Filtering device for filtering a fluid and method of operation thereof

Abstract

Filtering device (2, 80) for filtering a fluid, in particular a liquefied plastic, comprising: - a screen carrier housing (4, 23) with a screen carrier (12, 2, 56) receptable for receiving a screen carrier (12, 2, 56), at least one fluid inlet channel (8) and at least one fluid outlet channel (10): - at least one screen carrier (12, 2, 56) which is accommodated within the screen carrier receptacle (6, 54) so as to be movable along a longitudinal axis and has at least one screen carrier inlet (14), at least one screen carrier outlet (16) and at least one cavity (18) for accommodating a filter element (20, 78), the cavity (18, 66) being connected in a fluid-conducting manner to the screen carrier inlet (14, 62) and the screen carrier outlet (16, 64), and the screen carrier (12, 2, 56) being movable from a screen change position into a filtering position : wherein the filtering device (2) has a valve piston receptacle (22, 28, 68) for receiving a valve piston (24, 74) with a fluid inlet channel (8, 26, 58, 70) and a fluid outlet channel (10, 28, 26, 60, 72), and a valve piston (24, 74) received within the valve piston receptacle (22, 28, 68) so as to be movable along a longitudinal axis and having a through channel (32, 76), and wherein the valve piston (24, 74) can be moved into a production position in which the through channel (32, 76) overlaps the fluid inlet channel (8, 26, 58, 70) and the fluid outlet channel (10, 28, 26, 60, 72) of the valve piston receptacle (22, 28, 68): wherein the valve piston (24, 74) is movable into a venting position region in which the fluid outlet channel (10, 28, 26, 60, 72) is connected to the through channel (32, 76) via a filling recess (34), and wherein the filling recess (34) in the venting position region releases a variable flow cross-section (46, 52) between the through-channel (8, 10, 26, 28, 32, 36, 38, 58, 60, 70, 72, 76) and the fluid outlet channel (10, 28, 26, 60, 72) as a function of a position of the valve piston (24, 74) relative to the valve piston receptacle (22, 28, 68): wherein the filling recess (34) and / or the backflushing recess (42) has a cross-section (46, 52) which changes in at least one direction, preferably in the direction of the longitudinal axis of the valve piston (24, 74).

Description

[0001] Filtering device for filtering a fluid and method of operation thereof

[0002]

[0001] The invention relates to a filtering device for filtering a fluid, in particular a liquefied plastic, comprising a screen carrier housing with a screen carrier receptacle for receiving a screen carrier, at least one fluid inlet channel and at least one fluid outlet channel, a screen carrier which is received within the screen carrier receptacle so as to be movable along a longitudinal axis and has a screen carrier inlet, a screen carrier outlet and a cavity for receiving a filter element, the cavity being connected in a fluid-conducting manner to the screen carrier inlet and the screen carrier outlet, and the screen carrier being movable from a screen changing position into a filtering position. The invention also relates to a method for venting and backflushing a cavity of a filtering device.

[0003]

[0002] Filtering devices are used in plastic processing machines, for example, when there are high demands for the purity of the plastic to be processed. They are usually arranged between an extrusion device, which melts and conveys the plastic, and an application device. Such filtering devices for filtering a fluid are known from the prior art. For example, DE 10 2007 057 816 Al and DE 42 18 756 Cl describes such a filtering device with a screen carrier in which a filter element, also known as a screen, is arranged.

[0004]

[0003] DE 198 34 302 Al also refers to such a filtering device with a screen carrier in which a filter element, also known as a screen, is arranged. A movable piston is arranged upstream the screen carrier inlet channel having a contraction. By moving this piston, its contraction connects with the inlet channel so that a pre filling of the carrier cavity can be achieved.

[0005]

[0004] After some time in operation, such filter elements typically need to be changed or cleaned. For this purpose, the screen carrier is moved from a filtering position to a filter change position, the filter element is replaced or cleaned and the screen carrier is then moved from the filter change position to the filtering position. The challenge here is that the interior of the screen carrier, known as the cavity, is filled with air after the filter element has been replaced. When resuming the filtering process, however, it is essential to avoid introducing air into the production process.

[0006]

[0005] In order to avoid the introduction of air into the plastic fluid stream, it is known from the prior art to move the screen carrier into a screen carrier venting position, in which the plastic melt flows into the screen cavity and displaces the air contained in the cavity. As the inflowing plastic is taken from the plastic fluid stream to be filtered, a particular challenge with regard to filling the cavity is that filling the cavity too quickly from the plastic fluid stream has a negative effect on the system pressure, in particular causing undesirable system pressure fluctuations. In order to minimize this, filling recesses or so- called pre-flood grooves are known from the prior art, which are arranged in the area of the screen carrier and which serve to regulate the filling speed of the cavity.

[0007]

[0006] Although these systems have fundamentally proven themselves, there is still room for improvement. For instance, the construction shown in DE 198 34 302 Al has a very large cross-section that cannot contribute to a throttling and / or sensitive filling of a screen area after a screen change. There is no decisive throttle section and thus, no pressure consumption, such as pressure loss or throttling effect can be achieved. So, any fluid (melt) will flow completely unhindered and quickly into the empty screen area. In particular, it has been shown that such filtering devices known from the prior art have a high level of mechanical complexity. In the event that the screen piston is to be moved for the purpose of regulating the filling speed of the cavity, significant actuating forces are required to move the screen carrier, while at the same time high demands are placed on the feed accuracy of the screen carrier in order to enable targeted venting of the cavity. In addition, the movement of the screen carrier in the venting position may result in uneven flow conditions due to only partial overlapping of fluid inlet channels and fluid outlet channels with a screen carrier inlet or a screen carrier outlet, which may result in temporary adhesion of melt residues to wall sections. Depending on the viscosity of the melt (low- viscosity or viscous), a different overlap of the pre-flood groove and flow channel is always required in order to achieve a slow filling. With low-viscosity material, more throttling effect is required for a slow filling than with viscous material. Finding these different positions is difficult in practice.

