Ferrum AG, CH-5102 Rupperswil, Switzerland
A seal arrangement for a centrifuge
The invention relates to a solution for the bearing of a drive shaft for a rotatable basket as well as to the sealing of this bearing. The rotatable basked is a component of a centrifuge, in particular of a scraper centrifuge of the vertical type.
A centrifuge of this type is an example for a means for the carrying out of a separation of a solid/liquid mixture into its solid and liquid components. During centrifuging, a separation process for the separation of solid components from a liquid, the solid/liquid mixture is set into rotation. The centrifugal forces acting on the solid and on the liquid result in an increase in the sedimentation speed. In contrast to the sedimentation of the solid components of the mixture by the gravity acting on the particles, the solid particles are moved away from the axis of rotation by the action of centrifugal forces in a plane normal to the axis of rotation. The particles are collected in a filter mounted rotationally symmetrically around the axis of rotation. The filter is disposed in the jacket of a basket made in cylindrical manner in most cases or, alternatively thereto, the basket itself is designed as a filter. The basket contains passage openings for the liquid which is catapulted away from the outer wall of the basket in the direction of the stationary housing of the centrifuge. The following process steps

take place in a separation process for the separation of the solid components of the solid/liquid mixture in a centrifuge:
The centrifuge is filled via a filling device such as a filling pipe with a solution which contains solid particles to be separated. The solution is conveyed into the interior of the basket. In a further step, a centrifuging step takes place for the separation of the liquid from the solid particles. The particles are deposited as a cake on the inner side of the outer wall of the basket, the liquid is discharged through openings provided for this purpose in the basket and is collected in a container surrounding the basket. The filter cake can be cleaned of solvent residues by a washing process. Washing liquid is sprayed onto the filter cake. The washing liquid is driven out of the filter cake by the rotation. In addition, any solvent residues present in the filter cake are flushed out by the washing process. Solvents of this type should in many cases not be detectable in the filter cake for health reasons or ecological reasons or from the points of view of flammability of the product and its further processing capability. After the washing process, the filter cake is removed from the inner side of the outer wall of the basket, which is termed scraping in the technical world. For this purpose, a scraping means travels along the inner wall of the slowly rotating basket and removes the filter cake. The filter cake leaves the centrifuge space in a vertical scraper centrifuge with downward discharge through openings in the centrifuge base. Subsequently, the inner side of the outer wall of the basket is cleaned so that residual layers can be removed.
A seal arrangement is known from the prior art for a rotatable basket of a vertical centrifuge comprising a drive shaft which is arranged along a substantially vertical axis of rotation of the rotatable basket. The basket includes a basket hub, with the basket hub being

rotationally fixedly connected to the drive shaft and supporting the rotatable basket. A first bearing serves for the absorption of the forces arising through the rotary movement of the basket. At least one second bearing serves for the absorption of the forces acting in the direction of the axis of rotation. The drive shaft is journalled in a stationary housing part of the centrifuge which should be termed a flute tube in the following. The flute tube extends along at least a part of the drive shaft. The first and the second bearings are arranged between the drive shaft and the flute tube.
It is furthermore known from the prior art to provide a gap between the stationary flute tube and the rotating basket hub. The force-transmitting bearings are arranged at the end of the drive shaft coupled to the storage basket hub. A guide bearing is arranged in the vicinity of the end of the drive shaft and is connected to the drive apparatus. A V-belt pulley is typically flanged to this end of the drive shaft and supports a V-belt which is driven by an electric motor. The guide bearing is thus located between the drive shaft and the flute tube. The inner diameter of the flute tube is accordingly only negligibly smaller than the outer diameter of the bearings attached to the drive shaft.
A problem which occurs with a seal arrangement in accordance with the prior art is that the shaft is subjected both to torsional and bending strain. In addition, the shaft must also absorb dynamic forces which are introduced through the movement of the storage basket into the shaft. In particular with fast-running centrifuges with speeds in the range from 700 to 2,700 rpm, a high alternating bending stress results which requires a sufficient dimensioning of the shaft. The required shaft diameter then requires the selection of correspondingly large bearings, which also makes the inner diameter of the basket hub

