 20 through the nip (not shown in Figs . 1 and 2) .
• the loading means 1 and the press roll 2 are supported by a support beam arrangement.
• the support beam arrangement includes a support beam 4 and a support clamp 5 which are arranged on each end side of the loading means 1 and the press roll 2 in the machine cross direction.
• the clamps 5 may be opened and then the support beams 4 may be moved in vertical direction by a respective piston/cylinder arrangement 6 in order to allow maintenance of the pressing apparatus, for example, changing of the belt 20.
• the press roll 2 and the loading means 1 are supported from outside of the pressing apparatus by the support beam arrangement and bearing housing (the roll 2) .
• the support beams 4 are connected (i.e. a loading means support is linked with the clamp 5 to a press roll support) . This is to minimise the need of supporting elements around the pressing apparatus of the invention .
• Fig. 2 shows schematically the constitution of one edge portion of the pressure chamber 30 of the loading means 1 including a sealing member 40.
• the web moving direction is shown by an arrow W.
• the view of Fig. 2 is simplified to a straight constitution of the loading means 1 although the loading means 1 should have a concave curvature corresponding to the outer shape of the press roll 2 as shown in Fig 1.
• Fig. 2 shows only a part of the sealing member 40 and of the pressure chamber 30 in Fig. 2. Sealing is required at all edge portions of the pressure chamber 30.
• the surface of the sealing member 40 can be convex although it is drawn to similar shape as the belt 20.
• the fluid pressure in the pressure chamber 30 directly acts on the belt 20 and acts also on the rear of a sealing element 44 of the sealing member 40 via an opening in a sealing housing 42.
• the pressure force is schematically indicated by the vertical arrows in Fig. 2.
• the sealing element 44 is pressure-operated in accordance with the fluid pressure acting in the pressure chamber 30.
• the sealing arrangement between the belt 20 and the pressure chamber 30 has an adjustable fluid-filled gap between the belt 20 and the sealing member 40.
• the gap size is reduced with increasing pressure, so that the loading means 1 is applicable in a large range of pressures.
• an efficient lubrication between the belt 20 and the sealing member 40 is achieved by the pressure fluid. This reduces or even avoids wear of the contact portions between the belt 20 and the sealing element 44. Further, additional lubrication can be fed in front of the sealing member 40 in the web moving direction.
• Fig. 3 schematically shows a pressure chamber of a loading means (pressure means) 111 according to a second embodiment of the invention.
• the loading means 111 has three pressure chambers 30, 32, 34 and four pressure-operated sealing members 40, 50, 60, 70 along the web moving direction shown by the arrow W. Further, a front leakage sealing member 80 and an end leakage sealing member 90 are provided at respective end portions of the loading means 111 as seen in the web moving direction.
• the constitution of the sealing members 40 to 90 is similar to the constitution shown in Fig. 2.
• the loading means 111 has a low pressure and/or temperature chamber 30, a medium pressure and/or temperature chamber 32, and a high pressure and/or temperature chamber 34, which are pressure controlled by low pressure adjustment means 31, medium pressure adjustment means 33, and high pressure adjustment means 35, respectively. That is, the pressure and/or temperature of the chamber 34 are/is higher than that/those in the chamber 32, and the pressure and/or temperature of the chamber 32 are/is higher than that/those in the chamber 30.
• Leakage flow channels 81, 91 are provided between the front leakage sealing member 80 and the front sealing member 40 and the end sealing member 70 and the end leakage sealing member 90 in order to minimize a leakage flow outside of the pressing apparatus.
• the pressure fluid substantially presses the belt 20 along the whole length of the nip in the web moving direction W, i.e. from the front sealing member 40 to the end sealing member 70.
• the leakage sealing members 80, 90 and the pressure in the respective leakage chambers (channels) between the sealing members 80 and 40 or 70 and 90 may act on the belt 20.
• the leakage fluid is collected in the leakage flow channels 81, 91 and is reintroduced by the respective pressure adjustment means
• a pressure contact length (i.e. nip length) between the loading means 111 and the press roll 2 (not shown in Fig. 3) is limited to an area between the front and end sealing members 40 and 70. That is, leakage fluid removal takes place outside the effective nip length because the fluid pressure outside the pressure chambers 30, 32, 34 is low in comparison to the pressures acting in said chambers.
• sealing leakage flow from one pressure chamber to another pressure chamber can be controlled. This enables the use of a longer nip and allows a better control of the pressure distribution in the nip (pressure curve or pulse) .
• Figs. 4 to 13 show several applications of the above pressing apparatus embodiments according to the present invention in different pressing sections of a paper- or board-making machine for removing fluids from a web, which will be briefly explained below.
• reference numerals 100 and 200 indicate two felt loops, i.e. an upper felt 100 and a lower felt 200.
• the web W moves from the left to the right side in Fig. 4 (as shown by the arrow) .
• the press roll 2 is a grooved press roll which acts as a backing roll.
• the belt 20 is grooved in this arrangement.
