Filter assembly

Abstract

The invention relates to a filter assembly (10) for a fluid to be filtered, comprising a filter housing (12). First openings (36a) of through-channels (36) of a filter support wall (30, 32) and the dimensions of a cleaning piston (66) are matched together such that the total surface area of first openings (36a) extending into a receiving recess (68, 70) and regions of first openings (36a) adds up to a value F1, said value F1 being the same over a movement path of the cleaning piston (66) across the region of the first openings (36a) of the through-channels (36) of the filter support wall (30, 32).

Description

[0001] Filter arrangement

[0002] The invention relates to a filter arrangement according to the type specified in the preamble of claim 1 and to a method for filtering fluid with a filter arrangement.

[0003] Such filter arrangements are used in plastics processing. In plastics processing plants, plastic granules, ground material, or powdered components are often heated to liquid plastic for subsequent processing. The plastic granules are often made from recycled material, which often also contains contamination from foreign particles. Extruders, for example, are used as plastics processing plants. Extruders are conveying devices that, based on the principle of a screw conveyor, evenly press solid to viscous masses out of a forming opening under high pressure and high temperature. For example, in an extrusion process, they produce products such as flat films or blown films. Other systems also use gear pumps for this purpose.

[0004] The heated and viscous plastic, even from pure raw materials, is usually mixed with dirt particles. These dirt particles must be kept out of the plastics processing equipment and the final product. Suitable filters are used to filter these dirt particles out of the liquid plastic. The liquid plastic is passed through the filter assembly under pressure before the raw material is further processed in the plastics processing equipment.

[0005] To maintain a consistent processing process, a processing pressure as constant as possible is required. Therefore, the screen filters in the filter arrangements must be regularly replaced or cleaned to ensure consistent discharge and thus a constant processing pressure. For this purpose, various changing devices are used for the screens forming the filters. Currently used screen changing systems include piston screen changers, wheel screen filters, belt screen changers, rotary screen changers, and slide gate screens. Screen changing systems typically operate automatically and are mechanically or hydraulically driven. However, manual screen changing systems are also in use.

[0006] A generic filter arrangement for a fluid to be filtered is known from DE 20 2017 007 054 U1. The filter arrangement is provided with a filter housing which contains an inlet opening for an inlet channel and an outlet opening for an outlet channel. A flow body, which can be part of a piston for extending from the filter housing for a filter change of the filter arrangement, together with a filter screen and a stop wall for the filter screen, separates a first chamber and a second chamber in the filter housing from one another. The flow body has a filter support wall with a first side and a second side remote from the first side, which with its second side bears against the filter screen at least in some areas and holds the filter screen to the stop wall. The first chamber is connected to the inlet channel and the second chamber is connected to the outlet channel.The filter support wall is provided with passages with associated openings on each side of the filter support wall, through which the fluid is directed from the first chamber via the first opening through the passage to the second opening for filtering to the filter screen. The stop wall is also provided with passages with openings on each side of the stop wall, through which the filtered fluid is directed from the filter screen into the second chamber.

[0007] In addition, a movable cleaning piston is provided, which rests against the first side of the filter support wall with a guide region. The cleaning piston has at least one receiving recess arranged within the guide region, into which a portion of the first openings of the filter support wall extend. Furthermore, the cleaning piston is provided with a discharge channel for discharging the backflushed fluid, so that by moving the cleaning piston along the filter support wall, deposits on the filter screen and on the filter support wall are removed by backflushing a portion of the filtered fluid from the second space through the stop wall, the filter screen, the filter support wall, in each case via the second opening, the through-channel of the filter support wall, the first opening and the receiving recess of the cleaning piston into the discharge channel of the cleaning piston.To clean the filter screen and thus backwash the filter screen, the cleaning piston is gradually moved from a rest position outside the area of ​​the openings of the through-channels in the filter support wall into the area of ​​the openings of the through-channels in the filter support wall. The cleaning piston moves across the entire area of ​​the openings of the through-channels in the filter support wall to an opposite rest position or subsequently back to the rest position from which the cleaning piston started.

[0008] A problem with this known design, however, is that pressure fluctuations occur throughout the system during the backwashing process, as the initial backwashing or the subsequent backwashing of the individual backwashing sections changes the volume of the filtered fluid exiting the filter assembly. These pressure fluctuations have a particularly negative impact on tools such as nozzles, for example, in film production or granulation processes. During film production, the material can tear if the pressure is too low. However, as with all other extrusion processes, quality defects in the form of varying layer and wall thicknesses or granule sizes can also occur, which, however, must be avoided.

[0009] The invention is therefore based on the object of developing a filter arrangement according to the type specified in the preamble of claim 1 in such a way that, while avoiding the disadvantages mentioned, constant pressure conditions are created before and after the filter, with simultaneous effective backwashing, which thereby increases the quality in the process and the service life of the filter arrangement.

[0010] According to a first aspect, this object is achieved by the characterizing features of claim 1 in conjunction with its preamble features.

[0011] The subclaims form advantageous developments of the invention.

[0012] The invention is based on the finding that by aligning the receiving recess of the cleaning piston with the first openings in the filter support wall such that the sum of the cross-sectional area of ​​the first openings extending into the receiving recess of the cleaning piston is constant over the entire travel path of the cleaning piston along the filter support wall, the pressure during backwashing can always be kept constant, regardless of the travel position of the cleaning piston. The quality of the products can thus be kept at least constant. Furthermore, the service life of the filter assembly is improved.

