Methods for filtering a fluid using a backflushable filtering device, and filtering devices

Abstract

Filtering device (2, 80) for filtering a fluid, 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. 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).

Description

[0001] Methods for filtering a fluid using a backflushable filtering device, and filtering devices

[0002]

[0001] The invention relates to methods and filtering devices (also referred to as screen changers) for filtering a fluid, in particular liquefied plastic, such as thermoplastic, preferably having a high viscosity. The fluid is also referred to as polymer melt flow. The filtering device has a production mode (also referred to as filtration mode) and a backflush mode so that it can be backflushed, hereinafter referred to as backflushable filtering device.

[0003]

[0002] Such methods and filtering devices are used in plastic processing machines when there are high demands on the purity of the plastic to be processed further. They are typically positioned between an extrusion device, which melts and conveys the liquefied plastic, and an application device.

[0004]

[0003] DE 10 2022 106 334 Al and DE 20 2022 100 235 U1 each disclose a filtering device with two axially movable screen carriers (also referred to as screen pistons) on each of which screen areas with screens are arranged. During some time in operation, while the screen piston with its screen area is in the production position (or filtration position or production mode or filtration operation), residues accumulate on the screen on the inlet side, also called the filter side or dirt side, and such a contaminated screen is then cleaned through backflushing (or backflush position or backflush mode or backflush operation). In such a case, the screen piston is moved from the production position to a backflush position or screen change position by axial displacement, and in the backflush position liquid plastic flows through the screen in the opposite direction so that impurities in the form of solids, particles or fibers are detached from the screen and disposed of together with the liquid plastic. After backflushing, the screen piston is moved back to the production position and liquid plastic is cleaned again at the respective screen area. After several backflushes of this kind, a screen is then regularly replaced. Even after a screen has been replaced, the screen area must be introduced into the production process and can be backflushed several times at regular intervals.

[0005]

[0004] A disadvantage of the described backflushing according to the prior art is that, together with the impurities, a high quantity of liquid plastic is removed from the production process, which leads to greater overall losses of liquid plastic, as such quantities of liquefied plastic is not available for the production process anymore.

[0005] The invention is based on the objective of further developing a method and a filtering device in such a way that the disadvantages found in the prior art are avoided as far as possible, in particular a method is specified in which losses of plastic due to backflushing are reduced.

[0006]

[0006] The invention solves the problem according to a first aspect with a method for filtering a fluid, in particular liquefied plastic, using a filtering device.

[0007]

[0007] The filtering device comprises two or more screen areas wherein each screen area comprises a filter side and a clean side with a screen therebetween, wherein each screen area is configured to convey fluid in a filtration flow direction from its filter side to its clean side during filtration operation; convey fluid in a backflush flow direction from its clean side to its filter side during a backflush operation; feed fluid from its filter side to a filter side of another screen area of the two or more screen areas via a feed channel (there may be more than one feed channel within the filtering device).

[0008]

[0008] Each screen area may comprise a screen cavity and at least one screen. Each screen area has a filter side and a clean side. Fluid flows through each screen area in the direction of filtration flow during filtration operation and in an opposite direction of backflush flow during backflush operation. The screen cavity of each screen area can be connected to a backflush feed channel for introducing fluid for backflushing the screen area and a backflush discharge channel for discharging filter residues.

[0009]

[0009] In the backflush operation of the filtering device following steps are performed: a) conveying fluid from its clean side to its filter side of one screen area of the two or more screen areas; b) feeding this conveyed fluid from its filter side of the one screen area into the filter side of one or more other screen areas of the two or more screen areas via the feed channel; c) conveying this fed fluid in the filtration flow direction from the filter side of the one or more other screen area to the clean side of the one or more other screen areas; discharging fluid with filter residue via a backflush discharge channel of the filtering device.

[0010]

[0010] Preferably, in step d) only the fluid from the one screen area with filter residue is discharged via the backflush discharge channel.

[0011]

[0011] Advantageously, the invention makes use of the finding that backflushed fluid (liquified plastics) does not always contain filter residue or may contain low amounts of filter residue or may at least not contain filter residue throughout the entire backflush operation of that particular screen area. As there is fluid backflushed without high amounts of filter residue, discharging of backflushed fluid via a respective discharge channel is a massive waste of fluid (liquified plastic) that could be used in the production mode for subsequent applications.

[0012]

[0012] In step b) and c), the filter sides of the other screen areas may now include the filter residue from the screen area of step a).

[0013]

[0013] The inventive method ensures that fluid is largely kept within the production process by performing the steps a) to c) prior step d). So, clean material is kept in the production process and conveyed (filtered) via another screen area. Only as a follow-up step d), heavily contaminated fluid, having a huge amount of filter residue is discharged in step d) as concentrated manner via the backflush channel. So, it is ensured that the amount of liquid plastic that must be removed from the production process during backflush operation is reduced to its absolute minimum. According to the invention, the amount of discharged fluid to be disposed of, which is to be removed from the production process together with filter residue (filtered impurities due to backflushing), is substantially reduced. As a benefit, a substantial amount of liquid plastic can be kept (or returned) via steps a) to c) within the production process. This makes not only filtration but also the production process significantly more economical than in the prior art.

[0014]

[0014] According to the invention, this is achieved by separating sufficiently clean backflush material in the form of liquid plastic from dirty backflush material. The clean plastic material can remain in the process via steps a) to c) by feeding and conveying it to at least one further screen area of the filtering device via feed channels. Fluid that is more heavily soiled with filter residue is discharged through the backflush discharge channel, i.e. essentially the heavily soiled plastic material is discharged as waste.

[0015]

[0015] In a preferred embodiment, the method comprises after step c) and prior step d) the step cl) in which fluid is conveyed from the clean side of the other screen area to the filter side of the other screen area in its backflush operation of the other screen area. Accordingly, the fluid flowing back from one screen area is filtered via the other screen area (step c) and then, only the further filtered fluid is discharged in step d). In other words, during a backflush operation the backflushed fluid from the one screen area is conveyed entirely via one further screen area before it is discharged in step d). This may reduce the loss of backflushed fluid by half, as tests have shown.

[0016] Preferably, the steps a) and b) occur in a first backflush phase of the backflush operation in which neither the one screen area nor the other screen areas is connected to the backflush discharge channel. This is advantageous, as in a backflush operation it needs some time until the filter residue is released from the screen. This is mainly caused by the pressure values at which the fluid is conveyed in the filtration mode which leads to a strong adhesive force at which the filter residue remains at the screen. When, in opposite direction during backflush operation, the backflush fluid does not contain sufficient pressure or is not applied for a sufficient amount of time, the filter residue is not released (yet). Until this releasing of the filter residue (during the first backflush phase), the backflushed fluid is not contaminated to an extend that the fluid should be removed from the production process and so, for this first phase, steps a) to c) are applied to ensure that this relatively clean backflushed fluid is kept in the production process.

[0016]

[0017] Preferably, the step d) and step cl) occur in a second backflush phase of the backflush operation in which the one screen area or the other screen area is connected to the backflush discharge channel and the feed channel is closed. This is advantageous, in this second phase, the backflushed fluid is heavily enriched with dirt, meaning it is contaminated to an extend that it should not be used within the production process and for that it should not be conveyed (filtered) via the further screen area (anymore). In this second phase, step d) should be performed immediately, to avoid a congesting of the further screen area as this fluid is enriched with a high amount of filter residue that should be discharged immediately. The second phase may be the time when the releasing of the filter residue from the screen has finally started as the backflushed fluid may now have the appropriate pressure value for such a release or the amount of time for applying the backflush fluid is finally sufficient.

[0017]

[0018] The second backflush phase may be timely after the first backflush phase. To be more specific, if fluid is conveyed from a clean side to a filter side of the one screen area, there is a first time duration in which this fluid does not contain filter residue and there is a second time duration upon which the backflushed fluid should be discharged.

[0018]

[0019] Preferably, the first backflush phase ends when less than 50%, preferably less than 40%, more preferably between 30% to 40% of a fluid volume of a screen cavity of the one screen area is fed in step b). As tests have shown, the process is carried out particularly advantageously with a view to minimizing losses of fluid (liquified plastic), in which in the first backflush phase such amounts of fluid (most preferred approx. 30 - 40% of the fluid volume) of one screen area is fed to - meaning conveyed upstream of - the other screen area in step b).

[0020] The filtering device preferably also comprises a housing with at least one inlet for introducing the fluid and at least one outlet for discharging the fluid

[0019]

[0021] The filter sides of at least two different screen areas are connectable to each other by means of one or more feed channel, there may be more than one feed channel in the filtering device.

