Device and method for producing plastic granulate

Abstract

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.

Claims

1. A device for producing plastic granulate, the device comprising: a multi-shaft screw extruder for providing a plastic melt; an underwater pelletizing installation for producing plastic granulate that is located in pelletizing water from the plastic melt; a granulate changeover unit configured for separating dyed plastic granulate and undyed plastic granulate and configured for separating a post-treatment into a first post-treatment circuit for the dyed plastic granulate and a second post-treatment circuit for the undyed plastic granulate, the granulate changeover unit being disposed downstream of the underwater pelletizing installation in a conveying direction; a first separator installation configured for separating the dyed plastic granulate from the pelletizing water, the first separator installation being disposed downstream of the granulate changeover unit in the conveying direction and being part of the first post-treatment circuit; and a second separator installation configured for separating the undyed plastic granulate from the pelletizing water, the second separator installation being disposed downstream of the granulate changeover unit in the conveying direction and being part of the second post-treatment circuit and the second separator installation being parallel with the first separator installation.

2. The device as claimed in claim 1, wherein a pelletizing water changeover unit for feeding the pelletizing water from the first separator installation or the second separator installation to the underwater pelletizing installation is disposed between the first separator installation, the second separator installation and the underwater pelletizing installation.

3. The device as claimed in claim 2, wherein 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.

4. The device as claimed in claim 2, wherein 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.

5. The device as claimed in claim 1, wherein a pelletizing water container for feeding the pelletizing water from the first separator installation and the second separator installation is disposed between the first separator installation, the second separator installation and the underwater pelletizing installation.

6. The device as claimed in claim 1, wherein a pelletizing water pump is disposed between the first separator installation, the second separator installation and the underwater pelletizing installation.

7. The device as claimed in claim 6, wherein the pelletizing water pump is disposed between a pelletizing water container and the underwater pelletizing installation.

8. The device as claimed in claim 1, wherein at least one filter installation is disposed between the underwater pelletizing installation and at least one of the first separator installation and the second separator installation.

9. The device as claimed in claim 8, wherein the at least one filter installation comprises at least two pelletizing water filters disposed parallel to each other.

10. The device as claimed in claim 8, wherein the at least one filter installation is disposed between a pelletizing water container and the underwater pelletizing installation.

11. The device as claimed in claim 1, wherein a color granulate changeover unit for separating dyed plastic granulate and impure plastic granulate in a changeover of production from dyed plastic granulate to undyed plastic granulate is disposed downstream of the first separator installation.

12. The device as claimed in claim 11, wherein at least one first storage container for storing the dyed plastic granulate, and at least one second storage container for storing the impure plastic granulate are disposed downstream of the color granulate changeover unit.

13. The device as claimed in claim 12, wherein a return feed line for returning the impure plastic granulate in the production of the dyed plastic granulate extends from the at least one second storage container to the multi-shaft screw extruder.

14. The device as claimed in claim 12, wherein a classification installation for classifying the impure plastic granulate is disposed between the color granulate changeover unit, the at least one second storage container and another second storage container.

15. The device as claimed in claim 1, wherein the multi-shaft screw extruder comprises a first infeed opening for feeding undyed plastic material, and the multi-screw extruder comprises a second infeed opening for feeding at least one of dyeing agent and impure plastic granulate, wherein a first pelletizing water container is connected to the first separator installation, the first pelletizing water container being configured to receive the pelletizing water from the first separator installation, wherein a second pelletizing water container is connected to the second separator installation, the second pelletizing water container being configured to receive the pelletizing water from the second separator installation.

16. The device as claimed in claim 1, wherein the multi-shaft screw extruder comprises a housing having at least two mutually penetrating housing bores configured in the housing, wherein associated treatment element shafts are rotatingly drivable in the at least two mutually penetrating housing bores, the associated treatment element shafts being configured to mutually mesh and to scrape an internal wall of the housing.

