Screen wheel filter device for high-pressure filtration of a plastic melt

Abstract

Sieve wheel filter device (100) for the high-pressure filtration of a plastic melt, at least comprising a housing (10) which has at least: - an inlet plate (11) with at least one inlet channel (13), - an outlet plate (12) with at least one outlet channel (14); - at least one spacer element (15, 16, 17) arranged between the inlet plate (11) and the outlet plate (12) and a bearing ring (18) on which a sieve wheel (20) arranged between the inlet plate (11) and the outlet plate (12) is rotatably mounted, where: - the screening wheel (20) has a plurality of screening points (22.1 ... 22.13), each of which can be positioned and flowed through between the inlet and outlet channels (13, 14), - a lubricating gap is formed between the sieve wheel (20) and the inlet plate (12) and between the sieve wheel (20) and the outlet plate (12), - the inlet channel (13) and the outlet channel (14) each have a funnel mouth (13.1, 14.1) widening towards the screening wheel (20), between which a flow-through region (40) is formed; characterized by - that at least one radial pressure relief flow path is formed within at least one lubricating gap, which crosses an inner annular sealing web (23) of the screen wheel (20) and which extends between the flow-through region (40) and at least one pressure relief bore (42), - that the at least one pressure relief bore (42) is formed in the inlet plate (11) or in the outlet plate (12) and opens at the bearing ring (18) and - that the pressure relief bore (42) is fluidly connected to a relief opening (48) on the outside of the housing (10) via a pressure relief channel (42.1) formed in the housing (10).

Description

[0001] The invention relates to a filtering device for the high-pressure filtration of a plastic melt, having the features of the preamble of claim 1.

[0002] When filtering plastic melts, agglomerates or solid particles must be filtered out before the melt can be fed into a further processing system, such as an extrusion device with a nozzle. To ensure uninterrupted production, various types of filtering devices are available that allow the replacement of a filter screen during operation by inserting a new, uncontaminated screen into the flow channel and removing the contaminated one. A particular difficulty in filtering plastic melts is that it must be carried out at high temperatures and high pressures, which even in normal applications range between 250 bar and 300 bar.

[0003] A generic filtration device was fundamentally described in DE 3302343 A1 and EP 0 569 866 A1 and has been continuously improved since then. It enables the filtration of plastic melts and other medium- to high-viscosity fluids, whereby the distinction from low-viscosity media is determined by its design. The sieve wheel, which carries the individual sieve elements, is positioned between two housing plates that are held at a certain distance from each other so that, on the one hand, the sieve wheel can still be rotated and, on the other hand, the gap between the sealing surfaces of the sieve wheel and the adjacent sealing surfaces of the housing plates is so narrow in relation to the viscosity of the filtered medium that no leakage flows occur, which form in the gap open towards the outside.In short, a sieve wheel filtration device does not provide a hermetic seal to the outside; instead, the gap width is kept so small that the medium cannot flow along the gap to the outside due to its viscosity. Low-viscosity, aqueous media cannot be processed due to the open design.

[0004] DE 33 41 508 A1 also shows another filtering device of this type, which also discloses a drive device. This consists of a drive element in the form of a hydraulic cylinder attached to a side edge of the housing, a transmission lever, and a freewheel unit consisting of a pinion that engages with an external toothing of the sieve wheel and a freewheel that allows a return movement of the transmission lever without moving the sieve disc.

[0005] Other screening devices with a rotating screen wheel with multiple screening positions are known, for example, from DE 87 16 626 U1 or EP 0 287 048 A2. Special measures to increase leak tightness in high-pressure applications are not specified.

[0006] In the screening device disclosed in DE102016113979 B3, the tightness is increased by providing special force ratios in the plates braced against each other, whereby the gap width between the fixed housing elements and the movable screening wheel in the area of ​​the sealing surfaces is kept small and, consequently, leakage flows are limited.

