Filter assembly

Abstract

The present invention relates to a filter assembly (10) for a fluid to be filtered and comprising a filter housing (12). The first opening (36a) of the through-channel portion (36) of the filter support wall portions (30, 32) and the dimensions of the cleaning piston (66) are matched such that the total surface area of the first opening (36a) and the region of the first opening (36a) extending into the receiving recesses (68, 70) totals to a value F1, and the value F1 is the same over the movement path of the cleaning piston (66) across the region of the first opening (36a) of the through-channel portion (36) of the filter support wall portions (30, 32).

Description

Technical Field

[0001] The present invention relates to a filter assembly of the type defined in the preamble of claim 1, and a method of filtering a fluid using the filter assembly.

Background Art

[0002] This type of filter assembly is used in plastic processing. In a plastic processing system, plastic granules, recycled materials or powder components are often heated to a liquid state and then processed. It is not uncommon for plastic granules to be made from recycled materials, which often contain impurities due to foreign matter. As an example of a plastic processing system used for this purpose, there is an extruder. An extruder is a conveying device that utilizes the functional principle of a screw conveyor, and for example, in an extrusion process, to manufacture products such as flat films or blow films, it uniformly extrudes a viscous mass from a solid through a forming opening under high pressure and high temperature. In other systems as well, for this purpose, for example, a gear pump is used.

[0003] Even when pure raw materials are used, the heated and viscous plastic usually contains some dirty particles. It is necessary to prevent these dirty particles from mixing into both the plastic processing system and the final product. In order to filter these dirty particles from the liquid plastic, a suitable filter is used. The liquid plastic is passed through a filter assembly under pressure before the raw material is further processed in the plastic processing system.

[0004] In order to achieve a uniform processing process, it is necessary to keep the processing pressure as constant as possible. Therefore, in order to ensure uniform discharge and thus a constant processing pressure, it is necessary to periodically replace or clean the screen filter in the filter assembly.

[0005] For this purpose, various replacement devices are used for the screen that constitutes the filter. The currently used screen replacement systems include piston-type screen changers, screen wheel filters, belt-type screen changers, rotary-type screen changers, and flat slide valves. The screen replacement system usually operates automatically and is driven mechanically or hydraulically. However, manual screen replacement systems are also used.

[0006] A general filter assembly for the fluid to be filtered is known from German Utility Model Registration No. 20 2017 007 054 (U1). The filter assembly is provided with a filter housing including an inflow opening for the inflow duct and an outflow opening for the outflow duct. The flow body can be a part of a piston that extends out of the filter housing for filter replacement of the filter assembly, and together with the filter screen and the filter screen stop wall portion, separates the first chamber portion and the second chamber portion within the filter housing. The flow body has a filter support wall portion including a first side portion and a second side portion spaced apart from the first side portion, and this second side portion is in contact with the filter screen in at least a partial region and holds the filter screen against the stop wall portion. The first chamber portion is connected to the inflow duct, and the second chamber portion is connected to the outflow duct. Through-channel portions having associated openings are provided on both sides of the filter support wall portion, and the fluid flows from the first chamber portion through the first opening, through the through-channel portion, and to the second opening for filtering by the filter screen. Also, through-channel portions having openings on both sides of the stop wall portion are provided on the stop wall portion, and the filtered fluid is supplied from the filter screen into the second chamber portion through the through-channel portion.

[0007] Furthermore, a movable cleaning piston is provided, which piston abuts against a first side portion of a filter support wall having a guide region. The cleaning piston has at least one receiving recess disposed within the guide region, and a portion of a first opening of the filter support wall extends into this receiving recess. Further, the cleaning piston is provided with a discharge duct for discharging the backwashed fluid, whereby by moving the cleaning piston along the filter support wall, a portion of the filtered fluid is backwashed from the second chamber portion through the stop wall portion, the filter screen, the second opening, the filter support wall, the through-channel portion of the filter support wall, the first opening, and the receiving recess of the cleaning piston into the discharge duct of the cleaning piston, thereby removing deposits from the filter screen and the filter support wall.

[0008] To clean the filter screen and thus backwash the filter screen, the cleaning piston is continuously moved from a stationary position outside the region having the opening of the through-channel portion of the filter support wall into the region of the opening of the through-channel portion of the filter support wall. The cleaning piston moves across the entire region of the opening of the through-channel portion of the filter support wall to the opposite stationary position, or thereafter returns to the stationary position from which the cleaning piston started.

[0009] However, the problem with this prior art design is that as a result of the first backwash step and / or subsequent backwash steps of individual backwash sub-areas, the volume of the filtered fluid exiting the filter assembly changes, so that the backwash process causes pressure fluctuations throughout the system. In particular, these pressure fluctuations have an adverse effect on areas of tools such as nozzles, for example in the film manufacturing or pelletizing process. In film manufacturing, if the pressure is too low, the material may ultimately break. However, as with all other extrusion processes, quality defects may also occur in the form of changing layer thickness and wall thickness or pellet size, which must be avoided. SUMMARY OF THE INVENTION

[0010] For this reason, an object of the present invention is to avoid the above-mentioned drawbacks and at the same time achieve effective backwashing, while creating a constant pressure state upstream and downstream of the filter, thereby improving the quality of the process and the service life of the filter assembly. To this end, it is to improve a filter assembly of the type defined in the preamble of claim 1.

[0011] This object is achieved in a first aspect of the invention by a combination of the features of claim 1 and the features of its preamble.

