Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F9/00—Complete machines for making continuous webs of paper
  • D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/48—Suction apparatus
• • 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

Definitions

• the present invention relates to a method as set forth in the preamble of the appended claim 1 for dewatering the web in a paper or board machine.
• the invention relates also to an apparatus as set forth in the preamble of the appended claim 7 for carrying out the method.
• the paper and board machines are generally provided with a wire suction roll in an effort to give the web a sufficiently high dry matter content upstream of the press section. This also creates a sufficiently strong web prior to the action occurring in the press section.
• US-Patent 3,846,233 discloses a twin- wire papermaking machine wherein, within the end zone of a twin-wire dewatering zone, water is removed by means of a suction roll at which the lower wire deflects towards a pick-up suction roll while water is simultaneously removed through the upper wire as a result of tension of the wires as well as centrifugal force.
• the wire suction roll is one of the major consumers of energy as it requires a vacuum system. It is also expensive in terms of its construction.
• the wire suction roll creates also a noise problem during operation of the machine.
• the use of vacuum reduces the web temperature, which is harmful in the press section. All the above problems associated with suction are further emphasized due to the fact that the increasing machine speeds require an increased vacuum capacity.
• An object of the invention is to eliminate the above drawbacks and to introduce a method for dewatering the web prior to its passage to the press section without a wire suction roll, i.e. without the need for creating a vacuum at this point.
• a method of the invention is principally characterized by what is set forth in the characterizing section of the appended claim l. Water is removed from the web by means of a open-surfaced roll included in a pair of rolls, said roll and a roll mounted on the opposite side being used to develop such a pressing on the web that water squeezes out of the web into the open places in the roll surface and discharges from the roll by being hurled by centrifugal force.
• neither of the rolls included in the pair of rolls need be provided with suction and all the problems associated with a suction roll will be eliminated.
• Another object of the invention is to introduce an apparatus which does not involve the above drawbacks.
• an apparatus of the invention is principally characterized by what is set forth in the characterizing section of the appended claim 7.
• the pair of rolls provides a press nip, wherein one of the rolls is an open-surfaced roll for effecting the dewatering into the open places in its surface.
• Fig. 1 shows an apparatus of the invention in a side view
• Fig. 2 shows a second embodiment for an apparatus of the invention in a side view
• Fig. 3 shows a third embodiment for an apparatus of the invention in a side view
• Fig. 4 shows a fourth embodiment for an apparatus of the invention in a side view.
• Fig. 1 depicts the end zone of a Fourdrinier wire section in a papermaking machine, that is, a point at which a web W is transferred from a wire 1, upon which it has formed, into a press section.
• the end section includes a roll 2, guiding the wire 1 of a wire section in such a manner that the wire 1 and the web W lying on top of it are curving or deflecting in a certain sector ⁇ towards a drive roll 5, which at the same time serves as a reversing roll for the wire 1.
• said web W is transferred onto an upper press-section felt 7 by means of a pick-up suction roll 4, the felt running therearound and coming to contact with the web W.
• an additional roll 3 Opposite to the wire guiding roll 2 lies an additional roll 3, which is in contact with the web so as to produce a press nip N with the wire guiding roll.
• the additional roll 3 which thus replaces a previously used lump-breaker roll, is provided with an open surface, whereby the pressing between rolls 2, 3 included in the pair of rolls results in the transfer of water from the web W into the open places included in the surface of additional roll 3. Since the wire and web downstream of the press nip are curving away under the guidance of roll 2, this is a good location for a water receptacle 8 into which the water is hurled from the surface recesses of additional roll 3 by virtue of a centrifugal force produced by rotation of the same.
• the additional roll 3 can be a standard roll having preferably a hard and open surface (either a blind- drilled or through-drilled roll fitted with a wire sock or a smooth roll possibly fitted with a coarse wire sock) .
• the wire guiding roll 2 is set in a location previously occupied by a wire suction roll and, in turn, must have a type of surface which does not collect water from the web.
• the wire guiding roll 2 is a smooth-surface roll, having a surface hardness value of at least 50 PJ, preferably 50-200 PJ.
• the unit PJ is generally used for indicating the hardnesses of roll coatings in papermaking machin- es.
• nip N formed between the rolls with the applied loading values which may vary between 10 - 100 kN/m.
• the surface hardness and applied loading rate for the roll depend on the dry matter content of the web upstream of the nip N.
• Fig. 1 illustrates a separate wire loop or run, provided by an additional wire 6 and extending from the side of additional roll 3 through the press nip N.
• the additional roll 3 is in contact with the web W through the intermediary of additional wire 6, which arrives in the press nip N under the guidance of additional roll 3 and and curves thereafter under the guidance of roll 2 in sector and separates from top of the web W lying on the wire 1 downstream of said sector. Water presses from the nip N through the additional wire 6 into the additional roll 3.
• the winding of wire 6 at the roll 2 is controlled by means of a wire guide roll 9 included in the wire loop downstream of the additional roll 3.
• the separate wire loop provided by the additional wire 6 further includes normal tension rolls and washing sprays. Also the water receptacle 8 fits comfortably within the wire loop.
