Filter device for filtering out fibers from a flow, and method for operating same
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ARBURG GMBH & CO KG
- Filing Date
- 2025-11-10
- Publication Date
- 2026-05-21
Smart Images
Figure EP2025082522_21052026_PF_FP_ABST
Abstract
Description
[0001] Filter device for filtering fibers from a flow and method for its operation
[0002] Description
[0003] Reference to related applications
[0004] The present application refers to and claims priority of German patent application 10 2024 133 166.6, filed on 18.10.2022, the disclosure content of which is hereby expressly made the subject matter of the present application in its entirety.
[0005] Field of invention
[0006] The present invention relates to a filter device for filtering fibers from a flow, which is configured for feeding the fibers in the production of fiber-reinforced plastics, having the features according to the preamble of claim 1, a corresponding feeding device for feeding fibers with a filter device having the features according to the preamble of claim 16 and a method for operating a filter device for filtering fibers from a flow for such a feeding device having the features according to the preamble of claim 17.
[0007] State of the art
[0008] In the production of fiber-reinforced plastics, fibers such as glass fibers, carbon fibers, or fibers from renewable resources are incorporated into the plastics to increase their strength and stability. For this purpose, bundles of fibers are fanned out and cut into fiber pieces of the desired length in a shredding device. These pieces are then transported by a feeding device, such as a screw extruder, to a unit where raw materials, such as plastic granules, are plasticized. In this plasticizing unit, the molten plastics are mixed with the fiber pieces.
[0009] Such a feeding device typically consists of a screw conveyor through which the fiber pieces are transported towards the plasticizing unit. During the comminution of the fibers, waste products such as fiber dust or very short fiber fragments are generated. Both the fiber fragments and the waste products are drawn into the screw conveyor by the comminution device via a flow, such as an airflow, generated by a suction device. The fiber fragments are also drawn to the underside of the screw conveyor, or the side opposite the fiber feed point, thereby achieving a uniform distribution within a housing bore of the screw conveyor, particularly around the at least one conveying element located therein. Waste products, on the other hand, are removed from the airflow in the housing bore by a filter device located between the housing bore and the suction device.A disadvantage of the current state of the art is that the waste products lead to a blockage of the filter system after a relatively short time, resulting in increased maintenance requirements.
[0010] Previous solutions for filter systems use, for example, filter fleeces with fine-mesh filter structures, filters with perforations, or filters with filter lamellae.
[0011] EP 2218568 A1 discloses a screw machine for processing at least partially powdered bulk material, comprising a housing with at least one housing bore and a screw arranged in the housing bore. A vacuum housing section is provided, designed as a detachably mounted vacuum housing insert in which a metal fleece is interchangeably held as a gas-permeable wall section on a base body.
[0012] WO 2014 / 048667 A1 discloses a feeding device for fibers using a multi-screw machine for the lateral feeding of fibers into a processing plant for the production of fiber-reinforced plastics. The multi-screw machine comprises a housing, several intersecting housing bores, rotatably driven screw shafts arranged therein, and a feed opening. A suction device is provided for drawing the fibers through the feed opening into the housing bores, generating an airflow that draws the fibers in. The fibers are filtered out of the airflow by means of a filter device. To ensure a long service life, the filter device has several flow channels with a cross-section that widens abruptly in one direction of flow.
[0013] The filter assembly of WO 2014 / 048667 A1 consists of a series of interconnected metallic lamellae, between which flow channels form. These channels abruptly widen in cross-section and, in particular, in width in the direction of flow towards the underside of the filter assembly. This abrupt change affects the flow parameters, leading to vortex formation, turbulence, backflow at the separation point / area, and sudden pressure changes. The effect is comparable to flow resistance. Due to the inconsistent cross-sections, inconsistent pressure conditions or pressure differences arise within the flow channels. These promote fiber accumulation and clogging of the filter assembly.The special geometry of the filter pack, constructed from lamellae, with its inconsistent cross-sections in the flow direction and inconsistent pressure conditions, promotes a fanning effect, where the lamellae spread apart, leading to fiber accumulation and clogging. To counteract this, a high tightening torque is used during lamella assembly, which can, conversely, cause distortion or deflection of the lamellae, resulting in inconsistent cross-sections between them. During assembly, particularly after filter maintenance, contamination can occur in the flow channels and between the contact surfaces of the spacer plates between the lamellae, leading to assembly inaccuracies. These inaccuracies accumulate with each additional spacer plate.All of this can lead to unfavorable flow conditions. Similarly, assembly errors in the orientation of the individual lamellae can result in problematic flow patterns. Ultimately, all these problems can lead to fluctuations in the fiber content of fiber-reinforced plastics, preventing compliance with customer-required quality criteria. Finally, the geometry of the lamellae defines the installation position of the filter assembly, precluding any alternative arrangement, such as rotation.
[0014] DE 10 2012 217 586 A1 discloses an injection molding system for the production of fiber-reinforced plastic parts. The system comprises an injection molding device with a housing and two interconnected housing bores formed therein. Two screw shafts for melting and feeding plastic material into a mold are arranged in the housing bores. Each screw shaft is rotatably driven about a rotary axis and can be displaced along this axis. For feeding fibers, the injection molding system includes a feeding device by means of which cut fibers can be drawn directly into the housing bore through a feed opening. A filter device is arranged in the feed opening, comprising several adjacent filter elements, with each neighboring filter element forming a slit-shaped flow channel.
[0015] DE 102 01 869 A1 discloses a device for the production-stable, continuous feeding of lightweight, bulky materials with moderate to poor flowability into the melt of an extruder via twin-screw side-feeding devices or twin-screw auxiliary extruders with a shortened extrusion path. In this device, the materials, in the form of chips or short-cut fibers, are drawn into the screw flights by means of a vacuum below the conveying screws. Below the screw surface, the aspirated material and air streams are separated by a screen, and the air stream is extracted from the screw housing below the screen. On the screen, the material is gripped by the flanks of the conveying screws and conveyed through the screws in the conveying direction. An agitator is located above the screws, ensuring continuous loosening of the material.For process control, a cleaning element is integrated below the sieve to prevent the sieves from becoming clogged with material residues.