[0013] Furthermore, pressure fluctuations can be avoided through continuous backwashing, as the pressure fluctuations in the outlet channel caused by the cleaning piston moving into the area of ​​the openings in the filter support wall are eliminated. This further increases the quality of the products produced with this filter arrangement.

[0014] According to the invention, the first openings in the filter support wall and the dimensions of the cleaning piston are therefore coordinated such that the total area of ​​the openings and areas of openings extending into the receiving recess results in a value F1, wherein the value F1 is always the same over a travel path of the cleaning piston over the area of ​​the first openings in the through-channels of the filter support wall. The sum of the cross-sectional areas of the openings in the filter support wall extending into the receiving recess of the cleaning piston is thus always the same, regardless of the travel position of the cleaning piston, so that the pressure fluctuations that previously occurred when moving the cleaning piston, for example from one row of first openings in the filter support wall to the next row of first openings and, above all, when moving from the rest position into the area of ​​the first openings in the filter support wall, can be easily avoided.This involves a permanent backwash, which increases the service life until the filter needs to be changed.

[0015] According to an advantageous development of the invention, the cleaning piston has a first and a second end position. The travel path of the cleaning piston extends between the first and second end positions. The value F1 always remains the same both in the two end positions and throughout the entire travel path.

[0016] Rotating cleaning pistons are conceivable in principle. However, the travel path of the cleaning piston relative to the filter support wall is preferably linear, in particular exclusively linear.

[0017] Above all, several rows of first openings in the through-channels of the filter support wall can be provided in the direction of the travel path, starting from an end position of the cleaning piston. The centers of a row of first openings lie in a plane perpendicular to the travel path of the cleaning piston. The cross-sectional area of ​​a row has the value F2. Here, F1 = K x F2, with K > 0. In this context, it has proven advantageous for adjacent rows of first openings to be arranged offset from one another, in particular perpendicular to an axis of the cleaning piston, for example axially offset from the longitudinal axis and / or offset at an angle to the longitudinal axis.

[0018] In order to keep the design and thus also the production as simple as possible, the value F2 of the sum of the cross-sectional areas of a series of first openings corresponds to the value F1 .

[0019] At least the cross-sectional area of ​​each first opening and the cross-sectional area of ​​the adjoining through-channel can each be of identical design, in particular including their outer peripheral shape. For example, each first opening and the adjoining through-channel can have a circular cross-section with a diameter D and a radius R. Alternatively, each first opening and the adjoining through-channel can also have other cross-sections, e.g., hexagonal or oval.

[0020] According to one embodiment of the invention, the distance between the receiving recess of the cleaning piston in a travel direction of the cleaning piston is so large that it is equal to or greater than the diameter D of the first opening. This allows the cleaning piston to be kept compact in terms of its size in a simple manner.

[0021] The rows of the first openings can be arranged such that in a travel position of the cleaning piston and at K = 1 and thus F1 = F2, the first edge of the receiving recess of the cleaning piston is aligned with the edge of first openings of a row and these openings are located completely in the receiving recess, and the second edge of the receiving recess is aligned with the edge of first openings of an adjacent row whose openings are not located in the receiving recess.

[0022] The filter arrangement is therefore particularly suitable for applications that have high quality requirements, preferably for integration into a film production plant.

[0023] In principle, the cleaning piston can be adapted to the shape of the filter support wall. Preferably, the area of ​​the passage body associated with the cleaning piston, and thus the cleaning piston, is rotationally symmetrical. The filter support wall is adapted to the cleaning piston, and the filter screen and stop wall are adapted to the shape of the filter support wall. This results in simple production of the cleaning piston and the passage body.

[0024] According to one embodiment of the invention, the filter support wall, the filter screen and the stop wall extend in the circumferential direction only over a partial circumference of the cleaning piston.

[0025] The receiving recess of the cleaning piston can encompass at least this partial circumference, in particular the receiving recess of the cleaning piston extends at least over this partial circumference in the circumferential direction.

[0026] Preferably, the receiving recess of the cleaning piston is designed either as a groove with channels to the discharge channel or extends radially inwards to the discharge channel in the manner of a cylinder segment, depending on what is more favorable with regard to the specified dimensioning for the discharge of the backflushed fluid.

[0027] The filter screen and the stop wall can be divided into two parts, in particular each formed as two identical components.

[0028] The filter support wall also has at least two areas assigned to the filter screen and the filter support wall, in which the through-channels with the openings are provided.

[0029] Finally, at least two receiving recesses can also be provided in the cleaning piston, which are assigned to the areas with the first openings and passage channels of the filter support wall.

[0030] According to one embodiment of the invention, each component of the stop wall is designed as a cylinder segment. This extends only over a partial angle in the circumferential direction. In addition, it has outer walls that extend radially outward away from the filter screen and laterally encompass the area with the openings. The area with the radially outer openings of the stop wall is offset radially inward relative to the free end regions of the outer walls, i.e. the radially outward-facing end faces. To ensure secure arrangement of the stop wall and thus of the filter screen in the flow-through body, the flow-through body encompasses at least partially each of the outer walls up to the end faces, in particular completely.

