Method and arrangement for extruding recycled material

Abstract

The invention relates to a method for extruding recyclate, wherein the recyclate contains light materials and / or fibres and wherein the recyclate is first comminuted and compacted and, in a subsequent method step, is fed into an extruder (2). According to the invention, the recyclate is agglomerated in a press agglomerator and in the process is heated, and is divided into pellets, and, when still in the warm state, is fed into the extruder (2) with the material still having an inherent residual temperature of at least 50°C from the agglomeration. The invention also relates to an arrangement (1) comprising an extruder (2) which has an inlet for the material to be extruded, and a press agglomerator which has an inlet opening (6) for recyclate to be agglomerated and an outlet for the pellets produced, wherein the press agglomerator is arranged upstream of the extruder (2) such that the inlet of the extruder (2) is connected to the outlet of the press agglomerator.

Description

[0001] "Method and arrangement for extruding recycled material"

[0002] Description:

[0003] The invention relates to a method for extruding recycled material, so-called recyclate, and an arrangement for carrying out the method. Plastic materials are particularly suitable as recyclate. The recyclate can contain, among other things, films and fibrous components, e.g., plant fibers.

[0004] A generic procedure is known from practice.

[0005] For example, it is well known that the feed behavior of an extruder screw, which is used to feed the recyclate to the extruder, can be problematic. Feeding the extruder screw with the recyclate, especially with lightweight materials and fibers, is often difficult. The occurrence of air pockets in the extruder is unavoidable, but undesirable.

[0006] Air inclusions in the finished extruded material can either lead to shrinkage cavities, i.e. voids in the material, or at least to an interruption in the homogeneity of the material, for example when two areas are adjacent to each other with a "skin", so that later in a component there is no void at this point, but for example the mechanical load-bearing capacity of the material is considerably reduced - similar to what is known from a notch effect.

[0007] This can be counteracted by creating negative pressure zones in the extruder to achieve bubble separation. This is particularly successful with air pockets that extend to the outside of the material stream in the extruder or very close to the outside of the material stream, causing the outer skin of the material stream to rupture and allow the air to escape. However, air pockets located deeper inside the material cannot be removed from the material in this way.

[0008] As a further measure to avoid air pockets as much as possible, the aim can be to fill the screw flights of the extruder screw as completely as possible with material. This way, empty spaces or bubbles in the material are avoided as much as possible, both during the feeding of the extruder screw and during the subsequent process in which the material is conveyed through the extruder. To avoid voids as much as possible from the outset, it is therefore common practice to plug the extruder screw. In this process, the prepared particulate or fibrous material is conveyed into the inlet of the extruder screw by a feed screw. By tapering the cross-section in the conveying direction of the feed screw, e.g., a conical cross-section reduction, the fed material is compacted before it enters the extruder screw.

[0009] Another option for feeding the extruder screw with material as densely as possible is pre-treating the recyclate in a cutter-compactor. The recyclate is circulated in the cutter-compactor and shredded by the cutter-compactor's blades. This process causes the material to segregate: heavier components are pushed outwards more strongly by centrifugal force, while lighter components remain in the center of the cutter-compactor for longer. This significantly impairs the desired homogeneity of the material, which is later desired in the extruder. This is particularly true when not only the recyclate is fed into the extruder screw, but when additives are also added to the recyclate. Due to the segregation and the varying residence time in the cutter-compactor, the distribution of the additive in the material is also irregular.In addition to these two different reasons for inhomogeneities, the heat introduced into the material can also cause the material to "crimp." In this context, "crimping" refers to the temperature-induced deformation of the material, as can be observed, for example, when fibers or foils are held close to an open flame, where they bend and contract. Aside from the fact that crimping is generally undesirable anyway due to the changed material structure, the heat stress also occurs to varying degrees in the material due to the above-mentioned different residence times of different material components, so that some components crimp and others do not, which in a third respect causes inhomogeneities in the treated material.

[0010] When recyclate is extruded, in many cases no final products are produced, but rather granules which, similar to the granules made from virgin plastic, are used in the plastics processing industry to manufacture the respective products. The extruder, as provided for in the present invention, can therefore be followed by a cutting unit, for example a hot cutting unit, which cuts up the continuous strand of material emerging from the extruder to produce granules. The invention is based on the object of improving a generic method in such a way that the most dense and homogeneous filling of an extruder screw with material is possible. Furthermore, the invention is based on the object of specifying an apparatus for carrying out this method.

