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
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
  • D21F11/006—Making patterned paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
  • D21F11/14—Making cellulose wadding, filter or blotting paper
• • 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
• • 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
  • D21F9/02—Complete machines for making continuous webs of paper of the Fourdrinier type

Definitions

• the present invention relates to a paper making machine for making tissue paper.
• the invention also relates to a method of operating such a machine.
• a paper making machine for the production of tissue paper is known from U.S. patent0 No. 5393384.
• the paper machine shown therein has a belt impermeable to water which runs in a loop through an extended press nip formed by a shoe press and a counter roll.
• a press felt is conveyed through the press nip.
• a shoe press has been placed such that the press shoe is capable of acting on the tissue drying cylinder. It is stated that the drying effect of the shoe press generates a considerably higher degree5 of drying than a corresponding roll press and that this, in the conjunction with a
• nonabsorbent belt which avoids remoistening of the web results in considerably increased drying capacities of a press unit.
• U.S. patent No. 6547924 Another paper making machine for soft paper such as tissue is disclosed in U.S. patent No. 6547924.
• the paper making machine shown in that patent also uses a substantially0 impermeable belt but this belt is a texturing belt which has a web-contacting surface defining a multitude of regularly distributed depressions and surface portions located between the depressions.
• the belt is used for the purpose of texturing a relief pattern in a fibrous web in order to increase its bulk.
• the substantially impermeable belt runs in a loop through a press with a shoe press roll and a counter roll and around a transfer roll5 that forms a transfer nip with a Yankee dryer.
• U.S. patent No. 4144124 discloses a machine for manufacturing paper such a tissue paper.
• the machine disclosed in that patent comprises a twin-wire former and a press nip between an inner and an outer press roll.
• the upper or outer press roll is a suction roll which, together with a Yankee cylinder forms a second nip.
• An endless fabric such as a wire suitable for pattern embossing is may be used and is said to produce impressions in the paper at the press nips.
• This machine can use uses fewer rolls in the press section since the suction roll is used two nips, one nip with the so called “inner roll” and one nip with the Yankee cylinder.
• the invention relates to a paper making machine for making tissue paper.
• the inventive machine comprises a former in which a fibrous web may be formed.
• the former has a forming roll, a forming fabric and a felt.
• the machine further comprises a press with a first press member and a second press member.
• the second press member is arranged to form a dewatering nip with the first press member and the felt (i.e. the same felt as is used in the former) is arranged to pass through the dewatering nip.
• the machine further comprises a drying cylinder which is arranged to form a transfer nip with the first press member.
• a belt forms a loop around the first press member such that the belt passes through the dewatering nip and the transfer nip.
• the first press member is an extended nip roll that has a flexible jacket that forms a loop and a flexible support body within the loop of the flexible jacket.
• the flexible support body can be caused to press the flexible jacket radially outwards.
• the flexible support body is placed opposite the drying cylinder such that the support body can press the flexible jacket towards the drying cylinder to close the transfer nip.
• the first press member is also movable in relation to the drying cylinder such that the distance between the drying cylinder and the first press member can be increased in a separating movement or decreased in a closing movement.
• the paper making machine further comprises a mechanical stop arranged to halt the closing movement.
• the mechanical stop is arranged to halt the closing movement in a position where the transfer nip is not yet closed. Closure of the transfer nip will then require that flexible support body presses the flexible jacket radially outwards.
• the flexible support body comprises or is supported by at least one flexible hose extending in a cross machine direction and connected to a source of pressurized fluid such that pressurization of the at least one flexible hose will cause the flexible support body to either expand or move radially outwards.
• the belt may be an impermeable belt which has a smooth surface on the side that, in the transfer nip, faces the drying cylinder.
• the belt can also be an impermeable belt which has a textured surface on the side that, in the transfer nip, faces the drying cylinder.
• the belt may be a permeable belt which has a textured surface on the side that, in the transfer nip, faces the drying cylinder.
• the belt is can also be a permeable belt which has a smooth surface on the side that, in the transfer nip, faces the drying cylinder.