[0007] DE 39 02 061 A1 describes a screening device with a screen wheel for cleaning plastic melts in a high-pressure press. A backflushing device is provided to remove dirt adhering to the screen elements by flowing through them from the rear side of the screen elements, i.e., from the outflow side of the screening device. A lockable flushing channel is provided for this purpose. Despite mentioning the application in connection with high-pressure presses, no measures are mentioned to increase leak tightness in high-pressure applications.

[0008] DE 35 22 050 A1 shows a drive via a ratchet toothing on the outer circumference of the sieve wheel and a feed ram that engages with the toothing to move the sieve wheel step by step.

[0009] The particular advantages of this type of filtration device are that a large number of individual sieves can be placed on the sieve wheel, through which the fluid flows successively and which are easily accessible for cleaning or replacement on the side facing away from the flow channel. The construction of the filtration device is also simple and cost-effective due to the layered construction of the housing.

[0010] The main difficulty, however, lies in the sealing between the outer housing plates and the screen wheel enclosed between them. The housing parts must be clamped against each other, including the screen wheel, in such a way that the flow pressure does not cause the housing to expand too much and thus prevent corresponding leaks from forming through which excessive fluid escapes at the side edges of the housing. On the other hand, the screen wheel must be permanently mobile and can no longer rotate if it is clamped too tightly. Therefore, in all operating conditions, a certain minimum gap width must be maintained between the end sealing surfaces on the screen wheel and the opposing contact surfaces on the inlet and outlet plates. The required gap width also depends on the fluid to be processed and its viscosity, the processing temperature and the flow pressure in the area of ​​the screening point.While a fundamental aim is to ensure tightness, a sufficient gap width is always required to allow a very small escape of the fluid over the sealing webs and to form a kind of lubricating film on both ends of the screen wheel by the fluid itself.

[0011] Appropriate adjustment of the height of the screen wheel and the height of the spacer elements, which are also positioned between the inlet and outlet plates and enclose the screen wheel, allows for the setting of a gap width specific to the intended processing process. However, this gap width is in the range of a few micrometers, making the manufacture of the spacer elements and the associated screen wheel, which together form the so-called inner pairing inserted between the inlet and outlet plates, very difficult. Practice has shown that even with very careful calculation and manufacture of the gap widths, problems arise regarding the mobility of the screen wheel, which can only be remedied by reducing the preload, which in turn leads to the problem of leaks.

[0012] In the known, modern concepts of a screen wheel filtration device, at least two screen points are simultaneously located in the cross-sectional area through which the material flows, which is referred to below as the flow area. The flow area is the area of ​​​​surface against which the material flows from the front and can be used for filtration. Typically, a first screen point partially overlaps the flow area, so that the operating pressure builds up in the incoming screen cavity. Another screen point is positioned completely or almost completely within the flow area. Part of the second screen point or part of a third screen point is located at the upper edge, viewed in the direction of rotation, in partial overlap with the flow area.However, the screen cavities intersected by the flow area, which move into or out of it, are fully under operating pressure, even if their surface overlap with the flow area is only a small one. Therefore, the pressure range is larger than the flow area, enabling largely constant pressure operation of the filtration device, since there is no angular position of the screen wheel in which the flow path is completely or significantly interrupted.

[0013] The plastic enclosed in the thus-sealed screening area remains under operating pressure of up to 500 bar. This means that not only the area directly through which the fluid flows and the adjacent surface areas of those screening areas that are partially overlapping the flow area are under pressure, but also those screening cavities that have already moved out of the pressure area. Assuming a typical number of at least 10 screening areas, in particular 13 screening areas, on the screening wheel, the pressurized area extends in the direction of rotation between a first screening area that has just partially overlapped the flow area, up to the last screening area before entering a screen change position.Consequently, more than half of the screening points arranged on the screen wheel are under high internal pressure and contribute to the widening of the lubrication gap and cause leakage flows.