[0012] The dependent claims relate to further advantageous embodiments of the invention.

[0013] The present invention is based on the recognition that by adapting the receiving recess of the cleaning piston and the first opening of the filter support wall such that the total cross-sectional area of the first openings protruding into the receiving recess of the cleaning piston is the same over the entire movement path of the cleaning piston along the filter support wall, it is possible to keep the pressure constant during backwashing regardless of the movement position of the cleaning piston. This means that the quality level of the product can be kept at least constant. Furthermore, this improves the service life of the filter assembly.

[0014] Furthermore, since pressure fluctuations in the outflow duct caused by the cleaning piston moving within the area of the opening in the filter support wall are avoided, pressure fluctuations can be avoided by continuous backwashing. Thus, the quality of the product is further improved by this filter assembly.

[0015] According to the present invention, the first opening of the filter support wall and the dimensions of the cleaning piston are thus matched to each other such that the total area of the opening and the area of the opening extending into the receiving recess generates a value F1, and the value F1 is always the same over the movement path of the cleaning piston across the area of the first opening of the through-channel portion of the filter support wall. Thus, the total cross-sectional area of the openings of the filter support wall protruding into the receiving recess of the cleaning piston is always the same regardless of the movement position of the cleaning piston. Thereby, when moving the cleaning piston, for example, from one row of the first openings of the filter support wall to the next row of the first openings, particularly when moving the piston from the stationary position into the area of the first openings of the filter support wall, the pressure fluctuations that conventionally occurred can be easily avoided. As a result, permanent backwashing is performed, and the service life until the filter is replaced is extended.

[0016] According to a further advantageous development of the invention, the cleaning piston has a first and a second end position. The movement path of the cleaning piston extends between the first end position and the second end position. The value F1 remains the same at the two end positions as well as over the entire movement path.

[0017] In principle, it is conceivable to use a rotating cleaning piston. However, the movement path of the cleaning piston relative to the filter support wall is preferably linear, particularly exclusively linear.

[0018] In particular, starting from the end position of the cleaning piston and in the direction of movement, a plurality of rows of the first openings of the through-channel portion of the filter support wall can be provided. The central group of the series of first openings is present on a plane orthogonal to the movement path of the cleaning piston. The cross-sectional area for one row has a value F2. Here, F1 = K × F2, and K > 0.

[0019] In this regard, it has been proven advantageous to offset adjacent rows of the first openings relative to each other, in particular orthogonally to the axis of the cleaning piston, for example axially offset relative to the longitudinal axis and / or offset obliquely relative to the longitudinal axis.

[0020] In order to keep the design as simple as possible and thus also the manufacturing as simple as possible, the sum value F2 of the cross-sectional areas of one row of the first openings corresponds to the value F1.

[0021] At least, the cross-sectional area of each first opening and the cross-sectional area of the adjacent through-channel portion may have the same design, in particular also in terms of their outer peripheral shape. For example, each first opening and the adjacent through-channel portion may have a circular cross-section with a diameter D and a radius R. Alternatively, each first opening and the adjacent through-channel portion may have another cross-section, for example a hexagonal or elliptical cross-section.

[0022] According to one embodiment of the invention, the distance of the receiving recess of the cleaning piston in the moving direction of the cleaning piston is equal to or greater than the diameter D of the first opening. This makes it easier to keep the size of the cleaning piston compact.

[0023] In the case of K = 1 and thus F1 = F2, the rows of the first openings can be arranged such that at the moving position of the cleaning piston, the first edge of the receiving recess of the cleaning piston aligns with the edge of the first openings of one row, these openings are completely located within the receiving recess, and the second edge of the receiving recess aligns with the edge of the first openings of the adjacent row where the current opening is not located within the receiving recess.

[0024] Therefore, the filter assembly is particularly suitable for applications where high quality is required, preferably for incorporation into a film production system.

[0025] In principle, the cleaning piston can be adapted to the shape of the filter support wall. Preferably, the area of the diffuser body assigned to the cleaning piston, and thus the cleaning piston, is rotationally symmetric. The filter support wall is adapted to the cleaning piston, and the filter screen and the stop wall are adapted to the shape of the filter support wall. This facilitates the manufacture of the cleaning piston and the flow body.

[0026] According to an embodiment of the invention, the filter support wall, the filter screen and the stop wall extend only circumferentially over a partial circumference of the cleaning piston.

[0027] The receiving recess of the cleaning piston can comprise at least this partial circumference; in particular, the receiving recess of the cleaning piston extends circumferentially over at least this partial circumference.

[0028] Preferably, the receiving recess of the cleaning piston is designed either as a groove with a channel section to the discharge duct or as extending radially inwards to the discharge duct like a cylindrical segment, depending on which is more advantageous with respect to a predetermined dimension for discharging the backwashed fluid.

[0029] The filter screen and the stop wall can be divided into two parts, and in particular the two parts can be designed as two identical components.

[0030] Furthermore, the filter support wall has at least two regions assigned to the filter screen and the filter support wall, and through-channel sections with openings are provided in these regions.

[0031] Finally, at least two receiving recesses can also be provided in the cleaning piston, and these receiving recesses are assigned to the regions of the filter support wall having the first opening and the through-channel section.

