GB2197667A

GB2197667A - Wet press method

Info

Publication number: GB2197667A
Application number: GB08727001A
Authority: GB
Inventors: Nils Soderholm
Original assignee: Tampella Oy AB
Current assignee: Tampella Oy AB
Priority date: 1986-11-20
Filing date: 1987-11-18
Publication date: 1988-05-25
Anticipated expiration: 2007-11-18
Also published as: SE8704236D0; GB8727001D0; FI864735A0; FI90097B; SE467624B; GB2197667B; CA1314166C; DE3737332A1; SE8704236L; DE3737332C2; FI90097C; FI864735A

Description

2197667 1 A method for use in the press section of a paper machine The

invention relates to a method for use in the press section of a paper machine, wherein a web to be dried is led through the press section by closed feeding by passing it through nips between press rolls so that the web is constantly in contact with the surface of at least one felt, and wherein the web is led through at least two nips removing water from the web, one nip-being formed between two press rolls having a separate felt loop and the other between a suction roll provided with the separate felt loop and belongiig to the first nip as one press roll thereof and a third press roll having a separate felt loop.

This kind of press method is well-known in connection with paper machines. An example of a known method is the method described in U.S. Patent Specification 4 272 316. In this known method the nips are formed by three press rolls in such a manner that a suction roll forming the middlemost press roll forms one of the press rolls in both nips. Each one of the three press rolls is provided with a separate felt loop, so that the web to be dried is positioned between two felts in both nips.

A drawback of this known method is that the web to be dried is passed on to a subsequent treating step between two felts, i.e. in such a manner that after having passed through the nip the web makes contact with a felt moving around the suction roll. This results in rewetting problems, whereby the water removed from the web to the felt during the pressing tends to return to the web after the nip.

However, this method has been used, because it has been taken for granted in the art that the web 2 cannot be detached from the surface of a felt after having been sucked thereto without damaging the web surface. A compromise has thereby been resorted to by accepting the rewetting of the web due to the fact that it is simpler to remove the moistness than to repair a damaged web surface.

other examples of slightly different applications include the methods disclosed in Finnish Patent Specifications 50 652 and 66 666. These methods differ from the method of U.S. Patent Specification 4 272 316 in that one of the nips is formed between a third press roll which does not have a felt loop and a suction roll having a felt loop.

A drawback of the above methods is the diffi cult use thereof since the web feeding, for instance, is difficult to carry out. In addition, these known methods provide poor drainage properties. In this kind of prior press methods, difficulties arise in the web feeding at running speeds exceeding 10 m/s.

The present invention aims to provide a method by means of which the drawbacks of the prior art can be eliminated.

The present invention accordingly provides a method for use in the press section of a paper machine, wherein a web to be dried is led through the press section by closed feeding by passing it through nips between press rolls so that the web is constantly in contact with the surface of at least one felt, and wherein the web is led through at least two nips removing water between two and the other the separate from the web, one nip being formed press rolls having a separate felt loop between a suction roll provided with felt loop and belonging to the first nip as one press roll thereof and a third press roll having a separate felt loop wherein the web is after the second nip separated at least from the surface of the felt moving around the suction roll belonging to the first nip.

A major advantage of the method according to the invention is that a press utilizing the method can be operated even at running speeds exceeding 1000 m/min and nevertheless the drying degree is higher than with known methods. Improvement in the drying degree is due to the partial prevention of the rewetting phenomenon. The method according to the invention is also convenient for the operator because, for instance, there are no such web feeding problems as with 4 known methods. This is due to the closed feeding of the web. Another advantage of the invention is that it can be carried out flexibly so that the invention can also be advantageously taken into use in connection with existing press methods.

The invention will be described in the following in more detail with reference to the preferred embodiments shown in the attached drawings, in which:- Figure 1 is a general side view of a press section of a paper machine utilizing the method according to the invention, and Figure 2 illustrates another embodiment of the method according to the invention in the press section of a paper machine.

In the example of Figure 1, a web 1 to be dried is led to the press section on a wire 3 moving around a roll 2. The web 1 to be dried is detached from the wire 3 by means of a roll 4. The web 1 is detached from the wire 3 by suction from within the roll 4. After having been detached, the web is passed forwards on a felt 5 moving around the roll 4.

The web 1 positioned on the felt 5 is led on to the felt 6 so as to be positioned between the felts 5 and 6.

