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CN-116529050-B - Extrusion screw for a multi-screw extruder

CN116529050BCN 116529050 BCN116529050 BCN 116529050BCN-116529050-B

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 some of the longitudinal extensions of which are arranged on the periphery of the rotor body (50) in an open manner, wherein between the feed and metering section (30) and the rotor body (50) a cone (11) and a drive zone connected thereto is formed, in which drive zone the satellite screws (20) are each inserted via a drive pinion (21) into an outer toothed crown on the rotor body (50) or into an inner toothed crown on a stator ring (244) or in an inner wall body of an extruder housing (240) of the multi-screw extruder (100). At least two adjacent recesses (15) for the drive pinions (21) are each formed with at least one circumferentially closed bypass channel (13) which extends from an inlet opening (12) of the cone (11) to an outlet opening (14) arranged behind the drive pinions (21) as seen in the flow direction.

Inventors

  • D. Gnosis
  • D. Gnosis
  • S. Gnosis

Assignees

  • 格诺伊斯有限责任公司

Dates

Publication Date
20260508
Application Date
20211116
Priority Date
20201117

Claims (7)

  1. 1. An extrusion screw (100) for a multi-screw extruder (200), comprising at least: A feeding and metering section (30), -A rotor body (50) of larger diameter than the feeding and metering section (30), the rotor body (50) having a plurality of satellite screws (20) at least a part of the longitudinal extensions of which are arranged open on the periphery of the rotor body (50); Wherein between the feed and metering section (30) and the rotor body (50) there is formed a cone (11) and a drive zone connected thereto, in which drive zone the satellite screw (20) is respectively inserted via a drive pinion (21) into an outer crown on the rotor body (50) or into an inner crown on a stator ring (244) or in an inner wall of an extruder housing (240) of the multi-screw extruder (200); Characterized in that the drive zone is arranged on a supporting bearing element (10), the supporting bearing element (10) having, for each satellite screw (20), a recess (15) for receiving the drive pinion (21) and/or a bearing receptacle (16), the bearing receptacle (16) being intended to receive a bearing foot or bearing attached to the end of the satellite screw (20), In at least two adjacent recesses (15) for the drive pinions (21), in each case an elongated axial section is provided, in which at least one circumferentially closed bypass channel (13) is formed, which bypass channel (13) extends from an inlet opening (12) of the cone (11) to an outlet opening (14) arranged downstream of the drive pinions (21) in the flow direction, wherein the extent to which the bypass channel (13) extends in the axial direction is only to the extent to which the drive pinions (21) extend.
  2. 2. Extrusion screw (100) according to claim 1, wherein the longitudinal extension of at least a portion of the bypass channel (13) is configured as a tube having a triangular or trapezoidal cross section, wherein in cross section the acute angle of the triangle or the narrow side of the trapezoid is directed towards the central axis of the support bearing element (10) and the opposite wide base is arranged on the outer circumference of the support bearing element (10).
  3. 3. Extrusion screw (100) according to claim 1 or 2, characterized in that on the outer circumference of the support bearing element (10) at least one radial hole is drilled for each satellite screw (20), which radial hole extends to a groove (15) for the drive pinion (21) or to the bearing receptacle (16), respectively.
  4. 4. A multi-screw extruder (200) comprising at least one extruder housing (240) having an extruder bore (241), an extrusion screw (100) according to any one of claims 1 to 3 being rotatably supported in the extruder bore (241).
  5. 5. The multi-screw extruder (200) of claim 4, wherein an annular gap is configured between the outer circumference of the extrusion screw (100) and the outer circumference of the extruder bore (241) in the drive zone, the radial width of which is no more than 5 millimeters at maximum.
  6. 6. The multi-screw extruder (200) according to claim 4 or 5, characterized in that an annular gap is constructed between the outer circumference of the extrusion screw (100) and the inner circumference of the extruder bore (241) in the drive zone, the cross-sectional area of which is at most 20% of the sum of all cross-sectional areas of the bypass channel (13).
  7. 7. The multi-screw extruder (200) according to claim 5, wherein the internal crown is arranged on a stator ring (244), wherein the stator ring (244) is inserted into the extruder bore (241) in the drive zone and wherein, seen in longitudinal direction, a plugging ring (245) for defining the annular gap is arranged in front of the stator ring (244).

