SCREW FOR AN EXTRUDER OR CONVEYOR

Abstract

The invention relates to a screw (1) for an extruder or conveyor (20), in particular extruder screw, conveying screw or dosing screw for polymers, having a web (3) running helically around a core (2), wherein the web (3) is formed undercut on its active conveying flank (4) in a conveying direction (F) at least in a section of the screw (1).

Claims

1. A screw (1) for an extruder or conveyor (20), in particular extruder screw, conveying screw or dosing screw for polymers, having a web (3) running helically around a core (2), characterised in that the web (3) is formed undercut on its active conveying flank (4) in a conveying direction (F) at least in a section of the screw (1).

2. The screw according to claim 1, characterised in that the undercut is formed with an undercut angle (w2), measured in a vertex on the foremost edge (6) of the web (3) in the conveying direction (F), in a normal cutting plane (16) normal to the web (3), between an envelope (7) of the screw (1) and a tangent (8) to the active conveying flank (4), wherein the undercut angle (w2) is in the range of 30°≤w2≤90°.

3. The screw according to claim 1, characterised in that the undercut angle (w2) is in the range of 30°w2≤65°, in particular in the range of 40≤w2≤50°, preferably at about 45°.

4. The screw according to claim 1, characterised in that the active conveying flank (4), at least in a section of the screw (1), in a radially outer section (11), in particular up to 50% of the active conveying flank (4), is formed plane or uncurved in the normal cutting plane (16).

5. The screw according to claim 1, characterised in that the screw (1), at least in a section of the screw (1), comprises an intake depth (t1), measured between the envelope (7) and the core (2) in the region between two adjacent webs (3), for which applies: 0.03*d≤t1≤0.35*d, in particular 0.125*d≤t1≤0.35*d, wherein d is the outer screw diameter in this region.

6. The screw according to claim 1, characterised in that the core (2), at least in a section of the screw (1), in the region in which the active conveying flank (4) merges into the core (2) or screw base, comprises an additional recess (14) in which the core diameter is smaller than in the adjacent regions, wherein the following applies in particular to the additional depth (t2) of the recess (14): 0*t1≤t2≤t1.

7. The screw according to claim 1, characterised in that the active conveying flank (4), at least in a section of the screw (1), in the region in which the active conveying flank (4) merges into the core (2), comprises a curvature (R2), in particular in the shape of an arc, which extends at least over a range of >1 rad.

8. The screw according to claim 1, characterised in that a core section (15) adjacent to the recess (14) and straight in the normal cutting plane (16) is formed, which is inclined at an angle (w4) in the range of 0°≤w4≤45° to the envelope (7).

9. The screw according to claim 1, characterised in that the outer web surface (9) of the web (3), at least in a section of the screw (1), in the region adjacent to the foremost edge (6) of the web (3), preferably completely up to the rearmost edge (17), is formed uncurved in the normal cutting plane (16).

10. The screw according to claim 1, characterised in that the outer web surface (9), at least in a section of the screw (1), is oriented parallel to the envelope (7) and/or to the wall (23) of the housing (22) of an extruder (20).

11. The screw according to claim 1, characterised in that the passive conveying flank (12) of the web (3) adjoining the outer web surface (9) is formed plane or uncurved in the normal cutting plane (16), at least in a section of the screw (1), in a radially outer section (13) adjacent to the outer web surface (9), in particular up to a maximum of 70% of the passive conveying flank (12).

12. The screw according to claim 1, characterised in that the passive conveying flank (12), at least in a section of the screw (1), is inclined at a flank angle (w3) in the range of 30°≤w3≤90°, measured in a vertex on the rearmost edge (17) of the web (3) in the conveying direction (F), in a normal cutting plane (16) normal to the web (3), between the envelope (7) of the screw (1) and a tangent (18) to the passive conveying flank (12).

13. The screw according to claim 1, characterised in that the screw (1) is single-start or multi-start having a number of flights in the range of 2 to 20.

14. The screw according to claim 1, characterised in that the following applies to the pitch (S) of the screw (1): 0.1*d≤S≤5*d, wherein d is the outer screw diameter.

15. The screw according to claim 1, characterised in that the following applies to the web width (b) or the width of the outer web surface (9): 0*S≤b≤0.5*S, wherein S is the pitch (S) of the screw (1).

16. The screw according to claim 1, characterised in that the screw (1) is formed according to claim 1, only in the region distal to the conveying direction (F) or in the intake area of an extruder or conveyor (20), and in the remaining region the web (3) comprises no undercut.

17. An extruder or conveyor (20), in particular for polymers, having at least one screw (1) rotatably arranged in a housing (22) according to claim 1.