larger. Accordingly, in solutions from the prior art, it is necessary to arrange the bearings directly on the shaft, since considerable peripheral speeds result due to their inner diameters. Furthermore, seals must likewise be arranged directly on the shaft or via sleeves having the smallest possible diameters and moving along with the shaft. Such a high frictional heat arises in the seal due to the increase in the peripheral speed as a result of the required permitted shaft diameter that it cannot even be reduced to the permitted amount via a grease lubrication of the seal so that the seal material fails. Even lip seals of PTFE are only resistant in temperature ranges of up to 250°C with grease lubrication, with failure due to oxidation reactions (burning of the seal) occurring above said ranges.
The construction solution from the prior art consists of arranging the seals at the shaft in direct proximity to the suspension of the basket, whereby it is ensured that the peripheral speed in the seal region remains below the peripheral speed permitted as a maximum for the seal. A solution is obtained by this construction limitation in which the seals are arranged between the shaft and a stationary housing part, a component termed a flute tube in the following. The seals are arranged in direct proximity to the bearings so that the shaft section to be sealed is limited as much as possible to the section between the bearing on the drive side and the bearing or bearings in proximity to the suspension of the storage basket. The seal thus has the function of sealing the bearing against impurities and of sealing against the discharge of lubricant which is required for the lubrication of the bearings. Lubricant is transported to the bearings by means of lubricant bores at the interior of the flute tube. These lubricant bores are disadvantageous since their manufacture is associated with a high effort and/or cost. In particular with centrifuges with larger dimensions in which shafts are used with a total length of more than

1,000 mm, the bores of long passages with low diameters are complex in manufacture from a technical aspect. In addition, these bores must be designed such that a blockage is to be precluded in operation since otherwise the dismantling of the storage basket and of the bearings themselves is necessary for a cleaning of the lubricant bores under certain circumstances.
A further disadvantage is based on the fact that impurities of all kinds can enter into the bearing space due to the gap in accordance with the embodiment of the prior art. These impurities in particular arise due to particles which enter into the gap on the unloading of the centrifuge and by flushing or cleaning agents. On product changes, it is necessary to flush the whole centrifuge space. The inner centrifuge space is flooded so that dust, impurities and the like can enter into the gap between the basket hub and the flute tube and remain there so that the intermediate space can clog between the rotatable basket and the flute tube. As a result, not only can difficulties occur on startup due to increased frictional resistances, in particular with hard, crystalline products, which can result in an introduction of force into the bearings due to dynamic forces in operation which result in non-permitted bearing strains which can in extreme cases lead to the failure of the bearings, but also a contamination of the product can occur due to dirt particles which are carried out of the gap during operation. The contamination of the product in particular has to be fully precluded for the food industry and for pharmaceutical products. However, with the construction solution in accordance with the prior art, the gap is necessarily present between the storage basket hub and the flute tube. A sealing of the gap is not possible, on the one hand, due to the high peripheral speed of the storage basket, since the problem described above would occur. On the other hand, the sealing is also not successful because the storage basket is supported in a

cantilever manner on the shaft, which has the result that the storage basket undergoes deflections of up to some millimetres around its rest position in operation. The lip seals with the highest performance, however, permit a dynamic eccentricity of a maximum of 0.1 mm at 1,000 rpm. This eccentricity reduces further as the speed increases so that only a maximum of 0.05 mm can be tolerated at 3,000 rpm. It results on the basis of the aforesaid statements that an open gap between the flute tube and the basket hub cannot be avoided from a construction manner at present.
A further problem of the impurities is represented by the corrosion which can affect all parts of the bearing block, that is the totality of flute tube, bearings, seals and connection parts for fastening and centring of the same, in particular when blockages caused by impurities of this type are not accessible to inspection without a dismantling of the basket from the drive shaft or even of the bearing block. The corrosion can also affect the sealings of the bearings when acting on operating media in the very acidic or basic range so that the seals can also be affected in permanent operation, whereby a long-term sealing of the shaft bearings cannot be ensured. Seals of PFTE are admittedly said to have a sufficient resistance to chemicals, but abrasive particles in combination with chemically reactive substances, with frictional forces arising due to the high peripheral speeds, represent a high strain for any seal, in particular when highly reactive substances of this type act permanently on the seal over a longer period.
It is therefore known from the prior art to provide flushing nozzles in the gap between the cylinder drum hub and the bearing block. The arrangement of these flushing nozzles is complex due to the limited available space in the bearing block. In addition, the flushing nozzles

can become unusable due to clogging caused by impurities so that all the problems set forth up to now can also occur with this improved solution. For the aforesaid reasons, a flushing and/or a flooding of the intermediate space between the basket hub and the bearing block is disadvantageous because the gap is not easily accessible for cleaning and subsequent inspection and, consequently, correspondingly long refitting times must be anticipated. A product change can only take place for products to be used e.g. in the pharmaceutical industry or in the food industry when it can be proven that no traces of the preceding batch or other impurities can be detected in the apparatus processing the product. A gap in which such product residues and/or impurities can accumulate is therefore to be avoided as far as possible. If it should not be possible to dispense with a gap of this type for construction reasons, as the preceding example of the centrifuge shows, it is necessary in accordance with the regulations for pharmaceutical products or precursor stages of pharmaceutical products to prove the complete cleaning of the gap by means of an analytical process which reproduces the actual relationships in the gap, for example by determination of the concentration and/or of the composition of the impurities. Within the frame of a test of this kind, for example, a sample is taken from one of the surfaces bounding the gap and the degree of purity is determined via laboratory analyses.
An analysis of this type is practically not possible without the complete dismantling of the basket and of the bearing block of the centrifuge in accordance with the embodiment of the prior art. The design of the bearing block is preset by the mechanical strain by the operation in the hypercritical speed range and the multiple passing through the critical speed range of the drive shaft. Ensuring the required running smoothness in operation thus requires the greatest possible care in the dismantling of the bearing block and of the

