WO1993025753A1

WO1993025753A1 - Rotary former for manufacturing paper

Info

Publication number: WO1993025753A1
Application number: PCT/GB1993/001269
Authority: WO
Inventors: Brian William Attwood; Kenneth William Hamilton Loy
Original assignee: Black Clawson International Limited
Priority date: 1992-06-18
Filing date: 1993-06-15
Publication date: 1993-12-23
Also published as: GB9212909D0

Abstract

The invention relates to a rotary former for manufacturing paper or paperboard, in which a cylinder mould (1) is fitted with an endless foraminous forming band (4) on which paper making stock is deposited to form a web (6). The web (6) is transferred from the forming band (4) to a making felt (7) and the forming band is guided in a loop having a run (10) travelling adjacent the making felt for a predetermined distance downstream of the web transfer position (9).

Description

ROTARY FORMER FOR MANUFACTURING PAPER

The present invention relates to the manufacture of paper and paperboard and, more particularly, to the manu¬ facture of paper and paperboard by means of a rotary for¬ mer.

Typically, rotary formers consist of a cylinder mould which has a permeable construction comprising a base structure upon which is fitted a coarse mesh backing wire or fabric covered with a finer mesh facing or forming wire.

Associated with the cylinder mould is a flow system for supplying paper-making stock in the form of a fibrous suspension to the surface of the mould where drainage and accompanying web formation take place. Typical fibrous suspension supply arrangements are either of the restricted flow type or of the pressure forming type, as described in UK Patent Specification No. 1548925. In operation, for example as with a pressure former, the fibrous suspension is drained or dewatered through the cylinder mould under pressure, thus forming a fragile fibrous mat or web, and the drainage water associated with this action passes through the structures of the wire and the cylinder mould into the centre of the cylinder mould.

After preliminary forming has occurred, the fibrous web on the surface of the cylinder mould is transferred to a making felt with an associated couch roll. The couch roll applies a nip load through the cylinder mould, and further water associated with the fibrous web is squeezed out of the web into the forming wire, backing wire and cylinder mould structure. The web is arranged to adhere to the underside of the making felt (known as an under felt arrangement) and may be carried on the felt to further rotary forming units and finally to the press stage and drier section of the complete paper-making machine. In practice, it is found that at high speeds, that is, speeds above 150 m/min, in order to obtain satisfactory operation it is necessary to apply a low vacuum to the inside of the cylinder mould. The main purpose of this vacuum is to hold the drainage water, now associated with the forming and backing wires and the roll structure, to the mould so that, when it is thrown out by the action of centrifugal force, it does not interfere with the fragile fibrous web on the underside of the making felt.

At speeds above 150 m/min the throw-out of water can seriously disrupt the pulp web, and at higher speeds, that is above 200 m/min, the cylinder mould is often in the form of an expensive suction roll with associated vacuum application and related energy costs.

It is an object of the present invention to allevi¬ ate the complications of throw-out water and to enable a rotary former to operate at high speeds without risk of damage to the fibrous web and without requiring the use of an expensive suction roll and attendant energy intensive vacuum system.

Accordingly, the present invention consists in a rotary former for manufacturing paper or paperboard, in which the cylinder mould is fitted with an endless foraminous forming band on which paper-making stock is deposited to form a web, and in which the web is transferred from the forming band to a making felt and the forming band is guided in a loop having a run travelling adjacent the making felt for a predetermined distance downstream of the web transfer position.

With the invention, the web of paper making stock formed on the forming band as it passes about the cylinder mould comes into contact with the making felt at the web transfer position and is held against the making felt for a period of time by the run of the forming band travelling adjacent the making felt. Whilst in this position the fragile web between the forming band and making felt is protected from any throw out water from the cylinder mould. At the same time the web may be further dewatered and formed/reformed by suitable means disposed above and/or under the making felt or forming band.

The web may be transferred to the making felt at a pressure nip through which the forming band and making felt travel with the web sandwiched therebetween and which squeezes the web and produces further dewatering of the web. For example, the pressure nip may be formed between the cylinder mould and a couch roll.

Preferably, the forming band has a run travelling generally parallel to the making felt for a predetermined distance downstream of the transfer position or pressure nip and the web may be sandwiched between the making felt and the forming band throughout this ru .

Skimming or doctor means may be disposed within the loop of the forming band adjacent the upstream end of the run and serve to remove water from the inside of the forming band. This skimming or doctor means preferably comprises one or more deflector blades positioned close to the forming band and an associated splash guard extending adjacent the cylinder mould. The splash guard serves further to protect the web from throw-out water from the cylinder mould. The forming of the web may be controlled by varying the number of deflector blades and by adjusting the application pressure of the deflector blade(s) against the forming band.