Description

Extrusion screw for a multi-screw extruder Technical Field The present invention relates to an extrusion screw for a multi-screw extruder. Background It has proven to be suitable for the processing of plastic melts, in particular polyesters, to use a multi-rotation system (MRS), the basic case of which is described in WO 2003 033 A1. It comprises an extrusion screw with a so-called polymerization unit with a rotor body shaft between an inlet zone and an outlet zone for feeding and melting the plastic. The diameter of the output zone is significantly larger than in the other zones, and there are also a plurality of rotating satellite screws. With the multi-rotation system a significant improvement of degassing performance can be achieved over single screw and twin screw systems. This allows the residence time of the melt in the polymerization unit to be kept very short. A well known drive scheme provides the satellite screw with a drive zone that is located within the process chamber for degassing. The melt transferred from the metering zone is directed through the drive zone. In some applications, the energy input due to shear occurring in this region may be advantageous because it facilitates homogenization of the plastic melt. On the other hand, shear of the polymer in the drive zone may be detrimental to product performance. Disclosure of Invention The object of the present invention is therefore to improve the extrusion screws for MRS systems or multi-screw extruders equipped with MRS systems in such a way that the polymers processed by them are less affected by shearing. The solution is an extrusion screw or a multi-screw extruder according to the invention. According to the invention, the majority 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 which is formed in the support bearing element for the satellite screw and runs over the pinion. The advantage obtained is that the melt is not heated by shearing. For example, in the case of PET processing, it is advantageous if the melt is not completely plasticized and is therefore relatively cold, so that excessive decomposition of the melt already in the feed zone is avoided. Another advantage is obtained for the extrusion screw itself, namely that the risk of damage to the extrusion screw when the melt is contaminated is reduced. The screws may be supported in slide bearing bushings in front of and behind the pinion. By this way of support, contact of the pinion head with the bottom of the groove supporting the bearing element is avoided. Thereby possible wear can be avoided. For the effectiveness of the bypass channel, it is important that the bypass channel is selected to be large enough so that a major portion of the volumetric flow of polymer conveyed and processed by the extrusion screw is not directed through the drive zone. A sufficient cross section is also important in order to prevent incompletely plasticized feed screw material from clogging the channels and causing large pressure dips. Both can generate high head pressures at the end of the feed, resulting in significantly higher energy input and hence damage to the melt. In particular, the channel should provide a free cross section of at least 5mm, preferably 8 mm to 10 mm, in any dimension. A second solution of the invention consists in that the bypass channel extends around the outside of the crown, i.e. is provided in the wall of the extruder housing and/or in the stator ring. The annular gap between the outside of the support bearing element and the inside of the extruder bore in the housing should have a radial width of preferably 1mm to 3mm, at most 5mm. In the case of a diameter of 130mm, the annular gap is, for example, 1.6mm to 2.0mm. Preferably, the geometry is dimensioned such that the cross-sectional area formed between the outer circumference of the extrusion screw in the drive zone and the inner circumference of the extruder bore is at most 20% of the sum of all cross-sectional areas of the bypass channel. So that a substantial portion is led through the bypass channel to the pathway pinion. It is thereby defined that only a small volume flow flows over the periphery, so that the polymer can act as a lubricant in the drive zone, while a larger proportion of the volume flow is diverted onto the bypass channel and therefore does not experience shear in the drive zone. It is furthermore advantageous when the size of the annular gap is chosen small enough that foreign bodies of a size that can cause significant mechanical damage to the crown remain in the melt stream. Drawings The invention is explained in more detail below with the aid of examples and with reference to the accompanying drawings. The drawings show in detail: FIG. 1 is a perspective view of the components of an extrusion screw; FIG. 2 is a perspective view of a satellite screw carrier element; FIG. 3 is a perspective view of the compon