basket. The total refitting time for a new product, which includes the previously described cleaning and analysis, makes up a substantial portion, if not the main portion, of the cycle time, in particular when small batches of different respective products types have to be centrifuged. Accordingly, the centrifuge remains in an unproductive non-operating state over long periods, which results in a substantial cost disadvantage.
It is therefore an object of the invention to screen the intermediate space between the cylinder drum hub and the bearing block such that an entry of impurities into the intermediate space is stopped.
It is a further object of the invention to reduce the force components acting on the shaft.
The object is satisfied by the characterising portion of claim 1. The seal arrangement in accordance with claim 1 for a basket of a centrifuge arranged around an axis of rotation includes the basket which, via a basket hub and via a suspension of the basket, to a drive shaft coupled to a drive unit extending along the axis of rotation (6) in a bearing block. A seal for the sealing of a gap between the bearing block (and the basket hub is provided between the basket hub and the bearing block at the drive side.
Combined static and dynamic forces act on the drive shaft in the operating state. The dynamic forces include time-variable forces. The imbalance force can, however, also be subject to changes caused by operation, which can, inter alia, have the following cause. A filter cake is deposited in the basket on a progressing separation of the solid/liquid mixture, with it not to be expected that the filter cake is always distributed uniformly over the total periphery of the basket.

The centre of mass of the filter cake will therefore generally not come to lie at the symmetry axis of the basket, that is the axis of rotation of the drive shaft. This dynamic force, that is time variable force, which generally increases as the degree of deposition increases, is likewise introduced into the flute tube via the bearings so that the drive shaft does not have to absorb this force, as will be described in the following preferred embodiments.
In accordance with a preferred embodiment for the seal arrangement, the basket is supported in the bearing block such that a bearing force caused by dynamic forces is substantially decoupled from the drive shaft.
In accordance with a preferred embodiment, at least one first bearing is provided for the seal arrangement for the absorption of the dynamic forces created by the rotary movement of the basket and at least one second bearing is provided for the guidance of the drive shaft.
The seal arrangement includes, in accordance with a preferred embodiment, the bearing block and a flute tube which is arranged coaxially around the drive shaft. At least one of the bearings is arranged between the flute tube and the basket hub.
In accordance with a preferred embodiment for the seal arrangement, the basket hub is rotationally fixedly fastened to a first end of the drive shaft via the suspension of the basket. At least the second bearing is arranged in the vicinity of a second end on the drive shaft or the flute tube, with the second end being able to be coupled to a drive unit.

In accordance with a preferred embodiment for the seal arrangement, the drive shaft is arranged along the substantially vertical axis of rotation. The drive shaft in particular has a shaft diameter in a range from 10 to 300 mm, the shaft diameter specifically lies between 10 and 150 mm, preferably in a range from 50 to 150 mm, and the drive shaft has a length of 400 to 1,500 mm, in particular 400 to 1,000 mm, specifically 500 to 800 mm, preferably 600 to 700 mm, with the diameter of the basket lying in a range from 300 to 2,500 mm, in particular amounting to 300 to 2,000 mm, preferably lying in a range from 400 to 1,600 mm.
Due to the arrangement of the bearings, horizontal forces and imbalance forces of the bearing basket are absorbed by the flute tube. The drive shaft can essentially be designed for the absorption of torsion forces which are introduced by the drive means on the starting up and shutting down of the centrifuge, which has the result that the sufficiency can be found on its dimensioning with a substantially lower shaft diameter so that the shaft diameter can be reduced to up to one third with respect to the original shaft diameter.
Due to the reduction of the shaft diameter, a smaller diameter of the flute tube as well as lower peripheral speeds result, which, on the one hand, contributes to the increase of the service life of the bearings and, on the other hand, substantially reduces the peripheral speeds between resting and moving running surfaces to be sealed on the flute tube, drive shaft and/or basket hub so that completely new seal arrangements result.
The basket hub is supported on the flute tube, which not least results in an improvement of the running properties of the basket hub, since the basket hub can be supported at the flute tube over its total length,