[0031] The flow body, including the filter screen and stop wall, as well as the cleaning piston located within the flow body, can be part of a piston that can be extended from the filter housing for changing the filter screens. The individual components of the support wall and the individual components of the filter screen are then always arranged detachably within the flow body.

[0032] The through-channels of the filter support wall preferably extend radially relative to a concentric axis of the cleaning piston; in particular, these through-channels of the filter support wall are aligned with the associated through-channels of the stop wall. These can then also extend radially outward.

[0033] According to a further aspect, the invention is based on the finding that the quality of the end product and the service life of the filter arrangement can be increased by permanent backwashing, in particular with a permanently constant amount of backwashed fluid.

[0034] According to this aspect of the invention, a method for filtering fluid with a filter arrangement, in particular according to the filter arrangement just described, is therefore provided, in which a permanent backwashing of the filtered fluid in the filter arrangement takes place.

[0035] Preferably, the amount of backwashed fluid in the filter arrangement always remains the same.

[0036] For the operation of the filter arrangement, low-viscosity fluids, preferably with a viscosity in a range of 50 Pas to 5000 Pas, are filtered.

[0037] It is advantageous with regard to the service life of the filter arrangement if the cleaning piston is continuously moved back and forth from the first end position to the second end position.

[0038] The cleaning piston can be moved at a speed ranging from 10% to 200% of the discharge speed of the filtered fluid / inlet speed of the fluid to be filtered, in particular from 45% to 150%. Preferably, the amount of backflushed fluid is in a range of 0.1% to 2.0% of the fluid introduced into the filter arrangement, in particular from 0.5% to 1.0%.

[0039] Preferably, the filter support wall is provided with an inner sleeve and a base filter support wall. The inner sleeve comprises the first and second openings and the through-channels. This allows different requirements for the material or structure of the inner sleeve and the base filter support wall to be met. The parts can thus be optimized with regard to the material in relation to their application and the resulting loads. The manufacturing process is also simplified.

[0040] According to a further advantageous embodiment of the invention, the inner sleeve is detachably connected to the base filter support wall. This allows the openings and passages to be rheologically and flow-wise optimized and adapted according to the viscosity of the medium to be processed. Furthermore, the inner sleeve can be replaced in the event of wear, for example, abrasive wear caused by the constant movement of the backwash piston, to ensure reliable filtration over a longer period of time.

[0041] Preferably, the cross-sectional areas of the openings and the passages each have a height and a width. The height is several times greater than the width. This ensures that the dimensions of the cleaning piston are reduced in the longitudinal direction.

[0042] Preferably, the cross-sectional area of ​​the openings corresponds to 65% of the cross-sectional area of ​​the receiving recesses. This reduces the pressure on the inlet side of the filter support wall and increases the effective filter area.

[0043] According to a further advantageous embodiment of the invention, the shape of each opening corresponds to the shape of the associated receiving recess. This reduces the pressure on the inlet side of the filter support wall. Furthermore, the flow conditions for the fluid to be filtered are optimized.

[0044] Further advantages, features, and possible applications of the present invention will become apparent from the following description in conjunction with the exemplary embodiments illustrated in the drawings. The terms and associated reference symbols used in the list of reference symbols below are used in the description, claims, and drawings. In the drawings, the following definitions apply:

[0045] Fig. 1 is a perspective view obliquely from above of a filter arrangement in the manner of a piston screen changer with extended pistons according to the invention from a first side according to a first embodiment;

[0046] Fig. 2 is a perspective view obliquely from above of the filter arrangement of Fig. 1 from a second side;

[0047] Fig. 3 is a perspective view obliquely from above of the filter arrangement of Fig. 1 with retracted piston from a first side;

[0048] Fig. 4 shows a first longitudinal section through the filter arrangement of Fig. 3;

[0049] Fig. 5 shows a second longitudinal section through the filter arrangement of Fig. 3, offset by 90° around the longitudinal axis compared to the first longitudinal section;

[0050] Fig. 6a shows a cross section through the filter arrangement in the cleaning piston with a first type of cleaning piston of Fig. 3;

[0051] Fig. 6b shows a cross section through the filter arrangement in the cleaning piston with a second type of cleaning piston from Fig. 3;

[0052] Fig. 7 is a perspective view of Fig. 1, but with the stop walls arranged explosively away;

[0053] Fig. 8 is a perspective view of the piston of the filter assembly without the stop wall and filter screen, so that the filter support wall is visible;

[0054] Fig. 9 is a perspective view of a partially retracted piston of the filter assembly of Fig. 1 from the first side after the screen change; Fig. 10 is a longitudinal section through the filter assembly of Fig. 4 with a two-part filter support wall;

[0055] Fig. 11 is a perspective view of the piston of the filter assembly with the stop wall removed and slot-shaped through holes, and

[0056] Fig. 12 a perspective view of the inner sleeve of the filter assembly with end stop.

[0057] Figures 1 to 10 show a filter arrangement 10 according to the invention with a piston screen changer. Figure 10 shows a variant and Figures 11 and 12 show a further variant of the filter arrangement 10 according to the invention. The filter arrangement 10 comprises a housing 12 in which a piston 14 can be moved between a screen change position and a filter position as required. In the screen change position, a filter screen can be changed. In the filter position, a fluid can flow through the filter arrangement 10 and be filtered. In Figures 1, 2 and 7, the piston 14 is shown in the screen change position extended relative to the housing 12 and in Figures 3, 4, 5, 6a and 6b in the filter position retracted relative to the housing 12.

