Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/66—Pulp catching, de-watering, or recovering; Re-use of pulp-water
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F9/00—Complete machines for making continuous webs of paper
  • D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type

Definitions

• the present invention relates to improvements to continuous wet forming paper machines and more in particular, but not exclusively, to highspeed continuous machines to produce tissue paper.
• the invention relates to improvements to systems for reducing turbulence in the water-slurry circuit of these machines.
• State of the Art
• tissue paper i.e. thin paper mainly for domestic use, as well as for other uses, such as to replace textile cloths for polishing and cleaning.
• the so-called “crescent formers” the jet of fluid is directed at the point in which a felt of textile nature that will receive the wet sheet formed comes into contact with the filter fabric on which the required sheet will be formed. This contact takes place on the generatrix of a large diameter roller called “forming cylinder", which rotates at the peripheral speed at which the sheet is produced.
• the water pressed between the felt and the fabric is delivered from the latter at the same speed as the feed speed of the fabric on the forming cylinder and, by means of pressing force and above all centrifugal force, is ejected against a curved wall suitably shaped to allow the water to be recovered and conveyed to the collection vessel below, from where it is sent to the liquid return channel to reach the silo that acts as reservoir and once again feeds the pump that supplies the circuit.
• Management of the water recirculation phase has become of fundamental importance in order to reach high production speeds. This leads to the need to make use of means to reduce the speed at which the water falls into the collection vessel and is conveyed therefrom towards the discharge channel, so as to reduce the negative phenomena of entrainment and mixing of air in the circuit to a minimum, preventing the formation of foam that floats on top of the water and the formation of mists that disperse into the air in the entire sheet forming area.
• US-A-4.028.174 describes a system for reducing turbulence in the water delivered from a paper forming area in continuous machines.
• deflectors are positioned to collect the water ejected from the forming cylinder and feed it through holes produced in the deflectors. The water that passes through the holes in the deflectors then falls into the collection vessel below, from where it is recovered and recycled.
• Other systems to reduce the speed of the water eliminated from the paper web forming area are described in US patents nos. 4,267,017; 4,501 ,040; 4,790,909; 4,714,522.
• An object of the present invention is to provide a machine " and a method that allow a more effective reduction of turbulence in the water-slurry circuits in continuous paper forming machines, in particular for forming tissue paper. It is also an object of the invention to provide a machine and a method that allow at least partial reduction of the problems deriving from the formation of mists and/or incorporation of air in the water discharged from the paper web forming area.
• a continuous wet forming paper machine comprising: at least a first continuous flexible member and a second continuous flexible member, defining a forming area for forming a web of caveiulose fibers; a hea ⁇ box, to feed a slurry of water and cellulose fibers to said forming area; a vessel to collect the water eliminated from the web forming area; an arrangement to -slow said water eliminated from the web forming area; characterized in that said arrangement comprises: a curved surface arranged laterally to the web forming area, on the side from which said water is eliminated, said surface extending gradually away from the forming area and being oriented downward, the water forming a flow adhering to said guide surface; and a rotating damping member disposed between said guide surface and said collection vessel, below the guide surface, to receive the water coming from this guide surface and discharge it to said collection vessel at a substantially reduced speed.
• a rotating member is provided to slow the flow of water, receiving the flow itself in a blading and discharging it at a speed practically equal to zero, so as to greatly reduce the energy in the flow and consequently the turbulence thereof, preventing or in any case reducing the formation of mists and also reducing the turbulence and therefore the quantity of air incorporated in the water.
• figure 1 shows a side view of the web forming area in a continuous wet forming paper machine of the crescent former type incorporating the present invention in a first embodiment
• figure 2 shows an analogous view to the one in figure 1 in a second embodiment
• figure 3 shows a schematic cross section of the rotating damping member with relative blading.
• Figure 1 shows a schematic side view of the approach system of a continuous paper machine, in particular for tissue paper, in a crescent former configuration.
• the machine comprises a first continuous flexible member 1 , preferably constituted by a felt that is fed around a closed path, only partly represented here.
• a second continuous flexible member 3 preferably constituted by a fabric, which follows a closed path defined by guide rollers 5, 7, 9, 11 as well as by a roller 15 constituting the forming cylinder.
