Apparatus for filtering liquid plastic materials and associated method of operation - Patents.com

Abstract

The present invention relates to a device (2) for filtering liquid plastics, comprising: a housing (4) with an inlet (6) for introducing plastics and an outlet (8) for discharging the plastics; a screen carrier (12) accommodated in the housing (4), the screen carrier having a screen chamber (10) for accommodating a filter element (14); a filter element (14) arranged in the screen chamber (10) of the screen carrier (12), the filter element having a filter side (16) and a clean side (18), the filter element (14) being capable of communicating with the inlet (6) and the outlet (8) such that plastics flow through the filter element (14) in a filtering flow direction (56) from the filter side to the clean side, the filter element (14) being capable of communicating with the inlet (6) and the outlet (8) such that plastics flow through the filter element (14) in a filtering flow direction (56) from the filter side to the clean side, the filter element (14) being capable of filtering the plastics. the filter element (14) can be cleaned by backwashing, by plastic flowing against the filtration flow direction (56), - the filter element (14) has a backwash supply channel (20) connected in a fluid-guiding manner to the clean side (18) of the filter element (14), the backwash supply channel being arranged to supply plastic to the filter element (14) against the filtration flow direction (56), - the filter element (14) has a backwash discharge channel (22) connected in a fluid-guiding manner to the filter side (16) of the filter element (14), the backwash discharge channel being designed to discharge the backwashed plastic after it has passed through the filter element (14). In accordance with the present invention, a backwash screen carrier (24) is provided that is fluidly connected to the backwash discharge channel (22), the backwash screen carrier having a screen chamber (26) for receiving a backwash filter element (28) and a backflush filter element (28) disposed within the screen chamber (26), the backflush filter element (28) being designed to filter the backflushed plastic.

Description

[Technical field]

[0001] The present invention relates to a device for filtering liquid plastics, comprising: a housing with an inlet for introducing plastics and an outlet for discharging the plastics; a screen carrier accommodated in the housing, the screen carrier having a screen chamber for accommodating a filter element; a filter element arranged in the screen chamber of the screen carrier, the filter element having a filter side and a clean side, the filter element being connectable to the inlet and the outlet such that plastic flows through the filter element from the filter side to the clean side along a filtration flow direction and is filtered, the filter element being cleanable by backwashing, by the plastic flowing against the filtration flow direction; a backwash supply channel fluidly connected to the clean side of the filter element, the backwash supply channel being adapted to supply plastic to the filter element against the filtration flow direction; a backwash discharge channel fluidly connected to the filter side of the filter element, the backwash discharge channel being adapted to discharge the backwashed plastics after it has passed through the filter element.

[0002] [Citation to Related Applications] This application is a national phase application of International Application No. PCT / IB2023 / 050401, filed on January 17, 2023, which in turn claims the priority of German Application No. 202022100235.5, filed on January 17, 2022, both of which are incorporated by reference in their entireties. [Background technology]

[0003] Such filtration devices are known in the prior art. They are used in industrial production processes to filter plastics in liquid form, also called molten plastics. The filter elements used for filtration pick up contaminants from the molten plastic and must be regularly cleaned. For this purpose, it is known to feed the liquid plastic to the filter element counter to the filtration flow direction, in order that the contaminants fall off and are removed from the filter element. This process is also called backflushing. The plastic used for backflushing adsorbs the contaminant particles picked up on the filter side and is then discharged from the housing for disposal. Summary of the Invention [Problem to be solved by the invention]

[0004] Although such devices have proven useful in practice, there is still room for improvement. A particular drawback is that the plastic melt used for backflushing is lost during each backflushing process and is no longer available for use in the production process. Given the long duration of operation, this results in considerable loss costs and a large amount of contaminated plastic melt to be disposed of. [Means for solving the problem]

[0005] Against this technical background, the present invention is based on the task of further improving filtration devices and processes of the type described at the beginning so as to eliminate as far as possible the drawbacks found in the prior art. In particular, a filtration device was identified which reduces the amount of plastic melt lost due to the backflushing process.

[0006] According to the invention, this task is achieved by providing a filtration apparatus of the above-mentioned type, characterized in that the filtration apparatus has a backwash screen support fluidly connected to the backwash discharge channel, the backwash screen support having a screen chamber for receiving a backwash filter element, and the filtration apparatus further has a backflush filter element disposed in the screen chamber, the backflush filter element being adapted to filter the backflushed plastic.

