TW202600326A - Extruder for processing polymer materials - Google Patents

Abstract

This invention relates to an extruder or multi-screw extruder (1), particularly a twin-screw extruder (1), for processing and melting polymer materials and having at least two screws (3a, 3b, ...) rotating within a common shell (2), including a feed zone (A) for feeding the material to be processed into the extruder (1) and a downstream extrusion zone (C) for melting the material; wherein the shell (2) has at least one inlet (4) in the feed zone (A), formed in its shell wall and used to introduce the material to be processed into the gripping zone of the screws (3a, 3b, ...); wherein, in the extrusion zone (C), the screws... There is a substantially constant narrow screw gap (7) between the outer diameter of the screws (3a, 3b, ...) and the inner wall (8) of the shell (2) all the way to the screw outlet, wherein the shell (2) is provided with a bag-shaped portion (5) extending along a portion of the longitudinal section of the screws (3a, 3b, ...) in the feed area (A) or in the area around the inlet (4), the bag-shaped portion (5) having a screw gap (7') in its entire longitudinal direction, the screw gap (7') being larger than the screw gap (7) located in the extrusion area (C) between the outer diameter of the screws (3a, 3b, ...) and the inner wall (8) of the shell (2).

Description

Extruder for processing polymer materials

This invention relates to an extruder or multi-screw extruder for processing and melting polymer materials, as described in the preamble of claim 1. This invention also relates to an apparatus according to claim 15, comprising the aforementioned extruder, connected to a container or pretreatment unit (PCU), for processing or treating polymer materials, particularly for processing or treating recycled thermoplastic waste plastics.

Various designs of single-screw and multi-screw extruders for processing and melting polymer materials are known in the art.

Also known is an apparatus for the pretreatment and processing of polymer waste, particularly various thermoplastics, comprising a container, a cutting compactor or pretreatment unit (PCU), and an extruder connected thereto. The container is typically at least partially directly connected to the extruder and equipped with rotating tools; the mixing and crushing tools rotating within the container or PCU also support the loading or feeding process of the connected extruder. In the PCU, the pretreatment steps prior to extrusion, among other functions, include altering the shape and properties of the polymer material. Thermoplastic materials are mixed, heated, softened, compressed, pre-degassed, dried, dehumidified, cut, shredded, crystallized, and/or homogenized in a pretreatment unit to increase their bulk density, but the material has not yet been melted during these steps. The polymer, thus pretreated, is then fed into an extruder for compaction, and in particular, melting. Such combinations are well known, for example, from EP 2 558 263 or EP 2 689 908.

Extrusion processes are typically highly efficient when the screw fill factor remains constant and sufficiently high. Therefore, the extruder's feed zone or feeding process is very sensitive and has a significant impact on the final result and the quality of the recycled material. Unfavorable extruder feeding behavior can lead to output fluctuations, i.e., output varying over time, which is detrimental to the reliable operation of the extruder and the quality of the recycled material. Therefore, there are numerous attempts in the prior art to improve the extruder's feeding behavior and feeding process.

When processing thermoplastics (especially industrial or post-consumer waste), the raw form of the material (such as films, bottles, perforated mesh, cups, fibers, non-woven fabrics, textiles, etc.) is usually processed to transform it into a transportable form through pretreatment, crushing, or washing. These materials are typically processed using a single-screw extruder, which is an extruder with only one rotating screw.

However, for processing these types of materials, multi-screw extruders, especially twin-screw extruders, are often more advantageous. Twin-screw or multi-screw extruders are particularly suitable for finishing or special cleaning processes of polymers, as they are especially beneficial for achieving specific material qualities and for mixing these materials.

In a twin-screw extruder, two screws rotate side-by-side in a barrel or bore with an approximately elliptical cross-section, moving in the same or opposite directions of rotation. The material to be processed is fed through the extruder inlet, then melts during pressure build-up or material compression, and is subsequently pushed downstream inside the barrel. The melt is then fed into a tool or discharged from the extruder.

In a twin-screw extruder that rotates in the same direction, two parallel cylindrical or tapered screws rotate side by side with the same direction and speed in the barrel or shell. The conveying process or principle in the screw elements of a co-rotating twin-screw extruder is based on the so-called traction conveying principle or on the transfer of material from one screw to another in the screw meshing area. Therefore, unlike a single-screw extruder, a twin-screw extruder usually operates only in a partially filled state. In this way, on the one hand, a certain degree of forced propulsion effect can be achieved, and on the other hand, a good mixing effect is generated through transfer and surface renewal, and a uniform melt with the required temperature and pressure is fed into the subsequent tooling.

In a counter-rotating twin-screw extruder, two parallel cylindrical or tapered screws rotate in opposite directions. The gap between the screws is usually narrow, thus increasing the likelihood of wear. Counter-rotating twin-screw extruders are typically only operated with partial filling, partly to avoid excessive pressure buildup and wear on the screws and barrel.

Multi-screw extrusion systems typically use gravity feeding, and sometimes volumetric feeding, to keep the filling level of the extrusion system relatively constant. This usually results in the feeding area of a multi-screw extruder being partially filled. In contrast, a single-screw extruder can achieve a relatively constant filling level from the "full hopper" (i.e., the screw with the feeding area completely filled) along the length of the screw.

As mentioned earlier, the material entering the extruder is immediately conveyed downstream, generating a torque curve for the extruder drive related to the fill factor. Ideally, the extruder torque curve, or the fill factor (usually defined in kg/rpm) of a partially filled extruder, should be kept as constant as possible. This ensures high-quality polymer melting and avoids overheating of the polymer melt due to shear peaks. Excessive underfeeding, i.e., low fill factor, can lead to yield loss, shear peak formation, and inadequate polymer mixing. Therefore, maintaining a constant extruder fill factor is beneficial for the quality and economic efficiency of the recycled material.

Despite the efforts and measures mentioned above, it may still be impossible to effectively balance changes such as bulk density over time.

Based on this, the present invention proposes a design scheme for adjusting the structure of the extruder itself, or in particular adjusting the structure of key areas such as the extruder feed or input, or to support the feeding behavior and feeding process of the screw.