18. The extruder or conveyor (20) according to claim 17, characterised in that the screw (1) is formed, in particular exclusively, in the region of an opening (21) of the housing (22), in particular in the region of an intake opening or feeding opening (21) for the material, according to claim 1.

19. A device for the treatment of plastics, in particular of thermoplastic waste plastic for recycling purposes, having a container and/or cutting compressor (101) for pretreating the material to be processed, and an extruder or conveyor (20) connected thereto, in particular tangentially, according to claim 17 having a screw according to claim 1.

20. A device for the treatment of plastics, in particular of thermoplastic waste plastic for recycling purposes, having a container (101) for the material to be processed, wherein at least one rotating mixing and/or comminuting tool (103) rotatable about an axis of rotation (110) is arranged in the container (101) for mixing, heating and, if necessary, comminuting the plastic material, wherein a container opening (108) is formed in a side wall (109) of the container (101) in the region of the height of the or the lowermost mixing and/or comminution tool (103) closest to the bottom, through which the pretreated plastic material can be discharged from the interior of the container (101), wherein at least one extruder or conveyor (20) according to claim 17 is provided for receiving the material pretreated in the container (101), wherein the housing (22) of the extruder (20) includes an intake opening (21), located on its end face (107) or in its sheath wall, for the material to be gripped by the screw (1) and the intake opening (21) is in communication with the container opening (108).

21. The device according to claim 19, characterised in that in the region before the container opening (108) or in the region before the intake opening or feeding opening (21) of the conveyor or extruder (20) the direction of rotation of the mixing and/or comminuting tool (103) runs essentially counter to or in the opposite direction to the conveying direction (F) of the extruder (20).

Description

[0056] FIG. 1 shows a first embodiment of a screw geometry according to the present invention.

[0057] FIG. 2 shows a further embodiment of a screw geometry according to the present invention.

[0058] FIG. 3 shows the connection of an extruder according to the present invention to a container.

[0059] FIGS. 4a and 4b show a peeling screw according to the present invention.

[0060] FIGS. 5a and 5b show a standard screw for comparison.

[0061] FIGS. 6 and 7 show results of comparative tests.

[0062] In FIGS. 1 and 2 there is shown a detailed view of a first and a second embodiment of a screw geometry according to the invention. These are each normal sections through the web 3, i.e. at right angles to the front and rear web edges 6, 17, forming the normal cutting plane 16, which runs in the image plane in FIGS. 1 and 2. The course of this normal cutting plane 16 is also shown in FIG. 4a.

[0063] A screw 1 can be seen, which is arranged in an axis-rotatable manner in the interior of an indicated extruder or conveyor 20. This may be a compressing or agglomerating screw. The screw 1 has a core 2 as well as a web 3 running helically around this core 2. The web 3 has a front active conveying flank 4 pointing in conveying direction F and a rear passive conveying flank 12 pointing in the opposite direction.

[0064] In the radially outermost region are the outer web surfaces 9 with a foremost edge 6 pointing in conveying direction F and an opposite rearmost edge 17. The outer web surface 9 is curved in the circumferential direction of the screw, but formed straight and not curved in the normal cutting plane 16 and runs parallel to the wall 23 of the housing 22 of the extruder 20.

[0065] An envelope 7 of the screw 1 is formed by the outer web surfaces 9 and the foremost edges 16, respectively, the envelope 7 also being oriented parallel to the wall 23 in the present embodiments. Accordingly, the envelope 7 as well as the outer web surfaces 9 of the web 3 are oriented parallel to the central longitudinal axis of the screw 1.

[0066] The undercut of the active conveying flank 4 is defined by an undercut angle w2. This undercut angle w2 is measured at a vertex located on the foremost edge 6 of the web 3 in a conveying direction F. The angle w2 is formed between the envelope 7 and the tangent 8, which is placed through the vertex on the active conveying flank 4, namely in the normal cutting plane 16. In the present case, the same undercut angle w2 also results between the tangent 8 and a parallel to the central longitudinal axis, but in the case of conical screws there would be differences here. In the embodiment according to FIG. 1, the undercut angle w2 is approximately 45°.

[0067] In a radially outer section 11, the active conveying flank 4 has a plane design or this region is not formed curved in the normal cutting plane 16. This section 11 extends to about half of the active conveying flank 4 and then merges into the core 2 in a curved region. This curvature R2 is arc-shaped and extends over a region of slightly less than 2 rad.

[0068] In the embodiment according to FIG. 1, the diameter of the core 2 is essentially constant, at least in the section of the screw 1 shown. The intake depth 1 measured between the envelope 7 and the core 2 in the region between two adjacent webs 3 is about 25% of the screw diameter d in this region. As mentioned at the outset, the intake depth t1 in combination with the undercut is particularly advantageous for the intake behaviour.