[0008]

[0007] In view of the above, it was the objective for the invention for further developing a filtering device and a method of the type described above in such a way that the disadvantages found in the prior art are eliminated as far as possible. In particular, the invention was based on the task of simplifying the operation of the screen carrier and, in addition, optimizing the flow conditions in the area of the screen carrier, while at the same time ensuring that the system pressure remains within definable threshold values also when filling the cavity.

[0009]

[0008] According to the invention, the problem is solved in a device of the type mentioned above in that the filtering device has a valve piston receptacle for receiving a valve piston with a fluid inlet channel and a fluid outlet channel, and a valve piston with a through channel which is received within the valve piston receptacle so as to be movable along a longitudinal axis, and wherein the valve piston can be moved into a production position in which the through channel overlaps the fluid inlet channel and the fluid outlet channel of the valve piston receptacle, in which the through-channel is in overlap with the fluid inlet channel and the fluid outlet channel of the valve piston receptacle, wherein the valve piston is movable into a venting position region in which the fluid outlet channel is connected to the through-channel via a filling recess, and wherein the filling recess in the venting position region exposes a variable flow cross-section between the through-channel and the fluid outlet channel as a function of a position of the valve piston relative to the valve piston receptacle.

[0010]

[0009] The invention is based on the finding that the screen carrier actuation can be simplified by providing a valve piston receptacle with a valve piston, whereby it is now the valve piston - and not the screen carrier - that can be moved into a venting position region. This is achieved by the fluid inlet channel being connected to the through channel via a filling recess, and the filling recess in the venting position area releasing a variable flow cross-section between the through channel and the fluid outlet channel as a function of a position of the valve piston relative to the valve piston receptacle.

[0011]

[0010] The simplified screen carrier actuation is shown by the fact that the screen carrier can now only be moved into three positions, namely a filtration position, a screen change position and a position in which the air contained in the cavity after a screen change can be released into the environment. The regulation of the fluid mass flow for venting the cavity is no longer carried out by actuating, i.e. moving the screen carrier, but is realized by the valve piston. It has been shown that the overall cost of such control by means of a valve piston can be lower, as the valve piston has a lower mass, can be smaller in size and can therefore be moved precisely with less effort. In addition, the flow conditions in the area of the screen carrier can be optimized, as the screen carrier is motionless during venting of the cavity - and also in its filtration position - and therefore ideal flow conditions prevail. Furthermore, the discrete operating positions result in a well-defined overlap of the corresponding flow channels.

[0012]

[0011] The filling recess is formed in the valve piston receptacle and extends from the fluid outlet channel or the fluid inlet channel. According to an alternative embodiment, the filling recess may be formed in the valve piston and extends from the through channel adjacent to the fluid outlet channel or the fluid inlet channel.

[0012] In other words, the filling recess can thus be formed both in the valve piston receptacle and in the valve piston. If the filling recess is formed in the valve piston receptacle, it can extend from the fluid outlet channel or the fluid inlet channel. If the filling recess is formed in the valve piston, it can extend from the through channel either adjacent to the fluid outlet channel or the fluid inlet channel. In this way, depending on the application, the melt flow can be regulated either at the inlet or at the outlet of the passage channel.

[0013]

[0013] According to one embodiment, the valve piston is arranged upstream or downstream of the screen carrier in a flow direction of the fluid to be filtered. In this way, installation space requirements can be taken into account, and a particularly easily configurable filtering device can be specified.

[0014]

[0014] According to one embodiment, the fluid outlet channel of the valve piston holder is connected to the fluid inlet channel of the screen carrier housing in a fluid-conducting manner. This applies in particular to the case in which the valve piston is arranged downstream of the screen carrier in a flow direction of the fluid to be filtered. In the event that the valve piston is arranged upstream of the screen carrier in a flow direction of the fluid to be filtered, the fluid outlet channel of the valve piston receptable can be connected in a fluid-conducting manner to the fluid outlet channel of the screen carrier housing. In other words, depending on the configuration, either the fluid flow to the screen carrier or the fluid outflow from the screen carrier is regulated. This is done by means of a separate valve piston in each case.

[0015]

[0015] According to one embodiment, the screen carrier and the screen carrier housing each have at least one venting recess, in particular several venting recesses, which serve to release the air in the cavity during the filling of the cavity, and wherein the screen carrier can be moved into a screen carrier venting position in which the venting recesses of the screen carrier and the venting recesses of the screen carrier housing are at least partially overlapping. This configuration ensures that the air in the cavity can be released into the environment after a filter element has been replaced during filling of the cavity. According to one embodiment, the screen carrier has two or more cavities with correspondingly assigned inlet and outlet channels.

[0016]

[0016] In a second aspect of the invention or according to an advantageous further development of the invention according to the first aspect, it is proposed according to the invention that a backflush discharge channel is arranged in the valve piston receptacle and the valve piston has a backflush channel, wherein the valve piston in a backflush position region connects the backflush discharge channel via the backflush channel of the valve piston to the fluid outlet channel of the valve piston receptacle, so that backflush fluid can be discharged from the filter element.

