Screw element of double-screw extruder for efficient devolatilization of polymer solution

Abstract

The utility model relates to a screw element of a double-screw extruder for high-efficiency devolatilization of a polymer solution, and belongs to the technical field of dynamic devolatilization of screw extrusion, the screw element is provided with N threads, N is greater than or equal to 2, the screw edge of at least one end and not more than N-1 threads is provided with a reflux groove, the reflux groove is communicated with the adjacent screw groove, and the reflux groove is communicated with the screw groove. The backflow groove is formed in the screw edge contour face of the thread. The double-screw extruder has the effect of improving the devolatilization efficiency of the double-screw extruder.

Description

Technical Field

[0001] This application relates to the field of dynamic devolatilization technology in screw extrusion, and in particular to a screw element for a twin-screw extruder used for efficient devolatilization of polymer solutions. Background Technology

[0002] During polymer synthesis, most polymer systems exiting the reactor contain low-molecular-weight components such as residual monomers, organic solvents, water, and reaction byproducts, collectively referred to as volatiles. The content of these volatiles can be as high as tens of percent. The process of removing these volatiles from the polymer bulk is called devolatilization, which can improve the degree of polymerization and performance of the polymer, recover residual monomers and solvents, remove odors, and meet health and environmental requirements. Depending on the application of the polymer product, the target volatile concentration in the devolatilization process can range from several thousand to tens of ppm (parts per million). The energy consumption of the devolatilization process accounts for more than 60% of the total energy consumption in the entire polymer synthesis process. Therefore, efficient devolatilization is an important means to reduce polymer production costs and improve product quality.

[0003] In the devolatilization section of a twin-screw extruder, the material is conveyed forward by the screw and forms melt films at multiple locations under shearing and stretching action, thereby generating multiple mass transfer interfaces and promoting the transfer of volatiles from the liquid phase to the gas phase. For example... Figure 1 As shown, based on their formation location, mass transfer interfaces mainly include the following three types:

[0004] The first type is the melt film mass transfer interface on the inner wall of the barrel 01: In the space enclosed by the screw groove, screw ridge and inner wall of the barrel, the material forms a continuous melt film on the barrel wall due to the flow and stretching action. Its outer surface is exposed to the gas phase space and is the most important devolatilization interface, where volatiles can easily escape.

[0005] The second type is the melt mass transfer film interface at the root of the screw in the meshing zone 02: When using screw elements with a fully meshing structure, a thin melt film will be formed between the roots of the two screws, and its surface is also exposed to the gas phase, which is an additional high-efficiency devouring interface.

[0006] The third type is the spiral channel molten pool mass transfer interface 03: Since the material accumulates in the spiral channel to form a molten pool, its liquid surface can also serve as a mass transfer interface, but due to poor fluidity and small gas phase contact area, the devolatilization efficiency is low.

[0007] If a screw element with a partially meshing structure is used, a second type of interface will not be formed, and only a molten pool with low devolatilization efficiency exists at the root of the meshing zone. In contrast, the overall devolatilization capability is limited by the element structure lacking an efficient mass transfer interface.

[0008] Therefore, in summary, the existing screw structure has limited effective mass transfer interface in the devolatilization section. In particular, in some meshing structures, the lack of participation of the melt film interface at the screw root makes it difficult to further improve the devolatilization efficiency and meet the stringent requirements of polymer materials for low residual volatiles. Utility Model Content

[0009] In order to improve the devolatilization efficiency of twin-screw extruders, this application provides a twin-screw extruder screw element for efficient devolatilization of polymer solutions.

[0010] The present application provides a twin-screw extruder screw element for efficient devolatilization of polymer solutions, which adopts the following technical solution:

[0011] A twin-screw extruder screw element for efficient devolatilization of polymer solutions, the screw element having N threads, N≥2, wherein at least one thread and no more than N-1 threads have a reflux groove, the reflux groove being connected to its adjacent screw groove.