[0016] German patent application DE 10 2012 217 586 A1 discloses a screw conveyor with a device, a method for processing bulk material, and a processing plant for processing bulk material. The device includes a vacuum filter insert for degassing the bulk material. The vacuum filter insert is arranged in a housing of the screw conveyor downstream of its feed opening and has at least one filter element, such that the vacuum filter insert forms a gas-permeable wall section that borders the at least one housing bore of the screw conveyor. A protective element with a plurality of through-openings is arranged upstream of the at least one filter element in one degassing direction. The protective element serves as granule protection for the filter element and prevents granular bulk material from damaging the filter element.
[0017] JP 2002210805 A discloses a device for feeding fine powder raw material into an extruder, comprising a cylinder and two screws arranged in the cylinder. Fine powder raw material, supplied via a hopper, is fed into the extruder. Opposite vent openings are provided on the side walls of the cylinder. A sieve unit is provided at each vent opening. An opening on the outer wall surface of each vent opening is connected to a forced extraction chamber. The sieve unit has a trough-like receiving element, a sieve with a mesh size smaller than the average particle size of the powder raw material, and a frame-like retaining element. The sieve is arranged between the receiving element and the retaining element. The receiving element is slid over the retaining element and has several bores in its base opposite the sieve and the retaining element.The holding element has several grid-like vent channels through which a flow entering through the bores of the receiving element can escape. The base of the receiving element has a curvature corresponding to the cylinder wall. German patent DE 10 2019 118 093 A1 discloses the treatment of bulk materials, in particular the removal of dust from bulk materials such as granules, by means of a sealing unit and a dust collector for a flowing stream of granules. Dust removal is achieved by ionization, since the dust often adheres to the granules by means of electrostatic charging.
[0018] DE 102 14 654 B4 discloses a process for the continuous production of compounds from free-flowing plastic and finite natural and / or synthetic fibers using a twin-screw extruder, starting from commercially available delivery forms of the starting materials (fibers, polymer) and continuing to the finished compound product (granules, sheets or other semi-finished products) in a single process. In this process, the fibers are continuously prepared, opened, demetallized, dedusted, metered and forcibly fed into the extruder, then compounded with polymer and either underwater granulated as a compound or extruded into sheets or other semi-finished products.
[0019] EP 2810757 B1 discloses a fine powder raw material feeding device with a sieving unit, which has a comparable design to that described in the
[0020] JP 2002210805 A disclosed sieve unit.
[0021] Description of the invention
[0022] The invention is therefore based on the objective of providing a filter device that increases the reliability of the filter process and the quality of the fiber-reinforced plastics produced.
[0023] This problem is solved by a filter device according to the features of claim 1. The filter device comprises, as a filter element, at least one filter plate with a curvature, wherein the filter plate has at least one region with several slit-shaped flow channels which, in the operating state at a predetermined or predeterminable flow rate, have a Reynolds number below a critical Reynolds number above which the flow becomes turbulent, and are thus configured to form a laminar flow in the flow channels and a homogeneous and uniform pressure distribution in the region, wherein the filter device has a frame or a receptacle which has at least one curvature corresponding to the curvature of the wall, on which the at least one filter plate is replaceably mounted.The laminar flow in the flow channels advantageously leads to a homogeneous pressure distribution on the upper and lower surfaces of the at least one filter plate. This effectively slows down or ideally prevents the accumulation of waste products, such as fiber dust or short fiber fragments, in the filter system and thus clogging of the filter system. Furthermore, this improves the quality of the fiber-reinforced plastics produced, as a constant amount of fiber can be introduced into the plasticizing process, resulting in a precise, preferably consistent, desired fiber content in the fiber-reinforced plastic.Furthermore, this enables a reduction in the number of parts in the filter system, reduces the susceptibility to errors during filter assembly, simplifies assembly and maintenance, reduces cleaning time during preventive cleaning of the filter system, and thus achieves increased machine availability while simultaneously reducing costs.
[0024] The problem is also solved with a feeding device for supplying fibers during the production of fiber-reinforced plastics, comprising a filter device according to the features of claim 16. The feeding device further comprises a filter device according to any one of claims 1 to 15. This provides the advantages of the invention.
[0025] Furthermore, the problem is also solved by a method for operating a filter device for filtering fibers from a flow, such as an airflow, used to supply the fibers during the production of fiber-reinforced plastics, according to the features of claim 17. The filter device comprises, as a filter element, at least one filter plate with a curvature, which filter plate has at least one area with several slit-shaped flow channels. In the operating state, at a predetermined or predeterminable flow rate and a Reynolds number below a critical value, these channels generate laminar flow and a homogeneous and uniform pressure distribution. The advantages of the invention are thereby realized.
[0026] Beneficial further training is subject to dependent claims.
[0027] In a preferred embodiment of the filter device, the stability of the filter device is advantageously increased and maintenance simplified by the fact that the filter plate has a closed comb and that the slit-shaped flow channels are several parallel, slit-shaped flow channels, each with a constant flow cross-section and a predetermined length-to-width ratio. The closed comb increases the stability of the filter plate, which in turn also contributes to stable laminar flow. Likewise, the consistently uniform cross-sections or gap dimensions of the flow channels contribute to maintaining laminar flow.
[0028] Preferably, in one embodiment of the filter device, the wall accommodating the filter plate is a cylindrical wall with at least one housing bore and an inner radius for receiving a conveying element with a cylindrical cross-section, such as a screw shaft of a feeding device for supplying the fibers to a processing plant. The wall is designed to be swept by the conveying element, preferably without contact, as the filtered fibers are transported away from the housing bore. The filter element is pre-curved and has a curvature along the at least one housing bore corresponding to its shape. This ensures that the filtered fibers are reliably fed to the processing plant. Simultaneously, the conveying element regularly exposes the filter plate to maintain its filtering effectiveness.
[0029] In another embodiment of the filter device, the radius of curvature of the filter plate in its uninstalled state is larger than the inner radius of the wall. This allows the filter plate to be advantageously clamped and fixed to the wall using appropriate fixing elements such as grooves.
[0030] Preferably, in the operating state, the frame is arranged in a housing recess connected to the at least one housing bore. This advantageously increases the stability of the filter device and simplifies maintenance.
