PLANETARY ROLLER EXTRUDER WITH A DEGASSING SECTION

Abstract

A planetary extruder for producing and processing polymers includes a degassing section. The extruder includes a housing and a bushing arranged therein. The bushing has an internal toothing with a pitch diameter and a root circle. An externally toothed central spindle is arranged within the housing. Planetary spindles rotate about the central spindle between the central spindle and the bushing. A heat transfer fluid is guided through fluid channels which extend helically along an outer surface of the bushing and guide the heat transfer fluid axially. A degassing opening is provided to which a negative pressure is applied for degassing. A minimum radial thickness (t) of the bushing between the root circle of the internal toothing on an inside of the bushing and a bottom of the fluid channels on an outside of the bushing is selected based on the pitch diameter (d) of the internal toothing.

Claims

1. An extruder for producing and processing polymers and polymer mixtures, including a planetary roller degassing section, comprising: a housing; a bushing arranged within the housing, the bushing having an internal toothing with a pitch diameter and a root circle; an externally toothed central spindle arranged within the housing; planetary spindles, configured and disposed to rotate about the central spindle between the central spindle and the bushing while intermeshing with the toothing of the central spindle and the toothing of the bushing; a heat transfer fluid which is guided through fluid channels which extend helically along an outer surface of the bushing and guide the heat transfer fluid axially; and a degassing opening to which a negative pressure is applied for degassing, wherein at least three of the following set of four characteristics are met: a) a minimum radial thickness (t) of the bushing between the root circle of the internal toothing on an inside of the bushing and a bottom of the fluid channels on an outside of the bushing is selected based on the pitch diameter (d) of the internal toothing according to the following table: TABLE-US-00003 minimum material pitch diameter (d) thickness (t) d 85 mm t 4.5 mm 85 mm < d 125 mm t 4.5 mm 125 mm < d 165 mm t 5.0 mm 165 mm < d 190 mm t 5.7 mm 190 mm < d 225 mm t 5.6 mm 225 mm < d 265 mm t 5.7 mm 265 mm < d 290 mm t 6.0 mm 290 mm < d 350 mm t 6.0 mm .sup.d > 350 mm t 6.5 mm b) the extruder comprises fewer planetary spindles than a maximum number of planetary spindles that could be accommodated between the central spindle and the bushing; c) gas is extracted from a cavity formed at an inlet side of the extruder; d) gas is extracted through an idling side-arm extruder located on an outside of the planetary roller degassing section, the idling side-arm extruder being connected to the degassing opening in a melt-wetted area of the bushing and able to push melt which is forced out through the degassing opening back into the extruder.

2. The extruder as in claim 1, wherein the degassing opening is arranged at a degassing ring on an inlet side of the planetary roller degassing section, the degassing opening being connected via a channel of the degassing ring to a degassing line which leads outwards at a housing end of the planetary roller degassing section.

3. The extruder as in claim 2, wherein an upstream planetary roller section is arranged upstream of the planetary roller degassing section and the degassing ring of the planetary roller degassing section fits closely to a thrust ring of the upstream planetary roller section or forms a common ring construction with the thrust ring.

4. The extruder as in claim 2, wherein a negative pressure is applied to the degassing line.

5. The extruder as in claim 1, wherein a liquid seal is provided to prevent leaks between two or more components of the extruder.

6. The extruder as in claim 1, further comprising an idling side-arm extruder arranged outside the housing and connected to the degassing opening in a melt-wetted area of the bushing, wherein the idling side-arm extruder is configured to push melt that has been forced out through the degassing opening back into the into the planetary roller degassing section.

7. The extruder as in claim 6, wherein the idling side-arm extruder is a twin-screw extruder having screws which are at most 150 mm long.

8. The extruder as in claim 1, wherein a maximum number of planetary spindles (n) is selected based on the pitch diameter (d) of the internal toothing according to the following table: TABLE-US-00004 pitch diameter (d) max. number of planetary spindles (n) d 110 mm 5 110 mm < d 175 mm 7 175 mm < d 190 mm 8 190 mm < d 225 mm 9 225 mm < d 275 mm 11 275 mm < d 350 mm 15 .sup.d > 350 mm 20

9. The extruder as in claim 1, wherein the planetary roller degassing section comprises three planetary spindles which are uniformly distributed around the central spindle.

10. The extruder as in claim 1 having an extended degassing section, wherein either a) two planetary roller degassing sections are provided with common planetary spindles which extend into both planetary roller degassing sections or b) the housing comprises a first housing section and a second housing section which are connected by intermediate pieces and wherein the bushing extends into both housing sections.

11. The extruder as in claim 1, comprising a plurality of degassing openings.

12. The extruder as in claim 1, wherein the planetary roller degassing section is integrated in an extrusion line in which the planetary roller degassing section is aligned with other extruder sections/modules of the extrusion line or wherein in which the planetary roller degassing section is arranged in tandem with other extruder sections/modules of the extrusion line.

