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    • 专利摘要:
    17 ABSTRACT The inVention relates to an extended nip roll (5) capable of forrning a press nip (N) Witha counter roll (7) Which press nip (N) has an extension in a machine direction When theextended nip roll (5) cooperates With the counter roll (7). The extended nip roll (5)comprises a flexible jacket; an elastic press body (13) arranged inside the flexiblejacket. The top side (14) of the press body (13) is beveled in such a Way that, in themachine direction, a Working surface (15) of the top side has a doWnstream end (16)Which, in the machine direction, is followed by an exit side surface (17) that divergesfrom the interior surface (11) of the flexible jacket (10). The press body (13) further hasat least a first and a second intemal pressure chamber (18, 19). The pressure chambers(18, 19) can be pressurized such that the press body (13) expands. The first intemalpressure (18) chamber has an extension in the machine direction that does not extendbeyond the Working surface (15) and the second intemal pressure chamber (19) islocated doWnstream of the first intemal pressure chamber (18) and has an extension inthe machine direction beyond the doWnstream end (16) of the Working surface (15). TheWorking surface (15) and the exit side surface (17) are made of a material that has ahigher shore A hardness than the material in the rest of the press body (13). TheinVention also relates to an extended nip press and a paper machine in Which theextended nip roll is used. The inVention further relates to a method of operating theextended nip press.
    公开号:SE1250393A1
    申请号:SE1250393
    申请日:2012-04-19
    公开日:2013-10-20
    发明作者:Tord Gustavsson；Goeran Ekstroem；Jan Paulsson；Karl-Johan Tolfsson
    申请人:Metso Paper Sweden Ab；
    IPC主号:
    专利说明:

    AN EXTENDED NIP ROLL, AN EXTENDED NIP PRESS MAKING USE OF THEEXTENDED NIP ROLL, A PAPERMAKING MACHINE AND A METHOD OFOPERATING AN EXTENDED NIP PRESS FIELD OF THE INVENTION The invention relates to an extended nip roll, to an extended nip press that comprises theinventive extended nip roll and to a paper making machine comprising such an extendednip press. The invention also relates to a method of operating the inventive extended nipwherein a wet paper web is passed through the extended nip.
    BACKGROUND OF THE INVENTION The invention relates to the field of extended nip presses used in paper makingmachines. In a paper making machine, an extended nip press is norrnally used forpressing water out of a newly formed wet f1brous web but an extended nip may also beused for other purposes in a paper making machine, e. g. calendering. Although extendednip presses were first introduced for heavy grades such as paperboard, they later cometo be used also for lighter grades such as printing paper. In recent years, such presseshave also been used in machines for making tissue paper. In such machines, theextended nip press is often formed by an extended nip roll and a Yankee drying cylinderthat acts as a counter roll for the extended nip roll. An extended nip press is typicallyformed by an extended nip roll that comprises a rigid shoe with a concave surface. Therigid shoe of such an extended nip roll can be made of a material such as, for example,steel or aluminum. US patent No. 7527708 discloses how an extended nip can beformed by means of a device that does not use a steel shoe but instead a support bodywhich is elastically deforrnable. The support body disclosed in that document has intemal pressure chambers that can be connected to a pressure medium source.
    Generally, it is desirable that the pressure in the nip of an extended nip press rises fromthe beginning of the nip to reach a peak at the end of the nip. Such a pressure profile isadvantageous since it reduces re-wetting of the paper web when the web exits from thepress nip. In US 7527708, it is suggested that different pressure chambers are set underdifferent pressures such that a pressure curve describing a stepped course is obtained.
    It is an object of the present invention to provide an extended nip press that is designedin such a way that a suitable pressure profile is obtained.
    Another object of the invention is to provide an extended nip press in which the lubrication fiinctions in a reliable way.
