Extruder screw for a multi-screw extruder and multi-screw extruder

Abstract

Extruder screw (100) for a multi-screw extruder (200), at least comprehensively: - an inlet and metering section (30), - a rotor body section (50) with an increased diameter compared to the intake and metering section (30), which has a plurality of satellite worms (20) which are arranged exposed at least over part of their length on the outer circumference of the rotor body section (50); wherein a cone (11; 111; 211) and a drive zone adjoining it are formed between the feed and metering section (30) and the rotor body section (50), in which the satellite screws (20) each engage via a pinion (21) in an internal toothing in or on the inner wall of an extruder housing (40) of the multi-screw extruder (200); wherein the drive zone is formed on a support bearing element (10; 110; 210) which has a groove (15; 115; 215) for each satellite screw (20) to accommodate the pinion (21), characterized in that the satellite worms (20) are each mounted in at least one sliding bearing (70; 170) arranged next to the pinion (21) in the support bearing element (10; 110; 210), which is arranged at an axial position between the pinion (21) and the beginning of the worm web (22).

Description

[0001] The invention relates to an extruder screw for a multi-screw extruder with the features of claim 1 and a multi-screw extruder with the features of claim 6.

[0002] For processing polymer melts, especially polyester, a multi-rotation system (MRS) has proven effective, which is fundamentally described in WO 2003 033 240 A1. Further improved embodiments of the multi-rotation system (MRS) are described in DE 10 2018 130 102 A1 and DE 10 2017 111 275 A1. An MRS extruder contains an extruder screw which, between a feed zone for drawing in and melting the polymer and a discharge zone, includes a so-called poly-rotation unit with a rotor shaft. The latter has a significantly larger diameter than the other zones and also several rotating satellite screws. The multi-rotation system achieves a significant increase in degassing performance compared to single- and twin-screw systems. Consequently, the residence time of the melt in the poly-rotation unit can be kept very short.

[0003] The established drive concept features a drive zone for the satellite screws located within the treatment chamber designated for degassing. Positioning the drive zone directly at the upstream end of the multi-rotation unit is necessary in most applications and cannot be moved to the downstream end. This is essential to minimize the length of the extruder screw section subjected to the drive torque.

[0004] The melt transferred from the metering zone via the cone is guided through the drive zone of the satellite screws. In some applications, the energy input resulting from the shear occurring there can be advantageous because it promotes the homogenization of the polymer melt. On the other hand, the shearing of the polymer in the drive zone can be detrimental to the product properties.

[0005] The drive zone of the satellite screws is subjected to high stress in several respects. The gearing, consisting of the pinions attached to each satellite screw and a housing-side toothed ring with internal teeth, can only be lubricated by the hot polymer. Therefore, it is necessary for the polymer to flow through the drive zone. However, this also allows hard plastic particles, not fully melted in the metering zone, to enter the drive zone. Furthermore, during plastic recycling, contaminants such as metal particles or grains of sand may be present in the plastic melt. In addition, the melt pressure of the melt flowing around the outer circumference of the extruder screw causes the pinions of the floating satellite screws to be pressed into the receiving grooves on the satellite carrier element, resulting in significant wear on the tooth flanks and also subjecting them to considerable wear themselves.

[0006] CN 2 01 086 389 Y describes a multi-screw extruder, which, like an MRS extruder, has the following characteristic: one pinion of the satellite screw shafts meshes only with a toothed ring in the extruder bore, but not simultaneously—unlike in a planetary roller extruder—with the central main rotor shaft. The flow is not axial, but rather through an opening on the side of the housing. This means that the area where the satellite screw shafts are located is pressurized, so this extruder cannot be used for degassing. The satellite screw shafts are mounted in a flange attached to the rear of the driven main rotor shaft.

[0007] The object of the invention is therefore to improve an extruder screw for an MRS system or a multi-screw extruder equipped with it in such a way that the wear in the drive zone of the satellite screws is reduced.

[0008] The solution according to the present invention consists of an extruder screw with the features of claim 1 or a multi-screw extruder with the features of claim 6.

[0009] According to the invention, the satellite worms are supported in their grooves in the satellite worm carrier element at least on one side next to the pinion by means of a sliding bearing in order to counteract the melt pressure and to prevent the pinion from scraping the bottom of the groove with its outer flanks of the teeth. For this purpose, a bearing shoulder is formed between the area of ​​the worm that has a worm web and the area for receiving the pinion.

[0010] Furthermore, the end of the satellite screw can be designed as a bearing shoulder, which is supported in a bearing recess on the satellite screw carrier element. In this embodiment, the bearing recess is located directly behind the cone that forms the transition between the metering zone and the degassing zone.

