EP4658473A1

EP4658473A1 - Filtering device for removing impurities from a polymer melt

Info

Publication number: EP4658473A1
Application number: EP24709940.1A
Authority: EP
Inventors: Robert Middler
Original assignee: Nordson Corp
Current assignee: Nordson Corp
Priority date: 2023-01-31
Filing date: 2024-01-30
Publication date: 2025-12-10
Also published as: WO2024163378A1; DE102023102233A1

Abstract

The disclosure relates to a filtering device (1) for removing impurities (110), comprising a filter housing (3), a filter chamber (5), a housing inlet (7) and a housing outlet (9), a filter element (11) received in the filter chamber (5), and a metering device (18) in fluid communication with the filter chamber (5) for discharging (11) filtered impurities (110). The disclosure proposes that the metering device (18) has a piston pump (20) comprising a drive mechanism (28) and at least one piston (25) which can be moved along a longitudinal piston axis (K) and is adapted to convey the impurities (110), wherein the drive mechanism (28) includes a drive shaft (29) and is adapted to convert a rotation of the drive shaft (29) into a stroke action (H) of the piston (25). The disclosure further relates to a method of operation and a metering device.

Description

FILTERING DEVICE FOR REMOVING IMPURITIES FROM A POLYMER MELT

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority to German Patent Application No. 10 2023 102 233.4, filed January 31, 2023. the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein.

TECHNICAL FIELD

[0002] The disclosure relates to a filtering device for removing impurities from a polymer melt, comprising: a filter housing having a filter chamber, a housing inlet for feeding the polymer melt to be filtered into the filter chamber and a housing outlet for conducting the purified polymer melt out of the filter chamber, a filter element accommodated in the filter chamber for filtering the impurities out of the polymer melt, and a metering device in fluid communication with the filter chamber for metered discharge of the filtered impurities, wherein the metering device has a dirt outlet and is adapted to convey the impurities toward the dirt outlet. The disclosure also relates a metering device for a filtering device and to a method for operating a filtering device.

BACKGROUND

[0003] Filtering devices of the kind initially specified are generally known from the prior art. One example of such a filtering device is the BKG® HiCon™ R-Type 250 filter. In such filtering devices, impurities retained on the dirt side of the filter element are conveyed via a discharge screw to a dirt outlet. The removed impurities are firstly scraped from the dirt side of the filter element by means of scraper elements of a cleaning unit. The filter element is stationary during the process, and the cleaning unit, in particular a cleaning head having the scraper elements, as well as the discharge screw are driven rotationally via a drive shaft, the discharge volume of the filtering device largely depending on the driving power and thus on the rotational speed. The impurities conveyed to the dirt outlet by means of the discharge screw can then be destroyed or further processed.

[0004] Filtering devices are also known from DE202013101994; DE202018I01724; EP3010620; EP2907646 and EP0160782. [0005] Impurities removed from the melt include organic or inorganic materials such as wood or paper, metals or even non-metallic foreign substances, and polymeric foreign substances such as residues of other plastics. The impurities also contain some residues of the polymer melt itself.

[0006] In order to limit the amount of material discharged by the discharge screw at high internal pressures in the region of the filter element, it is necessary’ to cool the discharge screw region, which reduces the flowability of the mass containing the impurities and conveyed by the discharge screw. Such cooling is mostly provided on the outside of the housing in the region of the discharge screw. This is considered disadvantageous for energetic reasons. At the same time, it is necessary to keep the purified polymer melt free-flowing and therefore above its melting point, to allow the purified polymer melt to be conducted toward the housing outlet. To cool the impurities without adversely affecting the temperature of the purified polymer melt, the length of the discharge screw must therefore be relatively large. This disadvantageous^ increases the installation space of the entire filtering device. There is a need to simplify the overall technical design and to increase the energy efficiency of the filtering device.

[0007] This need is addressed by the disclosure, the object of which is to provide an alternative filtering device. The object of the disclosure, more specifically, is to specify a filtering device that allows a more compact structure, an adjustable output rate and energy' optimization.

SUMMARY

[0008] In a first aspect, the disclosure achieves the object specified above by means of the filtering device according to claim 1. The disclosure proposes that the metering device includes a piston pump having at least one piston which is movably accommodated along a longitudinal piston axis, and a drive mechanism for moving the piston, wherein the piston is adapted to convey the impurities portion-wise toward the dirt outlet, and the drive mechanism includes a drive shaft which is rotatably mounted about a rotational axis and adapted to convert a rotation of the drive shaft into a stroke action of the piston to convey the impurities. Compared to a metering device having a discharge screw, a metering device having a piston pump allows a reduced overall length. Piston pumps also obviate the need for a cooling unit or cooling device, as the pistons are designed to convey impurities axially toward the dirt outlet by performing their stroke action. The piston preferably has a thermal conductivity ranging from 15 W/(m*K) to 95 W/(m*K). The piston is preferably designed to keep the impurities, i.e. a mass containing the impurities, within a temperature range in which the impurities are free-flowing. To that end, the piston has a thermal conductivity such that temperature control of the metering device or the housing of the metering device is conducted to the impurities in order to keep them free-flowing. At the same time, the thermal conductivity is limited in such a way that any adhesion is reduced or completely prevented.

[0009] According to a preferred embodiment, the piston pump is an axial piston pump and has a cylinder block with a piston chamber. The piston chamber is designed to accommodate the piston. A workspace is preferably formed in the piston chamber and is bounded by an end face of the piston. The piston is also preferably designed to move along the longitudinal piston axis inside the piston chamber by performing its stroke action. A section on the inlet side of the piston chamber is preferably adapted for selective fluid communication with the filter chamber and the dirt outlet, depending on the stroke action. The section on the inlet side of the piston chamber preferably forms the workspace that is bounded by an end face of the piston and which is designed to temporarily receive impurities. The dirt outlet is preferably separated flui d-tightly from the filter chamber in such a way that the impurities move from the filter chamber into the workspace during the selective fluid communication of the filter chamber with the workspace, and the workspace is then separated fluid-tightly from the filter chamber before the workspace enters into fluid communication with the dirt outlet. The workspace is designed accordingly to meet that purpose.

[0010] The size of the workspace is preferably variable, depending on the stroke action of the piston. Rotation of the drive shaft thus determines the stroke action of the piston and thus a change in the size of the workspace. The stroke action is preferably divided into a suction stroke and a discharge stroke. During the suction stroke, the piston or end face is moved along the longitudinal piston axis away from the end section and into the piston chamber. This means that the workspace increases in size during the suction stroke, and an intake pressure is produced in the workspace that is smaller than the pressure prevailing in the receiving chamber and by means of which the impurities are conveyed out of the receiving chamber into the workspace. The stroke action of the piston thus produces a suction effect. During the discharge stroke, the piston or end face is moved through the piston chamber along the longitudinal piston axis toward the end section. This means that the workspace decreases in size during the suction stroke, and the impurities are conveyed out of the workspace into the discharge chamber by contact with the end face. Material, in particular impurities, is conveyed continuously by the suction stroke into the piston chamber as a result, before being conveyed out of the workspace into the dirt outlet by the combination of a discharge stroke and a rotation of the drive shaft. Due to its short linear movement, a stroke action allows the filtering device to be of compact design. The stroke action is preferably defined by a suction stroke for conveying the impurities into the workspace, and a discharge stroke for discharging the impurities out of the workspace to the dirt outlet.

