Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F3/00—Press section of machines for making continuous webs of paper
  • D21F3/02—Wet presses
  • D21F3/04—Arrangements thereof
  • D21F3/045—Arrangements thereof including at least one extended press nip

Definitions

• the invention relates to a press section in a paper or board machine according to the preamble of claim 1.
• the invention relates to a paper or board machine which is provided with at least a forming section, a press section and a dryer section and in which the press section is provided with separate press nips.
• a separate press nip is meant a press nip in which opposing press members define only one press nip.
• a separate press nip can be a roll nip or an extended nip.
• the opposite of a separate press nip is a press which is provided with a centre roll and in which the centre roll forms press nips with at least two other rolls.
• FI patent application 990557 discloses a method and an arrangement for treating a paper or board web.
• Figs. 4-6 show control of the surface properties of a web with chemicals, and examples suitable for a smoothing press nip.
• a tandem transfer belt is used underneath in the second and third nips.
• Dewatering is not symmetric because dewatering takes place in both directions in the first nip, upwards in the second nip, and no dewatering takes place in the third nip, but, instead, there is smoothing and application of the web because belts are placed on both sides of the web.
• the third press nip of these embodiments does not increase dry solids even though it improves the surface properties of the web, thus increasing the overall length of the paper machine.
• FI patent 95610 discloses a press section of a paper machine provided with a smoothing press.
• the paper web has a closed and supported draw through the press section and the press section comprises at least two successive separate press nips, dewatering of the paper web being carried out at least in the first one of said press nips, preferably between two press fabrics that receive water.
• the last press nip in the press section is a smoothing press nip which is separate from the preceding nip and in which no substantial dewatering is performed.
• the paper web is passed through the smoothing press nip from the preceding dewatering press nip on a transfer belt substantially not receiving water, on its substantially straight run, which is continued after the smoothing nip as a run of substantially the same direction, on which run some of the elongation of the paper web in the machine direction can be compensated for, which elongation takes place in the smoothing nip, by a difference in speed of the transfer belt.
• FIG. 2 shows an embodiment comprising three shoe press units in which the web is first passed through the first and the second shoe press unit which are placed underneath a counter roll, i.e. underneath the web, and the third shoe press is placed above a counter roll, i.e. above the web.
• FI patent application 981089 discloses a press section of a paper machine applying one or more press nips, through which the paper web to be pressed is passed as a substantially closed draw and in which press section there is at least one press nip provided with two water-receiving press felt, through which press nip the paper web runs between the press felts and after which last-mentioned nip the paper web is separated from one of the press felts and transferred on support of the other press felt substantially as a closed draw further.
• the last nip in the press section is an extended nip zone, in which one roll is a shoe roll provided with a hose shell and with a press shoe arrangement and the other roll is a press suction roll provided with a suction zone.
• the paper web is passed through the last extended nip zone between two water-receiving press fabrics and directly after the last extended nip zone the paper web is separated from one of the press fabrics and transferred, with the aid of a vacuum present in a suction zone of said press section roll, to follow the press fabric placed at the side of said press suction roll without substantial rewetting, and the paper web is passed on the latter press fabric as a closed draw onto a drying wire or equivalent of a dryer section following after the press section, onto which drying wire or equivalent the web is transferred as a suction roll transfer or by means of an equivalent arrangement.
• FI patent application 961518 discloses press section geometries in which a press section provided with a closed draw of a web in a paper or board machine comprises a first water-receiving upper fabric onto which the web is transferred on a suction zone of a pick-up roll from a forming wire at a pick-up point situated after its suction roll and after that there is a wire drive roll, from which the return run of the wire begins.
• the press comprises one or two successive press nips which press water from the web and between which the web has a totally closed draw such that it is supported by a fabric all the time.
• the press nips removing water are so-called extended nips, whose press zone is substantially longer than that of a sharp roll nip, and all press nips are additionally provided with two water-receiving press fabrics so that water is removed in them substantially symmetrically through both surfaces of the web.
• the embodiments shown in Figs. 1, 2 and 3 make use of a lightly loaded transfer nip, which nip is defined by a press roll, provided with a recessed surface and disposed within an upper wire loop, together with a first drying cylinder or equivalent.
• One object of the invention is to develop further a press section that has a closed draw and is suitable for speeds over 1800 m/min and advantageously over 2000 m/min, at which there are no problems with surface topography and absorption symmetry described above.
