FILTER SYSTEM FOR VISCOSE OR HIGHLY VISCOSE LIQUIDS, IN PARTICULAR PLASTIC MELTS AND METHOD FOR FILTRATION OF VISCOSE OR HIGHLY VISCOSE LIQUIDS

Description

[0001] Filter system for viscous or highly viscous liquids, in particular plastic melts, and process for filtering viscous or highly viscous liquids.

[0002] The invention relates to a method and a device for filtering viscous or highly viscous liquids, in particular plastic melts, using a filter plate.

[0003] To remove impurities from viscous or highly viscous liquids, especially plastic melts, state-of-the-art filtration devices using different filter designs are generally used.

[0004] Common contaminants in viscous or highly viscous liquids, such as plastic melts, include organic or inorganic contaminants such as metals, minerals, and the like, or contaminants from other polymers, foreign particles, excessively coarse additives, and their agglomerates. Other disruptive contaminants include degradation products of the viscous or highly viscous liquid that arise during use, production, or other proper or improper applications, such as excessive temperature exposure or during production, for example, in the case of plastics, due to excessive or insufficient cross-linking, such as gels.

[0005] Sieve plates or filter belts, so-called belt filters, are used as filters.

[0006] In any case, the openings of the corresponding filter must be smaller than the contaminants to be retained and separated from the viscous or highly viscous liquid.

[0007] Due to the deposition of contaminants on the filter belt or screen plate, the degree of contamination of the respective filter device increases more or less rapidly, depending on the degree of contamination of the viscous or highly viscous liquid and its throughput through the filter device. In the worst case, this can lead to virtually no liquid being able to pass through the filter.

[0008] Depending on the filter design used, a screen plate, for example, may need to be replaced or backwashed. Cleaning occurs depending on the degree of contamination, the pressure buildup, or at set times.

[0009] This generally results in a non-continuous material flow, as the melt may be routed through other chambers during the exchange or backflushing process, which can cause pressure surges and similar effects. The pressure buildup until the filter is changed changes the filtration conditions. Especially with highly contaminated materials with flat, film-like contamination, this can lead to the filter becoming blocked very quickly, resulting in very frequent change cycles with an interruption in the material flow.

[0010] For this reason, a filtration system with continuous cleaning of the filter is quite advantageous.

[0011] In continuous systems, for example, a plate or cylinder equipped with fine holes is rotated to clean the filter, or it is continuously cleaned by a rotating scraper or auger mounted on the screen surface in the material flow. The contaminants are then transported out through suitable transport channels and pressure-reducing mechanisms.

[0012] The disadvantage here is the mechanical contact between the cleaning device and the sieve plate or filter belt, which leads to significant wear on the sieve plate or filter belt, especially with high levels of mineral or metallic contamination. Furthermore, most systems have relatively large dead volumes with long material downtimes, which can promote melt degradation.

[0013] When the filter plate is cleaned by, for example, scrapers, screws and the like, the melt does not flow through the cleaning zone and a so-called "passing sieve effect" occurs, i.e. the comminution of the impurities and thus the passage of the impurities through the filter plate.

[0014] From AT 404562 B, for example, a filter device for liquids containing impurities is known, in which the filter is cleaned by a scraper element.

[0015] DE 10 2016 202 489 discloses a filter device comprising an inlet chamber, an outlet chamber, and a filter system that separates the inlet chamber and the outlet chamber. The flow direction of the liquid to be filtered runs at an angle of between 10° and 90°, in particular between 30° and 70°, relative to the surface normal of the filter. This tangential flow to the filter enables very small chamber volumes.

[0016] From DE 41 16 199 A1 a device for cleaning plastic melts is known, comprising a housing which comprises a flow channel and at least one filter element which can be moved transversely thereto, wherein the filter element can be moved from the flow channel into at least one cleaning chamber which is connected on the rear side of the filter element to the part of the flow channel which carries cleaned fluid and which has on the front side of the filter element at least one collecting channel with an outlet opening.