[0011] In order to compensate for tolerances that may occur, especially as a result of the heating or cooling of the extruder screw during operation, the bearing shoulders are not to be inserted directly into the respective bearing recess, but rather mounted in an additional bearing insert element placed there.

[0012] According to a preferred embodiment, the satellite worm is supported on both sides next to the pinion in sliding bearings.

[0013] Preferably, the bearing bores of the end bearing and the bearing on the other axial side of the pinion are each formed in a separate bearing insert element, which is inserted into the groove on the satellite screw carrier element. The outer contour of the bearing insert element largely corresponds to the inner contour of the receiving groove. Since this groove is preferably deeply cut, the bearing insert element is positively locked in the groove in the cross-sectional plane oriented transversely to the central axis without additional locking elements and can be inserted into the satellite screw carrier element together with the satellite screw. A groove is considered deeply cut if its cross-section covers an arc of more than 180°.

[0014] Preferably, the end bearing of the satellite screw is also formed by such a bearing insert element, which is inserted into the groove. This allows both bearing insert elements to be easily replaced in case of wear. A metallic material can be selected for them, which is further densified by hot isostatic pressing (HIP) to increase wear resistance. The satellite screw support element can thus be formed from other suitable materials, independent of the bearing strength requirements.

[0015] According to an advantageous embodiment, a significant proportion of the melt flow in the drive zone is not guided over the pinions, but rather in flow channels within the support bearing past the pinions.

[0016] This has the advantage that the melt is not heated by shear. For example, in PET processing, it is beneficial if the melt is not fully plasticized and therefore relatively cool, thus preventing excessive melt degradation in the feed zone. A further advantage for the extruder screw itself is that the risk of damage from melt contamination is reduced.

[0017] For the flow channels to be effective, it is important that they are large enough so that a significant portion of the volume flow of polymer conveyed and processed by the extruder screw is not routed through the drive zone. A sufficient cross-section is also important to prevent incompletely plasticized material from the feed screw from clogging the channels and causing a high pressure drop. Both of these factors result in high head pressure at the end of the feed, leading to a significantly higher energy input and thus preventing damage to the melt.

[0018] Specifically, the channels should offer a free cross-section of at least 5 mm in each dimension, preferably 8 mm to 10 mm.

[0019] It is also possible that the flow channels are routed around the outside of the gearing, i.e., inserted into the wall of the extruder housing and / or into the stator ring.

[0020] The annular gap between the outer surface of the support bearing element and the inner surface of the extruder bore in the housing should have a radial width of preferably 1 mm to 3 mm and a maximum of 5 mm. For example, with a diameter of 130 mm, the annular gap is dimensioned at 1.6 mm to 2.0 mm.

[0021] This ensures that only a small volume flow passes over the outer circumference, allowing the polymer to act as a lubricant in the drive zone, while the larger portion of the volume flow is distributed across the flow channels and thus experiences no shear in the drive zone. It is also advantageous if the annular gap is chosen to be small enough to retain foreign particles in the melt flow that are large enough to cause significant mechanical damage to the gear teeth.

[0022] The invention is explained in more detail below with reference to an exemplary embodiment and the drawings. The figures show in detail: Fig. 1. Parts of an extruder screw in perspective view: Fig. 2 a perspective view of the satellite screw carrier element according to a first embodiment; Fig. 3A, Fig. 3B each part of the extruder screw with the satellite screw carrier element according to Fig. 2 in perspective view; and Fig. 4 parts of a multi-screw extruder with the extruder screw in a side sectional view; Fig. 5 a perspective view of a satellite screw carrier element according to a second embodiment; Fig. 6 a perspective view of the back of the support bearing element after Fig. 5; Fig. 7 a perspective view of an arrangement of several satellite screws of the extruder screw; and Fig. 8 a perspective view of a satellite screw carrier element according to a third embodiment.

[0023] In Fig. Figure 1 shows a perspective view of parts of an extruder screw 100 for a multi-screw extruder. Specifically, the transition area between a feed and metering section 30 with a screw web 31 and a multi-screw section with several satellite screws 20 is shown. A cone 11 is formed between these sections, causing the diameter of the extruder screw 100 to widen in the flow direction. The cone 11 is part of a support bearing element 10. The satellite screws are each supported in grooves provided with a pinion 21 at their end within the support bearing element 10.

[0024] Between adjacent pinions 21, an elongated, axial section of the support bearing element 10 is provided, in which a tubular flow channel 13 is formed. The flow channel 13 extends from an inlet opening 12 on the cone 11 to an outlet opening 14, which is arranged beyond the pinions 21 in the axial extent of the extruder screw 100 and in the flow direction.

