WO1992013133A1 - Procede et dispositif relatifs a la presse d'une machine a papier et servant a detacher la bande de la face d'un cylindre de pression - Google Patents

Procede et dispositif relatifs a la presse d'une machine a papier et servant a detacher la bande de la face d'un cylindre de pression Download PDF

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Publication number
WO1992013133A1
WO1992013133A1 PCT/FI1992/000014 FI9200014W WO9213133A1 WO 1992013133 A1 WO1992013133 A1 WO 1992013133A1 FI 9200014 W FI9200014 W FI 9200014W WO 9213133 A1 WO9213133 A1 WO 9213133A1
Authority
WO
WIPO (PCT)
Prior art keywords
transfer
web
roll
press
suction
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/FI1992/000014
Other languages
English (en)
Inventor
Juhani Niskanen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Technologies Oy
Original Assignee
Valmet Paper Machinery Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Paper Machinery Inc filed Critical Valmet Paper Machinery Inc
Priority to DE69221123T priority Critical patent/DE69221123T2/de
Priority to CA002099379A priority patent/CA2099379C/fr
Priority to EP92902194A priority patent/EP0567484B1/fr
Publication of WO1992013133A1 publication Critical patent/WO1992013133A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • D21F3/0281—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
    • D21F3/00—Press section of machines for making continuous webs of paper
    • D21F3/02—Wet presses
    • D21F3/04—Arrangements thereof