[0012] By adopting the above technical solution, during the axial conveying of material along the screw, due to the pressure gradient before and after the screw channel, the material at the front end of the return channel (i.e., near the high-pressure end) will experience localized reverse flow along the direction of the return channel, thus forming a backflow. The screw ribs without a return channel still maintain the axial conveying of material, thereby forming a composite flow field in the conveying direction where the overall forward thrust and multiple bundles of reverse return flow intersect. The multiple return material bundles are distributed in the internal space of the barrel, and the return material bundles themselves form a fourth type of mass transfer interface area, which is beneficial to improving the devolatilization efficiency of the twin-screw extruder.

[0013] Optionally, the reflux groove is formed on the helical contour surface of the thread, and a plurality of reflux grooves are formed, which are arranged at equal intervals along the helical direction of the thread.

[0014] By adopting the above technical solution, the design of the reflux channel being opened on the screw thread profile surface allows the reflux material bundle to not only form a reflux material bundle, but also to pull the molten pool in the screw channel to change its morphology. The melt is stretched along the screw channel axis and extended upstream, resulting in an inclined distribution of the liquid surface on the molten pool. This increases the interface between the molten pool and the melt film mass transfer interface on the inner wall of the barrel. At the same time, the average thickness of the molten pool is reduced, which is conducive to the volatiles inside the molten pool being exposed to the gas phase more quickly through surface renewal, thereby further improving the devolatilization efficiency of the twin-screw extruder.

[0015] The reflux grooves are arranged at equal intervals along the spiral direction of the thread, which makes the axial distribution of the reflux disturbance effect of the material during the conveying process more uniform, enhances the periodic disturbance effect of the molten pool, and thus improves the renewal frequency and devolatilization stability of the melt interface.

[0016] Optionally, N is 2, meaning the screw element has a double-ended thread, and the return groove is opened on the thread ridge of one of the threads.

[0017] Optionally, the extension direction of the return groove has an angle with the central axis of the screw element.

[0018] By adopting the above technical solution, the inclined setting of the reflux tank is conducive to enhancing the reflux flow path of the material, allowing the material to stay in the tank for a longer time, which is more conducive to thinning the thickness of the molten pool, and thus helps to increase the mass transfer interface area.

[0019] Optionally, the return channel is inclined against the spiral direction of the screw rib, and the angle between the extension and through direction of the return channel and the central axis of the screw element is in the range of 10°-75°.

[0020] By adopting the above technical solution, the reverse tilt setting of the reflux tank is conducive to increasing the reflux path of the material, which in turn is conducive to enhancing melt disturbance, lengthening and thinning the screw channel melt pool, thereby increasing the mass transfer interface area and further improving the devolatilization efficiency.

[0021] Optionally, the reflux groove is inclined along the spiral direction of the screw thread, and the angle between the extension and through direction of the reflux groove and the central axis of the screw element is in the range of 10°-75°.

[0022] By adopting the above technical solution, although the return path is reduced when the return channel is set in a forward-sloping manner compared to that set in a reverse-sloping manner, it is more compliant with the mainstream conveying direction, has less interference with the mainstream thrust of logistics, and can take into account the stability of conveying.

[0023] Optionally, the extension direction of the return groove is parallel to the central axis of the screw element.

[0024] By adopting the above technical solution, the reflux trough is set as a straight trough, which minimizes the reflux path and has the least impact on the mainstream conveying. It is suitable for high-viscosity materials and ensures stable output.

[0025] Optionally, the bottom of the reflux trough can be a flat surface, an arc surface, a multi-segment connected flat surface, or a multi-segment connected arc surface.

[0026] Optionally, the screw element can be engaged in a full engagement or partial engagement manner.