[0031] Preferably, a stable fixation of the at least one filter plate and easy replacement or rotation of the at least one filter plate can be advantageously facilitated in a further embodiment of the filter device, taking into account the leaf spring-like properties of the at least one filter plate, which is pre-tensioned with its outer edges, which preferably run along a longer side of the filter plate, positively and / or frictionally locked in grooves of the frame or the receptacle, preferably both positively and frictionally locked. With the filter plate fixed in this way, replacement or rotation of the at least one filter plate about an axis transverse to its surface area can thus be carried out without tools and with comparatively little effort.
[0032] Advantageous for the efficiency of the feeding device and a more uniform distribution of the fibers in the plastic, in another preferred embodiment the filter device can have several adjacent filter plates with bulges, which are mounted on several corresponding bulges of the frame or the receptacle and which, in the operating state when using a multi-shaft screw machine with several adjacent, intersecting housing bores of the housing with a screw shaft arranged therein, can be arranged in a housing recess connected to the housing bores.The frame between the filter plates has at least one central web with grooves into which an outer edge of one of the several adjacent filter plates, which preferably runs along a longer side of the filter plate, is received in a form-fitting and / or force-fitting manner, preferably both form-fitting and force-fitting manner.
[0033] In a further preferred embodiment, replacing or rotating the at least one filter plate can be advantageously accomplished simply by the fact that the at least one filter plate has symmetrical properties and is designed to allow installation in the frame or receptacle rotated by 180°, and that the frame and the at least one filter plate are designed to allow replacement or rotation of the at least one filter plate by means of a sliding removal of the at least one filter plate from the grooves of the frame. Due to the symmetry properties of the filter plates, their service life can advantageously be extended by rotating the filter plates by 180°.
[0034] Preferably, the filter assembly has symmetrical properties and can therefore be installed in the housing recess rotated by 180°. Due to the symmetry of the mounted filter assembly, a rotation of the entire filter assembly by 180° is also possible.
[0035] This allows assembly errors to be avoided during the design phase and increases the service life of the filter system.
[0036] A preferred embodiment of the filter device enables both a particularly stable fixing of the at least one filter plate and a simple replacement or rotation of the at least one filter plate, advantageously in that the at least one filter plate is detachably fastened to the frame or the receptacle with two locking plates arranged at the end face of the frame, preferably by means of screws, and secured against displacement in the grooves.
[0037] Preferably, in a further embodiment, the stability of the at least one filter plate with regard to its vibration behavior and its deflection strength can be advantageously improved by the fact that the at least one filter plate preferably has several separate areas with several slit-shaped flow channels extending transversely to the at least one housing bore along a longer side of the filter plate.
[0038] Another preferred embodiment of the filter device or the method for operating a filter device enables particularly good results with regard to maintenance behavior, advantageously by designing the flow channels to generate a pressure drop in an optimal range of around 50 mbar. Tests have shown that at pressure drops of this value, clogging can be efficiently reduced or prevented. If the pressure drop becomes too large for a given gap width, the flow enters the turbulent range.
[0039] Preferably, the vibration behavior and the deflection strength of the at least one filter plate and the quality of the laminar flow in the flow channels are advantageously improved by the fact that the at least one filter plate has a thickness between 0.5mm and 2mm.
[0040] In a preferred embodiment, the frame or receptacle downstream of and following the filter plate has at least one chamber with a cross-section that remains constant in the flow direction. This allows the pressure conditions downstream of the filter plate to remain nearly constant, which advantageously contributes to maintaining laminar flow.
[0041] Preferably, in another embodiment, the effectiveness of the filter device can be advantageously improved by arranging the frame or the receptacle in the housing recess in a substantially airtight or flow-tight manner. When using a frame instead of a fixed installation or integration of the filter plate into the housing recess, a substantially airtight connection of the frame in the housing recess prevents the formation of undesirable turbulence in the filter device.
[0042] A preferred embodiment of the method for operating a filter device enables secure fixing of the at least one filter plate and yet allows for easy replacement or...A simple rotation of the at least one filter plate is advantageous in that the filter device has a frame or a receptacle on which the at least one filter plate is interchangeably mounted, wherein the frame has at least one curvature corresponding to the curvature of the at least one filter plate on which the at least one filter plate is mounted, that the at least one filter plate has leaf spring-like properties and is pre-tensioned with its outer edges, which run along a preferably longer side of the filter plate, positively and / or force-fit, preferably both positively and force-fit, and that the at least one filter plate can be replaced without tools by sliding it in the grooves of the frame by means of another filter plate identical to the at least one filter plate, which engages it on a preferably shorter side of the at least one filter plate.
[0043] In another preferred embodiment of the method, electrostatic charging of the fibers used is advantageously prevented by using an ionized airflow. This particularly prevents the fibers from adhering to parts of the feeding device.
[0044] The features listed individually in the patent claims can be combined in a technologically meaningful way and can be supplemented by explanatory facts from the description and by details from the figures, showing further embodiment variants of the invention.
[0045] The invention will now be explained in more detail using an exemplary embodiment. The figures shown are:
[0046] Fig. 1 shows a perspective view of a processing plant for the production of fiber-reinforced plastics,
[0047] Fig. 2 is a perspective sectional view of a feeding device,
[0048] Fig. 3 is a detail view of Fig. 2,
[0049] Fig. 4 shows a perspective view of a filter device,
[0050] Fig. 5 shows a perspective view of a frame,
[0051] Fig. 6 is a perspective exploded view of Fig. 4,
[0052] Fig. 7 shows a perspective view of a filter plate,
[0053] Fig. 8 shows a perspective view of a filter plate replacement process.
[0054] Fig. 9 shows a sectional view of a filter plate replacement process in operational condition,
[0055] Fig. 10 is a diagram that relates the pressure drop in the flow channels to the width of the flow channels.
[0056] Fig. 11 is a diagram that relates the Reynolds number of the flow in the flow channels to the width of the flow channels.
[0057] Detailed description of preferred embodiments
[0058] The invention will now be explained in more detail by way of example with reference to the accompanying drawings. However, the exemplary embodiments are merely examples and are not intended to limit the inventive concept to a specific arrangement. Before the invention is described in detail, it should be noted that it is not limited to the respective components of the device or the respective process steps, as these components and processes can vary. The terms used here are intended solely to describe particular embodiments and are not used restrictively. Furthermore, where the singular or indefinite articles are used in the description or in the claims, this also refers to the plural of these elements, unless the overall context clearly indicates otherwise.