Therefore, the purpose of this invention is to provide an extruder of the type described at the beginning of this document, which allows the filling degree of the extruder to be kept as constant as possible, or to support the screw feeding behavior and feeding process in an optimal manner, and to have, for example, greater tolerance to material differences and effects during operation.

This objective is achieved through the features of request item 1.

Therefore, the present invention provides an extruder or multi-screw extruder for processing and melting polymer materials, having at least two rotatable screws arranged side by side in a common housing, and more specifically, a twin-screw extruder having exactly two screws.

The extruder has an upstream feed zone in its typical basic structure, in which the material to be processed is introduced into the extruder, and a downstream extrusion zone in which the material is melted.

The extruder casing has at least one inlet formed on its casing wall within the feeding zone for introducing the material to be processed into the gripping zone of the screw.

In the downstream extrusion region, there is a screw gap between the screw outer diameter or screw sleeve and the inner wall of the casing. This gap is substantially constant and very small or narrow along the longitudinal direction of the extrusion region until the screw outlet, and completely surrounds the outer periphery of the screw.

In this article, "constant" means that the screw clearance does not change significantly throughout the entire extrusion zone (up to the screw outlet) and remains essentially constant. In an extruder with a cylindrical screw, the extrusion zone corresponds to the parallel section of the extruder.

In this article, "narrow" refers to the small distance between the screw and the inner wall compared to the screw diameter. It is usually only a fraction of a millimeter from the barrel, or less than 1mm when it is a new product.

However, the screw clearance does not need to be the same, constant, and narrow at every point or in every part of the extrusion zone; rather, it should remain so throughout the entire extrusion zone in the longitudinal direction. Deviations in the screw clearance within small sub-zones or variations or increases in certain special areas (such as the degassing zone or other inlet zones) do not affect the overall performance; even with these deviations, the screw clearance remains constant and narrow throughout the entire extrusion zone. Specifically, for example, in areas where there may be further feed and where melt is already present, and in areas where melt is degassed, there may be a large screw gap between the barrel and the screw. Melt or molten material is already present in all of these areas of the extrusion zone, which is the opposite of the bag-shaped area described below, where melting has not yet occurred.

According to the invention, the shell is further designed or includes a pouch-like portion extending along the screw and in the longitudinal section of the extruder section at the feed area or inlet. This pouch-like portion has a screw clearance along its entire longitudinal direction, which is larger than the screw clearance in the extrusion area between the screw outer diameter and the inner wall of the shell. The end of the pouch-like portion is located at the transition point leading to the extrusion area, from which point the screw clearance between the screw and the inner wall remains constant and narrow. Therefore, advantageously, the pouch-like portion extends to a point from which the screw outlet or to the parallel section of the extruder (suitable for extruders with cylindrical screws) maintains a small screw clearance at all times. Therefore, the screw clearance in the bag-shaped region is larger compared to the smaller screw clearance that is always maintained in the downstream extrusion region.

Accordingly, in the feeding area within the bag-shaped section, the diameter of the bag-shaped section is significantly larger than the outer diameter of the screw. In addition to the volume occupied by the screw, it can bring more material (including lightweight materials) into the influence area of the screw, especially for filling, draining, or conveying.

The increase in the feed area, i.e., the formation of the pouch or the increase in the screw clearance, may occur only in certain areas around the screw. Preferably, the increased screw clearance exists over the entire circumference of the screw, or over most of the screw circumference. Therefore, preferably, the pouch surrounds the screw in all directions, and the distance between the screw and the inner wall or the screw clearance is preferably approximately similar or uniform in all directions.

The bag-shaped section and its increased screw clearance or space facilitate the introduction of more material that would otherwise be impossible for the screw to transport into the extruder. By utilizing the distance between the screw and the barrel, or the increased screw clearance within the bag-shaped section, some material can escape or flow back during screw overfilling (i.e., when the screws are too close together to receive further material). Such overfilling can occur due to changes in material, such as higher bulk density or more fluid materials. Therefore, the correspondingly enlarged space in the bag-shaped section within the extruder's feed area provides compensation, thereby preventing overfilling or underfilling of the extruder.

Importantly, during operation, the material or particles in the bag-shaped area will not undergo a significant melting process, thus retaining a certain degree of agglomeration. Although the material may soften partially, it is not allowed to melt, much less completely melt; otherwise, the material cannot be pushed.

Such multi-screw extruders, especially twin-screw extruders, have many advantages in this regard. For example, the extruder has better feeding behavior, or higher output at a given screw diameter and speed. In addition, it has good conveying performance, short residence time, narrow residence time range, good self-cleaning ability, good dispersibility and homogeneity, flexible geometric design (based on modular structure), and good process control capabilities.

Through the extruder design of this invention, the filling degree can be kept very constant, and the screw feeding behavior is further improved with good output and stable output consistency, and the quality of the final polymer material can also be further improved.

According to an advantageous design, the longest or maximum length LE of the inlet is in the range of 0.2 Da ≤ LE ≤ 15 Da in the longitudinal direction parallel to the conveying direction or along the screw axis or in the direction parallel to these longitudinal axes.

Here, "Da" refers to the outer diameter of the screw closest to the inlet, which is measured at the downstream point of the inlet in the conveying direction. This definition of Da also applies to all cases involving Da in this text.

According to another advantageous design, the longest or maximum width BE or height of the inlet, measured along a direction perpendicular to the conveying direction or perpendicular to the screw axis longitudinally, is within the range of 0.1 Da ≤ BE ≤ 3 Da. Here, the width is not measured along the curvature of the barrel or the curve of the opening, but rather along the net width or height of the straight line between the opposite edges. Therefore, the width refers to the absolute width or height of the opening as seen in a side view or projected onto the intermediate section of the extruder.

Here, "longest or largest" refers to the maximum dimension of the inlet in the longitudinal or width extension direction. The specific shape of the inlet is not fixed or limited, and can be, for example, rectangular, square, circular or elliptical, etc. However, for the purpose of facilitating feeding, it is preferable to have an oval, elliptical or circular inlet without corners.