[0007] The present invention achieves that a large portion of the backflushed plastics can be returned to the process in purified form by re-filtering the backflushed plastics. Only a small portion of the backflushed plastics, also called the rinsing mass, which now contains a high concentration of dirt particles, needs to be discharged from the system and disposed of. This allows a significant reduction in the amount of plastics lost as a result of backwashing (synonymous herein with "backflush"), for example from about 1 liter per backwash operation to about 0.15 liters per backwash operation for the exemplary system.

[0008] This makes the operation of the filtration device more economical for the operator, which is especially true for highly contaminated plastic melt, since the higher number of backflushes required in this case means that the plastic melt lost through the backflushing process becomes more and more significant. Overall, the backflushing losses are thus reduced. The amount of plastic to be disposed of is reduced, which is also economically beneficial.

[0009] According to a preferred embodiment, the filtration device comprises a backflush filter element and a second backflush feed channel fluidly connected to the outlet, the second backflush feed channel being configured to feed the plastic filtered by the backflush screen support to the outlet. In this way, it is achieved that the plastic used for backflushing the filter element and filtered by the backflush screen support can be fed to the process. This reduces the amount of plastic that is discarded and returns a large portion of the plastic used for backflushing to the production process.

[0010] Preferably, according to another preferred embodiment, the filtration device comprises a pressure generating unit fluidly coupled to the backwash supply channel and / or the second backwash discharge channel, the pressure generating unit being configured to pump the plastic for backwash into the screen carrier and / or the backwash screen carrier in a direction opposite to the filtration flow direction. This pressure generating unit utilizes the finding that a more efficient backwash process can be achieved by applying additional pressure to the plastic used for backwash. For example, a good detachment of contaminants from the backwashed filter element can be achieved, in particular by applying a pressure pulse suddenly to the plastic used for backwash. In addition, the pressure generating unit facilitates the subsequent reintroduction of the filtered backwashed plastic into the process. By applying additional pressure by the pressure generating unit, the overall system pressure remains constant, and the plastic melt used for backflush can be reintroduced into the process along a pressure gradient.

[0011] Preferably, the pressure generating unit is connected to the discharge channel in a fluid conducting manner and is configured to remove plastic from the discharge channel and make it available for backflushing, in other words, the pressure generating unit provides its own supply from the discharge channel, removes plastic melt from the discharge channel and makes it available for backflushing at a pressure that is normally higher than the system pressure.

[0012] Thus, the plastic used for backflushing is removed from the filtration system and no external supply is required.

[0013] According to a preferred embodiment, the pressure generating unit comprises or is designed as one of the following elements: a piston, in particular a displacement plunger, a gear pump. In particular, the use of a piston in the form of a displacement plunger has been found to be optimal for providing pressurized plastic for backflushing.

[0014] According to a preferred embodiment, the housing has a feed channel fluidly coupled to the inlet so that plastic can be fed to the filter side of the filter element, and a discharge channel fluidly coupled to the outlet so that filtered liquid plastic can be discharged from the clean side of the filter element, the channels referred to here serving to feed the melt to be filtered to the filter side of the filter element and then discharge the filtered melt from the clean side of the filter element.

[0015] According to a variant embodiment, the screen chamber of the screen carrier and / or the backflush screen carrier is a first screen chamber, and the screen carrier and / or the backwash screen carrier has a second screen chamber, in which a second filter element is arranged. The use of several screen compartments and screens in the screen carrier or the backflush screen carrier has proven to be advantageous for the sequential filtering operation of the filtering device. For example, as will be explained in detail in connection with the description of the drawings, such an arrangement allows one of the filter elements to be used for normal filtering operation, while the second filter element is backwashed.

[0016] The present invention is further configured as follows: the filtration device has a second supply channel fluidly connected to the inlet so that plastic can be supplied to the filter side of the second filter element, and a second discharge channel fluidly connected to the outlet so that filtered plastic can be discharged from the clean side of the second filter element, and the second filter element can be connected to the second supply channel and the second discharge channel so that plastic passes through the second filter element from the filter side to the clean side in a filtration flow direction and is filtered. Preferably, the filtration apparatus further comprises a second backwash supply channel of the second filter element, the second backwash supply channel being fluidly coupled to the filter side of the second filter element and arranged to supply the backwash fluid to the second filter element in a direction opposite to the filtration flow direction; the filtration apparatus further comprises a second backwash discharge channel fluidly coupled to the clean side of the second filter element, the second backwash discharge channel being configured to discharge the backwash fluid after it has passed through the second filter element; and the second backwash discharge channel of the second filter element being fluidly coupled to the first or second backwash filter element of the backwash screen support. This exemplary embodiment is based on the principle that the second filter element and the second backwash filter element have the same configuration of feed and discharge channels, so that also for the second filter element, the plastic used to backwash this filter element is filtered and cleaned by the second backwash filter element, and a large part of the plastic melt used to rinse the second filter element can be pumped into the process after cleaning by the second backwash filter element. This configuration allows, overall, to use at least one filter element per screen support while backflushing another one to allow continuous filtration operation.

