SCREW TO BE USED IN AN EXTRUDER AND EXTRUDER

Abstract

A screw used in an extruder and an extruder having such a screw, in particular a screw used in a multiple-screw extruder and a multiple-screw extruder uses an additional connecting element directly leading from one segment to the next in order to relieve the mandrel. The screw includes a mandrel and a plurality of segments borne by the mandrel and arranged axially with respect to one another, a segment border between a first segment and an axially adjacent second segment has a separate cylindrical connecting element adapted to transmit a torque over the segment border. The ratio of a length of the connecting element to the diameter of the connecting element is higher than 11.

Claims

1. A screw to be used in an extruder comprises a mandrel and a plurality of segments borne by the mandrel and arranged axially with respect to one another, a segment border between a first segment and an axially adjacent second segment having a separate cylindrical connecting element adapted to transmit a torque over the segment border, wherein the ratio of a length of the connecting element to the diameter of the connecting element is higher than 11.

2. The screw according to claim 1, wherein the segment has a blind hole, with the connecting element being positioned in the blind hole with positive engagement.

3. The screw according to claim 1, wherein the ratio of the diameter of the screw root to the diameter of the connecting element lies within a range between 4 and 9.

4. The screw according to claim 1 further including an axially adjacent second segment having a separate angular connecting element adapted to transmit a torque over the segment border, wherein in the assembled state, a radial extension of the connecting element is larger than or equal to an extension in the circumferential direction.

5. The screw according to claim 1 wherein a segment border between a first segment and an axially adjacent second segment has a first separate connecting element and a second separate connecting element with a different geometry, wherein a connecting element is adapted to transmit a torque over the segment border.

6. The screw according to claim 1, wherein in the axial direction of the screw, the connecting element extends throughout a segment and the connecting element is adapted to transmit the torque also to a third and/or to an even more remote segment.

7. The screw according to claim 1, further including an axially adjacent second segment having a separate round connecting element or a connecting element with round edges, wherein the connecting element extends in the axial direction of the screw throughout a segment and is adapted to transmit a torque over the segment border to an adjacent segment and/or a segment next to the latter and/or to a segment even more remote.

8. The screw according to claim 1, wherein the connecting element is dimensioned such that a critical torque for connecting the segments by the connecting element is lower than a critical torque for one segment.

9. The screw according to claim 1, wherein the connecting element is a hollow body.

10. The screw according to claim 1, wherein the connecting element has a different material than the segments.

11. The screw according to claim 1, wherein the connecting element has a different material than the mandrel.

12. The screw according to claim 1, wherein the connecting element is arranged radially outside of the mandrel.

13. The screw according to claim 1, wherein the connecting element is arranged radially within the segments.

14. The screw according to claim 1, wherein the connecting element has an axial play between the segments.

15. The screw according to claim 1, wherein the connecting element extends through the segments free of clearance, in particular in the circumferential direction of the segments.

16. The screw according to claim 1, wherein the connecting element has a line contact with the mandrel in the axial direction of the screw.

17. The screw according to claim 1, wherein the connecting element has a circular recess facing the mandrel.

18. The screw according to claim 1, wherein the mandrel has a notch factor within the range between 1 and 1.2.

19. The screw according to claim 1, wherein the mandrel has a circular cross-section within the segments.

20. The screw according to claim 1, wherein the mandrel has a circular cross-section.

21. The screw according to claim 1, wherein the segments have a circular recess facing the mandrel.

22. The screw according to claim 1, wherein the segments have a close sliding fit with respect to the mandrel.

23. The screw according to claim 1, wherein the segments, at least one segment, in particular all but one, are designed so that they can rotate freely about the mandrel.

24. The screw according to claim 1, wherein the segments, the mandrel and the connecting element are adapted for transmitting at least 70%, in particular 80%, 90% or 100%, of a torque from one segment to the next via the connecting element.

25. The screw according to claim 1 having an axially adjacent second segment having a separate cylindrical connecting element adapted to transmit a torque over the segment border, wherein a length of a first segment is different from the length of a second segment.