[0032] According to one embodiment of the present invention, each component of the stop wall portion is designed as a cylindrical segment. This extends only over a part of the angle in the circumferential direction. Further, the stop wall portion has an outer wall portion that extends radially outward from the filter screen and surrounds laterally a region having an opening. The region having an opening on the radially outer side of the stop wall portion is offset radially inward with respect to the free end region of the outer wall portion, i.e., the radially outward end face.

[0033] In order to securely arrange the stop wall portion, and thus the filter screen, within the flow body, the flow body surrounds the outer wall portion at least in some regions, particularly completely up to the end face.

[0034] The flow body having the filter screen and the stop wall portion, and the cleaning piston arranged inside the flow body, can be part of a piston that can extend out of the filter housing in order to replace the filter screen. In any case, the individual components of the support wall portion and the individual components of the filter screen are thus arranged in a detachable manner within the flow body.

[0035] The through-channel portion of the filter support wall preferably extends radially with respect to the coaxial axis of the cleaning piston; in particular, these through-channel portions of the filter support wall are aligned with the associated through-channel portions provided in the stop wall portion. In this case, they may extend radially outward.

[0036] According to a further aspect, the present invention is based on the recognition that a permanent backwash, particularly a permanent backwash of a certain amount of fluid, can improve both the quality of the final product and the service life of the filter assembly.

[0037] Therefore, according to this aspect of the present invention, there is provided a method of filtering a fluid using a filter assembly, particularly a filter assembly of the type described above, in which a permanent backwash of the filtered fluid is performed within the filter assembly.

[0038] Preferably, the amount of fluid backwashed within the filter assembly remains constant at all times.

[0039] In particular, a fluid having a low viscosity, preferably a viscosity in the range of 50 Pa·s to 5,000 Pa·s, is filtered for the operation of the filter assembly.

[0040] With respect to the service life of the filter assembly, it is advantageous for the cleaning piston to be permanently reciprocated from the first end position to the second end position.

[0041] The cleaning piston can be moved at a speed in the range of 10% to 200%, particularly in the range of 45% to 150%, of the discharge rate of the filtered fluid / the inflow rate of the fluid to be filtered.

[0042] Preferably, the amount of fluid backwashed is in the range of 0.1% to 2.0%, particularly in the range of 0.5% to 1.0%, of the fluid flowing into the filter assembly.

[0043] The filter support wall portion is preferably provided with an inner sleeve portion and a base filter support wall portion. The inner sleeve portion includes first and second openings and a through-channel portion. This enables different requirements regarding the material or structure of the inner sleeve portion and the base filter support wall portion to be met. Thus, the components can be optimized with respect to these applications and the loads on the materials. This also simplifies the manufacturing process.

[0044] According to a further advantageous embodiment of the present invention, the inner sleeve portion is detachably connected to the base filter support wall portion. This enables the openings and the through-channel portion to be optimized and adapted rheologically and from the perspective of fluid technology with respect to the viscosity of the medium to be processed. Furthermore, in order to ensure reliable filtration over a longer filtration time, the inner sleeve portion is replaceable in the event of wear, for example, abrasion caused by the permanent movement of the backwashing piston.

[0045] Preferably, the cross-sectional areas of the opening and the through-channel portion each have a height and a width. The height is several times larger than the width. This ensures that the dimensions of the cleaning piston in the longitudinal direction are small.

[0046] Preferably, the cross-sectional area of the opening corresponds to 65% of the cross-sectional area of the receiving recess. This reduces the pressure on the inflow side of the filter support wall portion and increases the effective filter area.

[0047] According to a further advantageous embodiment of the invention, the shape of each opening corresponds to the shape of the associated receiving recess. This makes it possible to reduce the pressure on the inflow side of the filter support wall portion. Furthermore, this optimizes the flow state of the fluid to be filtered.

[0048] Further advantages, features and possible uses of the invention will become apparent from the following description with reference to the embodiments shown in the drawings.

[0049] Throughout this specification, the claims and the drawings, the terms and the associated reference signs listed in the following reference sign list are used.

Brief Description of the Drawings

[0050]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6a

Figure 6b

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

[0051] Figures 1 to 10 show a filter assembly 10 according to the present invention including a piston type screen changer. FIG. 10 shows a variant of the filter assembly 10 according to the present invention, and FIGS. 11 and 12 show other variants. The filter assembly 10 comprises a housing 12 within which a piston 14 is movable between a screen change position and a filtration position as required. At the screen change position, the filter screen can be replaced. At the filtration position, fluid can flow through the filter assembly 10 and be filtered. In FIGS. 1, 2 and 7, the piston 14 is in a screen change position extended with respect to the housing 12, and in FIGS. 3, 4, 5, 6a and 6b, the piston 14 is in a filtration position retracted with respect to the housing 12.

[0052] An inlet opening 16 is provided laterally on a first side of the housing 12 through which a fluid, for example a plastic fluid, having a low viscosity, preferably in the range of 50 Pa·s to 5,000 Pa·s, is supplied to the filter assembly 10, flows through the filter assembly 10 and is filtered in a process as will be described in detail below. The fluid is supplied to the housing 12 through the inlet opening 16 via a supply pipe (not shown). The supply pipe can be screwed to the housing 12 using a flange connection. For this purpose, the housing 12 has corresponding screw holes 18 as shown, for example, in FIGS. 1 and 3. The screws engage with these screw holes 18 and corresponding holes in the flange of the supply pipe, and the screws are used to fix the flange having the supply pipe to the housing 12.