[0020]

[0022] In a first implementation of the method, following steps may be performed:

[0021] - introducing fluid through the inlet in the filtration flow direction into at least one screen area of the plurality of screen areas for filtering and then discharging the filtered fluid through the outlet,

[0022] - backflushing of the one screen area of the plurality of screen areas by conveying fluid in the backflush flow direction in the one screen area of the plurality of screen areas and

[0023] - in a first backflush phase, feeding the fluid flowing back from the filter side of the one screen area of the plurality of screen areas to the filter side of at least another screen area of the plurality of screen areas , and conveying the fluid also from the one screen area of the plurality of screen areas through the at least another screen area of the plurality of screen areas,

[0024] - in a second backflush phase after the first backflush phase, discharge of fluid from the one screen area of the plurality of screen areas through the backflush discharge channel,

[0025] - re-introduction fluid through the inlet in the filtration flow direction into at least one screen area of the plurality of screen areas.

[0026]

[0023] The invention further solves the problem according to a first implementation with a device in that a control unit (controller) is provided and set up so that the drive or drives of the screen carrier (screen piston) and the pressure generator are controlled in such a way that the following process is carried out:

[0027] - introducing fluid through the inlet in the direction of filtration flow into the at least one screen area for filtering and then discharging the filtered fluid through the outlet,

[0028] - in a first backflush phase, backflushing of the screen area by conveying fluid in the backflush flow direction in the screen area and

[0029] - feeding the fluid flowing back in the first backflush phase from the filter side of the screen area to at least one further screen area to its filter side, and there conveying the fluid also from the screen area through the at least one further screen area,

[0030] - in a second backflush phase after the first backflush phase, discharge of fluid from the screen area that is more heavily contaminated with filter residue through the backflush discharge channel, re-introduction of fluid into the backflushed screen area in the direction of filtration flow.

[0031]

[0024] Advantageously, the invention makes use of the finding that it has been shown in practice that clean material initially comes out of the backflush outlet during backflushing. After some time, material comes out that is heavily enriched with dirt. The inventive method and device ensures that the clean material is largely returned to the process, and that the dirt is discharged in as concentrated a manner as possible. The method and the device for filtering according to the invention ensure that the amount of liquid plastic that has to be removed from the production process for backflushing is reduced during backflushing. According to the invention, the amount of waste plastic to be disposed of, which is to be removed from the production process together with filtered impurities due to backflushing, is substantially reduced. A substantial amount of liquid plastic can be returned to the production process by the method according to the invention to a significantly greater extent than has been possible in the prior art to date, in that liquid, clean plastic still to be used according to the invention is fed into the production process, while only liquid plastic heavily contaminated with impurities is removed from the production process by backflushing and disposed of. This makes not only the filtration but also the production process as a whole significantly more economical than in the prior art.

[0032]

[0025] According to the invention, this is achieved by separating sufficiently clean backflush material in the form of liquid plastic from dirty backflush material in the first backflush phase. The clean plastic material can remain in the process by feeding it to at least one further screen area on the filter side. In the second backflush phase - after the first backflush phase - fluid from the (first) screen area that is more heavily soiled with filter residue is discharged through the backflush discharge channel, i.e. essentially the heavily soiled plastic material is discharged as waste.

[0033]

[0026] The invention solves the problem according to another, second implementation with a method with the steps: introducing fluid through the inlet in the direction of filtration flowinto the at least one screen area for filtering and then discharging the filtered fluid through the outlet, backflushing the screen area by conveying fluid in the backflush flow direction in the screen area, feeding the backflushing fluid from the filter side of the screen area to at least one further screen area to its filter side, and there conveying the fluid also from the screen area through the at least one further screen area, backflushing the at least one further screen area by conveying fluid in the backflush flow direction in the at least one further screen area and discharging it through the backflush discharge channel, re-introduction of fluid into the backflushed screen area or the several backflushed screen areas in the direction of filtration flow for filtering.

[0034]

[0027] The invention solves the problem according to this second implementation also with a device in which a controller is provided and set up so that the drive or drives of the screen carrier and the pressure generator are controlled in such a way that the following method is carried out: introducing fluid through the inlet in the direction of filtration flow into the at least one screen area for filtering and then discharging the filtered fluid through the outlet, backflushing the screen area by conveying fluid in the backflush flow direction in the screen area, feeding the backflushing fluid from the filter side of the screen area to at least one further screen area to its filter side, and there conveying the fluid also from the screen area through the at least one further screen area, backflushing the at least one further screen area by conveying fluid in the backflush flow direction in the at least one further screen area and discharging it through the backflush discharge channel, re-introduction of fluid into the backflushed screen area or the several backflushed screen areas in the direction of filtration flow for filtering.

[0035]

[0028] With this second implementation, it is achieved that during backflushing the amount of liquid plastic which must be removed from the production process for backflushing is reduced, because a substantial amount of liquid plastic can be returned to the production process by the method according to the invention, in that primarily only heavily contaminated plastic is removed from the process and discharged. According to the invention, this is essentially achieved by directing the fluid flowing back from a screen area during backflushing from the filter side of the screen area to at least one further (second) screen area on its filter side, where it is returned to the filtration and production process by conveying the fluid from the first screen area through the at least one further, second screen area. This reduces the backflush loss, as tests have shown, for example by half.

[0036]

[0029] It is also provided that the method according to the previously described first implementation is combined with the previously described method according to the second implementation. Accordingly, the aspects of the invention are advantageously further embodied according to a preferred embodiment, in that the backflushing of at least one screen area takes place in two backflushing phases, namely in a first backflush phase, backflushing of a screen area by conveying fluid in the direction of the backflush flow in the screen area, and in a second backflush phase after the first backflush phase, discharge of fluid from the (first) screen area that is more heavily contaminated with filter residue through the backflush discharge channel or feed of the backflushed plastic with filter residue to a further screen area in the direction of filtration flow.

[0037]

[0030] This means that the backflushing of a screen area according to the second implementation is optionally carried out with a first backflushing phase according to the invention and a subsequent second backflushing phase according to the first aspect. In this way, the contaminants can be removed from the process and the device in an even more targeted manner with further reduction of plastic losses by - successive - backflushing.

[0038]

[0031] The method according to the invention is advantageously further developed with regard to the reduction of waste quantities due to the feedback by successively backflushing the several screen areas by first backflushing the substantially entire contents including filter residue from a first screen area to at least one further screen area until the last two screen areas have substantially the entire filter residue of the previously backflushed screen areas, and then subsequently discharging the collected filter residues from the last two screen areas out of the housing through the backflush discharge channel. In other words, several screen areas are successively backflushed and thus the filters are cleaned, and only after the last screen area has been backflushed is the accumulated, heavily contaminated plastic removed from the device and the process and disposed of. It is preferred, in particular, that after backflushing of a screen area, the backflushing takes place at a second and / or third and / or further screen area with a first and second backflushing phase according to the invention.

[0039]

[0032] The method is further developed in a proven manner by moving a displacement piston, which is movably arranged in a storage chamber, and whereby fluid is conveyed through the screen area or the several screen areas by axial movement in the backflush flow direction. Here, a fluid storage chamber is advantageously used to provide a required quantity of liquid plastic, and this stored quantity of plastic is conveyed by the displacement piston in a simple and reliable manner at the required pressure for backflushing. It is proposed that after the first backflush phase has been performed in steps a) to c), fluid that is more heavily contaminated with filter residue is discharged through the backflush discharge channel in a second backflush phase in step d).

[0040]

[0033] Preferably, step c) occurs in a filtration operation of the other screen area in which the fed fluid from step b) is conveyed together with additional fluid fed from an inlet of the filtering device. This ensures that the fluid in steps a) to c) from the one screen area is not lost in the production process but this fluid is still filtered by the further screen area.

[0041]

[0034] Preferably, in the backflush operation, fluid is received from a backflush feed channel. This backflush feed channel is either connected to one or more inlet channels of the filtering device or it is connected to a reservoir in which backflush fluid resides (e.g. the storage chamber further below) for the purpose of the backflush operation.

[0042]

[0035] Preferably, prior step a) and / or after step d) the one screen area of the two or more screen areas is in filtration operation in which all following steps are performed: al) receiving, from one or more inlets of the filtering device, fluid at its filter side; a2) conveying the received fluid in the filtration flow direction from its filter side to its clean side for filtering the received fluid; a3) discharging the conveyed fluid from step a2) through one or more outlets (8) of the filtering device. So, the filtering device can be switched between filtration mode and backflushing mode, whereas during filtration mode of one screen area, another screen area may be switched to backflushing mode.

