Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
2001-05-29
2003-02-11
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S358300, C162S361000, C100S153000
Reexamination Certificate
active
06517683
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a press in a machine for production or treatment of a continuously running web of cellulosic fibrous material, for instance a paper, tissue or board machine, which press comprises a press device and a counter element arranged opposite the press device, which is arranged to form a press zone in the form of an extended press nip in cooperation with the press device having a certain width in the machine direction W for pressing the fibrous web as it runs through the press nip, which press device comprises
a press shoe;
a support element for supporting and pressing the press shoe in direction towards the counter element via
at least one power device arranged between the press shoe and the support element for application of a certain pressure onto the fibrous web at the pressing operation;
a flexible and preferably impermeable belt that is arranged to run in a continuous loop around the support element and through the press nip having a sliding contact with the press shoe; and
a first guide for the press shoe arranged downstream of the press shoe, which first guide is movable between at least a first and a second position.
The present invention also relates to a method for altering the pressure profile in a press in a machine in which a continuously running web of cellulosic fibrous material is produced or is treated, for instance a paper, tissue or board machine, which press comprises a press device and a counter element arranged opposite the press device, which forms a press zone in the form of an extended press nip in cooperation with the press device having a certain width in the machine direction W so that a pressing of the fibrous web occurs during the passage through the press nip, which press device comprises
a press shoe;
a support element that supports and press the press shoe in direction towards the counter element via
at least one power device which is arranged between the press shoe and the support element and which power device is applying a certain pressure onto the fibrous web during the pressing operation;
a flexible and preferably impermeable belt that runs in a continuous loop around the support element and through the press nip having a sliding contact with the press shoe, and a first guide for the press shoe arranged downstream of the press shoe and which first guide is transferred by dismounting and/or adjustment between at least a first and a second position.
BACKGROUND OF THE INVENTION
Presses of above specified type are known in different designs and have since long ago been used in production of different paper and cardboard grades, especially for wet pressing with the intention to raise the dry solids content of the fibrous web, but may also be used for calendering with the intention to improve surface properties or other physical properties of the web. Typically for presses that comprise press devices having an extended press nip and which presses and press devices usually are named shoe presses and shoe press rolls respectively, is that they provide a plurality of advantages through their longer press nips compared with presses having a conventional press nip. The expression “a conventional press nip” implies in this context, a press nip in which two rigid rolls, having cylindrical cross-section, are cooperating with each other under pressure. However, the dwell time for the fibrous web in this type of press nip is only some few milliseconds because of the short press nip. In a shoe press, wherein the press nip normally is extended to approximately 20 to 30 cm, the dwell time, during which the wet fibrous web is exposed to a pressure, is considerably longer, which results in much higher water flows from the web. Additional advantages, which are achieved in comparison with presses having a conventional press nip and in which, also unlike shoe presses, an effective nip pressure can be obtained only in the press direction, are a higher dry solids content of the web at the same nip pressure, or a more lenient pressing for the web at a lower nip pressure with maintained dry solids content of the web. The latter is especially essential in the manufacture of tissue where a high pressure results in unwanted tissue properties. In the case of production of tissue, which has a low basis weight and which is used for production of household paper, for instance paper towels and other hygiene products, it is important that the bulk, i.e. the relationship between the volume and the weight of the paper, is high because high bulk paper has a desirable combination of softness and high absorption power.
However, it is also of great importance for the final properties of the fibrous web in question that the pressure in the nip is not just regulated in the press direction but also that the nip pressure in the machine direction and across this may be distributed in a suitable way within the press zone between the press shoe and the counter element, i.e. that a certain and defined pressure profile is maintained in every longitudinal section and cross-section within said press zone.
It is known, for instance through the American patent U.S. Pat. No. 4,713,147, see the
FIGS. 2
,
5
and
6
, to successively arrange several independently working arrangements of power devices in the machine direction between the press shoe and a fixed support element for these power devices to try to achieve a suitable distribution of pressure within the press zone between the press shoe and the counter element for the fibrous web in question. Each individual power device arrangement extends across the fibrous web and is thereby so arranged that it is working in the press direction towards the press shoe and thereby also towards the counter element having the fibrous web pressed there between. Then, by varying the pressure from each power device relative to the other power devices, seen in the machine direction, the position for the common pressure resultant force is transferred towards the press shoe in either the downstream or upstream direction and thereby also the distribution of pressure within the press zone. Through the same document, it is also known to alter the position for said pressure resultant force by means of a power device displaceable in the machine direction.
Consequently, all changes of the pressure profile must be done by shifting the configurations of the entire position of the actual power device arrangement in question and/or by adjusting the loads that are loaded against the press shoe by separate transverse rows of power devices, which configurations and/or adjustments first thereafter provide the desired alterations of the pressure profile by a small pivoting in the machine direction of an otherwise entirely fixed press shoe. However, it is desirable that the pressure profile may be set without transferring or adjusting the power device arrangement as an entity, while this is complicated both in a mechanical and control engineering way and which therefore is unfavorable, but which also means an essential change of the actual torque that the support element must endure.
In relation to I-beams, box girders have a higher torsional rigidity but they also have certain disadvantages. For instance, the assembly may become more complicated, which in its turn may make the shoe press construction more expensive. It is therefore desirable to find a shoe press construction that enables the use of an I-beam support element and in which shoe press construction the pressure profile may be changed without any risk for pivoting of said I-beam support element.
For instance, through the European patent application EP-A1-0 345 500 a press is known, in which several power devices are arranged as above, i.e. successively in the machine direction between the press shoe and a fixed support for the power devices, but which power devices each also comprises several press cylinders arranged in a row across the fibrous web and by which the distribution of pressure across the machine direction may be regulated by varying the pressure in each
Alston & Bird LLP
Hastings Karen M.
Metso Paper Karlstad AB
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