    DISCLOSURE OF THE INVENTION The invention relates to an extended nip roll capable of forrning a press nip with acounter roll which press nip has an extension in a machine direction when the extendednip roll cooperates with the counter roll. The inventive extended nip roll coniprises; aflexible jacket with an interior surface and an exterior surface and a press body arrangedinside the flexible jacket. The press body is elastically deforniable and it has a top sidethat faces the interior surface of the flexible jacket. The top side of the press body isbeveled in such a way that, in the machine direction, a working surface of the top sidehas a downstreani end which, in the niachine direction, is followed by an exit sidesurface that diverges froni the interior surface of the flexible jacket. The press bodyfurther has at least a first and a second internal pressure chaniber which internalpressure chanibers can be pressurized such that the press body expands. The firstinternal pressure chaniber has an extension in the niachine direction that does not extendbeyond the working surface and the second internal pressure chaniber is locateddownstreani of the first internal pressure chaniber and has an extension in the niachinedirection beyond the downstreani end of the working surface. The extended nip roll alsoconiprises a support for the press body which support provides support to sides of thepress body but allows the press body to expand in a direction towards the interiorsurface of the flexible jacket. The second internal pressure chaniber has such anextension in the niachine direction that niore than 30% of the extension (the niachinedirection length of the second internal pressure chaniber) extends beyond thedownstreani end of the working surface and in that the working surface and the exit sidesurface are niade of a niaterial that has a higher shore A hardness than the niaterial inthe rest of the press body.
    The press body niay be designed such that, in an unloaded state of the extended nip roll,the exit side surface downstreani of the working surface forrns an angle of 30° - 65°with a tangent to the working surface, preferably an angle in the range of 35° - 60°.
    The Working surface of the top side may be a flat surface in the unloaded state of theextended nip roll When the extended nip roll does not form a nip With a counter roll.Moreover, in the unloaded state of the extended nip roll, the exit side surfacedoWnstream of the Working surface may form an angle of 40° - 50° With the Workingsurface. Instead of being flat in the unloaded state of the roll, the Working surface may be, for example, a convex or concave surface.
    In embodiments of the invention, a part of press body may comprise a sole Which formsthe Working surface and the exit side surface. In such embodiments, the sole maypreferably have a thickness in the range of 1 mm - 30 mm, preferably 5 mm - 25 mm, even more preferred 10 mm - 25 mm.
    The sole may have a Shore A hardness that is higher than 90 Shore A While the part ofthe press body that surrounds the intemal pressure chambers has a hardness Which isless than 90 Shore A. Preferably the sole has a hardness of 93 Shore A - 100 Shore AWhile the part of the press body that surrounds the intemal pressure chambers has ahardness of 70 Shore A - 90 Shore A.
    The exit side surface is preferably separated from the Working surface by a roundededge Which has a first radius in an area adjacent the Working surface and a second radiusin an area adjacent the exit side surface and Wherein the second radius is smaller thanthe first radius. In embodiments of the invention, the first radius is in the range of 20 mm - 40 mm and the second radius is in the range of 6 mm - 15 mm.
    The rounded edge that separates the Working surface from the exit side surface may have an extension in the machine direction Which is in the range of 6 mm - 16 mm.
    In embodiments of the invention, the press body comprises also a third intemal pressurechamber Which, in the machine direction, is located upstream of the first intemal pressure chamber.
    Preferably, the intemal pressure chambers have a rectangular shape and a largerextension in the radial direction of the extended nip roll than in the machine direction.
    In embodiments of the invention, the press body comprises a lip located upstream of theWorking surface and Which lip protrudes in an upstream direction. The lip has an entrysurface that faces the interior surface of the flexible jacket and forms an angle of 2° - 50° With a tangent to the Working surface.
    A lubrication channel may advantageously be arranged to feed a lubricant to theworking surface. However, it should be understood that such a lubrication channel isoptional.
    Preferably, the press body may be covered by an exchangeable wear protection layer.However, it should be understood that embodiments without such a wear protection layer are conceivable.
    The invention also relates to an extended nip press comprising an extended nip roll asdescribed above and additionally comprising a counter roll cooperating with theextended nip roll. The counter roll can preferably be a roll that is arranged to be heated,e. g. a Yankee drying cylinder.
    The invention also relates to a paper making machine comprising an extended roll asdescribed above, a counter roll cooperating with the extended nip roll to form anextended nip press and a forrning section arranged upstream of the extended nip press.
    The invention also relates to a method of operating an extended nip press as describedabove wherein a wet paper web is passed through the extended nip and subj ected topressure as the web passes through the nip. The extended nip is operated such that thepressure rises as the web passes through the nip and reaches a peak as the web passesover the downstream end of the working surface of the press body.
    SHORT DESCRIPTION OF THEW DRAWINGS Figure l is a schematic representation of a paper making machine in which the inventive extended nip roll and extended nip press may be used.
    Figure 2 is a schematic cross sectional view of an extended nip press according to the invention.Figure 3 shows a desired pressure profile in an extended nip.Figure 4 shows a possible actual pressure profile in an extended nip.
    Figure 5 is a cross sectional view of a support for a press body used in an extended nip roll according to the invention.