[0043]

[0036] Preferably, after step c) and prior step d), the following steps are performed: c2) further feeding this conveyed fluid from its filter side of the other screen area into the filter side of a further screen area of the two or more screen areas via the feed channel; and c3) conveying this further fed fluid in the filtration flow direction from the filter side of the further screen area to the clean side of the further screen area. With that it is possible to further extend the backflushing operation to a further screen area, which may additionally be used. Preferably, in step d) of this preferred embodiment, only the fluid from the further screen area with filter residue is discharged via the backflush discharge channel.

[0044]

[0037] Preferably, after step c3), the steps c2) and c3) are repeated successively until the fluid is at least once conveyed through all remaining screen areas of the two or more screen areas so that substantially collected the entire filter residue of all previously backflushed screen areas. With that it is possible to further extend the backflushing operation to all remaining screen areas in successive manner, which means that all screen areas are backflushed one after the other - which hereinafter is also referred to as first backflush operation. So substantially the entire filter residue of all screen areas is collected prior discharging and with that a first backflush operation - which is a backflush operation on all existing screen areas within the filtering device - is completed.

[0045]

[0038] Preferably, in step d) fluid with all the collected filter residue is discharged via the backflush discharge channel. The discharge step d) is preferably applied only once within this first backflush operation so that filter residue from all screens in all screen areas is collectively discharged which avoids the waste of fluid for backflushing to a very large extent.

[0046]

[0039] Preferably, fluid is conveyed in the backflush operation by axially moving a displacement piston in a backflush fluid storage chamber. The applied principle for that is explained in greater details in EP 3 088 158 Bl, the entire content thereof is incorporated herein by reference.

[0047]

[0040] Preferably, the filtering device is switched from a filtration operation to a backflush operation by axially moving one or more screen pistons, each comprising one or more screen areas. The applied principle thereof is explained in greater details in EP 3 088 158 Bl, the entire content thereof is incorporated herein by reference.

[0048]

[0041] Preferably, the filtering device further comprises a first axially movable screen carrier having a first screen area and a second screen area arranged next to each other in the axial moving direction; and a second axially movable screen carrier having a third screen area and a fourth screen area arranged next to each other in the axial moving direction. As there is more than one screen carrier and each being moved independently, the filtering device can backflush only some of the two or more screen areas wherein the remaining screen areas remain in a filtration mode position. With such a concept, a continuous filtration is possible in which 50% or 75% of the screen areas remain in filtration mode and the other 50% or 25% are in backflush operation etc. The applied principle thereof is explained in greater details in EP 3 088 158 Bl, the entire content thereof is incorporated herein by reference.

[0049]

[0042] In a preferred embodiment, the one screen area of step a) may be the first screen area and the other one screen area of step c) may be the third screen area. So, there may be one common discharge channel that is configured for step d) for the first screen area as well as the third screen area within a housing of the filtering device. This may reduce the effort of realizing discharge channels for the backflush operation and reduce complexity during manufacturing of the filtering device.

[0050]

[0043] The further screen area of step c2) may be the second screen area. The remaining screen area of step c2) may be the fourth screen area. So, there may be one common discharge channel that is configured for step d) for the third screen area as well as the fourth screen area within a housing of the filtering device. This may reduce the effort of realizing discharge channels for the backflush operation and may reduce complexity during manufacturing of the filtering device.

[0051]

[0044] With such a setup and backflush sequence for the four screen areas, there may be a total of only two distinct backflush channels within the housing of the filtering device that are needed for step d).

[0052]

[0045] Preferably, a first backflush operation of the filtering device is completed when fluid is conveyed through all four screen areas of the filtering device in following order of screen areas: first screen area, third screen area, second screen area, fourth screen area and fluid with the filter residue collected from all these four screen areas is discharged in step d). With such a setup and backflush sequence for the four screen areas, the filter residue of all screen areas is collectively discharged which reduces the amount of fluid need for the entire first backflush operation.

[0053]

[0046] A first backflush operation may be followed by a further backflush operation that is subsequent to the first backflush operation. The first backflush operation is a backflush operation on all existing screen areas within the filtering device. The sequence of the screen areas through which fluid is conveyed may be the same as the sequence in the first backflush operation.

[0054]

[0047] A first backflush operation may be followed by a further backflush operation that is subsequent to the first backflush operation. The sequence of the screen areas through which fluid is conveyed in the further backflush operation is different from the sequence of screen areas in the first backflush operation.

[0055]

[0048] Preferably, a sequence of the screen areas for further backflush operation is as follows: second screen area, fourth screen area, first screen area, third screen area.

[0056]

[0049] Preferably, a sequence of the screen areas for further backflush operation is as follows: third screen area, first screen area, fourth screen area, second screen area.

[0057]

[0050] Preferably, a sequence of the screen areas for further backflush operation is as follows: fourth screen area, second screen area, third screen area, first screen area.

[0051] Preferably, a first backflush operation is followed by a second backflush operation and the sequence of the screen areas for the second backflush operation is second screen area, fourth screen area, first screen area, third screen area.

[0058]

[0052] Preferably, a second backflush operation is followed by a third backflush operation and the sequence of the screen areas for the third backflush operation is third screen area, first screen area, fourth screen area, second screen area.

[0059]

[0053] Preferably, a third backflush operation is followed by a fourth backflush operation and the sequence of the screen areas for the fourth backflush operation is fourth screen area, second screen area, third screen area, first screen area.

[0060]

[0054] So, in other words, an advantageous exemplary method control provides that screen areas, which are preferably arranged on two movable screen carriers, are backflushed in the sequence of screen areas 1 - 3 - 2 - 4. Furthermore, it has been shown to be advantageous if, in such a constellation, the screen areas are backflushed in the following sequences during the next backflush:

[0061] 2 - 4 - 1 - 3;

[0062] 3 - 1 - 4 - 2;

[0063] 4 - 2 - 3 - 1.

[0064]

[0055] The method is particularly advantageous with a filtering device in which at least two screen areas are arranged on a movable screen carrier and at least two screen carriers are provided.

[0065]

[0056] According to an aspect there is provided a filtering device for filtering a fluid, the fluid is preferably liquefied plastic, wherein the filtering device comprises two or more screen areas, wherein each screen area comprises a filter side and a clean side with a screen therebetween, wherein each screen area is configured to conveying fluid in a filtration flow direction from its filter side to its clean side during filtration operation; conveying fluid in a backflush flow direction from its clean side to its filter side during a backflush operation; feeding fluid from its filter side to a filter side of another screen area of the two or more screen areas via a feed channel; wherein the filtering device further comprises a controller (control unit, processor, controlling device) configured to operate the filtering device in a backflush operation according to a method as described above.

[0057] The filtering device may further comprise a housing; one ore more inlets for introducing the fluid (the unfiltered fluid) into the filtering device; one or more outlets for discharging the fluid (the filtered fluid); one or more screen carriers axially movable within the housing, so that each screen area is connectable to the backflush discharge channel for discharging the fluid with the filter residues.

[0066]

[0058] Preferably, the filtering device further comprising a backflush feed channel for feeding fluid to one or more of the two or more screen areas.

[0067]

[0059] Preferably, two or more screen areas of the two or more screen areas are arranged on one screen carrier and there are at least two screen carriers.

[0068]

[0060] The controller may be further configured to operate one or more drives for driving the one or more screen carriers.

[0069]

[0061] The filtering device may further comprise a pressure generator.

[0070]

[0062] The controller of the filtering device is preferably a programmable logic controller, PLC, or a processing unit. The PLC is preferably configured to operate the filtering device according to the method steps described above.

[0071]

[0063] Preferably, the controller of the filtering device is configured such, that its instructions can be updated to execute the steps of the above described method.

[0072]

[0064] According to another aspect of the present disclosure, a computer program comprising instructions which, when the program is executed by a controller, such as a programmable logic controller or processing unit, or a controller cause the controller to execute the steps of the method as described above.

