Method and apparatus for extruding recovery material

Abstract

The invention relates to a method for extruding a recycled material, the recycled material containing lightweight material and / or fibres, and the recycled material is first comminuted and compacted and is guided into an extruder (2) in a subsequent method step, it is proposed that the recycled material is agglomerated in a pressure granulator and the recycled material is heated at the time, and the recycled material is extruded into the extruder (2). The recycled material is divided into pellets and is conducted in the still hot state into the extruder (2) with a residual heat of at least 50 DEG C from the pellets, which is still inherent to the material. The invention further relates to a device (1) comprising: an extruder (2) having an inlet for the material to be extruded; the invention relates to an extruder (2) for producing granules, comprising an extruder (2) and a pressure granulator having an inlet (6) for the reclaimed material to be granulated and an outlet for the produced granules, the pressure granulator being arranged upstream of the extruder (2) such that the inlet of the extruder (2) is connected to the outlet of the pressure granulator.

Description

Technical Field

[0001] The invention relates to a method for extruding recycled material, so-called regrind, and a device for carrying out the method. As regrind, in particular plastic material is used. The regrind can contain, among other things, film and fiber-like components, for example also vegetable fibers. Background Art

[0002] Methods of this type are known from practice.

[0003] For example, it is known that the feeding performance of the extruder screw, which is used to convey the regrind to be extruded, to the extruder, can be problematic. In particular, for lightweight materials and fibers, it has proven increasingly difficult to load the extruder screw with regrind. The occurrence of air inclusions in the extruder is inevitable, but undesirable. Air inclusions can lead to shrinkage cavities in the extruded material, that is, cavities in the material, or, for example, if two regions are attached to each other in a "skin", so that although no cavities will occur at this point in the component later, the mechanical load-bearing capacity of the material is significantly reduced, similar to what is known from the notch stress concentration effect, and the air inclusions at least lead to interruptions in the homogeneity of the material.

[0004] Attempts can be made to counteract this by creating negative pressure areas in the extruder in order to achieve bubble separation. This is particularly effective for air inclusions that extend to the outside of the material flow in the extruder or to very close to the outside of the material flow, whereby the outer layer of the material flow breaks apart and the air can escape. However, air inclusions that are located deeper in the material cannot be removed from the material in this way.

[0005] As a further measure to avoid air inclusions as far as possible, it can be aimed at filling the screw groove of the extruder screw as completely as possible with the material, so that in this way, when charging the extruder screw and also in the further process flow of the material through the extruder, cavities or gas bubbles in the material are avoided as far as possible. Therefore, in order to avoid the formation of cavities as far as possible from the outset, it is known to block the extruder screw. In this case, the feed screw conveys the prepared granular or fibrous material to the feed opening of the extruder screw. Due to the fact that the cross section of the feed screw tapers in the conveying direction, for example, the cross section decreases conically, the supplied material is compacted before it enters the extruder screw.

[0006] As another possibility for loading the extruder screw with material as densely as possible, it is known from practice to pre-treat the regrind in a cutter compactor. The regrind is circulated in the cutter compactor and comminuted by the cutting of the cutter compactor. It can be seen here that the material separates: the heavier components are pushed outwards more strongly due to the centrifugal force, while the lighter components stay longer in the center of the cutter compactor. This seriously affects the material homogeneity that is sought to be achieved and is later desired in the extruder. This is especially true when the regrind is not only supplied to the extruder screw separately, but also when additives are added to the regrind.

[0007] Due to the separation and the different residence times in the cutter compactor, the distribution of the additive in the material is also uneven. In addition to these two different causes of inhomogeneity, the material can also "curl" due to the heat in the input material. In this case, "curling" refers to temperature-induced deformation of the material, such as can also be observed when fibers or films are kept near an open flame and then bend and shrink. In addition to the fact that this curling is in principle undesirable due to the changing material structure, due to the above-mentioned different residence times of different material parts, thermal loads occur in the material with different intensity, so that some parts curl while other parts do not curl, thus leading to inhomogeneities in the treated material in a third aspect.

[0008] In many cases, when regrind is extruded, a pellet is not produced as a final product, but rather a pellet which is used in the plastics processing industry similarly to pellets consisting of virgin plastics to produce corresponding products. Therefore, an extruder, such as the one provided within the scope of the invention, can be followed by a chopper, for example a hot chopper, which cuts up the continuous material strands emerging from the extruder and thus provides pellets. Summary of the invention

[0009] The object of the present invention is to improve a method of the generic type in such a way that the extruder screw is filled with material as densely and uniformly as possible. In addition, the object of the present invention is also to provide a device for carrying out the method.

