Device and method for producing plastic granulate

A device for producing dyed plastic granulate and undyed plastic granulate includes a multi-shaft screw extruder and an underwater pelletizing installation. A granulate changeover unit which separates the dyed plastic granulate from the undyed plastic granulate is disposed in a conveying direction downstream of the underwater pelletizing installation. The dyed plastic granulate is separated from the pelletizing water via a first separator installation, and the undyed plastic granulate is separated from the pelletizing water via a second separator installation. The separator installations are disposed so as to be mutually parallel. The device enables a simple, flexible and economical selective production of the dyed plastic granulate and the undyed plastic granulate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase Application of International Application PCT/EP2017/068949 filed Jul. 27, 2017, and claims the benefit of priority under 35 U.S.C. § 119 of European patent application Serial No. EP 16 184 551.6, filed on Aug. 17, 2016, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a device and to a method for producing plastic granulate.

TECHNICAL BACKGROUND

A device and a method for producing plastic granulate by means of a screw extruder and an underwater pelletizing installation is known from DE 10 2004 002 401 A1. A device of this type is used either exclusively for producing dyed plastic granulate, or exclusively for producing undyed plastic granulate, thus plastic granulate of natural color. A selective production of dyed and undyed plastic granulate by way of a device of this type is not possible since dyed plastic granulate would contaminate the undyed plastic granulate, and the undyed plastic granulate as such would no longer be marketable.

SUMMARY

The invention is based on the object of achieving a device which in a simple, flexible and economical manner enables the selective production of dyed and undyed plastic granulate.

This object is achieved by a device for producing plastic granulate, having a multi-shaft screw extruder for providing a plastic melt; an underwater pelletizing installation for producing from the plastic melt plastic granulate that is located in the pelletizing water, a granulate changeover unit for separating dyed plastic granulate and undyed plastic granulate, said granulate changeover unit in a conveying direction being disposed downstream of the underwater pelletizing installation; a first separator installation for separating the dyed plastic granulate from the pelletizing water, said first separator installation in the conveying direction being disposed downstream of the granulate changeover unit; and a second separator installation for separating the undyed plastic granulate from the pelletizing water, said second separator installation being disposed downstream of the granulate changeover unit in the conveying direction and so as to be parallel with the first separator installation. It has been acknowledged according to the invention that the multi-shaft screw extruder and the underwater pelletizing installation have sufficient self-cleaning, but the post-treatment of the plastic granulate that is disposed downstream of the underwater pelletizing installation has to be separated so as to avoid any contamination of undyed plastic granulate by dyed plastic granulate. A separation of the post-treatment into a first post-treatment circuit for the dyed plastic granulate and a second post-treatment circuit for the undyed plastic granulate, thus the plastic granulate of natural color, is possible on account of the granulate changeover unit that is disposed downstream of the underwater pelletizing installation. The granulate changeover unit is configured in such a manner, for example, that a discharge line of the underwater pelletizing installation, manually and/or automatically, is selectively connectable to a first conveying line of the first post-treatment circuit or a second conveying line of the second post-treatment circuit. The granulate changeover unit is preferably configured as a granulate turnout. Accordingly, a first separator installation for separating the dyed plastic granulate from the pelletizing water, and a second separator installation for separating the undyed plastic granulate from the pelletizing water are disposed downstream of the granulate changeover unit. The separator installations are disposed so as to be mutually parallel and are part of the respective associated post-treatment circuit. The first post-treatment circuit, or the first separator installation, respectively, in a transition period after the conversion from the production of the dyed plastic granulate to the production of the undyed plastic granulate serves in particular also for separating impure plastic granulate which still contains residual dyeing agent. On account of only a single multi-shaft screw extruder and a single underwater pelletizing installation being required, the complexity in terms of machine technology is significantly reduced such that the selective production of the undyed and the dyed plastic granulate is possible in a simple and economical manner. The selection between the first post-treatment circuit and the second post-treatment circuit is performed in a simple, rapid and flexible manner by activating or converting, respectively, the granulate changeover unit, such that high levels of flexibility and economy are guaranteed in the selective production of the dyed and the undyed plastic granulate. Cleaning is not required in the post-treatment circuit. The conversion from the production of the undyed plastic granulate to the production of the dyed plastic granulate is possible without problems since the dyed plastic granulate is not contaminated by the undyed plastic granulate. In the conversion of the production of the dyed plastic granulate to the production of the undyed plastic granulate, the first post-treatment circuit continues to be utilized in the transition period in which self-cleaning of the multi-shaft screw extruder and of the underwater pelletizing installation takes place, so as to avoid any contamination of the second post-treatment circuit and of the undyed plastic granulate. Additionally, a melt pump and/or a screen changeover installation which likewise carry out self-cleaning in the transition period can be disposed between the multi-shaft screw extruder and the underwater pelletizing installation.