• the extended nip roll may optionally also comprise a flexible support body that is placed opposite the second press member to cooperate with the second press member to form the dewatering nip.
• the second press member may be a grooved roll.
• the first press member is supported in bearing housings.
• the paper making machine may further comprise at least one actuator arranged to act on the bearing housings of the first press member to increase or decrease the distance between the first press member and the drying cylinder.
• the invention can also be described in terms of a method of operating such a machine.
• the method comprises moving the first press member from a first position at a first distance from the drying cylinder to a second position defined by the mechanical stop while the flexible support body has still not pressed the flexible jacket radially outwards.
• the flexible support body is caused to press the flexible jacket radially outwards such that it acts against the drying cylinder in the transfer nip (i.e. such that the transfer nip is loaded with a certain linear load).
• the extended nip roll also comprises a flexible support body that is placed opposite the second press member to cooperate with the second press member to form the dewatering nip.
• the inventive method may comprise operating the dewatering nip at a linear load in the range of 100 kN/m - 600 kN/m and a peak pressure of 6 MPa.
• the drying cylinder may be rotating already before the transfer nip is closed.
• the belt that passes through the transfer nip (and thus forms a loop around the first press member) may be used to drive the flexible jacket such that the flexible jacket rotates before the transfer nip is closed.
• the belt can be used to drive the flexible jacket to a speed that matches that of the drying cylinder before the transfer nip is closed or at least before the belt contacts the surface of the drying cylinder.
• the belt is used to drive the flexible jacket to match the speed of the drying cylinder while the outer surface of the flexible jacket is still at a distance of at least 40 mm from the surface of the drying cylinder.
• the inventive paper making machine may be defined in the following terms.
• the machine comprises a former in which a fibrous web may be formed.
• the former has a forming roll, a forming fabric and a felt.
• the machine further has a first press member and a second press member arranged to form a dewatering nip with the first press member.
• the felt i.e. the same felt as used in the former
• a drying cylinder is arranged to form a transfer nip with the first press member.
• a belt forms a loop around the first press member such that the belt passes through the dewatering nip and the transfer nip.
• one of the first press member and the second press member is an extended nip roll that has a flexible jacket that forms a loop and a flexible support body within the loop of the flexible jacket.
• the flexible support body can be caused to press the flexible jacket radially outwards.
• the support body further is placed opposite the other press member such that the support body can press the flexible jacket towards the other press member to close the dewatering nip.
• Either of the first press member and the second press member may be an extended nip roll.
• Figure 1 shows a layout of a paper making machine according to one embodiment.
• Figure 2 is a schematic representation of a press nip and a transfer nip in a paper making machine.
• Figure 3 shows a cross section of a support body used in the press nip of Figure 2.
• Figure 4 shows a cross section similar to Figure 3 but illustrating another way of arranging a support body for the press nip.
• Figure 5 is a schematic representation of a part of the paper making machine in which a press member is placed in a first position.
• Figure 6 is a schematic representation similar to Figure 5 but with the same press member placed in a second position.
• Figure 7 is a figure similar to Figure 5 and Figure 6 but showing an alternative design of one of the components used.
• Figure 8 is a schematic cross-sectional representation of the situation before the transfer nip has been closed.
• Figure 9 is a schematic cross-sectional representation of how the transfer nip has been closed.
• Figure 10a is a schematic representation substantially corresponding to Figure 5 but where second press member is shown.
• Figure 10 b is a schematic representation similar to Figure 10 a but showing the first press member in a position where it has moved closer to the drying cylinder.
• Figure 10 c is a schematic representation substantially similar to Figure 10a and 10b but where the flexible support bodies have been activated to act in the transfer nip and the press nip.
• Figure 1 la is a schematic representation of an embodiment of the invention.
• Figure 1 lb is a Figure similar to Figure 10a but showing a perspective view of the same components.
• tissue paper relates to paper having a relatively low basis weight. In most cases, this means a basis weight in the range of 10 g/m 2 - 50 g/m 2 although examples of tissue paper webs are known where the basis weight may lie outside this range. Unlike paperboard, tissue paper does not have to be stiff and tissue can therefore have a lower basis weight. In most cases, the basis weight for tissue paper may lie in the range of 15 g/m 2 - 40 g/m 2 and typical values may lie in the range of 15 g /m 2 - 30 g/m 2 or 20 g/m 2 - 30 g/m 2 .