[0053] Similarly, an outflow opening 20 is provided in the second side of the housing 12 remote from the first side, through which the filtered fluid is removed from the filter assembly 10 via a discharge pipe (not shown) for further processing. The discharge pipe can also be screwed to the housing 12 using a flange connection. For this purpose, the housing 12 has corresponding screw holes 22, as shown, for example, in FIG. 2. The screws engage these screw holes 22 and corresponding holes in the flange of the discharge pipe, and the screws are used to fix the flange having the discharge pipe to the housing 12.

[0054] For example, the filter assembly 10 can be an important part of a system for film production or granulation. Here, the filtered plastic fluid is supplied via a discharge pipe to a nozzle for discharging the filtered plastic fluid and is formed into a film that is sent out from the nozzle.

[0055] The drive for the piston 14 in the housing 12 for moving the piston between the screen exchange position and the filtration position is basically known and will not be described further here for this reason.

[0056] In particular, as shown in FIGS. 4 and 5, the inflow opening 16 is connected via an inflow pipe 24 extending inside the housing 12 and the piston 14 to a cylindrical interior 26 within the piston 14. The interior 26 is bounded radially outward and circumferentially by an inner wall portion 28 of the piston 14 and two filter support wall portions 30 and 32 in the form of cylindrical segments. The filter support wall portions 30, 32 each extend over an angle of approximately 120°. The closed inner wall portion 28 of the piston 14 also extends at an angle of 120° between the filter support wall portions 30 and 32.

[0057] Each of the filter support walls 30, 32 is provided with through holes 36 arranged radially with respect to the longitudinal axis 34 of the piston 14. The through holes 36 each have the same bore cross-section with a uniform diameter D and thus have a uniform radius R with an inner inflow opening 36a and an outer outflow opening 36b. Thus, the inflow opening 36a, the outflow opening 36b, and the through hole 36 have the same radius. Some center points of the inflow openings 36a of the through holes 36 are present on one plane and thus form a row of inflow openings 36a arranged adjacent to each other in the circumferential direction. Further rows of the inflow openings 36a are provided offset in the longitudinal and circumferential directions, and the central groups thereof are also present on one plane. The planes of the central groups of these rows extend parallel to each other. Further rows of the inflow openings 36 of the through holes 36 follow, each arranged offset with respect to the respective previous row, whereby substantially the entire inner surface of the filter support wall 30 is formed by the row groups of the inflow openings 36a of the through holes 36.

[0058] In another embodiment (not shown), the through holes 36, the inflow openings 36a, and the outflow openings 36b are provided in a slot shape radially with respect to the longitudinal axis 34. The height is many times larger than the width. The cross-sectional area of the through hole 36 corresponds to 75% of the cross-sectional area of the receiving recesses 68, 70 of the cleaning piston 66. The shape of the through hole 36 corresponds to the shape of the receiving recesses 68, 70 of the cleaning piston 66.

[0059] Each of the filter support walls 30, 32 is integrally formed with the piston 14 from the same material as the piston 14 and holds filter screens 38, 40 (see FIGS. 6a, 6b, and 7) that can be removed from the piston against stop walls 42, 44 that can also be removed from the piston. The stop walls 42, 44 also have through holes 46 aligned radially with respect to the longitudinal axis 34 of the piston 14, and the through holes 46 are aligned with the through holes 36 of the filter support wall 30 and are in particular flush with these.

[0060] The stop wall portions 42, 44 are recessed from the outer peripheral surface of the piston 14 and form outflow side chamber portions 48, 50 for the filtered fluid. The stop wall portion 42 has a side wall portion 42a that laterally partitions the outflow side chamber portion 48, and the side wall portion 42a completely surrounds laterally the surface having the through hole 46 of the stop wall portion 42. Similarly, the stop wall portion 44 has a side wall portion 44a that laterally partitions the outflow side chamber portion 50, and the side wall portion 44a completely surrounds laterally the surface having the through hole 46 of the stop wall portion 44. The side wall portions 42a, 44a align with the outer peripheral surface of the piston 14 in a correctly attached state. The piston 14 completely surrounds the side wall portions 42a, 44a on the sides. A clamp connection is used to hold the stop wall portions 42, 44 within the piston 14. The outflow side chamber portions 48, 50 are connected to the discharge pipe 52. For this purpose, the side wall portions 42a, 44a each have semi-circular recesses 42b, 44b on the outside, and the recesses 42b, 44b align with the discharge pipe 52 outside the piston, and the discharge pipe 52 is designed as a semi-circular recess.

[0061] The discharge pipe 52 extends from the outflow side chamber portions 48, 50 first laterally across the longitudinal axis 34 of the piston 14 on the outside, then extends along the longitudinal axis 34 of the piston 14, again extends laterally across the longitudinal axis 34 of the piston 14, then merges into the tubular region of the housing 12 and extends from there to the outflow opening 20 of the filter assembly 10. Inside the piston, the discharge pipe 52 has a U-shaped / semi-circular cross-section and extends outside the piston 14 and is bounded on the side opposite to the discharge pipe 52 by the cylindrical inner portion of the housing 12.

[0062] On two opposite sides of the receiving regions 14a, 14b for the stop wall portions 42, 44 of the piston 14, plates 54 are respectively provided, and these plates are screwed to the piston 14 by screws 54a. Each plate 54 has two groove portions 54b that facilitate removing the stop wall portions 42, 44 and then the filter screens 38, 40 from the piston 14. The groove portions 54b extend radially with respect to the longitudinal axis 34 of the piston 14 or an axis parallel to the longitudinal axis 34.