A device configured such that a pelletizing water changeover unit for feeding pelletizing water from the first separator installation or the second separator installation to the underwater pelletizing installation is disposed between the separator installations and the underwater pelletizing installation guarantees a simple selective production of the dyed and the undyed plastic granulate. On account of the pelletizing water changeover unit it is reliably guaranteed that no mixing of the pelletizing water of the first post-treatment circuit and of the pelletizing water of the second post-treatment circuit takes place. The pelletizing waters thus remain mutually separated in the post-treatment circuit. Any contamination by dyed plastic granulate remaining in the pelletizing water is in particular avoided on account thereof. The pelletizing water changeover unit is configured in such a manner, for example, that a first pelletizing water infeed line of the first post-treatment circuit, or a second pelletizing water infeed line of the second post-treatment circuit, manually and/or automatically, is selectively connectable to an infeed line of the underwater pelletizing installation. The pelletizing water changeover unit is preferably configured as a pelletizing water turnout.

A device configured such that a first pelletizing water container is disposed between the first separator installation and the pelletizing water changeover unit, and a second pelletizing water container is disposed between the second separator installation and the pelletizing water changeover unit guarantees a simple selective production of the dyed and the undyed plastic granulate. On account of a dedicated pelletizing water container being disposed in the respective post-treatment circuit, a separation of the pelletizing water of the post-treatment circuits is guaranteed in a simple and reliable manner. Any contamination by dyed plastic granulate remaining in the pelletizing water is avoided in a simple manner on account thereof.

A device configured such that a first pelletizing water pump is disposed between the first separator installation and the pelletizing water changeover unit, and a second pelletizing water pump is disposed between the second separator installation and the pelletizing water changeover unit guarantees a simple selective production of the dyed and the undyed plastic granulate. On account of a dedicated pelletizing water pump being disposed in the respective post-treatment circuit, the separation of the pelletizing water of the post-treatment circuits is guaranteed in a simple and reliable manner. Any contamination by dyed plastic granulate remaining in the pelletizing water is avoided on account thereof. The respective pelletizing water pump is in particular disposed so as to be downstream of the respective pelletizing water container.

A device configured such that a pelletizing water container for feeding pelletizing water from the separator installations is disposed between the separator installations and the underwater pelletizing installation guarantees a simple selective production of the dyed and the undyed plastic granulate. On account of the pelletizing water from the first separator installation and from the second separator installation being collected in a common pelletizing water container, the mixed pelletizing water can be filtered and purified in a simple manner. Any contamination by dyed plastic granulate remaining in the pelletizing water is avoided in a simple manner on account thereof.

A device configured such that a pelletizing water pump is disposed between the separator installations, in particular between the pelletizing water container, and the underwater pelletizing installation guarantees a simple selective production of the dyed and the undyed plastic granulate. On account of a common pelletizing water pump being disposed in a common pelletizing water infeed line, simple feeding of the pelletizing water to at least one filter installation and to the underwater pelletizing installation is possible. The pelletizing water pump is preferably disposed downstream of the common pelletizing water container.