[0017] According to a preferred embodiment, the screen support is a first screen support and the filtering device comprises a second screen support, which is configured similarly to the screen support according to any one of claims 1 to 8. This preferred embodiment also takes into account the idea that in particular three filter elements are available for the filtering process, so that the filtering device allows a permanent filtering operation even when one of the filter elements is being backwashed.

[0018] Preferably, the filter elements of the screen support have essentially the same pore size as the filter elements of the backwash screen support, so that the plastic melt processed by the backflush screen support has the same purity as the plastic melt filtered by the filter elements.

[0019] According to an alternative embodiment, the filtration device comprises an accumulator or storage device that is fluidly connected to the backwash drain channel and / or the second drain channel and arranged to store the backwash fluid from the backwash drain channel and / or the second backwash drain channel.

[0020] Preferably, the accumulator device comprises a piston, in particular an accumulator plunger.The use of a piston in the form of an accumulator plunger has been found to be particularly useful for forming the accumulator device.

[0021] The invention has been described above with reference to a filtering device. In another aspect, the invention relates to a method for operating a filtering device, in particular a filtering device according to one of the above embodiments. The invention achieves the task explained at the beginning with respect to the method, which method comprises the steps of: providing a filtering device with a screen support, the screen support having at least one filter element arranged in a screen chamber; filtering liquid plastic in a filtering flow direction by the filter element; backwashing the filter element with the filtered plastic against the filtering flow direction; directing the backwashed plastic after passing through the filter element to a backflush filter element; filtering the backflushed plastic by the backflush filter element.

[0022] The method uses the same advantages and preferred embodiments as the filtration device of the invention. In this respect, reference is made to the above description, the contents of which are incorporated herein. In summary, the method also makes use of the knowledge that the main part of the molten plastic used for backflushing is treated and returned to the process by filtration through the backflushing filter element. The amount of highly contaminated plastic that has to be discharged from the housing is significantly reduced. This makes the operation of the filtration device more economical for the operator, and this is especially true for highly contaminated plastic melts, since the high number of backflushes required in this case means that the plastic melt lost by the backflushing process becomes increasingly significant. Overall, the backflush losses are thus reduced.

[0023] The method further includes a step of combining the filtered backflushed plastics with the filtered liquid plastics. In other words, it is proposed to feed the filtered backflushed plastics with the filtered liquid plastics to a conventional process.

[0024] According to a preferred embodiment, the method further comprises the steps of backflushing the backflush filter element with the filtered liquid plastic and discharging the contaminated liquid plastic after backflushing the backflush filter element. This has the advantage that only a small amount of highly contaminated liquid plastic needs to be discharged from the housing after backflushing the backflush filter element. This amount of highly contaminated plastic to be discharged is significantly less than in the case of processes known in the prior art.

[0025] The method further comprises filtering the liquid plastic through the filter element and the backflush filter element, such that the backflush plastic is also in permanent flow through the backflush filter element when not being used to filter, thereby avoiding clumping and the like.

[0026] The method is further configured to backwash the filter element or the backflush filter element and the synthetic material used to trigger the backwash has a higher pressure than the synthetic material to be filtered, the pressure difference being in particular between 10 bar and 50 bar. [Please provide pressure differential ranges here, inventors].

[0027] The overpressure of the plastic used for backflushing compared to the system pressure before backflushing, on the one hand, makes it easier to remove contamination on the filter element, especially when a pressure pulse is applied to the plastic used for backflushing, and on the other hand, the overpressure makes it possible to accelerate the backflushing process and to facilitate reintroduction into the process, so that the drop in system pressure associated with reintroducing the filtered plastic into the process does not occur.

[0028] According to a preferred embodiment, the plastics used for the backflush are sucked in the backwash direction downstream of the filter element and / or the backflush filter element. In other words, in particular already filtered plastics are used for the backwash process. This prevents the backwash filter element from becoming contaminated on the clean side.