[0063] As shown in FIG. 8, a seal 56 is provided at the free end of the piston 14. Further, on the downstream sides of the supply pipe 24 and the discharge pipe 52 in the piston 14, additional seals 58 are provided in the longitudinal direction. The flow body 14c of the piston 14 is located between the seals 56, 58. During operation, the seals 56, 58 seal the flow region of the fluid passing through the piston 14 in the filtering position, that is, through the flow body 14c, and thus through the filter assembly 10 in the housing 12.

[0064] The end stop portion 60 is screwed to the end face of the piston 14 at the free end of the piston 14 protruding from the housing 12 in the filtering position. For this purpose, the piston 14 is provided with corresponding screw holes 62. Further, the end stop portion 60 is used to guide the piston rod 64 for the cleaning piston 66 that is movable within the interior 26. The cleaning piston 66 is located within the interior 26 and is in contact with the filter support wall portions 30, 32 and the inner wall portion 28 of the piston 14. The cleaning piston 66 is cylindrical and conforms to the inner contour of the piston 14 formed by the filter support wall portions 30, 32 and the inner wall portion 28. The piston rod 64 is firmly connected to the cleaning piston 66 and extends from the end stop portion 60 to the drive portion for the cleaning piston 66 on the side away from the end stop portion 60, where the drive portion is not shown in detail here. During the operation of the filter assembly, the cleaning piston 66 is continuously reciprocated between a first end position and a second end position by the drive portion. The end stop portion 60 also longitudinally partitions the interior 26.

[0065] The cleaning piston 66 is provided with two identically designed receiving recesses 68, 70 arranged on the outer peripheral surface and assigned to the filter support wall portions 30, 32. The receiving recess 68 is associated with the filter support wall portion 30, the receiving recess 70 is associated with the filter support wall portion 32, and the receiving recesses 68, 70 extend in the circumferential direction of the interior 26 along the row of the inlet openings 36a of the filter support wall portion 30. The receiving recesses 68, 70 are connected to a discharge duct 72 arranged concentrically with the cleaning piston 66 for discharging the backwashed fluid. Using a drive unit (not shown), the cleaning piston 66 is linearly and continuously moved from the starting position at the edges of the filter support wall portions 30, 32 to the end position at the remote edges of the filter support wall portions 30, 32 and back during the operation of the filter assembly 10. The direction of the movement path is parallel to the longitudinal axis 34 of the piston 14.

[0066] Due to the continuous movement of the cleaning piston 66 along the filter support wall portions 30, 32, the backwashed fluid, and thus the deposits from the stop wall portions 42, 44, the filter screens 38, 40, and the filter support wall portions 30, 32, are sent into the discharge duct 72 of the cleaning piston 66. The filtered fluid flows out from the outlet side chamber portions 48, 50 through the stop wall portions 42, 44, the filter screens 38, 40, and the filter support wall portions 30, 32, and returns into the receiving recesses 68, 70 and the discharge duct 72 of the cleaning piston 66. The fluid contaminated with impurities / deposits is then discharged in a known manner through the discharge duct 72.

[0067] The receiving recesses 68, 70 of the cleaning piston 66 extend over a part of the inflow openings 36a of the filter support wall portions 30, 32. The total area of the region of the inflow openings 36a or the partial region of the inflow openings 36a covered by the receiving recesses 68, 70 results in a predetermined total area having a value F1. As the cleaning piston 66 moves, the rows of the inflow openings 36a, and thus the partial regions of the inflow openings 36a, change continuously, but the value F1 remains the same throughout the movement path 66 of the cleaning piston at both the starting position and the end position.

[0068] The receiving recesses 68, 70 are at least as large as the diameter D of the through holes 36 of the filter support wall portions 30, 32 in the moving direction. The rows of the inflow openings 36a can be arranged such that at the moving position of the cleaning piston 66, the first edge of the receiving recesses 68, 70 of the cleaning piston 66 aligns with the edge of a row of the inflow openings 36a and these openings are completely located within the receiving recesses 68, 70. The second edge of the receiving recesses 68, 70 may align with the edge of the inflow openings 36a of the adjacent row. At this time, those inflow openings 36a are not located within the receiving recesses 68, 70.

[0069] The recesses 68, 70 are formed in the same manner respectively. The receiving recesses 68, 70 are each designed as a groove portion having a channel portion to the discharge duct 72, or can extend radially inward to the discharge duct 72 in the form of a cylindrical segment.

[0070] Furthermore, the mounting ring 74 is slidably arranged on the piston 14. The mounting ring 74 is provided with four handles 74a, 74b, 74c, 74d that can be used to move the mounting ring 74 on the piston 14. The piston 14 has a length that is larger than the width of the mounting ring 74 and the end stop portion 60 such that the piston 14 protrudes from the housing 12 in the filtering position. In the filtering position, the mounting ring 74 is arranged between the seal 56 and the end stop portion 60.

[0071] The individual filter support walls 30, 32, the filter screens 38, 40, and the stop walls 42, 44 each have the same design.

[0072] The mounting ring 74 is positioned such that the first stop surface 74e facing the housing 12 and the second stop surface 74f facing the end stop portion 60 are aligned parallel to each other in a plane. Similarly, the surface of the housing 12 associated with the mounting ring 74 and the surface of the end stop portion 60 associated with the mounting ring 74 are formed parallel to this.