[0014] DE 10 2017 100 032 A1 describes the relationships that arise with regard to the geometry of the screen gap during operation. The gap width is not a geometrically constant value during operation, since the gap is prepared by the internal pressure during filtration. By inserting a gap width adjustment layer between the spacer elements and one of the adjacent housing plates, a specific operating point can be set so that, on the one hand, the gap is large enough to be filled with the fluid, which also serves as a lubricant, and to enable the movement of the screen wheel, and, on the other hand, that the gap width is limited in relation to the maximum internal pressure during operation to such an extent that no major leakage flows occur.Uncontrolled leakage flows should be avoided to prevent components located on the outside of the filtration device, such as measuring sensors, a pivoting door on a screen changing station, or the drive for the step-by-step rotation of the screen wheel, from being affected by escaping fluid that solidifies on the outside. Such an adjustment of the operating point is readily possible for typical operating pressures of approximately 250 bar, up to a maximum of 300 bar, particularly by inserting a gap width adjustment layer. This should allow the screen wheel to move freely in a virtually pressureless state, while preventing or reducing leakage flows at maximum operating pressure.

[0015] The difficulty of adapting to a specific operating condition therefore lies not in designing the filtration device for a specific, narrowly constant operating point, but in ensuring operation in the range from 0 bar to the maximum operating pressure. Here, the known concepts reach their limits at the stated maximum pressures of 250 bar to 300 bar.

[0016] The object of the present invention is therefore to provide a high-pressure sieve wheel filtration device in which, without individual adjustment of the preload before or during operation, the functionality of the filtration device is to be ensured in a pressureless state as well as in another operating point in which the fluid is pressed through the filtration device at a high pressure of up to 500 bar or more.

[0017] This object is achieved by a sieve wheel filter device for the high-pressure filtration of a plastic melt having the features of claim 1.

[0018] The inventive concept provides for radial pressure relief flow paths. "Radial" in this sense refers to a flow from the position of the screen cavities inward toward the center or outward toward the outer circumference, overflowing an annular sealing surface on the screen wheel that defines the screen cavities, without the flow direction having to be strictly radial in the geometric sense.

[0019] In particular, the bearing ring on which the screen wheel is slidingly mounted can be used for further pressure relief. Plastic melt that flows through the screen gap widened near the pressure area enters the bearing ring, which is basically the intention for the purpose of forming a plain bearing. During high-pressure operation, however, more plastic melt locally enters the area of ​​the bearing ring than is needed there for lubrication. To prevent axial leakage flows from forming along the bearing ring, which then exit at the front of the housing inlet or outlet plate, at least one additional pressure relief bore is provided, which is preferably located at an angular position adjacent to the flow area or below it, up to a maximum of the lower low point of the bearing ring.For example, if the strainer location is at a 3 o'clock position, with 12 o'clock being the top of the housing and 6 o'clock being the bottom of the housing, then the radial pressure relief hole is preferably located at a position between 2 o'clock and 6 o'clock.

[0020] A further preferred embodiment of the invention provides for the additional provision of at least one pressure relief bore in the housing, which opens into the track swept by the screening points during rotation of the screen wheel and is fluidly connected to an outer side of the housing via a flow channel. The area near the pressure relief bore thus forms a pressure sink, and a tangential flow path is created, which extends essentially from the pressurized, enclosed screen cavity in the direction of rotation.

[0021] As a result, the screen cavities that were previously flowing through and are still under pressure when they are moved out of the flow zone are suddenly relieved of pressure. As a result, only the screen areas directly flowing through cause the housing to expand and the gap between the screen wheel and the adjacent housing plates to increase. However, there are no screen chambers that remain pressurized for a longer period of time, which would contribute to the expansion of the housing outside the pressure zone and where pressure reduction is only possible gradually through leakage flows.

[0022] The tangential pressure relief provided by the invention is achieved in such a way that the screening point located at the front and top in the direction of rotation overlaps the opening of a pressure relief bore as soon as this screening point has completely left the pressure zone and there is no longer any flow connection with the area through which the flow occurs. For this purpose, the geometric design ensures that the pressure relief bore opens into the track swept by the screening points as the screen wheel rotates and is fluidly connected to the outside of the housing via a flow channel. It is essential that the distance between the opening of the pressure relief bore and the front, upper edge of the funnel mouth of the inlet and outlet channels, viewed in the direction of rotation, is always greater than the maximum arc length of the screening points.This means that the screen cavity is initially completely separated from the area through which the fluid flows and that the screen wheel must then be turned slightly further until a flow connection can be established between the closed, but still pressurized, screen cavity and the pressure relief hole.

