Extruder screw, extrusion device having an extruder screw and method for plasticizing a plastic

Abstract

An extruder screw for plasticizing at least one plastic or plastic mixture, including a melting zone, a shaft zone and a mixing zone arranged between the melting zone and the shaft zone, wherein a conveying flight is formed in the melting zone and in the shaft zone, which extends helically along a longitudinal axis of the screw, wherein a conveying flight of the melting zone ends at an end of the melting zone towards the mixing zone and a conveying flight of the shaft zone begins at an end towards the mixing zone. A flight depth of the melting zone continuously decreases along the longitudinal axis of the screw to the mixing zone. Further, an extrusion device having the extruder screw and to a method for plasticizing at least one plastic or plastic mixture.

Claims

1. An extruder screw (1) for plasticizing at least one plastic or a plastic mixture, comprising a melting zone (2), a wave zone (3) having at least one conveying channel changing its depth in a wave-shaped manner in longitudinal direction, and a mixing zone (4) arranged between the melting zone (2) and the wave zone (3) in direct connection to the melting zone (2), wherein in the melting zone (2) and in the wave zone (3) a conveying flight (5, 6) is arranged, extending helically along a longitudinal axis of the screw, wherein a conveying flight (5) of the melting zone (2) ends at an end (7) of the melting zone (2) facing the mixing zone (4), and a conveying flight (6) of the wave zone (3) begins at an end (8) facing the mixing zone (4), and wherein a channel depth of the melting zone (2) increases continuously along the longitudinal axis of the screw towards the mixing zone (4).

2. The extruder screw (1) according to claim 1, wherein the wave zone (3) is arranged in direct connection to the mixing zone (4).

3. The extruder screw (1) according to claim 1, wherein the melting zone (2) is multiple-threaded.

4. The extruder screw (1) according to claim 1, wherein the wave zone (3) is multiple-threaded.

5. The extruder screw (1) according to claim 1, wherein the melting zone (2) is configured at least partially as a decompression zone.

6. The extruder screw (1) according to claim 1, wherein the mixing zone (4) has at least one mixing section (9, 10) promoting a distributive and/or disperse blending of a solid component with a plasticized component of the at least one plastic or plastic mixture.

7. The extruder screw (1) according to claim 6, wherein the at least one mixing section (9, 10) is configured materially in one piece with a screw section (11c) forming the mixing zone (4), or separately to the screw section (11c) forming the mixing zone (4).

8. The extruder screw (1) according to claim 6, wherein the at least one mixing section (10) is configured as a toothed disk (12), a perforated disk, a mixing pin (13), or a rhombic element (14) or has a strip-shaped elevation (15).

9. The extruder screw (1) according to claim 6, wherein the at least one mixing section (9) is configured as a shear gap (16a, 16b), a blister ring (18) or a wedge gap region (17).

10. An extrusion device having the extruder screw (1) according to claim 1.

11. A method for plasticizing at least one plastic or a plastic mixture by means of the extrusion device according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now explained more closely below with the aid of figures, in which context various example embodiments are presented to illustrate the ideas according to the invention.

(2) There are shown:

(3) FIG. 1 a schematic view of a portion of an extruder screw according to the invention in accordance with a first example embodiment, wherein the extruder screw is illustrated flattened and in a lying position, wherein the melting zone is configured as a decompression zone,

(4) FIG. 2 a detailed perspective illustration of a mixing zone used in FIG. 1 with mixing sections,

(5) FIGS. 3a to 3h further example embodiments with respect to the mixing sections able to be used in FIG. 1.

DESCRIPTION OF EXAMPLE EMBODIMENTS

(6) The figures are only schematic in nature and serve exclusively for an understanding of the invention. The identical elements are provided with the same reference numbers. It is also pointed out that the various features of the different figures and example embodiments can in principle be combined with one another.