[0011] This object is achieved by a method according to claim 1 and by a device according to claim 8.

[0012] In other words, the invention proposes installing a press agglomerator upstream of the extruder. This ensures largely uniform comminution and agglomeration even when a mixture of different materials is fed in. Press agglomerators are known in various designs, e.g., as punch presses, punch strand presses, screw presses, perforated roller presses, or roller presses, as flat or ring die pelletizers. The agglomerates can leave the press agglomerator as finished, separate shaped bodies, e.g., when they are pressed into these shaped bodies in the troughs of two opposing rollers of a roller press. Alternatively, a comminution unit can be installed downstream of the press agglomerator, e.g.,when the shaped bodies produced in a roller press are separated from one another only by lines of weakness, but are still attached to one another and are separated from one another in a downstream crusher, or when they are produced as a continuous strand of material which is divided into a large number of individual bodies by a downstream knife. Both the shaped bodies produced and the individual bodies are referred to as pellets in the context of this proposal. Therefore, according to the proposal, the recyclate processed in the press agglomerator can be fed to the extruder screw as material in granulate form. While granules often refer to bodies that are irregular, often random, in terms of their shape or size, the bodies used in the proposal have fairly uniform properties in terms of their shape or size, and are therefore referred to as pellets in the context of this proposal.Using the proposed process, even when using recycled material, the extruder screw can be fed with a material that is almost as advantageous in terms of homogeneity and has almost as uniform properties as is otherwise the case with virgin plastic granules. The pellets also enable a similarly dense filling of the extruder screw as when using virgin plastic granules, so that air pockets during and after extrusion can be largely avoided, and in any case can be prevented considerably more effectively than has previously been the case with recycled material. By filling the extruder screw as densely and homogeneously as possible, a continuous, maximum material throughput of the extruder is supported, thus ensuring its economically advantageous, highest possible output of material with the highest possible uniform and high quality.

[0013] The recyclate can, for example, be pelletized in a flat-die press, which also allows for the comminution and pelletization of fibrous materials and non-melting materials. Therefore, the use of a pelletizer, in particular a flat-die press, is mentioned in the description of the present proposal purely as an example of the design of a press agglomerator and not as a limitation. According to the proposal, it is further provided that the pellets emerging from the press agglomerator, with their inherent residual heat, are fed into the extruder screw via the shortest possible route and in the shortest possible time—preferably directly.The pellets are proposed to have a temperature of 50°C or more, and since they often leave the press agglomerator at temperatures of around 100°C, the temperatures at which the pellets enter the extruder are often significantly higher than 50 or 60°C, for example 80°C or even more than 90°C, depending on the design of the arrangement used.

[0014] Intermediate storage of the pellets is avoided wherever possible. Accordingly, the pellets do not need to be cooled, which is energy-intensive, to prevent them from sticking together during intermediate storage. Likewise, the energy required to heat the pellets after intermediate storage so that they can be processed in the extruder in an optimally plasticized state is eliminated. In order to avoid not only intermediate storage, but also long transport routes and the use of insulated containers or the like, this process aspect can be taken into account in the design of the arrangement by feeding the pellets from the pelletizer into the extruder screw via the shortest possible route, for example by connecting the pelletizer to the extruder, either directly or via a connecting pipe, a feed screw that is as short as possible, or the like, so that the inlet of the extruder, e.g.The extruder screw is connected to the outlet of the press agglomerator. Such a combination of system components can be referred to as a "PellEx" arrangement to illustrate the combination of pelletizer and extruder into a single unit.

[0015] Non-thermoplastic materials can also be processed in the pelletizer, so the recycled material used can, for example, contain non-thermoplastic plastics, plant fibers, or the like in addition to thermoplastics. Compared to other shredding systems that could be used for shredding recycled material, this is advantageous in that, for example, non-thermoplastic plastics, plant fibers, or other non-melting materials do not soften in a cutter-compactor and cannot be processed.

[0016] Additives can be added to the pelletizer because they are evenly distributed over the material and are therefore present evenly in the pellets.

[0017] In one embodiment, the pelletizer can be designed as a press agglomerator. Various designs of press agglomerators are known in practice and can be used within the scope of the present invention.