[0058] On a first side of the housing 12, an inlet opening 16 is provided laterally, through which low-viscosity fluids, preferably with a viscosity in a range of 50 Pas to 5,000 Pas, for example plastic fluids, are fed to the filter arrangement 10, flow through it and are filtered, as will be explained in more detail below. The fluid is fed to the housing 12 via the inlet opening 16 via a supply line (not shown here). The supply line can be screwed to the housing 12 via a flange connection. For this purpose, the housing 12 has corresponding threaded holes 18, see, for example, Fig. 1 and Fig. 3. Screws engage in these threaded holes 18 and corresponding holes in a flange of the supply line, which screws fasten the flange with the supply line to the housing 12.

[0059] Accordingly, on a second side of the housing 12, remote from the first side, an outlet opening 20 is provided, through which the filtered fluid is transported away from the filter assembly 10 for further processing via a discharge line (not shown here). This discharge line can also be screwed to the housing 12 via a flange connection. For this purpose, the housing 12 has corresponding threaded holes 22, see, for example, Fig. 2. Screws engage in these threaded holes 22 and corresponding holes in a flange of the discharge line, which screws fasten the flange with the discharge line to the housing 12.

[0060] For example, the filter assembly 10 can be an integral part of a film production or granulation system. In this case, the filtered plastic fluid is fed via the discharge line to a nozzle for dispensing the filtered plastic fluid and transferring it into a film to be dispensed from the nozzle.

[0061] The drive of the piston 14 in the housing 12 for moving between the screen change position and the filter position is basically known, so that it will not be discussed further.

[0062] As can be seen in particular from Fig. 4 and Fig. 5, the inlet opening 16 is connected to a cylindrical interior space 26 in the piston 14 via an inlet line 24 running in the housing 12 and in the piston 14. The interior space 26 is circumferentially delimited radially outwardly by inner walls 28 of the piston 14 and by two filter support walls 30 and 32 designed like cylinder segments. The filter support walls 30, 32 each span an angle of approximately 120°. The closed inner walls 28 of the piston 14 also run between the filter support walls 30, 32, each at an angle of 120°.

[0063] Through-bores 36 are provided in each filter support wall 30, 32, arranged radially to a longitudinal axis 34 of the piston 14. The through-bores 36 each have an identical bore cross-section with a uniform diameter D and thus a uniform radius R, with an inner inlet opening 36a and an outer outlet opening 36b. The inlet opening 36a, the outlet opening 36b, and the through-bore 36 are thus provided with the same radius. Several centers of inlet openings 36a of the through-bores 36 lie in one plane and thus form a row of inlet openings 36a arranged side by side in the circumferential direction. A further row of inlet openings 36a, the centers of which also lie in one plane, is provided, offset in the longitudinal direction and in the circumferential direction. The planes of the centers of the rows run parallel to one another.Further rows of inlet openings 36a of the through-bores 36 follow, each offset from the previous row, so that the inner surface of the filter support wall 30 is almost entirely formed by rows of inlet openings 36a of the through-bores 36. In an alternative embodiment not shown, the through-bores 36, the inlet openings 36a, and the outlet openings 36b are slit-shaped in the radial direction to the longitudinal axis 34. The height is several times greater than the width. The cross-sectional area of ​​the through-bores 36 corresponds to 75% of the cross-sectional area of ​​the receiving recess 68, 70 of the cleaning piston 66. The shape of the through-bores 36 corresponds to the shape of the receiving recess 68, 70 of the cleaning piston 66.

[0064] Each filter support wall 30, 32 is formed in one piece with the piston 14 and made of the same material and holds a filter screen 38, 40, see Fig. 6a, Fig. 6b, Fig. 7, which can be removed from the piston 14, against a stop wall 42, 44, which can also be removed from the piston. The stop wall 42, 44 also has through holes 46 which are radially aligned with respect to the longitudinal axis 34 of the piston 14 and which are aligned with the through holes 36 of the filter support wall 30, in particular are aligned with these.

[0065] The stop wall 42, 44 is set back from the outer peripheral surface of the piston 14 and forms an outlet chamber 48, 50 for the filtered fluid. The stop wall 42 has side walls 42a that laterally delimit this outlet chamber 48 and completely surround the surface with the through-bores 46 of the stop wall 42. Accordingly, the stop wall 44 has side walls 44a that laterally delimit the outlet chamber 50 and completely surround the surface with the through-bores 46 of the stop wall 44. When correctly assembled, the side walls 42a, 44a are flush with the outer peripheral surface of the piston 14. The piston 14 completely surrounds the side walls 42a, 44a laterally. The stop walls 42, 44 are held in the piston 14 by a clamping connection. The outlet chamber 48, 50 is connected to a discharge line 52.For this purpose, the side walls 42a, 44a each have semicircular recesses 42b, 44b on the outside, which are aligned with the discharge line 52 formed as a semicircular recess on the outside of the piston.