In a particularly advantageous embodiment, as described above, the bag-shaped portion has an inner diameter in its entire longitudinal direction that is larger than the screw clearance in the extrusion region, and the inner diameter Ti of the bag-shaped portion is defined and determined in the following manner:

These screws are arranged side by side, and the longitudinal axis of all the screws defines a common plane or lies on a common plane. This is particularly advantageous for implementations in which two identical cylindrical or tapered screws are arranged symmetrically side by side in the housing.

The inner diameter Ti of the bag-shaped portion is defined and measured as the length of a straight line between opposite regions of the inner wall of the shell, perpendicular to the aforementioned plane and intersecting the longitudinal axis of the screw closest to or adjacent to the inlet. Among these inner diameters Ti of the bag-shaped portion determined in this way, the inner diameter Ti with the largest length is determined and used.

The maximum inner diameter Ti satisfies the following condition: Ti = k × Di, where 1.7 ≤ k ≤ 9.6. Here, "Di" is defined as the inner diameter (core diameter) of the screw closest to the inlet, and Da is also measured at the downstream point from the inlet in the conveying direction.

Local deviations or partial changes or enlargements in the circumference (e.g., small spaces, circumferential protrusions, or channels in the shell or pouch) are not important. If such structures exist, the inner diameter Ti of the pouch is essentially determined by the virtual extension of the inner wall line.

In a parallel twin-screw screw, the ratio between Da and Di is usually specified by the manufacturer and represents performance characteristics such as output and torque.

In another advantageous design, the bag-shaped section has a length range LT, starting from the downstream point of the longitudinal inlet along the conveying direction or along the longitudinal axis of the screw and extending to the downstream end of the bag-shaped section, the length range LT being in the range of 0.2 Da ≤ LT ≤ 10 Da.

With its specially designed inlet and bag-shaped section, the extruder's filling degree can be kept extremely constant, the screw's feeding behavior can be further improved, and the output and output consistency can be increased. The extruder and the entire system consisting of the cutter compactor and extruder become more stable and efficient. In addition, the quality of the polymer material formed can be further improved and the economic efficiency of the operation can be increased.

According to an advantageous design, the length LE of the inlet is in the range of 0.3 Da ≤ LE ≤ 10 Da. Furthermore, it is advantageous that the width (BE) of the inlet (4) is in the range of 0.1 Da ≤ BE ≤ 2 Da, thereby ensuring particularly advantageous feeding behavior.

According to an advantageous design, for screws with Da ≤ 100 mm, 1.7 ≤ k ≤ 3, and/or for screws with Da > 100 mm, 3 < k ≤ 9. These values provide a favorable ratio for smaller or larger screw diameters.

According to another advantageous design, the length range LT of the bag-shaped part is within the range of 0.5 Da ≤ LT ≤ 6 Da, thereby enabling particularly advantageous material processing.

Downstream of the feed zone, a transition zone is preferably provided so that the geometry of the bag-shaped portion adapts from the feed zone to the extrusion zone. This adaptation of the screw diameter can begin within the feed zone; that is, the diameter of the bag-shaped portion is smaller downstream of the screw than upstream, thus forming a particularly conical shell, or a shell with a gradually decreasing cone shape, to facilitate material flow in the extrusion direction. Through the design of this particularly conical transition zone, the material can be advantageously further compacted.

In this case, preferably, starting from the downstream point of the inlet along the conveying direction or along the longitudinal axis of the screw shaft to the downstream end of the bag-shaped section, at least in the section where the length range LT of the bag-shaped section is greater than 50%, preferably greater than 70%, especially greater than 80%, more preferably greater than 90% or 95%, and most preferably throughout the entire length range LT, the length range is designed to be conical and/or gradually tapering at a uniform angle.

According to a structurally advantageous design, the inlet is located on the side of the extruder and/or leads only to the gripping area of one of the screws, and in particular, the central longitudinal axis of the inlet intersects the central longitudinal axis of the screw.

A particularly advantageous design is to design the extruder as a twin-screw extruder with two parallel cylindrical screws, or, advantageously, both screws are designed to be conical.

The two screws are preferably arranged side by side symmetrically. If they are cylindrical screws, the longitudinal axes of the screws are parallel to each other and parallel to the longitudinal axis of the shell. If they are tapered screws, the longitudinal axes of the screws are arranged at a certain angle to each other. In both cases, the longitudinal axis of the shell is located between the screws or between the longitudinal axes of the screws.

Advantageously, the two screws can be designed to rotate in the same or opposite directions, depending on the need.

Furthermore, advantageously, the screws are designed to mesh or interlock with each other, wherein the axial distance between the screws or between the central longitudinal axes of the screws is less than the screw diameter (outer diameter) Da over its entire length.

This design can further improve feeding behavior, increase conveying efficiency, reduce dwell time range, and improve process control.

According to another structurally advantageous design, to facilitate the introduction of the material to be processed into the extruder's inlet, a passive feeding element (especially a hopper) and/or an active feeding element (especially a pusher screw) can be provided, particularly by directly connecting the active and/or passive feeding elements to the extruder. The design of the feeding element has a significant impact on the feed and bulk density.

Therefore, the material to be processed can be introduced into the extruder through a passive hopper located on the side or top of the extruder. However, in practice, this design can usually only meet the requirements of a few materials that must have a certain degree of flowability, such as bottle grinding powder, agglomerates, or granules.

Most materials, such as film fragments, fiber fragments, and ground PET bottles, typically lack free flowability or have insufficient free flowability. Therefore, it is advantageous to use an active feed system to force the material into the extruder. For example, a feed screw with one or more screws can be installed and, for instance, directly coupled to the extruder. Although this can effectively balance the change in bulk density of the material being processed over time, it usually only achieves the desired bulk density balance to a certain extent.

An even more advantageous design is to connect a cutting compactor or PCU upstream, which can provide a very good balancing effect on a regular basis.