• the machine according to the invention comprises a former 2 in which a fibrous web may be formed.
• the former 2 has a forming roll 4, a forming fabric 5 and a felt 7.
• the forming fabric 5 is suitably a permeable wire.
• the forming fabric 5 is guided in a loop by guide rolls 6 and the felt 7 is guided in a loop partially by guide rolls 8 but also by the forming roll 4 and by a press member 13.
• the former 2 also has a head box 3 arranged to inject stock in a gap formed between the forming fabric 5 and the felt 7 as is known in the art.
• One or several felt dewatering devices 26 may be arranged to remove water from the felt 7 as is known in the art to which the invention pertains.
• the dewatering device 26 may be, for example, a Uhle box.
• the machine 1 also comprises a press 11 with a first press member 12 and a second press member 13.
• the second press member 13 is arranged to form a dewatering nip PN with the first press member 12 (see also Figure l ib and Figure l ib).
• the felt 7 is arranged to pass through the dewatering nip PN.
• the felt 7 forms a loop around the second dewatering member 13.
• water is pressed from the wet paper web and absorbed by the felt 7.
• One or several further felt dewatering devices may be arranged to dewater the felt 7 while the felt runs from the press 11 back to the forming roll (these further dewatering devices are not shown in Figure 1).
• the machine also comprises a drying cylinder 14.
• the drying cylinder may suitably be a Yankee drying cylinder which is internally heated by steam.
• the drying cylinder 14 can also be heated by other means, for example by infrared heaters (not shown).
• the drying cylinder 14 is arranged to form a transfer nip TN with the first press member 12 (see Figure 11a and Figure 1 lb).
• a belt 15 forms a loop around the first press member 12 such that the belt 15 passes through the dewatering nip PN and the transfer nip TN.
• guide rolls 16 may be arranged to guide the belt 15.
• the belt 15 may also be provided with a cleaning device (not shown) for cleaning the belt during operation of the machine.
• the first press member 12 is an extended nip roll that has a flexible jacket 17 that forms a loop and a flexible support body 18 within the loop of the flexible jacket 17 as is also shown in Figure 1 lb and Figure 1 lb.
• the first press member 12 may comprise two flexible support bodies 18, 19 in which case a first flexible support body 18 is arranged to act against the drying cylinder 14 and a second flexible support body 19 is arranged to act against the second press member 13.
• Each flexible support body 18, 19 can be caused to press the flexible jacket 17 radially outwards.
• the second press member 13 is suitably a roll.
• the second press member 13 may be provided with grooves 28 as best seen in Figure l i b. The use of a grooved roll in this position improves dewatering.
• the second press member may be a press roll with a smooth surface, for example a roll with a cover, e.g. an elastic cover such as a cover of rubber or a material with properties similar to rubber. The cover could also be a ceramic cover.
• the press member 13 may also be a roll without a cover.
• the belt 15 may be an impermeable textured belt.
• it may be an impermeable textured belt of the kind disclosed in U.S. patent No. 6547924, i.e. at least the surface facing the paper web is textured.
• the use of a textured belt can improve the bulk of the web by imparting a three-dimensional structure to the web.
• the belt 15 may also be a belt with a substantially smooth surface (i.e. at least the surface facing the paper web is smooth).
• smooth should be understood as meaning that the belt 15 has no texturing structure that is arranged to form a textured pattern in the paper web.
• the belt could be a belt of, for example, the kind disclosed in U.S. patent No. 5298124.
• the belt 15 is typically made of a material that is compressible to a certain degree and the belt 15 is often made of a material that may be heat sensitive. This is especially the case when the belt contains polymer materials.
• the belt 15 preferably comprises polyurethane such that at least the surface that contacts the paper web may be made of polyurethane, at least in part.
• the extended nip roll and the flexible support body 18 may be designed in a way shown in, for example, U.S. patent No. 7527708, the disclosure of which is hereby incorporated by reference.
• the design of such an extended nip roll and flexible support body will also be explained with reference to Figure 2 and Figure 3.
• the flexible support body 18 is placed within the loop of a flexible jacket 17 that can be made wholly or in part of, for example, polyurethane or a material with properties similar to polyurethane.
• the flexible jacket 17 may thus comprise polyurethane but possibly also other components.
• the external surface of the flexible jacket 17 may be smooth or substantially smooth but embodiments are conceivable where the flexible jacket 17 does not have a smooth outer surface.
