Extrusion screw for a multi-screw extruder

Abstract

The invention relates to an extrusion screw (100) for a multi-screw extruder (200), comprising at least: - a feed and metering section (30); - a rotor body (50) having a larger diameter than the feed and metering section (30), which rotor body has a plurality of satellite screws (20), at least a part of which are arranged openly on the outer circumference of the rotor body (50) with their longitudinal extension; wherein between the feed and metering section (30) and the rotor body (50) a hub (11) and a drive region connected thereto are configured, in which drive region the satellite screws (20) are respectively embedded in an outer toothing on the rotor body (50) via a drive pinion (21) or in an inner toothing on a stator ring (244) or in an inner wall of an extruder housing (240) of the multi-screw extruder (100). In at least two adjacent recesses (15) for the drive pinions (21) respectively at least one circumferentially closed bypass channel (13) is configured, which extends from an input opening (12) of the hub (11) to an output opening (14) arranged behind the drive pinion (21) in the flow direction.

Description

Technical Field

[0001] This invention relates to an extrusion screw for a multi-screw extruder. Background Technology

[0002] It has been proven that a multi-rotor system (MRS), whose basic characteristics are described in WO 2003 033 240A1, is suitable for processing plastic melts, especially polyesters. It comprises an extrusion screw with a so-called polymerization unit, consisting of a rotor body shaft, between the input and output zones for feeding and melting the plastic. The output zone has a significantly larger diameter compared to the other zones and also includes multiple rotating satellite screws. The multi-rotor system allows for a significant improvement in degassing performance compared to single-screw and twin-screw systems. This enables the melt to remain in the polymerization unit for a very short time.

[0003] Well-known drive schemes provide a drive zone for the satellite screw, located within the processing chamber used for degassing. The melt transferred from the metering zone is guided through this drive zone. In some applications, the energy input due to shear occurring in this zone can be advantageous, as it promotes the homogenization of the plastic melt. On the other hand, shearing of the polymer in the drive zone can be detrimental to product performance. Summary of the Invention

[0004] Therefore, the object of the present invention is to improve the extrusion screw for an MRS system or a multi-screw extruder equipped with an MRS system so that the polymer processed by it is less affected by shear.

[0005] The solution lies in an extrusion screw or multi-screw extruder according to the present invention.

[0006] According to the invention, most of the melt flow in the drive zone is not guided by the pinion driving the satellite screw, but rather in a closed bypass channel constructed within the support bearing element for the satellite screw and passing through the pinion. The advantage of this is that the melt is not heated by shear. For example, in processing PET, it is advantageous that the melt is relatively cool before it is fully plasticized, thus avoiding excessive decomposition of the melt in the input zone.

[0007] Another advantage for the extrusion screw itself is a reduced risk of damage to the screw due to melt contamination. The screw can be supported in sliding bearing bushings before and after the pinion.

[0008] This support method prevents the tip of the pinion from contacting the bottom of the groove supporting the bearing element. This avoids potential wear.

[0009] For the bypass channel to be effective, it is important to select a sufficiently large bypass channel so that the main portion of the volumetric flow of polymer conveyed and processed by the extrusion screw is not diverted through the drive zone. Sufficient cross-section is also important to prevent incompletely plasticized screw material from clogging the channel and causing large pressure drops. Both will result in high head pressures at the end of the feed, leading to significantly higher energy inputs that can damage the melt.

[0010] Specifically, the channel should provide a free cross-section of at least 5 mm in any dimension, preferably 8 mm to 10 mm.

[0011] The second solution of the present invention is that the bypass channel extends around the outside of the tooth crown, that is, it is disposed in the wall of the extruder housing and / or in the stator ring.

[0012] The annular gap between the outer side of the supporting bearing element and the inner side of the extruder orifice in the housing should have a radial width preferably from 1 mm to 3 mm, with a maximum of 5 mm. In the case of a diameter of 130 mm, the annular gap is, for example, from 1.6 mm to 2.0 mm.

[0013] Preferably, the dimensions of the geometry are determined such that the cross-sectional area formed between the outer periphery of the extrusion screw and the inner periphery of the extruder orifice in the drive zone is at most 20% of the sum of the cross-sectional areas of all the bypass channels. This ensures that the majority of the material is guided through the bypass channel to the pinion.