    Figure 6 is a cross sectional view of a press body according to the invention placed in asupport.
    Figure 7 is a cross sectional View showing in greater detail an embodiment of a press body for an extended nip roll according to the present invention.
    Figure 8 is a cross sectional View illustrating a part of a press body according to an embodiment of the invention.
    Figure 9 is a cross sectional View similar to Figure 9 but illustrating in greater detail a part of the press body according to the invention.
    Figure 10 is a cross sectional View similar to Figure 9 but including a part of the flexiblejacket.
    Figure ll is a cross sectional View that illustrates how an exchangeable wear protection layer can be placed over the press body.
    DETAILED DESCRIPTION OF THE INVENTION With reference to Figure l, a paper making machine l is shown which is suitable formaking tissue paper, i.e. paper such as toilet paper, kitchen towel or similar grades. Inmany practical applications, the tissue paper produced in such a machine may have abasis weight in the range of l5 g/mz - 25 g/mz but tissue paper having a basis weightoutside this range may also be produced. The paper making machine of Figure 1includes a forrning section 4 in which a head box 3l is arranged to inject stock in a gapbetween a forrning fabric 32 and a felt 33. The forrning fabric 32 would typically be aforaminous wire. The felt 33 is arranged to pass oVer a forrning roll 35 and the felt 33and the forrning fabric 32 are guided in their loops by guide rolls 34. From the forrningsection 4, a newly formed wet fibrous web W is transported by the felt 33 to a press nipN formed between an extended nip roll 5 and a counter roll 7. The counter roll 7 may bea Yankee drying cylinder but embodiments are conceivable in which the web W is firstpressed in a press nip before the Yankee drying cylinder and subsequently passed to theYankee drying cylinder. In the press nip N between the extended nip roll and thecounter roll 7, water is pressed out of the web W and absorbed by the felt 33 which iswater-receiving. The web W then passes over a Yankee drying cylinder which in theembodiment of Figure l is identical to the counter roll 7 for the extended nip roll 5. InFigure 1, it should be understood that the counter roll 7 (i.e. the Yankee drying cylinder)rotates in the direction of arrow “A”. On the Yankee drying cylinder, the web is driedby heat as water that remains in the web after the nip N is eVaporated by heat. The counter roll 7 may be heated by heating means that are symbolically indicated by the reference numeral 8 in Figure 1. In practice, the heating means may be a supply of hotsteam that is introduced to the interior of a Yankee drying cylinder. In principle, theheating means could be something else, for example an inductive heater located eitherinside or outside the counter roll 7. The dry solids content of the web as it reaches thepress nip may vary considerably but in many realistic cases, the dry solids content maybe on the order of 18 % - 22 % when the web W reaches the nip N. After the nip N, theweb W may have a dry solids content of 40 % - 55 % depending on such factors as, forexample, linear load in the nip and dry solids content before the nip N. The web W istypically doctored from the Yankee drying cylinder by means of a doctor 9. The ready-dried web W is then passed to a reel-up 3. It should be understood that what has beenexplained above with reference to Figure 1 may be applicable to all embodiments of the present invention.
    With reference to Figure 2, it can be seen that the press nip N is formed between anextended nip roll 5 and the counter roll 7. It should be understood that the extended niproll 5 can be moved away from the counter roll 7 such that the nip N is opened. Thepress nip N has an extension in the machine direction when the extended nip roll 5cooperates with the counter roll 7.
    The extended nip roll 5 comprises a flexible jacket 10 with an interior surface 11 and anexterior surface 12. The flexible jacket 10 is typically made of polyurethane orcomprises polyurethane. The flexible jacket 10 is shaped as a tube that extends in across machine direction. At its axial ends, it is norrnally connected to end walls that canrotate about an axis. Such arrangements are well known in the art of paper machineryand examples of fastenings for the axial ends of the flexible jacket are disclosed in, forexample, US patent No. 5904813 and European patent No. 1273701. The flexible jacket10 may thus define an enclo sed space. Advantageously, the extended nip roll 5 may beconnected to a source of pressurized air such that the enclosed space within the flexiblejacket 10 may be filled with pressurized air. Such an arrangement helps keeping theshape of the flexible jacket.