• the external face of the flexible jacket 17 may have grooves.
• flexible support body 18 may be formed by or comprise a body that can be described as a flexible hose with an internal cavity 31 that can be pressurized internally by means of pressurized fluid that is caused to flow into the internal cavity 31 from a source 22 of pressurized fluid that is connected to the internal cavity 31.
• the source of pressurized fluid 22 may be controlled by a control device 32.
• the control device 32 may be, for example, a computer.
• the support bodies 18, 19 are schematically shown as being connected to the same source 22 of pressurized fluid.
• each flexible support body 18, 19 may be connected to its own source 22 of pressurized fluid.
• the flexible support body 18 may be placed in a channel 30 of a holder 29. It should be understood that the support body 18 may be sealed at its axial ends.
• the flexible support body 18 is preferably made of an elastic material such that either the entire support body 18 or at least a part of is made of an elastic material such that the flexible support body is elastically deformable.
• the support body 18 can be made of, for example, plastic or rubber material such as polymers, possibly reinforced polymers. If pressurized fluid is fed into the internal cavity 31, the flexible support body 18 will expand radially outwards.
• the flexible jacket 17 is not shown but it should be understood that the flexible jacket 17 runs over the flexible support body 18.
• the flexible support body 18 expands radially outwards, it will press against the flexible jacket 17 such that also the flexible jacket 17 is pressed outwards.
• the flexible support body 18 which has an inner cavity 31 as described above also extends in the cross machine direction.
• the flexible support body 18 must not necessarily be shaped as in U.S. patent No. 7527708.
• Another kind of flexible support body arrangement is shown in Figure 4.
• the flexible support body 18 is a thin shoe with a concave surface.
• the concave surface faces outwards such that it can cooperate with a convex counter element such as a roll in order to form a nip with the convex counter element.
• the thin shoe that forms the flexible support body may be made of, for example, aluminum, and be sufficiently thin to allow the shoe to adapt to a large extent to the contour of a counter roll (such as a Yankee drying cylinder).
• the thin shoe is supported by one, two or more flexible hoses 33 that can be made of an elastic material or a material that is only flexible but not elastic.
• the flexible hose or flexible hoses 33 extend in the cross machine direction and are connected to a source of pressurized fluid 22 in the same way as described with reference to Figure 2 and Figure 3.
• a further thin sheet 35 and a number of separate intermediate pieces 34 may optionally be placed between the flexible support body 18 and the flexible hose(s) 33.
• the thin sheet 35 may serve to protect the flexible hoses 33 from the intermediate pieces 35.
• the intermediate pieces 34 can be capable of moving relative to each other in the radial direction (i.e. substantially in the press plane). Thereby, the flexible support body 18 can more easily adapt to the shape of a counter element such as a Yankee cylinder 14. If the flexible hose(s) 33 is (are) filled with pressurized fluid, this may cause the flexible hose(s) to expand and thereby cause the flexible support body 18 to move outwards against the inner surface of the flexible jacket 17 such that also the flexible jacket 17 is pressed radially outwards.
• the flexible support body 18 can thus be described as comprising or being supported by at least one flexible hose extending in a cross machine direction and connected to a source of pressurized fluid such that
• the extended nip roll may have an internal lubrication arrangement (not shown) to supply lubrication fluid (e.g. oil) to the inner surface of the flexible jacket 17 such that there will be a thin film of lubrication fluid between the flexible support body 18 (or support element 18) and the inner surface of the flexible jacket 17. Thereby, friction between the flexible jacket 17 and the flexible support body may be reduced.
• lubrication fluid e.g. oil
• Various arrangements for supplying a lubricant in an extended nip press are known in the art.
• the first flexible support body 18 is further placed opposite the drying cylinder 14 such that the flexible support body 18 can press the flexible jacket 17 towards the drying cylinder 14. Thereby, the flexible support body 18 can close the transfer nip TN.
• the first press member 12 is movable in relation to the drying cylinder 14. Thereby, the distance between the drying cylinder 14 and the first press member 12 can be increased in a separating movement or decreased in a closing movement.
• the first press member 12 is shown in a first position at a distance from the drying cylinder 14. When the first press member 12 is in this position, activation of the first flexible support body 18 is not sufficient to close the transfer nip TN since the distance between the flexible jacket 17 and the surface of the drying cylinder is too large. In practice, the distance may be 40 mm or more. It should be noted that, while the belt 15 that passes in a loop around the first press member 12 is not shown in Figure 5, the belt 15 will be there.