17. A method for producing plastic granulate, the method comprising the following method steps: providing a device for producing plastic granulate, the device comprising a multi-shaft screw extruder for providing a plastic melt, an underwater pelletizing installation for producing plastic granulate that is located in pelletizing water from the plastic melt, a granulate changeover unit configured for separating dyed plastic granulate and undyed plastic granulate and for separating a post-treatment into a first post-treatment circuit for the dyed plastic granulate and a second post-treatment circuit for the undyed plastic granulate, 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, the granulate changeover unit being disposed downstream of the underwater pelletizing installation in a conveying direction, the first separator installation being disposed downstream of the granulate changeover unit in the conveying direction and being part of the first post-treatment circuit, the second separator installation being disposed downstream of the granulate changeover unit in the conveying direction and being part of the second post-treatment circuit and the second separator installation being parallel with the first separator installation; producing the dyed plastic granulate via the multi-shaft screw extruder and the underwater pelletizing installation, and separating the dyed plastic granulate via the first separator installation; changing over the granulate changeover unit; producing the undyed plastic granulate via the multi-shaft screw extruder and the underwater pelletizing installation, and separating the undyed plastic granulate via the second separator installation.

18. The method as claimed in claim 17, wherein the granulate changeover unit is converted after a start of production of the undyed plastic granulate, and impure plastic granulate created up to conversion of the granulate changeover unit is separated via the first separator installation and a downstream color granulate changeover unit.

19. The method as claimed in claim 18, wherein the impure plastic granulate in a subsequent production of the dyed plastic granulate is at least partially fed to the multi-shaft screw extruder.

20. The method as claimed in claim 17, wherein a pelletizing water changeover unit is converted.

21. The method as claimed in claim 17, wherein the pelletizing water from at least one of the first separator installation and the second separator installation, prior to being fed to the underwater pelletizing installation, is filtered via at least one filter installation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic view of a device for selectively producing dyed and undyed plastic granulate according to a first exemplary embodiment;

(3) FIG. 2 is a sectional view of multi-shaft screw extruder of the device in FIG. 1; and

(4) FIG. 3 is a schematic view of a device for selectively producing dyed and undyed plastic granulate according to a second exemplary embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

(5) Referring to the drawings, a first exemplary embodiment of the invention is described hereunder by means of FIGS. 1 and 2. A device 1 for producing dyed plastic granulate G.sub.1 and undyed plastic granulate G.sub.2 comprises a multi-shaft screw extruder 2 having an underwater pelletizing installation 3 disposed downstream. The multi-shaft screw extruder 2 has a housing 4 in which two mutually penetrating housing bores 5, 6 are configured. Treatment element shafts 7, 8 are disposed so as to be rotatable about associated rotation axes 9, 10 in the housing bores 5, 6. The treatment element shafts 7, 8 by a drive motor 11 are rotatingly drivable in the same direction, thus in identical rotating directions, by way of an associated transfer gearbox 12. The treatment element shafts 7, 8 are configured so as to mutually mesh in a tight manner and so as to scrape an internal wall 13 of the housing 4. To this end, the treatment element shafts 7, 8 are mutually disposed in such a manner that a gap S.sub.1 delimited by the treatment element shafts 7, 8 has a dimension A.sub.1, wherein the following applies to the dimension A.sub.1 in relation to an external diameter D of the treatment element shafts 7, 8: 0.003≤A.sub.1/D≤0.05, in particular 0.004≤A.sub.1/D≤0.035, and in particular 0.011≤A.sub.1/D≤0.02.

(6) Furthermore, the treatment element shafts 7, 8 conjointly with the internal wall 13 configure a respective gap S.sub.2 which has an associated dimension A.sub.2, wherein the following applies to the ratio of the dimension A.sub.2 to the external diameter D: 0.004≤A.sub.2/D≤0.03, in particular 0.005≤A.sub.2/D≤0.025, and in particular 0.012≤A.sub.2/D≤0.019.