[0073] When replacing the filter screens 38, 40, the piston 14 moves from the filtration position to the screen replacement position. Next, an appropriate tool is engaged with the groove portion 54b, and the stop walls 42, 44 are lifted and removed from the piston 14, so that the stop walls 42, 44 are removed. Thereafter, the tool is inserted into the groove portion 54b, and the filter screens 38, 40 are lifted and removed from the piston 14. The filter screens 38, 40 are replaced, that is, new filter screens 38, 40 are inserted into the piston 14 again. Thereafter, the stop walls 42, 44 are inserted into the piston 14 again until the side walls 42a, 44a are aligned with the outer peripheral portion of the piston 14. To facilitate inspection and to prevent the stop walls 42, 44 from loosening and protruding beyond the outer peripheral portion of the piston 14, the mounting ring 74 is gripped by at least one of the handles 74a, 74b, 74c, 74d and pushed out beyond the stop walls 42, 44. Thereafter, the mounting ring 74 remains in this position. Then, the piston 14 moves from the screen replacement position to the filtration position. At this time, the mounting ring 74 moves with the first stop surface 74e relative to the associated surface of the housing 12. If necessary, the piston 14 is moved so that the surface of the end stop portion 60 associated with the removal ring 74 contacts the second stop surface 74f. This ensures that the stop walls 42, 44 do not protrude beyond the outer peripheral surface of the piston during the entire movement of the piston 14. The filter assembly 10 can now filter additional fluid again.

[0074] The present invention is characterized in that the filtered fluid is constantly backwashed within the filter assembly 10, thus avoiding pressure fluctuations due to backwashing. The amount of fluid backwashed within the filter assembly 10 always remains the same. The cleaning piston 66 is constantly reciprocated and moved from the starting position to the second end position. The cleaning piston 66 is movable at a speed in the range of 10% to 200%, particularly in the range of 45% to 150%, of the discharge rate of the filtered fluid / the inflow rate of the fluid to be filtered. Preferably, the amount of fluid backwashed is in the range of 0.1% to 2%, particularly in the range of 0.5% to 1.0%, of the fluid flowing into the filter assembly 10.

[0075] Figure 10 shows a modification of the embodiment according to the present invention described with reference to Figures 1 to 9, that is, a longitudinal sectional view of the filter assembly 10. The filter assembly 10 has a filter support wall portion 76 consisting of two parts. The filter support wall portion 76 includes an inner sleeve portion 78 and a base filter support wall portion 80 that receives and holds the inner sleeve portion. The inner sleeve portion 78 is detachably connected to the base filter support wall portion 80. When the inner sleeve portion 78 is inserted into the front end portion and the rear end portion of the inner chamber portion 26, it is located centrally along the longitudinal axis 34. In addition, the filter assembly 10 shown in Figure 10 is configured in exactly the same manner as that described with reference to the previous figures. Therefore, the same reference numerals are given here to indicate the same parts.

[0076] Figures 11 and 12 show further modifications of the embodiment according to the present invention. As shown in these figures, the through-hole 36, the inflow opening 36a, and the outflow opening 36b are slot-shaped in the radial direction with respect to the longitudinal axis 34. The height is many times larger than the width. The cross-sectional area of the through-hole 36 corresponds to 75% of the cross-sectional area of the receiving recesses 68, 70 of the cleaning piston 66. The shape of the through-hole 36 corresponds to the shape of the receiving recesses 68, 70 of the cleaning piston 66. The through-hole 36 is formed in the removable inner sleeve portion 78. The design of the slot shape of the through-hole 36 is an easy way to increase the actual filter surface area.

[0077] This embodiment shows an extendable piston 14 having a flow body 14c, filter support walls 30, 32, 76, filter screens 38, 40 and stop walls 42, 44. However, such an extendable piston 14 is also conceivable in several ways.

Description of Reference Numerals

[0078] 10 Filter assembly having a piston type screen changer 12 Housing 14 Piston 14a Receiving area (left) 14b Receiving area (right) 14c Flow body 16 Inlet opening 18 Threaded hole 20 Outlet opening 22 Threaded hole 24 Supply pipe 26 Inside 28 Inner wall of piston 14 30 Filter support wall (left) 32 Filter support wall (right) 34 Longitudinal axis of piston 14 36 Through holes in filter support walls 30, 32 36a Inlet opening 36b Outlet opening 38 Filter screen (left) 40 Filter screen (right) 42 Stop wall (left) 42a Side wall of stop wall 42 (left) 42b U-shaped recess in side wall 42a (left) 44 Stop wall (right) 44a Side wall of stop wall 44 (right) 44b U-shaped recess in side wall 44a (right) 46 Through holes in stop walls 42, 44 48 Outlet side chamber portion (left) 50 Outlet side chamber portion (right) 52 Discharge pipe Plate for one side of the receiving regions 14a, 14b of the 54 pistons 14 54a Screw for fixing the plate 54 54b Groove in the plate 54 for facilitating removal of the stop wall portions 42, 44 56 Seal 58 Additional seal 60 End stop portion 62 Screw hole at the front of the piston 14 64 Piston rod for the cleaning piston 66 66 Cleaning piston 68 Receiving recess (left) 70 Receiving recess (right) 72 Discharge duct 74 Mounting ring 74a Handle (left) 74b Handle (lower) 74c Handle (right) 74d Handle (upper) 74e First seating surface related to the housing 12 74f Second seating surface related to the end stop portion 60 76 Filter support wall portion 78 Inner sleeve portion 80 Basic filter support wall portion