• the first press member 12 is shown in a second position, close to the surface of the drying cylinder 14.
• the first press member 12 and the belt 15 are shown at a certain distance from the drying cylinder (i.e. there is still a gap).
• the belt 15 may optionally be in contact with the surface of the drying cylinder 14 even though the first flexible support body 18 has not yet been activated to press against the drying cylinder 14 and from a proper nip.
• first flexible support body 18 has already been activated to a limited extent when the first press member 12 reaches its second position although but that the first flexible support body 18 it is not fully activated until after the first press member 12 has reached its second position which is defined by the mechanical stop 23.
• Figure 6 shows how the first press member 12 has reached its second position while there is still a small gap between the first press member 12 and the drying cylinder 14 such that there is still a small gap separating the belt 15 from the surface of the drying cylinder 14.
• the machine 1 has at least one actuator 25 to move the first press member from its first position away from the drying cylinder 14 to its second position closer to the drying cylinder 14.
• the at least one actuator 25 may be a hydraulic cylinder.
• two hydraulic cylinders are used as actuators 25 to move the first press member 12 in a closing movement in the direction of arrow A in Figure 5.
• the first press member 12 is supported in bearing housings 24, i.e. the first press member has axial ends that are supported in bearing housings as is well known in the art of extended nip presses.
• the at least one actuator 25 may be arranged to act on the bearing housings 24 of the first press member 12 to increase or decrease the distance between the first press member 12 and the drying cylinder 14.
• the closing movement is shown as a linear movement but it should be understood that, in many embodiments, a turning movement, i.e. a movement in which the press member 12 moves along an arcuate (curved) path may be chosen or even preferred.
• the first press member 12 may be arranged to turn about a hinged connection (not shown).
• the paper making machine further comprises a mechanical stop 23 that is arranged to halt the closing movement. This can be made in a position where the flexible jacket 17 of the first press member 12 does not close the transfer nip TN unless the flexible support body 18 presses the flexible jacket 17 radially outwards.
• the mechanical stop 23 can be positioned such that there is a certain degree of contact between the belt 15 and the drying cylinder 14 already before the first flexible support body 18 has been caused to press against the drying cylinder 14. It should be understood that the mechanical stop 23 is a stationary machine part which blocks/prevents further movement of the first press member 12 when a part of the first press member comes into contact with the mechanical stop 23.
• the mechanical stop 23 may be secured to a fixed structure.
• the mechanical stop 23 may be secured to the floor on which the paper making machine stands or it may be secured to the machine frame of the paper making machine.
• the mechanical stop 23 may be designed to limit movement of the first press member in more than one direction. In Figure 7, this is represented by a mechanical stop 23 that has a V-shaped groove to receive a corresponding V-shaped projection on the bearing housing 24.
• the actuator or actuators 25 will often continue to press the first press member against the mechanical stop also during operation.
• the mechanical stop 23 acts against the bearing housings 24.
• the mechanical stop 23 could also act on some other part of the first bearing housing. For example, it could act on a journal extending beyond the bearing housing 24.
• the starting sequence may be as follows. Initially, the first press member 12 is in the position shown in Figure 5, i.e. at a first distance from the drying cylinder 14. The drying cylinder 14 is driven (i.e. it rotates). The belt 15 will now be driven by a drive arrangement.
• the drive arrangement for the belt 15 is not explicitly shown but the drive could be arranged in many different ways. For example, one or several guide rolls 16 for the belt 15 could be driven rolls.
• the belt 15 can then be used to drive the flexible jacket 17 of the first press member 12. Thereby, the flexible jacket 17 can be caused to rotate before the transfer nip TN is closed.
• the belt 15 is driven to a speed that matches that of the surface of the drying cylinder. Thereby, it can also drive the flexible jacket to the same speed. This is preferably done while the distance between the outer surface of the flexible jacket 17 is still at a distance of at least 40 mm away from the surface of the drying cylinder 14.
• the first press member 12 is then moved from its first position to a second position defined by the mechanical stop 23.
• the flexible support body 18 has still not pressed the flexible jacket 17 radially outwards.
• it may be activated but only to a very limited degree. Therefore, the transfer nip may still be open such that belt 15 is not yet in contact with the drying cylinder.