whereby the guidance of the basket hub is ensured. The basket hub is supported along its total length by the support of the basket hub in the flute tube. This support has the consequence that substantially tighter tolerances can be realised between the basket hub and the flute tube so that the sealing of the gap between the basket hub and the flute tube is made possible at all. The running smoothness of the basket hub can be increased by this support since a cantilever support of the basket hub can be dispensed with.
The reduced outer diameters also result in a reduction in the peripheral speeds so that the frictional heat arising in the operating state is reduced, whereby lip seals can be used for the sealing of the gap.
The revolutions of the basket lie in the range from 500 to 3,000 rpm. A range from 750 to 1,600 rpm is in particular preferred, with normal bearing lubrication being considered sufficient for up to 900 rpm and oil-lubricated bearings being able to be used above 900 rpm.
In accordance with a preferred embodiment for the seal arrangement, the gap can extend at least from the first to the second bearing.
In accordance with a preferred embodiment, the basket includes at least one discharge opening for the conveying out of the filter cake which is located in the vicinity of the gap, with a penetration of dust and/or particles and/or droplets and/or gases being able to be prevented by the seal.
In accordance with a preferred embodiment for the seal arrangement, a bearing lubrication can be carried out by a bore in the flute tube

which can be connected to a lubricant supply means outside the basket of the centrifuge.
In accordance with a preferred embodiment for the seal arrangement, there is a seal between a moving running surface arranged on a jacket surface of the basket hub and an oppositely arranged stationary running surface which is formed on the jacket surface of the flute tube.
In accordance with a preferred embodiment for the seal arrangement, at least one of the seals is made as a shaft seal and/or as a lip seal and/or as a peripheral seal.
In accordance with a preferred embodiment for the seal arrangement, the lip seal is arranged around an outer jacket surface of the basket hub.
In accordance with a preferred embodiment for the seal arrangement, the peripheral speed in the operating state at the contact surface of the seal to the moving running surface lies below 100 m/s, in particular below 75 m/s, specifically below 50 m/s, preferably below 40 m/s with grease lubrication, and/or amounts to a maximum of 10/ms, in particular a maximum of 5 m/s, particularly preferably a maximum of 1 m/s with a dry run.
In accordance with a preferred embodiment for the seal arrangement, intertisation means are provided for the generation and maintenance of an inert gas atmosphere in the space inside the basket hub enclosed by the seals.

In particular a vertical centrifuge can be provided with a seal arrangement in accordance with one of the preceding embodiments. A vertically positioned centrifuge is in particular suitable for small to medium batches with frequently changing product specifications, whereas a horizontally positioned, filtering scraper centrifuge is preferably used for high throughputs of constantly occurring suspensions in permanent operation. The area of application of filtering centrifuges covers a wide range of particle sizes from 0.1 to 10,000 pm, in particular 1 to 5,000 |um, preferably 1 to 1,000 |um. The suspensions to be centrifuged in particular have a solid content of more than 10%, preferably more than 20%, specifically more than 25%.
Sealing problems of this type occur with vertical centrifuges with both top discharging and bottom discharging since filter cake material can always move into the gap between the storage basket hub and the flute tube of the drive shaft because it is a case of small, light particles such as fine dust or emulsions or the like.
The invention will be explained in more detail with reference to the drawing. There are shown:
Fig. 1 a seal arrangement for a centrifuge of the prior art
Fig. 2 a section through a seal arrangement for a centrifuge in
accordance with the invention
Fig. 3 a detail of the seal arrangement in accordance with Fig. 2.
Fig. 4 a total view of a vertical centrifuge in accordance with the
invention with a drive unit.

It should be stated in advance that reference numerals above 100 belong to embodiments which have already been disclosed in the prior art.
In the preferred embodiment of the prior art shown in Fig. 1, the seal arrangement includes a basket 101 which is rotationally fixedly connected to a drive shaft 103 via a suspension 121. The suspension 121 is located at a first end 110 of the drive shaft which has a conical shape in this embodiment. The conical shape was selected to achieve weakening phenomena of the drive shaft 103 by a notch effect which is as low as possible. Every direct diameter transition of the drive shaft 103 is termed a weakening phenomenon which results in local load peaks under the effect of a load, with these load peaks corresponding to the effect of a notch. The drive shaft does not only have to absorb the total load of the basket 101 as well as the torsional forces, but also the dynamic forces which arise due to the rotary movement of the basket and/or of the drive shaft 103 itself. A periodically fluctuating alternating bending stress is introduced into the shaft by these dynamic forces which can result in fatigue failures, with it being known that fatigue failures of this type often have their starts in construction notches such as shaft shoulders with small transition radii. The suspension 121 is secured against rotation by means of a securing element 138. The securing element 138 is positioned by means of a cover 139. The drive shaft is rotatable about its axis of rotation 106 by means of a drive unit 112 not shown in more detail. A rotation of the drive shaft 103 can thus be transmitted via the suspension 121 of the basket 101 to a basket hub 102 and/or via a rib structure 126 to the jacket of the basket. The basket 121 is accordingly made as a rotationally symmetrical component whose axis of rotation coincides with the axis of rotation 106 of the drive shaft.