A device configured such that at least one filter installation is disposed between at least one of the separator installations, in particular between the pelletizing water container, and the underwater pelletizing installation guarantees a simple selective production of the dyed and the undyed plastic granulate. Simple cleaning of the pelletizing water is possible on account of the at least one filter installation. The at least one filter installation is disposed between at least one of the separator installations and a common pelletizing water container and/or between a common pelletizing water container and the underwater pelletizing installation, for example. Dyed plastic granulate and/or impure plastic granulate is preferably filtered from the pelletizing water by means of the at least one filter installation. The respective filter installation comprises at least one pelletizing water filter. The respective filter installation preferably has at least two pelletizing water filters which are disposed so as to be mutually parallel. The respective filter installation is in particular capable of being operated in such a manner that the at least two pelletizing water filters are capable of being operated conjointly and/or individually. Simple servicing or cleaning, respectively, and/or simple replacing of the respective pelletizing water filter are/is possible on account thereof.

A device configured such that the filter installation comprises at least two pelletizing water filters which are disposed so as to be mutually parallel guarantees a simple selective production of the dyed and the undyed plastic granulate. The pelletizing water filters are in particular capable of being operated conjointly and/or individually by means of shut-off elements. Simple servicing and/or simple replacing of the pelletizing water filters is possible on account thereof.

A device configured such that a color granulate changeover unit for separating dyed plastic granulate and impure plastic granulate in a changeover of the production from dyed plastic granulate to undyed plastic granulate is disposed downstream of the first separator installation guarantees a simple and economical selective production of the dyed and the undyed plastic granulate. A simple and reliable separation of the dyed plastic granulate and of the impure plastic granulate which is created in a transition period after the conversion of the production of the dyed plastic granulate to the production of the undyed plastic granulate is enabled on account of the color granulate changeover unit. The impure plastic granulate thus does not compromise the quality of the dyed plastic granulate. The impure plastic granulate can be marketed as such, or in a subsequent production of the dyed plastic granulate can be fed into the multi-shaft screw extruder and in this way be economically further processed. The color granulate changeover unit is configured in such a manner, for example, that the first separator installation, manually and/or automatically, is capable of being selectively connected to a classification line for the dyed plastic granulate or a classification line for the impure plastic granulate. The color granulate changeover unit is preferably configured as a color granulate turnout.

A device configured such that at least one first storage container for storing dyed plastic granulate, and at least one second storage container for storing impure plastic granulate are disposed downstream of the color granulate changeover unit guarantees a simple, flexible and economical selective production of the dyed and the undyed plastic granulate. Separate storing of the dyed plastic granulate and of the impure plastic granulate is possible in a simple manner on account of the color granulate changeover unit and the separate storage containers. The at least one second storage container, depending on the economics, in particular enables marketing of the impure plastic granulate or further processing in the multi-shaft screw extruder.

A device configured such that a return feed line for returning impure plastic granulate in the production of dyed plastic granulate is disposed from the at least one second storage container to the multi-shaft screw extruder guarantees an economical selective production of the dyed and the undyed plastic granulate. The return feed line enables the feeding of impure plastic granulate from the at least one second storage container to the multi-shaft screw extruder, and thus the further processing of the impure plastic granulate to a dyed plastic granulate.

A device configured such that a classification installation for classifying the impure plastic granulate is disposed between the color granulate changeover unit and a plurality of second storage containers increases the economy of the selective production of the dyed and the undyed plastic granulate. A classification of the impure plastic granulate into undersize, standard size, and oversize is possible on account of the classification installation. An associated second storage container is provided for the respective granulate size, thus the undersize, the standard size, and the oversize. Depending on the economics, the impure plastic granulate having a specific granulate size is either marketed or further processed in the multi-shaft screw extruder. For example, the impure plastic granulate having the standard size is marketed, whereas the impure plastic granulate having the undersize and the oversize is fed back into the multi-shaft screw extruder for further processing.