[0073]

[0065] Further features and advantages of the invention are apparent from the dependent claims and the following description, in which embodiments are explained in detail with reference to schematic drawings. In detail:

[0074] Fig. 1 shows a schematic, perspective view of a filtering device according to the invention capable of being operated according to a method according to the invention; Fig. 2 shows a side view of the filtering device of Fig. 1 with two screen carriers and four screen areas, each in production position with partially visible flow channels;

[0075] Fig. 3 shows a top view of the filtering device of Figs. 1 and 2 in the production position with partially visible flow channels;

[0076] Fig. 4 shows a side view of the filtering device of Figs. 1 to 3 with a screen area in a backflush position and the other screen areas in the production position with partially visible flow channels;

[0077] Fig. 5 shows a sectional view of a filtering device of Figs. 1 to 4 with a screen area in the backflush position at the beginning of a backflush operation and the other screen areas in a production position with partially visible flow channels;

[0078] Fig. 6 shows another sectional view the filtering device of Figs. 1 to 5 with the screen area in the backflush position during the backflush operation in a first backflush phase and the other screen areas in the production position ;

[0079] Fig. 7 shows a side view of the filtering device of Figs. 1 to 6 with a screen area in the backflush position during the backflush operation in a second backflush phase with partially visible flow channels and flow arrows and the other screen areas in the production position ;

[0080] Fig. 8 shows a sectional view of the filtering device of Figs. 1 to 7 with a screen area in the backflush position during the backflush operation in a second backflush phase at the end of the backflush operation and discharging of fluid with filter residue (heavily contaminated plastic);

[0081] Fig. 9 shows a sectional view of a pressure generating unit with displacement piston in a storage chamber as part of the filtering device according to the invention before moving a screen area in the backflush position for a backflush operation;

[0082] Fig. 10 shows a sectional view of the displacement piston in the storage chamber as part of the filtering device according to the invention in an operating state during production mode; Fig. 11 shows a view of the displacement piston in the storage chamber together with other channels as part of the filtering device according to the invention;

[0083] Fig. 12 shows another view of the displacement piston in the storage chamber together with other channels as part of the filtering device according to the invention;

[0084] Fig. 13 shows a schematic representation of a control unit of the filtering device according to the invention capable of being operated according to a method according to the invention and of drives controlled by means of the control unit.

[0085]

[0066] Fig. 1 shows a filtering device 2 for filtering a liquid plastic (also called "melt" or "fluid" or “polymer melt”) in a schematic representation. The device 2 has a housing 4, which is only shown schematically and not in detail, with an inlet 6 for introducing the liquified plastic in an unfiltered form and an outlet 8 for discharging the liquified plastic in a filtered form. During filtration, melt flows in the filtration flow direction 56 in a production mode of the filtering device 2. Two axially movable screen carriers (also referred to as screen pistons) 12, 13 are preferably accommodated in the housing 4. The number of screen carriers 12, 13 is not limiting, there can be more than two screen carriers 12, 13 or just one screen carrier and the inventive backflush operation method could be applied thereto as well. A pressure generating unit 32 (see Figs. 9 to 12 for a detailed explanation) is used for conveying fluid in a backflush mode for backflushing parts of the filtering device 2 in a backflush flow direction (opposite to the filtration flow direction 56). The pressure generating unit 32 is arranged in a part of the housing 4, which is explained further below and shown enlarged in Figs. 9 - 12.

[0086]

[0067] As Figs. 2 - 8 show, each screen carrier 12, 13 has two screen cavities 10, in each of which a screen 14 (also called screen 1, screen 2, screen 3, screen 4) is arranged. The number of screens per cavity 10 is not limiting for this disclosure. One screen area 1.1, 1.2, 1.3, 1.4 is formed on each of the screens 1, 2, 3, 4. The number of screen areas is not limiting within this disclosure, but at least two screen areas (means two or more screen areas) are used according to the invention. Each screen 14 has a filter side 16 and a clean side 18. The housing 4 also has one or more feed channels 36 connected in a fluid-conducting manner to the inlet 6 for feeding liquified plastic to the filter side 16 of one or more screens 14. Preferably there is one distinct feed channel 36 for one screen 14. Furthermore, the housing 4 has one or more discharge channel 38 assigned to the two or more screen areas 1.1, 1.2, 1.3, 1.4 and connected in a fluidconducting manner to the outlet 8 for discharging the filtered plastic from the clean side 18 of each screen 14. Preferably there is one distinct discharge channel 38 for one screen 14. In production operation (production mode), liquefied plastic flows in the screen area 1.1, 1.2, 1.3, 1.4 essentially in the filtration flow direction 56, see Figs. 3, 5, 6, 8.

[0087]

[0068] A plurality of grooves, flow channels and cavities and inlets and outlets and connections are arranged in the housing 4, the screen carriers 12, 13 and possibly other components in order to allow the melt to flow for filtration and backflushing optionally and selectively in the filtration flow direction 56 or against the filtration flow direction 56 in the backflushing flow direction 57. Filtering device 2 is set up and designed for the application of the described methods according to the invention in accordance with all described aspects.

[0088]

[0069] For this purpose, the screen carriers 12, 13 as shown (at least partly) in the figures 1 to 8 can be moved in a fundamentally known manner with the aid of an electrical control 80, control lines 88, a drive 82 for the screen carrier 12, a drive 84 for the screen carrier 13 and a drive 88 for a displacement piston 34 of the pressure generating unit 32, shown schematically in Figure 13, in such a way that suitable melt pressure and flow conditions are realized in the filtering device 2 within the channels and cavities. In this respect, reference is made in particular to the disclosures of DE 20 2022 100 235 U1 or EP 3 088 158 Bl, which in this respect are both fully incorporated by reference. The screen areas 1.1, 1.2, 1.3, 1.4 are arranged on the two screen carriers 12, 13 which can be moved axially within the housing 4 by means of screen carrier drives 82, 84 as shown in Figs. 3, 7 and illustrated schematically in Fig. 13. The control 80 is preferably a PLC and may execute steps according to the herein described backflush operation.

[0089]

[0070] For a backflush operation (herein also referred to as backflushing, which means conveying of fluid in a backflush flow direction 57) of the screen areas 1.1, 1.2, 1.3, 1.4, the filtering device 2 also has at least one backflush feed channel 20, which is connected to one or more clean sides 18 of screen areas in a fluid-conducting manner. This is shown in Fig. 2 and is set up to feed liquified plastic to each screen 14 of each screen area 1.1, 1.2, 1.3, 1.4, possibly with further channels, against the filtration flow direction 56, i.e. in the backflush flow direction 57. As Figs. 11 and 12 show, the backflush feed channel 20 is connected to the pressure generating unit 32, in particular to its storage chamber 35 in which liquified (filtered) plastic is stored. A displacement piston 34 is movably arranged with the storage chamber 35, cf. Figs. 11 and 12. In this respect, reference is made in particular to the disclosure of DE 20 2022 100 235 U1 or EP 3 088 158 Bl, which is fully incorporated by reference.

[0090]

[0071] The filtering device 2 also has one or more backflush discharge channels 22 as shown in Figs. 4 - 8, which are connected to respective filter sides 16 of each screen area in a fluidconducting manner and is set up to discharge the backflushed liquified plastic after it has passed through a screen 14. Each screen area 1.1, 1.2, 1.3, 1.4 can be connected to one or more backflush feed channels 20 for introducing fluid for backflushing the screen area 1.1, 1.2, 1.3, 1.4. Each screen area 1.1, 1.2, 1.3, 1.4 can be connected to one or more backflush discharge channel 22 for discharging fluid that contains filter residues. Each backflush discharge channel 22 can be separated into a first part discharge channel 22a and a second part discharge channel 22b which both form one backflush discharge channel 22. The separation of the discharge channel 22 into a first part 22a and a second part 22b may be advantageous to establish or deny a fluid-connection of different parts and channels within the filtering device 2 in filtration mode or backflush mode. In this respect, reference is made in particular to the disclosure of DE 20 2022 100 235 U1 or EP 3 088 158 Bl, which is included in its entirety by reference. Grooves 24 are formed on the outer surfaces of each screen carrier 12, 13.

[0091]

[0072] Fig. 4 and Fig. 6 show the filtering device 2 in a state in which screen area 1.1 (with screen 1 according to Fig. 2) is in a backflush position, while the other screen areas 1.2, 1.3, 1.4 are in a production position. Liquified plastic with fewer impurities in the first backflush phase is fed through channel 36 to the other screen areas 1.2, 1.3, 1.4, as illustrated in Fig. 6. None of the grooves 24 (as also shown in Fig. 4) formed on the outer surface of the screen carriers 12, 13 align or overlap with the second part backflush discharge channel 22b, which is the second part of the backflush discharge channel 22. In Fig. 4, the groove 24 and the backflush discharge channel 22b are aligned at the lower screen carrier 13 in screen area 1.3 (left screen area in the lower carrier 13 in Fig. 4), but melt cannot flow here because the screen area 1.1 in the upper screen carrier 12 is not in fluid-connected manner (as it has no contact) with the first part discharge channel 22a which is the first part of the backflush discharge channel 22.