Claims

1. A filter assembly (10) for a fluid to be filtered, having a filter housing (12), a) the filter housing (12) is provided with a flow body (14c), filter screens (38, 40), and stop wall portions (42, 44) for the filter screens (38, 40), which separate a first chamber portion (26) and second chamber portions (48, 50) from each other, b) the flow body (14c) has filter support wall portions (30, 32) having a first side and a second side remote from the first side, the second side being in contact with the filter screens (38, 40) at least in a predetermined region and holding the filter screens (38, 40) against the stop wall portions (42, 44), c) the first chamber portion (26) is connected to an inflow duct (24), and the second chamber portions (48, 50) are connected to an outflow duct (52), d) through-channel portions (36) having associated openings (36a, 36b) are provided on both sides of the filter support wall portions (30, 32), and the fluid flows from the first chamber portion (26) through the first opening (36a) through the through-channel portion (36) to the second opening (36b) for filtering by the filter screens (38, 40), e) through-channel portions (46) having openings on both sides of the stop wall portions are provided on the stop wall portions (42, 44), and the filtered fluid flows from the filter screens (38, 40) into the second chamber portion through the through-channel portions, f) a movable cleaning piston (66) is provided, i. the cleaning piston is in contact with the first side of the filter support wall portions (30, 32) having a guide region, ii. the cleaning piston has at least one receiving recess (68, 70) in the guide region, and a part of the first opening (36a) of the filter support wall portions (30, 32) extends into the receiving recess, iii. The cleaning piston is provided with a discharge duct (72) connected to the receiving recesses (68, 70) for discharging the backwashed fluid. By moving the cleaning piston (66) along the filter support wall portions (30, 32), a part of the filtered fluid is backwashed from the second chamber portions (48, 50) through the stop wall portions (42, 44), the filter screens (38, 40), the filter support wall portions (30, 32), and the receiving recesses (68, 70) of the cleaning piston (66) into the discharge duct (72) of the cleaning piston (66), thereby removing the deposits on the stop wall portions (42, 44), the filter screens (38, 40), and the filter support wall portions (30, 32). The first opening (36a) of the through-channel portion (36) of the filter support wall portions (30, 32) and the dimensions of the cleaning piston (66) are aligned with each other such that the total surface area of the first opening (36a) and the region of the first opening (36a) extending into the receiving recesses (68, 70) is a value F1. The value F1 is always the same across the movement path of the cleaning piston (66) crossing the region of the first opening (36a) of the through-channel portion (36) of the filter support wall portions (30, 32). A filter assembly characterized by this. **Claim 2** In the filter assembly according to claim 1, the cleaning piston (66) has first and second end positions, the movement path of the cleaning piston (66) extends between the first and the second end positions, and the value F1 remains always the same at the two end positions and throughout the entire movement path of the piston. A filter assembly characterized by this. **Claim 3** In the filter assembly according to claim 1 or 2, the movement path of the cleaning piston (66) is linear. A filter assembly characterized by this. **Claim 4** In the filter assembly according to claim 3, Starting from the end position of the cleaning piston (66), in the direction of the moving path, a plurality of rows of the first openings (36a) of the filter support wall portions (30, 32) are provided, and the central group of the first openings (36a) in one row exists on a plane orthogonal to the moving path, the cross-sectional area for one row has a value F2, and a filter assembly characterized in that F1 = K×F2, where K > 0.

5. In the filter assembly according to claim 4, adjacent rows of the first openings (36a) are offset from each other and are arranged, in particular, orthogonally to the axis of the cleaning piston (66), a filter assembly characterized thereby.

6. In the filter assembly according to claim 4 or 5, the value F2 of the total cross-sectional area of one row of the first openings is corresponding to the value F1, a filter assembly characterized thereby.

7. In the filter assembly according to any one of claims 1 to 6, at least the cross-sectional area of each first opening (36a) and the cross-sectional area of the through-channel portion (36) adjacent thereto are of the same shape, in particular also in terms of the outer peripheral shape, and preferably, each first opening (36a) and the adjacent through-channel portion (36) have a circular cross-section with a diameter D and a radius R, and particularly preferably, each first opening (36a) and the adjacent through-channel portion (36) have a hexagonal cross-section, a filter assembly characterized thereby.

8. In the filter assembly according to claim 6 or 7, the distance of the receiving recesses (68, 70) of the cleaning piston (66) in the moving direction of the cleaning piston (66) is equal to the diameter D of the first opening or is larger than the diameter D of the first opening, a filter assembly characterized thereby.

9. In the filter assembly according to claim 8, when the rows of the first openings have K = 1 and thus F1 = F2, at the moving position of the cleaning piston (66), the first edge of the receiving recesses (68, 70) of the cleaning piston (66) is flush with the edge of the first openings (36a) in one row, these openings are completely located within the receiving recesses, and the second edge of the receiving recesses (68, 70) is arranged to be flush with the edge of the first openings (36a) in the adjacent row where the current openings (36a) are not located within the receiving recesses (68, 70), a filter assembly characterized thereby.

10. In the filter assembly according to any one of claims 1 to 9, A filter assembly, characterized in that it is incorporated into a system for manufacturing or granulating a profile film or sheet.