A device configured such that the multi-shaft screw extruder for feeding undyed plastic material comprises a first infeed opening, and for feeding dyeing agent and/or impure plastic granulate comprises a second infeed opening guarantees a simple and flexible selective production of the dyed and the undyed plastic granulate. Separate feeding of the undyed plastic material, thus of the pulverulent plastic material of natural color, for example, and of the dying agent is performed through the two separate infeed openings. The dying agent is fed, for example, as pulverulent dying agent and/or as masterbatch granulate having the dying agent bound therein, and/or as impure plastic granulate having residual dying agent bound therein. Any contamination by dying agent in the region of the infeed openings in the production of the undyed plastic granulate is avoided on account thereof.

A device configured such that the multi-shaft screw extruder comprises a housing having at least two mutually penetrating housing bores that are configured therein, and such that associated treatment element shafts are disposed so as to be rotatingly drivable in the at least two housing bores, said treatment element shafts being configured so as to mutually mesh in a tight manner and so as to scrape an internal wall of the housing guarantees a simple, flexible and economical selective production of the dyed and the undyed plastic granulate. On account of the at least two treatment element shafts being configured so as to mutually mesh in a tight manner, said treatment element shafts are self-cleaning in a simple manner. Moreover, the internal wall of the housing is cleaned in a simple manner on account of the scraping configuration. The following applies to a dimension A1of a gap between the at least two treatment element shafts and/or a dimension A2of a gap between the respective treatment element shaft and the internal wall of the housing in relation to an external diameter D of the treatment element shafts:

0.003≤A1/D≤0.05, in particular 0.004≤A1/D≤0.035, and in particular 0.011≤A1/D≤0.02

0.004≤A2/D≤0.03, in particular 0.005≤A2/D≤0.025, and in particular 0.012≤A2/D≤0.019.

The invention is furthermore based on the object of achieving a method which in a simple, flexible and economical manner enables the selective production of dyed and undyed plastic granulate.

This object is achieved by a method for producing plastic granulate, comprising the following method steps: providing a device for producing plastic granulate according to the invention; producing dyed plastic granulate by means of the multi-shaft screw extruder and the underwater pelletizing installation, and separating the dyed plastic granulate by means of the first separator installation; changing over the granulate changeover unit; producing undyed plastic granulate by means of the multi-shaft screw extruder and the underwater pelletizing installation, and separating the undyed plastic granulate by means of the second separator installation. The advantages of the method according to the invention correspond to the already described advantages of the device according to the invention.

A method according to which the granulate changeover unit is converted after a start of the production of the undyed plastic granulate, and impure plastic granulate that is created up to the conversion of the granulate changeover unit is separated by means of the first separator installation and of a downstream color granulate changeover unit guarantees an economical selective production of the dyed and the undyed plastic granulate. In a transition period after the start of the production of the undyed plastic granulate, the impure plastic granulate that is first created by virtue of residual dying agent continues to be fed to the first separator installation and by means of a downstream color granulate changeover unit is separated, or kept separate, respectively, from the dyed plastic granulate. Once the self-cleaning of the multi-shaft screw extruder and of the underwater pelletizing installation has been completed, the granulate changeover unit is converted, and the undyed plastic granulate then produced is fed to the second separator installation.

A method according to which the impure plastic granulate in a subsequent production of dyed plastic granulate is at least in part fed to the multi-shaft screw extruder guarantees an economical selective production of the dyed and the undyed plastic granulate. On account of feeding the impure plastic granulate to the multi-shaft screw extruder, further processing of the impure plastic granulate to the dyed plastic granulate is performed.

A method according to which a pelletizing water changeover unit is converted guarantees a simple and flexible selective production of the dyed and the undyed plastic granulate. The pelletizing water used for the production of the dyed and the undyed plastic granulate is kept separate on account of the pelletizing water changeover unit. Any contamination of the undyed plastic granulate by dyed plastic granulate remaining in the pelletizing water is avoided on account thereof.