(7) In connection with FIG. 1, an example embodiment is shown which illustrates the idea according to the invention. The embodiments of the mixing sections 9, 10, as they are illustrated in FIGS. 2 and 3a to 3h are able to be applied in principle to the example embodiment of FIG. 1. The example embodiment of FIG. 1 illustrates the extruder screw 1 according to the invention in a schematic angled presentation. The extruder screw 1 serves in the usual manner for plasticizing at least one plastic/plastic component or a plastic mixture in the form of several plastic components. The extruder screw 1 is used in the usual manner in its operation in an extrusion device/extruder, which extrusion device is not illustrated further here for the sake of clarity. The extrusion device has, in a typical manner, a housing/extrusion housing with an inlet and an outlet. The extruder screw 1 extends with its zones 2, 3, 4, which are described more closely below, between the inlet and the outlet, and is rotatably arranged radially within a cylindrical wall of the housing. By means of this extruder screw 1, in operation of the extrusion device according to a production method an extrusion component/extruded component is manufactured, wherein the at least one plastic is fed to the inlet in solid form, is plasticized through the extruder screw 1 and finally at the outlet is ejected for the formation of the extrusion component. For the plasticizing, the at least one plastic passes through the zones 2, 3 and 4 of the extruder screw 1 which are described more closely below.

(8) In FIG. 1 it can be seen that the three zones 2, 3 and 4 are configured in the form of a melting zone 2, a mixing zone 4 and a wave zone 3. The mixing zone 4 adjoins downstream/in extrusion direction directly/immediately on to the melting zone 2. The wave zone 3 adjoins downstream directly/immediately on to the mixing zone 4. The melting zone 2 is formed at a first screw section 11a of the extruder screw 1; the wave zone 3 is formed at a second screw section 11b of the extruder screw 1; the mixing zone 4 is formed at a third screw section 11c of the extruder screw 1. The three screw sections 11a, 11b, 11c adjoin in axial direction of the extruder screw 1 therefore directly onto one another/continue directly into one another.

(9) In further embodiments, a further zone, for instance a metering zone, can also be arranged in addition between the melting zone 2 and the mixing zone 4. Also between the mixing zone 4 and the wave zone 3 in principle a further zone can be arranged. Respectively two zones 2, 3, 4 immediately adjoining one another along an imaginary screw longitudinal axis of the extruder screw 1 differ from one another in particular with regard to the configuration (flight pitch) or respectively the presence of a conveying flight 5, 6.

(10) Both the melting zone 2 and also the wave zone 3 have respectively at least one conveying flight 5, 6. In the melting zone 2 the conveying flight is designated as first conveying flight 5. In the wave zone 3 the conveying flight is designated as second conveying flight 6. The respective first and second conveying flight 5, 6 forms a main conveying flight. Each of the first and second conveying flights 5, 6 extends helically/in a helical-shaped manner/in a spiral-shaped manner along the imaginary longitudinal axis of the screw. The first conveying flight 5 and the second conveying flight 6 thus respectively form a screw thread on a radial outer side of the extruder screw 1.

(11) In a further embodiment, the melting zone 2 is configured to be only single-threaded. In further embodiments, the melting zone 2 is configured to be at least two-threaded, namely three-threaded. In this first example embodiment, however, it is configured to be two-threaded. The melting zone 2 thus has an intermediate conveying flight 22 in addition to the first conveying flight 5. To illustrate a (first) conveying channel 23 formed in the melting zone 2, the first conveying flight 5 is illustrated twice. The intermediate conveying flight 22 extends parallel to the first helically extending conveying flight 5, along the imaginary longitudinal axis of the screw. The intermediate conveying flight 22 is arranged in axial direction (along the imaginary longitudinal axis of the screw) of the extruder screw 1 between two screw/thread channels of the first conveying flight 5. The (first) conveying channel 23 formed by the first conveying flight 5 is divided by the intermediate conveying flight 22 into two partial conveying channels 24a and 24b. The first conveying flight 5 and the intermediate conveying flight 22, viewed in radial direction (with respect to the longitudinal axis of the screw) have the same height.

(12) In FIG. 1 the melting zone 2 is embodied in the form of a decompression zone. The channel depth (depth of the conveying channel 23/of the first and second partial conveying channels 24a and 24b) of the melting zone 2 increases along the longitudinal axis of the screw towards the mixing zone 4/downstream continuously/linearly. The channel depth of the melting zone 2 can therefore increase at least partially, in sections or completely along the longitudinal axis of the screw towards the mixing zone 4. Here it is also possible to leave the channel depth in the melting zone 2/decompression zone identical along the longitudinal axis of the screw partially, in sections or completely.