• the first press member is in its second position, there may be a distance (gap) between the outer surface of the flexible jacket 17 and the surface of the drying cylinder 14 which may be on the order of about 5 mm (the exact distance may of course vary from case to case).
• the belt 15 is somewhat closer since the belt 15 also has a certain thickness. Possibly, there is actually a light contact between the belt 15 and the surface of the cylinder 14.
• Figure 8 shows the situation after the first press member 12 has been brought to the position defined by the mechanical stop 23.
• a certain gap is shown but there may optionally also be a light contact between the belt 15 and the cylinder 14.
• the arrows in Figure 8 indicate the direction of movement of the belt 15, the flexible jacket 17 that is driven by the belt 15 and the direction of rotation of the drying cylinder 14. From this position, the flexible support body will be caused to press the flexible jacket radially 17 outwards in order to act against the drying cylinder 14. If there is a initially a gap between the belt 15 and the drying cylinder 14, activation of the first flexible support body 18 will cause this gap to be closed. The activation of the first flexible support body 18 and the effect of this will now be explained with reference to Figure 9.
• Figure 9 illustrates an embodiment where the flexible support body 18 is designed in the way explained with reference to Figure 3 but substantially the same procedure could be used with other embodiments of the flexible support body.
• the internal cavity 31 of the flexible support body has been filled with pressurized fluid to such an extent that the support body 18 has expanded radially outwards.
• the flexible jacket 17 and the belt 15 have been pressed in a direction towards the drying cylinder 14 to act against the drying cylinder 14.
• the transfer nip TN has been properly activated, i.e. loaded, (and closed if there was an initial gap) and the paper web will now be pressed against the drying cylinder 14 in the transfer nip TN and be transferred from the belt 15 to the surface of the drying cylinder 14.
• the holder 29 in which the flexible support body 18 is placed normally remains stationary while the flexible support body 18 expands radially outwards to activate the transfer nip TN (the holder 29 is normally a component that is fixed within the extended nip roll).
• Figure 10a is a schematic representation substantially corresponding to the situation depicted in Figure 5.
• Figure 10b the first press member 12 has been moved closer to the drying cylinder 14 and, at the same time, also closer to the second press member 13. In this position, there may still be a small gap between the flexible jacket 17 and the drying cylinder 14 or a small gap between the flexible jacket 17 and the second press element 13 but the flexible support bodies 18 and 19 have not yet been activated.
• a doctor blade 27 has been arranged to crepe the paper web W from the drying cylinder 14.
• the inventors have discovered that the use of a flexible support body in the transfer nip has the surprising effect that the bulk of the paper web is improved. Since bulk is often a desired property for tissue paper, this is of great practical value. Without wishing to be bound by theory, it is believed by the inventors that the use of a flexible support body causes the paper web to adhere stronger to the surface of the drying cylinder. The following creping operation by the doctor blade 27 may then have a greater effect on the paper such that bulk is increased.
• the first press member 12 may also comprise a second flexible support body 19.
• the second flexible support body 19 is placed opposite the second press member 13 to cooperate with the second press member 13 in order to form the dewatering nip PN.
• a substantially rigid shoe as in a conventional shoe press may also be used for the dewatering nip PN.
• the second press member 13 may be a roll with grooves 28 as shown in Figure 1 lb. It may also be, for example, a suction roll or a deflection-compensated roll.
• the dewatering nip PN When the dewatering nip PN is formed with a flexible support body 19, the dewatering nip PN may suitably be operated at a linear load in the range of 100 kN/m - 600 kN/m and a peak pressure of 6 MPa. In one embodiment contemplated by the inventors, the dewatering nip PN formed by a flexible support body may have a nip length of 125 mm - 140 mm and a linear load of 150 kN/m. When the dewatering nip is formed with a rigid shoe (i.e.
• the machine direction length of such a rigid shoe may be in the range of 50 mm - 150 mm while the linear load of the dewatering nip in such a case may be in the range of 200 kN/m - 1000 kN/m, preferably 300 kN/m - 1000 kN/m.
• the linear load may be in the range of 400 kN/m - 600 kN/m when a rigid concave shoe (e.g. a steel shoe) is used in the dewatering nip PN. This which can give an adequate dewatering without causing unnecessary bulk reduction.
• the transfer nip TN may be operated at a linear load which is, for example, in the range of 50 kN/m - 100 kN/m but it is believed by the inventors that higher linear loads (and higher pressure levels) in the transfer nip TN may actually have the benefit of improving the bulk since a higher linear load can cause the web W to adhere stronger to the surface of the drying cylinder 14.