[0017] A device with very wide filters is known from SU 1 110 651 A1.

[0018] From WO 2008 / 031127 A1, a filter device with a single filter plate in the form of a rotating disc is known, the width of which corresponds to at least twice the width of the active area.

[0019] The object of the present invention was to provide a filter device for filtering viscous or highly viscous liquids, in particular plastic melts, which enables continuous operation and also avoids the disadvantages of the prior art, in particular wear of the filter plate. The invention therefore relates to a filter system comprising a filter plate situated in a filter chamber, which is supported by a filter carrier plate, wherein either the filter plate is guided in grooves on the filter carrier plate by sliding elements or the filter carrier plate with the filter plate situated thereon is guided in the filter chamber by sliding elements, and wherein the filter system comprises at least one, preferably two, cleaning chambers connected to the filter chamber, wherein the filter plate is movable to the at least one cleaning chamber for cleaning.wherein the filter plate or the filter plate together with the filter support plate is guided in an oscillating movement during filtration to clean the filter plate, and wherein the filter plate is at least twice as wide as the active filter area in the filter zone, the filter zone being the area in which the liquid to be filtered passes through the filter plate and the filter support plate.

[0020] A further subject of the invention is a process for filtering viscous or highly viscous liquids, in particular plastic melts, characterized by the following process steps Feeding the viscous or highly viscous liquid into a filter chamber in which a filter plate is situated, which is guided in the filter chamber on the underside and / or laterally by sliding elements and which is guided in an oscillating movement during filtration. Feeding the viscous or highly viscous liquid through an inlet opening of the filter chamber. Discharging the liquid passing through the filter plate. Moving the filter plate to a cleaning chamber for cleaning. Discharging the contamination present on the filter plate via the cleaning chamber with the aid of conveyor devices or by a backwash process, wherein the filter plate is at least twice as wide as the active filter area in the filter zone, wherein the filter zone is the area in which the liquid to be filtered passes through the filter plate and the filter support plate, and wherein, when the filter plate is cleaned, melt continues to flow through it in the filter zone.

[0021] During the filter cleaning process, a cleaning device does not move across the surface of the filter plate or relative to it; instead, the filter plate is moved toward a cleaning chamber by movement on one or symmetrically on each side. A cleaning device, such as a scraper, does not move across the surface of the filter plate or relative to it; instead, the filter plate is moved toward one or symmetrically on each side of the cleaning chamber. This decouples the cleaning process from the filtration process.

[0022] A key advantage is that the melt continues to flow through the filter plate during cleaning, virtually eliminating the so-called "straining effect"—the comminution of contaminants and thus the passage of contaminants through the filter plate. Gels present in the melt, in particular, can be removed extremely effectively and are not forced through the filter plate during cleaning.

[0023] The filter zone is the area in which the liquid to be filtered passes through the filter plate and the filter carrier plate.

[0024] No filtration takes place in the cleaning zone.

[0025] Since there is no scraper constantly in contact with the plate, wear can be greatly reduced even when there are hard contaminants in the melt, such as mineral or metallic impurities.

[0026] According to the invention, the filter plate can be designed as a solid sieve plate or consist of a stack of one or more filter mats or foils. The sieve plate can be designed as a solid plate with holes produced, for example, by drilling, sinking EDM, water jet, laser, electron beam, particle beam (e.g., proton), etching, or the like. Depending on the design, the filter plate is preferably at least twice as wide as the active filter surface in the filter zone.

[0027] The filter plate or filter support plate is guided through grooves on the underside and sides, for example, by sliding elements. The sliding elements can be made of wear-resistant materials or bearing materials such as copper, aluminum bronze, sintered elements, or the like. The melt itself can also form a thin lubricating film here.

[0028] The filter plate can be supported in the filter chamber by a filter support plate, which also has openings for the passage of the melt.