• the additional wire 6 can be a second wire included in a two-part dewatering zone for removing water from the web therethrough in the opposite direction relative to the dewatering direction of wire 1.
• This wire is shown in fig. 1 by a dash- and-dot line and it can extend around a wire guid roll 9 located downstream of the nip N.
• Fig. 2 depicts a second alternative, wherein a wire loop created by the above-mentioned additional wire 6 travels on top of a web W all the way to a pick-up suction roll 4, whereby the web W is transferred from the wire 1 onto the additional wire 6 on the pick-up suction roll 4 and from the additional wire 6 by means of a suction box 10 onto a lower press felt 11.
• the additional wire 6 in figs. 1 and 2 travels on top of the web W downstream of the press nip N, it can separate from the web immediately after the press nip since the smooth-surfaced roll 2 guiding the wire 1 produces a vacuum downstream of the nip for holding the web W on said wire 1.
• the additional wire 6 is mainly significant in making sure that the web W travels in the right direction downstream of the nip N.
• the additional wire 6 is preferably a wire having a surface identical to that of the wire l.
• Another objective with respect to the additional wire 6 is that it should be relatively thin, i.e. it should have a low water holding capacity.
• the main benefit of the idea is an insignificant re-wetting, since a major portion of the water in the pressing action is forced to transfer into the wires and to the open roll.
• the lower the water holding capacity of the wires the more water transfers into the open roll and thereby the centrifugal force slings or hurls the water into an external receptacle.
• the lower water holding capacity of the wires also results in a higher dry matter content for the web downstream of the nip, and a positive effect will be apparent even at lower sheet grammages.
• the open-surfaced additional roll 3 can be covered not only by the additional wire 6 but also by a wire sock, which is not necessarily, however, needed, but its bare jacket surface can only be covered by the additional wire 6 at the nip N. It is also possible to employ an open-surfaced roll 3, wherein the bare jacket surface is covered by a coarse wire sleeve topped by a fine wire sock, without a separate additional wire 6.
• the open pattern of the roll surface can also be produced by means of a coarse wire sock, pulled over a smooth surface and provided with a sufficiently high water holding capacity. Fig.
• nip N created by rolls 2 and 3 is preceded by a second pair of rolls including rolls 2 ' and 3* , which are of the same type as the rolls 2 and 3 included in the down- stream pair of rolls but arranged in a reversed order, the open-surfaced dewatering roll 3' against the wire 1 and the opposite roll 2' in contact with the web W through the intermediary of an additional wire 6 extending both through a press nip N' created by the rolls 2' and 3' and through a press nip N of the rolls 2 and 3.
• Fig. 4 depicts a pair of rolls provided by rolls 2', 3' which is otherwise similar to that shown in fig. 3 except that the sector ⁇ , in which the wire 1 and the web W supported thereby are curving towards a pick-up suction roll, does not include an additional roll against the roll 2.
• the roll 2 may be a regular hard and smooth roll, which has an intact surface or possibly also an open surface.
• a transfer suction box 14 Between the rolls ' and Z against the wire 1 lies a transfer suction box 14 for making sure that the web W holds firmly against the wire while the additional wire 6 separates from top of the web W downstream of the nip
• All the above-mentioned rolls 2, 2' having a surface hardness of 50-200 PJ can also be replaced with a prior known shoe press loading roll for creating a smooth long nip with a low pressure, the smooth surface of a roll 2 or 2• having a hardness of 0 PJ.
• the first press nip N created by a pair of rolls must be located at the end zone of a wire section downstream of the last dewatering suction boxes at the point where the web has a dry matter content of at least 13 %. Such boxes are indicated in the figures with reference numeral 13.
• the applied solution reduces the re-wetting of the web substantially as only some of the water contained in the wires will be capable of returning into the wire.
• the sig- nificance of re-wetting becomes less and less as the grammage of the web increases.
• the invention can be used for considerable savings of energy and for reducing noise problems experienced in the machines.
• the press section downstream of the equipment operates more effectively since the decrease of web temperature caused by the vacuum of a suction roll will be avoided.
• the invent ⁇ ion can be used within a plurality of speed and grammage ranges. As a matter of fact, as the machine speeds are increasing, the functioning of the invention will be improved even further by virtue of an increased centrifugal force.
• the invention is applicable in machines having a configuration that is different from that of a Fourdrinier machine shown in figs. 1 and 2 wherein the wire 1 is a lower wire and the additional wire 6 is a short overhead wire loop or the upper wire of a twin-wire machine.
• the invention can be applied e.g. in twin-wire machines wherein, at the end of a vertical dewatering zone, one of the wires and the web supported thereby are guided by means of a suction roll towards a pick-up suction roll.

Landscapes

• Paper (AREA)
• Machines For Manufacturing Corrugated Board In Mechanical Paper-Making Processes (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8538117

Family Applications (1)

Country Status (8)

Cited By (3)

Families Citing this family (13)

Citations (1)

Family Cites Families (11)

• 1993
  • 1993-06-11 FI FI932671A patent/FI93237C/fi not_active IP Right Cessation
• 1994
  • 1994-06-10 DE DE69422984T patent/DE69422984T2/de not_active Expired - Fee Related
  • 1994-06-10 WO PCT/FI1994/000250 patent/WO1994029519A1/en active IP Right Grant
  • 1994-06-10 US US08/557,091 patent/US5820731A/en not_active Expired - Fee Related
  • 1994-06-10 EP EP94917017A patent/EP0704005B1/en not_active Expired - Lifetime
  • 1994-06-10 AT AT94917017T patent/ATE189717T1/de not_active IP Right Cessation
  • 1994-06-10 AU AU68476/94A patent/AU6847694A/en not_active Abandoned
  • 1994-06-10 CA CA002164705A patent/CA2164705A1/en not_active Abandoned

Patent Citations (1)

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