(13) In the example embodiment according to FIG. 1, it is pointed out that the wave zone 3 is configured as a conventional disperse plasticizing/melting zone. In a further embodiment, the wave zone 3 can be configured to be only single-threaded, however in this example embodiment it is configured to be two-threaded. The wave zone 3 is also equipped with a (second) intermediate conveying flight 25, which in turn is arranged between two threads of the (second) conveying flight 6 of the wave zone 3 which follow one another axially. The second intermediate conveying flight 25 extends parallel to the helically extending second conveying flight 6, along the imaginary longitudinal axis of the screw. The second intermediate conveying flight 25 divides a second conveying channel 26, formed by the second conveying flight 6, in turn into a first partial conveying channel 29a and a second partial conveying channel 29b. The wave zone 3 is configured as a wave-zone and therefore has a channel depth changing in a wave-shaped manner along the (second) conveying channel 26 of the wave zone 3.

(14) In a further embodiment, the radial height of the second intermediate conveying flight 25 is smaller than the radial height of the second conveying flight 6, so that a shear gap occurs at the second intermediate flight. In a further embodiment, the second conveying flight 6 and the second intermediate conveying flight change their radial height in sections along the second conveying channel 26, wherein the second conveying flight 6 and the second intermediate conveying flight 25 change their function alternately and serve in sections as conveying flight and as shear flight.

(15) The mixing zone 4 is arranged axially (with respect to the longitudinal axis of the screw) between the melting zone 2 and the wave zone 3. In the example embodiment of FIG. 1, the mixing zone 4 has no conveying flight. The first conveying flight 5 therefore ends at an end 7 of the melting zone 2 facing the mixing zone 4. The intermediate conveying flight 22 also ends at the end 7 of the melting zone 2 facing the mixing zone 4. In addition, the second conveying flight 6 begins in turn only at an end/start 8 of the wave zone 3 facing the mixing zone 4. The intermediate conveying flight 25 also begins only at the end 8 of the wave zone 3 facing the mixing zone 4. Therefore in this embodiment the mixing zone 4 is embodied in a flight-free manner. The mixing zone 4 therefore has no elongated elevations/flights which extend helically around at least one thread/around at least 360°.

(16) In FIG. 1 it can be seen furthermore that in the mixing zone 4, several mixing sections 9, 10 are present, which are only indicated schematically here, wherein these mixing sections 9, 10 in principle, as described below with reference to FIGS. 2 and 3a to 3h, can be configured differently.

(17) FIG. 2 shows a mixing zone 4 of the first example embodiment, in which several distributive mixing sections 10 are arranged. These distributive mixing sections 10 are embodied as separate mixing elements and are mounted non-rotatably on the extruder screw 1 in the region of the mixing zone 4. The (four) distributive mixing sections 10 are arranged spaced apart and adjacent to one another in axial direction of the longitudinal axis of the screw. The distributive mixing sections 10 are respectively configured as a toothed disk 12/toothed ring. The respective toothed disk 12 is thus provided with a ring-shaped base body on which several teeth 27 (spaced apart from one another in a circumferential direction), forming an outer toothing (straight toothing) are arranged.

(18) In connection with FIGS. 3a to 3h, it can be seen that these mixing sections 9, 10 can, however, also be embodied in principle differently. The distributive mixing sections 10, as explained more closely below, can in principle also be replaced by disperse mixing sections 9, or can be provided additionally to these.

(19) Compared to FIG. 2, it can be seen in FIG. 3a that the distributive mixing sections 10 essentially also can be configured directly/materially in one piece with the (third) screw section 11c of the extruder screw 1 forming the mixing zone 4. Each mixing section 10 is configured as an oblique toothing. The oblique toothing is thus formed by several strip-shaped integral elevations 15 arranged adjacent to one another in circumferential direction on the outer circumferential side of the extruder screw 1 in the mixing zone 4. The respective elevation 15 forms, in turn, a tooth 27.

(20) Whereas in FIG. 3a the formed oblique toothing is embodied as involute toothing, it is also possible according to FIG. 3b not to embody the toothing as involute toothing. However, the distributive mixing sections 10 in turn have elevations 15 running parallel to one another. With regard to the elevations 15, it is pointed out that these extend by a limited angular range around the outer circumferential side of the extruder screw 1 and respectively do not form a flight extending through 360° to a complete thread.

(21) In connection with FIG. 3c it is indicated that the distributive mixing sections 10 can also have several mixing pins 13 distributed in circumferential direction. In this example embodiment, the mixing pins are, in turn, embodied materially in one piece directly with the third screw section 11c. In principle it is also sufficient to equip the mixing section 10 with only one mixing pin 13.