[0017]

[0017] The second aspect of the invention or the advantageous further development of the invention according to the first aspect is based on the finding that the filtering device provides a backflush functionality. For this purpose, fluid is pressed through the filter element against the filtering direction in order to clean it. By configuring the valve piston receptacle in such a way that it has a backflush discharge channel and the valve piston can be brought into a backflush position region in which the backflush discharge channel is connected to the fluid outlet channel of the valve piston receptacle via the backflush channel of the valve piston, backflush fluid can be drained from the filter element and discharged from the filtering device. Once again, the advantage of this solution is that the screen carrier can remain in its filtering position when it is to be backflushed with fluid. The contaminated backflushed melt can be discharged by actuating the valve piston in such a way that the backflushing discharge channel is brought into overlap with the fluid outlet channel of the valve piston holder via the backflushing channel of the valve piston.

[0018]

[0018] According to one embodiment, the valve piston receptacle has a backflushing recess which extends from the fluid outlet channel of the valve piston receptacle, or the valve piston has a backflushing recess which extends from the backflushing channel, wherein the backflush recess in the backflush position area releases a variable flow cross-section between the backflush channel and the fluid outlet channel of the valve piston receptacle as a function of a position of the backflush channel relative to the fluid outlet channel of the valve piston receptacle.

[0019]

[0019] The backflush recess takes into account the fact that when backflushing filter elements, in which they are backflushed against the filtration direction using plastic melt for cleaning purposes, the plastic used for backflushing is usually removed from the plastic fluid flow to be filtered. Backflushing from the plastic fluid flow too quickly, which is synonymous with a large amount of material being removed in a short time, can also have a negative effect on the system pressure. When connecting spin nozzles, for example, such pressure fluctuations can have a negative impact on the spinning process, resulting in poor product quality or even breakage of the spun yarns.

[0020] The backflush recess now makes it possible to precisely adjust the backflush volume. This allows pressure fluctuations in the system to be minimized. The positioning of the valve piston can also be used to adjust the backflush volume. As described, the screen carrier can remain in a fixed position. Due to its smaller size and dimensions, actuation of the valve piston requires less actuating force and can be controlled more precisely overall. According to one embodiment, the filling recess and / or the backflush recess extend essentially parallel to the longitudinal axis of the valve piston. In this way, when the valve piston is displaced along its longitudinal axis, it can be achieved that a free cross-section of different sizes is released through the filling recess and / or the backflush recess between the adjacent channels.

[0020]

[0021] According to one embodiment, the filling recess and / or the backflush recess has a cross-section that changes in the direction of the longitudinal axis of the valve piston. As a result, the free flow cross-section can be optimized, and both the filling process and the backflush process can be finely adjusted so that pressure fluctuations in the overall system are largely avoided.

[0021]

[0022] According to one embodiment, the cross-section of the filling recess and / or the backflushing recess tapers in a direction radially outwards from a central axis of the through channel or a central axis of the fluid outlet channel of the valve piston receptacle.

[0022]

[0023] According to one embodiment, the cross-section of the filling recess and / or the backflush recess has a wedge-shaped or notch-shaped basic shape. This ensures that a particularly sensitive adjustment of the melt flow along the recesses is achieved.

[0023]

[0024] According to one embodiment, the backflush recess and the filling recess are arranged in the valve piston receptable. They are preferably arranged opposite each other.

[0024]

[0025] According to one embodiment, the valve piston can be moved from the backflush position area by moving the valve piston in a first direction into the venting position area and into the production position by moving it further in the first direction. In this way, by moving the valve piston along its longitudinal axis in the first direction or in an opposite direction, it can be achieved that the individual areas mentioned can be controlled.

[0025]

[0026] According to one embodiment, the cross-section of the through channel of the valve piston tapers from the fluid inlet channel to the fluid outlet channel.

[0027] According to one embodiment, the screen carrier is a first screen carrier and the valve piston is a first valve piston, wherein the screen carrier housing has a second screen carrier receptacle for receiving a second screen carrier with a fluid inlet channel and a fluid outlet channel, and a second screen carrier, which is received within the second screen carrier receptacle so as to be movable along a longitudinal axis, with a screen carrier inlet, a screen carrier outlet and a cavity for receiving a filter element, the cavity being connected to the screen carrier inlet and the screen carrier outlet in a fluid-conducting manner, and wherein the screen carrier can be moved from a screen change position into a filtering position, wherein the filtering device has a second valve piston receptacle for receiving a second valve piston with a fluid inlet channel and a fluid outlet channel, and a second valve piston with a passage channel, which is accommodated within the second valve piston receptacle so as to be movable along a longitudinal axis, and wherein the second valve piston is movable via a venting position region in a production position in which the passage channel is in overlap with the fluid inlet channel and the fluid outlet channel of the second valve piston receptacle. By providing two screen carriers in a filtering device, permanent filtering operation can be ensured, even if one of the screen carriers is in the screen change position. The other screen carrier can be used for filtering fluid.