In this context, an advantageous apparatus is provided for processing or treating polymeric materials, particularly for recycling thermoplastic waste, comprising at least one container or cutting compactor for the material to be processed, wherein the container contains at least one, and optionally multiple, tools rotatable or rotating about a rotation axis for moving, mixing, heating, and optionally crushing the material. An opening is provided within the container, particularly on the side wall of the container or at a height or in the area of the lowest or closest tool to the bottom, through which the pre-treated material is discharged from the container. Furthermore, the apparatus includes at least one extruder according to the invention for receiving the material discharged from the container, particularly, the extruder being directly connected to the container.

In a structurally advantageous design, within a container, multiple or at least two tools are positioned on different tool planes or at different distances from the bottom or lowest area of the container, and these tools are positioned within at least two overlapping working planes inside the container.

Furthermore, advantageously, the single tool or the lowest tool or the lowest tool plane is located in the container opening area or at a height position, and if necessary, at the height position of the extruder inlet connected thereto.

Accordingly, multi-screw extruders can also be directly connected to PCUs or cut-and-compactors to efficiently process polymer materials. The lowest tooling plane of the container, preferably consisting of a disc for mounting tools and located in the extruder opening area, allows pre-treated material to be fed into the extruder. In this case, the number of push cycles of the tools on the lowest tooling plane in the extruder opening area also affects the extruder's fill factor. Furthermore, the average bulk density of the material in the PCU, especially in the lowest region of the PCU, also has a significant impact on the fill factor.

Accordingly, the characteristics of the material introduced into the extruder, such as its humidity, compaction, and temperature within the PCU, can be considered and adjusted. This adjustment helps to avoid the adverse effects of significant fluctuations in extruder torque and tool speed caused by unfavorable settings on feed behavior and material quality.

Even simply mixing the material in the PCU can mitigate fluctuations in the bulk density of the input material to some extent. However, in some cases, simply performing the mixing process alone, and in most cases, performing a strengthening pretreatment process on the material in the PCU, is often insufficient to guarantee a sufficiently constant bulk density over a longer period. In fact, the bulk density of the treated material fluctuates around the average value over time, and this fluctuation has adverse effects and leads to the shortcomings described above. These shortcomings can be effectively overcome by the innovative design of the extruder of this invention.

The tools in the PCU are preferably disc-shaped, rod-shaped, or beam-shaped, especially those equipped with cutting tools.

If the tools are set on multiple tool planes, especially on multiple discs set up vertically, the tools do not have to be exactly the same size and can have different dimensions or diameters.

Advantageously, during the feeding process, the cutting compactor tool can serve as an aid in bringing the pretreated material into the extruder inlet, depending particularly on the screw rotation direction and the tool rotation direction. Relatedly, and advantageously, in the area in front of the container opening or in front of the feed inlet of the conveyor or extruder, the tool rotation direction in the lowest tool plane is substantially opposite to the extruder's conveying direction. Such a configuration is generally known, for example, from documents EP 2 558 263 B1 or EP 2 689 908 B1, which are now incorporated herein by reference.

Particularly advantageously, the screw shaft or the screw shaft closest to the inlet, or the inner wall of the shell or the screw sleeve, is tangent to the inner side wall of the container; preferably, the screw is connected at its end face to a drive, and the screw's conveying action proceeds from its opposite end to an outlet opening located at the end of the shell, particularly to the extruder head.

Furthermore, the opening of the PCU can be directly and adjacent to the inlet without a longer distance or, for example, via a transfer path of a conveyor screw, thereby enabling efficient and gentle material transfer.

Another advantageous feature is that the container is cylindrical or conical. However, although cylindrical is practical and easy to manufacture, the container does not necessarily have to be cylindrical. Other containers with different shapes than cylindrical containers, such as truncated conical containers or cylindrical containers with elliptical or oval planes, can be converted into cylindrical containers with the same capacity if the height of the container is assumed to be equal to its diameter. Containers whose height significantly exceeds the mixed fluid produced (considering safety distances) are not considered, and because such excessively high container heights are not used, they will not have any impact on material processing.

An advantageous device is characterized in that the extruder is tangentially connected to the container and/or the extruder housing has an inlet in its end face or housing wall for the screw or extruder screw to grasp material, and the inlet communicates with the container opening.

In another advantageous design, the container is essentially cylindrical with a flat bottom and cylindrical sidewalls aligned perpendicularly to it; the structure can be simplified if the axis of rotation of the tool is designed to coincide with the central axis of the receiving container; in yet another advantageous design, the axis of rotation of the tool or the central axis of the container is aligned perpendicular to and/or perpendicular to the bottom surface, which also applies to conical containers. These specific geometric shapes optimize feeding behavior in structurally stable and simple-to-construct devices.

In this case, and advantageously, the tool (or the lowest tool among multiple tools arranged vertically and vertically, closest to the bottom) and its opening are positioned close to the bottom, particularly in the area of the lowest quarter of the container's height. This distance is the distance from the lowest edge of the opening or inlet to the bottom of the container in the container's edge area. Since it is usually a rounded edge, this distance is measured downwards from the lowest edge of the opening along the virtual extension line of the sidewall to the outwards from the virtual extension line of the container's bottom. A suitable distance is 10 to 400 mm.

Furthermore, it is advantageous for processing if the outermost radial edge of the tool is close to the side wall of the container.

Particularly advantageously, an apparatus is provided having a cutting compactor or pretreatment unit (PCU) having at least one rotatable or rotating mixing and chopping tool that rotates about a rotation axis and a container opening formed on the side wall of the cutting compactor in the height region of the lowest tool closest to the bottom surface, to which a twin-screw extruder is tangentially connected and carries the pretreatment material.

