EP1069934A1

EP1069934A1 - Pulp filter or washer and sealing for use therein

Info

Publication number: EP1069934A1
Application number: EP99907639A
Authority: EP
Inventors: Jukka Heino; Harri Purontaus
Original assignee: Andritz Oy
Current assignee: Andritz Oy
Priority date: 1998-03-09
Filing date: 1999-03-09
Publication date: 2001-01-24
Also published as: FI990182A0; FI990182A; NO20004529L; NO20004529D0; CA2323049A1; NZ506876A; WO1999046025A1; PL342808A1; CN1302219A; JP2002506143A

Abstract

The present invention relates to a sealing for use in the sealing of a rotating member the sealing being particularly well suitable for sealing of the large-diameter parts of drums used in large wash and filter cylinders, and shafts, of the wood processing industry. The washer in question comprises a stationary outer shell (10), a wash liquid feed chamber (12) disposed inside the shell, which are defined by a perforated plate (16), and a rotating drum disposed inside said surface (16), the drum having a liquid permeable perforated surface (18) whereby the so-called pulp space (20) is defined between said perforated surface (16, 18), the washer being provided at both of its ends with sealing in order to seal the rotating drum mentioned relative to the stationary outer shell, the sealing being formed by a sealing box (26) and a sealing member disposed therein, and it is a characteristic feature of the washer mentioned that the sealing box (26) has been provided with means (40) for introducing pressure medium, preferably liquid, into the sealing box (26).

Description

PULP FILTER OR WASHER AND SEALING FOR USE THEREIN

The present invention relates to a pulp filter or a pulp washer and particularly to a sealing for use in the sealing of the rotating member thereof. The sealing solves well for example problems associated with the sealing of the large-diameter parts of drums used in large wash and filter cylinders of the wood processing industry. In addition to solving the problems in the sealing of drums, the sealing according to the invention is well applicable, for example, also in the sealing of the shafts of drum filters, disc filters and other corresponding filters of the wood processing industry.

A few sealing arrangements used in the sealing of the large-diameter parts of drums used in the large wash and filter cylinders are known, the operation of which in the so-called DRUMDISPLACER washer we use have proved some disadvantages and small problems, which are negligible in view of the operation and use of the apparatus itself. U.S. patent no. 4,795,170 discloses a packing arrangement used in the DRUMDISPLACER^® washers mentioned above. The packing comprises conventional so- called packing fillets four turns or laps of which have been wound around the washer drum in a packing body. The tightening of the packing may be performed in a way known from shaft sealings in the axial direction by means of a tightening ring. However, a drawback of this arrangement is that the tightening performed afterwards is uneven in different sealing turns. As the friction between the sealing ropes and the friction between both the shaft and the sealing box is high, the sealing turns resist the tightening; thus, the first sealing adjacent the tightening ring is compressed and pressed against the shaft while the rest of the sealing turns are compressed much less and the last one hardly at all. Naturally, this results in quick wearing of the first sealing turn and thus leaking of the sealing, or leaking of the sealing because of the too slack tightening.

Another sealing arrangement is disclosed in Finnish patent publication no. 66472 which is based on the use of the well-known old, braided packing rope. In the solution mentioned, the braided rope has been wound around a round piece to be sealed, supported in the axial direction by pressure plates and pressed against the shaft by means of a ring disposed outside the braided rope turns. Liquid brought from an outside pressure source is affecting behind the ring. Thus an even pressure is directed to each braided rope turn as opposed to the so-called packing box solutions, in which the tightening of the packing rope turns is performed in the axial direction. However, the sealing arrangement is despite its positive side very sensitive to damages. The pressure brought from an outside pressure source may for some reason, mechanical breaking, power failure etc.. disappear whereby the pressure prevailing inside the apparatus may easily open the sealing and cause extensive leakage and a long shot-down. It has also been noticed that as the surface of the sealing is not smooth but, as indicated by its name, braided from threads, fibers easily stick between the threads and penetrate gradually between the sealing and the rotating piece and cause leakage.

A problem associated with all the sealing arrangements mentioned above is that the sealing member tends to start rotating with the rotating piece with the result that the sealing efficiency decreases essentially. Thus, the use of various types of sealings and the weaknesses they all have shows that, opposite to what has been expected, this is a difficult sealing task. Based on the pressure difference to be sealed, which is about one bar, one could expect that sealing a point of this type is easy. However, when considering the facts that the sealing must be able to keep both mere liquid and pulp of high consistency (about 15 %) in spaces of their own, that the peripheral speed of the rotating drum is of the order of less than 0.5 m/s, that the temperature variations are between 40 and 100 degrees, and that the dimensions of the drum are necessarily not very accurate, particularly after the heat expansion, it is easy to believe that most sealing types do not meet the requirements set on the sealing.