(7) The multi-shaft screw extruder 2 furthermore has a first infeed opening 14 and a second infeed opening 15 which are configured in the housing 4 and open into the housing bores 5, 6. The infeed openings 14, 15 serve 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 plate 16 is disposed on the discharge side on the multi-shaft screw extruder 2, a plastic melt S in the form of plastic strands is generated by the multi-shaft screw extruder 2 being capable of being extruded through said perforated plate 16, said plastic strands in turn being capable of being cut to the plastic granulate G.sub.1 or G.sub.2, respectively, by means of at least one rotatingly drivable cutting blade 17. The at least one cutting blade 17 is rotatingly drivable by means of a blade drive motor 18. The perforated plate 16, the at least one cutting blade 17, and the blade drive motor 18 are part of the underwater pelletizing installation 3.

(8) A granulate changeover unit 20 which diverges a discharge line 21 of the underwater pelletizing installation 3 into a first conveying line 22 and a second conveying line 23 is disposed in a conveying direction 19 downstream of the underwater pelletizing installation 3. The granulate changeover unit 20 is preferably configured as a granulate turnout. The following explanations apply to a granulate changeover unit 20 of arbitrary configuration.

(9) The first conveying line 22 forms the start of a first post-treatment circuit in which a first separator installation 24, a first pelletizing water return feed line 25, a first pelletizing water container 26, and a first pelletizing water infeed line 27 having a first pelletizing water pump 28 are disposed in succession in the conveying direction 19. In an analogous manner, the second conveying line 23 forms the start of a second post-treatment circuit in which a second separator installation 29, a second pelletizing water return feed line 30, a second pelletizing water container 31, and a second pelletizing water infeed line 32 having a second pelletizing water pump 33 are disposed in succession in the conveying direction 19. The post-treatment circuits are disposed so as to be mutually parallel. The pelletizing water infeed lines 27 and 32 by means of a pelletizing water changeover unit 34 are reunited such that pelletizing water W.sub.1 of the first post-treatment circuit or pelletizing water W.sub.2 of the second post-treatment circuit is capable of being fed to the underwater pelletizing installation 3 by way of an infeed line 35. The pelletizing water changeover unit 34 is preferably configured as a pelletizing water turnout. The following explanations apply to a pelletizing water changeover unit 34 of any arbitrary configuration. An outlet line 36 which can be opened or closed by way of a shut-off element 37 proceeds from the infeed line 35.

(10) The pelletizing water containers 26, 31 have in each case one fresh water infeed line 38, 39 having an associated shut-off element 40, 41, as well as a pelletizing water heater 42, 43.

(11) The first separator installation 24 for separating the pelletizing water W.sub.1 and the dyed plastic granulate G.sub.1 comprises a first separator 44, a first agglomerate separator 45, and a first granulate dryer 46. A color granulate changeover unit 47 in the conveying direction 19 is disposed downstream of the granulate dryer 46. The color granulate changeover unit 47 is preferably configured as a color granulate turnout. The following explanations apply to a color granulate changeover unit 47 of arbitrary configuration. Proceeding from the color granulate changeover unit 47, a first classification line 48 extends to a first classification installation 49. The first classification installation 49 serves for classifying the dyed granulate G.sub.1 and, for example, has screens (not illustrated in more detail) which classify the dyed plastic granulate G.sub.1 into an undersize G.sub.11, a standard size G.sub.12, and an oversize G.sub.13. The first classification installation 49 on the exit side opens into a storage container B.sub.11 for the undersize G.sub.11, a storage container B.sub.12 for the standard size G.sub.12, and a storage container B.sub.13 for the oversize G.sub.13 of the dyed plastic granulate G.sub.1.

(12) The second separator installation 29 for separating the pelletizing water W.sub.2 and the undyed plastic granulate G.sub.2 has a second separator 50, a second agglomerate separator 51, and a second granulate dryer 52. A second classification line 53 connects the second granulate dryer 52 directly to a second classification installation 54. The second classification installation 54 serves for classifying the undyed plastic granulate G.sub.2 into an undersize G.sub.21, a standard size G.sub.22, and an oversize G.sub.23. To this end, the second classification installation 54 has screens (not illustrated in more detail). A storage container B.sub.21 for the undersize G.sub.21, a storage container B.sub.22 for the standard size G.sub.22, and a storage container B.sub.23 for the oversize G.sub.23 are disposed on the exit side of the second classification installation 54.