A method according to which pelletizing water from at least one of the separator installations, prior to being fed to the underwater pelletizing installation, is filtered by means of at least one filter installation guarantees a simple and flexible selective production of the dyed and the undyed plastic granulate. The pelletizing water, prior to being fed into the underwater pelletizing installation, is filtered and purified by means of the at least one filter installation. Any contamination of the undyed plastic granulate by dyed plastic granulate remaining in the pelletizing water is avoided on account thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, a first exemplary embodiment of the invention is described hereunder by means ofFIGS. 1 and 2. A device1for producing dyed plastic granulate G1and undyed plastic granulate G2comprises a multi-shaft screw extruder2having an underwater pelletizing installation3disposed downstream. The multi-shaft screw extruder2has a housing4in which two mutually penetrating housing bores5,6are configured. Treatment element shafts7,8are disposed so as to be rotatable about associated rotation axes9,10in the housing bores5,6. The treatment element shafts7,8by a drive motor11are rotatingly drivable in the same direction, thus in identical rotating directions, by way of an associated transfer gearbox12. The treatment element shafts7,8are configured so as to mutually mesh in a tight manner and so as to scrape an internal wall13of the housing4. To this end, the treatment element shafts7,8are mutually disposed in such a manner that a gap S1delimited by the treatment element shafts7,8has a dimension A1, wherein the following applies to the dimension A1in relation to an external diameter D of the treatment element shafts7,8: 0.003≤A1/D≤0.05, in particular 0.004≤A1/D≤0.035, and in particular 0.011≤A1/D≤0.02.

Furthermore, the treatment element shafts7,8conjointly with the internal wall13configure a respective gap S2which has an associated dimension A2, wherein the following applies to the ratio of the dimension A2to the external diameter D: 0.004≤A2/D≤0.03, in particular 0.005≤A2/D≤0.025, and in particular 0.012≤A2/D≤0.019.

The multi-shaft screw extruder2furthermore has a first infeed opening14and a second infeed opening15which are configured in the housing4and open into the housing bores5,6. The infeed openings14,15serve for separately feeding undyed plastic material M, or plastic material M of natural color, respectively, thus pulverulent plastic material M, for example, and dying agent F, for example of pulverulent carbon black or masterbatch granulate containing carbon black. A perforated plate16is disposed on the discharge side on the multi-shaft screw extruder2, a plastic melt S in the form of plastic strands is generated by the multi-shaft screw extruder2being capable of being extruded through said perforated plate16, said plastic strands in turn being capable of being cut to the plastic granulate G1or G2, respectively, by means of at least one rotatingly drivable cutting blade17. The at least one cutting blade17is rotatingly drivable by means of a blade drive motor18. The perforated plate16, the at least one cutting blade17, and the blade drive motor18are part of the underwater pelletizing installation3.

A granulate changeover unit20which diverges a discharge line21of the underwater pelletizing installation3into a first conveying line22and a second conveying line23is disposed in a conveying direction19downstream of the underwater pelletizing installation3. The granulate changeover unit20is preferably configured as a granulate turnout. The following explanations apply to a granulate changeover unit20of arbitrary configuration.

The first conveying line22forms the start of a first post-treatment circuit in which a first separator installation24, a first pelletizing water return feed line25, a first pelletizing water container26, and a first pelletizing water infeed line27having a first pelletizing water pump28are disposed in succession in the conveying direction19. In an analogous manner, the second conveying line23forms the start of a second post-treatment circuit in which a second separator installation29, a second pelletizing water return feed line30, a second pelletizing water container31, and a second pelletizing water infeed line32having a second pelletizing water pump33are disposed in succession in the conveying direction19. The post-treatment circuits are disposed so as to be mutually parallel. The pelletizing water infeed lines27and32by means of a pelletizing water changeover unit34are reunited such that pelletizing water W1of the first post-treatment circuit or pelletizing water W2of the second post-treatment circuit is capable of being fed to the underwater pelletizing installation3by way of an infeed line35. The pelletizing water changeover unit34is preferably configured as a pelletizing water turnout. The following explanations apply to a pelletizing water changeover unit34of any arbitrary configuration. An outlet line36which can be opened or closed by way of a shut-off element37proceeds from the infeed line35.