    A press body 13 is arranged inside the flexible jacket 10. The press body 13 iselastically deformable and has a top side 14 that faces the interior surface 11 of theflexible jacket 10 (see also Figure 6 and Figure 10). The press body 13 is placed in asupport 21 for the press body 13. The support 21 provides support to sides of the pressbody 13 but allows the press body 13 to expand in a direction towards the interiorsurface 11 of the flexible jacket 10. With reference to Figure 5, the support 21 has agroove 36 in which the press body 13 may be placed. The groove 36 has a bottom wall 37, an upstream wall 38 and a downstream wall 39. In Figure 6, it can be seen how thepress body 13 has been placed in the groove 36 of the support 21. The press body 13can be connected to a source of pressurized fluid in the same way as disclosed in USpatent No. 7527708. As described in US patent No. 7527708, the press body 13 can besealed (for example at its axial ends) and connected to a pressure medium source. Thepressure medium may be, for example, hydraulic oil. The press body 13 has at least afirst and a second intemal pressure chamber 18, 19 as can be seen in Figure 6, Figure 7,Figure 8 and Figure 11. In embodiments of the invention, the press body 13 mayoptionally have a third intemal press chamber 20 as can be seen in for example Figure7. The press body 13 may optionally also have more than three intemal pressurechambers and embodiments with four, five, six or even more intemal pressure chambersare conceivable. When the press body 13 is connected to a source of pressurizedmedium, the pressurized medium can be used to fill the intemal chambers 18, 19, 20.When the intemal chambers 18, 19, 20 are sealed (for example at the axial ends of thepress body 13), the intemal chambers 18, 19, 20 will become pressurized when they arefilled with pressurized fluid.
    It should be understood that the support 21 is in a fixed position and does not moveduring operation of the extended nip press. It may be supported by a support beam (notshown) that may carry rotatable end walls to which the axial ends of the flexible jacket10 are fixed as is known in the art and as explained above. When the intemal pressurechambers 18, 19, 20 are pressurized, the press body 13 will expand. The bottom wall 37and the upstream and downstream walls 38, 39 of the support 21 prevent or limitexpansion in the direction of those walls and the support 21 likewise has walls at itsaxial ends (not shown) that prevent or limit expansion in the axial direction. However,the top side 14 of the press body 13 is not limited by any wall of the support 21. At itstop side 14, the press body 13 is therefore free to expand in a direction towards theintemal surface 11 of the flexible jacket 10 when the internal pressure chambers arepressurized. When the intemal pressure chambers 18, 19, 20 are pressurized, the pressbody 13 will therefore expand. It should be understood that, when the extended nip roll5 is used, it is typically so that the press nip N is closed when the press body 13 iscaused to expand due to pressure in the intemal pressure chambers 18, 19, 20.
    In an extended nip press, the pressure profile should be unsymmetrical in such a waythat the peak pressure is achieved shortly before the end of the press nip whereafter thepressure is quickly reduced. Such a pressure profile reduces re-wetting of the paper web. It is also desirable that the pressure gradient at the beginning of the nip is relatively small such that the pressure initially is increased gently. Thereafter, thepressure should increase progressively until it reaches a peak at the end of the nip.
    With reference to Figure 3, a desirable pressure profile is illustrated. In Figure 3, thehorizontal axis (NL) represents nip length while the vertical axis (P) represents pressure.As can be seen in Figure 3, the nip pressure increases progressively with a smallpressure gradient in the beginning of the nip and a steeper rise in pressure towards theend of the nip. When the pressure rises gently in the beginning of the nip, the risk of web breaks becomes smaller.
    According to one aspect of the invention, the press body 13 is designed in such a way asto assist in producing a pressure profile where the peak pressure appears at the end ofthe nip. To achieve this purpose, the press body is designed in the following way. Withreference to Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10, the top side 14 of thepress body 13 is beveled in such a way that, in the machine direction, a working surface15 of the top side has a downstream end 16 which, in the machine direction, is followedby an exit side surface 17 that diverges away from the interior surface 11 of the flexiblejacket 10. The working surface 15 is that part of the top side 14 that is intended to actagainst the counter roll 7 to form the actual nip N.