The following description and accompanying drawings illustrate further advantages and designs of the present invention. The drawings schematically illustrate non-limiting exemplary embodiments. The present invention will be further described below with reference to the accompanying drawings. [Simplified Explanation of the Drawings]

In the figures, Figure 1a is a partial top sectional view of an embodiment of the extruder of the present invention; Figure 1b is a partial side sectional view of the extruder shown in Figure 1a; Figure 2 is a perspective view of the extruder of the present invention; Figure 3 is a partial sectional perspective view of the extruder of the present invention; Figure 4a is a cross-sectional view of the extruder of the present invention in extrusion region C; Figure 4b is a cross-sectional view of the extruder of the present invention in transition region B. Figure 4c is a cross-sectional view of the extruder of the present invention in the feed area A; Figures 5a and 5b are top and side views of the combination of the cutting compactor and extruder of the present invention, wherein the combination has a cylindrical screw; Figures 6a and 6b are top and side views of another combination of the cutting compactor and extruder of the present invention, wherein the combination has a tapered screw.

The diagrams in Figures 1a to 6b are for illustrative purposes only.

Figures 1a and 1b show a preferred embodiment of the multi-screw extruder 1 of the present invention, which is a co-rotating twin-screw extruder 1 comprising two identical and parallel cylindrical screws 3a and 3b, which rotate in a common housing 2 in a mutually engaging, side-by-side and symmetrical manner.

Figure 1a shows a partial top cross-sectional view of the extruder 1, in which the shell 2 is partially cut open or opened, revealing two screws 3a and 3b arranged side by side inside the shell 2.

Figure 1b shows a partial side cross-sectional view of the same extruder 1, showing the side inlet 4 and the screw 3a closest to or adjacent to the inlet 4.

An internal region 15 is formed inside the shell 2 (i.e., inside the inner wall 8). The screws 3a and 3b disposed in the internal region 15 rotate in the same direction and speed through the drive 31 shown on the left side of the figure, which is located upstream of the conveying direction 6.

The longitudinal axis 40 of the shell (i.e., the axis along which the shell 2 extends in the conveying direction 6) is located between the screws 3a and 3b and parallel to the longitudinal axis 3a' and 3b' when viewed from above (Fig. 1a, 5a, 6a), while when viewed from the side (Fig. 1b, 5b, 6b), it extends in the plane of the screws 3a and 3b and the longitudinal axis 3a' and 3b'.

The extruder 1 has a feeding area A in which the material to be processed (usually a polymer material to be recycled) is brought into the extruder 1. In the feeding area A, an inlet 4 is provided on the shell wall of the shell 2. The material to be processed is fed into the gripping area of the screws 3a and 3b through the inlet 4. The inlet 4 is formed on the side of the extruder 1 and is collected in the gripping area of the screw 3a.

Subsequently, an extrusion zone C is formed downstream, in which the screw clearance 7 between the outer diameters of the screws 3a and 3b and the inner wall 8 of the shell 2 is very narrow, approximately 0.2 mm, and this clearance remains almost constant. In this extrusion zone C, the polymer material melts and forms a polymer melt. It is worth noting that the screw clearance 7 may increase slightly in certain sections or locations, but this local variation is not significant; what is important is that the screw clearance 7 remains very small and constant throughout the entire length of the extrusion zone C.

In the feeding zone A, the shell 2 is widened or enlarged in or around the inlet 4 area, or has a bag-shaped portion 5 extending along the screws 3a and 3b in a specific longitudinal cross-section of the extruder 1. In the entire longitudinal direction or region of this bag-shaped portion 5, there exists a screw clearance 7' larger than the screw clearance 7 in the extrusion zone C, or a screw clearance 7' that increases circumferentially around the screws 3a and 3b. That is, the radial distance between the outer diameter of the screws 3a and 3b and the inner wall 8 of the shell 2 locally increases significantly in the area of the bag-shaped portion 5. The screw clearance 7' is substantially very similar throughout the circumferential direction, that is, the distances between the screws 3a and 3b and the inner wall 8 are approximately equal in each lateral cross-section. During operation, the material has not yet melted in the area of the bag-shaped part 5.

Viewed from the conveying direction 6, the end 11 of the bag-shaped part 5 is located at the beginning of the extrusion area C, that is, where the screws 3a and 3b are separated from the inner wall 8 only by a very narrow and constant screw gap 7 in the circumferential direction or on all sides.

The inlet 4 has a certain length extension as well as a certain width and height extension. In this case, the geometry of the inlet 4 is basically rectangular, but alternatively, a circular or elliptical shape without corners is also advantageous.

In this example, the maximum length LE of the inlet 4 is approximately 3 Da. This length LE is measured along the conveying direction 6 of the longitudinal axis 3a' or 3b' of the screws 3a and 3b, or in a direction parallel to them. "Da" refers to the outer diameter of the screw 3a closest to the inlet 4, i.e., the outer diameter of the adjacent screw 3a. "Da" is measured at the downstreammost point 9 along the conveying direction 6 inside the inlet 4.

Here, the maximum width or height BE of the inlet 4 is approximately 2 Da. This width BE is measured in the transverse direction 12, or in the direction perpendicular to the conveying direction 6, or in the direction perpendicular to the longitudinal axis 3a' or 3b' of the screws 3a and 3b. Here, the definition of "Da" is the same as above. However, the maximum width BE is not measured along the curved opening or radius of curvature, but is equal to the net height of the inlet 4 or the distance between the opposite edges.

As described above, the bag-shaped portion 5 has an increased inner diameter Ti in its entire area or longitudinal direction. The inner diameter Ti of the bag-shaped portion 5 is defined and measured in the following manner: the longitudinal axes 3a' and 3b' of the screws 3a and 3b define a common plane 13 or are located in a common plane 13. The inner diameter Ti is defined and measured by the length of a straight line that is perpendicular to the plane 13 and intersects the longitudinal axis 3a' of the screw 3a that is closest to or adjacent to the inlet 4. The straight line passes through the inner region 15 between the opposite faces of the inner wall 8 of the shell 2 (the upper and lower parts in FIG. 4c).

The maximum inner diameter Ti of the bag-shaped section is selected or determined, according to the present invention, by multiplying the coefficient k by the special relationship between the inner diameter Di of the screw 3a closest to the inlet 4. Similar to Da, Di is also determined or measured at the downstream point 9 of the inlet 4 in the conveying direction 6.