[001 1] The drive mechanism preferably has at least one bearing unit which is pivotable relative to the drive shaft and/or to the cylinder block and is adapted to cooperate with the piston in such a way that the piston is driven inside the piston chamber along a longitudinal piston axis by the drive shaft and performs the stroke action. Due to the bearing unit being inclined, the piston performs a variable stroke depending on the inclination angle of the bearing unit. A rotational movement of the shaft can thus be converted in a simple manner into an axial movement of the piston, in particular along the longitudinal piston axis, whereby strokes of different lengths are performed. The bearing unit is preferably in hinged engagement with the piston. Due to its hinged engagement with the bearing unit, the piston can thus perform a stroke action along the longitudinal piston axis even when the bearing unit pivots, with the longitudinal piston axis running parallel to the longitudinal axis.

[0012] It is further preferred that the bearing unit has a bearing surface that is non-rotatable in relation to the drive shaft and that the drive shaft is connected to the cylinder block so as to impart rotation to it. The cylinder block thus rotates together with the drive shaft, whereas the bearing unit is fixed at the non-rotating bearing surface at least. The rotational movement of the cylinder block causes the pistons to rotate about the rotational axis of the drive shaft, with the result that the pistons rotate with a section of the bearing unit relative to the bearing surface. The inclination of the bearing unit determines the stroke action along the longitudinal piston axis. The longitudinal piston axis preferably extends parallel to the rotational axis.

[0013] According to an alternative preferred embodiment, the bearing unit is operatively connected to the drive shaft. The cylinder block, the pistons accommodated therein and the bearing unit thus rotate together with the drive shaft. The rotational movement of the drive shaft is transferred to the bearing unit, and the rotational movement of the bearing unit results in a rotational movement of the pistons about the rotational axis. The inclination of the bearing unit preferably remains independent of the angle of rotation and determines the stroke action along the longitudinal piston axis. The pistons are guided inside the cylinder block, and due to the inclination of the beanng unit relative to the cylinder block, the stroke action of the pistons inside the cylinder block varies depending on the respective angle of inclination.

[0014] The metering device preferably has a drive means for driving the drive shaft, wherein the drive means includes an electric, pneumatic or hydraulic actuator. The drive shaft is thus driven automatically and in particular is controllable.

[0015] It is particularly preferred that the drive mechanism further comprises a pivoting unit for pivoting the bearing unit relative to the drive shaft and/or to the cylinder block by a variable pivot angle a. The stroke action of the pistons can thus be controlled via the pivot angle. In a piston pump operating at constant speed, the output volume can therefore be regulated by setting the pivot angle. This means that, depending on the angle, a higher output volume can be achieved while the rotational speed remains constant.

[0016] It is further preferred that the metering device has a cleaning port channel extending coaxially with the rotational axis and conically in the direction of the cylinder block, for connecting to the filter chamber. A cleaning port channel extending conically in the direction of the cylinder block, i.e. tapering in the direction of the cylinder block, allows a compact connection to the cylinder block or other components of the cleaning unit. The impurities can thus be conducted evenly out of the mostly cylindrical filter chamber, thus optimizing how the impurities are conducted. It is further preferred that the axial piston pump has a transfer element that includes a receiving chamber connected to the cleaning port channel, the dirt outlet, and a discharge chamber connected to the dirt outlet. The workspace in the cylinder block is preferably in fluid communication with the discharge chamber (39) during the discharge stroke and in fluid communication with receiving chamber during the suction stroke. The discharge chamber is thus separated in terms of fluid communication from the receiving chamber in each case, and fluid communication between the workspace and the respective discharge chamber or receiving chamber is allowed only selectively. A respective defined volume can thus be conveyed continuously via the discharge chamber to the dirt outlet.

[0017J The receiving chamber preferably has a receiving chamber inlet matching the cleaning port channel and a receiving chamber outlet extending arcuately and coaxially about the axial direction in sections at least. Alternatively or additionally, the discharge chamber has a discharge chamber outlet matching the dirt outlet and a discharge chamber inlet extending arcuately and coaxially about the axial direction in sections at least.

[0018] It is further preferred that the transfer element is provided in the form of a plate, in particular as a plate that is cylindrical at least in sections, having a first contact surface on the cleaning port channel side and a second contact surface on the workspace side. The receiving chamber inlet is preferably formed in the first contact surface, and the receiving chamber outlet is preferably formed in the second contact surface. In another preferred variant, the receiving chamber inlet is formed in the second contact surface and the receiving chamber outlet is formed in the first contact surface.

[0019] The receiving chamber outlet and the discharge chamber inlet each extend preferably through an elongate hole that extends at least in sections in a circumferential direction of the transfer element. This optimizes how the impurities are conducted. [0020] It is further preferred that the transfer element is provided in the form of a plate, in particular as a plate that is cylindrical at least in sections, the discharge chamber and the receiving chamber each being formed by an elongate hole that extends at least in sections in a circumferential direction of the transfer element. An elongate hole that extends in the circumferential direction in sections at least, and not completely, provides a simple structural design.

[0021] It is particularly preferred that a heater unit is associated with the cylinder block and/or the transfer element and is configured to control the temperature of the cylinder block and/or the transfer element, preferably an outer circumferential surface of the cylinder block and/or of the transfer element. Temperature control includes heating, in particular. Heating prevents or reduces any cooling of the polymer melt, so that the viscosity⁷ of the polymer melt is not increased as a result of local solidification. The flow times are thus reduced, and the efficiency of the filtering device is increased.

[0022] The piston pump preferably has at least one bearing for mounting the cylinder block and/or the piston and/or the transfer element. The piston pump preferably has at least one lubrication circuit which is designed to conduct lubricant to the bearing.

[0023] The piston pump preferably also has a lubricant outlet for letting lubricant out of the lubrication circuit. Any surplus lubricant can thus be removed from the lubrication circuit.

[0024] According to another preferred embodiment, the piston pump is a radial piston pump having a receiving chamber that is cylindrical at least in sections, a drive shaft which is mounted eccentrically in the receiving chamber, and one or more pistons which are arranged eccentrically around the drive shaft and which extend radially in relation to the receiving chamber. As an alternative to the axial piston pump, a radial piston pump provides a practical conveying mechanism for the impurities removed from the polymer melt by the filtering device.

[0025] The metering device preferably also includes a cleaning port comprising a number of through holes forming a flange connection with the filter housing, wherein the cleaning port includes the cleaning port channel. [0026] The metering device can thus be connected easily to the filter housing by means of a flange connection. The filter housing with the filter chamber and the filter element arranged thereon can be a conventional arrangement like the aforementioned BKG® HiCon™ R-Type 250 filtering device.

[0027] It is further preferred that the filtering device has a sieve drum which is arranged as a filter element in the filter chamber and which includes a dirt side and a clean side. The filtering device preferably also includes a cleaning unit, preferably a cleaning head having a plurality of scraper members, for dislodging impurities that have accumulated on the sieve drum. Impurities can thus be removed efficaciously from the filter element. A scraper member also allows hard components of the impurities to be dislodged. The filter element or sieve drum preferably filters the impurities from the polymer melt in such a way that the impurities are retained on the dirt side and the purified polymer melt flows out away on the clean side toward the housing outlet.