Definitions

  • the invention concerns a method in the press section of a paper machine for detaching the web from a smooth mantle face of a press roll, in which method a transfer zone is employed, over which a press fabric or a particular transfer 10 fabric is passed so as to accomplish a closed draw of the web, and said transfer zone as well as said fabric are arranged to form a transfer nip or a transfer zone with said roll face.
  • the invention concerns a press section of a paper machine, comprising 15 an arrangement of press rolls, which form one or several press nips with one another, the web being detached from a smooth-faced roll in said press section by means of a roll or an equivalent transfer member and being transferred further to the drying section or into a separate nip in the press section, in which press section a revolving suction-transfer roll or a corresponding static suction- 20 transfer box has been arranged to form a transfer nip or a transfer zone, which accomplishes a closed draw of the web, in connection with the smooth roll face, in which nip or zone the web is subjected to a negative pressure which attempts to detach the web from the roll face.
  • the first twin-wire nip is formed between a hollow-faced lower press roll and an upper press-suction roll.
  • Said suction roll forms the second nip with the smooth-faced centre roll of the press, and the third press nip is formed in connection with said centre roll.
  • this press section may include a separate nip, as a rule a fourth nip in the press, after which the web is transferred to the drying section.
  • the first twin-felt horizontal nip is formed between a lower hollow-faced roll and an upper press-suction roll, after which the web follows the upper fabric as a vertical run into the second nip, which is formed between a hollow-faced roll separate from the rolls in the first nip and the smooth-faced centre roll.
  • a third press nip which is provided with a felt, is formed by means of a hollow-faced press roll.
  • the web is detached from the smooth face of the centre roll in the press by means of a pulling force parallel to the running direction of the web as a free unsupported draw.
  • This free draw is quite critical in view of the operation of a paper machine.
  • a speed difference is employed which stretches the web, which results in certain drawbacks.
  • said unsupported draw forms a problem- atic point susceptible of breaks in the paper machine.
  • the negative pressure applied to the web in the suction zone of the transfer- suction roll produces a corresponding negative pressure between the web and the smooth face of the centre roll, which has the consequence that the web is not detached but follows the smooth face of the centre roll.
  • the wet breaking strength of newsprint is F M ⁇ 200 N/m, and the corresponding grammage is 42 g/m . and the moisture content in the first fret gap in the nip is « 42 %.
  • the typical strength values are average values, but the web breaks at the weakest point. If there is an occasional, local strength of 50 N/m in the web, the following velocity is obtained:
  • the web must be made generally stronger or more homogeneous (no weak points), or the free gaps must be eliminated.
  • the present invention endeavours to solve said prob ⁇ lems by means of elimination of the free gaps.
  • the general object of the present invention is to provide novel means in the detaching of the web from the centre roll or equivalent in the press section and in the transfer of the web into a separate nip or to the drying section.
  • the object of the present invention is to provide a method and a device for detaching the web from a smooth-faced press roll wherein the web need not be stretched, i.e. it is unnecessary to employ so-called draw and speed difference.
  • the object of the invention is to provide a press section in which, when necessary, it is possible to use a fully closed draw when the web is transferrec from the centre roll or from a corresponding other roll in the press to the drying section, as a rule onto its drying wire, or onto the press fabric of a separate nip.
  • the method of the invention is mainly characterized in that, at the transfer point, the temperature level of said roll face and/or of the web is set or regu ⁇ lated so high that the pressure of saturated vapour of the water present in connection with the web and with the roll face which corresponds to said temperature level is almost equally high as, or higher than, the pressure prevail ⁇ ing in said transfer zone.
  • the device in accordance with the invention is mainly characterized in that the device comprises a heating device or devices, by means of which the temperature level at the web that enters to the transfer point and/or the temperature level of said roll face can be raised to such a high level that a detrimentally high negative pressure, which would prevent the closed transfer of the web, is not formed at the transfer point.
  • Figure 1 is a schematic side view of the environment of application of the invention and of a first embodiment of the invention, in which the press fabric of the third nip is used as the transfer fabric in the transfer from the centre roll.
  • Figure 2 shows, in a way corresponding to Fig. 1. an embodiment of the inver- tion in which a separate transfer fabric is used that runs around the transfer- suction roll.
  • Figure 3 is a vertical sectional view in the machine direction of a transfer nip in accordance with the invention as accomplished by means of a transfer-suction roll.
  • Figure 4 shows an exemplifying embodiment of the invention in which the suction transfer takes place by means of a static transfer-suction box that comprises two parts.
  • Figures 1 and 2 are schematic illustrations of a press section of a paper machine, in which the paper web W, which comes from the forming wire 10 of the former, is dewatered by pressing.
  • the web W is transferred from the wire 10 at the pick- up point P by means of the press felt 12 on the suction zone 11a of the pick-up roll 11.