• the felt 1 is also fed around the forming cylinder 15.
• a headbox 17 feeds, for the entire width of the machine, a slurry of water and cellulose fibers between the felt 1 and the fabric 3. This slurry is pressed between the members 1 , 3, and most of the water, present in percentages exceeding 99% in weight, is eliminated by centrifugal force from the forming area between the felt 1 and the fabric 3 in the arc of contact ⁇ with the forming cylinder 15.
• a curved guide surface 19 is arranged in front of the forming cylinder 15 for guiding the water eliminated from the fabric 3 through centrifugal force, as indicated schematically by the arrows A.
• the quantity of water eliminated through the fabric 3 is substantial, considering that the production speed of these machines is in the order of 1000-2000 m/min and that the dry percentage in the slurry fed from the headbox 17 is often below 1%, for example in the order of 0.2-0.4% in weight.
• a collection vessel 21 for the discharged water is located, extending for the entire width of the machine, i.e. for the entire axial extension of the cylinder 15 and for the entire width of the felt 1 and of the fabric 3.
• This vessel is connected to a side discharge channel 22 from which the water is recovered to be conveyed to a circuit that once again feeds the headbox 17.
• the guide surface 19 has a scored configuration, i.e. geometrically constituted as locus of straight lines parallel to one another and parallel to the axis A-A of the forming cylinder 15.
• the curvature of the guide surface 19 is such that it extends gradually away from the cylindrical surface of the cylinder 15 (and consequently from the paper web forming area defined between the felt 1 and the fabric 3 in the contact area with the forming cylinder 15) extending downward.
• the surface 19 extends downward and terminates inferiorly with an edge 19A above a blading of a rotating damping member 23.
• the rotating damping member 23 rotates in the direction of the arrow f23 due to the kinetic energy of the water discharged from the surface 19 into the blading of the rotating damping member itself.
• the arrangement is such that the flow of water generated along the surface 19 (in substantially laminar flow conditions) is tangent to the rotating damping member 23 and does not cross it, as is instead the case in machines specifically provided with turbines for the sole purpose of recovering the kinetic energy of the water.
• the water discharged from the surface 19 into the blading 23P of the rotating damping member 23 is discharged substantially at zero speed at the lower part of the rotating damping member towards the collection vessel 21.
• the rotation axis 25 of the rotating damping member 23 is supported by the structure 27, inside which the collection vessel 21 for collecting the water is located.
• the guide surface 19 is carried by a pair of side panels 31 between which, as well as the guide surface 19, a wall 33 also extends, interposed between the cylinder 15 and the rotating damping member 23. Therefore, between the wall 33 and the guide surface 19 a duct 35 is defined, inside which the blading 23P of the rotating damping member 23 projects.
• the water that flows in a substantially laminar fashion along a guide surface 19 is made to fall onto the portion of blading 23P projecting inside the duct 35.
• the arrangement described above allows the flow of water discharged, i.e. eliminated through the fabric 3, to be "calmed", reducing turbulence and transforming it into a substantially laminar flow along the guide surface 19, to then slow it substantially in the rotating damping member 23 before discharging it into the collection vessel 21.
• This prevents, or in any case drastically reduces, the formation of mists and also substantially reduces the quantity of air incorporated due to the turbulence in the water collected in the tank 21.
• This substantially facilitates the recirculation of the water and reduces the need for suction of the mist that forms around the water discharge area, which conventionally must be filtered in specific purifiers to separate the water containing fiber residues from the air in which it is suspended.
• the assembly formed by the walls or side panels 31 , by the guide surface 19, and, if necessary, by the wall 33, is adjustable with an oscillating or sliding movement with respect to the position of the forming cylinder 15. This adjustability allows optimization of the position of the guide surface 19 with respect to the cylinder 15 and with respect to the rotating damping member 23, which is supported on the axis 25 fixed with respect to the structure 27.
• the assembly 31 , 19, 33 can also be moved away from the cylinder 15 by a degree sufficient to facilitate operations for replacing the fabric 3 or the felt 1 when this becomes necessary.