[0092]

[0073] In Figs. 5 and 6, the first part of the backflush discharge channel 22 formed in the housing 4 is shown as a partial backflush discharge channel 22a. Fig. 4 shows that the groove 24 of the screen carrier 12 does not overlap with the second part backflush discharge channel 22b, so that no liquefied plastic with contaminants (filter residue) can be discharged. Instead and according to the invention, the liquified plastic is directed to another one of the screen areas 1.2-1.4 to enable the inventive backflush operation.

[0093]

[0074] Discharging is shown in Fig. 8 by the hatched liquified plastic with heavier soiling in the first part discharge channel 22a in the housing 4, which in this state is in overlap with the groove 24, so that liquified plastic with heavier soiling (higher contamination, more filter residue) first flows through the groove 24 and then through the second partial discharge channel 22b; this occurs when groove 24 is aligned or overlaps with the second part backflush discharge channel 22b. The first backflush phase shown in particular in Figures 5 and 6 and the associated state of the filtering device 2 or the corresponding method step and the second backflush phase shown in Figure 8 and the associated state of the filtering device 2 or the corresponding process step can be realized by setting the screen carriers 12, 13 accordingly for each of the two or more screen areas 1.1 - 1.4.

[0094]

[0075] As Figs. 9 and 10 in particular also illustrate, the filtering device 2 has the pressure generating unit 32. The pressure generating unit 32 is designed in particular with a displacement piston 34, shown enlarged in Figs. 9 and 10, which is arranged in storage chamber 35 for storing melt and can be moved axially back and forth with a drive 86 (shown schematically in Fig. 13). The pressure generating unit 32 is connected to the backflush feed channel 20. The pressure generating unit 32 is connected to the discharge channel 38 in a fluid-conducting manner. The pressure generating unit 32 is also set up to remove melt from the discharge channel 38 and provide it for backflushing. In Figure 10, displacement piston 34 is in a position in which the so-called production of the liquefied plastic, i.e. its filtration, takes place. To backflush a screen area 1.1 - 1.4, the displacement piston 34 is moved axially downwards from the raised position shown in Figure 9, in which the storage chamber 35 is filled to the maximum with plastic, to a position approximately as shown in Figure 10. As a result, plastic is conveyed for backflushing through the respective backflush feed channel 20 (see Figures 9-12) to the respective one of the screen areas 1.1 - 1.4.

[0095]

[0076] As Figs. 5 - 8 show, the housing 4 has at least one feed channel 36 connected in a fluidconducting manner to the inlet 6 for feeding plastic to the filter side 16 of each screen 14. The housing 4 also has a discharge channel 38 connected in a fluid-conducting manner to the outlet 8 for discharging the filtered liquefied plastic from the clean side 18 of the respective screen area.

[0096]

[0077] The method using the filtering device 2 is carried out as described below.

[0097]

[0078] The filtration flow direction 56 shown in Figs. 1, 2 and 3 illustrates the plastic flow from the inlet 6 to the outlet 8 via the screen areas 1.1, 1.2, 1.3 and 1.4 during production in filtration mode. All four screen areas 1.1, 1.2, 1.3 and 1.4 comprise screens 14 and are used to filter the plastic melt. Specifically, the melt flows from the inlet 6 via the one or more feed channels 36 to each of the screens 14 of the screen areas 1.1, 1.2, 1.3, 1.4 and from there via a discharge channel 38 per each screen area 1.1, 1.2, 1.3, 1.4 to the outlet 8 (indicated in Fig. 1). In other words, the method steps al to a3 are carried out: al) receiving, from inlet 6 of the filtering device 2, fluid at a filter side 16 of a screen area, which may mean introducing fluid through the inlet 6 in the direction of filtration flow 56 into the at least one screen area 1.1 ; a2) conveying the received fluid in the filtration flow direction 56 from its filter side 16 to its clean side 18 for filtering the received fluid; and then a3) discharging the filtered (conveyed) fluid from step a2) through one or more outlets 8 of the filtering device 2.

[0098]

[0079] In the state shown in Fig. 4 - by moving the screen carriers 12, 13 accordingly by means of the drives 82, 84 - melt is fed to the screen 14 in the screen cavity 10 and thus to the screen area 1.1 by means of the displacement piston 34 of the pressure generating unit 32 starting from the clean side 18 via the backflush discharge channel 20 in a first backflush phase. As a result, the screen 14 and thus screen area 1.1 is backflushed, i.e. melt with contaminants that have accumulated on the filter side 16 of the screen 14 are detached from the screen 14 at screen area 1.1 and flow in the backflushing flow direction 57. In other words, the method step a) is carried out: a) conveying fluid from its clean side 16 to its filter side 18 of one screen area 1.1 of the two or more screen areas 1.1, 1.2, 1.3, 1.4, which may mean backflushing the screen area 1.1 by conveying fluid in the backflushing flow direction 57 in the screen area 1.1 in a first backflushing phase.

[0099]

[0080] As Figure 4 shows, the mixture of liquified plastic and filter residues detached from the screen 14 at a first screen area 1.1 reaches the area in which the one or more feed channels 36 lead downstream of the inlet 6 to the respective screen areas 1.1 to 1.4 by means of the feed channel 36 in the backflush flow direction 57. For this purpose, the screen carrier 13 is axially moved accordingly so that the screen area 1.1 is brought out of production position and moved into the backflush position, preferably in the first backflush phase. The other screen areas 1.2, 1.3, 1.4 remain in their respective production positions during this first backflush phase. In the first backflush phase, the melt has only little contamination, so mainly filtered melt is fed to the other screen areasl.2, 1.3, 1.4. The one or more feed channels 36 may always communicate with each other because they are connected to each other at the inlet 6 of the filtering device 2. In this first backflush phase, the melt, along with relatively minor impurities (filter residue), which is backflushed by the first screen area 1.1 in this first backflush phase, is fed back into the production, i.e. into the filtering operation of the other screen areas 1.2, 1.3, 1.4. This takes place via feed channels 36, which are connected to these screen areas 1.2, 1.3, 1.4 in the filtration flow direction 56. The melt backflushed at screen area 1.1 together with these minor impurities is thus fed in the first backflush phase to the filter side 16 of one or more of the other screen areas 1.2, 1.3, 1.4 and filtered there by means of the screens 14 of the other screen areas 1.2, 1.3, 1.4. In other words, the method step is carried out: c) conveying fed fluid from step b) in the filtration flow direction 56 from the filter side 16 of the one or more other screen areas 1.2, 1.3, 1.4 to the clean side 18 of the other screen area 1.2, 1.3, 1.4, which may mean feeding the returning fluid from the filter side of the screen area (1.1) to at least one further screen area (1.2, 1.3, 1.4) to its filter side, and there conveying the fluid also from the screen area 1.1. through the at least one further screen area 1.2. In this exemplary embodiment, fluid is conveyed or guided to one or preferably all, here three, other screen areas 1.2, 1.3, 1.4 on their filter side 16. It is not necessary, but preferred, that all other remaining screen areas, here three screen areas 1.2, 1.3, 1.4 receive the fluid from the first screen area 1.1, but inventively at least one other screen area does. There, the melt is filtered together with impurities, including impurities from the first screen area 1.1. These impurities from the first screen area 1.1 are thus filtered out at the at least one further screen area, in the embodiment example at the other three screen areas 1.2, 1.3 and 1.4. In other words, the plastic used for backflushing is fed back into the production after filtering by means of the first screen area 1.1.

[0100]

[0081] In other embodiments, it would also be possible for a filtering device 2 to have only two screen areas, and screen area 1.1 is backflushed in the manner described, and then the screen area 1.2 receives the backflushed fluid for filtering it in its filtration mode.