[0029] Further features and advantages of the invention will become apparent from the appended claims and the following description, in which exemplary embodiments are set forth in detail with the aid of schematic drawings. [Brief description of the drawings]

[0030] [Figure 1] 1 is a schematic diagram of a filtration device of the present invention. [Diagram 2] FIG. 1 is a perspective view of one embodiment of a filtration device of the present invention in a production position. [Diagram 3] FIG. 1 is a perspective view of one embodiment of a filtration device of the present invention in a production position. [Figure 4] FIG. 3 is a side view of the filtration device of FIG. 2. [Diagram 5] FIG. 4 is a plan view of the filtration device of FIG. 3. [Figure 6] FIG. 2 shows the filtration device of the present invention in an operational state in which the filter element is being backwashed. [Figure 7] FIG. 2 shows the filtration device of the present invention in an operating state in which the backwash element is backwashed. [Figure 8] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 9] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 10] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 11] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 12] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 13] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 14] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 15] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 16] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 17] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 18] FIG. 1 illustrates an exemplary sequence of steps in a backwash sequence. [Figure 19] 1 shows an alternative embodiment of the filtering device of the invention having a suction device in one operating state; [Figure 20] 4 shows a variant embodiment of the filtering device of the invention having a suction device in another operating state; FIG. [Figure 21] 4 shows a variant embodiment of the filtering device of the invention having a suction device in another operating state; FIG. [Figure 22] 4 shows a variant embodiment of the filtering device of the invention having a suction device in another operating state; FIG. [Diagram 23] 4 shows a variant embodiment of the filtering device of the invention having a suction device in another operating state; FIG. [Figure 24] 4 shows a variant embodiment of the filtering device of the invention having a suction device in another operating state; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] FIG. 1 shows, in a schematic diagram, an apparatus 2 for filtering liquid plastics. FIG. 2 shows a housing 4 (not shown in detail) with an inlet 6 for introducing plastics and an outlet 8 for discharging the plastics. A screen carrier or support 12 is housed within the housing 4. The screen carrier 12 has a screen chamber 10 in which a filter element 14 is housed. The filter element 10 has a filter side 16 and a clean side 18. The housing 4 further has a feed channel 36 fluidly connected to the inlet 6 for feeding plastics to the filter side of the filter element 14. The housing 4 further has a discharge channel 38 fluidly connected to the outlet 8 for discharging filtered plastics from the clean side 18 of the filter element 14.

[0032] The filtration apparatus 2 further includes a backwash feed channel 20 fluidly coupled to the clean side 18 of the filter element 14, the backwash feed channel being arranged to feed plastics to the filter element 14 in a direction opposite to the filtration flow direction 56. The apparatus 2 further includes a backwash discharge channel 22 fluidly coupled to the filter side 16 of the filter element 14, the backwash discharge channel being arranged to discharge the backwashed plastics after it has passed through the filter element 14. A backflush screen carrier 24 is fluidly coupled to the backflush discharge channel 22. The backflush screen carrier 24 includes a screen chamber 26 in which a backflush filter element 28 is housed. The backflush filter element 28 is adapted to filter the backflush plastics.

[0033] A second backwash feed channel 30 is provided between the backwash filter element 28 and the outlet 8. The second backflush feed channel 30 is positioned to feed plastics filtered by the backflush screen support 24 to the outlet 8.

[0034] The filtration device 2 further comprises a pressure-generating unit 32, which is connected to the backwash feed channel 20. The filtration device 2 further comprises a second backwash discharge channel 31, which is connected to the pressure-generating unit 32 and to the clean side of the backwash filter element 28. A discharge outlet 29 is provided on the filter side 25 of the backwash filter element 28, which serves to discharge the highly contaminated melt. The pressure-generating unit 32 is adapted to pump the plastics for backwash against the filtration flow direction 56 into the screen support 12 and the backwash support 24. In addition, the pressure-generating unit 32 is adapted to pump the plastics for backwash via the second backwash discharge channel 31 into the backwash filter 28. The highly contaminated plastics are then discharged via the discharge outlet 29.

[0035] The pressure generating unit 32 is specifically designed as a displacement plunger 34. The pressure generating unit 32 is connected in a fluid conducting manner to an outlet channel 38. The pressure generating unit 32 is also set up to take plastic for backflushing from the outlet channel 38 and use it for backflushing.

[0036] 2 and 3 show a device 2 for filtering liquid plastics in a perspective view. The device 2 comprises a housing 4 with an inlet 6 for introducing the plastics and an outlet 8 for discharging the plastics. A screen carrier 12 is arranged in the housing 4, which in this case is a first screen carrier 62. The screen carrier 12 comprises a screen chamber 10 housing a filter element 14. The filter element 14 comprises a filter side 16 and a clean side 18, not shown here. The filter element 14 is connectable to the inlet 6 and the outlet 8 such that the plastics of the filter element 14 flow in a filtering flow direction 56 from the filter side 16 to the clean side 18 for filtering. The device 2 further comprises a backwash feed channel 20, which is fluidly connected to the clean side 18 of the filter element 14 and is arranged to feed the plastics to the filter element 14 against the filtering flow direction 56.