[0066] The discharge line 52 runs from the outlet chamber 48, 50, initially transversely to the longitudinal axis 34 of the piston 14 on its outer side, then along the longitudinal axis 34 of the piston 14, finally again transversely to the longitudinal axis 34 of the piston 14, finally merges into a tubular region of the housing 12 and then runs to the outlet opening 20 of the filter arrangement 10. In the piston, the discharge line 52 is U-shaped / semicircular in cross-section and runs on the outer side of the piston 14 and is delimited on the side opposite the discharge line 52 by a cylindrical inner side of the housing 12. Two opposite sides of receiving areas 14a, 14b for the stop walls 42, 44 of the piston 14 are each provided with a plate 54, which is screwed to the piston 14 by means of screws 54a. The plate 54 has two grooves 54b in order to be able to remove the stop walls 42, 44 and then the filter screen 38, 40 more easily from the piston 14.The grooves 54b extend radially relative to the longitudinal axis 34 of the piston 14 or an axis parallel to the longitudinal axis 34.

[0067] Seals 56 are provided at the free end of the piston 14, see Fig. 8. In addition, further seals 58 are provided in the longitudinal direction after the supply line 24 and the discharge line 52 in the piston 14. The flow body 14c of the piston 14 is located between the seals 56, 58. During operation, the seals 56, 58 seal the flow area of ​​the fluid through the piston 14, i.e., through the flow body 14c, and thus through the filter arrangement 10 in the housing 12 in the filter position.

[0068] At the free end of the piston 14, which protrudes from the housing 12 in the filter position, an end stop 60 is screwed onto the end face of the piston 14. Corresponding threaded holes 62 are provided in the piston 14 for this purpose. In addition, a piston rod 64 for a cleaning piston 66, which can be moved within the interior 26, is guided over the end stop 60. The cleaning piston 66 is located within the interior 26 and bears against the filter support walls 30, 32 and the inner walls 28 of the piston 14. The cleaning piston 66 is cylindrical and adapted to the inner contour of the housing formed by the filter support walls 30, 32 and the inner walls 28 of the piston 14. The piston rod 64 is firmly connected to the cleaning piston 66 and extends on the side remote from the end stop 60 to a drive for the cleaning piston 66 (not shown in detail here).During operation of the filter assembly, the cleaning piston 66 is continuously moved back and forth by the drive between a first end position and a second end position. The end stop 60 also limits the interior space 26 in a longitudinal direction.

[0069] The cleaning piston 66 is provided with two identically designed receiving recesses 68, 70 arranged on the circumferential surface, which are assigned to the filter support walls 30, 32. The receiving recess 68 is assigned to the filter support wall 30 and the receiving recess 70 is assigned to the filter support wall 32 and extend in the circumferential direction of the interior space 26 corresponding to the rows of inlet openings 36a of the filter support walls 30. The receiving recesses 68, 70 are connected to a discharge channel 72 arranged concentrically in the cleaning piston 66 for discharging backflushed fluid. The cleaning piston 66 is continuously moved linearly from an initial position at the edge of the filter support walls 30, 32 to an end position at the remote edge of the filter support walls 30, 32 and back again using the drive (not shown here) during operation of the filter arrangement 10. The direction of the travel path is parallel to the longitudinal axis 34 of the piston 14.

[0070] As a result of the successive movement of the cleaning piston 66 along the filter support walls 30, 32, backwashed fluid and thus deposits from the stop walls 42, 44, from the filter screens 38, 40 and from the filter support walls 30, 32 reach the discharge channel 72 of the cleaning piston 66. The filtered fluid flows from the outlet spaces 48, 50 through the stop walls 42, 44, the filter screens 38, 40 and the filter support walls 30, 32 back through the receiving recesses 68, 70 and into the discharge channel 72 of the cleaning piston 66. The fluid containing impurities / deposits is discharged in a known manner via the discharge channel 72.

[0071] The receiving recesses 68, 70 of the cleaning piston 66 extend over a portion of the inlet openings 36a of the filter support walls 30, 32. The total area of ​​the sum of the areas of the inlet openings 36a or the partial areas of the inlet openings 36a covered by the receiving recesses 68, 70 results in a predetermined total area with the value Fi. The value Fi always remains the same over the travel path of the cleaning piston 66 in the starting position and the end position, although the rows of the inlet openings 36a and thus the partial areas of the inlet openings 36a continuously change with the travel of the cleaning piston 66.

[0072] The receiving recess 68, 70 is at least as large in the direction of travel as the diameter D of the through-bores 36 of the filter support walls 30, 32. A row of inlet openings 36a can be arranged such that, in a travel position of the cleaning piston 66, the first edge of the receiving recesses 68, 70 of the cleaning piston 66 is aligned with the edge of the inlet openings 36a of one row, and these openings are located completely within the receiving recesses 68, 70. The second edge of the receiving recesses 68, 70 can be aligned with the edge of the inlet openings 36a of an adjacent row. Their inlet openings 36a are not located in the receiving recesses 68, 70. The receiving recesses 68, 70 are each of identical design. The receiving recesses 68, 70 can each be designed as a groove with channels to the discharge channel 72 or can extend radially inwards to the discharge channel 72 in the manner of a cylinder segment.