[0028] According to a preferred embodiment, the filtering device further comprises a secondary' drive shaft adapted to drive the filter element and/or the cleaning head relative to one another, and a secondary drive means which is coupled to the secondary drive shaft to make it rotate. The secondary’ drive means is configured to drive the filter element and the cleaning unit, in particular a cleaning head having at least one scraper element, relative to one another. For example, the filter element can be driven, whereas the cleaning unit is stationary. It is also possible that the filter element is stationary and the cleaning unit is driven by the secondary drive means. It is also within the scope of the disclosure if the drive means for the cleaning unit and for the filter element operate in opposite directions. The secondary drive means is thus provided independently of the drive means for the metering device, and the rotational speeds of the filter element and the cleaning head can be coordinated with the drive shaft for the piston pump in a manner appropriate for the materials involved.

[0029] According to another preferred embodiment, the filtering device further comprises a secondary' drive shaft which is adapted to drive the filter element and/or the cleaning head relative to one another, wherein the filter element and/or the cleaning head is coupled to the secondary drive shaft and the drive means is further adapted to drive the secondary drive shaft. A common drive unit for driving the drive shaft and the secondary drive shaft is thus provided.

[0030] In a second aspect, the disclosure relates to a metering device which is in fluid communication with a filter chamber of the filtering device, for removing filtered impurities from a filter element accommodated in the filter chamber and for conveying the impurities toward a dirt outlet. The metering device thus includes the dirt outlet and can be brought into fluid communication with the filter chamber of the filtering device for metered removal of filtered impurities from the filtering device and for conveying the impurities toward the dirt outlet. According to the second aspect, the initially specified object is achieved by the metering device including a piston pump which has at least one movably accommodated piston and a drive mechanism for moving the piston, wherein the drive mechanism includes a drive shaft and is adapted to convert the rotation of the drive shaft into a stroke action of the piston. Such a metering device utilizes the advantages described with reference to the first aspect of the disclosure. Advantages and preferred embodiments described with reference to the filtering device according to the first aspect of the disclosure are therefore likewise advantages and preferred embodiments of the metering device according to the second aspect of the disclosure.

[0031] In a third aspect, the disclosure relates to the use of a metering device according to the second aspect of the disclosure which can be brought into fluid communication with a filter chamber of a filtering device. Accordingly, the use of such a metering device utilizes the advantages described with reference to the first aspect of the disclosure and the second aspect of the disclosure, and preferred embodiments of the metering device according to the second aspect of the disclosure are likewise preferred embodiments in respect of the third aspect of the disclosure.

[0032] In a fourth aspect, the disclosure relates to a method for cleaning a filter element of a filtering device, in particular of a filtering device according to the first aspect of the disclosure, the method comprising the steps of: feeding the polymer melt to be filtered into a filter chamber of the filtering device. filtering impurities from the polymer melt by means of a filter element accommodated in the filter chamber, in such a way that the impurities are retained on the dirt side and the purified polymer melt flows out on the clean side, cleaning the filter element of impurities by means of a cleaning unit, preferably a cleaning head having a plurality of scraper members, for dislodging impurities, conveying the impurities out of the filter chamber via a cleaning port channel of a metering device, performing a stroke action along a longitudinal piston axis by means of a piston driven by a drive mechanism, in such a way that the piston is moved about a rotational axis depending on a rotation of a drive shaft of the drive mechanism, and the impurities are conveyed toward a dirt outlet of the metering device.

[0033] Performing such a stroke action by at least one drive mechanism, in such a way that the piston is moved by the drive shaft of the drive mechanism, allows impurities which have been removed by the filter element to be discharged, with the advantages described with reference to the first aspect of the disclosure. Preferred embodiments described with reference to the first aspect of the disclosure are likewise preferred embodiments of the method according to the fourth aspect of the disclosure, and vice versa.

[0034] Preferably, the method further comprises the following substeps when performing the stroke action: performing a suction stroke to convey the impurities out of the cleaning port channel into a workspace of the metering device, performing a discharge stroke to convey the impurities out of the workspace to the dirt outlet, and discharging the filtered impurities through the dirt outlet. Due to its short linear movement, a stroke action allows the filtering device to be of compact design.

[0035] Preferably, the method further comprises the step of adjusting the stroke action by pivoting a bearing unit relative to the longitudinal piston axis and/or the rotational axis by a variable pivot angle. Adjusting the stroke action is understood here to mean adjusting the length of the stroke or the linear stroke action in the direction of the longitudinal piston axis. This length determines how far the piston moves along the longitudinal piston axis into the cylinder block during the suction stroke, thereby enlarging the workspace. The stroke action therefore proceeds away from cleaning port channel or the end section of the piston chamber. The discharge rate or the discharged volume flow rate can thus be varied independently of the speed of the drive shaft.

[0036] The filtering device according to the disclosure is preferably configured for use with a pelletizing apparatus, an extrusion machine, in particular a profile extrusion machine or a blown film line, and has appropriate coupling interfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Preferred embodiments of the disclosure shall now be described with reference to the attached Figures, in which:

[0038] Fig. 1 : shows a filtering device according to the prior art,

[0039] Fig. 2: shows a cross-sectional view' of a filtering device according to a preferred embodiment,

[0040] Fig. 3: shows a side view of a metering device for the filtering device, according to a preferred embodiment,

[0041] Fig. 4: shows a cross-sectional view' of the air metering device shown in Fig. 3,

[0042] Fig. 5: shows a transfer element of the metering device shown in Fig. 3 and Fig. 4;

[0043] Fig. 1 : shows a method for operating a filtering device as shown in Fig. 2.

DETAILED DESCRIPTION

[0044] Fig. 1 shows a perspective view' of a prior art filtering device 1 ’ for removing impurities 110 from a polymer melt 100 and having a filter housing 3 with a filter chamber 5.

[0045] Filter housing 3 has a housing inlet 7 for feeding the polymer melt

100 to be filtered into filter chamber 5, and a housing outlet 9 for conducting the purified polymer melt 120 out of filter chamber 5. Filtering device 1’ also has a dirt outlet 23’, through which the impurities 110 filtered out of the polymer melt 100 can be discharged from filter housing 3. A filter element 11 for filtering impurities 110 from polymer melt 100, and through which polymer melt 100 can be conducted, is arranged in filter housing 3 and filter chamber 5.

[0046] Filter element 11 has a '‘dirt side” 15 where impurities 110 accumulate and where impurities 110 are retained, and a ‘‘clean side” 17 where the purified polymer melt 120 flows away. The purified polymer melt 120 is then conducted to housing outlet 9.

[0047] Filtering device 1 also has a metering device 18’ for conducting the impurities 110 retained on the dirt side 15 away from the polymer melt 100 in a metered manner. Filtering device 1 preferably includes a cleaning unit 57 in the form of a cleaning head having a plurality of scraper members 57A for dislodging impurities 110 that have accumulated on filter element 11. the scraped-off impurities 110 flowing along dirt side 15 toward metering device 18’.

[0048] The impurities 110 removed by filter element 11 are then discharged from metering device 18‘ via dirt outlet 23 ’. A discharge screw 19 which is coupled to a drive shaft 29 and associated with metering device 18’ is arranged for that purpose in the region of dirt outlet 23’. The metering device 18’ is preferably cooled in the region of discharge screw 19. By means of discharge screw 19, the impurities 110 removed at filter element 11 are discharged from filter chamber 5, without being deposited to any significant extent on discharge screw 19. Drive shaft 29 extends in the axial direction and is driven rotationally about a rotational axis A by a secondary drive means 50, with the motion being transferred to discharge screw 19. Rotational axis A thus extends in the axial direction. The axial direction and the rotational axis of drive shaft 29 are therefore to be understood as synonyms.