    As best seen in Figure 7, the first intemal pressure chamber 18 has an extension in themachine direction that does not extend beyond the working surface 15. This means thatthe force generated in the first intemal pressure chamber is distributed over a part of theworking surface which is not shorter in the machine direction than the first intemalpressure chamber itself The pressure will therefore be distributed relatively evenly overthat part of the working surface 15. However, the pressure distribution will not beentirely even since the pressure distribution is also influenced by other factors, forexample by the pressure upstream and downstream of the first intemal pressure chamber18. With reference to Figure 8, the second intemal pressure chamber 19 is locateddownstream of the first intemal pressure chamber 18. As can be seen in Figure 8, thesecond intemal pressure chamber 19 has an extension L1 in the machine direction. Ascan also be seen in Figure 8, the second intemal pressure chamber 19 extends in themachine direction beyond the beyond the downstream end 16 of the working surface 15while a part of the second extemal pressure chamber 19 extends below a part of theworking surface 15 that is located upstream of the downstream end 16 of the workingsurface 15. The part of the working surface 15 that is located above the second intemalpressure chamber 19 has an extension L; on the machine direction which is less than the extension L1 of the second intemal pressure chamber 19. Therefore, the force generated by the pressure in the second internal pressure Chamber 19 Will be distributed over asurface that is smaller than the effective area of the second internal pressure chamber19. Consequently, the pressure on that part of the Working surface 15 on Which thesecond internal pressure chamber acts Will be higher than the pressure in the secondinternal pressure chamber 19, the pressure is “geared up”. In this Way, a pressure peak isobtained in the area immediately before the end of the press nip N. This pressure peakcan be obtained even if the pressure in the second intemal pressure chamber is the sameas or even someWhat lower than the pressure in the first intemal pressure chamber 18.The inventors have found that the second intemal pressure chamber 19 should havesuch an extension L1 in the machine direction that more than 30% of the extension (themachine direction length L1 of the second intemal pressure chamber 19) extendsbeyond the doWnstream end 16 of the Working surface 15, i.e. L; 5 0.70 L1. Preferablythe second intemal pressure chamber 19 has such an extension in the machine directionthat more than 40 % of the extension (machine direction length of the second intemalpressure chamber) extends beyond the doWnstream end 16 of the Working surface 15.Preferably, not more than 90 % of the extension should extend beyond the doWnstreamend 16. Even more preferred, not more than 70 % of the extension L1 should extendbeyond the doWnstream end 16. In many realistic embodiments, 40 % - 60 % of theextension L1 goes beyond the doWnstream end 16 of the Working surface 15. Forexample, 45 % - 50 % of the extension L1 of the second intemal pressure chamber 19 may go beyond the doWnstream end 16 of the Working surface 15.
    The inventors have found that, When the press body 13 is made of an elastic material,this has many advantages. One advantage is that the elasticity of the press body makes itpossible to expand the press body by means of pressurized fluid. Another advantage isthat the press body can adapt very accurately to the profile of the counter roll such that aregular pressure distribution can be obtained. HoWever, the inventors have found thatthe elasticity of the press body 13 can also result in a problem that is related precisely tothe pressure distribution. With reference to Figure 4, the inventors have found that, atthe end of the press nip and after the intended peak point IPP, the pressure can rise againsuch that a second peak SP results (see Figure 4). Such a second peak or “retum-peak”is harrnful because it counteracts lubrication at the area of the peaks. If the unintendedsecond peak is too high, that may also cause damage to the Web. The inventors havefound that the reason for the second peak is that, When the elastic material in the pressbody 13 is too soft, a part of the press body doWnstream of the actual Working surface may deforrn to such an extent that it actually meets the flexible jacket 10 and presses the external surface 12 of the flexible jacket 10 against the counter roll thereby causing asecond peak.
    The inventors have found that the second peak can be prevented or reduced if theWorking surface 15 and the exit side surface 17 are made of a material that has a highershore A hardness than the material in the rest of the press body 13.
    With reference to Figure 7, at least a part of the top side 14 can be made of a hardermaterial than the rest of the press body 13. In the embodiment of Figure 7, the part ofthe press body 13 that forms the Working surface 15 and the exit side surface 17 is asole 22. The sole 22 can be made in a harder material While the rest of the press body isa softer part 23. The sole 22 has a higher Shore A hardness than the part 23 in Which theintemal pressure chambers 18, 19, 20 are formed. The sole 22 may suitably have athickness in the range of 1 mm - 30 mm, preferably 5 mm - 25 mm, even morepreferred 10 mm - 25 mm. The sole should not be thinner than 1 mm since it could thenbecome too flexible Which Would increase the risk of a second peak. If it Were too thick,the ability of the sole 22 to adapt its shape to that of the counter roll could be reducedWhich Would be undesirable.