[0101]

[0082] As illustrated, for example, in Figures 7 and 8, in a second backflushing phase, after the end of the first backflushing phase (steps a) and b)), in which the melt with impurities is directed from the filter side 16 of the screen area 1.1 to the filter sides 16 of the other screen areas 1.2, 1.3, 1.4 and thus remains the fluid within production, a screen area is set up so that further melt with more highly concentrated impurities, which has accumulated on the filter side 16, is completely discharged from the device 2. In other words, method step d) applies in which fluid is discharged with filter residue. For this purpose, the inner channels are positioned, in particular by further displacement of the screen carriers 12, 13, so that the more heavily contaminated (residual) melt (fluid with filter residue) is completely discharged from the filtering device 2 through its backflush discharge channel 22, see Figs. 4, 5, 6, 7. Figs. 7 and 8 illustrate this second backflush phase. The backflush discharge channel 22 communicates with the filter side 16 of the screen area 1.1. Heavily contaminated melt is thus completely discharged from the device 2 through the discharge channel 22. In this second backflush phase, the feed channel 36 of screen area 1.1 no longer communicates with the other feed channels 36 of the other screen areas 1.2, 1.3, 1.4. Thus, for backflushing the screen area 1.1 first the fluid with less severe impurities is directed / conveyed into the feed channels 36 of the other screen areas 1.2, 1.3, 1.4, and in the second backflushing phase heavily contaminated melt with higher concentrations of impurities is completely discharged through the discharge channel 22 of the respective screen area 1.1. This backflush operation is described for backflushing the screen area 1.1. However, this backflush operation is fully applicable in analogous manner to all of the other screen areas 1.2, 1.3, 1.4.

[0083] In the embodiment example, the discharge channel 22 comprises a respective groove 24, which is formed on the outer periphery (surface) of the screen carriers 12, 13.

[0102]

[0084] For complete backflushing of one or more screen area 1.1, 1.2, 1.3, 1.4, the displacement piston 34 of the pressure generating unit 32 (Figs. 9 to 12) is actuated by means of its drive 86 with the aid of the control unit 80 (Fig. 13) and moved further downwards, see Figure 10, so that fluid is pressed into the screen area so strongly that complete backflushing of the respective screen area takes place and melt with heavy impurities is discharged through the backflush discharge channel 22.

[0103]

[0085] After cleaning a screen area in the manner described above, the previously described method steps al to a3 are carried out again, which in other words may mean: re-introduce(step al) fluid into the backflushed screen area 1.1 or the plurality of backflushed screen areas 1.2, 1.3, 1.4 in the filtration flow direction 56 for filtering (step a2) and then discharge (step a3) the filtered fluid through the outlet 8; i.e. that the screen area previously cleaned in the manner described is then again taken into production, again by corresponding displacement of the respective screen carrier 12, 13, in such a way that a connection from the inlet 6 is again realized and melt to be cleaned flows through the cleaned screen area in the direction of filtration flow 56.

[0104]

[0086] The displacment piston 34 is then retracted again when backflushing of a screen area has been completed in order to remove plastic melt from the production process and feed it into the storage chamber 35. This melt collects in a storage chamber 35, which accommodates the displacement piston 34. The screen carriers 12, 13 are in the production position described with reference to Fig. 2.

[0105]

[0087] The backflushing is advantageously affected by the described movement of a displacement piston 34, see in particular Figures 9-12, which is movably arranged in a storage chamber 35, and by axial movement the fluid is conveyed in the backflushing flow direction through the screen area or the plurality of screen areas. Alternatively, however, other pressure generating devices are also possible according to the invention in order to effect the backflushing, for example pumps such as piston pumps or gear pumps or the like.

[0106]

[0088] It is advantageous if, in the first backflush phase, approx. 30 - 40% of the fluid volume of one screen area 1.1 is successively conveyed upstream of the other screen area(s) 1.2, 1.3, 1.4 in the manner described above. It is also advantageous if, after the first backflush phase, fluid that is more heavily contaminated with filter residue is discharged through the backflush discharge channel 22 in a second backflush phase and is no longer fed to the other screen areas

[0107] 1.2, 1.3, 1.4.

[0108]

[0089] This backflush operation is described for backflushing the screen area 1.1. However, this backflush operation is fully applicable in analogous manner to all of the other screen areas 1.2,

[0109] 1.3, 1.4. In particular it is considered most advantageous if after step c) and prior step d), following steps c2) and c3) are performed: c2) further feeding this conveyed fluid from its filter side 16 of the other screen area 1.2, 1.3, 1.4 into the filter side 16 of a further screen area 1.3, 1.4 of the two or more screen areas 1.1, 1.2, 1.3, 1.4 via the feed channel 36; and step c3) conveying this further fed fluid in the filtration flow direction 56 from the filter side 16 of the further screen area 1.3, 1.4 to the clean side 18 of the further screen area 1.3, 1.4, wherein in step d) only the fluid from the further screen area 1.2, 1.3, 1.4 with filter residue is discharged via the backflush discharge channel 22.

[0110]

[0090] It is considered most advantageous if after step c3), these steps c2) and c3) are repeated successively until the fluid is conveyed through all remaining screen areas 1.1, 1.2, 1.3, 1.4 of the two or more screen areas 1.1, 1.2, 1.3, 1.4. Here it would be best, if in step d) fluid with collected filter residue is discharged via the backflush discharge channel 22.

[0111]

[0091] This above-described backflush operation may be referred to as “first backflush operation” (also referred to as backflush cycle) of the filtering device 2 and this cycle is completed when fluid is conveyed through all four screen areas 1.1, 1.2, 1.3, 1.4 of the filtering device 2. The sequence for backflushing the individual screen areas may occur in following order of screen areas: first screen area 1.1, third screen area 1.3, second screen area 1.2, and fourth screen area 1.4 and fluid with the filter residue collected from all four screen areas 1.1, 1.2, 1.3, 1.4 is discharged in step d. In other words and with particular reference to Figures 2, 3, 4 and 7, it is also exemplary and advantageous if the screen areas are backflushed in the order of the screen areas 1.3, then 1.3, then 1.2, and finally 1.4 in the first backflush operation.

[0112]

[0092] This first backflush operation / cycle is followed by a further backflush operation in which the sequence of the screen areas through which fluid is conveyed is different from the sequence of screen areas in the first backflush operation. The sequence of the screen areas for one or more further backflush operation / cycle is one of the following sequences: second screen area 1.2, fourth screen area 1.4, first screen area 1.1, third screen area 1.3; or it is third screen area 1.3, first screen area 1.1, fourth screen area 1.4, second screen area 1.2; or it is fourth screen area

[0113] 1.4, second screen area 1.2, third screen area 1.3, first screen area 1.1.

[0093] In particular, the first backflush operation / cycle is followed by a second backflush operation / cycle and the sequence of the screen areas for the second backflush operation / cycle is second screen area 1.2, fourth screen area 1.4, first screen area 1.1, third screen area 1.3.

[0114]

[0094] The second backflush operation / cycle may be followed by a third backflush operation / cycle and the sequence of the screen areas for the third backflush operation / cycle is third screen area 1.3, first screen area 1.1, fourth screen area 1.4, second screen area 1.2.

[0115]

[0095] The third backflush operation / cycle may be followed by a fourth backflush operation / cycle and the sequence of the screen areas for the fourth backflush operation / cycle is fourth screen area 1.4, second screen area 1.2, third screen area 1.3, first screen area 1.1. These backflush operations / cycles may be followed by each other in a continuous manner, such that in each production mode, one screen area is backflushed.

[0116]

[0096] In other words, the screen areas are flushed in the following sequences during the next backflush:

[0117] - 1.4 - 1.1 - 1.3;

[0118] - 1.1 - 1.4 - 1.2;

[0119] - 1.2 - 1.3 - 1.1.

[0120]

[0097] The control unit 80 (Fig. 13) may be set such that another backflush operation / cycle is started only after predefined time frame.

[0121]

[0098] The control unit 80 (Fig. 13) may be set such that another backflush operation / cycle is started as soon as a pressure sensor provides pressure sensor data that signal a predefined amount of contamination of one or more of the screen areas.

[0122]

[0099] It is further preferred, as shown, that at least two screen areas 1.1, 1.2 are arranged on a movable screen carrier 12, 13 and at least two screen carriers 12, 13 are provided, and the method is operated accordingly, but other numbers of screen areas and screen carriers can also be formed and operated in the manner according to the invention.

[0123]

[0100] To carry out the methods according to the invention, , the following individual steps may additionally or alternatively be carried out with the aid of the control unit 80:

[0101] The method is preferably carried out with several screen areas 1.1, 1.2, 1.3, 1.4 by successively backflushing the several screen areas 1.1, 1.2, 1.3, 1.4 by first backflushing the substantially entire contents including filter residue from a first screen area 1.1 to at least one further screen area 1.2 until the last screen area 1.4 has essentially the entire filter residue of the previously backflushed screen areas 1.1, 1.2, 1.3, and then discharging the collected filter residue from the last screen area 1.4 through the backflush discharge channel out of the housing 4. The dirt from screen 14 of screen area 1.1 and screen 14 of screen area 1.3 is additionally pressed onto screens 14 of screen area 1.2 and screen 14 of screen area 1.4 during backflushing without slushing out the melt to the outside. This halves the backflush loss up to this point.

