Suction rolls are used in paper machines on the one hand to gather water from the paper web, on the other hand to direct the paper web in the roller groups. By setting a vacuum inside the mantle of the perforated suction roll, the paper web can be made to stay in the desired way on the surface of the suction roll. The necessary vacuum is produced by vacuum chambers, which are confined between the mantle and the suction box with seal organs that cover the whole of the operating length of the suction roll. These seal organs each have a sealing that extends to the inner face of the mantle, and there are two or more of them inside one suction roll. The seal is quickly used up when constantly pressed against the inner face of the mantle. Several pressing and regulation devices have been developed primarily for the purpose of reducing the wearing of the seal. For example, the sealing presented in the solution of FI patent application number 955275 includes loading hoses. In this solution the seal is pressed onto the mantle with one loading hose, and it is slightly pressed back with the other hose while locking the sealing onto place. The principle is thus to lock the seal a small distance away from the mantle after the starting of the suction roll, whereby the wearing of the seal is essentially reduced.

Due to the bend of the suction box, the elastic limit of the seal comes quickly to an end. One of the problems of the present seals is in fact that they only give a small elastic movement length. It has not been possible to reduce the scale of the suction box and therefore the whole suction roll, because it has only been possible to allow the suction box a slight bend.

In order to reduce the wearing of seals, the abovementioned known solution has been carried out in a very complex way. Loading devices that include several components add to the risk of malfunctions. In addition, loading devices need to be manufactured accurately in order to function, which adds to the manufacturing and servicing expenses and further to the risk of malfunctions. The operating distance of loading devices is also limited, whereby they are only suited to sealings of a certain height.

The object of the invention is to produce a simple suction roll sealing that is suitable for different sealing heights, the mantle load of which can be regulated and with which it is possible to achieve an essentially wider elastic limit than at present. The characteristic features of a method according to the invention are presented in the accompanying patent claim 1 and the characteristic features of a suction roll sealing that uses the method are presented in patent claim 2. According to the present invention the seal itself operates as part of the loading device, whereby the sealing structure is more simple.

The loading hoses and other earlier facilities thus become useless when the pressure effect of the pressure medium is applied straight onto the lower surface of the seal. In addition to pressing the sealing against the mantle, it can be moved in the way desired in its holder. At the same time, however, the characteristics of the sealing stay the same irrespective of its wearing. Already existing holders can further be used in the installation of a sealing according to the invention, and the life of the seal can be lengthened simply by adding to its height.

In the following, the invention is presented in detail with reference to the accompanying figures that present one applica- tion of the invention, in which Figure 1 schematically presents sealings according to the invention as installed inside a suction roll, Figure 2 presents the cross section of a sealing according to the invention as seen from the compressed-air connec- tion, Figure 3 presents the cross section of a sealing according to the invention as seen from the end at the level of the surface of the sealing, Figure 4 presents another application as seen from the end as in figure 3 Figure 1 presents one roller group in a paper machine. In the process, the paper web 10 is directed from in between the suction roll 11 and its first counter roll 12 onto the suction roll 11. The paper web 10 is directed farther from the suction roll 11 through another counter roll 13. The sealing 14 according to the invention is attached to the suction box 15, which is situated inside the suction roll 11. In the example, there are three sealings 14 organised inside the suction roll 11 in the area between nips 16 and 17 formed by the suction roll 11 and the counter rolls 12 and 13. These sealings form the necessary vacuum chambers 18 and 19. In addition to directing the paper web 10, the suction roll 11 is used to remove humidity from the paper web 10.

Figure 2 presents a sealing 14 according to the invention in its operational position. A cross section of the ordinary holder 20 forms a U-shape. It has been manufactured from a cold-rolled steelplate, whereby its surfaces are naturally even. The glide surfaces only need little polishing. The holder 20 is attached to the structure of the suction box 15 from its other side. The holder 20 that is essentially of the same length as the suction roll 11 bends together with the suction box. The actual sealing 21 has been fitted tightly although

movably onto the holder 20. The wear surface 21.1 of the sealing 1 glides along the inner face of the mantle 23.

According to the invention, the holder 20, the lower surface 21.2 of the sealing 21 and the space 22 limited by them have been set to cooperate and to thereby form a loading device.