[0049] Fig. 2 shows a filtering device 1 according to the disclosure for removing impurities 110 from a polymer melt 100. Identical or similar components have identical reference signs.

[0050] Filtering device 1 includes a filter housing 3 having a filter chamber 5, a housing inlet 7 for feeding the polymer melt 100 to be filtered into filter chamber 5 and a housing outlet 9 for conducting the purified polymer melt 120 out of filter chamber 5. A filter element 11 for filtering impurities 110 from polymer melt 100 is accommodated in filter chamber 5.

[0051] Filtering device 1 also includes a metering device 18 in fluid communication with filter chamber 5, for metered discharge of the filtered impurities 110. Metering device 18 is shown in detail in a side view in Fig. 3 and in a cross-sectional side view in Fig. 4.

[0052] As shown in Fig. 2, filter element 11 is adapted to filter impurities 110 from polymer melt 100 in such a way that impurities 110 are retained on the dirt side 15 of filter element 1 1 and purified polymer melt 120 flows on the clean side 17 toward housing outlet 9.

[0053] The impurities 110 retained on the dirt side 15 are conveyed bymeans of metering device 18 toward a dirt outlet 23 (cf. Fig. 4) of metering device 18 for metered discharge.

[0054] Metering device 18 is connected by means of a cleaning port 51 to the filter housing 3 of filtering device 1. A cleaning port channel 13, which in Fig. 2 is in fluid communication with filter chamber 5 and dirt outlet 23, is formed in cleaning port 51. Cleaning port 51 is designed to form a flange connection 51A with filter housing 3. Cleaning port channel 13 extends conically and coaxially with rotational axis A and tapers in the direction of cylinder block 31.

[0055] Filter housing 3 and cleaning port 51 (not shown) have a number of through holes 53 to form a flange connection 51 A with filter housing 3. Cleaning port channel 13 is formed at least in sections in cleaning port 51. The conical shaped cleaning port channel 13 opens with a preferably hollow cylindrical section 13A into a matching receiving chamber inlet 38B (cf. Fig. 5) of transfer element 37.

[0056] A sieve drum 55 having dirt side 15 and clean side 17 is arranged in filter chamber 5. Sieve drum 55 therefore constitutes filter element 11. Filtering device 1 further comprises a cleaning unit 57, in the form of a cleaning head having a plurality of scraper members 57A, for dislodging impurities 110 that have accumulated on sieve drum 55. These are then conveyed along dirt side 15.

[0057] Metering device 18 includes a piston pump 20. Piston pump 20 has at least one and preferably four movably accommodated pistons 25 and a drive mechanism 28. Drive mechanism 28 includes a drive shaft 29 which is rotatably mounted about a rotational axis A and adapted to convert a rotation of drive shaft 29 into a stroke action H of piston 25 along a longitudinal piston axis K (cf. Fig. 4). Each of the longitudinal piston axes K is spaced a distance a from the rotational axis A of drive shaft 29. Drive mechanism 28 further comprises a drive means 30 which is designed here as an electric actuator 30A. Drive means 30 is designed to drive the drive shaft 29 about rotational axis A. The axial direction of drive shaft 29 and the rotational axis of drive shaft 29 are to be understood as synonyms.

[0058] In the embodiment shown, piston pump 20 is an axial piston pump 21 and has a cylinder block 31 which forms, at least in sections, a piston chamber 27 and which is designed to accommodate piston 25. Piston chamber 27 is adapted for selective fluid communication with filter chamber 5 or dirt outlet 23.

[0059] Piston chamber 27 has a workspace 27 A, the size of which can be varied depending on stroke action H. Workspace 27A is formed at an end section of piston chamber 27 on the side of cleaning port 51 and is bounded by an end face 25 A of piston 25.

[0060] Stroke action H is illustrated in Fig. 4 and is defined by a suction stroke Hl for conveying impurities 110 into workspace 27 A and a discharge stroke H2 for discharging impurities 110 from workspace 27A to dirt outlet 23.

[0061] Drive mechanism 28 also has at least one bearing unit 33 which is pivotable relative to drive shaft 29 and cylinder block 31. Bearing unit 33 is operatively connected in sections to drive shaft 29 and is inclined relative to cylinder block 31. Bearing unit 33 is hingedly connected to pistons 25 on a side facing away from end face 25A and is adapted to cooperate with piston 25 in such a way that piston 25 is driven along the longitudinal piston axis K inside cylinder block 31 and in particular inside piston chamber 27 by drive shaft 29 and performs stroke action H.

[0062] In that regard, bearing unit 33 preferably has a bearing surface 33 A that is non-rotatable in relation to drive shaft 29 and a bearing element 33B that is operatively connected to drive shaft 29. Bearing unit 33 also has a first hinge joint 34A and a second hinge joint 34B which are hingedly connected to pistons 25 and bearing element 33B. The rotation of drive shaft 29 causes bearing element 33B to rotate about a bearing rotational axis A’. In Fig. 2, bearing rotational axis A’ is inclined by a pivot angle a relative to the rotational axis A of drive shaft 29 and the longitudinal piston axis K.

[0063] Drive mechanism 28 further comprises a pivoting unit 35 for pivoting bearing unit 33 relative to drive shaft 29 and cylinder block 31 by the variable pivot angle a. The length L of stroke action H is calculated as L —

[0064] The filtering device 1 shown in Fig. 2 also includes a secondary drive shaft 49, and filter element 11 and sieve drum 55 are coupled here to secondary' drive shaft 49. A secondary drive means 50 is coupled to the secondary drive shaft 49 to make it rotate and is decoupled mechanically from the drive means 30 of drive shaft 29. Filter element 11 can thus be operated independently of the speed of drive shaft 29 at which the pistons 25 of metering device 18 are driven. Alternatively, the secondary drive shaft 49 can also be coupled to the drive means 30 of drive shaft 29 and be driven together with the latter by drive means 30.

[0065] Metering device 18, in particular the piston pump 20 provided in the form of axial piston pump 21 , further comprises a transfer element 37. As shown in Figs. 2 to 4, a heater unit 41 is associated with cylinder block 31 and transfer element 37. Heater unit 41 is arranged axially outside cylinder block 31 and transfer element 37 and abuts an outer circumferential surface 37 A of transfer element 37 in sections at least.

[0066] As shown in Fig. 4 and Fig. 5, transfer element 37 includes a receiving chamber 38, dirt outlet 23, and a discharge chamber 39 connected to dirt outlet 23. Receiving chamber 38 is connected to cleaning port channel 13 in order to convey impurities 110 out of filter chamber 5 into the workspace 27 A in cylinder block 31. Discharge chamber 39 is also connected to dirt outlet 23 in order to discharge impurities 110 via dirt outlet 23 during discharge stroke H2. Workspace 27A is also in fluid communication with the discharge chamber 39 of transfer element 37 during discharge stroke H2 and is in fluid communication with the receiving chamber 38 of transfer element 37 during suction stroke Hl . Impurities 110 can thus be fed via receiving chamber 38 into workspace 27 A during suction stroke Hl and impurities 110 can be discharged from workspace 27A to discharge chamber 39 during discharge stroke H2.

[0067] Piston pump 20 has bearings 43 for mounting cylinder block 31 and/or piston 25 and/or transfer element 37. Piston pump 20 also has a lubrication circuit 45 which is designed to conduct lubricant 130 to bearing 43.