26. The screw according to claim 25, wherein a segment at one end of the screw is longer than another segment.

27. An extruder having a screw according to claim 1.

28. A plant for manufacturing a product from thermoplastic, the plant having an extruder according to claim 27.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] In the following, the disclosure is explained in more detail by means of two examples of embodiment with reference to the drawings, wherein

[0113] FIG. 1 schematically shows a section of an extruder screw, the extruder screw having a mandrel and a plurality of segments borne by the mandrel and arranged axially with respect to one another, with a segment border between a first segment and an axially adjacent second segment having a separate angular connecting element adapted to transmit a torque over the segment border, wherein in the assembled state a radial extension of the connecting element is larger than or equal to an extension in the circumferential direction;

[0114] FIG. 2 schematically shows a section of an alternative extruder screw, the extruder screw having a mandrel and a plurality of segments borne by the mandrel and arranged axially with respect to one another, a segment border between a first segment and an axially adjacent second segment having a separate round connecting element, the connecting element extending throughout a segment in the axial direction of the screw and being adapted to transmit a torque over the segment border to an adjacent segment and/or to a segment next to the latter and/or to a segment more remote;

[0115] FIG. 3 schematically shows a section of an alternative extruder screw comprising several segments, in particular having a first and a last segment connected by connecting elements, and

[0116] FIG. 4 schematically shows a section through the alternative extruder screw from FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

[0117] The extruder screw 1 in FIG. 1 has a mandrel 2 and a plurality of screw segments 3 borne by the mandrel and arranged axially with respect to one another (the screw segment 3 is shown in a section perpendicular to the axis of the extruder directly adjacent to the segment border).

[0118] At the border between a first screw segment 3 and an axially adjacent second segment (masked in FIG. 1), the extruder screw has several separate angular connecting elements 4, 5, 6, 7, 8. The connecting elements 4, 5, 6, 7, 8 are adapted to transmit a torque over the segment border.

[0119] In their assembled state, a radial extension 10 of the connecting elements 4, 5, 6, 7, 8 is larger than or equal to an extension 9 in the circumferential direction.

[0120] Recesses (not referenced individually) in the screw segment 3 have a contour which is at least substantially identical with the contour of the connecting elements 4, 5, 6, 7, 8. The recesses are open in the direction of the segment axis (not referenced), that is, in the threaded state, open towards the mandrel 2, so that all connecting elements 4, 5, 6, 7, 8 can be removed from and inserted in the recesses axially and/or radially.

[0121] The alternative extruder screw 21 in FIG. 2 has a mandrel 22 and a plurality of segments 23 borne by the mandrel and arranged axially with respect to one another (in a section perpendicular to the axis of the extruder, a segment is shown directly adjacent to the segment border).

[0122] At the border between the segment 23 and an axially adjacent second segment (not shown), the alternative extruder screw 21 has several separate circular connecting elements 24, 25, 26, 27, 28, 29.

[0123] The connecting elements 24, 25, 26, 27, 28, 29 extend in the axial direction of the screw throughout a segment.

[0124] The connecting elements 24, 25, 26, 27, 28, 29 are adapted to transmit a torque over the segment border to an adjacent segment and/or a segment next to the adjacent segment and/or to an even more remote segment.

[0125] The alternative extruder screw 31 in FIGS. 3 and 4 has a mandrel 32 with an axis 33. For purposes of clarity, the spirals of the extruder screw are not shown. There is shown the screw root of the alternative extruder screw.

[0126] The alternative extruder screw 31 has several segments 34, 35, 36, 37, 38 borne by the mandrel 32 and arranged axially with respect to one another.

[0127] A first screw segment 37 and a last screw segment 38 have a configuration different from that of the other screw segments 34, 35, 36.

[0128] At the border between the screw segments 34, 35, 36, 37, 38, the extruder screw has a plurality of connecting elements 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50.

[0129] The connection between adjacent segments is always configured according to the same scheme. By way of example, the connection between the last segment 38 and the adjacent segment 36 is examined more closely here and is represented in FIG. 4 by a section through the last segment 38.

[0130] The connecting elements 45, 46, 47, 48, 49, 50 are shown which are arranged on a pitch circle within the segments 36, 38.

[0131] The connecting elements 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 are inserted with positive engagement in blind holes (not shown here for purposes of clarity).