[0023] Since plastic melts are compressible, pressure relief occurs automatically as a small amount of plastic melt escapes and is drained through the pressure relief hole. Once the pressure equalization is complete, the flow of plastic melt from the screen cavity abruptly stops, meaning the screen cavity remains filled.

[0024] By deliberately causing a one-time pressure relief of each contaminated screening point according to the preferred embodiment, the number of pressurized screening cavities can be limited to a maximum of three, of which at least two are in partial overlap with the flow area during operation and one is moved to the pressure relief bore.

[0025] Since pressure relief requires the removal of small amounts of the plastic fluid compressed in the screening area, the preferred method is to discharge the fluid from the pressure relief bore through a pressure relief channel that leads to the backwash area usually located on the underside of the screen wheel filtering device. The backwash device can loosen dirt particles adhering to the screen elements. This requires the removal of the plastic melt along with the dirt particles, keeping the underside of the filtering device free of other equipment and providing suitable collecting devices there.

[0026] In particular, the pressure relief hole is provided on the side of the inlet plate. The backwash channel and the pressure relief channels should, if possible, end in the same area of ​​the filtration device, namely in its lower area, as this allows the material to be directed directly from there by gravity into a collection container located below the filtration device.

[0027] It is also possible to provide at least one pressure relief hole on the outlet plate side, since cleaned melt is present there, and to connect the pressure relief hole directly to the depressurized part of the backflushing channel in the housing outlet plate. This allows the necessary backflushing of the screen insert elements in the screen cavities to be at least partially achieved with the amount of plastic melt that was diverted via the tangential flow path for pressure relief. Thus, the fluid escaping intermittently for pressure relief can perform an additional function, and the power of the backflushing device's drive mechanism, which, for example, moves a piston to perform the backflushing, can be reduced. In addition, less melt needs to be diverted from the production stream for backflushing.In a sieve wheel filter device which is already equipped with a backwash device, the pressure relief according to the invention does not result in any increased material loss in the balance.

[0028] A further advantageous embodiment also provides for the capture and redirection of radial leakage flows that arise from the pressure area toward the outer circumference of the screen wheel. These flow into the area of ​​the external toothing of the screen wheel, which is required for the drive. If plastic melt adheres to it and is transported to the outside of the housing, it can solidify, which may impair the drive after several rotations of the screen wheel. To counteract this, the invention provides for the introduction of an additional pressure relief opening in the gap between the toothing on the outer circumference of the screen wheel and the adjacent spacer element, so that any melt that may have penetrated the gap can be drained outwards by gravity, in particular also to the lower area of ​​the housing, from where it can drain into a collecting container located underneath.

[0029] It is advantageous to provide at least one tangential pressure relief channel on the side of the inlet plate because there is free access to the screen cavity, while facing away from it, i.e. on the back of the screen wheel, the opening is partially covered by the perforated plate inserted into the screen cavity, which supports the actual screen elements.

[0030] The cross-section in the direction of flow—that is, from the pressure relief bore to a relief opening on the underside of the housing—does not decrease along the flow path, but rather expands. This prevents foreign matter or plastic deposits, such as residual material from previous production cycles or degraded material, from causing a blockage in the channel, which would then impede pressure relief. This design with an expanding channel cross-section is preferably used for all channels used to remove material from the housing into a collecting tray.