[0018] A hot die can be installed downstream of the extruder. The resulting granules enter a liquid cooling medium, such as water, so that the individual granules are cooled, at least on the outside, to such an extent that they do not stick together during further transport or storage. The cooling medium absorbs the heat from the granules. It can be passed through a heat exchanger through which an air stream is blown. The resulting heated air can be used to preheat the recyclate before it is fed into the pelletizer, thus reducing the pelletizer's energy requirements.

[0019] The recyclate can advantageously be washed first in order to remove surface contaminants. Even if the recyclate is separated from the adhering wash water after washing, for example in a drum or similar equipment, a considerable amount of moisture adheres to the recyclate in the form of a surface film. In practice, it therefore often happens that material with a moisture content of more than 10%, e.g. up to 15%, is fed to the extruder screw. Apart from the fact that a considerable amount of energy is required in the extruder to heat this amount of moisture, convert it into steam and then discharge it from the extruder in steam form, this steam formation carries the risk of steam bubbles being formed, which create undesirable cavities in the material flow of the extruder and that they alsoThe negative pressure zones provided in the extruder cannot be removed from the material if they are located too deep within the material flow. Utilizing the process heat generated in the plant, e.g., from the hot die as mentioned above, to pre-dry the material before it enters the pelletizer therefore represents a significant energy advantage for the operation of the entire plant.

[0020] The invention is explained in more detail below using a purely schematic representation.

[0021] The drawing shows a perspective view of an assembly 1 for extruding recycled material, which assembly 1 serves to produce plastic granulate. The assembly 1 comprises an extruder 2, upstream of which is a pelletizer 3 as a press-agglomeration unit. Furthermore, a melt filter, in the illustrated embodiment in the form of a piston melt filter 4, and a water ring granulator 5 are connected downstream of the pelletizer 3.

[0022] Recycled material, which may contain thermoplastic components, thermosetting components, or even fibrous components, e.g., in the form of plant fibers, is fed into the pelletizer 3 through an inlet opening 6. The recyclate has previously been cleaned, e.g., dry in a friction washer or wet using water. In the case of wet washing, the washed recyclate has been pre-dried so that it enters the pelletizer 3 with the lowest possible moisture content.

[0023] In the illustrated embodiment, the pelletizer 3 is designed as a pelletizing press with a pan mill having three rotors 7 and a main drive 8. A die 9, on which the rotors 7 run, is mounted so as to be height-adjustable, so that the gap between the rotors 7 and the die 9 can be adjusted to suit the particular recyclate used and the desired properties of the pellets produced in the pelletizer 3. The die 9 has a plurality of openings in the form of bores through which the recyclate passes, so that a plurality of material strands are produced. An auxiliary drive 10 on the pelletizer 3 serves to drive a cutting device 11, which has, for example, one or more rotating cutting knives, so that the length of the resulting pellets can be adjusted by the rotational speed of the cutting device 11.

[0024] From the material strands emerging downward from the die 9, a plurality of pellets are produced by the cutting device 11. These pellets fall downward from the pelletizer 3 through a transfer chute 12. The pellets reach the extruder 2 through the transfer chute 12, taking the shortest possible route, without long transport routes, intermediate storage, or the like. In the transfer chute 12, the assembly 1 can have a dust separator, which serves to separate the dust portion of the material that could not be bound in the pellets from the pellets. The separated dust can be guided to the inlet opening 6 and thus reintroduced into the pelletizing process. In contrast to the illustrated embodiment, the pellets can pass directly into the extruder 2 through a differently designed, shorter transfer chute 12.In the illustrated embodiment, however, the addition of additives to the pellets is provided, so that these additives are subsequently mixed with the pellets in the extruder or on the way there, e.g. in a feed screw. The additives can be, for example, color pigments or reinforcing or filler materials such as talc, or the like. The additives can be in dust, powder, granular or liquid form or also in pellet form. The additives are then fed into the pellet stream in the feed zone of the extruder 2. It can be provided to use one or more additional press agglomerators, such as pelletizers, which can make additives that are difficult to dose meterable and feedable into the extruder 2 through compression.

[0025] The transfer chute 12 is therefore designed in such a way that two volumetric or gravimetric dosing stations 14 are connected to it, which serve to introduce the additives into the pellet stream. The pellets enriched with the additives pass through the transfer chute 12 into an extruder screw of the extruder 2, which is driven by a drive motor 15. An extruder gear, not visible in the drawing, is arranged behind the drive motor 15 in a housing 16 of the extruder 2. The housing of the extruder 2 surrounding the extruder screw can have longitudinal ribs on the inside to prevent the material moved by the extruder screw from rotating together with the extruder screw, which would impair the conveying effect of the extruder screw.