The loop c.t the farming band is conveniently sup¬ ported by guide and tensioning means, such as, a support roller at the downstream end of the loop and tensioning roller acting on the return run of the forming band between the support roller and the cylinder mould. The support roller may be a hollow roller, for example of the extractor type, to produce further dewatering of the web. Suction means, such as a suction box, may be disposed downstream of the transfer position or pressure nip for applying suction to the web through the making felt to assist in dewatering and transfer of the web to the felt.

The invention is particularly suitable for use in an under felt arrangement in which the cylinder mould is disposed below the making felt, and the web is transferred to the underside of the making felt for feeding to subse¬ quent stages of the paper making machinery.

The present invention also consists in a method of manufacturing paper or paperboard in which a web is formed from paper making stock deposited on an endless foraminous forming band fitted about a cylinder former and is transferred from the cylinder former to a making felt at a transfer position, and in which the forming band is guided in a loop having a run travelling adjacent the making felt for a predetermined distance downstream of the transfer position and protecting the web transferred to the felt from throw-out water from the cylinder former.

The invention enables the production of a web of papermaking stock at higher speeds and higher basis weights than hitherto. For example, a good quality product can be manufactured at speeds as high as 400 m/min and a single former can produce such a product with a basis weight of 200 g/m². The higher basis weight achievable with the invention enables a multi-ply paper or paperboard of a predetermined bulk to be produced with a reduced number of formers than would have been required hitherto.

In order that the present invention may be more readily understood, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which:-

Figure 1 is a side view of a rotary former accord¬ ing to one embodiment of the invention; and Figure 2 is a side view of a rotary former accord¬ ing to another embodiment of the invention.

Referring to Figure 1, the rotary former comprises a rotatable cylinder mould 1 having a cylindrical base structure 2 with a coarse mesh foraminous backing fabric 3, such as a backing wire, fitted about he circumference of the base structure 2. The cylinder mould 1 is further fitted with an endless foraminous forming band 4 of a finer mesh fabric, such as a fine wire mesh. An aqueous paper making stock comprising fibrous cellulosic material is deposited on the forming band 4 by a pressure former 5 and forms a fibrous web 6 by drainage into the cylinder mould 1.

A making felt 7 travels in a path generally tangen¬ tial to the cylinder mould 1 downstream of the pressure former 5. A couch roll 8 cooperates with the cylinder mould 1 to form a pressure nip 9 therewith through which the making felt 7 and the forming band 4 travel. The pressure nip 9 defines a transfer position at which the web 6 is transferred from the forming band 4 to the making felt 7.

The forming band 4 is guided in a loop and has a run 10 travelling adjacent the making felt 7 for a prede¬ termined distance downstream of the pressure nip 9. At the downstream end of the run 10, the loop turns about a sup¬ port roller 12. A tensioning roller 13 abuts the return run of the forming band between the support roller 10 and the cylinder mould and is movable (as indicated by arrows in the figure) to maintain a suitable tension in the loop.

A suction box 11 is disposed close to the making felt 7 for applying suction to the web 6 therethrough, to assist in dewatering and transfer of the web to the felt 7. Within the loop of the forming band 4, a skimming or doctor deflector 14 is disposed closely against the forming band 4 adjacent the upstream end of the run 10, for removing water from the inside of the forming band . The deflector 14 has an associated collecting tray and a splash guard 15 extending adjacent the circumference of the cylin¬ der mould 1 for protecting the sandwiched web from splash¬ es.

A cleaning shower 16 is disposed adjacent the circumference of the cylinder mould 1 upstream of the pressure former 5 for cleaning the forming band 4, the backing wire 3 and the base structure 2 of the cylinder mould.

In operation of the rotary former, the web 6 is dewatered by drainage through the cylinder mould 1, assisted by squeezing at the pressure nip 9, as in normal rotary operation of a typical rotary former. But down¬ stream of the nip 9, the web 6 remains sandwiched between the under side of the making felt 7 and the upper side of the forming band 4.

The action of the doctor deflector 14 is to remove any water hanging on the under side of the forming band 4, and protect the band 4 and the fibrous web 6 from being wetted by water thrown out from the cylinder mould 1. In some cases a reforming or improving of the web structure may be associated with the use of the deflector 14. Any water remaining in the structure of the forming band 4 downstream of the deflector 14 will not cause unsightly watermarks or damage to the fibrous web 6.