13. The extruder as in claim 12, wherein the extrusion line is equipped with a filler part and one or more of a) an additional degassing on the filler part, b) a gas extraction at an extruder outlet, and c) an additional material supply outside of the filler part.

14. The extruder as in claim 12, comprising an additional material supply which is a) a solids feed using a side-arm extruder and/or b) a liquid supply.

15. The extruder as in claim 12, comprising an additional liquid supply which is a) a pump or b) an extruder for melting an extrudable solid feedstock.

16. The extruder as in claim 15, wherein the additional liquid supply a) takes place through openings which are distributed over a length of the extrusion line on the housing thereof and/or b) through a ring construction with at least one opening, wherein the ring construction is arranged between two extruder sections/modules so that supply lines for liquids can be led through a gap between the two extruder sections/modules to the ring construction.

17. The extruder as in claim 15, wherein a ring construction is provided for injection between two extruder sections/modules which fits on a thrust ring located there or which forms a unit with a thrust ring if an extruder section/module located upstream of the ring construction is a planetary roller extruder section/module with thrust ring for the planetary spindles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0187] FIG. 1 shows part of a cross section of a bushing for a planetary roller extruder section/module intended for degassing. For simplicity of illustration the round bushing is shown flattened.

[0188] FIG. 2 shows an extruder with a planetary roller extruder section.

[0189] FIG. 3 shows a connection between two extruder modules.

[0190] FIG. 4 is a partially cut-open perspective view of a planetary extruder according to the prior art.

DETAILED DESCRIPTION

[0191] Referring to FIG. 4, a planetary extruder generally includes a housing 401. A bushing 403 is arranged within the housing. The bushing 403 has an internal toothing with a pitch diameter and a root circle. An externally toothed central spindle 405 is arranged within the housing 401. The central spindle 405 is connected to a drive (not shown) by a journal 409. Planetary spindles 407 are configured and disposed to rotate about the central spindle 405 between the central spindle 405 and the bushing 403 while intermeshing with the toothing of the central spindle 405 and the toothing of the bushing 403. A heat transfer fluid 411 is guided through fluid channels 413,414 which extend helically along an outer surface of the bushing and guide the heat transfer fluid axially.

[0192] FIG. 1 shows a detail of a bushing 1 for a planetary roller extruder section/module intended for degassing. For simplicity of illustration, the bushing 1 is shown in a flattened and straightened cross section. A toothing 2 is formed on the inside of the bushing 1. On the outside of the bushing 1 recesses/grooves form channels 3. The dimension in the very bottom between the teeth and in the very bottom of the channels is designated as 4. It refers to a minimum radial thickness 4 of the bushing 1 between a root circle of the internal toothing on an inside of the bushing and a bottom of the fluid channels 3 on an outside of the bushing.

[0193] FIG. 2 shows an extruder with a planetary roller extruder section 11 designed as a planetary roller extruder, a drive 10 and an outlet 16. The length of the section 11 corresponds to the desired length of the degassing line. The housing of section 11 is provided with flanges 13, 14 on both ends. An upstream flange 13 is used to clamp the planetary roller extruder section 11 to a corresponding flange 12 of the drive 10. A downstream flange 14 is clamped with a corresponding flange 15 of the outlet 16.

[0194] In its housing, section 11 is provided with an internally toothed bushing, a central spindle which is set in rotary motion by the drive. In the design example, four planetary spindles turn around the central spindle. The planetary spindles are evenly distributed on the circumference of the central spindle and intermesh both with the external teeth of the central spindle and with the internal toothing of the bushing.

[0195] Three degassing points are provided on the housing of the section. A first degassing point 18 is located at the hopper 17. The hopper is encapsulated so that the air arriving with the feedstock in the hopper can be removed.

[0196] Degassing further takes place at a second degassing point 19 and a third degassing point 20 by means of side-arm extruders (not shown) located on top of the housing and idling. The side-arm extruders are designed as twin-screw extruders and press back the melt forcing out of section 11. At the same time, a negative pressure is applied to the side arm extruders, which makes it easier for the gas released in section 11 to exit from section 11.

[0197] In another design example, a degassing ring (not shown) is provided instead of the third degassing point 20 at the end 21 of the extruder section 11. The degassing ring is located between the downstream flange 14 and corresponding flange 15 of the outlet 16. The two flanges 14, 15 form a common ring construction with the thrust ring for the planetary spindles. The ring construction is provided, on the side facing away from the thrust surface, with degassing openings, which open into an enclosed ring channel connected to a suction line.

[0198] FIG. 3 shows a design example where the degassing section is formed by two planetary roller extruder modules 30 and 31, the housings of which are clamped together at flanges 32, 33, with an intermediate piece 34. The housings 30, 31 are provided with a bushing which is internally toothed and corresponds with the planetary spindles or the central spindle of the planetary roller extruder modules. The toothing of both bushings is the same. In addition, the intermediate piece 34 is provided with the same toothing and dimensioned and arranged so that excessively long spindles protrude through both modules. In a further design example, a degassing point 35 is provided on the intermediate piece 34.