    Preferably, the sole 22 has a hardness higher than 90 Shore A While the softer part 23 ofthe press body 13 that surrounds the intemal pressure chambers 18, 19, 20 has ahardness Which is less than 90 Shore, preferably the sole has a hardness of 93 Shore A -100 Shore A While the softer part 23 of the press body that surrounds intemal pressurechambers 18, 19, 20 has a hardness of 70 Shore A - 90 Shore A. In one realisticembodiment considered by the inventors, the sole 22 may have a shore A hardness of 95While the softer part 23 that surrounds the intemal pressure chambers 18, 19, 20 mayhave a shore A hardness of 90. This means that the softer part 23 of the press body 13that surrounds the intemal pressure chambers 18, 19, 20 is sufficiently soft to deforrnand expand in response to increased pressure in the intemal pressure chambers 18, 19,20. At the same time, the sole 22 has such a hardness that it Will not easily deforrn to cause a second peak.
    In an unloaded state of the extended nip roll 5, the exit side surface 17 doWnstream ofthe Working surface 15 preferably forms an angle ß of 30° - 65° With a tangent to theWorking surface 15, preferably an angle ß in the range of 35° - 60° (see Figure 7). Inmany realistic embodiments, the Working surface 15 of the top side 14 is a flat surfacein the unloaded state of the extended nip roll 5 When the extended nip roll 5 does notform a nip With a counter roll 7. In such embodiments the exit side surface 17 doWnstream of the Working surface 15 may, in the unloaded state of the extended nip 11 roll 5, form an angle of 40° - 50° With the Working surface 15. When the exit sidesurface 17 forms an angle of 30° - 65° With the Working surface (or With a tangent to theWorking surface if the Working surface is not a flat surface in the unloaded state of theextended nip roll), the exit side surface 17 diverges to such an extend from the nip andthe flexible jacket 10 that the risk of a second peak is reduced. At the same time, there ismaterial doWnstream of the Working surface 15 that can contribute to support the pressbody 13 in the nip N.
    To further reduce the risk that a second peak occurs, the inventors have found that thearea in Which the Working surface 15 goes over into the exit side surface 17 shouldpreferably be shaped in a Way that counteracts any tendency of the press body 13 todeforrn such that a second peak occurs.
    With reference to Figure 9 and to figure 10, the exit side surface 17 is separated fromthe Working surface 15 by a rounded edge 24 Which has a first radius R1 in an areaadjacent the Working surface 15 and a second radius R; in an area adjacent the exit sidesurface 17. According to one advantageous embodiment of the invention, the secondradius R; is smaller than the first radius R1. Thereby, the rounded edge 24 first gentlytums aWay from the nip and then more abruptly. Such a shape of the rounded edge 24further reduces the risk of a second peak (“retum peak”). In many realistic embodimentsof the invention, the first radius R1 may be in the range of 20 mm - 40 mm While thesecond radius R; may be in the range of 6 mm - 15 mm. The rounded edge 24 is thusdivided into a first zone With a larger radius R1 and a second zone With a smaller radiusR;. In the machine direction, the rounded edge may have a total length Which is in the range of6 mm - 16 mm.
    With reference to Figure 7, embodiments are conceivable in Which the press body 13comprises also a third intemal pressure chamber 20 Which, in the machine direction, islocated upstream of the first intemal pressure chamber 18. Embodiments are alsoconceivable in Which there are more than three intemal pressure chambers. The use ofseveral intemal pressure chambers 18, 19, 20, makes it easier to produce a rising pressure profile since different pressures can be used in different pressure chambers 18,1 9, 20.
    The intemal pressure chambers 18, 19, 20 preferably have a rectangular shape and alarger extension in the radial direction of the extended nip roll 5 than in the machine direction. 12 Another aspect of the invention will now be explained with reference to Figure 6 and toFigure 7. In embodiments of the invention, the press body 13 optionally comprises a lip27 located upstream of the working surface 15. The lip 27 protrudes in an upstreamdirection and has an entry surface 28 that faces the interior surface 11 of the flexiblejacket 10 (it should be understood that, while the flexible jacket 10 is not shown inFigure 6 and Figure 7, it does in fact enclose the press body 13 and is arranged to runover the press body 13 during operation). The entry surface 28 forms an angle u of 2° -50° with a tangent to the Working surface 15. Preferably, it forrns an angle of about 5° -15° with a tangent to the working surface 15 or to the working surface itself when theworking surface 15 is flat in the unloaded state of the extended nip roll. In oneembodiment considered by the inventors, the entry surface 28 forrns an angle of 10°with the working surface which may then be flat in the unloaded state of the extendednip roll. By using a lip that protrudes rearwards from the working surface and beyondthe area of the top side 14 that can be acted upon by any of the internal pressurechambers 18, 19, 20, the pressure in the nip N can be given a gentle start, especiallywhen the entry surface 28 forrns an angle with the working surface 15. In that way, thelip 27 contributes to giving a smooth start to the pressure curve.