Thus no separate loading hoses or other spacers are needed in order to load the sealing 21. The sealing 21 that is profitably formed out of graphite rubber can be attached to the mantle 23 of the suction roll 11 simply by leading pressurised air through the connection 24 to the abovementioned space 22. The sealing 21 is further profitably sealed to the holder 20 with an o-ring band 25, which has been fitted to the grooves 26 on the lower surface of the sealing 21. The o-ring sealing 25 is sealed onto the inner surfaces 28 of the holder 20 in the manner shown in figure 2. The space 22 between the holder 20 and the sealing 21 has also been sealed in the end parts of the holder 20, which is discussed in more detail in relation to figure 3.

When the paper web 10 comes on top of the suction zone between nips 16 and 17, a vacuum rises in the vacuum chambers 18 and 19. In practice, the vacuum that operates in the suction holes sucks the sealing 21 against the mantle 23 although the pressure is removed from underneath the sealing 21. Hereby the sealing 21 rubs against the suction roll 11 with its wear surface 21.1 even though the pressure has been removed, and is used up at the same time. In order to reduce this wearing, a vacuum is formed according to the invention in the space 22 limited by the sealing 21 and the holder 20, by which vacuum the sealing 21 is pulled from is lower surface 21.2 away from the suction roll 11. In other words, a vacuum that neutralizes the effect of the suction that is directed towards the wear surface 21.1 is formed underneath the sealing 21, on the lower surface 21.2. The necessary vacuum is lower than the pressure that operates inside the suction roll, because the area of operation at the upper end of the sealing 21 is smaller due to the perforation of the suction roll 11. Normally the share of holes on the surface of the suction roll 11 on its operational

length is about 25*-.. Thereby a fourth of the vacuum that operates in the vacuum chamber is needed in the operating situation to neutralize the effect of suction. The effect of the auxiliary sealing 25 on need of the vacuum is slight.

In order to direct a suitable pressure underneath the sealing 21, the holder 20 contains at least one connection 24, which has been connected to the necessary valves and pressure regulators (not shown.) Profitably, each sealing has its own valve, whereby it is possible to compensate for the different circumstances of the sealings.

Figure 3 presents the holder 20 of the sealing 14 according to the invention in cross section. In order to enable the expan- sion of the sealing 21 during the operation, the holder 20 is, as is well known, open from its ends. Therefore the sealing of the end of the sealing 21 has to be made at the bottom 27 and on the sides 28 of the holder 20. One possible solution is presented in figure 3. Here an end sealing 30 that is essen- tially of the same width as the holder 20 is fitted to the groove 29 at the end of the sealing 21, which end sealing directs the auxiliary sealing 25 along the inner surfaces 27 and 28 of the holder 20 underneath the sealing 21. Furthermore, the end sealing 30 adapts to the movement of the sealing 21. In order to ensure the sealing, the seal organ 30 is loaded by a spring 31. In this solution, the vertical and horizontal movement of the sealing 21 does not affect the sealing.

Figure 4 presents an improved type of the end sealing. Func- tionally similar parts are presented by the same reference numbers as in figure 3. The bottom 27 of the holder 20 is cut open at the end of the holder, and the sides 28 are extended downwards. A flange 32 works as a continuation of the bottom 27. A rubber strip 33 is fitted onto the end of the sealing 21, which strip overlaps a certain distance with the auxiliary sealing 25 on the sides of the sealing 21. In order for this to happen, the rubber strip 33 extends farther on the sides along the sealing 21 than the middle part. When somewhat pressed, the

rubber strip 33 is of the same width as the inner space of the holder 20 and it is attached from one end with a bolt 26 to the flange 32. Hereby the rubber strip 33 fully closes the space 22 towards the end still allowing for the movement and heat expansion of the sealing 21.

The solution according to the invention is best suited to the second sealing in the direction of the entrance, and to latter sealings, and in some circumstances also to the first sealing.

It is possible to modify the structure to suit existing suction boxes without any significant alteration to the suction box.

The lightening of the load that has an effect on the sealing essentially lengthens the life of the sealing and further the servicing intervals. The service life can further be lengthened by sealings that are higher than normal, because it is possible e. g. by removing the loading hose to increase the wear height of the sealing by about 5 mm. The sealing according to the invention can in principle be used as long as it stays in its holder, supposing that an adequate sealing effect remains.