[0059] Fig. 1 shows a perspective view of a processing plant 40 for the production of fiber-reinforced plastics. This plant has a feeding device 20 for feeding fibers, such as glass fibers, carbon fibers or fibers made from renewable raw materials.
[0060] In the exemplary embodiment shown in Fig. 1, the unit is an injection molding unit 160 on an injection molding machine for processing plastics and other plasticizable materials with a machine stand 150, of which only the injection molding side is visible.
[0061] The design and operation of an injection molding machine are known to those skilled in the art. Plastics or other plasticizable materials are fed into the injection molding machine and mixed, plasticized, and homogenized in a plasticizing cylinder 175 (Fig. 2) of a plasticizing device 170 located in the injection molding unit 160. During the plasticizing process, plasticized material is metered in front of a conveying element 190, such as a screw conveyor. Subsequently, the plasticized material is injected by an axial movement of the conveying element 190 into a mold cavity of an injection mold (not shown in the drawing), which, in the operating state, is located between the mold carriers of the mold clamping unit. Of these mold carriers, only the stationary mold carrier 140 is visible in the figures; the rest of the mold clamping unit would be attached to the right side of this carrier in Fig. 1.During the injection process, the injection mold is closed by the mold clamping unit. Once the injected plasticized material has hardened in the mold cavity, the mold clamping unit opens the injection mold again, allowing the finished part to be removed. This process is repeated cyclically.
[0062] Fig. 2 shows a perspective sectional view of the feeding device 20, by means of which fibers are added to the material. Fig. 3 shows a detail view of Fig. 2. It shows a fiber shredding device 100, which first fans out a bundle of fibers and then cuts them to a desired length. In the exemplary embodiment, the fiber shredding device 100 is arranged above a feeding device 20. The feeding device 20 comprises a screw conveyor 30 for the lateral feeding of fibers, in the exemplary embodiment, into the processing plant 40 for the production of fiber-reinforced plastics. The screw conveyor 30 has a housing 70 with at least one housing bore 76, at least one screw shaft 80 arranged concentrically in the at least one housing bore 76 and driven about an associated axis of rotation, and a feed opening 72 for feeding the fibers into the at least one housing bore 76.
[0063] The feeding device 20 comprises a suction device (not shown) for drawing the cut fibers through the feeding opening 72 into the at least one housing bore 76 by means of a flow, such as an airflow, with a predetermined or predeterminable flow rate or air delivery rate. A filter device 10 with at least one filter element arranged in and transverse to the flow in a wall 51 for filtering fibers from the flow can be arranged for the feeding device 20 between the suction device and the at least one housing bore 76. Alternatively or additionally to the suction device, a blowing device can also be provided.
[0064] The flow is usually an airflow or another gaseous flow, which may also contain air. In principle, however, any fluid capable of flowing can be used to generate the flow.
[0065] The filter device 10 has at least one filter plate 52 as a filter element, as shown in Fig.
[0066] Figure 7 shows that, in the operating state, the filter plate is preferably arranged in a housing recess 74 connected to the at least one housing bore 76 and preferably has a curvature 90 corresponding to the shape of the at least one housing bore 76. The filter plate is a planar element, the surface having any shape, including three-dimensional shapes, here in the shape of the curvature 90.
[0067] The at least one filter plate 52 with curvature 90 has at least one area 64 which in the exemplary embodiment is essentially rectangular with several parallel, slit-shaped flow channels 58 extending transversely to the at least one housing bore 76.
[0068] In principle, the area can have any other shape. Instead of rectangular, it can be round, oval, or even polygonal, for example. Likewise, the slit-shaped flow channels 58 do not have to be arranged parallel to each other, provided that a suitable geometry ensures laminar flow through the filter plate 52. For example, concentric slit-shaped and / or annular or semi-annular flow channels are conceivable. In principle, the filter plate 52 does not have to have symmetrical properties, even though symmetry can offer advantages during maintenance and replacement of the filter plate. In the operating state, at least one flow channel 58 exhibits a Reynolds number Re below a critical Rec at a predetermined or predeterminable flow rate. kriton and is thus designed to form a laminar flow in and preferably before and after the flow channel 58 and a homogeneous and uniform pressure distribution in the area 64.
[0069] Advantageously, to increase the stability of the filter assembly 10 and to simplify maintenance, the filter assembly 10 has a frame 50 or a receptacle, as shown by way of example in Fig. 5, on which the at least one filter plate 52 is replaceably mounted, wherein the frame 50 has at least one curvature 90 corresponding to the curvature 90 of the at least one filter plate 52, on which the at least one filter plate 52 is mounted. The frame 50 can be designed such that either only one or more filter plates 52 can be accommodated.
[0070] The terms frame and mount are generally used synonymously and without restriction. They are suitable for holding the filter plates 52 in the filter assembly 10. In the following, the term "frame" will be used in this sense.
[0071] Preferably, the filter plate 52 is designed with a closed comb 53 to increase its stability, wherein the slit-shaped flow channels 58 included therein each have a constant flow cross-section and a predetermined ratio of length l to width b in order to influence the Reynolds number Re.
[0072] The wall 51, in which the filter plate 52 or filter device 10 is arranged, is preferably a cylindrical wall of the at least one housing bore 76 with an inner radius of a cylinder for receiving a conveying medium with a cylindrical cross-section, such as the screw shaft 80. It is designed and arranged so that it, and thus the filter element arranged within it, is preferably swept over by the conveying medium without contact during the removal of the filtered fibers. To accommodate the filter element in the wall 51, the filter plate 52 is pre-curved accordingly. Preferably, the radius of the curvature 90 of the filter plate 52 in its uninstalled state is larger than the inner radius of the wall 51.
[0073] The flow channels have the effect of several parallel Venturi nozzles. Preferably, in the operating state, at a predetermined or predeterminable flow rate in a flow direction 110, and at a resulting Rey-Nolds number Re with a value below a predetermined critical range of the Rey-Nolds number in which the flow can become turbulent, they generate a pressure drop Ap in a predetermined range. This results in laminar flows in the flow channels 58, which produce a homogeneous and uniform pressure distribution in the at least one area 64 of the at least one filter plate 52, which is designed as a closed comb 53.