• One object of the invention is to provide a press section of a paper or board machine which makes it possible to optimize surface topography and absorption at a speed over 1800 m/min and advantageously over 2000 m/min.
• the press section according to the invention is mainly characterized in what is stated in the characterizing part of claim 1.
• closed draw through the press section is accomplished as a substantially straight run and the press section includes at least three separate press nips which do not have any fabric loops in common with one another.
• the first press nip in the running direction of the web is a roll nip or a press suction roll nip, advantageously at lower speeds of over 1800 m/min, but with speeds increasing over 2000 m/min and with increasing dewatering need, an extended nip becomes an advantageous alternative. It is conceivable that in the case of three nips at high speeds all the nips are extended nips and, on the other hand, in the case of more nips than three at a lower speed mere roll nips can be used. The next two nips each have only one water-receiving fabric, which is placed in each nip on the opposite side of paper with respect to the other nip in the machine direction.
• both sides of the web are smoothed/evened out one at a time mechanically against a smooth surface, which smooth surface can be a smooth roll, known from a centre roll arrangement, or a transfer belt.
• a smooth surface can be a smooth roll, known from a centre roll arrangement, or a transfer belt.
• removal of water from the web takes place in the nip only in a direction away from the smooth surface, i.e. to the side of the water-receiving fabric.
• Transfer from the press section in accordance with the invention to a dryer section takes place, as known in itself, from a transfer belt, and in the embodiments in which a smooth surface is in an upper position in the last nip of the press section, transfer from a lower felt is used.
• a suction roll of powder metallurgy A press suction roll manufactured by means of powder metallurgy is described, for example, in FI patent 100422.
• the suction roll assures that the web remains on the surface of a porous fabric so that it shall not start following the more adhesive smooth surface of a roll/transfer belt.
• the smooth surfaces of press nips also affect the surfaces of the web mechanically, evening out the decrease of smoothness caused by coarse press fabrics.
• Shoe presses can also be used in connection with the invention.
• the press section in accordance with the invention provides good surfac properties of the web in respect of printability and also makes it possible to us high speeds, over 1800 m/min and advantageously over 2000 m/min, and enable good efficiency with a good moisture profile.
• the press section in accordance with the invention also facilitates the adjustmer of two-sidedness that takes place further in the paper machine line and which ca be performed mainly by means of calendering and application of chemicals. Th bulk possibly lost during pressing can be saved later by means of lighte calendering, which can be optimized further according to other desired surfac properties, as there is no need to correct absorption symmetry. On the other hand when press dry solids increase in more press nips than conventional, it may b ⁇ possible to manage with a shorter dryer section even though the press sectioi becomes longer.
• first nip th. web is transferred from the surface of an upper felt to a second press and, in the second nip, dewatering takes place downwards and the upper surface of the web i- either against a smooth roll or a smooth transfer belt.
• second nip dewatering takes place upwards and the lower surface of the web is against a transfer belt and the transfer of the web is from a lower fabric to a dryer section.
• a roll press is placed after the first nip in the second press, whereby a sufficient material displacement is achieved in the second nip, i.e. displacement of fines to the side of the lower surface of the web.
• a sufficient material displacement is achieved in the second nip, i.e. displacement of fines to the side of the lower surface of the web.
• the smoothness of the upper surface of the web improves because it is pressed against a smooth surface.
• Figure 1A is a schematic view of one embodiment of the invention.
• Figure IB is a schematic view of one variant of the first press nip in the embodiment of the invention shown in Fig. 1A.
• Figure 2 A is a schematic view of a second embodiment of the invention.
• Figure 2B is a schematic view of one alternative application of the embodiment of the invention shown in Fig. 2A.
• Figure 3 is a schematic view of a third embodiment of the invention.
• a web W formed in a forming section is passed to a pick-up point P situated on a forming wire 10 before reversing rolls 11, 12 placed within the loop of the forming wire 10.
• the pick-up point P is formed between the forming wire 10 and a roll 24 placed within the loop of a first water-receiving press felt 20 and provided with a suction sector 24a, so that the web W runs at the pick-up point P between the forming wire 10 and the first press felt 20.
• the web W is separated from the forming wire 10 and transferred to be supported by the first press felt 20.
• the web W is transferred on support of the lower surface of the first press felt 20 to a first press nip Nl, which is defined by two recessed surface press rolls 22 and 23 to form therebetween a roll nip Nl or a press suction roll nip (Fig. IB), in which case the upper roll 22 is a press suction roll provided with a suction zone and the other roll 23 is a recessed surface roll. In that connection, a felt suction roll 25 can be omitted.