[0014] This limits the flow to a small volumetric flow on the outer periphery, allowing the polymer to act as a lubricant in the drive zone, while a larger proportion of the volumetric flow is diverted to the bypass channel, thus avoiding shearing within the drive zone. Furthermore, it is advantageous that when the size of the annular gap is chosen to be small enough, foreign matter large enough to cause significant mechanical damage to the tooth crown is retained in the melt flow. Attached Figure Description

[0015] The invention will now be explained in more detail with reference to embodiments and the accompanying drawings. The drawings show in detail:

[0016] Figure 1 This is a perspective view of the components of the extrusion screw;

[0017] Figure 2 This is a perspective view of the satellite screw carrier component;

[0018] Figure 3 This is a perspective view of the components of the extrusion screw;

[0019] Figure 4 These are cross-sectional views of the components of a multi-screw extruder; and

[0020] Figure 5This is a perspective cross-sectional view of the components of a multi-screw extruder. Detailed Implementation

[0021] Figure 1 The components of the extrusion screw of a multi-screw extruder are shown in perspective view, specifically the transition area between the feed and metering section 30 with a screw web 31 and the multi-screw section with multiple satellite screws 20. A cone 11 is formed between the two, and the diameter of the extrusion screw widens along the flow direction on the cone 11. The cone 11 is part of the support bearing element 10. The end sections of the multiple satellite screws 20, each equipped with a drive pinion 21, are supported in this section. Between adjacent drive pinions 21, elongated axial sections of the support bearing element 10 are respectively provided, within which circumferentially closed tubular bypass channels 13 are constructed. The bypass channel 13 extends from the input opening 12 at the cone 11 to the output opening 14, which is arranged opposite the drive pinion 21 when viewed from the axial extension direction of the extrusion screw.

[0022] Figure 2 This is a perspective view of the support bearing element 10 from the rear. The support bearing element has a recess 15 for each satellite screw, in which a pinion is supported, and a bearing housing 16 located at the front of the head, into which the bearing feet (Lagerabsatz) of the satellite screw or pinion can be inserted. Lubrication of the bearings of the satellite screws (such as pinions) is achieved by polymer delivered by the extrusion screw. Since the bearing housing 16 is shielded from flow by the cone, holes 17 are provided, each extending into the bearing housing 16.

[0023] Figure 2 The tubular bypass channels 13 have a clearly visible triangular or trapezoidal cross-section. Because the acute angle of the triangular cross-section or the narrow side of the trapezoid faces the central axis, and the wide base of the triangle is located on the outer periphery, the space between the grooves 15 is optimally used for the pinion. The output openings 14 of each bypass channel 13 are not located at the end of the supporting bearing element 10; instead, these bypass channels 13 extend axially only to the extent reached by the pinion.

[0024] The advantages of this arrangement can be seen from... Figure 3As can be seen in the diagram, an extrusion screw having a feed and metering section 30, a satellite screw carrier element 10, and a satellite screw 20 is shown in perspective. A portion of a rotor body 50, which is connected to the satellite screw carrier element 10, is also shown. A groove 15 supporting the bearing element 10 continues through a groove 52 on the rotor body 50. The satellite screw 20 is guided within the groove, with the outer side of the groove open. The rotor body 50 has a portion of its own main screw web 51 between the grooves 52. Since the output opening 14 does not reach the end of the supporting bearing element 10, the melt flowing from the output opening 14 directly reaches the feed area of ​​the web 22 on the satellite screw and the main screw web 51 from the side.

[0025] Figure 4 A side cross-sectional view of the components of a multi-screw extruder 200 is shown. The view shows the components related to... Figure 3 The same section of the extrusion screw shaft 100 is rotatably supported in the extruder housing 240 having an extruder orifice 241. The extruder housing 240 has a housing portion 242 for accommodating the cone 11 and a housing portion 243 with a reduced diameter for accommodating the feed and metering section 30 of the extrusion screw.