[0074] Before discussing the invention in more detail, the physical relationship between the Reynolds number Re of the flow channels 58 and the gap width of the flow channels 58 of the filter device according to the invention will first be explained.
[0075] The pressure drop Ap in a flow channel is proportional to the volume flow rate V squared, with the flow resistance R as the proportionality factor:
[0076] Ap = R ■ V 2 (1)
[0077] The pressure drop Ap can also be defined via the resistance coefficient.
[0078] p Q
[0079] Ap = ( - v, with < = const.
[0080]
[0081] (2)
[0082] Substituting expression (2) into (1) yields the flow resistance R:
[0083] R • V 2 = l • - • v 2 and with V = v • A
[0084] 2
[0085] (3)
[0086]
[0087] R =
[0088] The total flow resistance value R Ges is less than the parallel individual resistances R sThe total resistance decreases with each additional flow channel. At a constant volume flow rate V, the pressure drop Ap at the filter device is reduced (see equation (1)).
[0089] The total flow resistance value R Ges is calculated from the individual resistance values R s according to the following relationship, where x and n represent the number of columns:
[0090] p — 1 _ R s Ges 1 (4) v M 2
[0091]
[0092] The homogeneous, uniform pressure distribution in area 64 leads to the following approach:
[0093] Ap s = Pces with (1) implies R s • s 2 = R Ges • V Ges 2 , cf. (3) at = const. From this it follows with (4):
[0094] > or R s ■ > R S ■ A =, \ ■ A. A ö Vs ö = R s ö ■ ( X.n )2 • V G Cr e Ss i 2 (5)
[0095]
[0096] From (5) the relationship of the volume flow follows, in accordance with the continuity equation (6):
[0097] Total
[0098] A
[0099]
[0100] = xn
[0101] The continuity equation is used for an incompressible flow:
[0102] V = const. (6) At the flow velocity v s at the gap:
[0103] > Vs > V(j es > V Suction device
[0104]
[0105] S As A Total A Total
[0106] From (2) the continuity equation (6) is used to calculate the slit width b:
[0107] > > Zf Zf / V Äk IV v LZ > 7 IP' ^Tot 2 Ö = H- 2 — (7)
[0108]
[0109] v 24p (xnl) 2
[0110] To establish a relationship between the gap width b and the flow behavior, the Reynolds number Re is used as a key figure:
[0111] “v<- • dh p -v - dh
[0112] Re = - — - = s h (8)
[0113] V 7]
[0114] With the hydraulic diameter d h as characteristic length:
[0115] 4 A s > 4 -l -b
[0116]
[0117] U s ~ 2 -(l+b) '
[0118] where:
[0119] “ V Ges es Re~v s ~ V s and V s ~ V Ges V. = - (10)
[0120]
[0121] A Ges xnlb
[0122] From (8), (9) and (10) the Reynolds number is:
[0123] Re — — • ^ Ges . 4 ' l ' b _ 2 p-Vges
[0124] (11)
[0125]
[0126] T] (xnlb) 2 (Z+ö) p - x - n (l+b)
[0127] Solving for the total volume flow rate yields: • > Re ■ r x- n (l+b) ''Ges —
[0128]
[0129] (12)
[0130] 2p
[0131] Substituting the total volume flow rate from (12) into the equation (7) for the width yields the following relationship for the width of the flow channels:
[0132] , Re - ri ■ i J7, 1 b =, — - 1= — > b = -. — (1 l ^8 ■ p ■ Ap - Re ■ T)y / ( i |s ■ p- 4p _ i
[0133]
[0134] Re • T) ( l
[0135] The symbols in the formula have the following meaning:
[0136] A Flow cross-sectional area
[0137] b: Width of the flow channel
[0138] d h characteristic length, hydraulic diameter
[0139] V. Length of the flow channel
[0140] Number of flow channels: 58 of the essentially rectangular area 64 Ap: pressure drop
[0141] R Flow resistance
[0142] Re Reynolds number
[0143] G: fluid-wetted circumference
[0144] v speed
[0145] 7: Volume flow
[0146] x: Number of essentially rectangular areas 64
[0147] : Pressure loss coefficient, resistance coefficient
[0148] p: dynamic viscosity
[0149] v: kinematic viscosity
[0150] p density
[0151] The following indices are sometimes used for the formula symbols:
[0152] S Flow channel
[0153] Total: Sum of all flow channels
[0154] In summary, the key formulas are:
[0155] 1 b — 1 8 • p - 4p 1 (13) Re • r] -J £ l 2 P'^Tot
[0156] (11)
[0157]
[0158] p ■ x ■ n (l+b) _ I ^ p- VTot 2 -J 2 A (7)
[0159]
[0160] p (xnZ) 2
[0161] This leads to the following conclusions:
[0162] • When the flow rate V is increased Ges (Suction capacity) and thus an increase in Re, the pressure drop Ap increases with the same filter plate 52, i.e. with the same flow channel width b. [see: (11), (13)]
[0163] • Conversely, if the same optimal pressure drop Ap at filter plate 52 is to be achieved, then an increase in the extraction power V is necessary. Ges (by control, software) and thus the Reynolds number Re a different filter plate 52 with an increased flow channel width b can be used, [see: (13)]
[0164] • Another way to operate with a constant pressure drop Ap at the filter plate 52 at optimum would be to keep the Reynolds number Re constant by using a filter plate 52 with a higher number n of flow channels, [see: (11)]
[0165] • To increase the pressure drop Ap at the filter plate 52, a filter plate 52 with a reduced flow channel width b is required at a constant Reynolds number Re. [see (13)]
[0166] • Note: The Reynolds number Re represents the velocity v s and therefore also the volume flow rate V Ges included. About the hydraulic diameter d h The flow channel width b is also included, with minimal effect due to the large ratio of flow channel length l to flow channel width b. [see (11)]
[0167] The inventive effect of the at least one filter plate 52 is achieved by a constant flow cross-section of the flow channels 58 with a predetermined, in particular large, ratio of length l to width b, which generate the effect of several parallel Venturi nozzles. With a predetermined, i.e., constant, flow rate and the predetermined width b, a Reynolds number Re is achieved as a parameter that generates an optimal pressure drop Ap.
