Extruder for processing polymer materials

Abstract

The invention relates to an extruder or multi-screw extruder (1) for processing and melting polymeric materials, comprising at least two screws (3a, 3b,...) which can rotate in a common housing (2), in particular a twin-screw extruder (1), and having: a feed region (A) for introducing the material to be processed into the extruder (1), and an extrusion region (C) located further downstream for melting the material, wherein: the housing (2) has, in the feed region (A), at least one feed opening (4) which is formed in the lateral wall thereof and is intended for introducing the material to be processed into the active region of the screws (3a, 3b,...); in the extrusion region (C), a narrow screw gap (7) is formed between the outer diameters of the screws (3a, 3b,...) and the inner wall (8) of the housing (2) and is essentially constant all the way to the screw outlet; the housing (2) has, in the feed region (A) or in a region around the feed opening (4), a pocket (5) which extends over a longitudinal portion of the extruder (1) along the screws (3a, 3b,...); the pocket (5) has, in its entire longitudinal extent and between the outer diameters of the screws (3a, 3b,...) and the inner wall (8) of the housing (2), a screw gap (7') which is wider as compared to the screw gap (7) in the extrusion region (C).

Description

[0001] Extruder for processing polymer materials

[0002] The invention relates to an extruder or multi-screw extruder for processing and melting polymeric materials according to the preamble of claim 1. The invention further relates to a device according to claim 15, comprising such an extruder which is connected to a container or a preconditioning unit (PCU) for processing or preparing polymer materials, in particular thermoplastic waste plastic for recycling purposes.

[0003] Single-screw extruders and multi-screw extruders for processing and melting polymer materials are well known in a wide variety of designs.

[0004] Also well known are devices comprising a combination of a container, cutter / compactor or preconditioning unit (PCU), and a connected extruder for the pretreatment and processing of polymer waste, especially of various thermoplastics. These are usually containers with rotating tools directly coupled to the extruder. The mixing and comminution tools rotating in the container or PCU also support the filling or feeding process of the connected extruder. This processing step in the PCU, which precedes the extrusion process, also has the task, among other things, of modifying the shape and properties of the polymer materials accordingly.In the pretreatment unit, the thermoplastic materials are mixed, heated, softened, compacted, pre-degassed, dried, dehumidified, cut, crushed, crystallized, and / or homogenized, among other processes, and their bulk density is increased. However, the materials are not yet melted there. The polymers pretreated in this way are then introduced into the extruder to be compacted, in particular melted. Such combination devices have long been known, for example, from EP 2 558 263 or EP 2 689 908.

[0005] The extrusion process is generally most efficient when the screw fill level is consistent and sufficiently high. The extruder feeding process is therefore sensitive and has a significant influence on the final result and the quality of the recyclates. Poor extruder feed behavior can, for example, lead to pumping of the volumetric throughput, i.e., a change in throughput over time, which is detrimental to reliable operation and the quality of the recyclates. Therefore, there has been no shortage of attempts in the state of the art to improve the feed behavior and feeding of extruders.

[0006] When processing thermoplastics, especially in the recycling of industrial or post-consumer waste, materials are often processed whose original form, e.g., films, bottles, lead frames, cups, fibers, nonwovens, textiles, etc., is converted into a transportable form through preprocessing, shredding, or washing. Single-screw extruders, i.e., extruders with only a single rotating screw, are frequently used for processing such materials.

[0007] However, multi-screw extruders, especially twin-screw extruders, are often advantageous for processing such materials. This is especially true when refining or special purification steps are required on the polymer. Twin-screw or multi-screw extruders are therefore particularly advantageous for achieving special material qualities and for compounding these materials.

[0008] In twin-screw extruders, two screws rotate side by side in a cylinder or bore with a roughly oval cross-section, either in the same or opposite directions of rotation. The material to be processed is fed through the extruder's inlet, then melted under pressure and material compaction, and conveyed downstream in the cylinder. The melt is then fed to a die or extruded from the extruder.

[0009] In co-rotating twin-screw extruders, two parallel cylindrical or two conical screws rotate next to each other in a cylinder or barrel with the same direction of rotation and speed. The transport processes or the conveying principle in the screw elements of a co-rotating twin-screw extruder are based on the so-called drag conveying principle or on the transfer of the material to be conveyed from one screw to the other in the engagement area of ​​the screws. Accordingly, twin-screw extruders, unlike single-screw extruders, are regularly operated only partially filled. This results in a certain amount of forced conveying on the one hand, and a good mixing effect through rearrangement and surface renewal on the other, and a homogeneous melt with the necessary temperature and pressure is conveyed into the downstream tool. In counter-rotating twin-screw extruders, two cylindrical orparallel or two conical screws rotating in opposite directions. The clearance between the screws is usually somewhat tight, and the tendency to wear is correspondingly higher. Counter-rotating twin-screw extruders are also generally operated partially filled, among other things to avoid excessive pressure buildup and the associated material wear on the screws and barrel.

[0010] Multi-screw extrusion systems are typically fed gravimetrically, sometimes volumetrically, to keep the fill level of the extrusion system largely constant. This consistently results in a partially filled screw in the feed zone of multi-screw extruders. A single-screw extruder, on the other hand, is generally capable of producing largely constant fill levels along the screw from a "full hopper," i.e., with a fully filled screw in the feed zone.

[0011] As previously explained, the material drawn into the extruder is transported immediately downstream in the extruder, resulting in a torque curve of the extruder drive that depends on the fill level. Generally, the attempt is made to keep the extruder's torque curve or the fill level of the partially filled extruder, which is usually defined in kg / revolution, as constant as possible. This results in high-quality melting of the polymers without shear peaks that can lead to excessive temperature rise in the polymer melt. Overfeeding the extruder, i.e., an insufficient fill level, can lead to throughput losses and shear peaks, but can also result in poorly homogenized polymers. Keeping the extruder fill level constant is therefore beneficial for the quality of the recyclates and for economic efficiency.

[0012] Despite all efforts and the provision of measures, it is possible that, for example, the bulk density variations cannot be sufficiently compensated over time.