  • the web W is transferred into the first dewatering nip N_ j , which is formed between the press-suction roll 16 and the hollow-faced 14' lower press roll 14.
  • the first nip N. is a two-felt nip, and it includes a lower felt 13 guided by the guide rolls 15.
  • Figs. 1 and 2 the press rolls 14,16,18, and 21 form a compact combination of rolls in which there are three subsequent nips N_,.N .Np. through which the web W runs as a closed draw, being constantly supported by a felt or roll face.
  • a fourth, separate nip N 4 is formed between a smooth-faced 30', large-diameter press roll 30 and a lower hollow-faced 31' press roll 31. After the fourth nip N 4 , the web W follows the smooth face 30', from which it is detached on the guide roll 39, being transferred onto the drying wire 36 of the drying section, which is guided by the guide roll 35.
  • the web W is made to adhere to the drying wire 36 by means of a suction box 37, being passed on the wire 36 into a multi-cylinder dryer (not shown).
  • a suction box 37 On the upper sector of the upper press roll 30 of the separate nip N 4 , there are jet means 29 followed by a doctor 28, which keeps the roll face 30' clean.
  • the press fabric 26 is separated from the web W by means of the guide roll 38, being passed back into connection with the web W into the transfer nip 30/39 over the transfer-suction roll 39.
  • the web W is detached from the roll face 30', and the web W is transferred over the roll 39 on the press fabric 26, being secured by the negative pressure in the suction zone 39b.
  • the web W is detached from the fabric 26 by means of the suction box 37 and is transferred onto the drying wire 36. Differing from the above, in Fig.
  • the press fabric 26, being guided by the guide roll 32b, is separated from the web W, which is transferred on the roll face 30' onto the suction zone 39a of the trans ⁇ fer-suction roll 30.
  • a particular transfer fabric 46 is passed, on which the web W is transferred onto the drying wire 36, being secured by the second suction zone 39b of the roll 39.
  • first steam supply box 17 On the suction sector 16a between the first and the second nip, there is a first steam supply box 17. In a corresponding way, between the second and third nip N and No, there is a second steam supply box 20 operating against the web W.
  • second steam supply box 20 By means of the hot steam fed out of the boxes 17 and 20, it is also possible to affect the elastic properties of the fibres in the web and the viscosity and the surface tension of the water present in the web so that the dewatering is inten ⁇ sified in the nips o and N,.
  • the temperature T of the web W and of the face 18' of the centre roll 18 is raised to such a level that the detaching of the web W and its transfer from the roll face 18' can be carried out successfully in the transfer nip Ng.
  • the raising of the temperature level T of the web W takes place by means of internal heating of the centre roll 18, an example of which is given in Fig. 4 by the axial bores 18b made into the roll mantle 18a, into which bores a heating medium, such as hot water or steam, is passed.
  • the roll mantle 18b may be heated by means of the steam boxes 17 and 20, in particular by means of the steam box 20, and also by means of various electric heaters, of which an induction heater 60 is shown as an example in Fig. 2.
  • the press construction described above is substantially known in prior art, and it is described above just as a background and as an environment of application for the present invention.
  • the web W follows the smooth face 18' of the centre roll 18, from which it is detached as a fully closed draw in accordance with the invention by means of a transfer-suction roll 40 provided with a drive or by means of a transfer-suction box 50 (Fig. 4).
  • a transfer-suction roll 40 provided with a drive or by means of a transfer-suction box 50 (Fig. 4).
  • the suction zones 40a,40b of the transfer-suction roll 40 the web W is transferred on the suction zone 25a of the second lower transfer-suction roll 25 onto the press felt 26, which carries the web W on its upper face into the fourth, separate nip N. in the press section.
  • the press felt 23 of the third nip No is passed after the nip No onto the guide roll 22a and from it into the transfer nip N so that said press felt 23 operates as a transfer fabric, which runs around the transfer-suction roll 40 and on which the web W is transferred on the suction zone 25 a of the second transfer-suction roll 25 onto the lower fabric 26 of the fourth press nip N -
  • a transfer fabric 41 of its own is arranged to run around the transfer-suction roll 40. which fabric 41 is passed into the transfer nip N ⁇ and separated from the transfer-suction roll 40 so that the web W follows the lower fabric 26 of the fourth press nip N 4 ⁇ Said transfer is secured, e.g., by means of choice of the surface properties of the fabrics 26 and 41 and possibly by means of the suction box 33.
  • there 5 are guide rolls and conditioning devices known per se, not shown in Fig. 2.
  • suction zone 40a The suction zone 40a is followed by the second suction zone 40b of the transfer-suction roll 40, on which the level of negative pressure is lower than that on the zone 40a, ensuring that the web W remains on support of the transfer fabric 23;41. It is an important feature in the embodiment of the closed draw of the invention that, before the transfer point, the smooth face 18'
  • Fig. 3 shows the environment of the transfer nip Ng between the centre roll 18 and the transfer-suction roll 40.
  • the transfer-suction roll 40 includes a perforated 0 42 roll mantle 41, in whose interior there are suction boxes.
  • Fig. 3 in respect of the suction boxes, just the sealing ribs 43 of the first suction zone 40a are shown, which operate against the smooth inner face 41' of the roll mantle 41.
  • the paper web W enters into the transfer nip Ng on the smooth face 18' of the centre roll 18. As a rule, the paper web W adheres tightly to the face 18' by the intermediate of a non-unified water film.