[0073] A mounting ring 74 is also slidably mounted on the piston 14. The mounting ring 74 is provided with four handles 74a, 74b, 74c, 74d, with the aid of which the mounting ring 74 can be moved on the piston 14. The piston 14 has a length dimensioned such that the piston 14 protrudes from the housing 12 in the filter position, namely by more than the proportion of the width of the mounting ring 74 and the end stop 60. In the filter position, the mounting ring 74 is arranged between the seal 56 and the end stop 60.

[0074] The individual filter support walls 30, 32, the filter sieves 38, 40, the stop walls 42, 44 are each designed identically.

[0075] The mounting ring 74 is aligned such that its first stop surface 74e facing the housing 12 and its second stop surface 74f facing the end stop 60 are aligned plane-parallel. The surface of the housing 12 associated with the mounting ring 74 and a surface of the end stop 60 associated with the mounting ring 74 are configured to be correspondingly parallel.

[0076] If the filter screens 38, 40 need to be replaced, the piston 14 moves from the filter position to the screen replacement position. The stop walls 42, 44 are then removed by engaging the groove 54b with an appropriate tool, lifting the stop walls 42, 44, and removing them from the piston 14. The tool is then engaged in the groove 54b, lifting the filter screens 38, 40, and removing them from the piston 14. The filter screens 38, 40 are replaced, i.e., new filter screens 38, 40 are reinserted into the piston 14. The stop walls 42, 44 are then reinserted into the piston 14 until the side walls 42a, 44a are aligned with the outer circumference of the piston 14. For easy inspection and to ensure that the stop walls 42, 44 do not come loose and protrude beyond the outer circumference of the piston 14, the mounting ring 74 is grasped by at least one of the handles 74a, 74b, 74c, 74d and pushed over the stop wall 42, 44.The mounting ring 74 remains in this position. The piston 14 then moves from the screen change position to the filter position. The mounting ring 74 moves with its first stop surface 74e against the associated surface of the housing 12. If necessary, the piston 14 is moved so far that the end stop 60, with its surface associated with the disassembly ring 74, rests against 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.

[0077] The invention is characterized in that a permanent backwashing of the filtered fluid takes place in the filter arrangement 10, whereby pressure fluctuations due to backwashing are avoided. The amount of backwashed fluid in the filter arrangement 10 always remains the same. The cleaning piston 66 is constantly moved back and forth from the starting position to the second end position. The cleaning piston 66 is moved at a speed which lies in a range of 10% to 200% of the discharge speed of the filtered fluid / input speed of the fluid to be filtered, in particular in a range of 45% to 150%. The amount of backwashed fluid lies in a range of 0.1% to 2% of the fluid introduced into the filter arrangement 10, in particular in a range of 0.5% to 1%.

[0078] Fig. 10 shows a variant of the embodiment according to the invention described in Figures 1 to 9, namely a longitudinal section of the filter arrangement 10. The filter arrangement 10 has a two-part filter support wall 76. The filter support wall 76 comprises an inner sleeve 78 and a base filter support wall 80 that receives and holds the inner sleeve. The inner sleeve 78 is detachably connected to the base filter support wall 80. The inner sleeve 78 is centered during insertion at the front and rear ends of the interior space 26 along the longitudinal axis 34. Otherwise, the filter arrangement 10 shown in Fig. 10 is constructed exactly as explained with reference to the previous figures. Therefore, the same reference numerals are used for the same parts.

[0079] Figs. 11 and 12 show a further variant of the embodiment according to the invention. In these figures, the through-bores 36, the inlet openings 36a, and the outlet openings 36b are slit-shaped in the radial direction to the longitudinal axis 34. The height is several times greater than the width. The cross-sectional area of ​​the through-bores 36 corresponds to 75% of the cross-sectional area of ​​the receiving recess 68, 70 of the cleaning piston 66. The shape of the through-bores 36 corresponds to the shape of the receiving recess 68, 70 of the cleaning piston 66. The through-bores 36 are introduced into the detachably designed inner sleeve 78. The slit-shaped design of the through-bores 36 increases the actual filter surface in a simple manner. The present embodiments show an extendable piston 14 with flow body 14c, filter support walls 30, 32, 76 filter screens 38, 40 and stop walls 42, 44.However, several such extendable pistons 14 are also conceivable.