(13) Furthermore, a third classification line 55 which leads to a third classification installation 56 extends so as to proceed from the color granulate changeover unit 47. The third classification installation 56 serves for classifying impure plastic granulate G.sub.3 which is created in a transition period after the conversion from the production of the dyed plastic granulate G.sub.1 to the production of the undyed plastic granulate G.sub.2 and is capable of being separated by means of the color granulate changeover unit 47 and is capable of being classified by means of the third classification installation 56. The third classification installation 56 thus serves for classifying the impure plastic granulate G.sub.3 into an undersize G.sub.31, a standard size G.sub.32, and an oversize G.sub.33. To this end, screens (not illustrated in more detail) are disposed in the third classification installation 56. A storage container B.sub.31 for the undersize G.sub.31, storage container B.sub.32 for the standard size G.sub.32, and a storage container B.sub.33 for the oversize G.sub.33 of the impure plastic granulate G.sub.3 are disposed on the exit side of the third classification installation 56.

(14) In order for the undersize G.sub.31 and the oversize G.sub.33 of the impure plastic granulate G.sub.3 to be returned to the multi-shaft screw extruder 2, a return feed line 57 is disposed between the storage container B.sub.31, or the storage container B.sub.33, respectively, and the multi-shaft screw extruder 2. To this end, a first return feed changeover unit 58 is disposed on the exit side of the storage container B.sub.31 such that the storage container B.sub.31 at the exit side opens into the return feed line 57 or a first outward transport line 59. In an analogous manner, a second return feed changeover unit 60 is disposed on the exit side of the storage container B.sub.33 such that the container B.sub.33 at the exit side opens either into the return feed line 57 or a second outward transport line 61. The return feed line 57 by way of the first infeed opening 14 or the second infeed opening 15 opens into the housing bores 5, 6. Feeding by way of the second infeed opening 15 is illustrated in an exemplary manner in FIG. 1. The return feed changeover units 58, 60 are preferably configured as return feed turnouts.

(15) The functioning mode of the device 1 is as follows:

(16) The production of the undyed plastic granulate G.sub.2 is described first. The multi-shaft screw extruder 2 is fed undyed plastic material M, or plastic material M of natural color, respectively, by way of the first infeed opening 14. The plastic material M is pulverulent, for example. The plastic material M is melted by means of the treatment element shaft 7, 8 such that an undyed plastic melt S is discharged from the housing bores 5, 6 and undyed plastic strands are extruded through the perforated plate 16. The undyed plastic strands by means of the rotating at least one cutting blade 17 are cut to the undyed plastic granulate G.sub.2. The plastic granulate G.sub.2 by means of the pelletizing water W.sub.2 is discharged from the underwater pelletizing installation 3 by way of the discharge line 21 and by way of the granulate changeover unit 20 is fed to the second post-treatment circuit. The undyed plastic granulate G.sub.2 by way of the second conveying line 23 makes its way to the second separator installation 29 which separates the undyed plastic granulate G.sub.2 from the pelletizing water W.sub.2 and dries said undyed plastic granulate G.sub.2. The undyed plastic granulate G.sub.2 by way of the second classification line 53 is subsequently fed to the second classification installation 54. The second classification installation 54 classifies the undyed plastic granulate G.sub.2 into the undersize G.sub.21, the standard size G.sub.22, and the oversize G.sub.23, said sizes for marketing or outward transporting being stored in the associated storage containers B.sub.21, B.sub.22, and B.sub.23.

(17) The pelletizing water W.sub.2 by way of the second pelletizing water return feed line 30 makes its way to the second pelletizing water container 31 and from there, by means of the second pelletizing water pump 33, by way of the second pelletizing water infeed line 32 and the pelletizing water changeover unit 34 back to the infeed line 35 which re-feeds the pelletizing water W.sub.2 to the underwater pelletizing installation 3. If required, pelletizing water W.sub.2 in the pelletizing water container 31 is topped up by way of the second fresh water infeed line 39, and the pelletizing water W.sub.2 is brought to a desired temperature by way of the second pelletizing water heater 43.