    Preferably, a lubrication channel 29 is arranged to feed a lubricant to the workingsurface 15. In the embodiment that is shown in Figure 7, the lubrication channel 29 islocated in the sole 22 but the lubrication channel 29 could also be located upstream ofthe point where the sole 22 begins. It should be understood that the extended nip rollmay also comprise additional means for supplying a lubricant. For example, a lubricantsuch as oil may be fed to the interior surface 11 of the flexible jacket 10 at a locationaway from the nip, for example immediately before the flexible jacket 10 reaches thenip N. It should also be understood that the extended nip roll 5 may be provided with means for evacuating such lubricant that has already been used.
    With reference to Figure 11, yet another feature shall be explained. Optionally, the pressbody 13 is may be covered by an exchangeable wear protection layer 30 that can besecured to the support upstream and downstream of the press body 13. The wearprotection layer 30 may be detachably secured to the support 21 by means of elements40 such as screws or bolts or other suitable fastening elements. The wear protectionlayer 30 can be, for example, a Thordon sheet.
    In operation, a web W is formed in the forrning section and passed to the extended nippress formed between the extended nip roll 5 and the counter roll 7 and subj ected to pressure as the web W passes through the nip N. The pressure will rise as the web W 13 passes through the nip N and reach a peak as the Web passes over the downstream endof the Working surface 15 of the press body 13.
    When the press body 13 has two internal pressure chambers 18, 19, the hydraulicpressure in the first internal pressure chamber 18 may be about 0.16 MPa duringoperation of the extended nip press While pressure in the second intemal pressurechamber 19 may be about 3.2 MPa. The peak pressure may then be on the order ofabout 6.5 MPa. In another embodiment, pressure in the first chamber 18 may be about0.9 MPa While pressure in the second intemal pressure chamber 19 may be about 2.6MPa and the peak pressure about 6 MPa. Depending on the shape of the press body 13and the pressure in the second intemal pressure chamber 19, peak pressure may besignificantly higher than 6.5 MPa. Due to the design of the press body, the peakpressure is thus clearly higher than the actual pressure in the second intemal pressurechamber 19. Generally speaking, a suitable pressure level in the first intemal pressurechamber 18 during operation may, in many embodiments, be 0.1 MPa - 0.6 MPa Whilethe pressure in the second intemal pressure chamber 19 may be in the range of 1.5 MPa- 5 MPa in many practical embodiments.
    It should be understood that, in the context of this application, the machine direction isthe direction in Which the Web moves from the forrning section to the reel-up.
    Although the invention has been described above in terms of an extended nip roll, anextended nip press, a paper making machine and a method of operating an extended nippress, it should be understood that these categories only reflect different aspects of oneand the same invention. The inventive extended nip roll can thus be used in theinventive extended nip press and the inventive extended nip press is used in the inventive machine and the inventive method.