[0080] Reference symbol list

[0081] 10 Filter arrangement with piston sieve change

[0082] 12 housings

[0083] 14 pistons

[0084] 14a Recording area - left

[0085] 14b Recording area - right

[0086] 14c Flow body

[0087] 16 Entrance opening

[0088] 18 threaded hole

[0089] 20 Exit opening

[0090] 22 threaded hole

[0091] 24 supply line

[0092] 26 Interior

[0093] 28 inner walls of the piston 14

[0094] 30 Filter support wall - left

[0095] 32 Filter support wall - right

[0096] 34 Longitudinal axis of the piston 14

[0097] 36 Through hole of the filter support wall 30, 32

[0098] 36a Entrance opening

[0099] 36b Exit opening

[0100] 38 Filter sieve - left

[0101] 40 Filter sieve - right

[0102] 42 Stop wall - left 42a Side wall of stop wall 42 - left

[0103] 42b U-shaped recess of the side wall 42a - left

[0104] 44 Stop wall - right

[0105] 44a Side wall of the stop wall 44 - right

[0106] 44b U-shaped recess of the side wall 44a - right

[0107] 46 Through hole of the stop wall 42, 44

[0108] 48 Exit room - left

[0109] 50 Exit room - right

[0110] 52 discharge line

[0111] 54 Plate for one side of the receiving area 14a, 14b of the piston 14

[0112] 54a Screw for fastening plate 54

[0113] 54b Groove in the plate 54 for easier release of the stop wall 42, 44

[0114] 56 Seal

[0115] 58 more seals

[0116] 60 end stop

[0117] 62 Threaded hole on the front side of the piston 14

[0118] 64 Piston rod for the cleaning piston 66

[0119] 66 cleaning pistons

[0120] 68 Recess - left

[0121] 70 Recess - right

[0122] 72 discharge channel

[0123] 74 Mounting ring

[0124] 74a Handle - left

[0125] 74b Handle - bottom

[0126] 74c Handle - right

[0127] 74d Handle - top

[0128] 74e first contact surface - assigned to the housing 12

[0129] 74f second contact surface - assigned to the end stop 60

[0130] 76 Filter retaining wall

[0131] 78 inner sleeve

[0132] 80 basic filter support wall

Claims

Patent claims for a filter arrangement (10) for a fluid to be filtered, comprising a filter housing (12), wherein a. a flow body (14c), a filter screen (38, 40) and a stop wall (42, 44) for the filter screen (38, 40) are provided in the filter housing (12), which separate a first chamber (26) and a second chamber (48, 50) from each other, b. the flow body (14c) has a filter support wall (30, 32) with a first side and a second side located away from the first side, the second side of which bears at least partially against the filter screen (38, 40) and holds the filter screen (38, 40) against the stop wall (42, 44), c. the first chamber (26) is connected to an inlet channel (24) and the second chamber (48, 50) to an outlet channel (52), d.in the filter support wall (30, 32) passage channels (36) with associated openings (36a, 36b) are provided on each side of the filter support wall (30, 32), through which the fluid is guided from the first chamber (26) via the first opening (36a) through the passage channel (36) to the second opening (36b) for filtering to the filter screen (38, 40), e. in the stop wall (42, 44) passage channels (46) with openings are provided on each side of the stop wall (42, 44), through which the filtered fluid is guided from the filter screen (38, 40) into the second chamber (48, 50), f. a movable cleaning piston (66) is provided, which i. rests against the first side of the filter support wall (30, 32) with a guide area, ii. at least one receiving recess (68, 70) within the guide area, into which part of the first openings (36a) of the filter support wall (30, 32) extends. iii. is provided with a discharge channel (72) connected to the receiving recess (68, 70) for the discharge of the backwashed fluid, so that by moving the cleaning piston (66) along the filter support wall (30, 32), deposits on the stop wall (42, 44), on the filter screen (38, 40) and on the filter support wall (30, 32) are removed by backwashing a portion of the filtered fluid from the second chamber (48, 50) through the stop wall (42, 44), the filter screen (38, 40), the filter support wall (30, 32), the receiving recess (68, 70) of the cleaning piston (66), into the discharge channel (72) of the cleaning piston (66), characterized in that the first openings (36a) of the passage channels (36) of the filter support wall (30, 32) and the dimensioning of the cleaning piston (66) are coordinated such that the total area of ​​the first openings (36a) extending into the receiving recess (68, 70) and areas of first openings (36a) yields a value Fi,wherein the value Fi is always the same over a travel path of the cleaning piston (66) over the area of ​​the first openings (36a) of the through-channels (36) of the filter support wall (30, 32). Filter arrangement according to claim 1, characterized in that the cleaning piston (66) has a first and second end position, the travel path of the cleaning piston (66) extends between the first and the second end position, and the value Fi remains constant both in the two end positions and over the entire travel path. Filter arrangement according to claim 1 or 2, characterized in that the travel path of the cleaning piston (66) is linear. Filter arrangement according to claim 3, characterized in that several rows of first openings (36a) of the filter support wall (30, 32) are provided in the direction of the travel path starting from an end position of the cleaning piston (66).wherein the centers of a series of first openings (36a) lie in a plane perpendicular to the travel path, wherein the cross-sectional area of ​​a series has the value F2, where Fi = K x F2, where K > 0. Filter arrangement according to claim 4, characterized in that adjacent series of first openings (36a) are arranged offset from one another, in particular perpendicular to, an axis of the cleaning piston (66).

6. Filter arrangement according to one of claims 4 or 5, characterized in that the value F2 of the sum of the cross-sectional areas of a series of first openings corresponds to the value Fi.

7. Filter arrangement according to one of the preceding claims, characterized in that at least the cross-sectional area of ​​each first opening (36a) and the cross-sectional area of ​​the adjoining passage channel (36) are each identical, in particular also their outer circumferential shape, preferably each first opening (36a) and the adjoining passage channel (36) has a circular cross-section with a diameter D and a radius R, particularly preferably each first opening (36a) and the adjoining passage channel (36) has a hexagonal cross-section.

8. Filter arrangement according to claim 6 or 7, characterized in that the distance of the receiving recess (68, 70) of the cleaning piston (66) in a direction of travel of the cleaning piston (66) is such that it is equal to or greater than the diameter D of the first opening.