[0010] This object is achieved by a method according to claim 1 and by a device according to claim 8 .

[0011] In other words, the invention proposes to provide a pressure granulator upstream of the extruder. The pressure granulator can also ensure approximately uniform comminution and granulation when a mixture of different materials is supplied. Pressure granulators are known in different designs, for example as die presses, die extruders, screw presses, perforated roller presses or roller presses, as flat or ring die granulators. For example, when the granules are pressed into a molded body in the recesses of two opposite rollers of a roller press, the granules can leave the pressure granulator as finished molded bodies separated from each other. Alternatively, it can be provided that a comminution unit can also be arranged downstream of the pressure granulator, for example, if the molded bodies produced in the roller press are separated from each other only by weakening lines, but are still connected to each other and separated from each other in a downstream crusher, or if the molded bodies are produced as a continuous material strip, which is divided into a plurality of individual pieces by a downstream knife. In the scope of the present proposal, both the produced molded bodies and the individual pieces are referred to as granules.

[0012] Thus, according to the proposal, the recyclate processed in the pressure pelletizer can be supplied to the extruder screw as a material in the form of granules. Granules usually refer to small pieces that are irregularly and usually randomly formed in terms of their shape or size, while the small pieces used according to the proposal have relatively uniform properties in terms of their shape or size, so that the small pieces are called granules within the scope of the proposal. Therefore, with the help of the method according to the proposal, when using recyclate, the extruder screw can also be loaded with such a material, which is almost equally favorable in terms of its uniformity and has nearly the same uniform properties as in the case of virgin plastic granules in other respects. Granules also make it possible to fill the extruder screw with a density similar to that when using virgin plastic granules, so that air inclusions can be basically avoided during and after extrusion, and at least significantly more effectively prevented than has been known from practice so far when using recyclate. By filling the extruder screw as densely and uniformly as possible, it is helpful to achieve a continuous and maximum possible material throughput of the extruder and thus to achieve an economically favorable and maximum possible material output of the extruder with the most uniform and high quality.

[0013] The regrind can be pelletized, for example, in a flat-die press, which allows comminution and pelletization of fibrous and infusible materials. For the design of the pressure pelletizer, the use of a pelletizer, in particular a flat-die press, is therefore mentioned in the description of the proposal by way of example and without limitation.

[0014] Furthermore, according to the proposal, it is provided that the pellets coming out of the pressure pelletizer with their inherent residual heat are guided over the shortest possible path and in the shortest possible time, that is, advantageously directly into the extruder screw. According to the proposal, the pellets have a temperature of 50° C. or higher, and since the pellets usually leave the pressure pelletizer at a temperature of about 100° C., the temperature of the pellets entering the extruder is usually significantly higher than 50 or 60° C., for example, at around 80° C., or even higher than 90° C., depending on the design of the equipment used.

[0015] Temporary storage of the pellets is avoided as much as possible. Therefore, it is not necessary to first cool the pellets with high energy consumption in order to prevent the pellets from sticking to each other during temporary storage. The energy consumption for heating the pellets after temporary storage is also saved, which is used to allow the pellets to be processed in the extruder in an optimal plasticized state. In order to avoid not only temporary storage but also long transportation distances and the use of insulating containers or the like, this method aspect can be taken into account when designing the device, that is, the pellets are guided from the pelletizer to the extruder screw over the shortest possible path, for example, by connecting the pelletizer to the extruder directly or via a connecting pipe, a feed screw that is as short as possible, or the like, so that at least the inlet of the extruder, for example its extruder screw, is connected to the outlet of the pressure pelletizer. This combination of device components can be called a "PellEx" arrangement to indicate that the pelletizer and the extruder are connected to form a common device.

[0016] Non-thermoplastic materials can also be processed in the granulator, so that the recycled material used can, for example, contain non-thermoplastics, vegetable fibers or the like in addition to thermoplastics. This is advantageous compared to other comminution plants that can be used to shred recycled material, because non-thermoplastics, vegetable fibers or other infusible materials cannot be softened and processed, for example, in a cutter compactor.

[0017] Additives can be added to the granulator since they are evenly distributed over the material and are therefore present evenly in the granules.

[0018] In one embodiment, the granulator can be designed as a pressure granulator. Various designs of pressure granulators are known from practice and can be used within the scope of the present invention.