[0025] Fig. Figure 2 shows a perspective view of the support bearing element 10. This element has a groove 15 for each satellite screw, in which its pinion is mounted, and a bearing recess 16 at the front, into which a bearing shoulder of the satellite screw or the pinion can be inserted. The bearings of the satellite screws and the pinion are lubricated by the polymer conveyed by the extruder screw. Since the bearing recesses 16 are shielded from the flow by the cone 11, radial bores 17 are provided, each extending from the outer circumference into the bearing recess 16.

[0026] In Fig. Figure 2 also clearly shows a trapezoidal, almost triangular cross-section of the flow channels 13. Because the apex of the triangular cross-sectional area points towards the central axis and the broad base is located on the outer circumference, the space between the pinions is optimally utilized. The outlet openings 14 of the flow channels 13 are not located at the end of the support bearing element 10; rather, the flow channels 13 extend axially only as far as the pinions reach.

[0027] The advantage of this arrangement arises from Fig. 3A. There, the extruder screw 100 with its feed and metering section 30, the support bearing element 10 and the satellite screws 20 is shown in perspective.

[0028] Additionally, a part of a rotor body section 50 is shown, which connects to the support bearing element 10.

[0029] The grooves 15 of the support bearing element 10 each extend into grooves 52 on the rotor body section 50. The satellite screws 20 are guided within these grooves, with their outer sides open. The rotor body section 50 has sections of its own main screw web 51 between the grooves 52. Because the outlet openings 14 of the flow channels 13 do not extend to the end of the support bearing element 10, the melt emerging from the outlet opening 14 flows directly laterally into the intake area of ​​the main screw web 51 and the webs 22 on the satellite screws 20.

[0030] Fig. 3B is similar to Fig. 3A. Compared to the representation in Fig. However, the rotor body section is not shown in Figure 3A. Furthermore, one of the pinions 21 of a satellite screw 20 has been removed to allow a view of the satellite screw 20's end section. The long section of the satellite screws 20 intended for polymer processing, which is provided with a web 22, terminates at a collar 23 whose diameter is large enough to largely cover a bearing shoulder 24 located behind it. This prevents excessive backflow from the extruder's degassing chamber into the pinion 21 area during operation.

[0031] The bearing shoulders 24 of the satellite screws 20 are each received in a bearing insert element 60, which is inserted into the groove 15 of the support bearing element 10. Behind the bearing point 24, a bearing section 25 is formed on each satellite screw 20, which receives the pinion 21. At the very end, a bearing shoulder 26 is formed, which engages directly in the bearing recess 16 in the support element 10 or in a sliding bearing element located therein.

[0032] Fig. Figure 4 shows parts of a multi-screw extruder 200 in a side sectional view. The same section of the extruder screw shaft 100 is shown as in Figure 4. Fig. 3A, which is rotatably mounted in an extruder housing 40 with an extruder bore 41. The extruder housing 40 has a transition housing part 42 for receiving the cone 11 and a housing part 43 with a reduced diameter for receiving the feed and metering section 30 of the extruder screw 100. In the drive zone, a stator ring 44 is inserted into the extruder bore 41, which has internal teeth into which the pinions 21 of the satellite screws 20 engage. In addition, a sealing ring 45 is inserted to allow adjustment of the annular gap between an inner wall of the extruder housing 40 and the outer circumference of the extruder screw 100 at this point.

[0033] Fig. Figure 5 shows a further embodiment of a support bearing element 110 with grooves 115 for receiving the satellite worms with their pinions. Bearing recesses 116 are formed on a rear section, which is designed as a cone 111. Each satellite worm has a sliding bearing element 170 with a clamping ring 171 inserted into these recesses. The clamping ring 171 serves to hold the sliding bearing element 170 in the support bearing element 110. Due to differing thermal expansion, the fit between the support bearing element 110 and the sliding bearing element 170 can change. The clamping ring 171 prevents the sliding bearing element 170 from rotating in the support bearing element 110.

[0034] For the respective second bearing point, a bearing insert element 160 with a bearing recess 161 is inserted into the groove 115. This differs from the first embodiment of the support bearing element according to the Fig. 3A, Fig. 3B and Fig. 4 is that the support bearing element 110 has flow channels 113 that are open at their outer circumference. A channel 118 branches off from each of these channels and opens into the bearing recess 161 of the bearing insert element 160 to ensure lubrication.

[0035] Fig. Figure 6 is a perspective view of the rear side of the support bearing element 110. Of particular note are the bores 117, which are each arranged between two inlet openings 112 of the flow channels 113 and laterally in the bearing recesses 116 (see Figure 6). Fig. 5) discharge to lubricate the sliding bearings located there with polymer diverted from the production flow.

[0036] Fig. Figure 7 shows three of the satellite snails 120, which are used for recording in the Fig. 5 and Fig. The support bearing element 110 shown in section 6 is determined.