9. Filter arrangement according to claim 8, characterized in that the rows of first openings (36a) are arranged such that in a travel position of the cleaning piston (66) and at K = 1 and thus Fi = F2 the first edge of the receiving recess (68, 70) of the cleaning piston (66) is aligned with the edge of first openings (36a) of a row and these openings are completely located in the receiving recess, and the second edge of the receiving recess (68, 70) is aligned with the edge of first openings (36a) of an adjacent row, the openings (36a) of which are not located in the receiving recess (68, 70).

10. Filter arrangement according to one of the preceding claims, characterized by integration into a system for profile film sheet production or granulation.

11. Filter arrangement according to one of the preceding claims, characterized in that the cleaning piston (66) is cylindrical, the filter support wall (30, 32) is attached to the The cleaning piston (66), the filter screen (38, 40), and the stop wall (42, 44) are adapted to the shape of the filter support wall (30, 32). Filter arrangement according to claim 11, characterized in that the filter support wall (30, 32), the filter screen (38, 40), and the stop wall (42, 44) extend circumferentially over a partial circumference of the cleaning piston (66). Filter arrangement according to claim 12, characterized in that the receiving recess (68, 70) of the cleaning piston (66) encompasses at least this partial circumference, in particular, the receiving recess (68, 70) extends circumferentially at least over this partial circumference. Filter arrangement according to claim 13, characterized in that the receiving recess (68, 70) is either designed as a groove with channels to the discharge channel (72) or extends radially inward in a cylindrical segment shape toward the discharge channel (72).Filter arrangement according to any one of claims 11 to 14, characterized in that the filter screen (38, 40) and the stop wall (42, 44) are formed in two parts, in particular each as two identical components. Filter arrangement according to claim 15, characterized in that the filter support wall (30, 32) has at least two areas associated with the filter screen and the filter support wall, in which the through-channels (36) with the openings (36a, 36b) are provided. Filter arrangement according to claim 16, characterized in that at least two receiving recesses (68, 70) are provided in the cleaning piston (66), which are associated with the areas with the first openings (36a) and through-channels (36) of the filter support wall (30, 32).Filter arrangement according to one of claims 15 to 17, characterized in that each part of the stop wall (42, 44) is designed as a cylindrical segment which extends only over a partial angle in the circumferential direction and extends radially outwards from the filter screen (38, 40), laterally encompassing the area with the openings (36b). The filter arrangement according to claim 18 is characterized in that the flow body (14c) encompasses the outer walls (42a, 44a) at least partially, and in particular completely, except for the outwardly facing end faces. The filter arrangement according to any of the preceding claims is characterized in that the flow body (14c), together with the filter screen (38, 40) and the stop wall (42, 44) as well as the cleaning piston (66) arranged within the flow body (14c), forms part of a piston (14) extendable from the filter housing (12) for changing the filter screens (38, 40), wherein the individual components of the stop wall (42, 44) and the individual components of the filter screen (38, 40) are detachably arranged in the flow body (14c).Filter arrangement according to claim 20, characterized in that at least two extendable pistons (14) with filter screens (38, 40) and stop walls (42, 44) as well as the cleaning piston (66) arranged within the flow bodies (14c) are installed. Filter arrangement according to any one of the preceding claims, characterized in that the through-channels (36) of the filter support wall (30, 32) extend radially with respect to a concentric axis of the cleaning piston (66), in particular these through-channels (36) of the filter support wall (30, 32) are aligned with mutually associated through-channels (46) of the stop wall (42, 44). Method for filtering fluid with a filter arrangement, in particular according to any one of the preceding claims, characterized by a continuous backflushing of filtered fluid in the filter arrangement (10). Method according to claim 23, characterized in that the quantity of backflushed fluid in the filter arrangement (10) remains constant.Method according to claim 23 or 24, characterized in that low-viscosity fluids, preferably with a viscosity in the range of 50 Pas to 5,000 Pas, are filtered.

26. Method according to one of claims 23 to 25, characterized in that the cleaning piston (66) is permanently moved back and forth from the first end position to the second end position.

27. Method according to one of claims 23 to 26, characterized in that the cleaning piston (66) is moved at a speed which is in a range of 10% to 200% of the discharge speed of the filtered fluid / inlet speed of the fluid to be filtered, in particular in a range of 45% to 150%.

28. Method according to one of claims 23 to 27, characterized in that the amount of backwashed fluid is in a range of 0.1% to 2.0% of the fluid introduced into the filter arrangement (10), in particular in a range of 0.5% to 1.0%.

29. Filter arrangement according to one of the preceding claims, characterized in that the filter support wall (76) is provided with an inner sleeve (78) and a base filter support wall (80), wherein the inner sleeve (78) comprises the first and second openings (36a, 36b) and the passage channels (36).

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

31. Filter arrangement according to one of the preceding claims, characterized in that the cross-sectional areas of the openings (36a, 36b) and the passage channels (36) each have a height and a width, wherein the height is many times greater than the width.

32. Filter arrangement according to one of the preceding claims, characterized in that the cross-sectional area of ​​the openings (36a, 36b) corresponds to 75% of the cross-sectional area of ​​the receiving recesses (68, 70).

33. Filter arrangement according to claim 32, characterized in that the cross-sectional shape of each opening (36a, 36b) corresponds to the cross-sectional shape of the associated receiving recess (68, 70).

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