[0168] The curved curve in Fig. 10 represents a Reynolds number Re as a parameter in a diagram that indicates the dependence of a pressure drop Ap on a width b of the flow channels. To the left of the curve is a region 125 with laminar flow, and to the right of the curve is a region 126 with turbulent flow. The laminar region 125 shows a minimum ("min.") and a maximum ("max.") possible value for the pressure drop Ap at which a filter device according to the invention operates substantially reliably. Also shown is an optimal range of pressure drop Ap, located between the marks marked "opt." The filter device according to the invention operates most effectively in this range.
[0169] Figure 11 illustrates the relationship between the width b of the flow channels and a Reynolds number Re, using various values of a pressure drop Ap as a parameter. The reference number 120 refers to a pressure above a critical Reynolds number Re. kritThe reference numeral 121 indicates the maximum permissible Reynolds number Re. Reference numeral 122 denotes a minimum possible pressure drop Ap, and reference numeral 124 a maximum possible pressure drop Ap at which the filter 10 still operates reliably. Reference numeral 123 denotes an optimal pressure drop Ap, preferably around 50 mbar, at which the filter 10 operates most effectively. Values between the minimum and maximum possible pressure drops, ideally within the optimal range, ensure that the Reynolds number Re remains within a range where laminar flow is still established. Conversely, if the pressure drop becomes too large for a given gap width, the flow enters the turbulent range.
[0170] A stable fixing of the at least one filter plate 52 and a simple exchange or rotation of the at least one filter plate 52 can be easily made possible by the fact that the at least one filter plate 52 has leaf spring-like properties and is pre-tensioned with its outer edges, which preferably run along a longer side 66 of the filter plate 52, but can also run along a shorter side, being received in grooves 62 of the frame in a form-fitting and force-fitting manner.
[0171] For the efficiency of the feeding device 20 and a more uniform distribution of the fibers in the plastic, it is advantageous if the filter device 10 has several adjacent filter plates 52 with bulges 90, which are mounted on several corresponding bulges 90 of the frame. In the operating state, when using a multi-shaft screw machine 30 with several adjacent, intersecting housing bores 76 of the housing 70, each with a screw shaft 80 arranged therein, these can be arranged in a housing recess 74 connected to the housing bores 76.In this case, the frame 50 has at least one central web 60 with grooves 62 between the filter plates 52, into which an outer edge 66 of one of the several adjacent filter plates 52, which runs along a preferably longer side 66 of the filter plate 52, is engaged in a form-fit and / or force-fit manner, preferably both form-fit and force-fit. This is illustrated by way of example in Figures 4 and 5.
[0172] Replacing or rotating the at least one filter plate 52 is easily accomplished because the at least one filter plate 52 has symmetrical properties and is designed to allow installation in the frame 50 rotated by 180°. The frame 50 and the at least one filter plate 52 are designed to allow replacement or rotation of the at least one filter plate 52 by means of a sliding removal of the at least one filter plate 52 from the grooves 62 of the frame 50. This reversal increases the service life of the filter plate 52. While in the prior art, the orientation during installation is relevant for filter packages consisting of spacer plates / lamellae due to the one-sided cross-sectional change in the flow channel, the design of the filter plate 52 and its mounting now ensures reliable installation.
[0173] The symmetry of the mounted filter assembly 10 also allows for a 180° rotation of the filter assembly. This simultaneously prevents errors during assembly (Poka-Yoke, meaning "avoiding unfortunate errors," refers to a principle consisting of several elements that includes technical precautions or devices for the immediate detection and prevention of errors). While in the prior art, the orientation during installation of the filter assembly consisting of spacer plates / lamellae is relevant due to the one-sided cross-sectional change in the flow channel, the design of the filter plate 52 and its mounting now ensures error-free installation reliability.
[0174] A particularly stable fixing of the at least one filter plate 52 and a simple replacement or rotation of the at least one filter plate 52 can be advantageously achieved, as shown in Fig. 6, by securing the at least one filter plate 52 on the frame 50 with two locking plates 54, which are arranged at the front of the frame 50 and are preferably detachably attached to it by means of screws 56, against displacement in the grooves 62.
[0175] The stability of the at least one filter plate 52 with respect to its vibration behavior and its deflection strength can be improved by the at least one filter plate 52 preferably having several, in the exemplary embodiment two, e.g. essentially rectangular, separated areas 64 with several slit-shaped flow channels 58 extending transversely to the at least one housing bore. This is shown by way of example in Fig. 7. Between the essentially rectangular separated areas 64, the at least one filter plate 52 can be arranged on at least one crossbar 92 of the frame 50, which supports the at least one filter plate. This gives the at least one filter plate 52 additional stability. Figs. 5 and 6 show the crossbars 92.
[0176] In one embodiment of the filter device 10, or of the method for operating a filter device 10, particularly good results with regard to maintenance behavior can be achieved by designing the flow channels 58 to generate a pressure drop Ap in the range of approximately 50 mbar. This corresponds approximately to the optimal range (line 123) in Fig. 11. Values up to the minimum values (line 122) and maximum values (line 124) specified therein are still possible. This effectively prevents clogging of the filter device 10. However, if this range is exceeded, i.e., if the pressure drop becomes too large for a given gap width, the system enters the turbulent range, which promotes fiber accumulation and clogging.
[0177] The vibration behavior and the deflection strength of the at least one filter plate 52 and the quality of the laminar flow in the flow channels 58 can be improved by the filter plate 52 having a thickness between 0.5mm and 2mm.
[0178] Preferably, the frame 50 is designed downstream of the filter plate 52 and following the filter plate as shown in Fig. 5, such that it has at least one chamber 49 with a cross-section that preferably remains constant in the flow direction. Preferably, the cross-section can also be matched to the cross-section of the filter plate 52 through which the flow passes. This helps to maintain homogeneous pressure conditions even after the flow has passed through the filter plate, which is beneficial for maintaining laminar flow. However, a different cross-sectional design is also possible from a fluid dynamics perspective. For example, the cross-section can also widen continuously to form an airflow amplifier. The effectiveness of the filter device 10 can be further improved if the frame 50 is arranged in the housing recess 74 in a substantially airtight or flow-tight manner.This avoids unwanted turbulence in the filter unit 10.