• the side panels 31 , the surface 19 and the wall 33 are pivoted around pivot pins 90 and can be made to oscillate by means of a jack 92 around this pivot pin to be moved away from the forming cylinder 15 and allow insertion or removal of the fabric and/or of the felt.
• the position of the pivot pins 90 is adjustable, for example, by mounting said pivot pins on supports (not shown) provided with slots for screw fastening to the fixed load bearing structure 27. By loosening the screws it is possible to adjust the pos ⁇ fiorT ⁇ f the pivot pins 90 and consequently of the edge 19A of the surface 19 with respect to the blading of the rotating damping member 23.
• the assembly formed of the side panels 31 , the surface 19 and the wall 33 is movable with respect to the forming cylinder 15 by means of jacks 100 that allow it to be moved towards and away from said cylinder.
• the operating position is defined by adjustable stops 102, the function of which is again to adjust the position of the surface 19 and of the discharge edge 19A thereof with respect to the blading of the rotating damping member 23.
• Figure 3 shows in greater detail a cross section of the profile of the rotating damping member 23 with the blading 23P thereof.
• the blading has a bucket configuration similar to the profile of the blading of a Pelton wheel, which allows the flow of water to be slowed efficiently, almost to zero speed.
• the rotating damping member takes the configuration of a roller constituted by a cylindrical envelope, the periphery of which is provided with channels whose shape and dimension are suitable to receive the flow of water coming from the paper web forming area and divert the orientation thereof, so as to take the speed of the jet of water to almost a zero value, this jet being made to fall from the rotating damping member into the collection vessel or channel at the same speed as the fall speed caused by the difference in level between the rotating damping member and the collection channel itself.
• the rotating damping member 23 can be used solely as a means to "calm" the flow of water and reduce the turbulence thereof.
• a braking member will advantageously be arranged on the axis of the rotating damping member 23 to absorb the energy transferred from the flow of water to the rotating damping member 23.
• the braking member can be of the same type as those commonly used in paper mills, for example to slow the reels on paper unwinders in winding machines.
• this energy can be used, for example, by mounting a specific electrical generator on the axis 25 of the rotating damping member 23, or in any other suitable manner.
• Figure 2 shows a modified embodiment of the machine according to the invention.
• the same reference numerals indicate the same or corresponding parts to those already described with reference to figure 1. These parts will not be described again with reference to figure 2.
• the main difference between the configuration in figure 2 and the configuration in figure 1 consists in the direction of rotation of the rotating damping member 23.
• the rotating damping member 23 rotates (arrow f23) in the opposite direction with respect to the direction of rotation (arrow f15) of the forming cylinder 15.
• the arrangement of the rotating damping member 23 is such that the direction of rotation f23 thereof is the same as the direction of rotation f15 of the forming cylinder 15.
• the rotating damping member 23 is positioned with the rotation axis 25 thereof between the ideal extension of the guide surface 19 and the forming cylinder 15, while in figure 1 the rotation axis 25 of the rotating damping member 23 is positioned, with respect to the ideal extension of the guide surface 19, on the opposite side to the forming cylinder 15.
• the mechanical connection represented by the belt 41 between the forming cylinder 15 and the rotating damping member 23 allows the angular speed of the rotating damping member 23 to be controlled by the same drive motor as the forming cylinder 15, thereby allowing optimization of the slowing function of the flow of water entrusted thereto.
• the rotating damping member 23 is substantially housed completely in the channel 35 defined between the surface 19 and the ideal downward extension thereof and the wall 33.
• a deflection surface 36 is also provided, to prevent water, directed to the rotating damping member 23, from accidentally falling in areas in which it could obstruct the rotation of the rotating damping member.

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• 2006
  • 2006-09-06 IT IT000216A patent/ITFI20060216A1/it unknown
• 2007
  • 2007-08-31 AT AT07827654T patent/ATE459749T1/de active
  • 2007-08-31 DE DE602007005147T patent/DE602007005147D1/de active Active
  • 2007-08-31 CN CN2007800331680A patent/CN101517161B/zh not_active Expired - Fee Related
  • 2007-08-31 EP EP07827654A patent/EP2061929B1/de not_active Not-in-force
  • 2007-08-31 WO PCT/IT2007/000600 patent/WO2008029427A1/en not_active Ceased

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