[0013] Against this background, the idea arises to adapt the extruder itself, or especially the critical area of ​​the feeding or intake of the extruder, in such a way that the intake behavior and feeding of the screw are supported.

[0014] It is therefore an object of the present invention to provide an extruder of the type mentioned at the outset with which the filling level of the extruder can be kept as constant as possible or with which the feed behavior and the feeding of the screw are supported in the best possible way and, for example, is also more tolerant to operational material differences and influences.

[0015] This problem is solved by the features of claim 1.

[0016] Accordingly, an extruder or multi-screw extruder for processing and melting polymeric materials is provided, comprising at least two rotatable screws arranged side by side in a common housing. In particular, a twin-screw extruder with exactly two screws is provided.

[0017] In its typical basic design, this extruder has an upstream feed area in which the material to be processed is introduced into the extruder, and an extrusion area further downstream in the material feed direction in which the material is melted.

[0018] Accordingly, the housing of the extruder has at least one intake opening formed in its casing wall in the intake area for introducing the material to be processed into the capture area of ​​the screws.

[0019] In the downstream extrusion area, there is a screw gap that is essentially constant and small or narrow, surrounding the screws circumferentially or on all sides, between the outer diameters or the envelopes of the screws and the inner wall of the barrel, i.e. over or along the longitudinal course of the extrusion area up to the screw outlet.

[0020] In this context, "constant" means that the screw gap does not change significantly throughout the extrusion range, i.e., up to the screw exit, and remains essentially constant. In extruders with cylindrical screws, the extrusion range therefore corresponds to the parallel part of the extruder.

[0021] In this context, “narrow” means a small distance to the inner wall in relation to the screw diameter, usually a distance of only a few 1 / 10 mm to the cylinder or a distance of less than 1 mm when new.

[0022] However, the screw gap does not have to be identical, constant, and narrow at every single point or in every section of the extrusion area; rather, this must be seen across the entire length of the extrusion area. Deviations in small sections or section-by-section changes or enlargements of the screw gap in specific areas, for example in the degassing area or in the area of ​​additional inlet openings, are not relevant; in spite of such deviations, a constant and narrow screw gap is still present throughout the entire extrusion area. In particular, in areas of any additional feed, where melt is already present, but also in areas where melt is degassed, larger screw gaps can occur in sections between the barrel and the screw. In all of these areas, there is already melt or molten material in the extrusion area.melted material is present, in contrast to the area of ​​the pocket described below, where no melting has yet taken place.

[0023] According to the invention, the barrel further comprises, or is designed as, a pocket in the feed area or in an area near the feed opening, which extends along the screws over a partial longitudinal section of the extruder. This pocket has, along its entire longitudinal extent, a screw gap between the outer diameters of the screws and the inner wall of the barrel, which is larger than the screw gap in the extrusion area. The end of the pocket is accordingly located at the transition into the extrusion area, from which point the screws are only spaced from the inner wall by the constant, narrow screw gap. The pocket thus advantageously extends to the point from which the screw gap remains constantly small up to the screw outlet or, in extruders with cylindrical screws, to the parallel part of the extruder.Accordingly, the circumferential screw gap is larger in the pocket area than in the downstream extrusion area, where the screw gap is constantly small.

[0024] Accordingly, the diameter of the intake area in the pocket is significantly larger than the outer diameter of the screws. This advantageously makes it possible to bring material, including light materials, into this space beyond the screw's fill volume, into the screw's sphere of influence, particularly for tamping, trickling, or conveying.

[0025] The enlargement of the feed area or the pocket or the enlarged screw gap can also be formed only in a circumferential partial area around the screws. However, the enlarged screw gap preferably exists over the entire circumference around the screws or over large parts or areas of the circumference of the screws. The pocket therefore preferably surrounds the screws on all sides. Approximately similar or uniform distances or screw gaps between the screws and the inner wall are preferable. The pocket and the enlarged screw gap or space there advantageously lead to more material being taken into the extruder than the screws could convey. By spacing the cylinder from the screw or the enlarged screw gap in the area of ​​the pocket, part of the material can be fed into the extruder in the event of overfilling of the screws - ieThe closely spaced section of the screws following the screw can no longer absorb the material, causing it to escape or even flow back. Such overfilling can occur, for example, due to a change in the material, such as a higher bulk density, a more free-flowing material, etc. The correspondingly expanded space of the pocket in the extruder's feed area thus also serves as a compensating element. This makes it possible to avoid both underfeeding and overfeeding of the extruder.

[0026] It is crucial that no significant melting processes occur in this area of ​​the pocket during operation, so that a certain degree of lumpiness of the material or particles remains. While partial softening may occur, the material must not be melted, and certainly not completely melted, as otherwise production would come to a standstill.

[0027] Such a multi-screw extruder, especially a twin-screw extruder, offers a number of advantages in this context. For example, it offers favorable feed characteristics and a higher throughput for a given screw diameter at a defined speed. Furthermore, it offers good conveying, short residence times, a narrow residence time range, good screw self-cleaning, good dispersing and homogenizing properties, flexible geometry design thanks to its modular design, and good process control.

[0028] The inventive design of the extruder allows its filling level to be kept very constant and the feeding behavior of the screw to be further improved with good throughput and stable throughput consistency, and also the quality of the final polymer materials to be further increased.

[0029] According to an advantageous embodiment, it is further provided that the longest or maximum length LE of the intake opening, measured parallel to the conveying direction or in the longitudinal direction of the axial longitudinal axes of the screws or parallel to these longitudinal axes, is in the range of 0.2 Da < LE < 15 Da.

[0030] "Da" is defined as the outer diameter of the screw closest to the intake opening, measured at the furthest downstream point of the intake opening in the conveying direction. This definition of Da also applies to all existing uses of Da.

[0031] According to a further advantageous embodiment, it is provided that the longest or maximum width BE or height of the feed opening, measured perpendicular to the conveying direction or perpendicular to the axial longitudinal axes of the screws, lies in the range of 0.1 Da < BE < 3 Da. The width is not measured along the curvature of the cylinder or the curved course of the opening, but as the clear width or height on a straight line directly between the opposite edges, i.e., it is the absolute width or height of the opening in side view or projected onto the central sectional plane of the extruder.