[0029] In each case, the filter support plate is designed to guarantee an optimal compromise between permeability (i.e., low flow resistance) and optimal strength. The openings in the filter support plate can be round, polygonal, elongated, or similar, arranged perpendicularly or at an angle to the surface, for example, to enable better flow distribution. The cross-sections and directions of the openings can also vary in their longitudinal profile.

[0030] Furthermore, the filter carrier plate can be made of several layers, materials and combinations.

[0031] For example, the surface can be designed with a particularly friction-reducing soft or hard layer or structure in order to facilitate the sliding of the filter element.

[0032] A particularly strong, tensile material can be placed beneath the surface of the filter support plate. The filter support plate is made, for example, of hardened steel with a highly lubricating material, such as bronze, applied to its surface.

[0033] During the filtration process, the filter plate is moved back and forth over the stationary filter support plate in the filter chamber, i.e., oscillates. The stationary filter support plate then acts as a separator in the melt stream.

[0034] In this case, the filter plate is preferably designed as a solid plate, since it must be able to directly absorb the forces generated by the plate being pushed back and forth.

[0035] In a further embodiment of the invention, the entire filter plate can oscillate with the filter support plate arranged underneath, which simultaneously absorbs the force caused by the pressure difference in the melt flow.

[0036] In this case, the filter plate can be designed as a thin plate, foil, or mat, since it does not have to absorb any sliding forces. The force required to move the filter plate and the filter support plate is greater in this case than in the case where only the filter plate is moved.

[0037] However, a combination of these designs is also possible, for example, where a compact but thin filter plate is oscillated over a filter support plate. Suitable measures must be taken to absorb the higher frictional forces caused by the high melt pressure. This is achieved, in particular, by sliding elements made of wear-resistant materials or bearing materials.

[0038] The movement or oscillation of the filter plate or the filter plate and the filter carrier plate can be effected by an electric, hydraulic, pneumatic or other mechanical drive.

[0039] A cleaning chamber is located on one or both sides of the filter chamber. This cleaning chamber is positioned slightly higher than the filter plate itself in the direction of the filter inlet to additionally collect surface contaminants. The cleaning chamber is sealed off from the filter chamber by means of locking elements, which, either alone or in combination with additional cleaning elements, seal the cleaning chamber from the filter chamber.

[0040] The locking and / or cleaning elements can be controlled mechanically, by levers or gates, by a lifting movement, by springs, by melt pressure, or independently by electrical, mechanical, pneumatic, or hydraulic means. The contact pressure of the locking and / or cleaning elements can be varied as required depending on the application.

[0041] Scraper units are preferred as cleaning elements.

[0042] The scrapers themselves are replaceably mounted on a base unit. The scrapers can be made of metals or alloys. Sandwich structures, each with various surface coatings such as PVD or CVD, DLC or ceramic layers, or plastics and combinations thereof, are also possible. The material combination of the scraper and screen is crucial here, enabling optimal cleaning while minimizing wear.

[0043] The scrapers are designed as wedges, blades, knives, rollers, lamellae, driven screws, or combinations of these. In a special design, a cleaning device can also be integrated. For example, during the reverse movement, one or more scrapers are guided through a slotted plate, and the contaminants are scraped off as they are pulled through.

[0044] Depending on the level of dirt, materials, filter material, etc., the contact pressure can be varied almost as desired with this system to ensure optimal cleaning effect with minimal filter wear.

[0045] The filter plate is moved by at least one slider that seals the cleaning chamber from the outside.

[0046] In a special embodiment, the filter plate can be designed at the end in such a way that the seal is achieved by raising the filter plate to the height of the cleaning chamber itself.

[0047] Furthermore, several sealing and / or cleaning elements can be arranged in series.

[0048] The plate is now moved into the cleaning chamber, with the piston moving sideways and the volume of the cleaning chamber being released. During this phase, the actual cleaning elements are not in contact with the plate surface, or are only in light contact. Only when the plate has been partially retracted, for example, halfway into a cleaning chamber, is it essentially sealed off from the filter chamber by the locking and / or cleaning elements.