[0124]

[0102] As the dirt from screen 14 of screen area 1.2 and screen 14 of screen area 1.4 is also only flushed out with part of the flush volume, the backflush losses are reduced even further. The flushing volume of the two remaining dirty screens is also only partially flushed out. Here again, the first portion of relatively clean melt is flushed out of the screen cavity before the other three and only the heavily soiled portion of melt is flushed outside.

[0125]

[0103] In the following, a chain of steps is described for one backflush operation / cycle:

[0126] Screen 14 of screen area 1.1

[0127] 1. displacement piston 34 is pulled up;

[0128] 2. screen 14 of screen area 1.1 is moved to backflushing position This means that all channels on the clean side 18 only have contact with internal channels but not to the outlet 6 of the filtering device 2; the filter side 16 of the screen 14 of screen area 1.1 is connected to the inlet 6.

[0129] 3. screen carrier 13 moves to the backflush release position

[0130] 4. displacement piston 34 moves completely forward to the end of backflush position. The entire backflush volume from screen cavity 10 of screen area 1.1, including dirt, is pressed into the filter sides 16 of the remaining three other screen areas 1.2, 1.3, 1.4. The amount of dirt for these remaining three other screen areas 1.2, 1.3, 1.4 is thus increased by 33%. Screen 14 of screen area 1.1 is clean. 5. screen carrier 13 moves to production position

[0131] 6. screen carrier 12 moves into production position

[0132] Screen 14 of screen area 1.3

[0133] 7. displacement piston 34 is pulled up

[0134] 8. screen 14 of screen area 1.3 is moved to backflush position. This means that all channels on the clean side 18 only have contact with internal channels but not to the outlet 6 of the filtering device 2; the filter side 16 of the screen 14 of screen area 1.3 is connected to the inlet 6; screen 14 of screen area 1.3 is moved to a compression position The fluid conveyed from screen 14 of screen area 1.3 is not discharged (step d), but is fed to the filter sides 16 of the three other screens 1.1, 1.2, 1.4 including the dirt from the screen 14 from screen area 1.3. However, as screen 14 of screen area 1.1 is already backflushed and as a consequence, this screen is clean, the screens 14 of screen area 1.2 and the screen 14 of screen area 1.4 are heavily soiled, the majority of the volume flow passes through the (already clean) screen 14 of screen area 1.1. If the same flushing procedure were now used as for screen 14 of screen area 1.1, the dirt would not be distributed evenly in front of the remaining three other screens 14 of screen areas 1.1, 1.2, 1.4, but would end up for the most part in front of screen 14 of screen area 1.1. In principle, only the dirt from screen 14 of screen area 1.3 would disadvantageous^ be pushed over to screen 14 of screen area 1.1. To avoid such disadvantageous scenario, the already clean screen 14 of screen area 1.1 is isolated for the brief moment that screen 14 of screen area 1.3 is backflushed. The backflushed fluid of screen 14 of screen area 1.3 is thus evenly distributed to only screen 14 of screen area 1.2 and screen 14 of screen area 1.4.

[0135] 10. displacement piston 34 moves completely forward to the end of backflush position. The entire backflush volume from screen 14 of screen area 1.3, including dirt, is conveyed to the filter side 16 of screen 14 of screen area 1.2 and screen 14 of screen area 1.4. The amount of dirt at the filter sides 16 of these two screens 14 (screen area 1.2 and 1.4) has now doubled in this backflush operation. Screen 14 of screen area 1.1 remains clean.

[0136] 11. screen carrier 12 moves to production position

[0137] 12. screen carrier 13 moves to production position. So far, no backflush material has been discharged (step d), only the dirts from screen 14 of screen area 1.1 and screen 14 of screen area 1.3 have been evenly distributed to screens 14 of screen area 1.2 and 1.4.

[0138] Screen 14 of screen area 1.2

[0139] 13. displacement piston 34 is pulled up

[0140] 14. screen 14 of screen area 1.2 is moved to the backflush position. This means that all channels on the clean side 18 only have contact with internal channels but not to the outlet 6 of the filtering device 2; the filter side 16 of the screen 14 of screen area 1.3 is connected to the inlet 6.

[0141] 15. screen carrier 13 moves to the backflush release position

[0142] 16. displacement piston 34 is advanced until 30 to 40% of the flushing volume is flushed before the other three screens 14 of screen areas 1.1, 1.3, 1.4. This melt is still almost clean.

[0143] 17. screen 14 of screen area 1.2 moves to the backflush position

[0144] 18. displacement piston 34 moves completely forward to the end of backflushing position. The heavily contaminated part of the melt from screen 14 of screen area 1.2 may be conveyed through the backflush feed channel.

[0145] 19. screen carrier 13 moves into production position 20. screen carrier 12 moves into production position

[0146] Screen 14 of screen area 1.4

[0147] 21. displacement piston 34 is pulled up

[0148] 22. screen 14 of screen area 1.4 moves to the backflush position

[0149] 23. screen carrier 12 moves to the backflush release position

[0150] 24. displacement piston 34 is advanced until 30 to 40% of the flushing volume is flushed before the other three screens 14 of screen areas 1.1, 1.2, 1.3. This melt is still almost clean.

[0151] 25. screen 14 of screen area 1.4 moves to backflush position

[0152] 26. displacement piston 34 moves completely forward to the end of backflush position. The heavily contaminated part of the melt from screen cavity 14 of screen area 1.4 may be conveyed through the backflush feed channel.

[0153] 27. screen carrier 12 moves into production position

[0154] 28. screen carrier 13 moves to production position

[0155] 29. displacement piston 34 moves to production position

[0156]

[0104] The steps for an optional compression have been omitted from the following step chain in order to describe the new function more clearly. Compression is compatible with this step chain and can be added. The next backflush should be carried out laterally reversed so that all screens 14 are cleaned evenly. List of reference signs

[0157] 2 Filtering device

[0158] 4 Housing

[0159] 6 Inlet

[0160] 8 Outlet

[0161] 10 Screen cavity

[0162] 12 Screen carrier

[0163] 13 Screen carrier

[0164] 14 Screen

[0165] 1.1 Screen area

[0166] 1.2 Screen area

[0167] 1.3 Screen area

[0168] 1.4 Screen area

[0169] 16 Filter side

[0170] 18 Clean side

[0171] 20 Backflush feed channel

[0172] 22a First part of backflush discharge channel

[0173] 22b second part of backflush discharge channel

[0174] 24 Groove

[0175] 30 Backflush feed channel

[0176] 32 Pressure generating unit

[0177] 34 Displacement piston

[0178] 35 Storage chamber

[0179] 36 Feed channel

[0180] 38 Discharge channel

[0181] 56 Direction of filtration flow

[0182] 57 Direction of backflush flow

[0183] 80 Control unit

[0184] 82 Drive for screen carrier

[0185] 84 Drive for screen carrier

[0186] 86 Drive for displacement piston

[0187] 88 Control cables

Claims

Patent claims1. A method for backflushing a filtering device (2), the filtering device (2) is configured for filtering a fluid, wherein the fluid is preferably liquefied plastic, wherein the filtering device (2) comprises:• two or more screen areas (1.1, 1.2, 1.3, 1.4), wherein each screen area (1.1, 1.2, 1.3, 1.4) comprises a filter side (16) and a clean side (18) with a screen (14) therebetween, wherein each screen area (1.1, 1.2, 1.3, 1.4) is configured to: o conveying fluid in a filtration flow direction (56) from its filter side (16) to its clean side (18) during filtration operation; o conveying fluid in a backflush flow direction (57) from its clean side (16) to its filter side (18) during a backflush operation; o feeding fluid from its filter side (16) to a filter side (16) of another screen area of the two or more screen areas (1.1, 1.2, 1.3, 1.4) via a feed channel (36); wherein the backflush operation of the filtering device (2) comprising the steps of: a) conveying fluid from its clean side (16) to its filter side (18) of one screen area (1.1) of the two or more screen areas (1.1, 1.2, 1.3, 1.4); b) feeding this conveyed fluid from its filter side (16) of the one screen area (1.1) into the filter side (16) of one or more other screen areas (1.2, 1.3, 1.4) of the two or more screen areas (1.1, 1.2, 1.3, 1.4) via the feed channel (36); c) conveying this fed fluid in the filtration flow direction (56) from the filter side (16) of the other screen areas (1.2, 1.3, 1.4) to the clean side (18) of the other screen area (1.2, 1.3, 1.4); d) discharging fluid with filter residue via a backflush discharge channel (22) of the filtering device (2).