A solution of the problems described above has been disclosed in Finnish patent no. 912744. The solution comprises a sealing member and a propelling member to be disposed and clamped with a clamping sleeve in a sealing box. The sealing member is placed in the sealing box so that it lies against the surface of a rotating drum. The propelling member on the other hand is supported against the radially outer wall of the sealing box. The sealing member in turn has a T- formed cross section so that the stem portion of the T is disposed in a groove of corresponding size in the propelling member. An essential feature of the sealing member is that the friction between the sealing member and the propelling member is clearly higher than the friction between the sealing member and the surface to be sealed. This is secured in the approach according to this embodiment by arranging a part of the sealing member inside the propelling member. The sealing member is preferably made of plastics material the friction coefficient of which is low and the chemical and temperature resistance are good. The width of the sealing surface in the axial direction is preferably a little smaller than the width of the propelling member so that when the propelling member/members is/are compressed with the clamping sleeve, neither the sleeve nor the back wall can get in touch with the sealing member. The sealing works so that when the sealing element or pair is pressed to its place in the sealing box around the rotating drum the propelling member, which preferably is made of elastic rubber material, is compressed in the axial direction and at the same time tends to expand in the radial direction pressing the sealing member tightly against the rotating piece. The sealing according to the invention can, in a single application, replace two braided sealing rope turns but several sealing elements may be used side by side if desired.

As a preferred further improvement of the embodiment described above, an embodiment is worth mentioning, according to which the propelling member is formed of an annular rubber tube and the sealing member is pressed against the surface of the drum by pressure introduced inside the rubber tube.

There are problems involved also in the approaches described above. Firstly, the ring used as the sealing member made of teflon or corresponding relatively hard plastics material. Secondly, the sealing member while pressed against the surface of the drum creates quite a high force which is revealed, in addition to the heating of the sealing and thus loading and wearing of it, also by wear of the drum surface. The result is in any case a decreased sealing capacity. Further, all the above sealing methods require a special sealing water arrangement bringing clean water to the sealings in order to prevent increase of the friction between the sealing and the surface to be sealed and to prevent heating and breaking down of the sealing. In a way, this is lubrication of the sealing via a separate liquid inlet. Some of the above approaches require also a separate propellant arrangement for providing pressure in the propelling member, either pressurized air or pressurized liquid.

The present invention strives for avoiding the disadvantages of the sealings mentioned above by means of a sealing which has a remarkably longer life than the prior art approaches and the price of which is only a fraction of that of the prior art arrangements.

The characteristic features of the sealing of the invention are disclosed in the appended patent claims.

The arrangement according to the invention provides for example the following advantages over the prior art: • the sealing member cannot rotate with the drum;

• the sealing member conforms readily to the surface to be sealed;

• small friction coefficient relative to the surface to be sealed which results in a small torque whereby

• higher pulp feed pressure may be used ; • higher washing liquid feed pressure may be used;

• in other words, the pulp space may be completely filled also with pulps which are more difficult to treat and the washing becomes more efficient;

• the price of the arrangement is very economical; • the structure is very simple and reliable:

• no pressurized external propellants;

• no special piping for introducing the propellant to the sealing;

• no sealing water, or piping for sealing water, is required

• no plastics components (thus plastics does not end up in the process even if the sealing is broken); • temperature fluctuations do not affect the operation of the sealing (no expanding plastics);

• installation time is shorter because

• there are only two loose components • no vulcanizing of rubbers

• no screw joints of T profiles

• no joints or locking bores of water rings;

• economical design:

• expensive water ring, T profiles and propelling members are avoided; • the arrangement may be applied in modernizations of all existing washers, particularly of DRUMDISPLACER^® washers.

At least some of the advantages mentioned above are reached also when using the sealing arrangement according to the invention in sealing the shafts of washers or disc, cylinder or corresponding filters. Thus, the sealing according to the invention serves both as the sealing of the filter element of the washer or the filter and the sealing of their shaft.