[0049] Subsequently, an outlet channel is opened by means of a valve or the geometry of the filter plate. This outlet channel can incorporate appropriate elements such as active or passive screws, spirals, or labyrinth-like structures. Furthermore, the outlet channel can be thermally separated from the filter, allowing the viscosity of the discharged material to be specifically influenced via dedicated heating or cooling systems.

[0050] The valves can be designed as piston, ball valve, gate, linear or rotary, and can be operated mechanically, pneumatically or hydraulically.

[0051] In a special embodiment, the blocking and cleaning slide can be designed as a valve.

[0052] For example, a profiled groove is mounted lengthwise on the slide valve, through which the contaminants are directed to a channel integrated into the slide valve. During the cleaning cycle, this slide valve is in contact with the filter. In precisely this position, the channel integrated into the slide valve is flush with a hole in the slide valve's support plate, thus opening a channel to the outside, either directly or via the aforementioned pressure-reducing elements, through which the contaminants are directed to the outside.

[0053] In this embodiment, additional valve units can be dispensed with.

[0054] The filter plate is then moved in the opposite direction. The slide or the end of the filter plate reduces the volume of the cleaning chamber, while simultaneously cleaning the surface of the filter plate with the locking wedges or additional scraper profiles, rotating screws, rollers, and the like. The contaminants are discharged into the cleaning chamber along with the melt residue.

[0055] To simplify discharge across the width, the slides or cleaning elements can be arranged diagonally or in a V-shape, for example. In the case of a V-shaped arrangement of the cleaning elements, two channels are provided.

[0056] In a further embodiment, two cleaning chambers can be provided.

[0057] In this case, the filter is only cleaned on one side up to about half or preferably about 1 / 3 of the total length of the filter in the first chamber and at the same time is moved into the second symmetrically arranged chamber on the opposite side.

[0058] Due to the special design, it is also possible to backwash the filter surface with a material stream from the opposite side during cleaning, i.e. before or during pushing back into the active position.

[0059] For this purpose, material can be actively pushed from the clean side against the now almost pressure-free opposite side in the cleaning chamber either by an actively controlled valve or by appropriate overflow channels.

[0060] Alternatively, a volume of filtered material can be provided on the underside of the cleaning chamber in such a way that a flow of cleaned material is possible at the bottom when the filter is moved into the cleaning chamber. For this purpose, overflow channels are provided that are open when the carrier or filter plate is in its final position. During the cleaning movement, these overflow channels are closed, and the clean material is forced from below through the filter carrier plate and the filter plate.

[0061] Since melt can also be filtered into the filter chamber and through the filter plate when the filter plate is moved into the cleaning chamber, such backflushing can also be carried out to a lesser extent without the use of overflow channels.

[0062] Of course, special non-return valves can also be installed in the discharge channels. After the cleaning process, it is also possible to apply active substances, additives, catalysts, etc., for example, to modify the properties of the melt, using suitable metering valves and devices or via the scraper elements, past which the filter plate is moved in the opposite direction to return it to the filtering position.

[0063] According to a further embodiment, two filter chambers are each connected to a common melt channel by means of a switchable valve in such a way that in one state of the switchable valve the melt flows through the first filter chamber and in the other state of the switchable valve the melt flows through the second filter chamber.

[0064] Preferably, the valve is designed to allow parallel operation. Three or more filter chambers can also be connected in parallel via such valves, so that at least one of the filters always ensures melt flow.

[0065] In a further embodiment, two or more filter chambers can be arranged one above the other or next to each other in series, so that the outflow of the preceding one is connected to the inflow of the following one and the melt is successively passed through the two or more belt filters.

[0066] The contaminant is discharged in the form of a filter cake, either sideways in the direction of the sieve movement, at 90° to it, or upwards. It is important that the contaminants are depressurized to atmospheric pressure.