The drive shaft 103 is journalled in a bearing block 122 which includes a flute tube 104 in addition to the bearings (107, 108, 109). The bearing block 122 furthermore includes a seal 118, with three shaft seals being arranged sequentially in the embodiment shown. The seal 118 is received in a reception means 120 which is fastened to the flute tube via a screw connection 130. The reception means 120 is designed as a series of flanges which each receive one shaft seal so that, on assembly, the flanges can be stacked over one another without gaps and can be sealed by means of a termination element 131 and/or sleeve elements with respect to impurities which can be located in the gap 113. The sealing action also includes a sealing with respect to the discharge into the gap 113 of lubricant which is used for the lubrication of the bearings. Sealing elements 132 such as O rings can be provided between the flanges and/or between the flanges and the terminating element 131 or the sleeve element 133. A connector element 134 rotationally fixedly connected to the drive shaft 103 is provided with a running surface which is designed in its surface quality such that the seal 118 designed as a shaft seal can slide over this surface without being heated in a non-permitted manner by frictional heat. It is advantageous to arrange the running surface on the connector element 134 since the manufacture of the running surface on this connector element 134 can take place substantially more simply and more cost effectively than on the drive shaft itself. However, positioning means 135 for the connector element 134 have to be provided which permit a fixing of the connector element 134 on the drive shaft. High demands are made on the shape and position tolerances of this connector element since it must be ensured, on the one hand, that no central offset occurs between the drive shaft and the connector element 134 so that the sealing effect of the seal is ensured and non-permitted pressing pressures do not act on the seal at any point which can result in a reduced sealing effect

and/or an overheating of the seal. On the other hand, the mass distribution of the connector element 134 can be made such that the centre of mass lies on the axis of rotation of the drive shaft 106 so that no dynamic forces, in particular no imbalance forces, are introduced into the shaft. The required precision in production results in the total bearing block becoming more expensive.
It is additionally necessary to provide a cleaning possibility to clean the gap 113 periodically from impurities or to prevent impurities from moving into the gap 113 by means of a continuously usable flushing process. In the embodiment shown, an infeed for a cleaning agent is shown which is designed as a tube 136 through which a cleaning agent is introduced into a peripheral bore 137 which is arranged in the boring block 122 between the reception means 120 and the terminating element 131. Additional sealing elements 132 are required to seal the peripheral bore 137 such that the penetration of cleaning agents into the bearing regions is avoided. Nozzles, not shown, are arranged in the terminating element 131 so that cleaning agent can be discharged into the gap 113.
Instead of a periodic cleaning, provision can also be made to introduce an inert gas continuously into the gap 113 via the tube 136 described and the peripheral bore 137 by means of nozzles. The gap is continuously flushed with inert gas so that impurities are carried out of the gap 113 with the flushing flow. This variant is used when reactive media are subjected to centrifuging so that there is the risk of unwanted chemical reactions or even explosions.
The embodiment of the seal arrangement in accordance with the invention shown in Fig. 2 consists of a basket 1 of a centrifuge, in particular of a vertical centrifuge with bottom discharge, said basket 1

being arranged rotatably, via a basket hub 2, around an axis of rotation 6 and being rotationally fixedly connected, via a basket hub 2 and via a suspension 21 of the basket 1, to a drive shaft 3 coupled to a drive unit 12 extending along the axis of rotation 6 in a bearing block (4, 7, 8, 9, 20, 24). A seal (18, 19) for the sealing of a gap 13 between the bearing block (4, 7, 8, 9, 20, 24) and the basket hub 2 is provided between the basket hub 2 and the bearing block (4, 7, 8, 9, 20, 24) at the drive side.
In the preferred embodiment shown in Fig. 2 and Fig. 3, the seal arrangement includes a basket 1 which is rotationally fixedly connected to a drive shaft 3 via a suspension 21. The suspension 21 is located at a first end 10 of the drive shaft which has a cylindrical shoulder in this embodiment. The suspension is rotationally fixedly connected to the first end 10 of the drive shaft 3 by means of a key. The key connection is preferably selected since it requires a low effort in production and can consequently be produced more cost effectively. Due to the decoupling of dynamic and/or quasi-static forces of the basket from the torsional forces introduced into the drive shaft by the drive unit, which was described above, the drive shaft is at best only exposed to alternating bending stresses which are of no weight with respect to the torsional forces so that a non-permitted strain of the construction notches can be precluded. Cost-effective construction alternatives thus arise in the design of the drive shaft which were not available due to the combined strain of the drive shaft such as is known from the prior art. Alternatively to this, provision can be made for the seat of the suspension 21 of the storage basket 1 to have a conical shape such as was disclosed in the embodiment of the prior art. The conical shape is selected to achieve weakening phenomena of the drive shaft 3 by a notch effect which is as low as possible. The drive shape must admittedly absorb the total load of the basket 1 as