A few preferred embodiment of the sealing according to the invention will be described below with reference to the accompanying drawing figures of which

Fig. 1 illustrates a preferred embodiment of the sealing according to the invention;

Fig. 2 illustrates another preferred embodiment of the sealing according to the invention;

Fig. 3 illustrates a third preferred embodiment of the sealing according to the invention; and Fig. 4 illustrates a fourth preferred embodiment of the sealing according to the invention.

Fig. 1 illustrates one end of a so-called DRUMDISPLACER^® washer, partly in section. The washer in question comprises, as far as the components visible in the figure are concerned, a stationary outer shell 10, a wash liquid feed chamber 12 disposed inside the shell, its end ring 14, and stationary substantially cylindrical perforated plate 16 defining it at the wall by the shaft. The washer further comprises a washing cylinder disposed at a distance inside the perforated plate 16 mentioned, the diameter of the cylinder being of the order of 3 - 5 m and the length 3 - 10 m and the surface of the cylinder being formed correspondingly of a substantially cylindrical perforated plate 18. Between the perforated plate 16 defining the wash liquid feed chamber 12 and the perforated drum plate 18. there is a space 20 preferably divided with axial partition walls (not illustrated) into compartments, into which the fiber suspension to be washed is fed. The space in question is defined on the drum end side by an end cylinder 22 of the drum which in the axial direction extends clearly outside the space 20. A so-called filtrate chamber 24 is located inside the perforated plate 18 of the drum. The washer further includes sealing means for the drum, the sealing means comprising a sealing box 26 defined by the end ring 14 of the feed chamber 12, or a corresponding member, by a sealing box outer ring 28 having a surface 28S to be sealed, by a counter member 30 and the drum end cylinder 22 having a surface 22S to be sealed, and a sealing disposed in the box. In this embodiment, the sealing comprises a bottom ring 32, which may be made of metal, for example steel, or for example of solid rubber, resting against the counter member 30, and a lip sealing 34 provided against the ring. The function of the sealing box 26 at the end of the DRUMDISPLACER^® washer is to seal the pressurized pulp space 20 relative to the outside of the washer. In other words, the objective is to prevent both the pulp and the wash liquid used in washing the pulp from leaking out via the end of the washer.

According to a preferred embodiment of the invention this objective is reached by using a lip sealing 34 in the sealing housing 26 so that pressure medium is brought to the pressurized side of the sealing box 26, i.e. to the side open towards the pulp space 20, which medium presses the lips of the sealing 34 against the surface 22S and 28S to be sealed. The medium in question is preferably washing liquid used in washing the pulp. The pressure medium is introduced to the sealing box at a pressure a little higher than the pressure prevailing in the space 20 so that the flow in the slot 36 between the end ring 14 and the end cylinder 22 takes place from the sealing box 26 toward the pulp space 20. This ensures that fibers cannot penetrate from the pulp space 20 via the slot 36 to the sealing box 26. An essential feature of the invention is that sealing of the drum end is provided by arranging the liquid flow in the slot 36 between the end ring 14 and the end cylinder 22 to take place from the sealing box or corresponding means towards the pulp space. This is effected by introducing liquid to the sealing box at a pressure higher than the pressure in the pulp space 20. Further, the volume of liquid flowing via the slot to the pulp space 20 may be controlled by appropriate adjustment of the slot 36, particularly in relation to the pressures in the sealing box and the pulp space, or the pressure difference.

Fig. 1 also illustrates how washing liquid Wl may be introduced to the feed chamber 12 via a duct 38. The duct 38 has been provided with a branch 40 bringing wash liquid to the sealing box 26 to serve as pressure medium. The branch has preferably been provided with a pressure increasing pump 42, to ensure a pressure difference between the feed chamber 12 and the sealing box 26. The lip sealing 34 has been secured to the bottom ring 32 or through it to the counter member 30 with for example screws or corresponding means.