[0067] In the simplest case, this is achieved by a spiral or screw conveyor. To actively convey the contaminants outward after the chamber valve, a separate spiral or screw conveyor can be used for each side, or, if the discharge channels converge, a common spiral or screw conveyor can convey the material outward. This must not result in excessive further melt degradation to avoid generating deposits in the discharge area.

[0068] In another embodiment, the material can be actively cooled during application, so that only viscous or even solidified contaminants escape. For this purpose, a cold runner is provided in the filter, thermally decoupled from the heated system.

[0069] In the Figures 1 to 7 Embodiments of the method according to the invention are shown.

[0070] This means 1The filter chamber 2The filter plate 3The filter support plate 4The impurities (filter cake) 5, 5aA cleaning chamber 6, 6aA gate valve with integrated valve 7The discharge channel in the cleaning chamber 8Sliding bearing 9A conveyor screw for removing the filter cake 10The viscous or highly viscous liquid to be filtered, for example, the plastic melt to be filtered 11The filtrate of the viscous or highly viscous liquid 12A gate element 13An insulation layer 14Heating or cooling channels 15The melt chamber for backflushing 15aThe backflushed melt 16The gate valve for moving the filter or filter support plate 17The melt inflow 18The melt outflow 19A shut-off element for forced backflushing 20Solidified contaminant material 21The cleaning zone 22The filter zone

[0071] In Figure 1 A method for cleaning the filter is shown in which the filter is cleaned without backwashing.

[0072] The device consists of a filter chamber 1, a filter plate 2, which is supported by a filter carrier plate 3.

[0073] As in Figure 1 As shown in Figure a, during the filtering process of a viscous or highly viscous liquid 10, the impurities are deposited on the filter plate 2 as a filter cake 4.

[0074] To clean the filter plate 2 of the filter cake 4, the valve 6, which in this case is designed as a piston, is actuated, and the filter cake 4 is guided into the cleaning chamber 5 and removed from the cleaning chamber through the channel 7. The filter cake 4 is removed by sliding the filter plate 2, optionally together with the filter support plate 3, in the direction of the arrow, whereby the filter plate 2 is transported to a second cleaning chamber 5a and the process is carried out until the filter plate is completely cleaned.

[0075] In Figure 2A method for cleaning the filter with free backwash is shown.

[0076] Due to the pressure difference in front of and behind the filter plate 2 that occurs during the cleaning of the filter, part of the filtrate 11 from the melt chamber for the backwash 15 is pressed back through the filter carrier plate 3 and the filter plate 2 in the backwash zone 21 under the filter cake 4 ( Figure 2b) . The backwashed melt 15a lifts the filter cake 4 and is thus more easily pressed into the channel 7 of the cleaning chamber 5.

[0077] The removal of the filter cake 4 is carried out by moving the filter plate 2, if necessary together with the filter carrier plate 3, in the direction of the arrow, whereby the filter plate 2 is transported to a second cleaning chamber 5a and the process is carried out for further cleaning of the filter plate.

[0078] In Figure 3A process for filtration with forced backwashing is shown. Here, the backwashing process is initiated by sealing the backwash zone 15 by the slide movement. The filter system has an additional shut-off element 19. The material is forced through the filter from below with increased pressure and the cleaning process of the filter plate is analogous to that in Figure 2 procedure described.

[0079] Figure 4 shows a filter design in which filter plate 2 and filter support plate 3 oscillate together, i.e., are pushed back and forth. The filter support plate 3 is mounted on plain bearings 8 in the filter chamber 1.

[0080] Figure 5 shows an embodiment of the filter in which only the filter plate 2 is oscillated. The filter plate 2 is mounted on plain bearings 8, which are located on the filter support plate 3.

[0081] In Figure 6An embodiment for removing the filter cake 4 from the cleaning chamber is shown. In the channel 7, the pressure is reduced from a pressure level P1 to a pressure level P0 by changing the cross-section, and the filter cake 4 is transported out of the channel.