[0068] Piston pump 20 also has a lubricant outlet 47 for letting lubricant 130 out of lubrication circuit 45.

[0069] As shown in Fig. 5, in particular, transfer element 37 is preferably in the form of a plate 36, in particular as a cylindrical plate 36. Plate 36 has a first contact surface 36A on the cleaning port channel 13 side and a second contact surface 36B on the workspace 27A side.

[0070] Receiving chamber 38 has a receiving chamber inlet 38B that is designed to match cleaning port channel 13 and which is thus formed in the first contact surface 36A of transfer element 37. Receiving chamber 38 also has a receiving chamber outlet 38A extending arcuately and coaxially about rotational axis A, in sections at least, and which is thus formed in the second contact surface 36B.

[0071] Discharge chamber 39 also has a discharge chamber outlet 39B that matches dirt outlet 23 and is formed between the first contact surface 36A and the second contact surface 36B of transfer element 37. Discharge chamber 39 also has a discharge chamber inlet 39A extending arcuately and coaxially about rotational axis A, in sections at least, and which is formed in the second contact surface 36B. Receiving chamber 38 is in the form of an elongate hole 38A that extends coaxially with rotational axis A and, at least in sections, arcuately. Discharge chamber 39 is likewise in the form of an elongate hole 39A that extends, at least in sections, arcuately and coaxially about rotational axis A.

[0072] Fig. 6 shows a method 1000 for cleaning a filter element 11 of a filtering device 1 as shown in Fig. 2, for example. In the following, reference is to the filtering device shown in Fig. 2. In a first step 1100, method 1000 involves feeding the polymer melt 100 to be filtered into the filter chamber 5 of filtering device 1. In a second step 1200, impurities 110 are filtered from polymer melt 100 by the filter element 11 accommodated in filter chamber 5, in such a way that the impurities 110 are retained on the dirt side 15 and the purified polymer melt 120 flows out on the clean side 17. Filter element 11 is a sieve drum 55. In a third step 1300, method 1000 involves cleaning filter element 11 of the filtered impurities 110, which is preferably done by cleaning unit 57, in particular by the cleaning head 57 with a plurality of scraper members 57A for detaching impurities 110. In a fourth step 1400, method 1000 involves conveying the impurities 110, which have preferably been scraped off, out of filter chamber 5 through the cleaning port channel 13 of metering device 18. In a fifth step 1500, method 1000 involves stroke action H being performed by the one or more pistons 25 driven by drive mechanism 28, in such a way that the respective piston 25 is moved according to the rotation of a drive shaft 29 of drive mechanism 28, and impurities 110 are conveyed toward the dirt outlet 23 of metering device 18.

[0073] The fifth step 1500 preferably involves, as a first substep 1510, performing suction stroke Hl to convey the impurities 110 out of cleaning port channel 13 into the workspace 27 A of metering device 18, and in a second substep 1520, performing discharge stroke H2 to convey the impurities 110 out of workspace 27A into discharge chamber 39 and finally, in a third substep 1530, discharging the filtered impurities 110 out of discharge chamber 39 and through dirt outlet 23 during discharge stroke H2.

[0074] It is further preferred that, in a sixth step 1600 that may be carried out before the fifth step, method 1000 involves adjusting stroke action H by pivoting bearing unit 33 by a variable pivot angle a relative to drive shaft 29 and cylinder block 31 by means of pivoting unit 35. Depending on pivot angle a and the resulting adjustable stroke action H, the size of workspace 27A changes in which impurities 110 are temporarily received for discharge via dirt outlet 23. A greater length of stroke action H results in a larger workspace 27A and thus in a greater volumetric flow rate of impurities 110.

[0075] The following are a number of nonlimiting EXAMPLES of aspects of the disclosure.

[0076] One EXAMPLE: a filtering device includes a filter housing (3) having a filter chamber (5), a housing inlet (7) for feeding the polymer melt to be filtered (100) into the filter chamber (5) and a housing outlet (9) for conducting impurities (1 10) out of the filter chamber (5). The filtering device in addition includes a filter element (11) accommodated in the filter chamber (5) for filtering the impurities (110) out of the polymer melt (100). The device moreover includes a metering device ( 18) in fluid communication with the filter chamber (5) for metered discharge of the filtered impurities (110), where the metering device (18) has a dirt outlet (23) and is adapted to convey the impurities (110) toward the dirt outlet (23). The device also includes characterized in that the metering device (18) includes a piston pump (20) having at least one piston (25) which is movably accommodated along a longitudinal piston axis (K) and a drive mechanism (28) for moving the piston (25), where the piston (25) is adapted to convey the impurities (110) portionwise toward the dirt outlet (23). The device further includes where the drive mechanism (28) includes a drive shaft (29) which is rotatably mounted about a rotational axis (A) and adapted to convert a rotation of the drive shaft (29) into a stroke action (H) of the piston (25).