well as the torsional forces and also any dynamic forces which occur due to the rotary movement of the drive shaft 3 itself when the centre of mass of the drive shaft does not lie on the axis of rotation. A periodically fluctuating alternating bending stress is introduced into the drive shaft by these dynamic forces which can result in fatigue failures, with it being known that fatigue failures of this type often have their starts in construction notches. A variant having a conical drive shaft part for the reception of the suspension 21 of the basket is thus in particular suitable for large centrifuges in which the weight forces of the drive shaft 3 cannot be neglected with respect to the torsional forces. The suspension 21 is secured against rotation by means of a securing element analogously to the embodiment shown in Fig. 1. The securing element and the suspension 21 of the basket 1 are positioned by means of a cover.
The drive shaft is rotatable about its axis of rotation 6 by means of a drive unit 12 not shown in more detail. An electric motor is in particular provided as the drive unit 12 and can be flanged directly to the drive shaft or, alternatively to this, can be coupled to the drive shaft 6 by means of a transmission apparatus, in particular a belt drive 11. A rotation of the drive shaft 3 can thus be transmitted via the suspension 21 of the basket 1 to a basket hub 2 and/or via a rib structure 26 to the jacket 27 of the basket 1. The basket 21 is accordingly made as a rotationally symmetrical component whose axis of rotation substantially coincides with the axis of rotation 6 of the drive shaft. The drive shaft 3 is journalled in a bearing block 22 which includes a flute tube 4 in addition to the bearings (7, 8, 9).
The arrangement of the bearings (7, 8, 9) differs considerably from the prior art since the seal arrangement in accordance with Fig. 2 or Fig. 3 for a basket 1 of a centrifuge which is arranged rotatably about an

axis of rotation 6 such that the basket 1 is rotationally fixedly connected, via a basket hub 2 and via a suspension 21 of the basket 1, to a drive shaft 3 coupled to a drive unit 12 extending along the axis of rotation (6) in a bearing block (4, 7, 8, 9, 20, 24) in that the basket 1 is supported in the bearing block (4, 7, 8, 9, 20, 24) such that a bearing force caused by dynamic forces is substantially decoupled from the drive shaft 3. In the present embodiment, the two bearings (7, 8) are thus arranged between the flute tube 4 and the basket hub 2. The bearings (7, 8) are attached, where possible, in the vicinity of the first end 10 of the drive shaft 3 so that the largest possible running smoothness of the rotating storage basket 1 is ensured. The dynamic forces which result from the movement of the basket are introduced into the flute tube 4 via the bearings (7, 8). In particular imbalance forces are to be understood by these dynamic forces. These imbalance forces are variable in time during the start-up of the centrifuge and during the shut-down phase. During the stationary operation of the centrifuge, the imbalance force can be subject to periodic fluctuations due to a non-rotationally symmetrical mass distribution of the basket 1 and can vary due to reloading of the centrifuge. The period duration corresponds to one rotation of the drive shaft. Imbalance forces which are variable in time can also act on the bearings in addition to these periodically fluctuating imbalance forces due to the non-uniform distribution of the separated material on the jacket 27 of the basket 1 and/or due to non-uniform liquid discharge through the openings in the jacket 27 of the basket. All these forces are now, however, no longer absorbed by the drive shaft 3. The advantage results from this that a drive shaft 3 with a substantially smaller outer diameter can be used than was possible with a centrifuge of the same construction and of the same size in the prior art.

The bearing 9 is essentially a guide bearing and serves for the introduction of radial forces, which can be caused by the movement of the basket hub 2, into the flute tube 4. The bearing 9 is also advantageously arranged between the basket hub 2 and the flute tube
The bearing block 22 furthermore includes a seal 18, with a shaft seal being arranged as close as possible to the inlet opening into the gap 13 in the embodiment shown such that the bearing 9 can be sealed with respect to impurities which move into the gap 13 through the inlet opening. The seal 18 is arranged between a stationary running surface 17, which is part of the flute tube 4, and a moving running surface 14, which is made as part of the basket hub 2 or as a sleeve element 28 rotationally fixedly connected to the basket hub 2. The part of the gap 13 lying upstream and still freely accessible for particles from the filter cake 5 can be sealed by a further seal which is made as a lip seal 19 so that it appears that no gap at all would be present for the filter cake to be conveyed out of the basket. The lip seal 19 is received in a reception means 20 which is fastened to the flute tube via a screw connection 29. The reception means 20 is in particular made as part of a tube or as part of a sleeve in which recesses are provided for the reception of at least one lip seal 19. The recess serves as a holder for the lip seal 19, with the base surface of the recess forming a stationary running surface 16 on which a lip of the lip seal 19 lies. The assembly of the reception means 20 takes place such that the reception means is attached to the flute tube 4 directly by means of a screw connection or to the flute tube 4 via a flange connection 23. The gap 13 is sealed against impurities by the two seals (18, 19). The seal 19 is advantageously formed at the outer side of a sleeve element 28 which is rotationally fixedly connected to the basket hub 2. A moving running surface 15 extends between the