Fig. 2 illustrates a sealing arrangement according to another preferred embodiment of the invention in which the counter member 30 has been sealed with an O ring 50 relative to the surface 28S and in which a one-sided lip sealing 54, the lip of which is disposed against one of the surfaces to be sealed 22 S, has been secured (in the embodiment illustrated with screws although also other securing means are applicable) to the surface of the counter member 30 facing the sealing box 26. In this case the O ring seals the sealing box 26 between the components 28 and 30, which are stationary in relation to each other, and the lip sealing 54 seals between the stationery counter member 30 and the end cylinder 22 of the rotating drum. The above design works also as such, at least if pressure medium is introduced to the sealing box 26 as illustrated in Fig. 1, which is quite possible. However, the embodiment illustrated in Fig. 2 has been completed by providing an intermediate ring 56, preferably secured with bolts in the sealing box 26 in its end ring 14 at the side facing the pulp space 20 for sealing the slot 36 between the end ring 14 and the end cylinder 22. The function of the intermediate ring 56 mentioned is primarily to adjust the liquid flow from the sealing box or corresponding space to the pulp space to be appropriate, and secondarily to prevent fibers from penetrating from the pulp space 20 to the sealing box 26. The use of the intermediate ring makes possible considering the special properties of each washer. For example, the various pressure differences between the pulp space and the sealing box, which clearly influence the flow in the slot between the intermediate ring and the end cylinder, may be better taken into account by adjusting the slot mentioned by means of for example intermediate rings of different sizes without having to interfere with the dimensioning of the mechanical apparatus, such as the end ring 14, of the washer. In this embodiment, there is also a flushing nozzle 58 provided to open in the slot 36 and to rotate with the drum, through which flushing water is sprayed at a relatively high pressure to the slot 36 in order to blow out fibers which possibly have penetrated into the slot. The design of the nozzle 58 is preferably such that it directs a rotating flushing water jet into the slot 36, whereby the jet washes also the fibers drifted into the area between the nozzle 58 and the intermediate ring 56 off from the slot 36.

Figure 3 illustrates a sealing arrangement according to a third embodiment of the invention in which the counter member 30 has been sealed with an O ring 50 relative to the surface 28S, as in the previous embodiment. In this embodiment the one-sided lip sealing 64 has been secured, preferably with bolts, to the end cylinder 22, i.e. the lip sealing 64 has been secured to a rotating member. The lip of the lip sealing 64 rests against the surface 30S of the counter member 30 facing the sealing box 26. If desired, although not necessarily, and as illustrated in Fig. 3, a wearing ring 66 may be provided in the surface 3 OS of the counter member 30 and the material of the wearing ring may have better wear resistance properties than the material of the counter member 30. The ring 66 may also be replaceable whereby both the elements taking care of the sealing are easy to replace with new ones, for example in a situation where material which wears out the sealing surfaces has flown into the sealing box during unusual operating conditions or because of false running. In a corresponding way, also in connection with other embodiment of this invention, a special wearing surface may be used which is in contact with the lip of the lip sealing and which has either gliding properties or wearing resistance better than the base material. The wearing ring or the wearing surface may of course be replaced by treating the base material so that its wearing and glide properties are improved. Figure 3 also illustrates how a pressure medium duct 40 may be connected to the sealing box 26, as illustrated in Fig. 1, by means of which the lip of the sealing 64 is pressed against the surface 30S of the counter member 30 or the wearing ring 66. The figure further illustrates an intermediate ring 56 as in Fig. 2 although it may be dispensed with and the liquid flow between the sealing box and the pulp space may be arranged appropriate also in the way illustrated in Fig. 1. However, in the case that the pressure of the pressure medium, preferably liquid, introduced into the sealing box 26 is the same as the pressure in the pulp space the use of the intermediate ring 56 is justified.

Figure 4 illustrates yet another embodiment of the invention in which the flushing of the slot 36 between the end ring 14 and the end cylinder 22 has been arranged in a slightly different way than in the embodiments described above. The sealing of the sealing box 26 itself may be provided in practice by any method described in the embodiments above or in fact in any way within the scope of protection of the invention; thus in Fig. 4, the sealing method illustrated in Fig. 2 has been used, as an example. In this embodiment, pressure medium preferably liquid and more preferably pulp washing liquid, is introduced into the sealing box 26, via two routes. So-called sealing water mentioned in association with the previous embodiments is introduces via duct 40 and it is used to press the lip of the lip sealing 54 against the surface 22S to be sealed. In this embodiment, there is a partition wall 72 provided in the sealing box 26, which wall defines a space 74 at the sealing box 26 end adjacent the pulp space 20. A flushing duct 76 leads into the space 74 either in the way illustrated in the figure through the partition wall 72 or directly through the outer ring 28 into the space 74. The partition wall 72 has been sealed relative to the sealing box at both its ends at the sealing box 26 periphery. The partition wall has preferably been secured to the outer ring 28 while, for example, a rubber washer 78 seals the partition wall 72 relative to the surface 28S. The inner edge of the partition wall 72 is sealed by a lip 80 dragging along the surface 22S. The target of the embodiment illustrated in the drawing is to create in the sealing box 26 and the space 74 conditions under which the slot 36 remains clean without the cleaning arrangements illustrated in the previous figures. The idea is to introduce liquid into the space 74 at a pressure higher than the pressure prevailing in the pulp space 20. Then the liquid flow in the slot 36 takes place from the sealing box 26 to the pulp space 20. Liquid is introduced via the duct 40 to another section of the sealing box 26 at a lower pressure but by dimensioning the 10