[0077] The above-noted EXAMPLE may further include any one or a combination of more than one of the following EXAMPLES: The filtering device of the above-noted EXAMPLE characterized in that the piston pump (20) also has a variable workspace (27A) which is adapted for selective fluid communication with the filter chamber (5) and the dirt outlet (23), where the piston pump (20) is adapted to convey the impurities (110) into the workspace (27A) by means of a suction stroke (Hl) of the piston (25) and to discharge the impurities (110) out of the workspace (27 A) to the dirt outlet (23) by means of a discharge stroke (H2) of the piston (25). The filtering device of the above-noted EXAMPLE characterized in that the piston pump (20) is an axial piston pump (21) and has a cylinder block (31) with a piston chamber (27) designed to accommodate the piston (25), and where the workspace (27 A) is formed in the piston chamber (27) and is bounded by an end face (25 A) of the piston (25). and the drive mechanism (28) has at least one bearing unit (33) which is pivotable relative to the drive shaft (29) and/or to the cylinder block (31) and is adapted to cooperate with the piston (25) in such a way that the piston (25) is driven along a longitudinal piston axis (K) inside the piston chamber (27) by the drive shaft (29) and performs the stroke action (H), where the workspace (27 A) can be varied depending on the stroke action (H). The filtering device of the above-noted EXAMPLE characterized in that the bearing unit (33) is operatively connected to the drive shaft (29) and hingedly connected to the piston (25), where the bearing unit (33) is pivotable relative to the cylinder block (31). The filtering device of the above-noted EXAMPLE characterized in that the drive mechanism (29, 31, 33, 35) further comprises a pivoting unit (35) for pivoting the bearing unit (33) relative to the drive shaft (29) and/or to the cylinder block (31) by a variable pivot angle (a). The filtering device of the above-noted EXAMPLE to 6, characterized in that the metering device (18) has a cleaning port channel (13) extending coaxially with the rotational axis (A) and conically in a direction of the cylinder block (31), for connecting to the filter chamber (5), and in that the axial piston pump (21) has a transfer element (37) that includes a receiving chamber (38) connected to the cleaning port channel (13), the dirt outlet (23), and a discharge chamber (39) connected to the dirt outlet (23), where the workspace (27 A) is in fluid communication with the discharge chamber (39) during the discharge stroke (H2) and in fluid communication with the receiving chamber (38) during the suction stroke (Hl). The filtering device of the above-noted EXAMPLE characterized in that the receiving chamber (38) has a receiving chamber inlet (38B) matching the cleaning port channel (13) and a receiving chamber outlet (38A) extending arcuately and coaxially about the axial direction (A) in sections at least, and/or in that the discharge chamber (39) has a discharge chamber outlet (39B) matching the dirt outlet (23) and a discharge chamber inlet (39A) extending arcuately and coaxially about the axial direction (A) in sections at least. The filtering device of the above-noted EXAMPLE to 12, includes: -a secondary drive shaft (49) which is adapted to drive the filter element (1 1) and/or the cleaning head (57) relative to one another, where the filter element (11) and/or the cleaning head (57) is coupled to the secondary drive shaft (49) and the drive means (30) is further adapted to drive the secondary drive shaft (49). The metering device of the above-noted EXAMPLE to 14, where the metering device (18) is in fluid communication with a filter chamber (5) of the filtering device (1) for cleaning a filter element (11) accommodated in a filter chamber (5) of the filtering device (1) of filtered impurities (110) and for conveying the impurities (110) toward a dirt outlet (23), characterized in that the metering device (18) includes a piston pump (20) which has at least one piston (25) which can be moved along a longitudinal piston axis and a drive mechanism (28) for moving the piston (25), where the drive mechanism (28) includes a drive shaft (29) and is adapted to convert the rotation of the drive shaft (29) into a stroke action (H) of the piston (25). The metering device of the above-noted EXAMPLE which can be brought into fluid communication with a filter chamber (5) of a filtering device (1). The method of the above-noted EXAMPLE to 14, comprising the steps of: -feeding the polymer melt to be filtered (100) into a filter chamber (5) of the filtering device (1), -filtering impurities (110) from the polymer melt (100) by means of a filter element (11) accommodated in the filter chamber (5), in such a way that the impurities (110) are retained on the dirt side (15) and the purified polymer melt (120) flows out on the clean side (17), - cleaning the filter element (11) of the filtered impurities (110), preferably by means of a cleaning head (57) having at least one and preferably a plurality of scraper members (57A) for dislodging the impurities (110), -conveying the impurities (110) out of the filter chamber (5) via a cleaning port channel (13) of a metering device (18), -performing a stroke action (H) along a longitudinal piston axis (K) by means of at least one piston (25) driven by a drive mechanism (28), in such a way that the piston (25) is moved about a rotational axis (A) depending on a rotation of a drive shaft (29) of the drive mechanism (28), and the impurities (110) are conveyed toward a dirt outlet (23) of the metering device (18). The method of the above-noted EXAMPLE the step of performing a stroke action (H) includes the substeps of: - performing a suction stroke (Hl) to convey the impurities (110) out of the cleaning port channel (13) into a workspace (27A) of the metering device (18), -performing a discharge stroke (H2) to convey the impurities (110) out of the workspace (27A) to the dirt outlet (23), and -discharging the filtered impurities (110) through the dirt outlet (23). The method of the above-noted EXAMPLE includes the steps of: - adjusting (1600) the stroke action (H) by pivoting a bearing unit (33) relative to a drive shaft (29) of the drive mechanism (28) by a variable pivot angle (a). The filtering device of the above-noted EXAMPLE characterized in that a heater unit (41) is associated with the cylinder block (31) and/or the transfer element (37) and is configured to control the temperature of the cylinder block (31) and/or the transfer element (37), preferably an outer circumferential surface (37A) of the cylinder block (31) and/or of the transfer element (37). The filtering device of the above-noted EXAMPLE characterized in that the metering device (18) has a drive means (30) for driving the drive shaft (29), where the drive means (30) includes an electric, pneumatic or hydraulic actuator (30A). The filtering device of the abovenoted EXAMPLE characterized in that the metering device (18) further comprises a cleaning port (51) comprising a number of through holes (53) forming a flange connection (51 A) with the filter housing (3), where the cleaning port (51) includes the cleaning port channel (13). The filtering device of the above-noted EXAMPLE characterized in that the filtering device (1) has a sieve drum (55) which is arranged as a filter element (11) in the filter chamber (5) and which includes a dirt side (15) and a clean side (17), where the impurities (110) are retained on the dirt side (15) and purified polymer melt (120) flows out on the clean side (17) toward the housing outlet (9). The filtering device of the above-noted EXAMPLE includes: -a cleaning unit (57). in particular a cleaning head (57) having a plurality of scraper members (57A), for dislodging impurities (110) that have accumulated on the sieve drum (55). The filtering device of the above-noted EXAMPLE includes: -a secondary⁷ drive shaft (49) adapted to drive the filter element (11) and/or the cleaning head (57) relative to one another, and -a secondary drive means (50) for driving the filter element (11) and/or the cleaning head (57) and which is coupled to the secondary drive shaft (49) so as to impart rotation and which is decoupled mechanically from the drive means (30) of the drive shaft (29).

List of reference signs

[0079] 1, 1 ’ Filtering device

[0080] 3 Filter housing

[0081] 5 Filter chamber

[0082] 7 Housing inlet

[0083] 9 Housing outlet

[0084] 11 Filter element

[0085] 13 Cleaning connection channel

[0086] 13A Hollow cylindrical section

[0087] 15 Dirt side

[0088] 17 Clean side

[0089] 18, 18’ Metering device

[0090] 19 Discharge screw

[0091] 20 Piston pump

[0092] 21 Axial piston pump

[0093] 23, 23’ Dirt outlet

[0094] 25 Piston

[0095] 25 A End face

[0096] 27 Piston chamber

[0097] 27A Workspace

[0098] 28 Drive mechanism

[0099] 29 Drive shaft

[0100] 30 Drive means

[0101] 30A Actuator

[0102] 31 Cylinder block

[0103] 33 Bearing unit

[0104] 33A Bearing surface

[0105] 34A First hinge joint

[0106] 34B Second hinge joint

[0107] 35 Pivoting unit

[0108] 36 Plate

[0109] 36A Contact surface [0110] 36B Contact surface

[011 1] 37 Transfer element

[0112] 37A Circumferential surface

[0113] 38 Receiving chamber

[0114] 38A Receiving chamber outlet

[0115] 38B Receiving chamber inlet

[0116] 39 Discharge chamber

[0117] 39A Discharge chamber inlet

[0118] 39B Discharge chamber outlet

[0119] 41 Heater unit

[0120] 43 Bearing

[0121] 45 Lubrication circuit

[0122] 47 Lubricant outlet

[0123] 49 Secondary drive shaft

[0124] 50 Secondary drive means

[0125] 51 Cleaning port

[0126] 51A Flange connection

[0127] 53 Through holes

[0128] 55 Sieve drum

[0129] 57 Cleaning unit, cleaning head

[0130] 57A Scraper members

[0131] 100 Polymer melt

[0132] 110 Impurities

[0133] 120 Polymer melt

[0134] 130 Lubricant

[0135] 1000 Method

[0136] 1100 Feeding in the polymer melt to be filtered

[0137] 1200 Filtering of impurities

[0138] 1300 Cleaning the filter element

[0139] 1400 Conveying the impurities

[0140] 1500 Performing a stroke action

[0141] 1510 Performing a suction stroke [0142] 1520 Performing a discharge stroke

[0143] 1530 Discharging the filtered impurities

[0144] 1600 Adjusting the stroke action

[0145] Hl Suction stroke

[0146] H2 Discharge stroke

[0147] H Stroke action

[0148] A Rotational axis

[0149] AaDistance

[0150] L Length

[0151] K Piston axis

[0152] a Pivot angle

Claims

1. A filtering device (1) for removing impurities (110) from a polymer melt (100), comprising: a filter housing (3) having a filter chamber (5), a housing inlet (7) for feeding the polymer melt to be filtered (100) into the filter chamber (5) and a housing outlet (9) for conducting impurities (110) out of the filter chamber (5), a filter element (11) accommodated in the filter chamber (5) for filtering the impurities (110) out of the polymer melt (100), and a metering device ( 18) in fluid communication with the filter chamber (5) for metered discharge of the filtered impurities (110), wherein the metering device (18) has a dirt outlet (23) and is adapted to convey the impurities (110) toward the dirt outlet (23), characterized in that the metering device (18) includes a piston pump (20) having at least one piston (25) which is movably accommodated along a longitudinal piston axis (K) and a drive mechanism (28) for moving the piston (25), wherein the piston (25) is adapted to convey the impurities (110) portion-wise toward the dirt outlet (23), wherein the drive mechanism (28) includes a drive shaft (29) which is rotatably mounted about a rotational axis (A) and adapted to convert a rotation of the drive shaft (29) into a stroke action (H) of the piston (25).