[0027] By adopting the above technical solution and using a fully meshing screw element, there are three mass transfer interfaces: the melt film mass transfer interface on the inner wall of the barrel, the melt mass transfer film interface at the screw root in the meshing zone, and the melt pool mass transfer interface in the screw groove, resulting in good devolatilization effect. Although the partially meshing screw element lacks the melt mass transfer film interface at the screw root in the meshing zone, which has a certain impact on the devolatilization effect, compared with the fully meshing screw element, the partially meshing screw element has lower shear force, avoiding the situation of molecular weight reduction and product color darkening, and is more suitable for polymers with high requirements for optical and mechanical properties.

[0028] Optionally, the screw diameter D of the screw element is 30-500mm, and the lead of the screw element is 0.5-3D.

[0029] In summary, this application includes at least one of the following beneficial technical effects:

[0030] 1. During the axial conveying of material along the screw, due to the pressure gradient before and after the screw channel, the material at the front end of the return channel (i.e., near the high-pressure end) will experience localized reverse flow along the return channel direction, thus forming a backflow. The screw ribs without a backflow channel continue to maintain the axial conveying of material, thereby forming a composite flow field in the conveying direction where the overall forward thrust and multiple bundles of reverse backflow intersect. The multiple backflow material bundles are distributed in the internal space of the barrel, and the backflow material bundles themselves form a fourth type of mass transfer interface area, which is beneficial to improving the devolatilization efficiency of the twin-screw extruder.

[0031] 2. The design of the reflux channel on the screw thread profile allows the reflux material bundle to not only form a reflux material bundle, but also to pull the molten pool in the screw channel to change its morphology. The melt is stretched along the screw channel axis and extended upstream, resulting in an inclined distribution of the liquid surface on the molten pool. This increases the interface between the molten pool and the melt film mass transfer interface on the inner wall of the barrel. At the same time, the average thickness of the molten pool is reduced, which is conducive to the volatiles inside the molten pool being exposed to the gas phase more quickly through surface renewal, thereby further improving the devolatilization efficiency of the twin-screw extruder.

[0032] 3. The reflux channels are arranged at equal intervals along the spiral direction of the thread, which makes the axial distribution of the reflux disturbance of the material during the conveying process more uniform, enhances the periodic disturbance effect of the molten pool, and thus improves the renewal frequency of the melt interface and the devolatilization stability; 4. The reverse inclined setting of the reflux channels is conducive to increasing the reflux path of the material, which in turn is conducive to enhancing the melt disturbance, lengthening and thinning the spiral channel molten pool, thereby increasing the mass transfer interface area and further improving the devolatilization efficiency;

[0033] 5. The return trough is designed as a straight trough, which minimizes the return path and has the least impact on the main conveyor, making it suitable for high-viscosity materials and ensuring stable discharge.

[0034] 6. The screw element adopts a fully meshing type, which has three mass transfer interfaces: the melt film mass transfer interface on the inner wall of the barrel, the melt mass transfer film interface at the screw root in the meshing zone, and the melt pool mass transfer interface in the screw groove, resulting in good devolatilization effect;

[0035] While partially meshing screw elements lack the melt transfer film interface at the screw root in the meshing zone, which somewhat affects the devolatilization effect, compared to fully meshing screw elements, partially meshing screw elements have lower shear force, avoiding the reduction in molecular weight and darkening of product color, making them more suitable for polymers with high optical and mechanical performance requirements. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the structure of the melt film mass transfer interface on the inner wall of the barrel, the melt film mass transfer interface at the root of the screw in the meshing zone, and the melt pool mass transfer interface in the screw groove, as described in this application.

[0037] Figure 2 This is a schematic diagram illustrating the structure of the melt film mass transfer interface on the inner wall of the barrel, the melt film mass transfer interface at the root of the screw in the meshing zone, the melt pool mass transfer interface in the screw groove, and the reflux jet mass transfer interface.

[0038] Figure 3 This is a schematic diagram of the overall structure of Embodiment 1 of this application.

[0039] Figure 4 This is a schematic diagram of the overall structure of Embodiment 2 of this application.

[0040] Figure 5 This is a schematic diagram of the overall structure of Embodiment 3 of this application.