  • the temperature T of the face 18' and of the web W and of the water film that makes the web adhere to the face 18' has been raised to such a level that the water present between the roll face 18' and the web W and partly in the struc ⁇ ture of the web W is vaporized as its volume is increased in the transfer nip Ng when the web W is sucked towards the transfer fabric 44 by means of the negative pressure p « in the suction zone 40a of the roll 40.
  • the maximum negative pressure that can arise here is the pressure pg of saturated vapour prevailing at said temperature T.
  • a negative pressure can be sucked between the paper web W and the transfer fabric 44, the absolute value of said negative pressure being p « ⁇ pg.
  • the length of the transfer nip Ng has been dimensioned such that there is time enough for generation of full negative pressure between the paper web W and the transfer fabric 44.
  • the outer face of the mantle 41 of the transfer-suction roll 40 may be provided with a soft coating, by whose means the length of the transfer nip Ng can be extended to make it large enough.
  • the reference S denotes the point or line at which the paper web W is separated from the face 18', because in the gap A that is opened, no higher negative pressure can arise than the pressure pg of saturated water vapour corresponding to the temperature T.
  • the temperature T of the face 18' of the centre roll 18 and of the web when they enter into the transfer nip Ng is in the invention, as a rule, in the range of T K 50...100°C, which corresponds to the range of pressure of saturated water vapour (absolute values) of pg « 0.13...1.0 bar.
  • a temperature range that is particularly favourable and practical in view of the objectives of the invention is the range T « 65...75°C, which corresponds to the range of pressure of water vapour of p s « 0.25...0.40 bar.
  • Fig. 4 shows an embodiment of the invention in which a static suction box 50 is employed in stead of a revolving suction roll 40.
  • a static suction box 50 Inside the suction box 50, two suction chambers 50a and 50b are fitted, whose open ends are defined by horizontal sealing ribs 53, over which the transfer fabric 44 is passed.
  • a negative pressure p « prevails that in the transfer nip Ng the web W is separated from the roll face 18' as a closed draw.
  • the second suction zone 50b there is a lower level of negative pressure (as a rule in a range of pi « 0.1 bar), whereby it is ensured that the web W follows the transfer fabric 44.
  • the suction chambers 50a and 50b communicate with the suction ducts 55a and 55b of the suction box 50 by the intermediate of the pipes 54a and 54b.
  • the suction box 50 the web W is transferred on the transfer fabric 55 into a transfer nip formed by the rolls 32 and 45, after which the web W is separated from the transfer fabric 44 and is transferred onto the support of the press felt 26, to which it is made to adhere by means of the negative pressure in the suction box 33.
  • Said temperature level T of the web W and the roll face 18' that enter into the transfer nip N is regulated to a level suitable in view of the invention by means of internal heating systems 18b in the roll 18 or by means of steam boxes 17 and/or 20.
  • the internal heating systems in the roll 18 may also include heating media passed into the interior of the roll mantle 18a, such as steam or hot water.
  • the induction heater 60 is connected with a unit 61 for the supply of electric power. If necessary, the induction heater 60 and the other heaters may also be arranged so that, by its means, the transverse temperature profile of the roll face 18' and the web W before the transfer nip Ng and in the nip area is controlled so that said profile is optimal in view of the transfer of the web W, as a rule as uniform as possible, e.g., in view of the different properties of adhesion to the roll face 18' possessed by different pulp qualities.
  • the inven ⁇ tion can also be applied to a press section in which there is no separate nip N 4 , but the web W is transferred as a closed draw from the fabric that runs over the transfer-suction roll 40 into the drying section, e.g. onto its drying wire, so that the press fabric 26 shown in Figs. 1 and 2 corresponds to the drying wire in the first wire group, on which fabric the web W is passed as a single-wire draw through the first drying group.
  • Figs. 1 and 2 show such a "Sym-Press-II” press section in which the suction roll 16 forms two nips N-, and No.
  • the invention can also be applied to other press geometries, such as the applicant's "Sym-Press-O" press section, in which, after the press-suction roll 16, the web W has a vertical draw supported by the fabric 12 and. in stead of the press-suction roll 16, there is a separate press roll in connection with the centre roll 18.
  • the negative pressure that prevails in the suction zone 40a,50a of the suction roll 40 or of the suction box 50 is exactly equal to the vapour pressure corresponding to the temperature T of the roll face 18 or of the web W, but in some special situations a lower level of negative pressure may also be adequate, which level is, however, chosen such that it substantially promotes the detaching of the web W without a detrimentally high pulling tension applied to the web. This is the case, e.g., with thicker paper qualities and/or with stronger pulps.
  • the scope of the invention also includes such embodiments differing from the above in which the temperature level T of the face 18' of the centre roll 18 is set at the level of T > 100°C, in which case, in the transfer of the web W, a zone with negative pressure is not necessarily needed inside the transfer fabric 23;44. According to the present-day estimation, however, the method and the device of the invention can be accomplished optimally so that expressly a suction zone 40a,50a is employed in which a pressure p Q lower than the atmospheric pressure has been set to prevail.