pressures correctly, conditions are pursued during which some liquid flows also under the lip 80 into the slot 36 according to the ejector principle which would give a sealing well lubricated with liquid at the lip 80 and a sealing ensured with a slightly elevated pressure (friction) at the lip sealing 54 itself.

Materials usable as the lip sealing are EPDM rubber and other corresponding rubber materials. The sealing, a well as the bottom ring possibly used with it, is as uniform as possible. In other words, the structure should have as few joints as possible. Due to the treatment of the sealing, a solution has been tested, in which the sealing comprises two sealing strips of equal length; thus the joints are located at the opposites sides of the drum periphery.

As already was stated above, the sealing according to the present invention is applicable in addition to the sealing of the filter element of the drum washer, i.e. sealing of the end of the drum washer surface, also to the sealing of the shafts of for example drum or disc filters.

Also in most of these applications the object to be sealed is an object having a large diameter, often more than 500 mm, relative to a fiber suspension having a fairly low pressure. The applications described in association with the above embodiments may be modified to serve as shaft sealing by replacing the rotating drum of the embodiments with the rotating shaft of the filter in question.

In addition to the previous examples, the filter or the washer may also be for example a disc filter comprising discs having wire surfaces or being otherwise water permeable, disposed side by side on a horizontal shaft. The shaft with the discs has been placed in a vat so that fiber suspension or other suspension to be filtered in the vat covers the discs at least nearly up to the shaft. In some cases the suspension covers the discs even up to a level above the shaft. 11

The drum filter in turn may be of the same type as the drum washer described above but the structure of the filter may be remarkably simpler. At its simplest, a drum filter is formed of a wire surface secured at its ends to a horizontal shaft, or of a perforated cylinder disposed in a vat containing fiber suspension or some other suspension to be filtered.

Both in disc filters and in drum filters, the filter elements, i.e. discs comprising in most cases adjacent sections, or the drum are supported via the shaft onto the ends of the vat whereby the shaft is mounted on bearings to the ends of the vat and also sealing relative to the end of the vat. In most applications, the washers are atmospheric; thus the pressure directed to the sealing comes from the hydrostatic pressure of the suspension, only. In other words, the pressure of the liquid used for the sealing need not be much higher than atmospheric and it still is capable of preventing the suspension from flowing into the sealing space.

Figure 5 illustrates a shaft sealing according to a preferred embodiment of the invention. The reference numbers used in the drawing are partly the same as in the previous figures. Reference number 28 refers to the outer ring of a sealing box 26 inside which there is a counter member 30 sealed by an O ring 50. The rotating means to be sealed, in this embodiment the shaft, has been assigned the reference number 82. Unlike in the previous embodiments, the sealing members 84 and 86 between the counter member 30 and the end ring 14 have been separated from each other by a spacer 88 which is of the same type as the so-called water ring in the so-called braided sealings. In other words the spacer 88 is a ring having an inlet opening at least at the duct 40 for feeding the sealing liquid into the sealing box 26. Further, unlike in the embodiments in the previous figures, there is a sealing ring 84 having two lips. For all the other parts and function, the sealing illustrated in Fig. 5 corresponds to the disclosure of Figures 1 - 4.

As can be seen from the above description, a new type of a sealing arrangement has been developed which may within the scope of protection defined by the appended patent claims deviate even remarkably from the alternative embodiments described above. It is 12

obvious that the alternative embodiments presented above as examples, only, leave also other corresponding applications for the user to choose from. For example, the drum sealing may be of another type than the lip sealing; in some cases the use of a conventional O ring is very suitable. Thus, all sealing arrangements which comprise the solution defined in the first patent claim are included in the scope of protection of the present invention. Further, the approach according to the invention is well suitable for use also outside the wood processing industry in applications in which large, preferably cylindrical surfaces moving in relation to each other have to be sealed relative to each other.