[0037] On the left is a satellite screw 120 with screw guide 122 without additional parts. The screw guide 122 ends at a collar 123. Behind this is a bearing section 125.

[0038] In the middle satellite worm 120, a pinion 121 is mounted on the bearing section 125. This includes not only a toothed area, but also a bearing shoulder 124, 126 with spiral grooves on each side of it to improve lubrication.

[0039] The one on the far right in Fig. The 7 satellite snails shown (120) are mounted on: - the pinion 121; - a bearing insert element 160 into which the bearing shoulder 124 of the pinion 121 is inserted; - a sliding bearing element 170 into which the bearing shoulder 126 is inserted; and - a clamping ring 171 surrounding the sliding bearing element 170.

[0040] Fig.Figure 8 shows a third embodiment of a support bearing element 210, which again has a cone 211 at one end and a plurality of undercut grooves 215 around its circumference, in which the drive zone of the satellite worms with their pinions is formed. In the support bearing element 210, the bearing receptacles 261 for the two bearing points of the satellite worms are provided on both sides of the respective pinion in separate bearing insert elements 260. Flow channels 213 extend from inlet openings 212 on the cone 211 to outlet openings 214. Channels 218 branch off from the flow channel 213 and extend into the bearing receptacles 261 of the bearing insert elements 260. In this embodiment as well, the outer contour of the bearing insert elements 260 is adapted to the inner contour of the grooves 215 so that they are positively locked in a plane transverse to the central axis. The axial fixing of the bearing insert elements 260 is achieved by shoulders on the satellite worms. Reference symbol: 200 multi-screw extruders 100 extruder screws 10; 110; 210 Support bearing element 11; 111; 211 cone 12; 112 Entrance 13; 113 Flow channel 14; 214 Exit opening 15; 115; 215 Nut 16; 116; 216 Storage recess 17; 117; 217 bore 118; 218 Channel 20; 120 satellite snail 21; 121 pinion 22; 122 Schneckensteg 23; 123 Bund 24; 124 Stock sales 25; 125 Bearing section for receiving the pinion 26; 126 Stock sales 30 Inlet and metering section 31 Snail Bridge 40 extruder housings 41 Extruder bore 42 Transition housing part 43 Housing part 44 Stator ring with internal teeth 45 Stauring 50 Rotor body section 51 Main snail bridge 52 Nut 70; 170 sliding bearing element 60; 160; 260 Bearing insert element 161; 261 stock recordings

Claims

[1] Extruder screw (100) for a multi-screw extruder (200), comprising at least: - a collection and metering section (30), - a rotor body section (50) which is larger in diameter than the intake and metering section (30) and which has a plurality of satellite screws (20) which are arranged openly on the outer circumference of the rotor body section (50) over at least part of their length; wherein a cone (11; 111; 211) and an adjoining drive zone are formed between the intake and metering section (30) and the rotor body section (50), in which drive zone the satellite screws (20) each engage via a pinion (21) in an internal toothing in or on the inner wall of an extruder housing (40) of the multi-screw extruder (200); wherein the drive zone is formed on a support bearing element (10; 110; 210) which has a groove (15; 115; 215) for receiving the pinion (21) for each satellite screw (20), characterized by that the satellite screws (20) are each mounted in at least one sliding bearing (70; 170) arranged next to the pinion (21) in the support bearing element (10; 110; 210) which is arranged at an axial position between the pinion (21) and the beginning of the screw flight (22). [2] Extruder screw (100) according to claim 1, characterized by that the satellite screws (20) each have an end-side bearing shoulder (26) which is mounted in a plain bearing (70; 170) in a bearing receptacle (16; 116; 216) in the support bearing element (10; 110; 210) or in a bearing insert element (60; 160; 260) inserted therein. [3] Extruder screw (100) according to claim 1 or 2, characterized bythat at least one bearing receptacle (16; 116; 216) for the plain bearing (70; 170) is formed in a bearing insert element (60; 160; 260) which is releasably inserted into the groove (15; 115; 215). [4] Extruder screw (100) according to claim 3, characterized by that the groove (15; 115; 215) is undercut and that the bearing insert element (60; 160; 260) is held in a positive-locking manner in the groove (15; 115; 215) in a plane transverse to the central axis of the extruder screw (100). [5] Extruder screw (100) according to one of claims 2-4, characterized by that at least one bore (17; 117; 217) is provided on the outer circumference of the support bearing element (10; 110; 210) for each plain bearing (70; 170), which bore extends into the groove (15; 115; 215) for the pinion (21) or into the bearing receptacle (16; 116; 216). [6] Multi-screw extruder (200), comprising at least one extruder housing (40) with an extruder bore (41) in which an extruder screw (100; 100'; 100") according to one of the preceding claims is rotatably mounted.

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