[0179] According to the invention, the filter device 10 is operated by a method for filtering fibers from a flow, such as an airflow, for a feeding device 20 for supplying the fibers in the production of fiber-reinforced plastics. The feeding device 20 comprises a screw conveyor 30 for laterally feeding fibers into a processing plant 40 for the production of fiber-reinforced plastics. The screw conveyor 30 has a housing 70 with at least one housing bore 76, a screw shaft 80 arranged concentrically in the at least one housing bore 76 and driven about an associated axis of rotation, and a feed opening 72 for feeding the fibers into the at least one housing bore 76.The feeding device 20 also includes a suction device for sucking the fibers through the feeding opening 72 into the at least one housing bore 76 by means of the flow with a predetermined flow rate, wherein the filter device 10 can be arranged between the suction device and the at least one housing bore 76.
[0180] The filter device 10 comprises at least one filter plate 52, which, in the operating state, can be arranged in a housing recess 74 connected to the at least one housing bore 76 and has a curvature 90 along the at least one housing bore 76 corresponding to its shape. The at least one filter plate 52 has at least one area 64 with several parallel, slit-shaped flow channels 58 extending transversely to the at least one housing bore 76, each with a constant flow cross-section and a predetermined, in particular large, ratio of length l to width b, which generate the effect of several parallel Venturi nozzles, each of which, in the operating state, at the predetermined flow rate in a flow direction 110 and a resulting Reynolds number Re with a value below a predetermined critical range, generates a pressure drop Δp in a predetermined range.This creates laminar flows in the flow channels 58, which generate a homogeneous and uniform pressure distribution in the at least one substantially rectangular area 64 of the at least one filter plate 52.
[0181] The method for operating a filter device 10 enables secure fixing of the at least one filter plate 52 while still allowing for easy replacement or rotation of the filter plate 52, by providing the filter device 10 with a frame 50 on which the at least one filter plate 52 is replaceably mounted. The frame 50 has at least one curvature 90 corresponding to the curvature 90 of the at least one filter plate 52, on which the at least one filter plate 52 is mounted.
[0182] The at least one filter plate 52 has leaf spring-like properties and is pre-tensioned with its outer edges 66, which extend along a preferably longer side of the filter plate 52, being positively and / or frictionally engaged in grooves 62 of the frame 50, preferably both positively and frictionally. The at least one filter plate 52 can also be replaced without tools by sliding it in the grooves 62 of the frame 50 using another filter plate 52 identical to the at least one filter plate 52, which engages it at a shorter side 68 of the at least one filter plate 52. Figure 8 illustrates the procedure for replacing or rotating a filter plate 52. The filter plate 52 located in the frame 50 is pushed out of the grooves 62 of the frame 50 to the right by the filter plate 52 shown on the left in the figure and can then take its place.The filter plate 52, once extended, can also be rotated 180° around an axis of rotation perpendicular to its surface and reinserted. This effectively increases the service life of the filter plate 52 and saves costs.
[0183] Figures 9a to 9c show a sectional view of how, for example, a filter plate 52 can be replaced during operation. As shown in Figures 9a and 9b, the filter assembly 10 is moved downwards into a replacement position within the housing recess 74. The housing 70 serves as an axial detent and thus acts as a locking plate (stop). In the replacement position, as shown in Figures 9a to 9c, a pocket 94 with a radius corresponding to the curvature 90 is provided in the housing 70 as an inlet and outlet for the filter plates 52. In the replacement position, the filter plate 52 can be removed as shown in Figures 9a to 9c.
[0184] As shown in Fig. 9c, the filter assembly 10 is replaced according to the description above for Fig. 8. Then, as shown in Figs. 9b and 9c, the filter assembly 10 is moved back up into the working position in the housing recess 74, as shown in Fig. 9a.
[0185] To remove fiber dust and excessively short fibers, an airflow amplifier can also be provided downstream of the filter unit 10. For this purpose, the air in the housing 70 upstream of the filter unit 10 and / or additional compressed air can be used. If air is supplied through special openings (bores) for compressed air on the underside of the filter unit 10 at a preferably shallow angle, with a cross-section that increases as the opening widens, an increased volume flow is achieved. A compressed air connection can be connected to the bores via distribution lines corresponding to a "multi-jet nozzle". This can also be done in combination with ionized air and can also represent an alternative to an extraction system.
[0186] During the execution of the process, electrostatic charging of the fibers used can be prevented by using an ionized airflow. In particular, this prevents the fibers from adhering to parts of the feeding device, resulting in a more uniform distribution of the fibers during transport and thus also within the plastic of the product being manufactured.
[0187] It goes without saying that this description may be subject to various modifications, changes, and adaptations, which are equivalent to the attached claims. Reference numeral list
[0188] 10 filter unit, 76 housing bore,
[0189] 20 Feeding device, 80 Worm shaft,
[0190] 30 screw machine, 90 curvature,
[0191] 40 Processing plant, 92 Crossbeam,
[0192] 49 room, 94 pocket (Fig. 9a -9c),
[0193] 50 Frame, 100 Fiber shredding device, 51 Wall, 110 Flow direction,
[0194] 52 Filter plate, 120 Range of critical Reynolds numbers 53 Comb, 121 Critical Reynolds number Re krit , 54 fuse plate, 122 Δp = min.,
[0195] 56 screw, 123 Δp = opt.,
[0196] 57 Outer edge, 124 Δp = max.,
[0197] 58 flow channel, 125 laminar area,
[0198] 60 central jetty, 126 turbulent area,
[0199] 62 groove, 140 non-movable mold carrier, 64 area, 150 machine stand,
[0200] 66 longer side of the filter plate, 160 injection molding unit,
[0201] 68 shorter side of the filter plate, 170 plasticizing device,
[0202] 70 housings, 175 plasticizing cylinders,
[0203] 72 feed openings, 190 conveying resources.