The rotary former shown in Figure 2 has a similar structure to that of Figure 1, and like reference numerals are used in the two figures to indicate like parts. In this embodiment, further dewatering of the web is facili¬ tated by a second couch roll 18 forming a pressure nip 19 with the support roll, which is in the form of a hollow extractor roll 20.

The fragile fibrous web is thus protected from the effects of damage from extraneous fluid following the forming section, so that higher speeds of manufacture are possible than those attainable with the traditional under felt rotary former type machine. For example, it is possi¬ ble to operate at speeds in excess of 300 m/min.

Because of the ability to apply extra dewatering action to the web it is possible to run at higher basis weights per unit former than are possible with previous equipment. The equipment described can be associated either with completely new formers or may be added to existing equipment. It may also be used for the production of multi- ply paper and paperboard, in which one or more rotary formers, such as shown in Figure 1 or 2, are arranged successively to apply one or more additional web plies to a previously formed web carried on the underside of the making felt 7.

Whilst various embodiments of the invention have been described, it will be appreciated that modifications may be made without departing from the scope of the inven¬ tion as defined by the appended claims. For example, a suction box 11 may alternatively or in addition be positioned underneath the run 10 for assisting in dewater¬ ing of the web.

Claims

1. A rotary former for manufacturing paper or paper¬ board, in which a cylinder mould (1) is fitted with an endless foraminous forming band (4) on which paper making stock is deposited to form a web (6), and in which the web (6) is transferred from the forming band (4) to a making felt (7) and the forming band is guided in a loop having a run (10) travelling adjacent the making felt for a prede¬ termined distance downstream of the web transfer position.

2. A rotary former according to claim 1, in which the web (6) is transferred to the making felt (7) at a pressure nip ( 9 ) through which the forming band and making felt travel with the web sandwiched therebetween.

3. A rotary former according to claim 2, in which the pressure nip (9) is formed between the cylinder mould (1) and a couch roll (8).

4. A rotary former according to claim 1, 2 or 3, in which skimming or doctor means (14) is disposed within the loop of the forming band (4) adjacent the upstream end of the run (10) and serves to remove water from the inside of the forming band.

5. A rotary former according to claim 4, in which the skimming or doctor means includes at least one deflector blade positioned close to the forming band and an associat¬ ed splash guard extending adjacent the cylinder mould.

6. A rotary former according to any preceding claim, in which the loop (10) of the forming band (4) is supported by guide and tensioning means (12,13,20).

7. A rotary former according to claim 6, in which the guide and tensioning means includes a support roller (20) at the downstream end of the loop (10), said support roller being a hollow roller adapted to produce further dewatering of the web.

8. A rotary former according to claim 6, including a second couch roll (18) forming a pressure nip (19) with the hollow support roll (20).

9. A rotary former according to any preceding claim, including suction means disposed downstream of the transfer position or pressure nip (9) for applying suction to the web through the making felt (7) to assist in dewatering and transfer of the web to the felt.

10. A rotary former according to any preceding claim, in which the cylinder mould (1) is disposed below the making felt (7) and the web (6) is transferred to the underside of the making felt at the transfer position.

11. A method of manufacturing paper or paperboard, in which a web (6) is formed from papermaking stock deposited on an endless foraminous forming band (4) fitted about a cylinder former (1) and is transferred from the cylinder former to a making felt (7) at a transfer position, and in which the forming band (4) is guided in a loop having a run (10) travelling adjacent the making felt (7) for a predetermined distance downstream of the transfer position and protecting the web transferred to the felt from throw- out water from the cylinder former.

12. A method according to claim 11, in which the web (6) is transferred to the making felt (7) at a pressure nip (9) through which the forming band and making felt travel with the web sandwiched therebetween and which squeezes the web and produces dewatering of the web.

13. A method according to claim 11 or 12, in which the run (10) of the forming band travels generally parallel to the making felt (7) for a predetermined distance downstream of the transfer position or pressure nip (9) with the web (6) being sandwiched between the making felt and forming band throughout the run.

14. A method according to claim 11, 12 or 13, including removing water from the inside of the run (10) of the forming band.

15. A method according to claim 11, 12, 13 or 4, lincluding dewatering the web (6) downstream of the trans¬ fer position or pressure nip (9) and along the run (10) of the forming band by applying suction and/or pres¬ sure to the run and/or the adjacent making felt.

16. A method according to any preceding claim 11 to 15 for producing multi-ply paper and paperboard, in which the making felt carries a previously formed web into the trans¬ fer position or pressure nip (9).