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  • Paper (AREA)
  • Replacement Of Web Rolls (AREA)

Abstract

Procédé et dispositif relatifs à la presse d'une machine à papier et servant à détacher la bande (W) de la face externe lisse (18') d'un cylindre de pression (18). Dans le procédé et le dispositif, on utilise une zone de transfert (40a, 50a) sur laquelle passe une bande de toile (23) ou une toile de transfert spéciale (44) pour exercer une tension en circuit fermé sur la bande (W). La zone de transfert (40a, 50a), ainsi que ladite toile (23, 44) constituent un pincement (NS) ou zone de transfert avec la face du cylindre (18'). Le niveau de la température (T) de la face du cylindre (18') et/ou de la toile (W) au point de transfert, est réglé afin que la pression (pS) de vapeur saturée de l'eau présente dans la bande (W) et sur la face du cylindre (18') et correspondant audit niveau de température (T) soit sensiblement aussi élevée, ou un peu plus élevée que la pression (pO) réglée pour se maintenir dans ladite zone de transfert (40a, 50a), ladite pression (pO) étant, de préférence, inférieure à la pression atmosphérique.
PCT/FI1992/000014 1991-01-18 1992-01-20 Procede et dispositif relatifs a la presse d'une machine a papier et servant a detacher la bande de la face d'un cylindre de pression Ceased WO1992013133A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
DE69221123T DE69221123T2 (de) 1991-01-18 1992-01-20 Verfahren und vorrichtung in der presspartie einer papiermaschine zum lösen der bahn von einer presswalzenoberfläche
CA002099379A CA2099379C (fr) 1991-01-18 1992-01-20 Dispositif de la section des presses d'une machine a papier servant a degager la bande de la soupape d'un rouleau de presse et methode correspondante
EP92902194A EP0567484B1 (fr) 1991-01-18 1992-01-20 Procede et dispositif relatifs a la presse d'une machine a papier et servant a detacher la bande de la face d'un cylindre de pression

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI910288A FI92941C (fi) 1991-01-18 1991-01-18 Menetelmä ja laite paperikoneen puristinosalla rainan irrottamiseksi puristintelan pinnalta
FI910288 1991-01-18

Publications (1)

Publication Number Publication Date
WO1992013133A1 true WO1992013133A1 (fr) 1992-08-06

Family

ID=8531762

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI1992/000014 Ceased WO1992013133A1 (fr) 1991-01-18 1992-01-20 Procede et dispositif relatifs a la presse d'une machine a papier et servant a detacher la bande de la face d'un cylindre de pression

Country Status (6)

Country Link
EP (1) EP0567484B1 (fr)
AT (1) ATE155837T1 (fr)
CA (1) CA2099379C (fr)
DE (1) DE69221123T2 (fr)
FI (1) FI92941C (fr)
WO (1) WO1992013133A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4427281A1 (de) * 1994-08-02 1996-02-08 Voith Gmbh J M Verfahren zum Einfädeln einer Faserstoff-Bahn, insbesondere in eine Papierherstellungsmaschine
US5503716A (en) * 1992-03-05 1996-04-02 Valmet Paper Machinery, Inc. Device for guiding a leader of a web in a paper machine
US5637147A (en) * 1993-07-07 1997-06-10 Billhoefer Maschinenfabrik Gmbh Calendar for producing a sheet having wax-containing dispersion thereon
EP0903437A2 (fr) * 1997-09-20 1999-03-24 Voith Sulzer Papiermaschinen Gesellschaft mbH Procédé pour diminuer l'adhésion entre une bande fibreuse humide et un rouleau rotatif
WO2004057104A1 (fr) * 2002-12-20 2004-07-08 Upm-Kymmene Corporation Structure d'une ligne de contact pour machine a papier ou analogue