[0031] The invention is described in more detail below with reference to the exemplary embodiment shown in the drawings. The figures show in detail: Fig. 1 a perspective view of a housing of a sieve wheel filter device, Fig. 2 the perspective view as in Fig. 1, with the inlet plate of the housing removed; Fig. 3 a perspective view of the sieve wheel filter device without sieve wheel, in an intermediate plane; Fig. 4 a perspective view of the sieve wheel filter device with the inlet plate partially cut and shown transparent; Fig. 5 a perspective view of the sieve wheel filter device with sieve wheel in an intermediate plane; Fig. 6 a perspective sectional view through the rotation axis of the sieve wheel; and Fig. 7 an enlarged detail from Fig. 6.

[0032] Fig. 1 shows a perspective view of a housing 10 of a screen wheel filtration device 100 for the high-pressure filtration of a plastic melt, specifically with a view of an inlet plate 11 with an inlet channel 13. An outlet plate 12 is connected to the inlet plate 11 via spacer elements 15, 16, with a gap formed between them in which a screen wheel is mounted. All three adjacent elements of the housing 10, i.e. the inlet plate 11, the spacer elements 15, 16, and the outlet plate 12, are screwed together via housing clamping elements 19.1 to 19.7 and clamped against one another with a preload designed for the operating pressure. The central axis of the housing clamping element 19.1 in the center of the housing simultaneously forms the axis of rotation of the screen wheel. A drive device 30 for the screen wheel is arranged on the outside of the housing 10.

[0033] Fig. 2 is a perspective view of the screen wheel filter device 100 as in Fig. 1, but with the inlet plate removed so that the inner intermediate layer with the sieve wheel 20 is visible. In addition, a further spacer element 17 is visible, which seamlessly connects the two lateral spacer elements 15, 16 at the upper edge of the housing. As a result, the sieve wheel 20 is almost completely enclosed on the outer circumference. Openings in the housing 10 thus only exist at the top left in the area of ​​a drive pinion 31, which engages with a gear ring 21, and on the underside in the form of a relief opening 48, which serves to enable the targeted outflow of melt into a collecting container placed below the filtering device. In the illustrated embodiment, the filtering device has a drive that acts on the gear ring 21 via a drive pinion 31.In the case of an alternative drive via a pawl which engages with a suitable toothing on the outer circumference, the housing has at least one further opening in the upper area at the engagement point of the drive.

[0034] The sieve wheel 20 is designed in a conventional manner with a plurality of sieve points 22.1...22.13; in the illustrated embodiment, 13 sieve points are provided. The sieve points 22.1...22.13 are each delimited by an inner annular sealing web 23 on the surface of the sieve wheel 20, an outer, annular sealing web 24, and sealing webs 25 extending therebetween, leading from the inside to the outside. A stationary bearing ring 18 is arranged in the center, on which the sieve wheel 20 is mounted. A plain bearing is formed between the outer side of the bearing ring and the inside of the central bore of the sieve wheel 20. A gear ring 21 is formed on the outer circumference of the sieve wheel 20.

[0035] The housing clamping elements 19.1 to 19.7 cause compression of the spacer elements 15, 16, 17 clamped between the outer housing plates within a pre-tensioning surface, thereby reducing the distance between the inlet and outlet plates 11, 12 and the sieve wheel 20 enclosed therebetween.

[0036] The dotted line corresponds to the contours of the funnel-shaped openings of the inlet and outlet channels on the screen wheel 20 and represents the flow area 40 that can be used for filtration. The screen wheel 20 rotates counterclockwise. Fig. In the angular position of the screen wheel 20 shown in Figure 2, the screen point 22.1 is partially overlapped with the flow area 40. As a result, the operating pressure prevails throughout the entire screen point 22.1. The screen point 22.2 is located entirely within the flow area 40. The screen point 22.3 is also partially overlapped with the flow area 40, so that the operating pressure prevails there as well. The screen point 22.4 is rotated out of the flow area 40, whereby the fluid stored therein is still under operating pressure.