2. The filtering device (1) according to claim 1, characterized in that the piston pump (20) also has a variable workspace (27 A) which is adapted for selective fluid communication with the filter chamber (5) and the dirt outlet (23), wherein the piston pump (20) is adapted to convey the impurities (110) into the workspace (27A) by means of a suction stroke (Hl) of the piston (25) and to discharge the impurities (110) out of the workspace (27 A) to the dirt outlet (23) by means of a discharge stroke (H2) of the piston (25).

3. The filtering device (1) according to claim 1 or 2, characterized in that the piston pump (20) is an axial piston pump (21) and has a cylinder block (31) with a piston chamber (27) designed to accommodate the piston (25), and wherein the workspace (27 A) is formed in the piston chamber (27) and is bounded by an end face (25 A) of the piston (25), and the drive mechanism (28) has at least one bearing unit (33) which is pivotable relative to the drive shaft (29) and/or to the cylinder block (31) and is adapted to cooperate with the piston (25) in such a way that the piston (25) is driven along a longitudinal piston axis (K) inside the piston chamber (27) by the drive shaft (29) and performs the stroke action (H), wherein the workspace (27 A) can be varied depending on the stroke action (H).

4. The filtering device (1) according to one of the preceding claims, characterized in that the metering device (18) has a drive means (30) for driving the drive shaft (29), wherein the drive means (30) includes an electric, pneumatic or hydraulic actuator (30A).

5. The filtering device (1) according to claim 3 or 4, characterized in that the bearing unit (33) is operatively connected to the drive shaft (29) and hingedly connected to the piston (25), wherein the bearing unit (33) is pivotable relative to the cylinder block (31).

6. The filtering device (1) according to claim 4 or 5, characterized in that the drive mechanism (29, 31, 33, 35) further comprises a pivoting unit (35) for pivoting the bearing unit (33) relative to the drive shaft (29) and/or to the cylinder block (31) by a variable pivot angle (a).

7. The filtering device (1) according to any one of claims 3 to 6, characterized in that the metering device (18) has a cleaning port channel (13) extending coaxially with the rotational axis (A) and conically in the direction of the cylinder block (31), for connecting to the filter chamber (5). and in that the axial piston pump (21) has a transfer element (37) that includes a receiving chamber (38) connected to the cleaning port channel (13), the dirt outlet (23), and a discharge chamber (39) connected to the dirt outlet (23), wherein the workspace (27A) is in fluid communication with the discharge chamber (39) during the discharge stroke (H2) and in fluid communication with the receiving chamber (38) during the suction stroke (Hl).

8. The filtering device (1) according to claim 7, characterized in that the receiving chamber (38) has a receiving chamber inlet (38B) matching the cleaning port channel (13) and a receiving chamber outlet (38A) extending arcuately and coaxially about the axial direction (A) in sections at least, and/or in that the discharge chamber (39) has a discharge chamber outlet (39B) matching the dirt outlet (23) and a discharge chamber inlet (39A) extending arcuately and coaxially about the axial direction (A) in sections at least.

9. The filtering device (1) according to one of the preceding claims, characterized in that a heater unit (41) is associated with the cylinder block

(31) and/or the transfer element (37) and is configured to control the temperature of the cylinder block (31) and/or the transfer element (37), preferably an outer circumferential surface (37A) of the cylinder block (31) and/or of the transfer element (37).

10. The filtering device (1) according to one of the preceding claims, characterized in that the metering device (18) further comprises a cleaning port (51) comprising a number of through holes (53) forming a flange connection (51 A) with the filter housing (3), wherein the cleaning port (51) includes the cleaning port channel (13).

11. The filtering device (1) according to one of the preceding claims, characterized in that the filtering device (1) has a sieve drum (55) which is arranged as a filter element (11) in the filter chamber (5) and which includes a dirt side (15) and a clean side (17), wherein the impurities (110) are retained on the dirt side (15) and purified polymer melt (120) flows out on the clean side (17) toward the housing outlet (9).

12. The filtering device (1) according to claim 11. further comprising: a cleaning unit (57). in particular a cleaning head (57) having a plurality of scraper members (57A), for dislodging impurities (110) that have accumulated on the sieve drum (55).

13. The filtering device (1) according to claim 12. further comprising: a secondary drive shaft (49) adapted to drive the filter element (11) and/or the cleaning head (57) relative to one another, and a secondary drive means (50) for driving the filter element (11) and/or the cleaning head (57) and which is coupled to the secondary drive shaft (49) so as to impart rotation and which is decoupled mechanically from the drive means (30) of the drive shaft (29).

14. The filtering device (1) according to claims 1 to 12, further comprising: a secondary drive shaft (49) which is adapted to drive the filter element (11) and/or the cleaning head (57) relative to one another, wherein the filter element (11) and/or the cleaning head (57) is coupled to the secondary drive shaft (49) and the drive means (30) is further adapted to drive the secondary drive shaft (49).

15. A metering device (18) for a filtering device ( 1 ) for removing impurities (110) from a polymer melt to be filtered (100), in particular for a filtering device (1) according to any one of claims 1 to 14, wherein the metering device (18) is in fluid communication with a filter chamber (5) of the filtering device (1) for cleaning a filter element (11) accommodated in afilter chamber (5) of the filtering device (1) of filtered impurities (110) and for conveying the impurities (110) toward a dirt outlet (23), characterized in that the metering device (18) includes a piston pump (20) which has at least one piston (25) which can be moved along a longitudinal piston axis and a drive mechanism (28) for moving the piston (25), wherein the drive mechanism (28) includes a drive shaft (29) and is adapted to convert the rotation of the drive shaft (29) into a stroke action (H) of the piston (25).

16. Use of a metering device (18) according to claim 15 which can be brought into fluid communication with a filter chamber (5) of a filtering device (1).

17. A method for cleaning a filter element (11) of a filtering device (1), in particular of a filtering device (1) according to any one of claims 1 to 14, comprising the steps of feeding the polymer melt to be filtered (100) into a filter chamber (5) of the filtering device (1), filtering impurities (110) from the polymer melt (100) by means of a filter element (11) accommodated in the filter chamber (5). in such a way that the impurities (110) are retained on the dirt side (15) and the purified polymer melt (120) flows out on the clean side (17), cleaning the filter element (11) of the filtered impurities (110), preferably by means of a cleaning head (57) having at least one and preferably a plurality of scraper members (57A) for dislodging the impurities (110), conveying the impurities (110) out of the filter chamber (5) via a cleaning port channel (13) of a metering device (18), and performing a stroke action (H) along a longitudinal piston axis (K) by means of at least one piston (25) driven by a drive mechanism (28), in such a way that the piston (25) is moved about a rotational axis (A) depending on a rotation of a drive shaft (29) of the drive mechanism (28), and the impurities (110) are conveyed toward a dirt outlet (23) of the metering device (18).