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI120239B (fi) 2008-06-19 2009-08-14 Metso Paper Inc Rainanmuodostuskone ja menetelmä rainanmuodostuskoneessa

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4889598A (en) * 1987-01-23 1989-12-26 Valmet Paper Machinery, Inc. Method for detaching a web from a surface of a roll with inductive heating
US4919759A (en) * 1987-01-23 1990-04-24 Valmet Paper Machinery Inc. Control of detachment of a paper web from a roll using heat
US4948466A (en) * 1988-04-13 1990-08-14 Valmet Paper Machinery Inc. Method for heating a cylinder or roll with an electrically conductive ceramic outer layer

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4889598A (en) * 1987-01-23 1989-12-26 Valmet Paper Machinery, Inc. Method for detaching a web from a surface of a roll with inductive heating
US4919759A (en) * 1987-01-23 1990-04-24 Valmet Paper Machinery Inc. Control of detachment of a paper web from a roll using heat
US4948466A (en) * 1988-04-13 1990-08-14 Valmet Paper Machinery Inc. Method for heating a cylinder or roll with an electrically conductive ceramic outer layer

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5503716A (en) * 1992-03-05 1996-04-02 Valmet Paper Machinery, Inc. Device for guiding a leader of a web in a paper machine
US5989393A (en) * 1992-03-05 1999-11-23 Valmet Corporation Method and device for guiding a leader of a web in a paper machine
US5637147A (en) * 1993-07-07 1997-06-10 Billhoefer Maschinenfabrik Gmbh Calendar for producing a sheet having wax-containing dispersion thereon
DE4427281A1 (de) * 1994-08-02 1996-02-08 Voith Gmbh J M Verfahren zum Einfädeln einer Faserstoff-Bahn, insbesondere in eine Papierherstellungsmaschine
EP0903437A2 (fr) * 1997-09-20 1999-03-24 Voith Sulzer Papiermaschinen Gesellschaft mbH Procédé pour diminuer l'adhésion entre une bande fibreuse humide et un rouleau rotatif
WO2004057104A1 (fr) * 2002-12-20 2004-07-08 Upm-Kymmene Corporation Structure d'une ligne de contact pour machine a papier ou analogue

Also Published As

Publication number Publication date
ATE155837T1 (de) 1997-08-15
FI910288A0 (fi) 1991-01-18
CA2099379A1 (fr) 1992-07-19
FI910288L (fi) 1992-07-19
FI92941B (fi) 1994-10-14
FI92941C (fi) 1995-01-25
EP0567484A1 (fr) 1993-11-03
DE69221123D1 (de) 1997-08-28
DE69221123T2 (de) 1997-11-20
CA2099379C (fr) 2000-04-25
EP0567484B1 (fr) 1997-07-23

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Pikulik 1.1 Approach Flow System The forming process is preceded by an approach flow system that receives the aqueous fiber suspension, or stock, and prepares it for the forming process. Fibres are produced using kraft process or other pulping/bleaching processes (see Bleaching of wood pulps) and the proportions of fibers from different sources are blended here. Drained water from the forming process, known as whitewater, contains useful fibrous material and is continuously recycled back into the stock. Screens and centrifugal cleaners in the approach flow system remove oversize and heavy contaminants from the pulp. Additives such as minerals, pigments and dyes are introduced to make particular grades of paper and paper board. Air bubbles may be removed from the pulp suspension. The mass concentration, or consistency, of the suspension is kept low to prevent fibre flocculation prior to forming and is usually adjusted to a value in the range of 0.5 to 1.5%.

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