[0204] 74 Housing recess,
Claims
Patent claims 1. Filter device (10) for filtering fibers from a flow, in particular from an airflow, configured for supplying the fibers in the production of fiber-reinforced plastics, with at least one filter element arranged in and transverse to the flow in a wall (51), characterized in that at least one filter plate (52) with a curvature (90) is provided as a filter element, which has at least one area (64) with several slit-shaped flow channels (58) which, in the operating state at a predetermined or predeterminable flow rate, has a Reynolds number (Re) with a value below a critical Reynolds number (Re) krit) exhibit and are thereby designed to form a laminar flow in the flow channels (58) and a homogeneous and uniform pressure distribution in the at least one area (64), wherein the filter device (10) has a frame (50) or a receptacle which has at least one curvature (90) corresponding to the curvature of the wall (51), on which the at least one filter plate (52) is replaceably mounted.
2. Filter device according to claim 1, characterized in that the filter plate (52) has a closed comb (53) and that the slit-shaped flow channels (58) are several parallel extending slit-shaped flow channels (58) each with a constant flow cross-section and a predetermined ratio of length ( / ) to width (b).
3. Filter device according to claim 1 or 2, characterized in that the wall (51) is a cylindrical wall of at least one housing bore (76) with an inner radius for receiving a conveying means with a cylindrical cross-section, such as a screw shaft (80) of a feeding device (20) for feeding the fibers into a processing plant (40), and is arranged to be preferably swept over by the conveying means arranged in the at least one housing bore (76) during the removal of the filtered fibers without contact, and that the filter element is pre-curved and has a curvature (90) corresponding to the shape of the at least one housing bore (76).
4. Filter device according to one of the preceding claims, characterized in that a radius of the curvature (90) of the filter plate (52) in the uninstalled state is larger than the inner radius of the wall (51).
5. Filter device (10) according to one of claims 3 or 4, characterized in that in the operating state the frame (50) is arranged in a housing recess (74) connected to the at least one housing bore (76).
6. Filter device (10) according to one of the preceding claims, characterized in that the at least one filter plate (52) has leaf spring-like properties and is pre-tensioned with its outer edges (57), which run along a preferably longer side (66) of the filter plate (52), in grooves (62) of the frame (50) in a form-fitting and / or force-fitting manner.
7. Filter device (10) according to one of claims 3 to 6, characterized in that the filter device (10) has several filter plates (52) arranged side by side with bulges (90) which are mounted on several corresponding bulges (90) of the frame (50) and which, in the operating state when using a multi-shaft screw machine (30) with several adjacent interpenetrating housing bores (76) with a screw shaft (80) arranged therein, can be arranged and that the frame (50) has at least one central web (60) with grooves (62) between the filter plates (52) which are configured to receive outer edges (57) of the filter plates (52) in a form-fitting and / or force-fitting manner.
8. Filter device (10) according to one of the preceding claims, characterized in that the at least one filter plate (52) has symmetrical properties and is thereby configured to allow installation rotated by 180° in the frame (50), and that the frame (50) and the at least one filter plate (52) are configured to allow replacement or rotation of the at least one filter plate (52) by means of a sliding removal mechanism.
9. Filter device (10) according to one of claims 5 to 8, characterized in that the filter device (10) has symmetrical properties and is therefore designed to be installed in the housing recess (74) rotated by 180°.
10. Filter device (10) according to one of claims 6 to 9, characterized in that the at least one filter plate (52) on the frame (50) is secured against displacement in the grooves (62) by two locking plates (54) which are arranged at the front of the frame (50) and are detachably attached thereto.
11. Filter device (10) according to one of the preceding claims, characterized in that the at least one filter plate (52) has several substantially rectangular separated areas (64) arranged along a preferably longer side of the filter plate (52) with several slit-shaped flow channels (58).
12. Filter device (10) according to one of the preceding claims, characterized in that the flow channels (58) are configured to generate a pressure drop (Δp) in a range around 50 mbar.
13. Filter device (10) according to one of the preceding claims, characterized in that the at least one filter plate (52) has a thickness between 0.5 mm and 2 mm.
14. Filter device (10) according to one of the preceding claims, characterized in that the frame (50) has at least one space (49) with a cross-section that remains constant in the direction of flow downstream of the filter plate (52) and following the filter plate (52).
15. Filter device (10) according to one of claims 5 to 14, characterized in that the frame (50) is arranged in the housing recess (74) in a substantially airtight or flow-tight manner.
16. Feeding device (20) for feeding fibers in the production of fiber-reinforced plastics, comprising at least one screw machine (30) for feeding fibers into a processing plant (40) with a housing (70) having at least one housing bore (76), a screw shaft (80) arranged concentrically in the at least one housing bore (76) and driven about an associated axis of rotation, and a feed opening (72) for feeding the fibers into the at least one housing bore (76), wherein the feeding device (20) has a suction device for drawing the fibers through the feed opening (72) into the at least one housing bore (76) by means of a flow, in particular an airflow, with a predetermined flow rate, and with a filter device (10) arranged between the suction device and the at least one housing bore (76) for filtering the fibers out of the flow. characterized by a filter device (10) according to one of the preceding claims.
17. Method for operating a filter device (10) for filtering fibers from a flow, in particular from an air flow, for supplying the fibers in the production of fiber-reinforced plastics, with at least one filter element arranged in and transverse to the flow in a wall (51), characterized in that at least one filter plate (52) with a curvature (90) is used as a filter element, which has at least one area (64) with several slit-shaped flow channels (58) which, in the operating state at a predetermined or predeterminable flow rate, has a Reynolds number (Re) with a value below a critical Reynolds number (Re). krit ) generate a laminar flow in the flow channels (58) and a homogeneous and uniform pressure distribution in the area (64).
18. Method according to claim 17, characterized in that the flow channels (58) generate a pressure drop (Δp) in a range of around 50 mbar.
19. Method according to claim 17 or 18, characterized in that the at least one filter plate (52) is mounted interchangeably on a curvature of a frame (50), wherein the curvature of the frame corresponds approximately to the curvature (90) of the at least one filter plate (52), and that the at least one filter plate (52) is received in a leaf spring-like and pre-tensioned manner with its outer edges (66) in grooves (62) of the frame (50) in a form-fitting and / or force-fitting manner, and that the at least one filter plate (52) can be replaced without tools by sliding it in the grooves (62) by means of a further filter plate (52) identical to the at least one filter plate (52), which engages on a side (68) of the at least one filter plate (52).
20. Method according to one of claims 17 to 19, characterized in that an ionized airflow is used as the flow.