[0026]

[0028] According to one embodiment, the filtering device has a control device which is set up and designed in such a way that it changes the position of the valve piston in the venting position region during venting of the cavity stepwise and repeatedly by means of control signals in such a way that the fluid pressure, in particular in the fluid inlet channel and / or in the fluid outlet channel, remains within a definable pressure region during venting of the cavity, in particular in the fluid inlet channel and / or in the fluid outlet channel, remains within a definable pressure region during venting of the cavity, a variable flow crosssection between the through channel and the fluid outlet channel of the valve piston receptacle being released by means of the filling recess when the valve piston is moved in the venting position region. Such a gradual and repetitive change in the position of the valve piston is a quickly effective and efficient measure for maintaining the overall system pressure during screen changes within predefined threshold values. There is preferably no need to adjust the pumping capacity of a melt pump - for example by changing the speed of the pump drive. A stepwise and repetitive control of the position of the valve piston according to the invention has a continuous effect on the cause of the pressure fluctuation, namely the filling speed of the cavity, which is influenced by the position of the valve piston. The free flow cross-section for filling the cavity can thus be very precisely adjusted and varied in such a way that only very small, negligible effects on the fluid pressure in the system occur. This means that deviations from the target system pressure that exceed the permissible limit values can be quickly compensated for by reducing the filling speed of the cavity by moving the valve piston.

[0027]

[0029] According to one embodiment, the valve piston is driven by a drive device that is designed as an electric drive, in particular as a linear motor or stepper motor. Such a drive enables the valve piston to be driven precisely, allowing the screen carrier to be moved precisely to desired positions, for example a venting position region. According to one embodiment, a position sensor is assigned to the valve piston to determine the position of the valve piston. The advantage of such a sensor is that the exact position of the valve piston can be determined and fed back to the control device. This realizes a monitoring functionality and thus improves the overall process quality.

[0028]

[0030] According to one embodiment, the filtering device has a control device which is set up and designed in such a way that it changes the position of the valve piston during backflushing of the cavity in the backflush area by means of control signals in such a way that the fluid pressure, in particular in the fluid inlet channel and / or in the fluid outlet channel, remains within a definable pressure region during backflushing, remains within a definable pressure region during backflushing, whereby when the valve piston is moved in the backflushing position region, a variable flow cross-section between the backflushing channel and the fluid outlet channel of the valve piston receptacle is released by means of the backflushing recess. In this way, it can also be ensured that the overall system pressure fluctuations remain minimal when backflushing a filter element, even if melt material from the production process is used for backflushing.

[0029]

[0031] According to one embodiment, the filtering device has at least one pressure sensor for measuring the fluid pressure in the fluid inlet channel and / or the fluid outlet channel. This is particularly advantageous for determining system pressure fluctuations.

[0030]

[0032] The invention has been described above with reference to a filtering device. In a further aspect, the invention relates to a method for venting a cavity of a filtering device, in particular a filtering device as described above. The invention solves the task described at the beginning with respect to the method, in that the method comprises the steps of moving the screen carrier into a venting position, changing the position of the valve piston during venting of the cavity in the venting position region in a stepwise and repetitive manner such that the fluid pressure, in particular in the fluid inlet channel and / or in the fluid outlet channel, remains within a definable pressure region during venting of the cavity, with a variable flow cross-section between the passage channel and the fluid outlet channel of the valve piston receptacle being released by means of the filling recess when the valve piston is moved in the venting position region.

[0031]

[0033] The method makes use of the same advantages and preferred embodiments as the filtration device according to the invention and vice versa. In this respect, reference is made to the above explanations, and their content is hereby incorporated.

[0032]

[0034] According to one embodiment, the method comprises the step of changing the position of the valve piston during backflushing of the cavity in the backflushing position area in such a way that the fluid pressure, in particular in the fluid inlet channel and / or in the fluid outlet channel, remains within a definable pressure region during backflushing of the cavity, whereby a variable flow cross-section between the backflushing channel and the fluid outlet channel of the valve piston receptacle is released by means of the backflushing recess when the valve piston is moved in the backflushing position area. This ensures that the system pressure remains within definable limits even during backflushing.

[0033]

[0035] The invention is described in more detail below by preferred embodiments with reference to the accompanying figures.

[0034]

[0036] It is shown in:

[0035] Fig. 1 a side view of an embodiment of a filtering device according to the invention;

[0036] Fig. 2a and 2b the filtering device according to the invention in a filtration position, shown in a sectional view;

[0037] Fig. 3 the filtering device according to the invention in a venting position;

[0038] Fig. 4 the filtering device according to the invention in a backflush position;

[0039] Fig. 5a and 5a alternative embodiment of a filtering device according to the invention in a filtration position; and

[0040] Figs. 6a and 6a side view and perspective view of a screen piston according to the invention.

[0037] Figures 1, 2a and 2b show a filtering device 2 for filtering a fluid, in particular a liquefied plastic. The filtering device 2 comprises a screen carrier housing 4. The screen carrier housing 4 has a screen carrier receptacle 6 for receiving a screen carrier 12. The screen carrier housing 4 further comprises at least one fluid inlet channel 8 and at least one fluid outlet channel 10. A screen carrier 12 is accommodated within the screen carrier receptacle 6 so as to be movable along a longitudinal axis LS. The screen carrier 12 has at least one screen carrier inlet 14, at least one screen carrier outlet 16 and at least one cavity 18 for receiving a filter element 20. In the exemplary embodiments of Figs. 1 to 6, a screen carrier 12 is shown which has a cavity 18. However, the screen carrier 12 can also have two or more cavities. The cavity 18 is connected in a fluid-conducting manner to the screen carrier inlet 14 and the screen carrier outlet 16. In Figures 1 and 2, the screen carrier is shown in a filtration position FS. It can also be moved into a screen change position not shown here.

[0041]

[0038] The filtering device 2 also has a valve piston receptacle 22 for receiving a valve piston 24. The valve piston receptacle 22 has a fluid inlet channel 26 and a fluid outlet channel 28. The valve piston receptacle 22 further comprises a valve piston 24 received within the valve piston receptacle 22 for movement along a longitudinal axis LV. The valve piston 24 has a through channel 32. The valve piston 24 is movable into a production position P, which is shown in Figures 1 and 2. In this production position P, the through- channel 32 overlaps with the fluid inlet channel 26 and the fluid outlet channel 28 of the valve piston receptacle 22.