The pelletizing water containers26,31have in each case one fresh water infeed line38,39having an associated shut-off element40,41, as well as a pelletizing water heater42,43.

The first separator installation24for separating the pelletizing water W1and the dyed plastic granulate G1comprises a first separator44, a first agglomerate separator45, and a first granulate dryer46. A color granulate changeover unit47in the conveying direction19is disposed downstream of the granulate dryer46. The color granulate changeover unit47is preferably configured as a color granulate turnout. The following explanations apply to a color granulate changeover unit47of arbitrary configuration. Proceeding from the color granulate changeover unit47, a first classification line48extends to a first classification installation49. The first classification installation49serves for classifying the dyed granulate G1and, for example, has screens (not illustrated in more detail) which classify the dyed plastic granulate G1into an undersize G11, a standard size G12, and an oversize G13. The first classification installation49on the exit side opens into a storage container B11for the undersize G11, a storage container B12for the standard size G12, and a storage container B13for the oversize G13of the dyed plastic granulate G1.

The second separator installation29for separating the pelletizing water W2and the undyed plastic granulate G2has a second separator50, a second agglomerate separator51, and a second granulate dryer52. A second classification line53connects the second granulate dryer52directly to a second classification installation54. The second classification installation54serves for classifying the undyed plastic granulate G2into an undersize G21, a standard size G22, and an oversize G23. To this end, the second classification installation54has screens (not illustrated in more detail). A storage container B21for the undersize G21, a storage container B22for the standard size G22, and a storage container B23for the oversize G23are disposed on the exit side of the second classification installation54.

Furthermore, a third classification line55which leads to a third classification installation56extends so as to proceed from the color granulate changeover unit47. The third classification installation56serves for classifying impure plastic granulate G3which is created in a transition period after the conversion from the production of the dyed plastic granulate G1to the production of the undyed plastic granulate G2and is capable of being separated by means of the color granulate changeover unit47and is capable of being classified by means of the third classification installation56. The third classification installation56thus serves for classifying the impure plastic granulate G3into an undersize G31, a standard size G32, and an oversize G33. To this end, screens (not illustrated in more detail) are disposed in the third classification installation56. A storage container B31for the undersize G31, storage container B32for the standard size G32, and a storage container B33for the oversize G33of the impure plastic granulate G3are disposed on the exit side of the third classification installation56.

In order for the undersize G31and the oversize G33of the impure plastic granulate G3to be returned to the multi-shaft screw extruder2, a return feed line57is disposed between the storage container B31, or the storage container B33, respectively, and the multi-shaft screw extruder2. To this end, a first return feed changeover unit58is disposed on the exit side of the storage container B31such that the storage container B31at the exit side opens into the return feed line57or a first outward transport line59. In an analogous manner, a second return feed changeover unit60is disposed on the exit side of the storage container B33such that the container B33at the exit side opens either into the return feed line57or a second outward transport line61. The return feed line57by way of the first infeed opening14or the second infeed opening15opens into the housing bores5,6. Feeding by way of the second infeed opening15is illustrated in an exemplary manner inFIG. 1. The return feed changeover units58,60are preferably configured as return feed turnouts.

The functioning mode of the device1is as follows:

The production of the undyed plastic granulate G2is described first. The multi-shaft screw extruder2is fed undyed plastic material M, or plastic material M of natural color, respectively, by way of the first infeed opening14. The plastic material M is pulverulent, for example. The plastic material M is melted by means of the treatment element shaft7,8such that an undyed plastic melt S is discharged from the housing bores5,6and undyed plastic strands are extruded through the perforated plate16. The undyed plastic strands by means of the rotating at least one cutting blade17are cut to the undyed plastic granulate G2. The plastic granulate G2by means of the pelletizing water W2is discharged from the underwater pelletizing installation3by way of the discharge line21and by way of the granulate changeover unit20is fed to the second post-treatment circuit. The undyed plastic granulate G2by way of the second conveying line23makes its way to the second separator installation29which separates the undyed plastic granulate G2from the pelletizing water W2and dries said undyed plastic granulate G2. The undyed plastic granulate G2by way of the second classification line53is subsequently fed to the second classification installation54. The second classification installation54classifies the undyed plastic granulate G2into the undersize G21, the standard size G22, and the oversize G23, said sizes for marketing or outward transporting being stored in the associated storage containers B21, B22, and B23.