seal 19 and the sleeve element 28 so that the seal 19 can slide over this moving running surface 15. The advantage of the arrangement of the seals 18 and 19 on oppositely disposed sides of the sleeve element 28 is due to the fact that a labyrinth-like passage forms between the two seals. Any individual dirt particles passing the lip seal can thus already be captured in the labyrinth-like passage so that they do not even reach the seal 18. A certain sealing effect is thus provided by the labyrinth-like passage. A sleeve element (28) is provided because it permits a simple production of the moving running surfaces (14, 15). In particular with a small centrifuge, at least the seal 18 can also be provided directly between the flute tube 4 and the basket hub 2 because the frictional heat arising at the lower peripheral speeds is too low to effect a non-permitted heating of the seal so that such high demands also do not have to be made on the surface quality of the moving running surface (14, 15).
A complex and/or expensive construction including sealing elements 132 (see Fig. 1) between the flanges and/or between the flanges and the terminating element 131 or sleeve element 133, such as is described in the prior art, thus becomes obsolete. The connector element 134 which is rotationally fixedly connected to the drive shaft 103 and which was fitted with a moving running surface which likewise required a high surface quality so that the seal 118 designed as a shaft seal can slide over this surface without heating too much in a non-permitted manner due to frictional heat is also no longer necessary since the seals (18, 19) can be arranged at the gap entry.
In accordance with the embodiment of Fig. 2 or Fig. 3, it is no longer necessary to provide a cleaning possibility to periodically clean the gap 13 of impurities or to prevent impurities from moving into the gap 13 by means of a continuously usable flushing process. The seals can be

arranged at the gap entry due to the force decoupling and to the accordingly resulting reduction in the diameter of the drive shaft 3 and of the flute tube 4 so that particles of the filter cake to be conveyed out can no longer "see" a gap 13 and thus the risk of any contamination of the bearing arrangement can be precluded.
The variant also becomes superfluous of introducing an inert gas through the tube 136 described in Fig. 1 and the peripheral bore 137 into the gap 113 continuously by means of nozzles in order to continuously flush the gap with inert gas so that impurities are conveyed out of the gap 113 with the flushing stream since no impurities can enter into the gap 13 during operation and in the assembled state. The centrifuge in accordance with the invention is thus possible for use for reactive and/or explosive media without the aforesaid complicated and/or expensive flushing because the risk of unwanted chemical reactions or even explosions no longer exists as long as the function of the seals is ensured due to the sealing of the region of the seal arrangement. The seals are relatively easily accessible for an inspection so that the maintenance of the centrifuge is also simplified.
Fig. 4 shows a total view of a sealing arrangement of a vertical centrifuge. The storage basket 1 is shown in the unloaded state in this case. Discharge openings for a liquid are shown over the surface of the storage basket, said liquid leaving the basket due to the centrifuging through the discharge openings and being able to be collected in the housing which is arranged around the basket 1. The basket 1 includes the basket hub 2 which is supported on the flute tube 4 by means of the seal arrangement in accordance with the invention. The drive shaft 3 is rotationally fixedly connected to the basket 1 and is driven via a V-belt drive by an electric motor serving as the drive unit.

The V-belt drive can be dispensed with in a variant not shown. The drive motor in this case is directly connected to the drive shaft 3 by means of a flange connection.
Reference numeral list
1. basket
2. basket hub
3. drive shaft
4. flute tube
5. filter cake
6. axis of rotation
7. bearing
8. bearing
9. bearing
10. first end of the drive shaft
11. second end of the drive shaft
12. drive unit
13. gap
14. moving running surface
15. moving running surface
16. stationary running surface
17. stationary running surface
18. shaft seal
19. lip seal
20. reception means
21. suspension
22. bearing block
23. flange connection
24. flange
25. connection means
26. rib structure
27. jacket
28. sleeve element
29. screw connection
Reference numeral list for the prior art (Fig. 1)
101. basket
102. basket hub
103. drive shaft
104. flute tube
105. filter cake
106. axis of rotation
107. bearing
108. bearing
109. bearing
110. first end of the drive shaft
111. second end of the drive shaft
112. drive unit
113. gap
114. moving running surface
115. moving running surface
116. stationary running surface
117. stationary running surface
118. shaft seal
119. lip seal
120. reception means
121. suspension
122. bearing block
123. flange connection
124. flange
125. connection means
126. rib structure
127. jacket