[0037] The device 2 further comprises a backwash discharge channel 22 fluidly connected to the filter side 16 of the filter element 14, the backwash discharge channel being arranged to discharge the backwashed plastics after passing through the filter element 14. The filtration device further comprises a backflush screen support 24 fluidly connected to the backflush discharge channel 22, on which the screen chamber 26 and the backwash filter element 28 are provided. A second backwash supply channel 30 is arranged between the backwash filter element 28 and the outlet 8, the second backwash supply channel being adapted to supply the plastics filtered by the backwash screen carrier 24 to the outlet 8. The filtration device 2 further comprises a pressure generating unit 32 fluidly connected to the backwash supply channel 20 and the second backwash discharge channel 31. The pressure generating unit 32 is adapted to pump the plastics for backwashing into the screen support 12 and the backwash screen support 24 against the filtration flow direction (56).

[0038] The housing 4 further comprises a feed channel 36 fluidly coupled to the inlet 6 for feeding plastic to the filter side 16 of the filter element 14. The housing 4 further comprises a discharge channel 38 fluidly coupled to the outlet 8 for discharging the filtered liquid plastic from the clean side 18 of the filter element 14. The pressure generating unit 32 is fluidly coupled to the discharge channel 38, the pressure generating unit adapted to take and provide plastic from the discharge channel 38 for backwashing. The respective screen chambers 10, 26 of the screen carrier 12 and the backwash screen carrier 24 are in this case first screen chambers 10, 26, the screen carrier 12 comprising a second screen chamber 40 in which a second filter element 44 is housed. The backwash support 24 comprises a second backwash filter element 46. The filtration device 2 comprises a second feed channel 48 fluidly coupled to the inlet 6 for feeding plastic to the filter side 52 of the second filter element 44. The filtration device 2 further has a second exhaust channel 50 fluidly coupled to the outlet 8 for exhausting the filtered plastic from the clean side 54 of the second filter element 44 .

[0039] The second filter element 44 is connectable to the second supply channel 36 and the second discharge channel 50 such that the plastic material flows from the filter side 52 to the clean side 54 in a filter flow direction 56 for filtration. The filtration device 2 further includes a second backwash supply channel 58 of the second filter element 44 fluidly coupled to the filter side 52 of the second filter element 44, the second backwash supply channel being arranged to supply the backwashed fluid to the second filter element 44 in a direction opposite to the filter flow direction 56. The filtration device 2 further includes a second backwash discharge channel 60 fluidly coupled to the filter side 52 of the second filter element 44, the second backwash discharge channel being arranged to discharge the backwashed fluid after passing through the second filter element 44. The second backwash discharge channel 60 of the second filter element 44 is fluidly connectable to the second backwash filter element 46 of the backwash screen support 24. The filtering device further comprises a second screen carrier 64. The second screen carrier 64 is constructed similarly to the screen carrier 12 or the first screen carrier 62. Therefore, a detailed description thereof will be omitted.

[0040] In the views shown in Figures 2 and 3, the filtration device 2 is in the production position. In the production position, the plastic melt is fed via the inlet 6, then by the feed channels 36, 48 and feed channels not labeled below to the filter elements 14, 44 and the lower filter element, where it is filtered, and then discharged via the discharge channels 38, 50 and the lower discharge channel in the direction of the outlet 8. Furthermore, via the backflush discharge channels 22, 58, the unfiltered melt reaches the backflush filter element 28 and is likewise filtered there, and then discharged in the direction of the outlet 8 by the second backflush feed channel 30 and the second backflush feed channel (not shown) of the second filter element, which is arranged in a correspondingly mirror image relationship. This applies in an analogous manner to the second screen support 64, which will not be described in detail.

[0041] 4 is a side view of the filtration device 2, where the cross-sectional plane is perpendicular to the longitudinal axis of the second carrier 12 or 62 and 64. FIG. 5 is a plan view, where the cross-sectional plane through the screen support 12 or 62 is perpendicular to the longitudinal axis of the displacement plunger 34.

[0042] The arrows depicted in Figure 5 indicate the flow of plastic from inlet 6 to outlet 8 via filter elements 14, 44 and backflush filter elements 28, 46. A total of six filter elements are used to filter the molten plastic. In particular, melt flows from inlet 6 to filter elements 14, 44 via feed channels 36, 48 and from there to outlet 8 via discharge channels 38, 50. Another plastic stream flows from inlet 6 by backflush discharge channels 22, 60 to backflush filter elements 28, 46, respectively, where it is filtered and then flows to outlet 8 via backflush feed channels 20, 50.