11. In the filter assembly according to any one of claims 1 to 10, The cleaning piston (66) is cylindrical, the filter support wall portions (30, 32) are adapted to the cleaning piston (66), and the filter screens (38, 40) and the stop wall portions (42, 44) are adapted to the shape of the filter support wall portions (30, 32). A filter assembly characterized by this.

12. In the filter assembly according to claim 11, The filter support wall portions (30, 32), the filter screens (38, 40) and the stop wall portions (42, 44) extend circumferentially over a partial circumference of the cleaning piston (66). A filter assembly characterized by this.

13. In the filter assembly according to claim 12, The receiving recesses (68, 70) of the cleaning piston (66) comprise at least this partial circumference, and in particular the receiving recesses (68, 70) extend circumferentially over at least this partial circumference. A filter assembly characterized by this.

14. In the filter assembly according to claim 13, The receiving recesses (68, 70) are designed either as a groove having a channel portion to the discharge duct (72) or extend radially inward to the discharge duct (72) in the form of a cylindrical segment. A filter assembly characterized by this.

15. In the filter assembly according to any one of claims 11 to 14, The filter screens (38, 40) and the stop wall portions (42, 44) are designed in two parts, and in particular each of the two parts is designed as two identical parts. A filter assembly characterized by this.

16. In the filter assembly according to claim 15, The filter support wall portions (30, 32) further have at least two regions assigned to the filter screen and the filter support wall portions, and through-channel portions (36) having the openings (36a, 36b) are provided in these regions. A filter assembly characterized by this.

17. In the filter assembly according to claim 16, At least two receiving recesses (68, 70) are provided in the cleaning piston (66), and the receiving recesses are assigned to regions of the filter support wall portions (30, 32) having the first opening (36a) and the through-channel portion (36). A filter assembly characterized by this.

18. In the filter assembly according to any one of claims 15 to 17, Each part of the stop wall portions (42, 44) is designed as a cylindrical segment that extends only over a part of the angle in the circumferential direction, and includes outer wall portions (42a, 44a) that laterally surround the region having the opening (36b) and extend radially outward from the filter screens (38, 40). A filter assembly characterized by this.

19. In the filter assembly according to claim 18, The flow body (14c) surrounds the outer wall portions (42a, 44a) at least in part, particularly completely up to the outward-facing end surface. A filter assembly characterized by this.

20. In the filter assembly according to any one of claims 1 to 19, The flow body (14c) having the filter screens (38, 40) and the stop wall portions (42, 44), and the cleaning piston (66) disposed inside the flow body (14c) are part of a piston (14) that can extend out of the filter housing (12) to replace the filter screens (38, 40), and the individual components of the stop wall portions (42, 44) and the individual components of the filter screens (38, 40) are detachably disposed within the flow body (14c). A filter assembly characterized by this.

21. In the filter assembly according to claim 20, A filter assembly, characterized in that it has at least two extendable pistons (14) having filter screens (38, 40) and stop wall portions (42, 44), and the cleaning piston (66) disposed inside the flow body (14c) is attached thereto.

22. In the filter assembly according to any one of Claims 1 to 21, the through-channel portions (36) of the filter support wall portions (30, 32) extend radially with respect to the coaxial axis of the cleaning piston (66), and in particular these through-channel portions (the sixth 30) of the filter support wall portions (30, 32) are aligned with the associated through-channel portions (46) of the stop wall portions (42, 44). A filter assembly characterized by this.

23. A method of filtering a fluid using the filter assembly according to any one of Claims 1 to 22, characterized in that the filtered fluid is continuously backwashed within the filter assembly (10).

24. In the method according to Claim 23, characterized in that the amount of fluid backwashed within the filter assembly (10) remains the same.

25. In the method according to Claim 23 or 24, characterized in that the fluid to be filtered has a low viscosity, preferably a viscosity in the range of 50 Pa·s to 5,000 Pa·s.

26. In the method according to any one of Claims 23 to 25, characterized in that the cleaning piston (66) is constantly reciprocated from the first end position to the second end position.

27. In the method according to any one of Claims 23 to 26, characterized in that the cleaning piston (66) is moved at a speed in the range of 10% to 200%, particularly 45% to 150%, of the discharge speed of the filtered fluid / the inflow speed of the fluid to be filtered.

28. In the method according to any one of Claims 23 to 27, characterized in that the amount of fluid backwashed is in the range of 0.1% to 2.0%, particularly 0.5% to 1.0%, of the fluid flowing into the filter assembly (10).

29. In the filter assembly according to any one of Claims 1 to 28, The filter support wall portion (76) is provided with an inner sleeve portion (78) and a base filter support wall portion (80), and the inner sleeve portion (78) includes the first and second openings (36a, 36b) and the through-channel portion (36). A filter assembly characterized by that.

30. In the filter assembly according to claim 29, The filter assembly is characterized in that the inner sleeve portion (78) is detachably connected to the base filter support wall portion (80).

31. In the filter assembly according to any one of claims 1 to 30, The cross-sectional areas of the openings (36a, 36b) and the through-channel portion (36) each have a height and a width, and the height is several times larger than the width. A filter assembly characterized by that.

32. In the filter assembly according to any one of claims 1 to 31, The cross-sectional area of the openings (36a, 36b) corresponds to 75% of the cross-sectional area of the receiving recesses (68, 70). A filter assembly characterized by that.

33. In the filter assembly according to claim 32, The cross-sectional shape of each opening (36a, 36b) corresponds to the cross-sectional shape of the associated receiving recess (68, 70). A filter assembly characterized by that.

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