[0032] This refers to the longest or maximum dimension of the longitudinal or width extension of the intake opening. The exact shape of the intake opening is not determined or specified; it can be rectangular, square, round, or oval, for example. Corner-free intake openings, especially oval, elliptical, or circular, are preferred in terms of intake behavior.

[0033] In a particularly advantageous embodiment, as already described above, the pocket has an inner diameter that is larger than the screw gap in the extrusion area along its entire length. The inner diameter Ti of the pocket is defined and determined as follows:

[0034] The screws are arranged side by side, and the axial longitudinal axes of all screws define a common plane or lie in a common plane. This is particularly advantageous in embodiments in which exactly two identical cylindrical or conical screws are arranged symmetrically next to each other in the housing.

[0035] The inner diameter Ti of the pocket is then defined and measured as the length of a straight line perpendicular to this plane and intersecting the longitudinal axis of the screw closest to or adjacent to the intake opening between the opposing sections of the inner wall of the housing. Of these inner diameters Ti of the pocket thus determined, the inner diameter Ti with the greatest length is then determined and used.

[0036] This largest internal diameter Ti satisfies the condition Ti = k * Di, where: 1.7 < k < 9.6. "Di" is defined as the inner (core) diameter of the screw closest to the intake opening, measured, as is Da, at the point furthest downstream of the intake opening in the conveying direction. Local deviations in small partial areas of the circumference or changes or enlargements in certain sections, e.g. small spatial or circumferential bulges or channels in the housing or pocket are not relevant. If such structures are present, the imaginary extension of the line of the inner wall is essentially used to determine the internal diameter Ti of the pocket.

[0037] For parallel twin screws, the ratio between Da and Di is regularly specified by the manufacturers and is a performance characteristic for throughput, torque, etc.

[0038] In a further advantageous embodiment, the pocket has a length range LT, starting from the furthest downstream point of the intake opening in the conveying direction or in the longitudinal direction of the axial longitudinal axes of the screws, to the downstream end of the pocket. This length range LT lies in the range of 0.2 Da < LT < 10 Da.

[0039] The special design of the feed opening and the pocket allows the extruder's fill level to be kept extremely constant. The screw's feeding behavior is further improved, increasing throughput and throughput consistency. The extruder, and the entire system consisting of cutter-compactor and extruder, becomes significantly more stable and efficient. Furthermore, the quality of the resulting polymer materials can be further improved, increasing operating efficiency.

[0040] According to an advantageous embodiment, the length LE of the intake opening is in the range of 0.3 Da < LE < 10 Da. Furthermore, it is advantageously provided that the width (BE) of the intake opening (4) is in the range of 0.1 Da < BE < 2 Da. In this way, a particularly advantageous intake behavior is ensured.

[0041] According to an advantageous embodiment, it is provided that for screws with Da < 100 mm the following applies: 1.7 < k < 3 and / or that for screws with Da > 100 mm the following applies: 3 < k < 9. These values ​​offer favorable conditions for smaller or larger screw diameters.

[0042] According to a further advantageous embodiment, the length range LT of the pocket is in the range of 0.5 Da < LT < 6 Da. This allows for particularly advantageous processing of the material.

[0043] In the downstream section of the intake zone, a transition zone can advantageously be provided, which adapts the geometry of the pocket from the intake zone to the extrusion zone. This adaptation to the screw diameter can already begin in the intake zone. This means that downstream along the screw, the diameter of the pocket is smaller than upstream. This creates a shell, in particular a conical one, or the housing is tapered, e.g., conically, to enable easier flow of the materials in the extrusion direction. The design of such a transition zone, in particular a conical one, advantageously results in further compaction of the material.

[0044] In this context, it is advantageous if the length range LT of the pocket, starting from the furthest downstream point of the intake opening in the conveying direction or in the longitudinal direction of the axial longitudinal axes of the screws to the downstream end of the pocket, is designed to taper continuously or conically at a uniform angle at least in a partial section of > 50%, preferably > 70%, in particular > 80%, more preferably > 90% or > 95% of the length of the length range LT, preferably over substantially the entire length of the length range LT.

[0045] According to a further structurally advantageous embodiment, it is provided that the feed opening is formed laterally on the extruder and / or opens only into the detection area of ​​one of the screws, wherein it is provided in particular that the central longitudinal axis of the feed opening intersects the central longitudinal axes of the screws.

[0046] A particularly advantageous design is achieved when the extruder is configured as a twin-screw extruder with exactly two cylindrical screws aligned parallel to each other. Alternatively, but equally advantageous for corresponding applications, it is possible for the two screws to be conical.

[0047] The two screws are advantageously arranged symmetrically next to each other. In cylindrical screws, the longitudinal axes of the screws are aligned parallel to each other and to the longitudinal axis of the barrel. In conical screws, the longitudinal axes of the screws are aligned at an angle to each other. In both cases, a barrel longitudinal axis runs between the screws or the longitudinal axes of the screws.

[0048] Depending on the requirements, it is advantageous if the screws are designed as co-rotating or counter-rotating screws.

[0049] Furthermore, it is advantageous if the screws are designed as intermeshing or meshing screws, with the axial distance between the screws or the central longitudinal axes being smaller than the (outer) screw diameter Da over their entire length. Such designs generally result in, among other things, even further improved intake behavior, improved conveying, a narrower residence time range, and good process control.

[0050] According to a further advantageous design, a passive feed element, in particular a hopper, and / or an active feed element, in particular a stuffing screw, is provided for introducing the material to be processed into the extruder's intake opening. In particular, the active and / or passive feed elements are connected directly to the extruder. The feed elements also influence the feeding and bulk densities.

[0051] The materials to be processed can thus be fed into the extruder via a passive hopper, which is located either on the side of the extruder or on top. However, it has been shown that this is only sufficient for a limited number of materials. The materials would primarily need to have a certain flow properties, such as bottle regrind, but also agglomerates or granules.