[0042]

[0039] The valve piston 24 can also be moved into a venting position region E, which is shown in Figure 3. In the venting position region E, the fluid inlet channel 26 is connected to the through channel 32 via a filling recess 34. In the venting position region E, the filling recess 34 releases a variable flow cross-section between the through channel 32 and the fluid outlet channel 28 as a function of a position of the valve piston 24 relative to the valve piston receptacle 22. As shown in Figures 1 to 3 is , the filling recess 34 is formed in the valve piston receptacle 22 and extends from the fluid outlet channel 28. Alternatively, however, it can also extend from the fluid inlet channel 26, not shown here.

[0043]

[0040] In the embodiment example shown in Figures 1 to 3, the valve piston is arranged upstream of the screen carrier 12 in a flow direction of the fluid to be filtered. In this case, the fluid outlet channel 28 of the valve piston receptacle 22 is connected in a fluidconducting manner to the fluid inlet channel 8 of the screen carrier housing 4. The screen carrier 2 and the screen carrier housing 4 each have three venting recesses 21, 23. The venting recesses 21, 23 serve to release the air present in the cavity 18 during the filling of the cavity 18. In this respect, the screen carrier 12 can be moved into a screen carrier venting position SE, which is indicated in Figure 3, in which the venting recesses 21 of the screen carrier 12 and the venting recesses 23 of the screen carrier housing 4 are at least partially overlapping, so that air which is in the cavity 18 after a filter element 20 has been changed can leave the screen carrier housing 4 through the venting recesses 21, 23.

[0044]

[0041] A backflush discharge channel 36 is arranged in the valve piston receptacle 22. In addition, the valve piston 24 has a backflush channel 38. The valve piston 24 can be brought into a backflush position region R, which is shown in Figure 4. In the backflush position region R, the valve piston 24 connects the backflush discharge channel 36 via the backflush channel 38 of the valve piston 24 to the fluid outlet channel 28 of the valve piston receptacle 22, so that backflush fluid can be discharged from the filter element 20. In the state shown in Figure 4, the backflush fluid is supplied via the fluid outlet channel 10. From there, the fluid reaches the filter element 20, loosens dirt particles from it and reaches the backflush discharge channel 36 via the fluid inlet channel 8 and the fluid outlet channel of the valve piston receptacle 28 via the backflush channel 38. From there, the contaminated melt can be discharged. The valve piston receptacle 22 has a backflushing recess 42. The backflushing recess 42 extends from the fluid outlet channel 28 of the valve piston receptacle 22. In the backflushing position region R, the backflushing recess 42 releases a variable flow cross-section between the backflushing channel 38 and the fluid outlet channel 28 of the valve piston receptacle 22 as a function of a position of the backflushing channel 38 relative to the fluid outlet channel 28 of the valve piston receptacle 22. The filling recess 34 and the backflushing recess 42 extend substantially parallel to the longitudinal axis LV of the valve piston 24, with the filling recess 34 and the backflushing recess 42 having a cross-section 46, 48 that changes in the direction of the longitudinal axis LV of the valve piston 24. In particular, the cross-section 46, 48 of the filling recess 34 and the backflushing recess 42 tapers in a direction radially outwards from a central axis 50 of the through channel 32 or a central axis 44 of the fluid outlet channel 26 of the valve piston receptacle 22. In particular, the cross-sections 46, 48 of the filling recess 34 and the backflushing recess 42 have a wedge-shaped or notch-shaped basic shape. In this case, the backflush recess 42 and the filling recess 34 are arranged opposite one another in the valve piston receptacle 22. Overall, the valve piston 24 can be moved from the backflushing position region R by moving the valve piston 24 in a first direction D into the venting position region E and by further movement in the first direction D into the production position P. A cross-section 52 of the through channel 32 of the valve piston 24 tapers from the fluid inlet channel 26 to the fluid outlet channel 28.

[0042] As shown in Figures 1 to 5, the screen carrier 12 is a first screen carrier 12 and the valve piston 24 is a first valve piston 24. The screen carrier housing 4 has a second screen carrier receptacle 54 for receiving a second screen carrier 56. The second screen carrier receptacle 54 has a fluid inlet channel 58 and a fluid outlet channel 60. Furthermore, the screen carrier housing 4 has a second screen carrier 56 received within the second screen carrier receptacle 54 so as to be movable along a longitudinal axis LS and having a screen carrier inlet 62, a screen carrier outlet 64 and a cavity 66 for receiving a filter element 78. The cavity 66 is connected in a fluid-conducting manner to the screen carrier inlet 62 and the screen carrier outlet 64. The screen carrier 56 can be moved from a screen change position to a filtering position FS. The filtering device 2 further comprises a second valve piston receptacle 68 for receiving a second valve piston 74 with a fluid inlet channel 70 and a fluid outlet channel 72. The filtering device 2 has a second valve piston 74 with a through channel 76, which is received within the second valve piston receptacle 68 so as to be movable along a longitudinal axis LV. The second valve piston 74 can be moved via a venting position region E into a production position P, in which the through-channel 76 is in overlap with the fluid inlet channel 70 and the fluid outlet channel 72 of the second valve piston receptacle 68.