• the web W runs in the first press nip Nl between the first water-receiving press felt 20 serving as an upper press fabric and a first water-receiving press felt 21 serving as a lower press fabric. Dewatering of the web W takes place in the first press nip Nl into both press felts 20, 21. In the embodiments which use a press suction roll, water is also removed through a suction zone into the suction roll.
• the travel of the web W with the upper press felt 20 is assured by means of a vacuum in a suction zone 25a of an upper suction roll 25, and the web W is separated from the first press felt 20 by means of a vacuum in a suction zone 34a of a lower transfer suction roll 34 and caused to adhere to a second lower press fabric 30, which may also be a press felt, on the upper surface of which the web W is transferred to a second press nip N2, which is defined between a roll 32 and a press suction roll 33 provided with a suction zone 33 a.
• the suction zone 33 a of the suction roll 33 preferably has a large sector and a high vacuum, assuring that the web adheres to the desired felt already before the press nip and follows the felt after the nip in order that the web should not follow the smooth roll.
• the web W is transferred on support of the second press fabric 30 and transferred by means of a suction zone 44a of a transfer suction roll 44 to be supported by a subsequent upper press felt 40 and to a third press nip N3, which is defined between an extended nip press roll 42 and a counter roll 43.
• the embodiment shown in Fig. 2A mainly corresponds to the embodiment described in connection with Fig. 1A and its variants, but in the embodiment shown in Fig. 2A, the second press nip N2 is formed such that in the second nip 42 there is an upper transfer belt 31 and as the lower fabric 30, as in the embodiment shown in Fig. 1A, there is a press felt 30.
• the web W is passed on the lower surface of the transfer belt 31 onto a transfer fabric 60, onto which the web W is transferred by means of a suction zone 64a of a transfer suction roll 64 and on support of the felt 60 the web W is passed by means of a suction zone 44a of a suction roll 44 to be transferred so as to be supported by the upper fabric 40 of the third press nip N3.
• the embodiment of the invention shown in Fig. 2B mainly corresponds to the embodiment shown in Fig. 2A except that each nip Nl, N2, N3 has been formed into an extended nip, in which one roll is an extended nip roll 22; 33; 42 and the other roll is its counter roll 23; 32; 43.
• Fig. 3 shows an embodiment of the invention in which the web W is passed from a forming wire 10 of a forming section before a reversing roll 11 to a pick-up point P, at which the web W is passed by means of a suction zone 24a of a suction roll 24 so as to be supported by a first water-receiving press felt 20 and the web W is passed to a first press nip Nl, which is defined between two recessed surface press rolls 22, 23 or between a press suction roll and a recessed surface press roll (as in Fig. IB).
• a lower press felt 21 also receives water.
• Adherence to the surface of the lower press felt 21 is assured by means of a vacuum in a suction zone 26a of a transfer suction roll 26 and the web W is passed by means of a vacuum in a suction zone 35a of a suction roll 35 so as to be supported by an upper press felt 31 of a second press nip N2.
• the second press nip N2 is formed into an extended nip press between an extended nip roll 32 and a counter roll 33.
• the lower fabric in this press nip N2 is a water-receiving press felt 30.
• the web W On its support the web W is passed onto a transfer suction roll 44, and by means of a vacuum in a suction zone 44a of the transfer suction roll 44 the web W is passed to be supported by an upper felt 40, on which the web is passed to a third nip N3, which is a smoothing press nip formed between rolls 42 and 43.
• the roll 42 is a press suction roll which is provided with a suction zone 42a. Dewatering takes place into a suction zone 42a of the suction roll.
• the web is passed from the felt 40 to a subsequent felt 70 by means of a vacuum in a suction zone 74a of a suction roll 74, and by means of the felt 70 the web is passed to a subsequent smoothing nip N4 formed between a press suction roll 73 and a suction roll 72.
• the suction zones 42a and 73a of the suction rolls 42 and 73 preferably have a large sector and a high vacuum, assuring that the web adheres to the desired felt already before the press nip and that it follows the felt after the nip in order that the web should not follow the smooth roll.
• the web W is passed to a dryer section to be supported by a drying wire 50, as described above in connection with Figs.
• Fig. 3 can also be accomplished such that only one press nip that receives water in both directions is placed before the smoothing press nips N3, N4, in that case in the first press nip Nl there can be a nip defined by a shoe roll and a recessed surface roll or a nip defined by a shoe roll and a press suction roll.

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Citations (10)

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• 2002
  • 2002-11-19 FI FI20022057A patent/FI116400B/fi not_active IP Right Cessation
• 2003
  • 2003-10-10 WO PCT/FI2003/000751 patent/WO2004046459A1/en not_active Application Discontinuation
  • 2003-10-10 CN CN200380102937.XA patent/CN1738941B/zh not_active Expired - Fee Related
  • 2003-10-10 US US10/535,431 patent/US20060011319A1/en not_active Abandoned
  • 2003-10-10 AU AU2003274174A patent/AU2003274174A1/en not_active Abandoned
  • 2003-10-10 EP EP03758152A patent/EP1576232B1/de not_active Expired - Lifetime
  • 2003-10-10 DE DE60328414T patent/DE60328414D1/de not_active Expired - Lifetime

Patent Citations (10)

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