    权利要求:
    Claims (1)
    [1] 1. An extended nip roll (5) capable of forrning a press nip (N) With a counter roll(7) Which press nip (N) has an extension in a machine direction When theextended nip roll (5) cooperates With the counter roll (7), the extended nip roll(5) comprising; a flexible jacket (10) With an interior surface (11) and anexterior surface (12); a press body (13) arranged inside the flexible jacket (10),the press body (13) being elastically deforrnable and having a top side (14) thatfaces the interior surface (11) of the flexible jacket (10), the top side (14) of thepress body (13) being beveled in such a Way that, in the machine direction, aWorking surface (15) of the top side has a doWnstream end (16) Which, in themachine direction, is followed by an exit side surface (17) that diverges from theinterior surface (11) of the flexible jacket (10), the press body (13) furtherhaving at least a first and a second internal pressure chamber (18, 19) Whichinternal pressure chambers (18, 19) can be pressurized such that the press body(13) expands, the first internal pressure (18) chamber having an extension in themachine direction that does not extend beyond the Working surface (15) and thesecond intemal pressure chamber (19) being located doWnstream of the firstintemal pressure chamber (18) and having an extension in the machine directionbeyond the doWnstream end (16) of the Working surface (15); a support (21) forthe press body (13) Which support (21) provides support to sides of the pressbody (13) but allows the press body (13) to expand in a direction towards theinterior surface (11) of the flexible jacket (10), characterized in that the secondintemal pressure chamber (19) has such an extension in the machine directionthat more than 30% of the extension extends beyond the doWnstream end (16) ofthe Working surface (15) and in that the Working surface (15) and the exit sidesurface (17) are made of a material that has a higher shore A hardness than the material in the rest of the press body (13). An extended nip roll according to claim 1, Wherein, in an unloaded state of theextended nip roll (5), the exit side surface (17) doWnstream of the Workingsurface (15) forms an angle of 30° - 65° With a tangent to the Working surface (15), preferably an angle in the range of 35° - 60°. An extended nip roll according to claim 1, Wherein the Working surface (15) ofthe top side (14) is a flat surface in the unloaded state of the extended nip roll (5) When the extended nip roll (5) does not form a nip With a counter roll (7) and 10. 11. Wherein, in the unloaded state of the extended nip roll (5), the exit side surface(17) doWnstream of the Working surface (15) forms an angle of 40° - 50° Withthe Working surface (15). An extended nip roll according to any of claims 1 - 3, Wherein a part of pressbody (13) comprises a sole (22) Which forrns the Working surface (15) and theexit side surface (17) and Which sole (22) has a thickness in the range of 1 mm - 30 mm, preferably 5 mm - 25 mm, even more preferred 10 mm - 25 mm. . An extended nip roll according to claim 4, Wherein the sole (22) has a hardness higher than 90 Shore A While the part of the press body (13) that surrounds theintemal pressure chambers (18, 19, 20) has a hardness Which is less than 90Shore, preferably the sole has a hardness of 93 Shore A - 100 Shore A While thepart of the press body that surrounds intemal pressure chambers (18, 19, 20) hasa hardness of 70 Shore A - 90 Shore A. An extended nip roll according to any of claims 1 - 5, Wherein the exit sidesurface (17) is separated from the Working surface (15) by a rounded edge (24)Which has a first radius in an area adj acent the Working surface (15) and asecond radius in an area adj acent the exit side surface (17) and Wherein the second radius is smaller than the first radius. An extended nip roll according to claim 6, Wherein the first radius is in the range of 20 mm - 40 mm and the second radius is in the range of 6 mm - 15 mm. An extended nip roll according to any of claims 6 or 7, Wherein the roundededge (24) that separates the Working surface (15) from the exit side surface (17)has an extension in the machine direction Which is in the range of 6 mm - 16 1'I11'I1. An extended nip roll according to any of claims 1 - 8, Wherein the press bodycomprises also a third intemal pressure chamber (20) Which, in the machinedirection, is located upstream of the first intemal pressure chamber (18). An extended nip roll according to any of claims 1 - 9, Wherein the intemalpressure chambers (18, 19, 20) have a rectangular shape and a larger extensionin the radial direction of the extended nip roll (5) than in the machine direction. An extended nip roll according to any of claims 1 - 10, Wherein the press body (13) comprises a lip (27) located upstream of the Working surface (15) Which lip 12. 13. 14. 15. 16 (27) protrudes in an upstreani direction, the lip (27) having an entry surface (28)that faces the interior surface (11) of the flexible jacket (10) and forrns an angleof 2° - 50° With a tangent to the Working surface (15) and Wherein, preferably, a lubrication channel (29) is arranged to feed a lubricant to the Working surface (15). An extended nip roll according to any of clainis 1 - 10, Wherein the press body(13) is covered by an exchangeable Wear protection layer (30). An extended nip press (2) con1prising an extended nip roll according to any ofclainis 1 - 12 and a counter roll (7) cooperating With the extended nip roll (5),the counter roll (7) preferably being a roll that is arranged to be heated, e. g. aYankee drying cylinder. A paper n1aking n1achine con1prising an extended nip roll (5) according to anyof clainis 1 - 12, a counter roll (7) cooperating With the extended nip roll (5) toforn1 an extended nip press (2) and a forrning section (4) arranged upstreani ofthe extended nip press (2). A n1ethod of operating an extended nip press (2) according to clain1 13 Whereina wet paper Web (W) is passed through the extended nip press and subj ected topressure as the Web passes through the nip (N) of the extended nip press (2) andin Which the pressure rises as the Web passes through the nip (N) and reaches apeak as the Web passes over the downstreani end of the Working surface (15) ofthe press body (13).
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    同族专利:
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    SE536539C2|2014-02-11|
    引用文献:
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