[0052] The vast majority of materials, such as shredded film, shredded fiber, and even ground PET bottles, generally lack these free-flowing properties, or do so only to a sufficient degree. Therefore, active feeding systems that force the material into the extruder are advantageously used. For example, a stuffing screw with one or more screws can be provided and, for example, directly coupled to the extruder. While this also satisfactorily achieves sufficient compensation for the bulk density variations of the materials being processed over time, it is often only possible to a certain extent.

[0053] Even more advantageous is the upstream connection of a cutter-compactor or a PCU, which can regularly create a very good balance.

[0054] In this context, an advantageous device for processing or preparing polymer materials, in particular thermoplastic waste plastic for recycling purposes, is provided with at least one container or cutter-compactor for the material to be processed, wherein at least one tool, optionally several rotatable or rotating tools, which can be rotated or rotated about an axis of rotation, is or are arranged in the container for moving, mixing, heating and optionally comminuting the material, wherein in the container, in particular in a side wall of the container, in particular in the region of the orthe height of the lowest or ground-nearest tool, a container opening is formed through which the pretreated material can be discharged from the interior of the container, and with at least one extruder according to the invention for receiving the material discharged from the container, wherein it is provided in particular that the extruder is connected directly to the container.

[0055] A structurally advantageous embodiment provides that several, at least two, tools are arranged in the container in different tool levels or at different distances from the bottom surface or lowest region of the container and that the tools are arranged in the container in at least two tool levels lying one above the other.

[0056] Furthermore, it is advantageous if the only tool or the lowest tool or the lowest tool level is arranged in the area or at the height of the container opening, and if necessary also at the height of the feed opening of the extruder connected to it.

[0057] Multi-screw extruders can also be advantageously coupled directly to a PCU or cutter-compactor for the processing of polymer materials. The lowest tool level of the container, which preferably consists of a disc onto which tools can be mounted and is located in the area of ​​the extruder opening, feeds the pretreated materials into the extrusion device. In such cases, the number of stuffing cycles of the tools in the lowest tool level in the area of ​​the extruder opening also influences the extruder's fill level. Furthermore, the average bulk density of the materials in the PCU, particularly in the lowest area of ​​the PCU, corresponding to the average compaction, is also responsible for the fill level.

[0058] This makes it possible to take into account and compensate for the properties of the material entering the extruder, such as moisture content, compaction, and material temperature, right in the PCU. Unfavorable settings can manifest themselves, for example, in significant fluctuations in the extruder torque and tool speed, which can be detrimental to feeding behavior and material quality, among other things.

[0059] Even the mere mixing of the materials in the PCU has a dampening effect on any bulk density fluctuations of the input materials to a certain (minor) degree. However, mixing alone, and often also intensive pretreatment of the materials in the PCU, is insufficient in some cases, and it is not always possible to keep the bulk density sufficiently constant over a longer period. Rather, the bulk density of the processed materials fluctuates upwards and downwards from an average value over time. This is already disadvantageous and causes the disadvantages described. These can be compensated for by the inventive design of the extruder.

[0060] The tools in the PCU are advantageously discs, bars or beams, in particular with knives arranged on them.

[0061] If tools are arranged in several tool levels, in particular several disks on top of each other, they can, but do not have to, be the same size, and can therefore also have different dimensions or diameters.

[0062] The feed behavior is also advantageous, among other things, depending on how the cutter-compactor's tools introduce the pretreated material into the extruder's feed opening or support this process. This depends, among other things, on the direction of rotation of the screw and the direction of rotation of the tools. In this context, it has proven advantageous if, in the area upstream of the container opening or in the area upstream of the feed opening or feeding opening of the extruder, the direction of rotation of the tool of the lowest level runs essentially opposite to or in the opposite direction to the conveying direction of the extruder. Such arrangements are already known in principle, for example from EP 2 558 263 B1 or EP 2 689 908 B1, and are incorporated into the present disclosure by reference.

[0063] It is particularly advantageous if the longitudinal axis of the screw or the longitudinal axis of the screw closest to the intake opening or the inner wall of the housing or the envelope of the screw runs tangentially to the inside of the side wall of the container, wherein the screw is preferably connected to a drive at its front end and conveys at its opposite front end to an outlet opening arranged at the front end of the housing, in particular an extruder head.

[0064] It is also advantageous if the opening in the PCU is connected immediately and directly to the intake opening without any long distance or transfer path, e.g. a conveyor screw. This enables effective and gentle material transfer. An advantageous device is further characterized in that the container is cylindrical or conical. However, the container does not necessarily have to have a circular cylindrical shape, although this shape is advantageous for practical and manufacturing reasons. Container shapes deviating from the circular cylindrical shape, such as truncated cone-shaped containers or cylindrical containers with an elliptical or oval floor plan, can be converted to a circular cylindrical container of the same capacity, assuming that the height of this fictitious container is equal to its diameter.Container heights that significantly exceed the resulting mixing vortex (taking the safety distance into account) are not taken into account, since this excessive container height is not used and therefore no longer has any influence on the material processing.

[0065] An advantageous device is characterized in that the extruder is connected tangentially to the container and / or that the housing of the extruder has an inlet opening located on its front side or in its jacket wall for the material to be grasped by the screw or screws of the extruder, and the inlet opening is connected to the container opening.

[0066] In a further advantageous embodiment, the receiving container can be substantially cylindrical, with a flat base surface and a cylindrical side wall aligned vertically thereto. Furthermore, it is structurally simple if the axis of rotation of the tool(s) coincides with the central axis of the receiving container. In a further advantageous embodiment, the axis of rotation of the tool(s) or the central axis of the container is aligned vertically and / or perpendicular to the base surface. This also applies analogously to conical containers. These special geometries optimize the feed behavior in a structurally stable and simply constructed device.

[0067] In this context, it is also advantageous to provide that the tool, or, if several tools are arranged one above the other, the lowest tool closest to the ground, as well as the opening are arranged a short distance from the floor surface, in particular in the region of the lowest quarter of the height of the receiving container. The distance is defined and measured from the lowest edge of the opening or the feed opening to the container floor in the edge area of ​​the container. Since the corner edge is usually rounded, the distance is measured from the lowest edge of the opening along the imaginary extensions of the side wall downwards to the imaginary extension of the container floor outwards. Suitable distances are 10 to 400 mm.