(22) In connection with FIG. 3d, the distributive mixing section 10 is embodied as a group of rhombic elements 14/rhomboid elevations 15 distributed in axial direction and in circumferential direction. The rhombic elements 14 are also formed materially in one piece on the outer circumferential side of the extruder screw 1.

(23) In connection with FIGS. 3e to 3h it can be seen that the distributive mixing sections 10 are able to be replaced by disperse mixing sections 9. In FIG. 3e the disperse mixing section 9 is configured as a blister ring region/a blister ring 18 in the mixing zone 4. This blister ring region 18 has several circular indentations/recesses distributed in circumferential direction and in axial direction of the extruder screw 1.

(24) In FIGS. 3f and 3g further possible disperse mixing sections 9 in the form of shear gaps 16 are illustrated. In FIG. 3f several shear gaps 16 are arranged running obliquely on the outer circumferential side of the extruder screw 1. In FIG. 3g a meander-shaped shear gap 16 is illustrated.

(25) In FIG. 3h the disperse mixing section 9 is embodied as a ring-shaped wedge gap region 17/wedge gap element.

(26) The various mixing sections 9 and 10, as illustrated in FIGS. 3a to 3h, are known in principle from U.S. Pat. No. 6,136,246 A, for which reason the further embodiments named herein for these mixing sections are deemed to be integrated herein.

(27) Instead of the use of the toothed disk 12, in principle it is also possible to configure the distributive mixing section 10 as a perforated disk/pierced disk. The perforated disk is preferably formed as a disk having several through-holes distributed in circumferential direction and running axially, and is fastened to the extruder screw 1 in the same manner as the toothed disks 12.

(28) In principle it is also pointed out that in further example embodiments the various mixing sections, i.e. the disperse and distributive mixing sections 9, 10 can be freely combined with one another, both as separate elements and also as a one-piece/integral element.

(29) In operation of the extrusion device according to the invention, the solid bed is comminuted to as small a particle size as possible before the entry into the wave-zone (wave zone 3), in order to increase the melting performance. Between the melting part of the screw 1 in the form of the melting zone 2, which is configured as a decompression zone, which can have a single-threaded or multiple-threaded embodiment, and the wave zone 3, a mixing zone 4 is placed, which achieves a more intensive as possible fragmentation and distribution of the solid bed and as good an intermixing as possible between solid and melt. Distributive and/or disperse mixing elements (mixing sections) 9, 10 are deliberately used. Distributive mixing elements 10 can be, inter alia, toothed disks 12, perforated disks, mixing pins 13 and/or rhombic elements 14. In this case, shear gaps 16a, 16b, blister rings 18 and/or wedge gap elements 17 are suitable as disperse mixing elements 9. Through the use of distributive and disperse mixing elements 9, 10, a distinctly more intensive intermixing is achieved in the mixing zone 4 and a more intensive distribution and fragmentation of the solid bed. In addition, the embodiment of the melting zone 2 as a decompression zone assists a washing out of the solid bed and thus, in turn, as more intensive a fragmentation and distribution of the solid bed as possible and as good an intermixing as possible between solid and melt.

(30) Thereby, the particle size of the residual solid, which is transferred into the wave zone 3, is distinctly reduced, for which reason the wave zone 3 plasticizes more efficiently and thus also a higher plasticizing performance is achieved. In addition to the mixing elements 9, 10, preferably any flights can be removed in the mixing zone 4, in order to enable a free flow of the melt or respectively a free blending of the melt and of the solid. Through the free flow, the efficiency of the mixing elements 9, 10 is further increased, because transverse flows occur, which bring about an additional intermixing and redistribution.

LIST OF REFERENCE NUMBERS

(31) 1 extruder screw 2 melting zone 3 wave zone 4 mixing zone 5 first conveying flight 6 second conveying flight 7 end of the melting zone 8 end of the wave zone 9 disperse mixing section 10 distributive mixing section 11a first screw section 11b second screw section 11c third screw section 12 toothed disk 13 mixing pin 14 rhombic element 15 elevation 16a first shear gap 16b second shear gap 17 wedge gap region 18 blister ring region 19 barrier flight 20 third conveying flight 21 aperture 22 intermediate conveying flight first intermediate conveying flight 23 first conveying channel 24a first partial conveying channel 24b second partial conveying channel 25 second intermediate conveying flight 26 second conveying channel 27 tooth 28 longitudinal axis of the screw 29a first partial conveying channel 29b second partial conveying channel