[0043] In the state shown in FIG. 5, the melt is fed into the screen chamber 10 and thus into the filter element 14 by the push-out plunger 34 starting from the clean side 18 via the backflush discharge channel 20. This backflushes the filter element 14, i.e. causes the contaminants deposited on the filter side 16 of the filter element 14 to fall off from the filter element 14. The mixture of plastic and contaminants that have fallen off from the filter element 14 then flows by the backflush discharge channel 22 to the backflush filter element 28, in particular to the filter side 25 of the backflush filter element 28. The backflushed melt is now filtered by the backflush filter element 28 and from here flows via the second backflush discharge channel 31 into the discharge channel 38, which then opens into the outlet 8. In other words, the plastics used for backflushing are sent back into the process after filtration by the backflush filter element 28. The second filter element 44 remains connected to the inlet 6 via the feed channels 36, 48, and this second filter element is available for filtration.

[0044] In Fig. 7, the backwash filter element 28 is backwashed. Here too, the displacement plunger 34 delivers pressurized plastic melt into the backwash feed channel 20, which passes through a second backwash feed channel 30 to the backwash filter element 28, in particular to the clean side 27 of the backwash filter element 28. The plastic causes contaminants to fall out of the filter side 25 of the backwash filter element 28, and the highly contaminated plastic mixture is then pumped in the direction of the discharge outlet 29, from where it is discharged.

[0045] Figures 8 to 18 show in detail the individual process steps carried out to flush the filter element 14 by the backflush filter element 28. In the condition shown in Figure 8, firstly the displacement plunger 34 is retracted to remove the plastic melt from the production process. This collects in a reservoir 65 formed in the displacement plunger 34. The screen carrier 12 or 62 and 64 are in the production position already described with reference to Figure 5.

[0046] In Fig. 9 the backflush screen support 24 has been moved to the so-called locked position, moving the screen compartments 26, 42 of the backflush screen carrier 24 away from the inlet 6 and the outlet 8. In the state shown in Fig. 10 the second screen carrier 64 has been moved to the so-called backwash release position, in which the lower filter elements arranged in the second screen carrier 64 are moved away from the respective backwash supply channels 20 and thus no direct connection to the displacement plunger 34 exists. The second screen carrier 64 remains in production via the discharge channel 38.

[0047] In the state shown in Fig. 11, the second screen support 62 has been moved to a so-called compressed position. In this position, the second filter element 44 is separated from the channel leading to the displacement plunger 34. However, the second filter element 44 is still connected to the outlet 8 via the second discharge channel 50, so that the plastic melt can be filtered by the second filter element 44. The filter element 14 is separated from the feed channel 36 and the discharge channel 38. The filter element 14 is still only connected to the displacement plunger 34 via the backflush feed channel 20.

[0048] In the state shown in Figure 10, the displacement plunger 34 is depressed. This pressurizes the melt in the reservoir 65 and also the backflush feed channel 20 and the screen chamber 10. In the state shown in Figure 13, the support 12 is moved so that the screen chamber 10 and the filter element 14 are momentarily in communication with the backflush channel 63 which is temporarily open to atmospheric pressure. The pressurized compressed melt quickly loosens the debris and causes it to fall out of the filter element 14. The second filter element 44 remains in production.

[0049] In the state shown in Fig. 14, the screen carrier 12 has been moved slightly to the right. The illustrated state corresponds to the compressed position from Fig. 11. In Fig. 15, the second screen carrier 64 has been moved to the so-called backflush release position. The filter elements of the second screen support 64 remain in the production position.

[0050] 16, the backwash screen carrier 24 has now been moved into communication with the backwash discharge channel 22, the filter element 14 and the backwash filter element 28. On the outlet side, the backwash screen support 24 is directly connected to the outlet 8.

[0051] 17, the displacement plunger 34 is moved downwardly so that the plastic melt contained in the reservoir 65 is pumped back through the filter element 14 and then through the backflush filter element 28. The melt filtered by the backflush filter element 28 is sent to the outlet 8 and thus to the production process. The dirt from the filter element 14 is now located in front of the backflush element 28.

[0052] In the condition shown in FIG. 18, the screen support 12 or 62 and both the second screen support 64 and the backflush screen support 24 have been returned to the production position 20 so that all six filter elements are now filtering the plastic melt directed to the inlet 6 in the direction of the outlet 8.

[0053] Figure 19 shows an alternative embodiment of a filtering device 2 which is essentially identical in construction to the embodiment of filtering device 2 described in Figures 1 to 18, but which further comprises a storage device 66. The storage device 66 comprises a first accumulator or storage plunger 68 and a second accumulator or storage plunger 70. An annular channel 72 is formed in the lower region of each of the storage plungers 68,70.