[0068] Furthermore, it is advantageous for machining if the radially outermost edges of the tool reach close to the side wall of the container.

[0069] Particularly advantageous is a device comprising a cutter-compactor or a preconditioning unit (PCU) with at least one mixing or comminuting tool that can rotate or rotate about a rotational axis, and with a container opening formed in the side wall of the cutter-compactor at the height of the lowest tool closest to the ground. A twin-screw extruder, into which the pretreated material is introduced, is tangentially connected to this container opening.

[0070] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. The invention is schematically illustrated in the drawings using non-limiting exemplary embodiments and will be described below by way of example with reference to the drawings.

[0071] Fig. 1 a shows an embodiment of an extruder according to the invention in a partial sectional view from above.

[0072] Fig. 1 b shows the extruder according to Fig. 1 a in a partial sectional view from the side.

[0073] Fig. 2 shows an extruder according to the invention in perspective view.

[0074] Fig. 3 shows an extruder according to the invention in a perspective partial sectional view.

[0075] Fig. 4a shows a cross-section of an extruder according to the invention in the extrusion area C.

[0076] Fig. 4b shows a cross-section of the extruder in the transition area B.

[0077] Fig. 4c shows a cross-section of the extruder in the feed area A.

[0078] Fig. 5a and 5b show a cutter-compactor-extruder combination according to the invention with cylindrical screws from above and from the side.

[0079] Fig. 6a and 6b show an alternative cutter-compactor-extruder combination with conical screws from above and from the side.

[0080] The representations in Figures 1 to 6 are only schematic.

[0081] Fig. 1 a and 1 b show an exemplary advantageous embodiment of a multi-screw extruder 1 according to the invention. In the present case, it is a co-rotating twin-screw extruder 1 with two identical, cylindrical, parallel screws 3a, 3b, which are arranged next to one another for rotation in a common housing 2, symmetrically to one another, meshing or intermeshing with one another.

[0082] Fig. 1a shows a top view of the extruder 1. It is a partial sectional view in which the housing 2 is partially cut open, providing a view of the interior of the housing 2 and the two adjacent screws 3a, 3b.

[0083] Fig. 1 b also shows a partial sectional view of the same extruder 1 from the side and one can see the lateral feed opening 4 and the screw 3a closest to or adjacent to the feed opening 4.

[0084] An inner region 15 is formed within the housing 2, i.e., within the inner walls 8. The screws 3a, 3b arranged in the inner region 15 are set in rotation with the same direction of rotation and at the same speed by a drive 31, shown on the left in the figures, located upstream of the conveying direction 6.

[0085] A housing longitudinal axis 40, i.e. the axis of the housing 2 running along the conveying direction 6, runs centrally between the two screws 3a, 3b and parallel to the longitudinal axes 3a', 3b' when viewed from above (Fig. 1 a, 5a, 6a) and when viewed from the side (Fig. 1 b, 5b, 6b) in the plane of the screws 3a, 3b and the longitudinal axes 3a', 3b'.

[0086] The extruder 1 has an intake area A, into which the materials to be processed, typically polymer materials intended for recycling, are introduced into the extruder 1. In this intake area A, the intake opening 4 formed in the casing wall of the housing 2 is located, through which the material to be processed is brought into the collection area of ​​the screws 3a, 3b. In this case, the intake opening 4 is formed on the side of the extruder 1 and opens into the collection area of ​​the screw 3a.

[0087] Subsequently, an extrusion region C is formed downstream. In this region, the screw gap 7 formed between the outer diameters of the screws 3a, 3b and the inner wall 8 of the barrel 2 is largely very narrow at approximately 0.2 mm and largely constant. The melting of the polymer material and the formation of a polymer melt also take place in this extrusion region C. It is understood that there may be sections or positions where the screw gap 7 is locally larger; however, such local changes are irrelevant in this case, and the entire length of the extrusion region C, in which the screw gap 7 is consistently small on average, must be considered.

[0088] In the feed area A, the barrel 2 is widened or enlarged in an area of ​​or around the feed opening 4 or has a pocket 5 extending over a certain longitudinal section of the extruder 1 along the screws 3a, 3b. In the entire longitudinal extent or area of ​​the pocket 5, there is a screw gap 7' which is larger than the screw gap 7 of the extrusion area C, or screw gaps 7' which are enlarged circumferentially around the screws 3a, 3b are formed, i.e. the radial distance between the outer diameter of the screws 3a, 3b and the inner wall 8 of the barrel 2 is sometimes significantly increased in the area of ​​the pocket 5. The screw gaps 7' are essentially very similar everywhere around their circumference, i.e. the screws 3a, 3b are approximately the same distance from the inner wall 8 on all sides in every cross-section. In the area of ​​the pocket 5, no melting of the material occurs during operation.

[0089] The end 11 of the pocket 5 is located at the beginning of the extrusion area C as seen in the conveying direction 6, i.e. where the screws 3a, 3b are circumferentially or on all sides only separated from the inner wall 8 by the largely narrow and constant screw gap 7.

[0090] The intake opening 4 has a certain length as well as a certain width and height. The geometric shape of the intake opening 4 is essentially rectangular in this case, but round or oval shapes without corners are also advantageous.

[0091] In the present example, the longest length LE of the intake opening 4 is approximately 3 Da. The length LE is measured in the conveying direction or longitudinal direction 6 of the longitudinal axes 3a' and 3b' of the screws 3a, 3b, or parallel to them. "Da" is the outer diameter of the screw 3a closest to the intake opening 4, i.e., the adjacent screw 3a. "Da" is measured in the area of ​​the intake opening 4, specifically at the point 9 of the intake opening 4 located furthest downstream in the conveying direction 6, i.e., at the end point 9 of the intake opening 4 located furthest downstream.

[0092] The longest width or height BE of the intake opening 4 in this case is approximately 2 Da. The width BE is measured in the transverse direction 12 or perpendicular to the conveying direction 6 or at right angles to the axial longitudinal axes 3a', 3b' of the screws 3a, 3b. The same definition for Da as stated above applies here as well. The longest width BE is not measured along the curved opening or along the radius of curvature, but corresponds to the direct or clear height or the distance between the opposite edges of the intake opening 4.