The pelletizing water W2by way of the second pelletizing water return feed line30makes its way to the second pelletizing water container31and from there, by means of the second pelletizing water pump33, by way of the second pelletizing water infeed line32and the pelletizing water changeover unit34back to the infeed line35which re-feeds the pelletizing water W2to the underwater pelletizing installation3. If required, pelletizing water W2in the pelletizing water container31is topped up by way of the second fresh water infeed line39, and the pelletizing water W2is brought to a desired temperature by way of the second pelletizing water heater43.

The conversion of the production from the undyed plastic granulate G2to the dyed plastic granulate G1is possible in a simple manner. In order for the dyed plastic granulate G1to be produced, infeeding of the plastic material M is interrupted, and the multi-shaft screw extruder2is operated until empty. The granulate changeover unit20and the pelletizing water changeover unit34are subsequently converted, and plastic material M is fed to the multi-shaft screw extruder2by way of the first infeed opening14, and dyeing agent F is fed by way of the second infeed opening15. The dyeing agent F is configured so as to be pulverulent, for example, or is bound in a masterbatch granulate. The dyeing agent F is carbon black, for example. Additionally or alternatively, the screw extruder by way of the return feed line57is fed the undersize G31and/or the oversize G33of the impure plastic granulate G3which is stored in the associated storage containers B31and B33. The dyed plastic melt S is generated by means of the treatment element shaft7,8in the housing bores5,6and is discharged through the perforated plate16. The extruded dyed plastic strands by means of the at least one cutting blade17are cut to the dyed plastic granulate G1. The dyed plastic granulate G1by means of the pelletizing water W1is discharged from the underwater pelletizing installation3by way of the discharge line21and fed to the first post-treatment circuit. The dyed plastic granulate G1by way of the first conveying line22is fed to the first separator installation24which separates the dyed plastic granulate G1from the pelletizing water W1and dries said dyed plastic granulate G1. The dried dyed plastic granulate G1by way of the color granulate changeover unit47is fed to the first classification line48and the downstream first classification installation49. The first classification installation49classifies the dyed plastic granulate G1into the undersize G11, the standard size G12, and the oversize G13which for outward transporting or marketing, respectively, are stored in the associated storage containers B11, B12, and B13.

The pelletizing water W1by way of the first pelletizing water return feed line25makes its way to the first pelletizing water container26and by means of the first pelletizing water pump28from there by way of the first pelletizing water infeed line27and the pelletizing water changeover unit34back to the infeed line35which re-feeds the pelletizing water W1to the underwater pelletizing installation3. If required, pelletizing water W1in the pelletizing water container26is topped up by way of the first fresh water infeed line38, and the pelletizing water W1is brought to a desired temperature by way of the first pelletizing water heater42.

The conversion of the production from the dyed plastic granulate G1to the undyed plastic granulate G2is problematic since the multi-shaft screw extruder2and the underwater pelletizing installation3are contaminated by the dyeing agent F. In order for the production to be converted, infeeding of dyeing agent F and/or of the undersize G31or the oversize G33, respectively, of the impure plastic granulate G3is interrupted such that the multi-shaft screw extruder2is exclusively fed the plastic material M. Moreover, the color granulate changeover unit47is converted such that the impure plastic granulate G3now created is fed to the third classification installation56by way of the third classification line55. The multi-shaft screw extruder2and the underwater pelletizing installation3in a transition period carry out self-cleaning in which the plastic melt S generated in the multi-shaft screw extruder2by virtue of the tightly meshing configuration of the treatment element shafts7,8and the scraping of the internal wall13removes residual dyeing agent F from the multi-shaft screw extruder2and subsequently cleans the perforated plate16and the at least one cutting blade17. The impure plastic granulate G3created in the underwater pelletizing installation2by way of the granulate changeover unit20is fed to the first post-treatment circuit and by way of the first separator installation24is separated from the pelletizing water W1and is fed to the third classification installation56in the manner already described. The third classification installation56classifies the impure plastic granulate G3into the undersize G31, the standard size G32, and the oversize G33which are stored in the associated storage containers B31, B32, and B33. Depending on the economics, the undersize G31and the oversize G33by way of the return feed changeover units58,60can be stored for onward transporting or marketing, respectively, or for return feeding. The standard size is merely stored for onward transporting or marketing, for example.

