GB2028886A

GB2028886A - Wet Press

Info

Publication number: GB2028886A
Application number: GB7849555A
Authority: GB
Original assignee: Tampella Oy AB
Current assignee: Tampella Oy AB
Priority date: 1978-08-21
Filing date: 1978-12-21
Publication date: 1980-03-12
Also published as: SE7813203L; BR7900058A; JPS5530483A; IT1109919B; FI782549A; IT7919083A0; DE2854690A1; CA1099551A

Abstract

An extended nip press for a paper machine for removing water from a fiber web comprises several press rolls (2, 2', 3, 3') forming at least four separate press nips (4, 4', 5, 5') with a common press roll (1). A first press zone (PV) is limited by two press nips (4, 5) and a second press zone (PV'), by further two press nips (4', 5') along the surface of said common press roll (1). Each press zone comprises a pressure medium chamber (9, 9') limited by the secondary press rolls (2, 2', 3, 3') and a pressure medium impervious band (11, 11') passing through the press nips over the press zone in order to press said band against said common press roll. The fiber web (15) is carried by a porous felt (12, 12') through all press nips and is in both press zones subjected to a pressure action against said common press roll. The pressure chambers are positioned on opposite sides of said common press roll so that the displacing pressure forces caused by the pressure zones upon said common press roll at least partially nullify each other. <IMAGE>

Description

SPECIFICATION Extended Nip Press for a Paper Machine This invention relates to an extended nip press for a paper machine for removing water from a fiber web passing through the press, said press comprising several press rolls, of which one press roll is common to the remaining press rolls and forms press nips with said remaining press rolls, a porous felt for conveying the web to be treated through the press nips into contact with press rolls, a pressure medium impervious band following said felt, and a sealed pressure medium chamber positioned between said press rolls, said chamber in the machine direction being limited by the band portion between two nips, by one of the rolls in each of said two nips and by a sealing element positioned between said rolls and, forming a press zone subjecting said band to a pressure action.

In Applicant's earlier US-Patent Application No. 922 393, filed on July 5, 1 978 and GB Patent Application No. 24 061, filed on May 30, 1978, an extended press zone has been suggested by means of which the web to be treated is pressed against the peripheral surface of a common press roll and which press zone extends a substantial distance in the peripheral direction of said common press roll. The pressure is produced by means of a pressure medium chamber extending in the machine direction along the peripheral surface area between the press nips formed by said common press roll and two additional press rolls. The object is to press the web to be treated during its movement through the press zone against said peripheral surface area of the common press roll by means of the medium pressure acting in said pressure medium chamber.However, such an extended press zone applies substantial forces on the common press roll and, due to the eccentric location of the press zone, causes in relation to the common press roll substantial bearing forces and a considerable bending of said common press roll, which makes the practical application of such an extended press nip difficult.

The object of this invention is to obtain an extended nip press in which the bearing forces applied on the common press roll due to the press zone formed by the pressure medium chamber are entirely or partially avoided and the bending of the press roll is controlled and reduced. This object is achieved by means of an extended nip press according to the invention which is characterized in that at least two press zones are formed by separate pressure medium chambers arranged on different sides of said common press roll so that the forces caused by said press zones on said common press roll at least partially nullify each other.

The invention is based on the idea that the press zone formed by the pressure medium chamber and earlier suggested by the Applicant is in a way divided into two parts positioned as separate independent press zone units on different sides of the common press roll in such a way that the force actions, i.e. the nip loads and the pressure medium loads applied by the separate press zones on the common press roll nullify each other. In this way, it is possible to influence the resultant force applied on the bearings of the common press roll due to the press zones and to eliminate said resultant force entirely or partially. As the resultant force applied on the common press roll decreases, also the bending of the roll decreases to a corresponding extent.

The press zones may be located symmetrically or asymmetrically around the common press roll and the press zones may be of equal or different length in the peripheral direction of the common press roll. By combining these alternatives it is possible to affect in each particular case in the most appropriate way the magnitude and direction of the resultant force applied on the common press roll due to the press zones. When desired, it is even possible to apply on the common press roll an action which reduces the bearing forces as well as the bending caused by its own weight.

When using two or more press zones, it is possible to use in the separate zones a nip pressure and a medium pressure which in each particular case is most appropriate for treating the web. Likewise, the invention makes it possible to press the web during the pressing step against separate felts. This can be realized by providing each press zone with a felt and a band of its own which form a closed loop.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a schematic side view of one embodiment of an extended nip press according to the invention, and Figure 2 is a schematic side view of a second embodiment of an extended nip press.

The extended nip press shown in Figure 1 of the drawing comprises a common press roll 1 and four rolls 2, 2', 3, 3' located around said common press roll in parallel with each other and extending in the transverse direction of the paper machine. The press rolls 2 and 3 roll against the common press roll 1 and form therewith two press nips 4, 5. At a radial distance from the common press roll there is positioned between the press rolls 2 and 3 a beam or a casing 6 in parallel with the rolls and supporting edge seals 7 abutting against the peripheral surfaces of the corresponding press rolls 2 and 3. Accordingly, there is formed between the rolls 1, 2, 3 and the casing 6 a pressure medium chamber 9 closed at both ends in the transverse direction of the machine and sealed with end walls not shown in Figure 1.The pressure medium chamber is connected to a pressure medium source (not shown) for supplying the chamber with pressure medium and for producing the desired medium pressure in the chamber 9. The press zone caused by the pressure medium is indicated by the reference PV.