[0093] The pocket 5, as previously described, has an enlarged inner diameter Ti over its entire area or longitudinal extent. The inner diameter Ti of the pocket 5 is determined or measured as follows: The axial longitudinal axes 3a', 3b' of the screws 3a, 3b define a common plane 13 or lie in a common plane 13. The inner diameter Ti is then defined and measured as the length of a straight line aligned normal to this plane 13 and intersecting the longitudinal axis 3a' of the screw 3a nearest or adjacent to the intake opening 4 through the inner area 15 between the mutually opposite surfaces of the inner wall 8 (top and bottom in Fig. 4c) of the housing 2.

[0094] The largest inner diameter Ti of the pocket is selected or determined and, according to the invention, determined by a special relationship between a factor k multiplied by the inner diameter Di of the screw 3a closest to the intake opening 4. Analogously to Da, Di is also determined or measured at the point 9 of the intake opening 4 furthest downstream in the conveying direction 6.

[0095] The pocket 5 further has a special length range LT, which begins at the furthest downstream point 9 of the feed opening 4, continues in the conveying direction or longitudinal direction 6 of the screws 3a, 3b and reaches to the end 11 of the pocket 5, wherein the end 11 of the pocket 5 is known to be located where an enlarged screw gap 7' no longer exists, but where the parallel region of the extruder 1 or the extrusion region C begins and the screw gap 7 is essentially small and constant. In the present example, the length range LT is approximately 6 Da, whereby the above definition also applies to Da, that Da is the diameter of the screw 3a closest to the feed opening 4 at point 9.

[0096] The length range LT of the pocket 5 lies in a transition region B of the extruder 1. The length range LT is therefore the downstream part of the pocket 5 and in this region the barrel 2 tapers from its enlarged configuration in the region of the pocket 5 to the small screw gap 7 in the extrusion region C. In the present case, this is achieved by the barrel 2 being designed to taper conically in sections. In a first section immediately downstream of the feed opening 4, the screw gap 7' is still of constant size and the barrel 2 has the shape of a cylinder. Only after around 20 to 30% of the length range LT does the enlarged screw gap 7' begin to reduce, and a conical section accordingly follows up to the end 11 of the pocket 5. The conical region preferably adjoins as closely as possible, if necessary even directly, behind the end or point 9 of the feed opening 4.

[0097] In the present case, as can be seen in Figs. 1 a and 1 b, the pocket 5 is expanded circumferentially on all sides around the screws 3a, 3b, or the screw gap 7' is enlarged circumferentially everywhere, and in the region of the pocket 5 there are correspondingly approximately equal radial distances or essentially similar screw gaps 7' between the screws 3a, 3b and the inner wall 8. However, it is also possible that only partial regions of the pocket 5 are expanded, i.e. that the pocket 5 is only spaced from the screws 3a, 3b in a certain circumferential region, but not in others.

[0098] Fig. 2 shows a schematic and not to scale representation of a perspective view of the relevant area of ​​an embodiment of a twin-screw extruder 1 according to the invention. On the far left is the drive 31, via which the two screws 3a, 3b are driven. The material to be treated reaches the capture area of ​​the nearest screw 3a via the feed opening 4. In this area, or in the feed area A, the housing 2 is enlarged and forms the pocket 5 according to the invention. Downstream of this, the conically tapered transition area B can be seen, in which the screw gap 7' decreases and becomes a very small, constant screw gap 7 in the extrusion area C at the end 11 of the pocket 5.

[0099] Fig. 3 shows a perspective view of an embodiment from an opposite direction, with a portion of the housing 2 graphically removed. Here, too, the interior region 15 of the housing 2 or the pocket 5, the tapered transition region B, and the adjoining extrusion region C are visible.

[0100] The same explanations apply to Figs. 2 and 3 as to Figs. 1 a, 1 b.

[0101] Figs. 4a, 4b, 4c show cross sections through an extruder 1 according to the invention or through the barrel 2, and also through the screws 3a, 3b, at different positions at right angles to the longitudinal axes 3a', 3b' or to the barrel longitudinal axis 40.

[0102] Fig. 4a shows a cross-section in extrusion area C. Visible is the very small screw gap 7 of < 1 mm, which essentially remains unchanged throughout the extrusion area C. Fig. 4b shows a cross-section in transition area B, specifically in the area of ​​the conical taper. Here, the screw gap 7' is already larger than the screw gap 7. This cross-section is therefore already in the area of ​​the pocket 5, and there is a certain spacing or space between the inner wall 8 and the screws 3a, 3b.

[0103] Fig. 4c shows a cross-section in the area of ​​pocket 5, specifically in the area of ​​intake opening 4. The screw gaps 7' have reached their maximum size here, and the inner diameter Ti of pocket 5 is also largest in this area. Plane 13, spanned by the longitudinal axes 3a', 3b', is visible. The inner diameter Ti runs through the longitudinal axis 3a' of the screw 3a and is perpendicular to plane 13.

[0104] In the schematic Figs. 5a and 5b, an advantageous embodiment of an overall device according to the invention for processing or preparing polymer materials, in particular thermoplastic waste plastic for recycling purposes, is shown from two different perspectives, from above and from the side, respectively.

[0105] The basic structure and the basic functioning of such a cutter-compactor-extruder combination is sufficiently known, for example from EP 2 558 263 or EP 2 689 908, and is only briefly described below.

[0106] The overall device comprises a cylindrical container or cutter-compactor or a preconditioning unit (PCU) 100 for receiving the polymer material to be processed. Such a container 100 is already well known, for example, from EP 123 771. The container 100 is cylindrical with a flat bottom surface and a cylindrical side wall 400 aligned vertically thereto.