(18) The conversion of the production from the undyed plastic granulate G.sub.2 to the dyed plastic granulate G.sub.1 is possible in a simple manner. In order for the dyed plastic granulate G.sub.1 to be produced, infeeding of the plastic material M is interrupted, and the multi-shaft screw extruder 2 is operated until empty. The granulate changeover unit 20 and the pelletizing water changeover unit 34 are subsequently converted, and plastic material M is fed to the multi-shaft screw extruder 2 by way of the first infeed opening 14, and dyeing agent F is fed by way of the second infeed opening 15. 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 line 57 is fed the undersize G.sub.31 and/or the oversize G.sub.33 of the impure plastic granulate G.sub.3 which is stored in the associated storage containers B.sub.31 and B.sub.33. The dyed plastic melt S is generated by means of the treatment element shaft 7, 8 in the housing bores 5, 6 and is discharged through the perforated plate 16. The extruded dyed plastic strands by means of the at least one cutting blade 17 are cut to the dyed plastic granulate G.sub.1. The dyed plastic granulate G.sub.1 by means of the pelletizing water W.sub.1 is discharged from the underwater pelletizing installation 3 by way of the discharge line 21 and fed to the first post-treatment circuit. The dyed plastic granulate G.sub.1 by way of the first conveying line 22 is fed to the first separator installation 24 which separates the dyed plastic granulate G.sub.1 from the pelletizing water W.sub.1 and dries said dyed plastic granulate G.sub.1. The dried dyed plastic granulate G.sub.1 by way of the color granulate changeover unit 47 is fed to the first classification line 48 and the downstream first classification installation 49. The first classification installation 49 classifies the dyed plastic granulate G.sub.1 into the undersize G.sub.11, the standard size G.sub.12, and the oversize G.sub.13 which for outward transporting or marketing, respectively, are stored in the associated storage containers B.sub.11, B.sub.12, and B.sub.13.

(19) The pelletizing water W.sub.1 by way of the first pelletizing water return feed line 25 makes its way to the first pelletizing water container 26 and by means of the first pelletizing water pump 28 from there by way of the first pelletizing water infeed line 27 and the pelletizing water changeover unit 34 back to the infeed line 35 which re-feeds the pelletizing water W.sub.1 to the underwater pelletizing installation 3. If required, pelletizing water W.sub.1 in the pelletizing water container 26 is topped up by way of the first fresh water infeed line 38, and the pelletizing water W.sub.1 is brought to a desired temperature by way of the first pelletizing water heater 42.

(20) The conversion of the production from the dyed plastic granulate G.sub.1 to the undyed plastic granulate G.sub.2 is problematic since the multi-shaft screw extruder 2 and the underwater pelletizing installation 3 are contaminated by the dyeing agent F. In order for the production to be converted, infeeding of dyeing agent F and/or of the undersize G.sub.31 or the oversize G.sub.33, respectively, of the impure plastic granulate G.sub.3 is interrupted such that the multi-shaft screw extruder 2 is exclusively fed the plastic material M. Moreover, the color granulate changeover unit 47 is converted such that the impure plastic granulate G.sub.3 now created is fed to the third classification installation 56 by way of the third classification line 55. The multi-shaft screw extruder 2 and the underwater pelletizing installation 3 in a transition period carry out self-cleaning in which the plastic melt S generated in the multi-shaft screw extruder 2 by virtue of the tightly meshing configuration of the treatment element shafts 7, 8 and the scraping of the internal wall 13 removes residual dyeing agent F from the multi-shaft screw extruder 2 and subsequently cleans the perforated plate 16 and the at least one cutting blade 17. The impure plastic granulate G.sub.3 created in the underwater pelletizing installation 2 by way of the granulate changeover unit 20 is fed to the first post-treatment circuit and by way of the first separator installation 24 is separated from the pelletizing water W.sub.1 and is fed to the third classification installation 56 in the manner already described. The third classification installation 56 classifies the impure plastic granulate G.sub.3 into the undersize G.sub.31, the standard size G.sub.32, and the oversize G.sub.33 which are stored in the associated storage containers B.sub.31, B.sub.32, and B.sub.33. Depending on the economics, the undersize G.sub.31 and the oversize G.sub.33 by way of the return feed changeover units 58, 60 can 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.