[0019] A hot chopper can be arranged downstream of the extruder. In this case, the granules produced here are introduced into a liquid cooling medium, for example water, so that the individual granules are cooled at least externally, so that the granules do not stick to each other during further transportation or storage. The cooling medium absorbs heat from the granules. The cooling medium can be guided through a heat exchanger through which an air stream is blown. Accordingly, the heated air can be used to preheat the regrind before it is fed into the granulator, so that the energy requirement of the granulator can be reduced.

[0020] That is to say, advantageously, the reclaimed material can be first cleaned so as to remove surface impurities from the reclaimed material. Even when the reclaimed material is separated from the attached washing water after being cleaned in a drum or similar equipment, a large amount of moisture still remains attached to the reclaimed material in the form of a surface water film. Therefore, in practice, it constantly occurs that the material with more than 10%, for example up to 15% moisture is supplied to the extruder screw. In addition to requiring large energy consumption in the extruder to heat these moistures, convert them into steam and then discharge them from the extruder in the form of steam, forming steam in this way also brings the following risk, that is, forming steam bubbles, which form undesirable cavities in the material flow of the extruder, and if the steam bubbles are located too deep inside the material flow, these steam bubbles also cannot be derived from the material in the negative pressure area provided in the extruder when necessary. Therefore, these process heats that occur in the equipment, for example, the process heat from the hot shredder for drying the material before entering the granulator constitutes a significant energy advantage for the operation of the entire equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention is explained in more detail below with reference to purely schematic drawings. DETAILED DESCRIPTION

[0022] The drawing shows a perspective view of a device 1 for extruding recycled material, which is used to produce plastic granules. The device 1 comprises an extruder 2, upstream of which a granulator 3 is arranged as a device for pressure granulation. In addition, a melt filter in the form of a piston melt filter 4 in the illustrated embodiment and a water ring granulator 5 are arranged downstream of the granulator 3.

[0023] The recyclate, which may contain thermoplastic components, thermosetting plastic components or also fiber components, for example in the form of vegetable fibers, is fed into the granulator 3 via the inlet 6. The recyclate has previously been cleaned, for example dry in a friction washer or wet with water. In the case of wet cleaning, the cleaned recyclate is pre-dried so that it enters the granulator 3 with as little moisture as possible.

[0024] In the embodiment shown, the pelletizer 3 is designed as a pelletizing press with a roller mill having three rollers 7 and a main drive 8. The die 9 on which the rollers 7 run is supported in a height-adjustable manner, so that the gap between the rollers 7 and the die 9 can be adjusted in accordance with the respective recyclate used and the desired properties of the pellets produced in the pelletizer 3. The die 9 has a plurality of through-holes in the form of drill holes, through which the recyclate is passed, so that a plurality of material strands are produced. An auxiliary drive 10 on the pelletizer 3 is used to drive a chopping device 11, which has, for example, one or more circumferential chopping knives, so that the length of the resulting pellets can be set by the rotation speed of the chopping device 11.

[0025] A plurality of pellets are produced from the material strands discharged downward from the die 9 by means of a chopping device 11, and the pellets fall downward from the pelletizer 3 via a conveying chute 12. The pellets reach the extruder 2 via the conveying chute 12 over the shortest possible path without long transport paths, temporary storage or the like. The device 1 can have a dust collector in the conveying chute 12, which serves to separate dust components of the material that cannot be incorporated into the pellets from the pellets. The separated dust can be guided to the inlet 6 and thus reintroduced into the pelletizing process.

[0026] Unlike the embodiment shown, the pellets can enter the extruder 2 directly via a shorter conveying chute 12 of different design. However, in the embodiment shown, it is provided that additives are added to the pellets, so that these additives are then mixed with the pellets in the extruder or on the way to the extruder, for example in a feed screw. The additives can be, for example, pigments or reinforcing agents or fillers, such as, for example, talcum powder or the like. The additives can be in the form of dust, powder, granules or liquid or also in the form of pellets. The additives are then fed into the pellet stream in the feed zone of the extruder 2. It can be provided that one or more additional pressure granulators, such as, for example, a granulator, are used, which can make it possible to meter additives that are difficult to meter by compacting and make them possible to feed into the extruder 2.

[0027] Therefore, the conveying chute 12 is extended in such a way that two volumetric or weight metering stations 14 can be connected to the conveying chute, which are used to introduce additives into the pellet flow. The pellets with added additives enter the extruder screw of the extruder 2 driven by the drive motor 15 through the conveying chute 12, wherein the extruder transmission device not visible in the figure is arranged behind the drive motor 15 in the housing 16 of the extruder 2. The housing of the extruder 2 surrounding the extruder screw can have ribs extending in the longitudinal direction on the inside to prevent the material moved by the extruder screw from rotating with the extruder screw, which would affect the conveying effect of the extruder screw.