• the flexible support body 18 in the transfer nip TN is formed by a flexible hose with an internal cavity 31 (see Figure 3)
• the length of the transfer nip TN in the machine direction may suitably be in the range of 30 mm - 100 mm and preferably 30 mm - 80 mm.
• a length in this range is advantageous for achieving good adhesion of the web to the drying cylinder while avoiding unnecessarily large dimensions of the components used.
• This may also be a suitable length for the transfer nip TN when the flexible body 18 is arranged according to the embodiment of Figure 4.
• a suitable highest pressure in the transfer nip TN may be in the range of 1 MPa - 3 MPa.
• the highest pressure in the transfer nip TN may be 2 MPa or about 2 MPa.
• peak pressures up to 6 MPa may be tested or possibly even higher peak pressures.
• the flexible support body 18 that is used for the transfer nip TN may possibly have a longer nip length than 80 mm.
• the flexible support body 18 may have several chambers that may be individually pressurized as disclosed in US patent No. 7527708 (such an embodiment is shown in Fig. 12 of US patent No. 7527708).
• nip length in the transfer nip TN may be in the range of 50 mm - 150 mm. For such longer transfer nips, the linear load can be made higher.
• the belt 15 may be an impermeable belt which has a smooth surface on the side that faces the paper web, i.e. the side that, in the transfer nip TN, faces the drying cylinder 14.
• Such a belt may be used in order to secure a correct web transfer after the dewatering nip PN.
• the smooth surface of the belt ensures that the web follows the belt 15 after passage of the dewatering nip PN instead of following the water-receiving felt 7.
• the belt 15 may advantageously be an impermeable belt which has a textured surface on the side that, in the transfer nip, faces the drying cylinder 14. This entails the advantage that the bulk of the paper web W can be increased.
• the belt 15 is, at least to some extent, a belt that is permeable to water. This may be the case both when the belt 15 is textured and when it is smooth.
• the advantage is gained that the first press member has a well-defined position before the transfer nip TN is activated. This is of particular importance if the first press member 12 has two flexible support bodies 18, 19 (or a flexible support body 18 for the transfer nip TN and a rigid shoe for the dewatering nip PN). If the first press member has two flexible support bodies and is required to form both a press nip PN with the second press member 13 and a transfer nip TN with the drying cylinder, it is important that the position of the first press member is well defined when these nips are to be closed/activated.
• the use of a mechanical stop also entails the advantage that an operator of the machine can control the closing of the transfer nip TN and the press nip PN more accurately.
• the mechanical stop makes it possible to place the first press member 12 in the position defined by the mechanical stop but in which it is not necessarily so that any of the nips TN, PN is closed.
• the operator of the machine can then close those nips (or bring the nips to their operational load in case they are already closed) by activating the flexible support bodies 18, 19. If the operator wants to load the nips PN, TN in any special sequence, for example loading the dewatering nip PN before the transfer nip is closed, this is also possible.
• the first press member 12 can be brought to a well-defined position near the drying cylinder 14 before the flexible support body 18 is activated, the risk that the pressure in the flexible hose of the support body 18 should become too high before the nip is properly closed can be avoided.
• a suitable machine speed may be up to 2200 m/minute.
• machine speed may be in the range of 1000 m/minute - 2200 m/minute.
• Suitable speeds would normally be about 1500 m/minute - 2200 m/minute to give the web a suitable dwell time for dewatering in the nip in combination with the need to keep up a production output.
• the machine width may be in the range of 2 - 8 meters.
• machine width may be 3.5 - 7 meters.
• machines wider than 8 meters are conceivable (for example machines up to a width of 10 meters or more).
• Machines narrower than 2 meters may also be considered.
• the pulp used in the process may be, for example, chemical pulp. Depending on the end user's needs, virgin pulp or recycled may be used.

Landscapes

• Paper (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=47601367

Family Applications (1)

Country Status (5)

Cited By (7)

Families Citing this family (1)

Citations (4)

Family Cites Families (2)

• 2011
  • 2011-07-28 SE SE1150723A patent/SE536201C2/sv not_active IP Right Cessation
• 2012
  • 2012-07-26 CN CN201280046455.6A patent/CN103890264B/zh active Active
  • 2012-07-26 WO PCT/SE2012/050848 patent/WO2013015739A1/en active Application Filing
  • 2012-07-26 PL PL12818302.7T patent/PL2737125T3/pl unknown
  • 2012-07-26 EP EP12818302.7A patent/EP2737125B1/en active Active

Patent Citations (4)

Also Published As

Similar Documents

Legal Events