130. screw connection
131. terminating element
132. sealing element
133. sleeve element
134. connector element
135. positioning means for connector element
136. passage
137. peripheral bore
138. securing element
139. cover

Claims
1. A seal arrangement for a basket (1) of a centrifuge, said basket
(1) being rotatably arranged around an axis of rotation (6) and rotationally fixedly connected, via a basket hub (2) and via a suspension (21) of the basket (1), to a drive shaft (3) coupled to a drive unit (12) extending along the axis of rotation (6) in a bearing block (4, 7, 8, 9, 20, 24), characterised in that a seal (18, 19) is provided at the drive side between the basket hub (2) and the bearing block (4, 7, 8, 9, 20, 24) for the sealing of a gap (13) between the bearing block (4, 7, 8, 9, 20, 24) and the basket hub (2).
2. A seal arrangement in accordance with any one of the preceding
claims, wherein the basket (1) is supported in the bearing block
(4, 7, 8, 9, 20, 24) such that a bearing force caused by dynamic
forces is substantially decoupled from the drive shaft (3).
3. A seal arrangement in accordance with any one of the preceding
claims, wherein at least one first bearing (7, 8) is provided for the
reception of the dynamic forces arising by the rotary movement
of the basket and at least one second bearing (9) is provided for
the guidance of the drive shaft (3).
4. A seal arrangement in accordance with any one of the preceding
claims, wherein the bearing block (4, 7, 8, 9, 20, 24) includes a
flute tube (4) which is coaxially arranged around the drive shaft
(3), and wherein at least one of the bearings (7, 8, 9) is arranged
between the flute tube (4) and the basket hub (2).

5. A seal arrangement in accordance with any one of the preceding
claims, wherein the basket hub (2) is rotationally fixedly fastened
to a first end (10) of the drive shaft via the suspension (21) of the
basket (1) and at least the second bearing (9) is arranged in the
vicinity of a second end (11) on the drive shaft or the flute tube
(4), with the second end (11) being able to be coupled to a drive
unit (12).
6. A seal arrangement in accordance with any one of the preceding
claims, wherein the drive shaft (3) is arranged along the
substantially vertical axis of rotation (6), the drive shaft in
particular has a shaft diameter in a range from 10 to 300 mm,
the shaft diameter specifically lies between 10 and 150 mm,
preferably in a range from 50 to 150 mm, and the drive shaft has
a length from 400 to 1,500 mm, in particular 400 to 1,000 mm,
specifically 500 to 800 mm, preferably 600 to 700 mm, with the
diameter of the basket lying in a range from 300 to 2,500 mm, in
particular amounting to 300 to 2,000 mm, preferably lying in a
range from 400 to 1,600 mm.
7. A seal arrangement in accordance with any one of the preceding
claims, wherein the gap (13) extends at least from the first
bearing (7, 8) to the second bearing (9).
8. A seal arrangement in accordance with any one of the preceding
claims, wherein the basket (1) includes at least one discharge
opening for the conveying out of the filter cake which is located
in the vicinity of the gap (13), with a penetration of dust and/or
particles and/or droplets and/or gases being able to be
prevented by the seal (18, 19).

9. A seal arrangement in accordance with any one of the preceding
claims, wherein a bearing lubrication can be carried out through
a bore in the flute tube (4) which can be connected to a lubricant
supply means outside the basket (1) of the centrifuge.
10. A seal arrangement in accordance with any one of the preceding
claims, wherein a seal (18, 19) is arranged between a moving
running surface, which is formed on a jacket surface of the
basket hub (2) and an oppositely disposed stationary running
surface (16, 17) which is formed on the jacket surface of the flute
tube.
11. A seal arrangement in accordance with any one of the preceding
claims, wherein at least one of the seals (18, 19) is made as a
shaft seal and/or as a lip seal and/or as a peripheral seal.
12. A seal arrangement in accordance with any one of the preceding
claims, wherein the lip seal is arranged around an outer jacket
surface of the basket hub (2).
13. A seal arrangement in accordance with any one of the preceding
claims, wherein the peripheral speed in the operating state at the
contact surface of the seal with the moving running surface lies
below 100 m/s, in particular below 75m/s, specifically below 50
m/s, preferably below 40 m/s with grease lubrication and/or
amounts to a maximum of 10 m/s, in particular to a maximum
of 5 m/s, preferably to a maximum of 1 m/s on a dry run.
14. A seal arrangement in accordance with any one of the preceding
claims, wherein intertisation means are provided for the

generation and maintenance of an inert gas atmosphere in the space inside the basket hub (2) enclosed by the seals (18, 19).
15. A vertical centrifuge having a bearing arrangement in accordance with any one of the precedin