[0107] A rotatable or rotating tool 300a, 300b is arranged in the container 100. The tool 300a, 300b here is a flat carrier disk with knives mounted on its upper side, arranged at a short distance from the base surface, rotating about a rotational axis 200 and aligned parallel to the base surface. The carrier disk is driven to rotate via a motor via an axis, wherein the motor is located below the container 100. The rotational axis 200 or the axis is arranged in the central longitudinal axis or center axis of the container 100. The tool 300a, 300b serves, among other things, to move, mix, heat, and comminute the material present in the container 100. Accordingly, the thermoplastic materials are mixed, heated, softened, compacted, pre-degassed, dried, dehumidified, cut, comminuted, crystallized, and / or homogenized in the container 100, and their bulk density is increased.By rotating the tool 300a, 300b, a mixing vortex is formed in the material and the material remains in the container 100 for a certain residence time and is pretreated there accordingly.

[0108] At the level of the single tool 300a, 300b in the present case, or at the level of the lowest tool level, a container opening 500 is formed in the side wall of the container 100. The housing 2 or the feed opening 4 of the extruder 1 is tangentially connected to this container opening 500, whereby the polymer material being pretreated in the container 100 is brought into the extruder 1 or into the collection area of ​​the screws 3a, 3b, specifically in the region of the pocket 5. This extruder 1 is designed analogously to Figs. 1a and 1b, and the relevant explanations are adopted here. Especially with multi-screw extruders, the feed or feeding is particularly sensitive, and constant feeding at as consistent a level as possible is particularly important. The present introduction of the material pretreated in this way into the pocket 5 of the twin-screw extruder 1 is particularly advantageous.The direction of rotation of the tool 300a of the lowest level (arrow) runs in the area of ​​the container opening 500 or the opening 4 essentially opposite to or in the opposite direction to the conveying direction 6 of the extruder 1.

[0109] The outer edges of the tool 300a, 300b extend relatively close to the side wall 400. The tools or knives are located at approximately the same height or level as the central longitudinal axes 3a', 3b' of the screws 3a, 3b of the extruder 1.

[0110] In practical operation, the plastic material to be processed, usually in the form of plastic waste, bottles, or foil, is introduced into container 100. The plastic material is comminuted and mixed by the rotating tool 300a, 300b, among other things, and is thereby heated and softened, but not melted, by the introduced mechanical friction energy. After a certain residence time in container 100, the softened but not melted material is discharged from container 100 through container opening 500 and fed into pocket 5 of extruder 1, or the extruder 1 is partially fed in this way.

[0111] The schematic Figs. 6a and 6b show a further advantageous embodiment of an overall device according to the invention in views from above and from the side, respectively. The same explanations apply to Figs. 6a and 6b as to Figs. 5a and 5b. In contrast, the direction of rotation of the tool 300a (arrow) is reversed from that in Fig. 5a. Furthermore, the direction of rotation of the screws 3a, 3b is opposite to each other. Furthermore, the screws 3a, 3b are not cylindrical, but conical. Accordingly, the longitudinal axes 3a', 3b' are not aligned parallel to each other, and the extruder 1 in the extrusion area C is also not parallel, but rather conically adapted to the course of the screws 3a, 3b. The inner diameter Ti is determined analogously, and the largest inner diameter of the pocket is located on the far left in Fig. 6b, upstream of the intake opening 4.

[0112] Example:

[0113] The following test was carried out on an exemplary test system according to the invention. This was a PCU (Preconditioning Unit) /

[0114] Twin-screw extruder combination with the following system configuration:

[0115] The system configuration (comparable to the schematic device shown in Figs. 5a and 5b) used a preconditioning unit (PCU), a container, or a cutter / compactor, which had a tool with a variable-speed drive. A single (lower) tool level was constructed, located in the area of ​​the container opening or in the area of ​​the extruder inlet.

[0116] The twin-screw extruder used here had the following specific

[0117] Dimensions or parameters:

[0118] Length (LE) of the feed opening (4): 2.38 Da or 150 mm

[0119] Width (BE) of the feed opening (4): 1.11 Da or 70 mm Outer diameter Da of the screws (3a, 3b): 63 mm Inner diameter Di of the screws (3a, 3b): approx. 40 mm Largest inner diameter (Ti) of the pocket (5): 80 mm Length range (LT) of the pocket (5): 6 Da or 378 mm Two identical cylindrical screws, parallel, co-rotating, intermeshing The speed of the tools in the PCU was controlled so that the energy was introduced into the material in such a way that a certain material temperature was reached. The material temperature was measured using measuring systems that protrude into the material or record the temperature non-contacting from the side or above. This temperature was essentially determined by the polymer introduced. It had to be ensured that the incoming material chips reached a certain temperature that was close to the softening temperature of the polymer.This ensured a certain degree of pre-compaction, thus homogenizing the bulk density in the PCU, and also facilitated the melting process in the extruder, as the material was heated to near its softening point. Since the softening temperatures of the thermoplastic polymers used here are in the range where water evaporates, the residual moisture in the incoming material was also removed.

[0120] HDPE bottle granules were used as the test material. This material was obtained from used containers from the hygiene sector, such as shampoo bottles, or from cleaning products, such as household cleaners. This material was first shredded and then pre-cleaned in a washing system. The basic properties or parameters of this material are that it is free-flowing, but it has varying bulk densities and moisture contents.

[0121] It was demonstrated that the extruder fill level could be kept very constant and sufficiently high. The feeding behavior of the twin-screw extruder, the throughput, and the throughput consistency were significantly improved. The quality of the HDPE granules obtained in this way was also very satisfactory. The entire recyclate met the optical and mechanical requirements. The regranulate produced was blown into household cleaner bottles, and varying amounts of recyclate were added to the virgin material.

Claims

Patent claims:

1. Extruder or multi-screw extruder (1) for processing and melting polymeric materials with at least two screws (3a, 3b, ...) rotatable in a common housing (2), in particular a twin-screw extruder (1), with an intake area (A) for introducing the material to be processed into the extruder (1), and a further downstream extrusion area (C) for melting the material, wherein the housing (2) in the intake area (A) has at least one intake opening (4) formed in its jacket wall for introducing the material to be processed into the capture area of ​​the screws (3a, 3b, ...), wherein in the extrusion area (C) there is a narrow screw gap (7) that is essentially constant up to the screw outlet between the outer diameters of the screws (3a, 3b, ...) and the inner wall (8) of the housing (2), characterized in that the housing (2) in the intake area (A) orin an area around the feed opening (4) has a pocket (5) extending over a partial longitudinal section of the extruder (1) along the screws (3a, 3b, ...), wherein the pocket (5) has, over its entire longitudinal extent, a screw gap (7') which is enlarged compared to the screw gap (7) in the extrusion area (C) between the outer diameters of the screws (3a, 3b, ...) and the inner wall (8) of the housing (2).