[0082] In Figure 7 The filter cake 4 is removed in a controlled manner by means of a screw conveyor 9.

[0083] In Figure 8 For the removal of the filter cake, 4 cooling channels 14 are provided in the cleaning chamber, so that the pressure in the cleaning chamber is reduced by cooling. The insulation layer 13 serves to decouple the temperature of the discharge channel 7, thus, by maintaining a lower temperature than in the filter, the temperature of the material to be discharged can be lowered and the viscosity increased.

[0084] Figure 9 shows an embodiment according to Figure 7, in which the pressure reduction occurs through active cooling through cooling channels 14. As a result, solidified material emerges at the end of the discharge channel 2.

Claims

1. A filter system comprising a filter plate (2) which is located in a filter chamber (1) and is supported by a filter carrier plate (3), wherein either the filter plate (2) is guided on the filter carrier plate (3) by sliding elements in grooves or the filter carrier plate (3) with the filter plate (2) located thereon is guided in the filter chamber (1) by sliding elements, and wherein the filter system has at least one, preferably two, cleaning chamber(s) (5, 5a) connected to the filter chamber (1), wherein the filter plate (2) is movable to the at least one cleaning chamber (5, 5a) for cleaning, characterized in that the filter plate (2), or the filter plate (2) together with the filter carrier plate (3), is guided in an oscillating movement during filtration for cleaning the filter plate (2), and that the filter plate is at least twice as wide as the active filter surface in the filter zone (22), wherein the filter zone (22) is the region in which the liquid (10) to be filtered passes through the filter plate (2) and the filter carrier plate (3).

2. The filter system according to claim 1, characterized in that the cleaning chamber(s) (5, 5a) is / are sealed off from the filter chamber (1) by barrier element(s).

3. The filter system according to claim 2, characterized in that the barrier element(s) can be moved mechanically, in a manner controlled by levers or linkages, by a lifting movement, by springs, the melt pressure, or independently electrically, mechanically, pneumatically or hydraulically.

4. The filter system according to claim 2 or 3, characterized in that the barrier element(s) is / are configured as a barrier slider (6, 6a) with an integrated valve, via which the filter cake (4) can be removed from the cleaning chamber (5, 5a).

5. The filter system according to one of claims 1 to 4, characterized in that an additional cleaning device in the form of a scraper unit is provided.

6. The filter system according to one of claims 1 to 5, characterized in that the filter plate (2) is configured as a plate, foil or mat.

7. The filter system according to one of claims 1 to 6, characterized in that a screw conveyor (9) for discharging the filter cake (4) is provided in the cleaning chamber (5, 5a).

8. A method for filtering viscous or highly viscous liquids (10), in particular plastic melts, characterized by the following method steps: - feeding the viscous or highly viscous liquid (10) into a filter chamber (1) in which a filter plate (2) is located, which is guided in the filter chamber (1) on the underside and / or laterally by sliding elements and which is guided in an oscillating movement during filtration - feeding the viscous or highly viscous liquid (10) through an inlet opening of the filter chamber (1) - discharging the liquid passing through the filter plate (2) - moving the filter plate (2) to a cleaning chamber (5, 5a) for cleaning - removing the contamination present on the filter plate (2) via the cleaning chamber (5, 5a) with the aid of conveying devices or by a backwashing process, wherein the filter plate (2) is at least twice as wide as the active filter surface in the filter zone (22), wherein the filter zone (22) is the region in which the liquid (10) to be filtered passes through the filter plate (2) and the filter carrier plate (3), and wherein, during cleaning of the filter plate (2), melt continues to flow through it in the filter zone (22).

9. The method according to claim 8, characterized in that the method is carried out using a filter system according to one of claims 1 to 7.

10. The method according to claim 8 or 9, characterized in that the backwashing process is initiated by the pressure difference upstream and downstream of the filter plate (2).

11. The method according to claim 8 or 9, characterized in that the backwashing process is initiated by sealing the backwashing chamber.