[0054] A first storage plunger 68 is connected to the backwash discharge channel 22, which first storage plunger forms part of the backwash discharge channel 22 together with an annular channel 72. A second storage plunger 70 is connected to the backwash discharge channel 60 of the second filter element 44. Similarly, the storage plungers 68, 70 are also connected to the filter element of the second screen support 64, although for clarity only reference will be made to the first screen support 12. The storage device 66 further has a channel opening into the inlet 6.

[0055] When the storage plungers 68, 70 are in the position shown in Figure 19, circulation of melt is possible via the backflush discharge channel 22 and via the backflush discharge channel 60 of the second filter element 44 via the respective annular channel 72. In Figure 19, the filtration device 2 is in the production position. Plastic fed to the inlet 6 flows through all six filter elements. The plastic is filtered therethrough to the outlet 8 as already described with reference to Figures 2 and 3.

[0056] 20 is a side view of the exemplary embodiment of the filtration device 2 shown in FIG. As can be seen, the storage plunger 68 is connected to both the first screen support 62 and the second screen support 64 in the manner just described. Melt flows from the filter side 16 of the filter element 14 via the backwash discharge channel 22, which allows perpetual circulation by annular channel 72 through the storage device 66 to the backwash filter element 28 where it is filtered and delivered to the outlet 8.

[0057] Figure 21 shows the flow of plastic in the production position by arrows in another example. In the state shown in Figure 22, the melt is pumped backwards by the displacement plunger 34 through the filter element of the second screen carrier 64 described below to the storage device 66, so that the first storage plunger 68 is moved upwards. This state is shown in plan view in Figure 23.

[0058] In FIG. 24, the backflushed melt is pumped by a first storage plunger 68 through the backflush filter element 28 and then discharged towards the outlet 8 . [Explanation of symbols]

[0059] 2 Filtration device 4. Housing 6 entrance 8 exit 10 Screen chamber or screening room 12 Screen carrier or support 14 Filter element 16 Filter side 18 Clean Side 20 Backwash Supply Channel 22 Backwash discharge channel 24 Backflush screen carrier or support 25 Filter side of backwash filter element 26 Screen chamber for backflush screen support 27 Inside of the backwash filter element 28 Backwash filter element 29 Exhaust outlet 30 Second Backwash Supply Channel 31 Second backwash discharge channel 32 Pressure generating unit 34 Displacement Plunger 36 Supply Channels 38 Exit Duct 40 Second Screen Chamber of Screen Tray 42 Second screen chamber of backflush screen support 44 Second Filter Element 46 Second Backwash Filter Element 48 Secondary Supply Channel 50 Second Exit Channel 52 Filter side of second filter element 54 Clean side of second filter element 56 Filtration flow direction 58 Backwash supply channel for second filter element 60 Backwash discharge channel of second filter element 61 Channels 62 First Portafilter 63 Ducts that open to the atmosphere depending on operating conditions 64 Second screen carrier or support 65 Reservoir 66 Storage Device 68 First storage plunger 70 Second storage plunger 72 Ring Channel

Claims

1. An apparatus (2) for filtering liquid plastics, comprising: - a housing (4) with an inlet (6) for introducing said plastics and an outlet (8) for discharging said plastics, - a screen carrier (12) accommodated in said housing (4), said screen carrier having a screen chamber (10) for accommodating a filter element (14), - a filter element (14) arranged in the screen chamber (10) of the screen carrier (12), the filter element having a filter side (16) and a clean side (18); The filter element (14) can be connected to the inlet (6) and the outlet (8) so that the plastic flows through the filter element (14) from the filter side to the clean side along a filtering flow direction (56) and is filtered, and the filter element (14) can be cleaned by backwashing by the plastic flowing in a direction opposite to the filtering flow direction (56); - a backwash feed channel (20) fluidly coupled to the clean side (18) of the filter element (14), the backwash feed channel being arranged to feed plastic to the filter element (14) against the filtration flow direction (56); a backwash discharge channel (22) fluidly connected to the filter side (16) of the filter element (14), the backwash discharge channel being adapted to discharge the backwashed plastics after it has passed through the filter element (14), a backwash screen support (24) fluidly coupled to the backwash discharge channel (22), the backwash screen support having a screen chamber (26) for receiving a backwash filter element (28); The filtration device (2) comprises a backflush filter element (28) disposed within the screen chamber (26), the backflush filter element (28) adapted to filter the backflushed plastic.

2. 2. The filtration device (2) of claim 1, further comprising a second backwash feed channel (30) fluidly coupled to the backwash filter element (28) and the outlet (8), the second backwash feed channel (30) adapted to feed the plastic filtered by the backwash screen support (24) to the outlet (8).