[0041] Figure 6 This is a schematic diagram of the overall structure of Embodiment 4 of this application.

[0042] Figure 7 This is a schematic diagram of the overall structure of Embodiment 5 of this application.

[0043] Figure 8 This is a schematic diagram of the overall structure of Embodiment 6 of this application.

[0044] Figure 9 This is a schematic diagram of the overall structure of Embodiment 7 of this application.

[0045] Figure 10 This is a schematic diagram of the overall structure of Embodiment 8 of this application.

[0046] Figure 11 This is a schematic diagram of the overall structure of Embodiment 9 of this application.

[0047] Figure 12 This is a schematic diagram of the overall structure of Embodiment 10 of this application.

[0048] Figure 13 This is a schematic diagram of the overall structure of Embodiment 11 of this application.

[0049] Figure 14 This is a schematic diagram of the overall structure of Embodiment 12 of this application.

[0050] Figure 15 This is a schematic diagram of the overall structure of Embodiment 13 of this application.

[0051] Figure 16 This is a schematic diagram of the overall structure of Embodiment 14 of this application.

[0052] Explanation of reference numerals in the attached drawings: 01, melt film mass transfer interface on the inner wall of the barrel; 02, melt film mass transfer interface at the root of the screw in the meshing zone; 03, melt pool mass transfer interface in the screw groove; 1, screw element; 11, screw ridge; 111, reflux groove; 12, screw groove. Detailed Implementation

[0053] The following is in conjunction with the appendix Figure 1-16 This application will be described in further detail.

[0054] This application discloses a screw element for a twin-screw extruder used for efficient devolatilization of polymer solutions. The screw element 1 has N threads, where N≥2. At least one thread ridge 11, but no more than N-1 threads, has a return groove 111, which communicates with its adjacent thread groove 12. The specific number of threads ridge 11 with the return groove 111 is determined according to actual processing requirements. If the screw element 1 has a double-threaded design, then only one thread ridge has the return groove 111. If the screw element has a triple-threaded design, then either one thread circumference has the return groove 111, or two threads have the return groove 111. The design of having the return groove 111 on only one thread of a triple-threaded design is more conducive to stable material conveying, i.e., it is more suitable for conveying materials with higher requirements for output or high viscosity. Having the return groove 111 on two threads of a triple-threaded design increases the material return stream, which is more conducive to improving the devolatilization effect. Therefore, the specific number of screw threads 11 with reflux grooves 111 can be determined according to actual working requirements (material output and material viscosity, etc.).

[0055] The screw element 1 has a screw diameter D of 30-500mm and a lead of 0.5-3D. Several return grooves 111 are provided, arranged equidistantly along the helical direction of the screw thread. The spacing between adjacent return grooves 111 can be 0.04-0.2D, and the groove depth can be 0.1-0.2D. Smaller spacing between return grooves 111 results in more material return streams and better volatilization, but also increases resistance to mainstream material transport. Larger spacing reduces volatilization, but decreases mainstream material transport resistance. Smaller groove depth results in finer material return streams, increasing surface area and shortening the diffusion path of volatiles to the gas phase, leading to better volatilization. However, excessively small groove depth results in a small return flow rate, also causing poor overall volatilization. Conversely, excessively large groove depth reduces the overall mechanical strength of the screw element. Therefore, the specific spacing and depth of the reflux troughs 111 can be determined through system simulation and based on actual conditions.