[0037] Fig. 3 is a perspective view of the screen wheel filter device 100 as shown in the Fig. 1 and Fig. 2, where the screen wheel has also been removed; for orientation regarding the position of the screen wheel, only its gear rim 21 is indicated. The contour of the funnel mouth 14.1 of the outlet channel 14 corresponds to the flow area 40. A backwash channel begins at a lateral opening 12.2 on the outlet plate 12 and opens into an elongated, slot-shaped backwash nozzle 49 in the lower area of ​​the screen wheel. During backwashing, fluid is drawn in at an intake opening 47 on the clean side of the screens and, by means of amplification by a shot piston guided in the backwash channel 12.2, is forced out at the backwash nozzle 49.

[0038] Fig. Figure 4 shows the filtration device 100 with all housing elements and the sieve wheel 20, wherein the right-hand area of ​​the inlet plate 11 of the housing, in which the inlet channel 13 is arranged, is shown partially sectioned and transparent. A screen change position 10.1 is provided on the left side of the housing, where the inlet plate 11 is open so that the screen elements can be changed there. The screen change position 10.1 can be closed by a door (not shown). Clearly visible is the widening of the inlet channel 13 to form a funnel opening 13.1. This is identical in position and shape to the funnel opening 14.1 (see Fig. 3) at the outlet plate 12. In between, the dotted flow area 40 is formed, in which the plastic melt flows through the sieve elements inserted into the sieve positions 22.1 ...22.13.

[0039] At the position of the screen wheel 20 in Fig. 4, screen position 22.5 is currently overlapping with the pressure relief bore 41, which is guided laterally onto the screen wheel 20 and continues downwards into a pressure relief channel 41.1. The screen cavity at screen position 22.5 is therefore already depressurized. Screen position 22.4, which follows during counterclockwise rotation, is still under high internal pressure. It is no longer overlapping with the flow area 40 and is completely blocked off from the next screen position 22.3 by the sealing web 25. Screen positions 22.2, 22.3 are located completely in the flow area 40. Screen position 22.1 is just beginning to overlap with the flow area 40. If a screen change has previously taken place, pre-flooding takes place at this point and the internal pressure builds up.

[0040] Another pressure relief bore 42 leads from the side directly into the plain bearing surface between the inner circumference of the bearing bore of the sieve wheel 20 and the bearing ring 18 firmly clamped in the housing. It continues downwards in another pressure relief channel 42.1.

[0041] Fig. Figure 5 shows a vertical section through the housing 10 with a view of the screen wheel 20, wherein the section plane runs in an intermediate plane in which a lubrication gap is formed and parallel to the plane of the screen wheel 20. The dotted arrows indicate the approximate flow directions of the plastic melt from screen points 22.2, 22.3 in the flow area 40 or in the vicinity thereof towards the pressure relief bores 41, 42. They differ in that the flow to the first pressure relief bore 41 occurs at the top in the track of the screen points 22.1...22.13 of the screen wheel and is thus approximately "tangential", while the flow to the second pressure relief bore 42 at the bottom overcomes the inner annular sealing web 23 on the screen wheel 20 and is therefore referred to as "radial".

[0042] Fig. Figure 6 is a perspective sectional view through the rotational axis of the sieve wheel 20, which is also the central axis of the housing clamping element 19.1 and the bearing ring 18. The lower pressure relief bore 42 is arranged in the sectional plane and continues downward into the pressure relief channel 42.1.

[0043] An important detail with regard to the pressure relief effected by the second pressure relief bore 42, the so-called “radial” pressure relief, becomes an important detail of the preferred embodiment of a sieve wheel filter device 100 according to the invention only by enlarging in Fig.7. Where the bearing ring 18 and the bore of the screen wheel 20 lie against one another and form a plain bearing 26, the bearing ring 20 and the screen wheel are each provided with a chamfer on the edge, so that the two adjacent chamfers form an annular channel 43 with a triangular cross-section, which is significantly larger in volume than the annular gap of the plain bearing 26 and which enables the removal of plastic melt for the purpose of pressure relief, without having to change any housing parts or the pairing of the screen wheel 20 and the bearing ring 18. List of reference symbols 100 screen wheel filter device 10 housings 10.1 Screen change position 11 Inlet plate 12 Outlet plate 13 Inlet channel 13.1 Funnel mouth opening 14 Outlet channel 14.1 Funnel mouth opening 15, 16, 17 spacer elements 18 Bearing ring 19.1-19.7 Housing clamping elements 20 sieve wheel 21 sprocket 22.1...22.13 sieve positions 23 inner sealing bar 24 outer sealing bar 25 Sealing bar 26 plain bearings 30 Drive device 40 flow area 41 Pressure relief hole 41.1 Pressure relief channel 42 Pressure relief hole 42.1 Pressure relief channel 43 Ring Canal 47 Feed opening 48 relief opening 49 Backwash nozzle