[0028] The pellets fall through the conveyor chute 12 at a temperature of about 80° C. to 100° C. and therefore enter the extrusion process directly with their inherent waste heat. The conveyor chute 12 is connected at its lower end to the feed connection of the extruder 2, in particular to the extruder screw of the extruder, which can be a single-screw extruder, a twin-screw extruder or a multi-screw extruder.

[0029] The extruder 2 has in its housing 16 a vacuum degassing device 17, which serves to separate volatile substances from the melt. Impurities and dirt particles are removed from the extruded material strand in a piston melt filter 4 arranged downstream of the extruder 2. The extruded and purified material strand is then granulated in a hot chopper, which in the illustrated embodiment is designed in the form of a water ring granulator 5. Here, an intense heat transfer from the heat-extracted pellets to the water occurs, so that the surface temperature of the pellets is reduced, so that the pellets do not subsequently adhere to one another.

[0030] The water heated in this way is used for pre-drying the washed recyclate: for example, the water can be cooled in a water / air heat exchanger and the heated air blown onto the washed recyclate before the recyclate enters the granulator 3. Alternatively, the heated water can output its heat in a heat exchanger to a medium, which is used to heat elements, which themselves achieve pre-drying of the washed recyclate by radiant heat. Alternatively, the heated water itself can also be used to heat the elements without a heat exchanger, which achieve pre-drying of the washed recyclate by radiant heat.

[0031] Reference numerals list

[0032] 1 device

[0033] 2 Extruder

[0034] 3 Granulator

[0035] 4 Piston Melt Filter

[0036] 5. Water Ring Granulator

[0037] 6 Input ports

[0038] 7 Roller

[0039] 8 Main drive

[0040] 9 Mould

[0041] 10 Auxiliary drives

[0042] 11Chopping device

[0043] 12 Conveyor chute

[0044] 14 Metering Station

[0045] 15. Drive motor

[0046] 16 Shell

[0047] 17Negative pressure degassing equipment

Claims

1. A method for extruding recycled material, wherein: The recycled material contains lightweight materials and / or fibers, and the recycled material is first crushed and compacted, and in a subsequent method step it is directed to the extruder (2), The invention is characterized in that the recycle material is pelletized in a pressure pelletizer and heated in the process, and the recycle material is divided into pellets and is introduced into an extruder (2) in a still hot state with residual heat from the pellets of at least 50° C. still inherent in the material.

2. The method according to claim 1, characterized in that The regrind is granulated by comminuting and mixing the regrind in a wheel mill.

3. The method according to claim 1 or 2, characterized in that: The regrind was pelletized in a flat die press.

4. The method according to any one of the preceding claims, characterized in that The pellets produced are conducted directly from the pressure pelletizer to the extruder (2).

5. The method according to any one of the preceding claims, characterized in that Before the recycle is directed to the pressure agglomerator, the recycle is washed.

6. The method according to any one of the preceding claims, characterized in that The heat released by the extruded material is used via a heat exchanger as process heat or space heating.

7. The method according to claims 5 and 6, characterized in that The heat released by the extruded material via the heat exchanger is used as process heat to heat the air, and the cleaned regrind is dried by the heated air.

8. A device (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 pressure pelletizer having an inlet (6) for the regrind to be pelletized and an outlet for the pellets produced, wherein: The pressure granulator is arranged upstream of the extruder (2) so that the inlet of the extruder (2) is connected to the outlet of the pressure granulator.

9. The device according to claim 8, characterized in that The pressure pelletizer is designed as a pelletizer (3) in the form of a flat die press and is arranged above the inlet of the extruder (2).

10. The device according to claim 8 or 9, characterized in that A filter device is arranged downstream of the extruder (2), which is designed to filter foreign particles and dirt particles from the extruded material.

11. The device according to any one of claims 8 to 10, characterized in that A chopper is arranged downstream of the extruder (2), which is designed to granulate the extruded material.

12. The device according to claim 11, characterized in that The telescopic chopper is designed as a water ring granulator (5).

13. The device according to claim 11 or 12, characterized in that The shredder is operatively connected to a heat exchanger so that heat is transferred to the air flow, and a fan is designed to direct the heated air flow to the regrind before the regrind enters an inlet (6) of the granulator (3).

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