[0056] The reflux groove 111 can be formed on the profile surface of the screw ridge 11 of the thread, or it can be formed on the side of the screw ridge 11. When the reflux groove 111 is formed on the profile surface of the screw ridge 11, it not only forms a material reflux stream but also changes the morphology of the molten pool in the screw groove 12. The melt is stretched along the axial direction of the screw groove 12 and extends upstream, resulting in an inclined distribution of the liquid surface on the molten pool. This increases the molten pool interface in the screw groove 12 and reduces the average thickness of the molten pool, which facilitates the faster exposure of volatiles inside the molten pool to the gas phase through surface renewal, thereby further improving the devolatilization efficiency of the twin-screw extruder. Conversely, when the reflux groove 111 is formed on the side of the screw ridge 11 (e.g., ...), it can also be formed on the side of the screw ridge 11 of the thread. Figure 16 As shown, although the impact on the molten pool of the screw channel 12 is minimal, it can reduce the adhesion of the reflux stream to the inner wall of the barrel, thereby reducing the impact on the mass transfer interface of the melt film on the inner wall of the barrel. The specific location of the reflux channel 111 can be determined through system simulation and based on actual conditions.

[0057] The screw element 1 can be fully engaged or partially engaged. The fully engaged screw element 1 utilizes three mass transfer interfaces: the melt film interface on the inner wall of the barrel, the melt film interface at the screw root in the engagement zone, and the melt pool interface in the screw channel 12, resulting in good devolatilization performance. The partially engaged screw element 1 lacks the melt film interface at the screw root in the engagement zone, which slightly affects the devolatilization performance. However, compared to the fully engaged screw element, the partially engaged screw element has lower shear force, avoiding molecular weight reduction and product color darkening, making it more suitable for polymers with high optical and mechanical performance requirements.

[0058] The extension direction of the return groove 111 forms an angle with the central axis of the screw element 1. The return groove 111 can be inclined against the helical direction of the screw ridge 11, that is, the return groove 111 can be deflected counterclockwise. The return groove 111 can also be inclined with the helical direction of the screw ridge 11, that is, the return groove 111 can be deflected clockwise. Whether the return groove 111 is deflected clockwise or counterclockwise, the angle between the extension direction of the return groove 111 and the central axis of the screw element 1 is within the range of 10°-75°.

[0059] The reverse-sloping design of the reflux trough 111 increases the material's reflux path, thereby enhancing melt turbulence, lengthening and thinning the molten pool of the screw channel 12, and increasing the mass transfer interface area, which further improves the devolatilization efficiency. While the forward-sloping design of the reflux trough 111 reduces the reflux path compared to the reverse-sloping design, it offers better conformity to the mainstream conveying direction, less interference with the mainstream thrust of the material flow, and better balances conveying stability.

[0060] The return trough 111 can also be configured such that its extension direction is parallel to the central axis of the screw element 1. The return trough 111 is configured as a straight trough, minimizing the return path while having minimal impact on the main conveying flow. This is suitable for high-viscosity materials and ensures stable discharge. Therefore, the appropriate opening direction of the return trough 111 can be selected by comprehensively considering factors such as the material's devolatilization requirements, conveying requirements, and material viscosity.

[0061] The bottom of the reflux trough 111 can be a flat surface, an arc surface, a multi-segment connected flat surface, or a multi-segment connected arc surface, etc.

[0062] like Figure 2 The implementation principle of this application embodiment is as follows: During the axial conveying of material along the screw, due to the pressure gradient before and after the screw groove 12, the material at the front end of the return groove 111 (i.e., near the high-pressure end) will experience local reverse flow along the direction of the return groove 111, thus forming a backflow. The screw rib 11 without the return groove 111 still maintains the axial conveying of material, thereby forming a composite flow field in the conveying direction where the overall forward thrust and multiple bundles of reverse backflow intersect. The multiple backflow material bundles are distributed in the internal space of the barrel, and the backflow material bundles themselves form a fourth type of mass transfer interface area. According to the formula:

[0063]

[0064] CDN: Deviation capability index; the higher the value, the higher the deviation efficiency.

[0065] A p : Main mass transfer interface area, including the mass transfer interface of the melt film on the inner wall of the barrel and the mass transfer interface of the molten pool in the screw channel; Τ p Update time of the main interface;

[0066] Af Auxiliary interface area, such as the local mass transfer interface area formed due to reflux, shear disturbance, etc.

[0067] T f : Auxiliary update time;

[0068] M: Mass flow rate of the melt.