[0045]

[0043] As schematically indicated in Figure 1, the filtering device 2 also has a control device 80. The control device 80 is set up and designed such that it changes the position of the valve piston 24 in the venting position region E during venting of the cavity 18 by means of control signals in a stepwise and repetitive manner such that the fluid pressure, in particular in the fluid inlet channel 8 and in the fluid outlet channel 10, remains within a definable pressure region during venting of the cavity 18. When the valve piston 24 is moved into the venting position region E, a variable flow cross-section between the through channel and the fluid outlet channel 28 of the valve piston receptacle 22 is released by means of the filling recess 34.

[0046]

[0044] The schematically depicted control device 80 or a second control device 80 is furthermore set up and designed in such a way that it changes the position of the valve piston 24 during backflushing of the cavity 18 in the backflush area R by means of control signals in such a way that the fluid pressure, in particular in the fluid inlet channel 8 and in the fluid outlet channel 10, remains within a definable pressure region during backflushing, remains within a definable pressure region during backflushing, whereby a variable flow cross-section between the backflushing channel 38 and the fluid outlet channel 28 of the valve piston receptacle 22 is released by means of the backflushing recess when the valve piston 24 is moved in the backflushing position region R. In the same way, the second valve piston 74 can also be controlled by the control device 80 in conjunction with the second screen carrier 56.

[0047]

[0045] Figures 5a and 5b show an alternative embodiment example of a filtering device 2, which differs from the embodiment examples of Figures 1 to 4 in that the filling recess 34 is formed in the valve piston 24 and extends from the through-channel 32. In addition, the valve piston 24 has a backflush recess 42, which extends from the backflush channel 38. Thus, both the backflush recess 42 and the filling recess 34 are formed in the valve piston 24 - and not in the valve piston receptacle 22, as shown in Figures 1 to 4. As shown schematically in Figure 5a, the filtering device 2 has a pressure sensor pl, p2 for measuring the fluid pressure in the fluid inlet channel 8 or the fluid outlet channel 10.

[0048]

[0046] Figures 6a and 6b schematically illustrate the screen carrier 12. As can be seen from the figures, the screen carrier 12 has a screen carrier inlet 14, a screen carrier outlet 16 and a cavity 18 for receiving a filter element 20 not shown here. The cavity 18 is connected to the screen carrier inlet 14 and the screen carrier outlet 16 in a fluid-conducting manner. In addition, the figures show the venting recesses 21 of the screen carrier 12, which can be brought into overlap with corresponding venting recesses of the screen carrier housing 23 in order to enable venting of the cavity 18 in a venting position region E after a screen change process.

[0049] List of reference symbols

[0050] 2 Filtering device

[0051] 4 Screen carrier housing

[0052] 6 Screen carrier receptable

[0053] 8 Fluid inlet channel

[0054] 10 Fluid outlet channel

[0055] 12 Screen carrier

[0056] 14 Screen carrier inlet

[0057] 16 Screen carrier outlet

[0058] 18 Cavity

[0059] 20 Filter element

[0060] 21 Ventilation openings in the screen carrier

[0061] 22,22' Valve piston receptacle

[0062] 23 Ventilation cut-outs in the receptacle housing

[0063] 24,24' Valve piston

[0064] 26 Fluid inlet channel of the valve piston receptacle

[0065] 28 Fluid outlet channel of the valve piston receptacle

[0066] 32 Through channel

[0067] 34 Filling recess

[0068] 36 Backflush discharge channel

[0069] 38 Backflush channel

[0070] 40 Inside of the filter element

[0071] 42 Backflush recess

[0072] 44 Center axis of the fluid outlet channel of the valve piston receptacle

[0073] 46 Cross-section of the filling recess

[0074] 48 Cross-section of the backflush recess

[0075] 50 Center axis of the through channel

[0076] 52 Cross-section of the through channel

[0077] 54 Second screen carrier receptable

[0078] 56 Second screen carrier

[0079] 58 Fluid inlet channel of the second receptacle

[0080] 60 Fluid outlet channel of the second receptacle

[0081] 62 Screen carrier inlet of the second screen carrier

[0082] 64 Screen carrier outlet of the second screen carrier

[0083] 66 Cavity of the second screen carrier

[0084] 68 Second valve piston receptable 70 Fluid inlet channel of the second valve piston receptable

[0085] 72 Fluid outlet channel of the second valve piston receptable

[0086] 74 Second valve piston

[0087] 76 Through channel of the second valve piston 78 Second filter element

[0088] 80 Control unit

[0089] D First direction

[0090] E Venting position region

[0091] FS Filtration position of the screen carrier LS Longitudinal axis of the screen carrier receptacle

[0092] LV Longitudinal axis of the valve piston pl First pressure sensor p2 Second pressure sensor

[0093] P Production position R Backflush position region

[0094] SE Venting position of the screen carrier

Claims

Patent claims1. Filtering device (2) for filtering a fluid, in particular a liquefied plastic, comprising:- a screen carrier housing (4) with a screen carrier receptable (6) for receiving a screen carrier (12), at least one fluid inlet channel (8) and at least one fluid outlet channel (10),- at least one screen carrier (12) which is accommodated within the screen carrier receptacle (6) so as to be movable along a longitudinal axis (LS) and has at least one screen carrier inlet (14), at least one screen carrier outlet (16) and at least one cavity (18) for accommodating a filter element (20), the cavity (18) being connected in a fluidconducting manner to the screen carrier inlet (14) and the screen carrier outlet (16), and the screen carrier being movable from a screen change position into a filtering position (FS),- wherein the filtering device (2) has a valve piston receptacle (22) for receiving a valve piston (24) with a fluid inlet channel (26) and a fluid outlet channel (28), and a valve piston (24) received within the valve piston receptacle (22) so as to be movable along a longitudinal axis (LV) and having a through channel (32), and wherein the valve piston (24) can be moved into a production position (P) in which the through channel (32) overlaps the fluid inlet channel (26) and the fluid outlet channel (28) of the valve piston receptacle (22),- wherein the valve piston (24) is movable into a venting position region (E) in which the fluid outlet channel (28) is connected to the through channel (32) via a filling recess (34), and wherein the filling recess (34) in the venting position region (E) releases a variable flow cross-section between the through-channel (32) and the fluid outlet channel (28) as a function of a position of the valve piston (24) relative to the valve piston receptacle (22),- wherein the filling recess (34) and / or the backflushing recess (42) has a cross-section (46, 48) which changes in at least one direction, preferably in the direction of the longitudinal axis (LV) of the valve piston (24).