[0026] The pellets fall through the transfer chute 12 at a temperature of approximately 80 to 100 °C and thus enter the extrusion process directly with their inherent residual heat. At its lower end, the transfer chute 12 connects to the feed nozzle of the extruder 2, in particular its extruder screw, which can be a single-screw, twin-screw, or multi-screw extruder.

[0027] The extruder 2 has a vacuum degassing system 17 within its housing 16, which serves to separate volatile substances from the melt. In the piston melt filter 4, which is located downstream of the extruder 2, impurities and dirt particles are removed from the extruded material strand. The extruded and cleaned material strand is then granulated in a hot die, which in the illustrated embodiment is designed as a water ring granulator 5. This results in intensive heat transfer from the granules, from which heat is extracted, to the water, so that the surface temperature of the granules is reduced to such an extent that they subsequently do not stick together.

[0028] The water heated in this way is used to pre-dry the washed recyclate: for example, it can be cooled in a water / air heat exchanger, and the heated air is blown onto the washed recyclate before it enters the pelletizer 3. Alternatively, the heated water can transfer its heat to a medium in a heat exchanger, which serves to heat elements that, in turn, pre-dry the washed recyclate through radiant heat. Alternatively, the heated water itself, without a heat exchanger, can serve to heat the aforementioned elements that pre-dry the washed recyclate through radiant heat. Reference symbols:

[0029] arrangement

[0030] Extruder

[0031] Pelletizer

[0032] Piston melt filter

[0033] Water ring granulator

[0034] Inlet opening

[0035] runner

[0036] Main drive

[0037] die

[0038] Power take-off

[0039] teeing device

[0040] transfer shaft

[0041] Dosing station

[0042] drive motor

[0043] Housing

[0044] Vacuum degassing system

Claims

Claims:

1. A method for extruding recycled material, wherein the recycled material contains lightweight materials and / or fibers, and wherein the recycled material is first shredded and compacted and in a subsequent process step fed into an extruder (2) is carried, characterized in that the recycled material is agglomerated and heated in a press agglomerator and divided into pellets, and is carried in the extruder (2) while still warm, with a residual heat of at least 50°C still inherent in the material from agglomeration.

2. Method according to claim 1, characterized in that the recycled material is pelletized by being crushed and mixed in a roller mill.

3. Method according to claim 1 or 2, characterized in that the recycled material is pelletized in a flat die press.

4. Method according to one of the preceding claims, characterized in that the produced pellets are fed directly from the press agglomerator into the extruder (2).

5. Method according to one of the preceding claims, characterized in that the recycled material is washed before being fed into the press agglomerator. A method according to any one of the preceding claims, characterized in that the heat released from the extruded material is used as process heat or for space heating by means of a heat exchanger. A method according to claims 5 and 6, characterized in that the heat released from the extruded material is used as process heat to heat air by means of a heat exchanger, and that the washed recyclate is dried using the heated air. An arrangement (1) for carrying out the method according to any one of the preceding claims, comprising an extruder (2) having an inlet for the material to be extruded, and a press agglomerator having an inlet opening. (6) for recycled material to be agglomerated and an outlet for the pellets produced, wherein the press agglomerator is arranged upstream of the extruder (2) such that the inlet of the extruder (2) is connected to the outlet of the press agglomerator. Arrangement according to claim 8, characterized in that the press agglomerator is designed as a pelletizer (3) in the form of a flat die press and is arranged above the inlet of the extruder (2). Arrangement according to claim 8 or 9, characterized in that a filter device is arranged downstream of the extruder (2). is designed to filter out contaminants and dirt particles from the extruded material. Arrangement according to one of claims 8 to 10, characterized in that a downstream discharge is arranged after the extruder (2), which is designed to granulate the extruded material. Arrangement according to claim 11, characterized in that the discharge is configured as a water ring granulator (5). Arrangement according to claim 11 or 12, characterized in that the discharge is effectively connected to a heat exchanger in such a way that heat is transferred to an airflow, and that a blower arrangement is configured in such a way that it directs the heated airflow onto the recyclate before the latter enters the inlet opening (6) of the pelletizer (3).

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