The bag-shaped section 5 also has a specific length range LT, starting from the downstream point 9 of the inlet 4 and extending along the conveying direction or longitudinal direction 6 of the screws 3a and 3b to the end 11 of the bag-shaped section 5, where the end 11 of the bag-shaped section 5 is located where there is no longer an increase in the screw clearance 7', and is located at the beginning of the parallel area of the extruder 1 or the extrusion area C, where the screw clearance 7 is substantially small and constant. In this example, the length range LT is approximately 6 Da, where "Da" is defined as described above, that is, Da is the outer diameter of the screw 3a closest to the inlet 4, measured at point 9.

Here, the length range LT of the bag-shaped section 5 is located in a transitional region B of the extruder 1. Therefore, the length range LT is the downstream portion of the bag-shaped section 5, in which the shell 2 gradually tapers from its increased portion in the bag-shaped section 5 to the small screw gap 7 in the extrusion region C. This is achieved by the partial conical contraction of the shell 2. In the first section downstream of the inlet 4, the screw gap 7' remains unchanged in size and the shell 2 is cylindrical. However, after the length range LT increases by about 20% to 30%, the screw gap 7' begins to decrease and gradually becomes a conical section until it reaches the end 11 of the bag-shaped section 5. Preferably, the conical section should be connected as closely as possible, and if necessary, even directly to the end of input 4 or point 9.

Here, as shown in Figures 1a and 1b, the pouch-shaped portion 5 increases circumferentially on all sides surrounding the screws 3a and 3b, or the screw clearance 7' increases circumferentially everywhere and in the area of the pouch-shaped portion 5, there are corresponding approximately equal radial distances or substantially similar screw clearances 7' between the screws 3a and 3b and the inner wall 8. However, the pouch-shaped portion 5 may also be increased only locally, that is, the pouch-shaped portion 5 forms a larger clearance between the screws 3a and 3b only in a specific circumferential area, but not in other areas.

Figure 2 shows a schematic perspective view (not drawn to scale) of important areas of an embodiment of the twin-screw extruder 1 according to the present invention. The leftmost side shows the drive 31, which drives the screws 3a and 3b. The material to be processed enters the gripping area of the closest screw 3a through the inlet 4. In this area or the feeding area A, the shell 2 is designed to be larger and forms the bag-shaped part 5 of the present invention. Downstream from here, a conical transition area B can be seen, in which the screw gap 7' becomes smaller and becomes a very small and constant screw gap 7 in the extrusion area C at the end 11 of the bag-shaped part 5.

Figure 3 shows a perspective view of the embodiment viewed from opposite directions, in which part of the shell 2 is deleted for clarity of illustration. In this figure, the inner region 15 of the shell 2 or bag-shaped portion 5, the gradually contracting transition region B, and the subsequent extrusion region C can be seen.

The descriptions of Figures 2 and 3 are similar to those of Figures 1a and 1b.

Figures 4a, 4b, and 4c show cross sections of the extruder 1 of the present invention, which cut through the shell 2 and the screws 3a and 3b at different positions, and these cross sections are perpendicular to the longitudinal axes 3a' and 3b' or the shell longitudinal axis 40.

Figure 4a shows a cross section of the extrusion region C, in which a very small screw clearance 7, less than 1 mm, can be clearly seen. This screw clearance remains essentially constant in the extrusion region C.

Figure 4b shows the cross section in the transition region B, especially in the conical contraction region, where the screw clearance 7 is larger than the screw clearance 7'. Therefore, the cross section is located in the area of the bag-shaped part 5, and there is a certain distance or space between the inner wall 8 and the screws 3a and 3b.

Figure 4c shows a cross-section of the bag-shaped portion 5, particularly in the inlet 4 region, where the screw clearance 7' reaches its maximum size and the inner diameter Ti of the bag-shaped portion 5 also reaches its maximum value. The plane 13 formed by the longitudinal axes 3a' and 3b' can be seen, with the inner diameter Ti passing through the longitudinal axis 3a' of the screw 3a and perpendicular to the plane 13.

In Figures 5a and 5b, preferred embodiments of the apparatus for processing or treating polymer materials, particularly for recycling thermoplastic waste, are shown from two different angles, one from above and one from the side.

The basic structure and working principle of this combination of cutting compactor and extruder are well known, for example from EP 2 558 263 or EP 2 689 908, and will be briefly introduced below.

The entire apparatus includes a cylindrical container or cutting compactor or pretreatment unit (PCU) 100 for receiving polymer material to be processed. Such a container 100 is known, for example, in EP 123 771, and is cylindrical with a flat bottom and cylindrical sidewalls 400 oriented perpendicularly thereto.

The container 100 contains a rotatable or rotating tool 300a, 300b. This tool 300a, 300b is a flat support plate mounted near the bottom of the container and rotates around a rotation axis 200, parallel to the bottom surface. A cutter is mounted on the top of the support plate. The support plate is rotated by a motor via a shaft located below the container 100. The rotation axis 200 or the shaft is positioned on the central longitudinal axis or central axis of the container 100.

Tools 300a and 300b are used to move, mix, heat, and pulverize materials within container 100. Thermoplastic materials are mixed, heated, softened, compressed, pre-degassed, dried, dehumidified, cut, shredded, crystallized, and/or homogenized within container 100, thereby increasing their bulk density. The materials form mixing vortices through the rotation of tools 300a and 300b, remain within container 100 for a certain period, and undergo appropriate pretreatment there.

In this embodiment, a container opening 500 is formed on the side wall of the container 100 at the height of a single tool 300a, 300b or at the height of the lowest tool plane. The shell 2 or inlet 4 of the extruder 1 is tangentially connected to this container opening 500. In this way, the pretreated polymer material in the container 100 is brought into the extruder 1 or into the gripping area of the screws 3a, 3, i.e., the area of the bag-shaped portion 5. The design of the extruder 1 is similar to that of Figures 1a and 1b, and therefore will not be described in detail. The feeding process is particularly important, especially for multi-screw extruders, and continuous horizontal feeding as consistently as possible is crucial. Introducing the material pretreated in the manner described above into the bag-shaped portion 5 of the twin-screw extruder 1 has particular advantages. In the area of container opening 500 or opening 4, the rotation direction of tool 300a on the lowest plane (indicated by the arrow) is basically opposite to the conveying direction 6 of extruder 1, i.e., it runs in reverse.