18. The method according to claim 17, the step of performing a stroke action (H) further comprising the substeps of: performing a suction stroke (Hl) to convey the impurities (110) out of the cleaning port channel (13) into a workspace (27A) of the metering device (18). performing a discharge stroke (H2) to convey the impurities (110) out of the workspace (27A) to the dirt outlet (23), and discharging the filtered impurities (110) through the dirt outlet (23).

19. The method according to claim 17 or 18, further comprising the steps of: adjusting (1600) the stroke action (H) by pivoting a bearing unit (33) relative to a drive shaft (29) of the drive mechanism (28) by a variable pivot angle (a).

20. A filtering device configured to remove impurities from a polymer melt, the filtering device comprising: a filter housing having a filter chamber, a housing inlet configured to feed the polymer melt to be filtered into the filter chamber and a housing outlet configured to conduct impurities out of the filter chamber; a filter element accommodated in the filter chamber configured to filter the impurities out of the polymer melt: and a metering device in fluid communication with the filter chamber and configured for metered discharge of the filtered impurities, wherein the metering device has a dirt outlet and is configured to convey the impurities toward the dirt outlet, wherein the metering device includes a piston pump having at least one piston which is movably accommodated along a longitudinal piston axis and a drive mechanism configured to move the piston, wherein the piston is configured to convey the impurities portion-wise toward the dirt outlet, and wherein the drive mechanism includes a drive shaft which is rotatably mounted about a rotational axis and configured to convert a rotation of the drive shaft into a stroke action of the piston.

21. The filtering device according to claim 20, wherein the piston pump also has a variable workspace which is configured for selective fluid communication with the filter chamber and the dirt outlet, wherein the piston pump is configured to convey the impurities into the variable workspace by means of a suction stroke of the piston and to discharge the impurities out of the variable workspace to the dirt outlet by means of a discharge stroke of the piston.

22. The filtering device according to claim 21, wherein the piston pump is an axial piston pump and has a cylinder block with a piston chamber designed to accommodate the piston, wherein the variable workspace is formed in the piston chamber and is bounded by an end face of the piston, wherein the drive mechanism has at least one bearing unit which is pivotable relative to the drive shaft and/or to the cylinder block and is configured to cooperate with the piston in such a way that the piston is driven along the longitudinal piston axis inside the piston chamber by the drive shaft and performs the stroke action, and wherein the variable workspace can be varied depending on the stroke action.

23. The filtering device according to claim 20, wherein the metering device has a drive means configured to drive the drive shaft, and wherein the drive means includes an electric, pneumatic or hydraulic actuator.

24. The filtering device according to claim 22, wherein the bearing unit is operatively connected to the drive shaft and hingedly connected to the piston, and wherein the bearing unit is pivotable relative to the cylinder block.

25. The filtering device according to claim 24, wherein the drive mechanism further comprises a pivoting unit configured to pivot the bearing unit relative to the drive shaft and/or to the cylinder block by a variable pivot angle.

26. The filtering device according to claim 22, wherein the metering device has a cleaning port channel extending coaxially with the rotational axis and conically in a direction of the cylinder block, the cleaning port channel configured to connect to the filter chamber, wherein the axial piston pump has a transfer element that includes a receiving chamber connected to the cleaning port channel, the dirt outlet, and a discharge chamber connected to the dirt outlet, and wherein the variable workspace is in fluid communication with the discharge chamber during the discharge stroke and in fluid communication with the receiving chamber during the suction stroke.

27. The filtering device according to claim 26, wherein the receiving chamber has a receiving chamber inlet matching the cleaning port channel and a receiving chamber outlet extending arcuately and coaxially about an axial direction in sections at least, and/or wherein the discharge chamber has a discharge chamber outlet matching the dirt outlet and a discharge chamber inlet extending arcuately and coaxially about the axial direction in sections at least.

28. The filtering device according to claim 26, further comprising a heater unit associated with the cylinder block and/or the transfer element and configured to control a temperature of the cylinder block and/or the transfer element.

29. The filtering device according to claim 22, wherein the metering device further comprises a cleaning port comprising a number of through holes forming a flange connection with the filter housing, and wherein the cleaning port includes the cleaning port channel.

30. The filtering device according to claim 23, further comprising a sieve drum which is arranged as a filter element in the filter chamber and which includes a dirt side and a clean side. wherein the impurities are configured to be retained on the dirt side and a purified polymer melt is configured to flow out on the clean side toward the housing outlet.

31. The filtering device according to claim 30, further comprising: a cleaning head having a plurality of scraper members configured to dislodge impurities that have accumulated on the sieve drum.

32. The filtering device according to claim 31 , further comprising: a secondary drive shaft configured to drive the filter element and/or the cleaning head relative to one another; and a secondary⁷ drive means configured to drive the filter element and/or the cleaning head and which is coupled to the secondary drive shaft so as to impart rotation and which is decoupled mechanically from the drive means of the drive shaft.

33. The filtering device according to claim 31, further comprising: a secondary drive shaft configured to drive the filter element and/or the cleaning head relative to one another, wherein the filter element and/or the cleaning head is coupled to the secondary' drive shaft and the drive means is further configured to drive the secondary drive shaft.

34. A metering device for a filtering device configured to remove impurities from a polymer melt to be filtered, the metering device comprising: means for cleaning a filter element accommodated in a filter chamber of a filtering device of filtered impurities and for conveying the impurities toward a dirt outlet; a piston pump which has at least one piston which is movably accommodated along a longitudinal piston axis; and a drive mechanism configured to move the piston, wherein the drive mechanism includes a drive shaft and is configured to convert a rotation of the drive shaft into a stroke action of the piston.

35. A method of using a metering device according to claim 34, the method comprising: bringing the metering device into fluid communication with the filter chamber of the filtering device.

36. A method for cleaning a filter element of a filtering device, the method comprising: feeding a polymer melt to be filtered into a filter chamber of the filtering device; filtering impurities from the polymer melt by means of a filter element accommodated in the filter chamber, in such a way that the impurities are retained on a dirt side of the filter element and a purified polymer melt flows out on a clean side of the filter element; cleaning the filter element of the filtered impurities by means of a cleaning head having at least one scraper member configured to dislodge the impurities; conveying the impurities out of the filter chamber via a cleaning port channel of a metering device: and performing a stroke action along a longitudinal piston axis by means of at least one piston driven by a drive mechanism, in such a way that the piston is moved about a rotational axis depending on a rotation of a drive shaft of the drive mechanism, and the impurities are conveyed toward a dirt outlet of the metering device.

37. The method according to claim 36, wherein performing the stroke action further comprises: performing a suction stroke to convey the impurities out of the cleaning port channel into a workspace of the metering device; performing a discharge stroke to convey the impurities out of the workspace to the dirt outlet; and discharging the filtered impurities through the dirt outlet.

38. The method according to claim 36, further comprising: adjusting the stroke action by pivoting a bearing unit relative to a drive shaft of the drive mechanism by a variable pivot angle.

39. The filtering device according to claim 28, wherein the heater unit is configured to control the temperature of an outer circumferential surface of the cylinder block and/or of the transfer element.