[0026] In the drive zone, a stator ring 244 is inserted into an extruder bore 241. The stator ring has an internal toothed crown into which the drive pinion 21 of the satellite screw 20 is embedded. Additionally, a plugging ring 245 is inserted to limit the annular gap between the inner wall of the housing and the outer periphery of the extrusion screw 100 in this position, and its width can be adjusted.

[0027] Figure 5 The multi-screw extruder 200 is shown again in a perspective cross-sectional view. It is designed as a degassed extruder. Therefore, in addition to other housing components 242, 243, the extruder housing 240 includes a connecting flange 247 with a suction opening 248. The suction opening 249 is located at the beginning of the main screw web 51, meaning that the plastic melt can be degassed after the fan-shaped area at the cone 11. More suction openings can be connected downstream.

[0028] The path of the molten plastic from the feed and metering section 30 through the cone 11 and the bypass channel 13 is indicated by a dashed arrow. It can be seen that a large portion of the molten plastic therefore flows through the toothed stator ring 244, into which the invisible pinion of the satellite screw 20 is embedded.

Claims

1. An extrusion screw (100) for a multi-screw extruder (200), comprising at least: -Feeding and metering section (30). - A rotor body (50) with a diameter larger than the feed and metering section (30), the rotor body (50) having a plurality of satellite screws (20), at least a portion of the longitudinal extension of the satellite screws being exposed on the outer periphery of the rotor body (50); A cone (11) and a drive zone connected thereto are constructed between the feeding and metering section (30) and the rotor body (50). In this drive zone, the satellite screw (20) is respectively embedded in the external tooth crown on the rotor body (50) via a drive pinion (21), or embedded in the internal tooth crown on the stator ring (244) or in the inner wall of the extruder housing (240) of the multi-screw extruder (200); The characteristic feature is that the drive area is disposed on the support bearing element (10), the support bearing element (10) having a groove (15) and / or a bearing receiving portion (16) for accommodating the drive pinion (21) for each satellite screw (20), the bearing receiving portion (16) for accommodating a bearing foot or bearing attached to the end of the satellite screw (20), At least two adjacent grooves (15) for the drive pinion (21) are provided with elongated axial sections for supporting bearing elements (10), and at least one circumferentially closed bypass channel (13) is constructed in the elongated axial sections. The bypass channel (13) extends from the input opening (12) of the cone (11) to the output opening (14) arranged in the flow direction behind the drive pinion (21). The bypass channel (13) extends axially only to the extent reached by the drive pinion (21).

2. The extrusion screw (100) according to claim 1, characterized in that, At least a portion of the longitudinal extension of the bypass channel (13) is configured as a tube with a triangular or trapezoidal cross-section, wherein, in the cross-section, the acute angle of the triangle or the narrow side of the trapezoid faces the central axis of the support bearing element (10), and the opposite wide base is arranged on the outer periphery of the support bearing element (10).

3. The extrusion screw (100) according to claim 1 or 2, characterized in that, At least one radial hole is drilled on the outer periphery of the support bearing element (10) for each satellite screw (20), the radial hole extending to the groove (15) for the drive pinion (21) or to the bearing housing (16).

4. A multi-screw extruder (200) comprising at least one extruder housing (240) having an extruder orifice (241) in which an extrusion screw (100) according to any one of claims 1 to 3 is rotatably supported.

5. The multi-screw extruder (200) according to claim 4, characterized in that, An annular gap is constructed between the outer periphery of the extrusion screw (100) and the outer periphery of the extruder orifice (241) in the drive zone, with a maximum radial width of 5 mm.

6. The multi-screw extruder (200) according to claim 4 or 5, characterized in that, An annular gap is constructed between the outer periphery of the extrusion screw (100) in the drive zone and the inner periphery of the extruder orifice (241), with a maximum cross-sectional area of ​​20% of the sum of all cross-sectional areas of the bypass channel (13).

7. The multi-screw extruder (200) according to claim 5, wherein the internal tooth crown is disposed on the stator ring (244), the stator ring (244) being inserted into the extruder bore (241) in the drive zone, and in the longitudinal direction, a plugging ring (245) for defining the annular gap is disposed in front of the stator ring (244).

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