[0069] The presence of the reflux material bundle makes A f Increasing the size of the reflux groove, and creating it on the spiral ridge profile surface, will increase the interfacial area of ​​the spiral groove molten pool, i.e., A. p The increase in CDN and the increased reflux jet also increase the disturbance of the molten pool. The update time of the main interface is small. With the molten flow rate remaining constant, the increase in CDN leads to an increase in devolatilization efficiency.

[0070] Example 1

[0071] like Figure 3 The screw element 1 has a full engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11 profile (the side of the thread ridge 11 furthest from the central axis of the screw element 1). The return grooves 111 are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 30 mm, the lead of the screw element 1 is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth of the return groove 111 is 0.1D. The return grooves 111 are inclined along the helical direction of the thread ridge 11, and the angle between the extension direction of the return groove 111 and the central axis of the screw element 1 is within 10°. The bottom of the return groove 111 is flat.

[0072] Example 2

[0073] like Figure 4 The screw element 1 has a full engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11. These return grooves are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 45 mm, the lead is 2.75D, the spacing between adjacent return grooves 111 can be 0.15D, and the groove depth is 0.15D. The return grooves 111 are inclined against the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within the range of 45°. The bottom of the return groove 111 is flat.

[0074] Example 3

[0075] like Figure 5The screw element 1 has a full engagement mechanism and a double-ended thread. One thread has a return groove 111 on its thread ridge 11. The return grooves 111 are equidistantly arranged along the helical direction of the thread. The screw diameter D of the screw element 1 is 30 mm, the lead of the screw element 1 is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth of the return groove 111 is 0.1D. The extension direction of the return groove 111 is parallel to the central axis of the screw element 1. The bottom of the return groove 111 is flat.

[0076] Example 4

[0077] like Figure 6 The screw element 1 has a full engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11. These return grooves are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 30mm, and the lead is 3D. The spacing between adjacent return grooves 111 can be 0.2D, and the groove depth is 0.1D. The return grooves 111 are inclined along the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within 15°. The bottom of the return grooves 111 is an arc surface.

[0078] Example 5

[0079] like Figure 7 The screw element 1 has a full engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11. These return grooves are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 500 mm, the lead is 0.5D, the spacing between adjacent return grooves 111 can be 0.04D, and the groove depth is 0.1D. The return grooves 111 are angled against the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within the range of 45°. The bottom of the return grooves 111 is an arc surface.

[0080] Example 6

[0081] like Figure 8 The screw element 1 has a full engagement mechanism and a double-ended thread. One thread has a return groove 111 on its thread ridge 11. These return grooves 111 are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 30 mm, the lead is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth is 0.1D. The extension direction of the return grooves 111 is parallel to the central axis of the screw element 1. The bottom of the return groove 111 is an arc surface.

[0082] Example 7

[0083] like Figure 9 The screw element 1 uses partial engagement, also known as SK-type engagement. The screw element 1 has a double-ended thread, with a return groove 111 formed on the profile of the thread ridge 11 of one of the threads. The return grooves 111 are equidistantly arranged along the helical direction of the thread. The screw diameter D of the screw element 1 is 30mm, the lead of the screw element 1 is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth of the return groove 111 is 0.1D. Furthermore, the return grooves 111 are inclined along the helical direction of the thread ridge 11, and the angle between the extension direction of the return groove 111 and the central axis of the screw element 1 is within the range of 10°. The bottom of the return groove 111 is flat.

[0084] Example 8

[0085] like Figure 10 The screw element 1 has a partial engagement mechanism and is equipped with a double-ended thread. One thread has a return groove 111 on its thread ridge 11 profile. The return grooves 111 are equidistantly arranged along the helical direction of the thread. The screw diameter D of the screw element 1 is 45 mm, the lead of the screw element 1 is 2.75D, the spacing between adjacent return grooves 111 can be 0.15D, and the groove depth of the return groove 111 is 0.15D. Furthermore, the return grooves 111 are inclined against the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within the range of 45°. The bottom of the return groove 111 is flat.