Claims

13We claim:

1. A filter or a washer comprising mainly a filter element disposed on a horizontal shaft and a vat into which the shaft mentioned has been mounted on bearings and the filter or the washer has been provided at their both ends with a sealing in order to seal the filter element mentioned, the shaft mentioned or both so that leaking of the material to be filtered outside the apparatus is prevented, the sealing being formed of a sealing box (26) and of a sealing member disposed therein, characterized in that the sealing box (26) mentioned has been provided with means (40) for bringing pressure medium, preferably liquid, into the sealing box (26).

2. A filter or a washer as claimed in claim 1, characterized in that the sealing member mentioned is a lip sealing (35, 54, 64).

3. A filter or a washer as claimed in claim 1 or 2, characterized in that the medium mentioned is water Wl used for washing the material to be treated, or recycled filtrate.

4. A filter or a washer as claimed in claim lor 2, characterized in that the pressure of the pressure medium mentioned is higher than the pressure in the space (20) containing material to be treated.

5. A filter or a washer as claimed in claim 1 or 2, characterized in that the sealing box (26) has been divided with a partition wall (72) into two compartments and pressure medium is brought into both of these.

6. A filter or a washer as claimed in claim 5, characterized in that the partition wall (72) mentioned is sealed at both its edges, i.e. it has been sealed both relative to the outer ring (28) of the sealing box (26) and either the surface (22S) of the filter element end cylinder (22) or the surface of the shaft. 14

7. A filter or a washer as claimed in claim 5, characterized in that the pressure of the medium in the part of the sealing box (26) facing the space containing material to be treated (i.e. space 74) is higher than the pressure in the space containing material to be treated.

8. A filter or a washer as claimed in claim 2, characterized in that the sealing box (26) is defined by the end ring (14) of the feed chamber (12), the outer ring (28) of the sealing box, either the end cylinder (22) of the rotating filter element or the shaft and the counter member (30), and that the lip sealing (64) mentioned has been secured either to the end cylinder (22) of the rotating filter element or to the shaft.

9. A filter or a washer as claimed in claim 8, characterized in that the counter member (30) of the sealing box (26) has been provided at the lip of the lip sealing (64) with a ring (66), or its surface against the lip of the lip sealing (64) has been treated in order to improve its wear and/or glide properties.

10. A filter or a washer as claimed in claim 2, characterized in that the sealing box (26) is defined by the end ring (14) of the feed chamber (12), the outer ring (28) of the sealing box, either the end cylinder (22) of the rotating filter element or the shaft and the counter member (30), and that the lip sealing (34, 54) mentioned has been secured to the counter member (30).

11. A filter or a washer as claimed in claim 2, characterized in that the sealing box (26) is defined by the end ring (14) of the feed chamber (12), the outer ring (28) of the sealing box, either the end cylinder (22) of the rotating filter element or the shaft and the counter member (30), and that the lip sealing (34, 54) mentioned has been secured to the counter member (30) via a bottom ring (32).

12. A filter or a washer as claimed in claim 10 or 11, characterized in that either the surface (22S) of the end cylinder (22) of the rotating filter element or the surface of the shaft has been provided with a ring at the lip of the lip sealing (34, 54). 15

13. A filter or a washer as claimed in claim 1 or 2, characterized in that the sealing box (26) is defined at its end facing the space (20) containing material to be treated by an end ring (14) to which an intermediate ring (56) has been secured for controlling the flow in the slot between the sealing box (26) and the space (20) containing material to be treated.

14. A sealing for sealing a rotating surface, preferably the drum of a fiber suspension drum washer or a drum filter, or the shaft of a disc filter or a drum filter or a drum washer, the sealing being disposed in a sealing box (26) between the rotating cylinderlike piece (22) and the outer shell surrounding it, or part thereof, characterized in that the sealing mentioned is a lip sealing (54).

15. A sealing as claimed in claim 14, characterized in that the lip sealing(34, 54) mentioned (64) has been secured to the sealing box (26).

16. A sealing as claimed in claim 14, characterized in that the lip sealing mentioned (64) has been secured to the rotating cylinder-like piece (22).

17. A sealing as claimed in claim 14, characterized in that the surface facing the lip of the lip sealing mentioned (34, 54, 64) has been either treated in order to improve its glide and/or wear properties, or a special wearing ring or surface (66) has been provided in the surface in question.