The web 1 is transported between the felts 5 and 6 to a first nip N1 which is formed between press rolls 7 and 8. The felt 5 is thus arranged to move both around the roll 4 and the press roll 8. The felt 6, in turn, is arranged to move around the press roll 7. The press roll 8 is a suction roll and a grip zone 9 thereof sucks the web 1 into contact with the felt 5, whereby the web is detached from the surface of the felt 6 and is passed on the felt 5 towards a second nip N2 formed between the press roll 8 and a third press roll 10.

1 The third press roll 10 is provided with a separate felt loop formed by a felt 11. At the second nip N the web 1 to be dried is positioned between the felts 5 and 11.

After the nip N2 the web 1 is separated from the surface of the felt moving around the press roll 8, so that the rewetting is prevented.

The web 1 is passed on towards a subsequent treating step on the surface of the felt 11 moving around the third press roll 10. The subsequent treating step may thereby be e.g. a subsequent press 12 formed by rolls 13, 14. The rolls 13, 14 preferably form an extended press zone N3, a so called extended nip. The felt 11 is thereby preferably arranged to move around the press roll 14, too. The press roll 13 is provided with a separate felt loop 15 as is conventional. The moisture transferred to the felt 11 in the second nip can be removed prior to the press 12 e.g. by means of a felt suction box 16.

The embodiment of Figure 1 is preferably used when the invention is applied to a new apparatus, i.e. in cases where the utilization of the invention has been taken into consideration from the very beginning of the planning of the new apparatus.

The embodiment sho,n in Figure 2 can be utilized in an existing apparatus. The example of Figure 2 is fully similar to that of Figure 1 up to the second nip. Accordingly, the same reference numerals as in Figure 1 have been used in Figure 2 at'corresponding points.

The web 1 to be dried is brought to the nip N1 quite similarly as is described above in connection with Figure 1. The loops of the felts 5, 6 are arranged similarly as in the example of Figure 1. The nips N1, N2 are formed in the same way as in Figure 1, 6 i.e. by means of the press rolls 7, 8 and 10. The press roll 8 is a suction roll.

The example of Figure 2 differs from that of Figure 1 in that a felt 110 moving around the third press roll 10 is a separate felt which does not move around a press roll 14 of the subsequent press 12. The press roll 14 is thus provided with a separate felt loop 111.

In the armngffrent of Figure 2, the web to be dried is after the nip N1 first separated from the surface of the felt 5 and thereafter also from the surface of the felt 110 moving around the third press roll 10. The web 1 is thereby forwarded by open feeding to a subsequent treating step which may be e.g. the subsequent press 12. In this embodiment the press rolls 13, 14 of the press 12 are have separate felt loops 15, 111. The rolls 13, 14 preferably form an extended press zone N3, a so called extended nip.

The arra-)gaTent of Figure 2 can be especially advantageously applied to existing apparatuses by providing these with the felt 110 moving around the third press roll. The structures of the press 12 need not be modified.

The above embodiments are by no means intended to restrict the invention, but the invention can, of course, be modified in various ways within the scope of the claims. Accordingly, it is obvious that when applying the method according to the invention, the felt loops need not be exactly similar to those shown in the figures but other kind of arrargments are possible as well. Naturally, any suitable arrangffnents can be used in the press rolls and in the guide rolls of the felts, etc.

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Claims

C 1 a i m s:

1. A method for use in the press section of a paper machine, wherein a web to be dried is led through the press section by closed feeding by passing it through nips between press rolls so that the web is constantly in contact with the surface of at least one felt, and wherein the web is led through at least two nips removing water from the web, one nip being formed between two press rolls having a separate felt loop and the other between a suction roll provided with the separate felt loop and belonging to the first nip as one press roll thereof and a third press roll having a separate felt loop wherein the web is after the second nip separated at least from the surface of the felt moving around the suction roll belonging to the first nip.

2. A method according to claim 1, wherein the web is separated only from the surface of the felt moving around the suction roll belonging to the first nip and is led to a subsequent treating step on the surface of the felt moving around the third press roll.

3. A method according to claim 1, wherein the web is first separated from the surface of the felt moving around the suction roll belonging to the first nip and thereafter also from the surface of the felt moving around the third press roll whereafter the web is led to a subsequent treating step by open feeding known per se.

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4. A method the subsequent an extended

5.

according to claim 2 or 3, wherein treating step is a press comprising press zone.

A method for use in the press section of a paper machine substantially as hereinbefore describeO with reference to Figure 1 or Figure 2.