The outer edges of tools 300a and 300b extend relatively close to the sidewall 400. These tools or cutters are located at approximately the same height or plane as the central longitudinal axes 3a' and 3b' of the extruder screws 3a and 3b.

In actual operation, the plastic material to be processed is usually brought into container 100 in the form of plastic waste, bottles, or films. The plastic material is crushed and mixed by rotating tools 300a and 300b, and heated and softened by applied mechanical friction energy, but not melted. The softened but unmelted material remains in container 100 for a certain period of time, and then is discharged from container 100 through container opening 500 and fed into bag-shaped section 5 of extruder 1, or extruder 1 is partially fed in this manner.

In Figures 6a and 6b, another preferred embodiment of the entire device of the invention is shown from two different angles, namely from the top and the side.

Figures 6a and 6b are described in the same way as Figures 5a and 5b, except that the rotation direction of tool 300a (indicated by the arrow) is opposite to that in Figure 5a. Furthermore, the rotation directions of screws 3a and 3b are opposite to each other, and screws 3a and 3b are conical rather than cylindrical. Therefore, the longitudinal axes 3a' and 3b' are not parallel to each other, and the extruder 1 is not parallel in the extrusion area C, but rather conical to match the direction of screws 3a and 3b. The inner diameter Ti is determined in a similar manner, and the maximum inner diameter of the bag-shaped portion is located on the leftmost side upstream of inlet 4 in Figure 6b.

Example: The following tests were performed on a typical test apparatus conforming to the present invention, which is a combination of a PCU (pretreatment unit) and a twin-screw extruder with the following configuration: Device type Remarks PCU (container) 1300 mm in diameter EREMA Extrusion unit Twin screws running in the same direction Melt filter RTF 4/134 EREMA; 150µm filtration Granulation HG 152 thermal cutting EREMA Granulation System

In the above configuration (similar to the device shown in Figures 5a and 5b), a pretreatment unit (PCU) or container or cutting compactor is used, which has a tool with a variable speed drive, and a single (lower) tool plane located at the container opening or in the extruder feed area.

The twin-screw extruder used here has the following specific specifications and parameters: Length (LE) of inlet (4): 2.38 Da or 150 mm Width (BE) of inlet (4): 1.11 Da or 70 mm Outer diameter (Da) of screws (3a, 3b): 63 mm Outer diameter (Di) of screws (3a, 3b): approximately 40 mm Maximum inner diameter (Ti) of bag (5): 80 mm Length range (LT) of bag (5): 6 Da or 378 mm Two identical, parallel, co-rotating, interlocking cylindrical screws

The rotational speed of the tool in the PCU is controlled to input energy into the material, thereby achieving a specific material temperature. The material temperature is measured using a measuring system inserted into the material or non-contactly from the side or top. This temperature is primarily determined by the polymer being introduced; it is essential to ensure that the incoming material chips reach a temperature close to the softening polymer temperature. This ensures that the material has undergone a certain degree of pre-compaction within the PCU, i.e., that the bulk density has been homogenized within the PCU. Furthermore, tempering the material to near its softening point facilitates the melting process in the extruder. Since the softening temperature of the thermoplastic polymer used is within the range of water evaporation, residual moisture introduced into the material is also removed.

Here, HD-PE bottle granules were used as the test material. This material was obtained from old containers (such as shampoo bottles) or cleaning containers (such as household cleaners) in the personal hygiene product sector. The material was first pulverized and then pre-washed in a washing machine. The basic properties or parameters of this material are good flowability and different bulk densities and different moisture contents.

Test results show that the extruder maintains very constant filling and high filling density, and the feed behavior, output, and output consistency of the twin-screw extruder have been significantly improved. The quality of the HD-PE granules obtained in this way is also very satisfactory. The entire recycled material meets optical and mechanical requirements, and the produced recycled granules can be used to blow-dry household cleaning agent bottles or to add different amounts of recycled material to new materials.

1: Extruder 2: Shell 3a, 3b: Screw 3a', 3b': Longitudinal axis 4: Inlet 5: Bag-shaped section 6: Conveying direction 7, 7': Screw clearance 8: Inner wall 9: Downstream point 11: End 12: Lateral direction 13: Common plane, plane 15: Internal area 31: Drive 40: Shell longitudinal axis 100: Container 200: Rotating shaft 300a, 300b: Tool 400: Side wall 500: Container opening A: Feeding area B: Transition area BE: Height C: Extrusion area Da: Outer diameter Di: Inner diameter LE: Length LT: Length range Ti: Inner diameter

1: Extruder

2: Shell

3a, 3b: Screws

3a', 3b': Longitudinal axis

4:Input port

5: Sac-like portion

6: Conveying direction

7,7': Screw clearance

8: Inner wall

9: Downstream point

11: End

12: Horizontal, lateral direction

15: Internal Areas

31: Driver

40: Shell longitudinal axis

A: Feeding area

B: Transitional area

C: Extrude into the area

LE: Length

LT: Length range

Claims (17)