[0069] The passive conveying flank 12 adjoins downstream of the rearmost edge 17 counter to the conveying direction F and has a radially outer section 13 which is formed plane or not curved in the normal cutting plane 16. In the embodiment according to FIG. 1, this section 13 extends over about 60% of the length of the passive conveying flank 12 and then merges into the region of the core 2 via an arc-shaped curvature R1. The passive conveying flank 12 is inclined accordingly, namely at a flank angle w3 measured at the vertex located on the rearmost edge 17 of the web 3 in a conveying direction F. The flank angle w3 is formed in this case between the envelope 7 and a tangent 18 to the passive conveying flank 12 passing through the apex, namely in the normal cutting plane 16. In the embodiment according to FIG. 1, the angle w3 is about 30°:

[0070] In the embodiment according to FIG. 2, the shape or geometry of the webs 3 is similar to that in FIG. 1, namely both in the design of the undercut and in the shape of the webs 3. However, in contrast to FIG. 1, an additional recess 14 is formed in the region in which the active conveying flank 4 merges into the core 2 or screw base. In this, the diameter of the core 2 is somewhat smaller than in the adjacent regions of the core 2, defining an additional depth t2 compared to the intake depth t1. In the embodiment according to FIG. 2, this additional depth t2 is about 20% of the intake depth t1. This recessed screw base has a straight core section 15 in the normal cutting plane 16, which is inclined at an angle w4 of about 20° to the envelope 7 or to the remaining region of the core 2. This recess 14, together with the undercut, also results in advantageous intake behaviour.

EXAMPLES

[0071] The following comparative tests were carried out on an Intarema 1108 TE cutting compressor/extruder combination:

TABLE-US-00001 Device type Comment Process unit Intarema 1108 TE Diameter container 1100 mm; Diameter extruder 80 mm Melt filter RTF 4/34 Filtration 12/64 Granulation HG 154 D Perforated plate 20 × 3

[0072] All process parameters as well as the input materials were kept constant, only the screw geometry was varied. A standard extruder screw without undercut and with an angle w2=95° (“standard screw”) was chosen as comparison screw. As a screw according to the invention, an extruder screw—similar in the other aspects—with undercut with an undercut angle w2=450 was chosen (“peeling screw”). The specifications and relevant geometries are shown in detail in FIGS. 5a, 5b for the standard screw and in FIGS. 4a, 4b for the peeling screw:

TABLE-US-00002 Standard screw Peeling screw Diameter d [mm] 79.8 79.8 Pitch [mm] 80 80 Web width b [mm] 8 8 Intake or screw 16 16 depth t1 [mm]

[0073] The respective absolute throughput and the throughput consistency, thus the behaviour of the throughput over longer periods, were evaluated. The influence of increasing material density, represented by the temperature in the PCU, was also evaluated. The results are summarized in FIGS. 6 and 7.

Example 1

[0074] Test material 1:

TABLE-US-00003 Polymer Expanded polystyrene EPS Material form Grist Bulk density 10-15 g/l Moisture dry Pollution Clean, production waste Comments Constant bulk density

TABLE-US-00004 Standard screw (w2 = 95°) Peeling screw (w2 = 45°) Through- Through- PCU put PCU put temper- Through- con- temper- Through- con- ature put sistency ature put sistency [° C.] [kg/h] [%] [° C.] [kg/h] [%] 100 300 14 100 320 9 105 320 12 105 341 7 110 333 14 110 354 5 115 346 11 115 387 2 120 350 13 120 405 3

[0075] In FIG. 6 the results, in particular for throughput and consistency, are shown.

Example 2

[0076] Test material 2:

TABLE-US-00005 Polymer Polypropylene PP Material form Foam polymer Bulk density 130-140 g/l Pollution Clean [0077] Comments|Comminuted with a mill with a sieve insert with 80 mm holes

TABLE-US-00006 Standard screw (w2 = 95°) Peeling screw (w2 = 45°) Through- Through- PCU put PCU put temper- Through- con- temper- Through- con- ature put sistency ature put sistency [° C.] [kg/h] [%] [° C.] [kg/h] [%] 95 325 6 95 360 3 100 330 4 100 371 1 105 351 5 105 385 2 110 366 4 110 404 3 115 375 5 115 425 1

[0078] In FIG. 7 the results, in particular for throughput and consistency, are shown.

[0079] It can be seen that with the undercut screw according to the present invention, higher throughputs were achieved in each case with improved throughput consistency at the same time.