2. Filtering device (2) according to claim 1, wherein the filling recess (34) and / or the backflush recess (42) extends substantially parallel to the longitudinal axis (LV) of the valve piston (24).

3. Filtering device (2) according to claim 1 or 2, wherein the cross-section (46, 48) of the filling recess (34) and / or the backflushing recess (42) tapers in a direction radially outwards from a central axis (50) of the through channel (32).

4. Filtering device (2) according to claim 1 or 2, wherein the cross-section (46, 48) of the filling recess (34) and / or the backflushing recess (42) tapers in a direction radially outwards from a central axis (44) of the fluid outlet channel (26) of the valve piston receptacle (22).

5. Filtering device (2) according to any one of the preceding claims, wherein the crosssection (46, 48) of the filling recess (34) and / or the backflush recess (42) has a wedge- shaped basic shape.

6. Filtering device (2) according to any one of the preceding claims 1 to 4, wherein the cross-section (46, 48) of the filling recess (34) and / or the backflush recess (42) has a notch-shaped basic shape.

7. Filtering device (2) according to any of the preceding claims, wherein the filling recess (34) is formed in the valve piston receptacle (22) and extends from the fluid outlet channel (28) or the fluid inlet channel (26).

8. Filtering device (2) according to any of the preceding claims 1 to 6, wherein the filling recess (34) is formed in the valve piston (24) and extends from the through channel (32) adjacent to the fluid outlet channel (28) or the fluid inlet channel (26) .

9. Filtering device (2) according to any of the preceding claims,- wherein the valve piston (24) is arranged upstream of the screen carrier (12) in a flow direction of the fluid to be filtered.

10. Filtering device (2) according to any of the preceding claims, wherein the fluid outlet channel (28) of the valve piston receptacle (22) is connected in a fluid-conducting manner to the fluid inlet channel (8) of the screen carrier housing (4).

11. Filtering device (2) according to any of the preceding claims 1 to 9, wherein the fluid outlet channel (28) of the valve piston receptacle (22) is connected in a fluid-conducting manner to the fluid outlet channel (10) of the screen carrier housing (4).

12. Filtering device (2) according to any of the preceding claims 1 to 8, wherein the valve piston (24) is arranged downstream of the screen carrier (12) in a flow direction of the fluid to be filtered.

13. Filtering device (2) according to any of the preceding claims 1 to 8 with 12, wherein the fluid outlet channel (28) of the valve piston receptacle (22) is connected in a fluidconducting manner to the fluid inlet channel (8) of the screen carrier housing (4).

14. Filtering device (2) according to any of the preceding claims 1 to 8 with 12, wherein the fluid outlet channel (28) of the valve piston receptacle (22) is connected in a fluidconducting manner to the fluid outlet channel (10) of the screen carrier housing (4).

15. Filtering device (2) according to one of the preceding claims, wherein the screen carrier (2) and the screen carrier housing (4) each have at least one venting recess (21, 23), for releasing the air present in the cavity (18) during filling of the cavity (18).

16. Filtering device (2) according to claim 15, wherein the screen carrier (12) can be moved into a screen carrier venting position (SE) in which the venting recesses (21) of the screen carrier (12) and the venting recesses (23) of the screen carrier housing (4) are at least partially overlapping.

17. Filtering device (2) according to claim 15 or 16, wherein the screen carrier (2) and the screen carrier housing (4) each have a plurality of venting recesses (21, 23).

18. Filtering device (2) according to one of the preceding claims, wherein a backflush discharge channel (36) is arranged in the valve piston receptacle (22) and the valve piston (24) has a backflush channel (38), and wherein the valve piston (24) in a backflush position region (R) connects the backflush discharge channel (36) via the backflush channel (38) of the valve piston (24) to the fluid outlet channel (28) of the valve piston receptacle (22), so that backflush fluid can be discharged from the filter element (20).

19. Filtering device (2) for filtering a fluid, in particular a liquefied plastic, comprising:- a screen carrier housing (4) with a screen carrier receptable (6) for receiving a screen carrier (12), at least one fluid inlet channel (8) and at least one fluid outlet channel (10),- at least one screen carrier (12) which is accommodated within the screen carrier receptacle (6) so as to be movable along a longitudinal axis (LS) and has at least one screen carrier inlet (14), at least one screen carrier outlet (16) and at least one cavity (18) for accommodating a filter element (20), the cavity (18) being connected in a fluidconducting manner to the screen carrier inlet (14) and the screen carrier outlet (16), and the screen carrier being movable from a screen change position into a filtering position (FS),- wherein a backflush discharge channel (36) is arranged in the valve piston receptacle (22) and the valve piston (24) has a backflush channel (38), and wherein the valve piston (24) in a backflush position region (R) connects the backflush discharge channel (36) via the backflush channel (38) of the valve piston (24) to the fluid outlet channel (28) of the valve piston receptacle (22), so that backflush fluid can be discharged from the filter element (20).