• water save-all means 300 are optionally arranged after the press nip. After the water save-all means 300 in the web moving direction a transfer nip is provided.
• the belt 20 may be detached from the felt 100 immediately after the press nip by using a belt leading roll.
• This type of press nip arrangement is used in a press section with one, two or even more press nips as a first press nip.
• first and second belts 20 are smooth and made of metal. Further, the belts 20 may have additional heating means 25 shown by the dotted rectangular areas in Fig. 5.
• first nip one side of the web W is guided by the first belt 20.
• An upper felt 100 is arranged on the other side of the web W along the first nip.
• second nip the other side of the web W is guided by the second belt 20.
• a lower felt 200 is arranged on the one side of the web W along the second nip.
• FIG. 6 another press section is shown having three press nips, wherein the last press nip in the web moving direction W is a press nip arrangement (pressing apparatus) according to the invention, wherein the web W is guided on a belt 20 and a felt 100.
• a press roll 2 is a smooth impermeable center roll, and the belt 20 has a grooved shape .
• the web W is transferred to a drying section of the paper and board-making machine.
• Fig. 7 shows a press section having two press nips, wherein the second press nip has the pressing apparatus of the invention.
• the web W is arranged between a felt 100 guided by a belt 20 and a transfer belt 22.
• the belt 20 can be a grooved belt or a smooth belt in this press section.
• Fig. 8 shows a press section having three press nips, wherein the second press nip has the pressing apparatus according to the invention.
• a press roll 2 is a suction roll.
• the suction roll 2 is a grooved roll in this press section.
• a belt 20 has a smooth surface and is heated by a belt heating means 25 which is a heating chamber in this press section.
• a deflection roll of the belt 20 may be used as the belt heating means 25.
• Fig. 9 shows a press section having two press nips.
• the second press nip uses a pressing apparatus according to the invention .
• a press roll 2 is a grooved roll, and a belt 20 has a smooth surface and/or is made of metal.
• the belt 20 is heated by a belt heating means 25 which is a heating chamber using steam for heating the belt 20.
• water save-all means 300 are arranged.
• impingement dryers 400 are provided in order to further dry the web W by means of air or gas flows.
• Fig. 10 shows another press section having three press nips, wherein the second and third press nips have pressing apparatus according to the invention.
• a felt 100 has felt conditioning devices 110.
• the felt conditioning devices 110 are arranged upstream and downstream of the second nip in the web moving direction.
• Fig. 11 shows a press section which is similar to the press section shown in Fig. 10.
• belts 20 are directly heated by belt heating rolls 25 acting as belt heating means 25 which are arranged upstream of the respective press nips. All three guiding rolls 25 can also be heated.
• Figs. 12 and 13 show examples for detaching the web W (see broken line in the Figs.) from the felt 100 immediately after the web W has passed through the press nip so that rewetting of the web after passing through the nip can be limited or even avoided.
• both the felt 100 and the pressing apparatus of the invention i.e. the loading chamber 1 or 111 and the press roll 2 along the press nip
• both the felt 100 and the belt 20 are guided downwards after passing through the nip along the web moving direction.
• This pressing arrangement (a so-called “downwards-directed" pressing arrangement of the belt 20 and the felt 100) ensures that the belt 20 still guides the web W after the press nip, wherein the web W is smoothly detached from the felt 100.
• the last nip(s) of a press section should have higher pressure levels compared to the previous nips in order to efficiently remove water from the web.
• the support element can be a beam and corresponding heavy load carrying structure on the backside of the pressure means, a load-carrying element and support beam inside the press roll (backing roll) , or a support nip roll on the opposite side of the press roll compared to pressure means.
• pressure chamber pressure for loading the sealing elements
• another loading source or mechanism i.e., separate pressure sources, springs, 0-rings and/or the like.
• sealing element may be locked into a definite position to provide a smooth and constant sliding resistance between the belt and the pressure means.
• the belt has a smooth surface and/or an embossed surface in order to give the web side guided by the respective belt surface a desired appearance.
• embossed surface of the belt is used, "mirror" like finishing of a smooth belt may be avoided.
• the length of the press nip is up to 150 cm, preferably, up to 70 cm, along the moving direction of the web.
• the pressure medium used in the above embodiments is normally water.
• water with additives, oil or air or even other gases may be used as the pressure medium.
• the belt of the pressing apparatus is made of metal.
• the belt can be made of synthetics or ceramic materials.
• various different combinations of at least two of the above materials may be used for the belt constitution.

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• 2007
  • 2007-08-21 WO PCT/EP2007/058673 patent/WO2009024186A1/fr active Application Filing
  • 2007-08-21 EP EP07802756A patent/EP2179087B1/fr not_active Not-in-force
  • 2007-08-21 CN CN200780100258.7A patent/CN101778975B/zh not_active Expired - Fee Related
  • 2007-08-21 AT AT07802756T patent/ATE528442T1/de not_active IP Right Cessation

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