2. The method according to claim 1, further comprising after step c) and prior step d): cl) conveying fluid from the clean side (16) of the one or more other screen area (1.2, 1.3, 1.4) to the filter side (18) of the one or more other screen area (1.2, 1.3, 1.4) in its backflush operation of the other screen area (1.2, 1.3, 1.4), wherein in step d) only the fluid from the one or more other screen area (1.2, 1.3, 1.4) with filter residue is discharged via the backflush discharge channel (22).

3. The method according to claim 1 or 2, wherein the steps a) and b) occur in a first backflush phase of the backflush operation in which neither the one screen area (1.1) nor the other screen areas (1.2, 1.3, 1.4) is connected to the backflush discharge channel (22).

4. The method according to one of the preceding claims, wherein step d) and when depending on claim 2, also step cl) occurs in a second backflush phase of the backflush operation in which the one screen area (1.1) or when depending on claim 2 the one or more other screen areas (1.2, 1.3, 1.4) are connected to the backflush discharge channel (22).

5. The method according to claim 4, wherein the second backflush phase is timely after the first backflush phase.

6. The method according to one of the claims 3 to 5, wherein the first backflush phase ends when approx. 30% to 40% of a fluid volume of a screen cavity (10) of the one screen area (1.1) is fed in step b).

7. The method according to one of the preceding claims, wherein step c) occurs in a filtration operation of the one or more other screen areas (1.2, 1.3, 1.4) in which the fed fluid from step b) is conveyed together with additional fluid fed from an inlet of the filtering device (2).

8. The method according to one of the preceding claims, wherein in the backflush operation, fluid is received from a backflush feed channel (20).

9. The method according to one of the preceding claims, wherein prior step a) and / or after step d) the one screen area (1.1) of the two or more screen areas (1.1, 1.2, 1.3, 1.4) is in filtration operation in which all following steps are performed: al) receiving, from one or more inlets (6) of the filtering device (2), fluid at its filter side (16); a2) conveying the received fluid in the filtration flow direction (56) from its filter side (16) to its clean side (18) for filtering the received fluid; a3) discharging the conveyed fluid from step a2) through one or more outlets (8) of the filtering device (2).

10. The method according to one of the preceding claims, wherein after step c) and prior step d), following steps are performed: c2) further feeding this conveyed fluid from its filter side (16) of the other screen area (1.2, 1.3, 1.4) into the filter side (16) of a further screen area (1.3, 1.4) of the two or more screen areas (1.1, 1.2, 1.3, 1.4) via the feed channel (36); andc3) conveying this further fed fluid in the filtration flow direction (56) from the filter side (16) of the further screen area (1.3, 1.4) to the clean side (18) of the further screen area (1.3, 1.4), wherein in step d) only the fluid from the further screen area (1.2, 1.3, 1.4) with filter residue is discharged via the backflush discharge channel (22).

11. The method according to claim 10, wherein after step c3), the steps c2) and c3) are repeated successively until the fluid is conveyed through all remaining screen areas (1.1, 1.2, 1.3, 1.4) of the two or more screen areas (1.1, 1.2, 1.3, 1.4).

12. The method according to claim 10 or 11, wherein in step d) fluid with collected filter residue is discharged via the backflush discharge channel (22).

13. The method according to one of the preceding claims, wherein fluid is conveyed in the backflush operation by axially moving a displacement piston (34) in a backflush fluid storage chamber (35).

14. The method according to one of the preceding claims, wherein the filtering device (2) is switched from a filtration operation to a backflush operation by axially moving one or more screen carriers (12, 13), each comprising one or more screen areas (1.1, 1.2, 1.3, 1.4).

15. The method according to one of the preceding claims, wherein the filtering device (2) further comprises: o a first axially movable screen carrier (12) having a first screen area (1.1) and a second screen area (1.2) arranged next to each other in the axial moving direction; o a second axially movable screen carrier (13) having a third screen area (1.3) and a fourth screen area (1.4) arranged next to each other in the axial moving direction.

16. The method according to claim 15, wherein the one screen area of step a) is the first screen area (1.1) and the other one screen area of step c) is the third screen area (1.3).

17. The method according to claim 15 or 16, wherein when depending on claim 10 or 11, the further screen area (1.2) of step c2) is the second screen area (1.2)18. The method according to one of the claims 15 to 17, wherein when depending on claim10 or 11, the remaining screen area of step c2) is the fourth screen area (1.4).

19. The method according to one of the claims 15 to 18, wherein a first backflush operation of the filtering device (2) is completed when fluid is conveyed through all four screen areas (1.1, 1.2, 1.3, 1.4) of the filtering device (2) in following order of screen areas: first screen area (1.1), third screen area (1.3), second screen area (1.2) fourth screen area (1.4) and fluid with the filter residue collected from all four screen areas (1.1, 1.2, 1.3, 1.4) is discharged in step d).

20. The method according to claim 19, wherein the first backflush operation is followed by a further backflush operation in which the sequence of the screen areas through which fluid is conveyed is different from the sequence of screen areas in the first backflush operation.

21. The method according to claim 20, wherein the sequence of the screen areas for further backflush operation is one of the following sequences: second screen area (1.2), fourth screen area (1.4), first screen area (1.1), third screen area (1.3); third screen area (1.3), first screen area (1.1), fourth screen area (1.4), second screen area (1.2); fourth screen area (1.4), second screen area (1.2), third screen area (1.3), first screen area (1.1).

22. The method according to claim 20 or 21, wherein the first backflush operation is followed by a second backflush operation and the sequence of the screen areas for the second backflush operation is second screen area (1.2), fourth screen area (1.4), first screen area (1.1), third screen area (1.3).

23. The method according to claim 22, wherein the second backflush operation is followed by a third backflush operation and the sequence of the screen areas for the third backflush operation is third screen area (1.3), first screen area (1.1), fourth screen area (1.4), second screen area (1.2).

24. The method according to claim 23, wherein the third backflush operation is followed by a fourth backflush operation and the sequence of the screen areas for the fourth backflush operation is fourth screen area (1.4), second screen area (1.2), third screen area (1.3), first screen area (1.1).

25. A filtering device for filtering a fluid, the fluid is preferably liquefied plastic, wherein the filtering device (2) comprises:• two or more screen areas (1.1, 1.2, 1.3, 1.4), wherein each screen area (1.1, 1.2, 1.3, 1.4) comprises a filter side (16) and a clean side (18) with a screen (14) therebetween, wherein each screen area (1.1, 1.2, 1.3, 1.4) is configured to: o conveying fluid in a filtration flow direction (56) from its filter side (16) to its clean side (18) during filtration operation; o conveying fluid in a backflush flow direction (57) from its clean side (16) to its filter side (18) during a backflush operation; o feeding fluid from its filter side (16) to a filter side (16) of another screen area of the two or more screen areas (1.1, 1.2, 1.3, 1.4) via a feed channel (36); wherein the filtering device further comprises a controller (80) configured to operate the filtering device (2) in a backflush operation according to one of the preceding claims.

26. The filtering device (2) according to claim 25, further comprising:• a housing (4);• one ore more inlets (6) for introducing the fluid;• one or more outlets (8) for discharging the fluid;• one or more screen carriers (12, 13) axially movable within the housing (4) so that each screen area (1.1, 1.2, 1.3, 1.4) is connectable to the backflush discharge channel (22) for discharging the fluid with the filter residues.

27. The filtering device (2) according to claim 26, further comprising a backflush feed channel (20) for feeding fluid to one or more of the two or more screen areas (1.1, 1.2, 1.3, 1.4).

28. The filtering device (2) according to one of the claims 26 or 27, wherein two or more screen areas are arranged on one screen carrier (12, 13) and there are at least two screen carriers (12, 13).

29. The filtering device (2) according to one of the claims 26 to 28, wherein the controller (80) is further configured to operate one or more drives (82, 84, 86) for driving the one or more screen carriers (12, 13).

30. The filtering device (2) according to one of the claims 26 to 29, further comprising a pressure generator.

31. A computer program comprising instructions which, when the program is executed by a controller, cause a filtering device to execute the steps of the method according to one of the claims 1 to 24.

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