20. Filtering device (2) according to claim 18 or 19, wherein the valve piston receptacle (22) has a backflushing recess (42) which extends from the fluid outlet channel (28) of the valve piston receptacle (22).

21. Filtering device (2) according to claim 18 or 19, wherein the valve piston (24) has a backflushing recess (42) which extends from the backflushing channel (38).

22. Filtering device (2) according to claim 20 or 21, wherein the backflush recess (42) in the backflush position area (R) releases a variable flow cross-section between the backflush channel (38) and the fluid outlet channel (28) of the valve piston receptacle (22) as a function of a position of the backflush channel (38) relative to the fluid outlet channel (28) of the valve piston receptacle (22).

23. Filtering device (2) according to one of the preceding claims, wherein the backflush recess (42) and the filling recess (34) are arranged in the valve piston receptacle (22) and are arranged opposite one another.

24. Filtering device (2) according to one of the preceding claims, wherein the valve piston (24) can be moved from the backflush position region (R) into the venting position region (E) by moving the valve piston (24) in a first direction (D) and into the production position (P) by moving it further in the first direction (D).

25. Filtering device (2) according to one of the preceding claims, wherein a cross-section (52) of the through-channel (32) of the valve piston (24) tapers from the fluid inlet channel (26) to the fluid outlet channel (28).

26. Filtering device (2) according to one of the preceding claims,- wherein the screen carrier (12) is a first screen carrier (12) and the valve piston (24) is a first valve piston (24),- wherein the screen carrier housing (4) has a second screen carrier receptacle (54) for receiving a second screen carrier (56) with a fluid inlet channel (58) and a fluid outlet channel (60), and a second screen carrier (56) received within the second screen carrier receptacle (54) movably along a longitudinal axis (LS) with a screen carrier inlet (62), a screen carrier outlet (64) and a cavity (66) for receiving a filter element (78), wherein the cavity (66) is fluid-conductive with the screen carrier inlet (62) and the screen carrier outlet (64), a screen carrier outlet (64) and a cavity (66) for receiving a filter element (78), the cavity (66) being connected in a fluid-conducting manner to the screen carrier inlet (62) and the screen carrier outlet (64), and wherein the screen carrier (56) can be moved from a screen change position to a filtering position (FS), wherein the filtering device (2) has a second valve piston receptacle (68) for receiving a second valve piston (74) with a fluid inlet channel (70) and a fluid outlet channel (72), and a second valve piston (74) with a through channel (76) received within the second valve piston receptacle (68) so as to be movable along a longitudinal axis (LV), and wherein the second valve piston (74) is movable via a venting position region (E) into a production position (P) in which the through channel (76) is in overlap with the fluid inlet channel (70) and the fluid outlet channel (72) of the second valve piston receptacle (68).

27. Filtering device (2) according to one of the preceding claims, wherein a control device (80) is set up and designed in such a way that it changes the position of the valve piston (24) in the venting position region (E) during venting of the cavity (18) stepwise and repeatedly by means of control signals in such a way that the fluid pressure, in particular in the fluid inlet channel (8) and / or in the fluid outlet channel (10), remains within a definable pressure region during venting of the cavity (18), a variable flow cross-section between the through-channel (32) and the fluid outlet channel (28) of the valve piston receptacle (22) being released by means of the filling recess (34) when the valve piston (24) is moved in the venting position region (E).

28. Filtering device (2) according to one of the preceding claims, wherein a control device (80) is set up and designed such that it changes the position of the valve piston (24) during backflushing of the cavity (18) in the backflushing region (R) by means of control signals in such a way that the fluid pressure, in particular in the fluid inlet channel (8) and / or in the fluid outlet channel (10), remains within a definable pressure region during backflushing, wherein a variable flow cross-section between the backflushing channel (38) and the fluid outlet channel (28) of the valve piston receptacle (22) is released by means of the backflushing recess (42) when the valve piston (24) is moved in the backflushing position region (R).

29. Filtering device (2) according to one of the preceding claims, wherein at least one pressure sensor (pl, p2) is provided for measuring the fluid pressure in the fluid inlet channel (8) and / or the fluid outlet channel (10).

30. Method for venting a cavity (18) of a filtering device (2), in particular a filtering device (2) according to one of the preceding claims, comprising the steps of:- Moving the screen carrier (12) to a venting position ,- Changing the position of the valve piston (24) during venting of the cavity (18) in the venting position region (E) in a stepwise and repetitive manner such that the fluid pressure, in particular in the fluid inlet channel (8) and / or in the fluid outlet channel (10), remains within a definable pressure region during venting of the cavity (18), wherein when the valve piston (24) is moved in the venting position region (E), a variable flow cross-section between the through channel (32) and the fluid outlet channel (28) of the valve piston receptacle (22) is released by means of the filling recess (34).

31. Method for backflushing a cavity (18) of a filtering device (2), in particular a filtering device (2) according to one of the preceding claims, comprising the steps of- Changing the position of the valve piston (24) during backflushing of the cavity (18) in the backflushing position region (R) in such a way that the fluid pressure, in particular in the fluid inlet channel (8) and / or in the fluid outlet channel (10), remains within a definable pressure region during backflushing of the cavity (18), wherein, when the valve piston (24) is moved in the backflushing position region (R), a variable flow cross-section between the backflushing channel (38) and the fluid outlet channel (28) of the valve piston receptacle (22) is released by means of the backflushing recess (42).

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