The roll group 1, 2 and 3 further includes an endless pressure medium impervious band 11 running around the rolls 2, 3 and a porous press felt 12 likewise running around the rolls 2, 3 upon the band 1 A paper web to be dried and to be passed through the press is indicated by the reference numeral 1 5. The web, felt and the band pass through the press nips 4 and 5 and are in the area between said nips abutting against the peripheral surface of the common press roll 1.

The press rolls 2', 3' are arranged on the opposite side of the press roll exactly in the same way as the rolls 2 and 3 described above, wherefore equivalent elements are indicated by corresponding reference numerals provided with an apostrophe. In this way, there is formed on the diametrically opposite side of the common press roll 1 in relation to the press zone PV an equally long press zone PV', as shown in Figure 1.

In order to dry the web, it is passed through both press zones around the common press roll 1.

In the press nips, a normal pressure produced by the press nip is applied on the web, and in the press zones the pressure medium applies on the web a pressure action through the band along the entire area between the nips. The water in the web is therefore removed into the felts.

It will be noted that both press zones apply on the common press roll 1 forces each striving to displace said roll in the horizontal direction, but as the press zones are located on diametrically opposite sides of the common press roll, both opposite forces nullify each other provided that the medium pressures and the nip pressures are equally big in both press zones. Thus, the press zones do not cause any extra loads in the bearings of the common press roll 1 nor any bending of the roll. The use of two separate felts is of advantage as regards the drying process.

The extended nip press shown in Figure 2 differs from the preceding embodiment first of all in that the press zones are of different length in the peripheral direction of the common press roll and secondly in that the press zones are arranged asymmetrically around the common press roll 1.

In this case, the first press zone PV1 is smaller in the peripheral direction of the press roll 1 than the second press zone PV2. The press zones are, moreover, located somewhat displaced toward the lower half of the common press roll so that the press zones apply in the common press roll an upwardly directed resultant force action relieving the roll. In additon, it is possible to affect the size and direction of the resultant force action produced by the press zones by using in the press zones a medium pressure and/or a nip pressure of a different magnitude.

The embodiment shown in Figure 2 differs from Figure 1 also in that the separate felts are replaced by a felt 1 2 common to both press zones.

The drawing and the specification relating thereto are only intended to illustrate the idea of the invention. In its details, the nip press according to the invention may vary considerably within the scope of the claims. It is possible to arrange around the common press roll more than two press zones.

Claims

1. An extended nip press for a paper machine for removing water from a fiber web passing through the press, said press comprising several press rolls (1, 2, 3, 2', 3') of which one press roll (1) is common to the remaining press rolls (2, 3, 2', 3') and forms press nips (4, 5, 4', 5') with said remaining press roll, a porous felt (12) for conveying the web (15) to be treated through the press nips into contact with said press rolls, a pressure medium impervious band (11) following said felt, and a sealed pressure medium chamber (19) positioned between said press rolls, said chamber in the machine direction being limited by the band portion between two nips, by one of the rolls in each of said two nips and by a sealing element (6) positioned between said rolls, and forming a press zone (PV) subjecting said band to a pressure action, characterized in that at least two press zones (PV, PV', PV1, PV2) are formed by separate pressure medium chambers (9, 9') arranged on different sides of said common press roll (1) so that the forces caused by said press zones on said common press roll at least partially nullify each other.

2. A press according to claim 1, characterized in that the separate pressure medium chambers (9, 9') forming said press zones (PV, PV') are arranged symmetrically around said common press roll (1).

3. A press according to claim 2, characterized in that the separate pressure medium chambers (9, 9') forming said press zones (PV, PV'( are arranged on diametrically opposite sides of said common press roll (1).

4. A press according to claim 1, characterized in that the pressure medium chambers (9, 9') forming said press zones (PV1, PV2) are arranged asymmetrically around said common press roll (1).

5. A press according to claim 2 or 4, characterized in that said press zones (PV, PV') are of the same length in the peripheral direction of said common press roll (1).

6. A press according to claim 2 or 4, characterized in that said press zones (PV1, PV2) are of different lengths in the peripheral direction of said common press roll (1).

7. A press according to claim 1, characterized in that each press zone (PV, PV') is provided with a felt (12) and a band (11) of its own forming a closed loop.

8. A press according to claim 1, characterized by four press rolls (2, 3, 2', 3') positioned around said common press roll (1) and forming four press nips (4, 5, 4', 5') with said common press roll, by first sealing element (6) provided between two first press rolls (2, 3) and a second sealing element (6') provided between the two remaining press rolls (2', 3'), by a first endless band (11) and a felt (12) passing through two first press nips (4, 5) and abutting against said common press roll, and a second endless band (11') and a felt (12') passing through the two remaining press nips (4', 5') and abutting against said common press roll, by a first pressure medium chamber (9) defined between the part of said first band (11) abutting against said common press roll (1), both said first press rolls (2, 3) and said first sealing element (6) and a second pressure medium chamber (9') defined between the part of said second band (11') abutting against said common press roll (1), said two remaining press rolls (2', 3') and said second sealing element (6'), said pressure medium chambers being closed with end walls at the opposite ends of said common press roll, and by said pressure medium chambers being located on opposite sides of said common press roll (1) so as to form along the periphery of said common press roll two separate press zones (PV, PV') spaced apart in said peripheral direction.