2. Extruder (1) according to claim 1, characterized in that the end (11) of the pocket (5) is located at the transition into the extrusion area (C), from which the screws (3a, 3b, ...) are only spaced from the inner wall (8) by the screw gap (7) on all sides.

3. Extruder (1) according to one of claims 1 to 2, characterized in that the longest length (LE) of the feed opening (4) measured in the conveying direction or in the longitudinal direction (6) of the axial longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...) is in the range of 0.2 Da < LE < 15 Da, where Da is the outer diameter of that screw (3a, 3b) which is closest to the feed opening (4), measured at the point (9) of the feed opening (4) which is furthest downstream in the conveying direction.

4. Extruder (1) according to one of claims 1 to 3, characterized in that the longest width (BE) of the feed opening (4) measured in the transverse direction (12) transverse to the conveying direction (6) or transverse to the axial longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...) is in the range of 0.1 Da < BE < 3 Da.

5. Extruder (1) according to one of claims 1 to 4, characterized in that the pocket (5) has an enlarged inner diameter (Ti) along its entire longitudinal extent, wherein the screws (3a, 3b, ...) are arranged side by side and the axial longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...) define a common plane (13) or lie in a common plane (13), wherein the inner diameter (Ti) of the pocket (5) is defined and measured as the length of a straight line oriented normal to this plane (13) and intersecting the longitudinal axis (3a') of the screw (3a) nearest or adjacent to the feed opening (4) between the mutually opposite regions of the inner wall (8) of the housing (2). wherein the following applies to the largest inner diameter (Ti) of the pocket (5): Ti = k * Di where: 1 ,7 < k < 9.6 where Di is the inner diameter of the screw (3a, 3b, ...) which is closest to the intake opening (4), measured at the point (9) of the intake opening (4) which is furthest downstream in the conveying direction.

6. Extruder (1) according to one of claims 1 to 5, characterized in that the pocket (5) has a length range (LT) starting from the furthest downstream point (9) of the feed opening (4) in the conveying direction or in the longitudinal direction (6) of the axial longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...) to the downstream end (11) of the pocket (5), wherein the length range (LT) is in the range of 0.2 Da < LT < 10 Da.

7. Extruder (1) according to one of claims 1 to 6, characterized in that the length (LE) of the feed opening (4) is in the range of 0.3 Da < LE < 10 Da.

8. Extruder (1) according to one of claims 1 to 7, characterized in that the width (BE) of the feed opening (4) is in the range of 0.1 Da < BE < 2 Da.

9. Extruder (1) according to one of claims 1 to 8, characterized in that for the determination of the inner diameter (Ti) for Da < 100 mm the following applies: 1.7 < k < 3 and / or that for Da > 100 mm the following applies: 3 < k < 9.

10. Extruder (1) according to one of claims 1 to 9, characterized in that the length range (LT) of the pocket (5) is in the range of 0.5 Da < LT < 6 Da.

11. Extruder (1) according to one of claims 1 to 10, characterized in that the length region (LT) of the pocket (5), starting from the furthest downstream point (9) of the feed opening (4) in the conveying direction or in the longitudinal direction (6) of the axial longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...) to the downstream end (11) of the pocket (5), is conical and / or continuously tapered at a uniform angle at least in a partial section of > 50%, in particular > 80%, preferably > 90%, of the length of the length region (LT), in particular substantially over the entire length of the length region (LT).

12. Extruder (1) according to one of claims 1 to 11, characterized in that the feed opening (4) is formed laterally on the extruder (1) and / or opens only into the detection area of ​​one of the screws (3a, 3b, ...), wherein it is provided in particular that the central longitudinal axis of the feed opening (4) intersects the central longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...).

13. Extruder (1) according to one of claims 1 to 12, characterized in that the extruder (1) is designed as a twin-screw extruder with two mutually parallel, co-rotating or counter-rotating and intermeshing cylindrical screws (3a, 3b) or with two co-rotating or counter-rotating and intermeshing conical screws (3a, 3b).

14. Extruder (1) according to one of claims 1 to 13, characterized in that a passive feed element, in particular a hopper, and / or an active feed element, in particular a stuffing screw, is provided for introducing the material to be processed into the intake opening (4), wherein it is provided in particular that the active and / or the passive feed element is connected directly to the extruder (1).

15. Device for processing or preparing polymer materials, in particular thermoplastic waste plastic for recycling purposes, with at least one container or cutter-compactor (100) for the material to be processed, wherein at least one tool (300a, 300b, ...) rotatable or rotating about a rotation axis (200), optionally several rotatable or rotating tools (300a, 300b, ...) is or are arranged in the container (100) for moving, mixing, heating and optionally comminuting the material, wherein in the container (100), in particular in a side wall (400) of the container (100), in particular in the region of or at the height of the lowest or bottom-most tool (300a), a container opening (500) is formed through which the pretreated material can be discharged from the interior of the container (100), and with at least one extruder (1) according to one of claims 1 to 14, for receiving the material discharged from the container (100), wherein it is provided in particular that the extruder (1 ) is directly connected to the container (100).

16. Device according to claim 15, characterized in that in the container (100) several, at least two, tools (300a, 300b, ...) are arranged in different tool levels or at different distances from the bottom surface or lowest region of the container (100) and that the tools (300a, 300b, ...) in the container (100) are arranged in at least two superimposed tool levels.

17. Device according to claim 15 or 16, characterized in that the tool (300a) or the lowest tool (300a) or the lowest tool level is arranged in the area or at the level of the container opening (500), and optionally also at the level of the feed opening of the extruder (1) connected thereto.

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