3. 2. The filtering device (2) according to claim 1, further comprising a pressure generating unit (32) fluidly coupled to the backwash supply channel (20) and / or the second backwash discharge channel (31), the pressure generating unit (32) being configured to pump plastic for backwash into the screen carrier (12) and / or the backwash screen carrier (24) against the filtering flow direction (56).

4. 4. The filtration device (2) of claim 3, wherein the housing (4) has a supply channel (36) fluidly connected to the inlet (6) to supply plastic to the filter side of the filter element (14) and a discharge channel (38) fluidly connected to the outlet (8) to discharge the filtered liquid plastic from the clean side (18) of the filter element (14).

5. Said pressure generating unit (32) comprises the following components: - a piston, in particular a displacement plunger (34), - Gear pump 4. The filtering device (2) according to claim 3, which is configured as any one of the following:

6. 4. The filtration device (2) of claim 3, wherein the pressure generating unit (32) is fluidly coupled to the discharge channel (38) and adapted to remove plastic from the discharge channel (38) and provide the plastic for backflushing.

7. 2. The filtration device (2) of claim 1, wherein the screen chamber (10, 26) of the screen carrier (12) and / or the backflush screen carrier (24) is a first screen chamber (10, 26), and the screen carrier (12) and / or the backwash screen carrier (24) has a second screen chamber (40, 42), and a second filter element (44, 46) is arranged in the second screen chamber (40, 42).

8. - a second feed channel (48) fluidly connected to said inlet (6) for feeding plastic to the filter side (52) of said second filter element (44); a second discharge channel (50) fluidly connected to said outlet (8) to allow said filtered plastic to be discharged from said clean side (54) of said second filter element (44); The second filter element (44) may be in communication with the second supply channel (36) and the second exhaust channel (50) such that the plastic passes through the second filter element (44) from the filter side (52) to the clean side (54) in the filtration flow direction (56) and is filtered; a second backwash supply channel (58) of the second filter element (44), the second backwash supply channel being fluidly coupled to the filter side (52) of the second filter element (44) and arranged to supply a backwash fluid to the second filter element (44) against the filtration flow direction (56); a second backwash discharge channel (60) fluidly coupled to the clean side (54) of the second filter element (44), the second backwash discharge channel being configured to discharge the backwash fluid after it has passed through the second filter element (44); 8. The filtration device (2) of claim 7, wherein the second backwash discharge channel (60) of the second filter element (44) is fluidly coupled to the first or second backwash filter element (28, 46) of the backwash screen support (24).

9. The filtration device (2) of claim 1, wherein the screen support (12) is a first screen support (62) and the filtration device (2) has a second screen support (64), the second screen support (64) being configured similarly to the screen support (12) of any one of claims 1 to 8.

10. 2. The filtration device (2) of claim 1, wherein the filter elements (14, 44) of the screen support (12) have substantially the same pore size as the filter elements (28, 46) of the backwash screen support (24).

11. 9. The filtration device (2) of claim 8, further comprising a storage device (66) connected in a fluid conducting manner to the backwash discharge channel (22) and / or the second discharge channel (50) and arranged to store backwash fluid from the backwash discharge channel (22) and / or the second backwash discharge channel (60).

12. 12. The filtering device (2) according to claim 11, wherein the storage device (66) comprises a piston, in particular a storage plunger (68).

13. A method for operating a filtration device (2), in particular a filtration device (22) according to any one of claims 1 to 12, comprising: providing a filtration device (2) with a screen support (12), said screen support (12) having at least one filter element (14) arranged in a screen chamber (10), - filtering said liquid plastic in a filtering flow direction (56) by said filter element (14), - backwashing the filter element (14) with the filtered plastic against the filtration flow direction (56), - directing the backwashed plastics after passing through the filter element (14) to a backflush filter element (28), - filtering said backflushed plastics through said backflush filter element (28).

14. The method of claim 13 further comprising the step of: combining the filtered backflushed plastic with the filtered liquid plastic.

15. - backflushing the backflush filter element (28) with the filtered liquid plastic; The method of claim 13, further comprising the step of: - discharging contaminated liquid plastic after backflushing the backflush filter element (28).

16. The method of claim 13, wherein the filtering of the pre-liquid plastic is performed by both the filter element (14) and the backflush filter element (28).

17. 14. The method according to claim 13, wherein the synthetic material used to backwash the filter element (14) or the backflush filter element (28) and to trigger the backwashing has a higher pressure than the synthetic material to be filtered, the pressure difference being in particular between 10 bar and 50 bar.

18. 14. The method of claim 13, wherein the artificial material used for the backwash is sucked in a backwash direction downstream of the filter element (14) and / or the backflush filter element (28).

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