An extruder or multi-screw extruder (1), particularly a twin-screw extruder (1), for processing and melting polymer materials and having at least two screws (3a, 3b, ...) rotating within a common housing (2), comprising: a feed zone (A) for feeding the material to be processed into the extruder (1) and an extrusion zone (C) located further downstream for melting the material; wherein the housing (2) has at least one inlet (4) at the feed zone (A), formed in its housing wall and used to introduce the material to be processed into the gripping zone of the screws (3a, 3b, ...); in the extrusion zone (C), the screws (3a, 3b, ...)... There is a substantially constant narrow screw gap (7) between the outer diameter of the shell (2) and the inner wall (8) of the shell (2) all the way to the screw outlet; characterized in that the shell (2) has a bag-shaped portion (5) in the feed area (A) or in the area around the inlet (4) extending along the longitudinal section of the extruder (1) of the screws (3a, 3b, ...), the bag-shaped portion (5) having a screw gap (7') in its entire longitudinal direction, the screw gap (7') being larger than the screw gap (7) in the extrusion area (C) between the outer diameter of the screws (3a, 3b, ...) and the inner wall (8) of the shell (2). The extruder (1) as described in claim 1, wherein the end (11) of the bag-shaped portion (5) is located at the transition point into the extrusion region (C), from which the screws (3a, 3b, ...) are separated from the inner wall (8) only through the screw gap (7). The extruder (1) as described in claim 1 or 2, wherein the maximum length (LE) of the inlet (4), measured along the conveying direction or along the longitudinal direction (6) of the axial longitudinal axis (3a', 3b', ...) of the screws (3a, 3b, ...), is within the range of 0.2 Da ≤ LE ≤ 15 Da, where Da refers to the outer diameter of the screws (3a, 3b) closest to the inlet (4) and is measured at the downstream point (9) of the inlet (4) in the conveying direction. The extruder (1) as described in any of claims 1 to 3, wherein the maximum width (BE) of the inlet (4), measured along the transverse direction (12) of the conveying direction (6) or along the longitudinal axis (3a', 3b', ...) of the screws (3a, 3b, ...), is in the range of 0.1 Da ≤ BE ≤ 3 Da. The extruder (1) as described in any of claims 1 to 4, wherein the bag-shaped portion (5) has an enlarged inner diameter (Ti) along its entire longitudinal direction; 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 are located on the common plane (13). 3) Above; wherein the inner diameter (Ti) of the bag-shaped portion (5) is defined and measured as the length of a straight line between the relative areas of the inner wall (8) of the shell (2), perpendicular to the plane (13) and intersecting the longitudinal axis (3a') of the screw (3a) closest to or adjacent to the inlet (4); wherein the maximum inner diameter (Ti) of the bag-shaped portion (5) satisfies the following condition: Ti = k × Di, where 1.7 ≤ k ≤ 9.6; wherein Di is the inner diameter of the screws (3a, 3b, ...) closest to the inlet (4), measured at the downstream point (9) of the inlet (4) in the conveying direction. The extruder (1) as described in any of claims 1 to 5, wherein the bag-shaped portion (5) has a length range (LT) from the downstream point (9) of the inlet (4) along the conveying direction or along the longitudinal direction (6) of the axial longitudinal axis (3a', 3b', ...) of the screws (3a, 3b, ...) to the downstream end (11) of the bag-shaped portion (5), the length range (LT) being in the range of 0.2 Da ≤ LT ≤ 10 Da. The extruder (1) as described in any of claims 1 to 6, wherein the length (LE) of the input inlet (4) is in the range of 0.3 Da ≤ LE ≤ 10 Da. The extruder (1) as described in any of claims 1 to 7, wherein the width (BE) of the input (4) is in the range of 0.1 Da ≤ BE ≤ 2 Da. The extruder (1) as described in any of claims 1 to 8, wherein the determination of the inner diameter (Ti) for Da ≤ 100 mm is subject to: 1.7 ≤ k ≤ 3, and/or the determination of the inner diameter (Ti) for Da > 100 mm is subject to: 3 < k ≤ 9. The extruder (1) as described in any of claims 1 to 9, wherein the length (LT) of the bag-shaped portion (5) is in the range of 0.5 Da ≤ LT ≤ 6 Da. The extruder (1) as described in any one of claims 1 to 10, wherein, from the downstream point (9) of the inlet (4) along the conveying direction or along the longitudinal direction (6) of the axial longitudinal axis (3a', 3b', ...) of the screws (3a, 3b, ...) to the downstream end (11) of the bag-shaped portion (5), at least in the portion of the length range (LT) of the bag-shaped portion (5) greater than 50%, particularly in the portion greater than 80%, preferably in the portion greater than 90%, and more particularly, substantially over the entire length range (LT), the length range is designed to be conical and/or gradually tapered at a uniform angle. The extruder (1) as described in any of claims 1 to 11, wherein the input inlet (4) is located on the side of the extruder (1) and/or leads only to the gripping area of one of the screws, in particular the central longitudinal axis of the input inlet (4) intersects the central longitudinal axes (3a', 3b', ...) of the screws (3a, 3b, ...). The extruder (1) as described in any one of claims 1 to 12, wherein the extruder (1) is designed as a twin-screw extruder having two cylindrical screws (3a, 3b) that are parallel to each other, rotate in the same direction or opposite direction and mesh with each other, or having two tapered screws (3a, 3b) that rotate in the same direction or opposite direction and mesh with each other. The extruder (1) as described in any of claims 1 to 13, wherein a passive feeding element, particularly a hopper, and/or an active feeding element, particularly a pusher screw, are provided for introducing the material to be processed into the inlet (4), and in particular the active and/or passive feeding elements are directly connected to the extruder (1). An apparatus for processing or treating polymeric materials, particularly for recycling thermoplastic waste plastics, comprising: at least one container or cutting compactor (100) for the material to be processed, wherein the container (100) is provided with at least one, optionally multiple, tools (300a, 300b, ...) rotatable or rotating about a rotation axis (200), the tools being used for moving, mixing, heating, and optionally crushing the material; wherein within the container (100), particularly in the container... On the side wall (400) of the device (100) or particularly in the area or height of the lowest or closest to the bottom tool (300a), there is a container opening (500) through which pretreated material is discharged from the container (100); and at least one extruder (1) as described in any one of claims 1 to 14 for receiving the material discharged from the container (100), wherein, in particular, the extruder (1) is directly connected to the container (100). The device as described in claim 15, wherein, within the container (100), a plurality of or at least two tools (300a, 300b, ...) are disposed on different tool planes or at different distances from the bottom surface or lowest region of the container (100), and the tools (300a, 300b, ...) are disposed in at least two overlapping working planes within the container (100). The device as described in claim 15 or 16, wherein the tool (300a) or the lowest tool (300a) or the lowest tool plane is disposed in the area or height of the container opening (500), and if necessary, at the height of the inlet of the extruder (1) to which it is connected.