Once self-cleaning in the transition period has been completed, infeeding the plastic material M is interrupted and the multi-shaft screw extruder2is operated until empty. The granulate changeover unit20and the pelletizing water changeover unit34are subsequently converted. The undyed plastic granulate G2is now produced again and fed to the second post-treatment circuit by infeeding the plastic material M, in the manner already described.

The device1according to the invention enables the selective production of dyed plastic granulate G1and of undyed plastic granulate G2by way of only a single multi-shaft screw extruder2and a single underwater pelletizing installation3. On account thereof, the complexity in terms of machine technology is comparatively minor. The impure plastic granulate G3that is produced in the conversion of the production from the dyed plastic granulate G1to the undyed plastic granulate G2is fed to the first post-treatment circuit and separated. Depending on the economics, the impure plastic granulate G3is marketed or in the subsequent production of the dyed plastic granulate G1is fed back to the multi-shaft screw extruder2and further processed. The device1thus enables a simple, flexible and economical production selectively of dyed plastic granulate G1and undyed plastic granulate G2.

A second exemplary embodiment of the invention is described hereunder by means ofFIG. 3. As opposed to the first exemplary embodiment, the first post-treatment circuit comprises the first conveying line22, the first separator installation24, and the first pelletizing water return feed line25, as well as a pelletizing water container26that is common to the second post-treatment circuit, and a common pelletizing water infeed line27having a common pelletizing water pump28and a common filter installation62. Accordingly, the second post-treatment circuit comprises the second conveying line23, the second separator installation29, the second pelletizing water return feed line30, as well as the common pelletizing water container26, and the common pelletizing water infeed line27having the common pelletizing water pump28and the common filter installation62. Proceeding from the granulate changeover unit20, the post-treatment circuits are separate up to the pelletizing water return feed lines25,30, and from the pelletizing water container26up to the pelletizing water infeed line27configure a common post-treatment circuit. On account thereof, the pelletizing water changeover unit34is dispensed with such that the pelletizing water infeed line27transitions to the infeed line35. The filter installation62comprises two pelletizing water filters63,64which are disposed so as to be mutually parallel in the pelletizing water infeed line27. The pelletizing water filters63,64can be operated or conjointly or separately by way of shut-off elements (not illustrated in more detail) of the filter installation. The pelletizing water filters63,64can thus be operated conjointly or so as to exclude the pelletizing water filter63or so as to exclude the pelletizing water filter64. Servicing or replacing the pelletizing water filter63,64is possible in a simple manner on account thereof. The pelletizing water W1from the first separator installation24makes its way into the common pelletizing water container26by way of the first pelletizing water return feed line25. Accordingly, the pelletizing water W2from the second separator installation29makes its way into the common pelletizing water container26by way of the second pelletizing water return feed line30. The mixed pelletizing water W by means of the pelletizing water pump28is fed to the filter installation62by way of the pelletizing water infeed line27. Plastic granulate G1, G2and/or G3which is located in the pelletizing water W is filtered from the latter by means of the pelletizing water filters63,64in the filter installation62. The pelletizing water W which after the filter installation62is fed to the underwater pelletizing installation3by way of the infeed line35is thus purified of residual plastic granulate G1, G2and/or G3.

Reference in terms of the further construction and of the further functioning mode of the device1is made to the first exemplary embodiment.