Claims

[1] Screen wheel filter device (100) for the high-pressure filtration of a plastic melt, at least comprising a housing (10) which has at least: - an inlet plate (11) with at least one inlet channel (13), - an outlet plate (12) with at least one outlet channel (14); - at least one spacer element (15, 16, 17) arranged between the inlet plate (11) and the outlet plate (12) and a bearing ring (18) on which a sieve wheel (20) arranged between the inlet plate (11) and the outlet plate (12) is rotatably mounted, where: - the screening wheel (20) has a plurality of screening points (22.1 ... 22.13), each of which can be positioned and flowed through between the inlet and outlet channels (13, 14), - a lubricating gap is formed between the sieve wheel (20) and the inlet plate (12) and between the sieve wheel (20) and the outlet plate (12), - the inlet channel (13) and the outlet channel (14) each have a funnel mouth (13.1, 14.1) widening towards the screening wheel (20), between which a flow-through region (40) is formed; characterized by , - that at least one radial pressure relief flow path is formed within at least one lubricating gap, which crosses an inner annular sealing web (23) of the screen wheel (20) and which extends between the flow-through region (40) and at least one pressure relief bore (42), - that the at least one pressure relief bore (42) is formed in the inlet plate (11) or in the outlet plate (12) and opens at the bearing ring (18) and - that the pressure relief bore (42) is fluidly connected to a relief opening (48) on the outside of the housing (10) via a pressure relief channel (42.1) formed in the housing (10). [2] Screen wheel filter device (100) according to claim 1, characterized by that an annular channel (43) is formed in the sieve wheel (20) and / or in the housing (10), which is in flow connection with an annular plain bearing (26) formed between the bearing ring (18) and the sieve wheel (20). [3] Sieve wheel filter device (100) according to claim 2, characterized by that the annular channel (43) is formed by a chamfer on the outer circumference of the bearing ring (18) and on the inner circumference of the bore of the sieve wheel (20) receiving the bearing ring (18). [4] Sieve wheel filter device (100) according to one of claims 1 to 3, characterized by that at least one tangential pressure relief flow path is formed within at least one lubricating gap, which extends between the flow-through region (40) and at least one pressure relief bore (41) opening upstream of the flow-through region (40) in the direction of rotation. [5] Sieve wheel filter device (100) according to claim 4, characterized by , that - that the pressure relief bore (41) is formed in the inlet plate (11) and / or in the outlet plate (12); - that the pressure relief bore (41) opens into the track swept over by the screening points (22.1, ..., 22.13) during rotation of the screening wheel (20); - that when a screening point (22.1 ... 22.n) is covered by at least one pressure relief bore (41), there is no overlap of the screening point (22.1 ... 22.n) with the flow area (40) and - that the pressure relief bore (41) is fluidly connected to an outer side of the housing (10) via a pressure relief channel (41.1). [6] Screen wheel filter device (100) according to claim 5, characterized bythat the distance between the mouth of the pressure relief bore (41) and the respective front edge of the flow area (40) in the direction of rotation is greater than the maximum extent of the sieve points (22.1, ..., 22.13) in the direction of rotation. [7] Screen wheel filter device (100) according to one of the preceding claims, characterized by that the filtering device is provided with a backwashing device and that the pressure relief channel (42.1) of the lower pressure relief bore (42) and a backwashing channel leading to a backwashing nozzle (49) open at a common relief opening (48) on the underside of the housing (10).

Images