(21) Once self-cleaning in the transition period has been completed, infeeding the plastic material M is interrupted and the multi-shaft screw extruder 2 is operated until empty. The granulate changeover unit 20 and the pelletizing water changeover unit 34 are subsequently converted. The undyed plastic granulate G.sub.2 is now produced again and fed to the second post-treatment circuit by infeeding the plastic material M, in the manner already described.

(22) The device 1 according to the invention enables the selective production of dyed plastic granulate G.sub.1 and of undyed plastic granulate G.sub.2 by way of only a single multi-shaft screw extruder 2 and a single underwater pelletizing installation 3. On account thereof, the complexity in terms of machine technology is comparatively minor. The impure plastic granulate G.sub.3 that is produced in the conversion of the production from the dyed plastic granulate G.sub.1 to the undyed plastic granulate G.sub.2 is fed to the first post-treatment circuit and separated. Depending on the economics, the impure plastic granulate G.sub.3 is marketed or in the subsequent production of the dyed plastic granulate G.sub.1 is fed back to the multi-shaft screw extruder 2 and further processed. The device 1 thus enables a simple, flexible and economical production selectively of dyed plastic granulate G.sub.1 and undyed plastic granulate G.sub.2.

(23) A second exemplary embodiment of the invention is described hereunder by means of FIG. 3. As opposed to the first exemplary embodiment, the first post-treatment circuit comprises the first conveying line 22, the first separator installation 24, and the first pelletizing water return feed line 25, as well as a pelletizing water container 26 that is common to the second post-treatment circuit, and a common pelletizing water infeed line 27 having a common pelletizing water pump 28 and a common filter installation 62. Accordingly, the second post-treatment circuit comprises the second conveying line 23, the second separator installation 29, the second pelletizing water return feed line 30, as well as the common pelletizing water container 26, and the common pelletizing water infeed line 27 having the common pelletizing water pump 28 and the common filter installation 62. Proceeding from the granulate changeover unit 20, the post-treatment circuits are separate up to the pelletizing water return feed lines 25, 30, and from the pelletizing water container 26 up to the pelletizing water infeed line 27 configure a common post-treatment circuit. On account thereof, the pelletizing water changeover unit 34 is dispensed with such that the pelletizing water infeed line 27 transitions to the infeed line 35. The filter installation 62 comprises two pelletizing water filters 63, 64 which are disposed so as to be mutually parallel in the pelletizing water infeed line 27. The pelletizing water filters 63, 64 can be operated or conjointly or separately by way of shut-off elements (not illustrated in more detail) of the filter installation. The pelletizing water filters 63, 64 can thus be operated conjointly or so as to exclude the pelletizing water filter 63 or so as to exclude the pelletizing water filter 64. Servicing or replacing the pelletizing water filter 63, 64 is possible in a simple manner on account thereof. The pelletizing water W.sub.1 from the first separator installation 24 makes its way into the common pelletizing water container 26 by way of the first pelletizing water return feed line 25. Accordingly, the pelletizing water W.sub.2 from the second separator installation 29 makes its way into the common pelletizing water container 26 by way of the second pelletizing water return feed line 30. The mixed pelletizing water W by means of the pelletizing water pump 28 is fed to the filter installation 62 by way of the pelletizing water infeed line 27. Plastic granulate G.sub.1, G.sub.2 and/or G.sub.3 which is located in the pelletizing water W is filtered from the latter by means of the pelletizing water filters 63, 64 in the filter installation 62. The pelletizing water W which after the filter installation 62 is fed to the underwater pelletizing installation 3 by way of the infeed line 35 is thus purified of residual plastic granulate G.sub.1, G.sub.2 and/or G.sub.3.

(24) Reference in terms of the further construction and of the further functioning mode of the device 1 is made to the first exemplary embodiment.

(25) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.