[0086] Example 9

[0087] like Figure 11 The screw element 1 has a partial engagement mechanism and a double-ended thread. One thread has a return groove 111 on its thread ridge 11. The return grooves 111 are equidistantly arranged along the helical direction of the thread. The screw diameter D of the screw element 1 is 30 mm, the lead of the screw element 1 is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth of the return groove 111 is 0.1D. The extension direction of the return groove 111 is parallel to the central axis of the screw element 1. The bottom of the return groove 111 is flat.

[0088] Example 10

[0089] like Figure 12The screw element 1 has a partial engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11. These return grooves are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 30mm, the lead is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth is 0.1D. The return grooves 111 are inclined along the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within 15°. The bottom of the return grooves 111 is an arc surface.

[0090] Example 11

[0091] like Figure 13 The screw element 1 has a partial engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11. These return grooves are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 500 mm, the lead is 0.5D, the spacing between adjacent return grooves 111 can be 0.04D, and the groove depth is 0.1D. The return grooves 111 are angled against the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within the range of 45°. The bottom of the return groove 111 is an arc surface.

[0092] Example 12

[0093] like Figure 14 The screw element 1 has a partial engagement mechanism and a double-ended thread. One thread has a return groove 111 on its thread ridge 11. The return grooves 111 are equidistantly arranged along the helical direction of the thread. The screw diameter D of the screw element 1 is 30 mm, the lead of the screw element 1 is 3D, the spacing between adjacent return grooves 111 can be 0.2D, and the groove depth of the return groove 111 is 0.1D. The extension direction of the return groove 111 is parallel to the central axis of the screw element 1. The bottom of the return groove 111 is an arc surface.

[0094] Example 13

[0095] like Figure 15The screw element 1 has a full engagement mechanism and a double-threaded design. One thread has a return groove 111 on its thread ridge 11. These return grooves are equidistant along the helical direction of the thread. The screw diameter D of the screw element 1 is 45mm, the lead is 2.75D, the spacing between adjacent return grooves 111 can be 0.15D, and the groove depth is 0.15D. The return grooves 111 are inclined against the helical direction of the thread ridge 11, and the angle between the extension direction of the return grooves 111 and the central axis of the screw element 1 is within the range of 75°. The bottom of the return groove 111 is flat.

[0096] Example 14

[0097] like Figure 16 The screw element 1 has a full engagement mechanism and is equipped with a double-ended thread. One thread has a through-flow groove 111 on its side edge. The grooves 111 are equidistantly arranged along the helical direction of the thread. The screw diameter D of the screw element 1 is 30mm, the lead is 3D, the spacing between adjacent grooves 111 can be 0.2D, and the groove width is 0.1D. The extension direction of the grooves 111 is parallel to the central axis of the screw element 1. The bottom of the grooves 111 is an arc surface.

[0098] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A twin-screw extruder screw element for efficient devolatilization of polymer solutions, characterized in that: The screw element (1) has N threads, N≥2, wherein at least one threaded edge (11) of the screw thread (11) has a return groove (111) which is connected to the adjacent screw groove (12).

2. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1, characterized in that: The return groove (111) is formed on the profile surface of the thread ridge (11). A plurality of return grooves (111) are formed and are arranged at equal intervals along the helical direction of the thread.

3. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1 or 2, characterized in that: N is 2, that is, the screw element (1) is provided with a double-ended thread, and the return groove (111) is opened on the screw edge (11) of one of the threads.

4. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1, characterized in that: The extension direction of the return groove (111) is at an angle to the central axis of the screw element (1).

5. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 4, characterized in that: The return groove (111) is opened at an angle against the spiral direction of the screw ridge (11), and the angle between the extension and through direction of the return groove (111) and the central axis of the screw element (1) is in the range of 10°-75°.

6. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 4, characterized in that: The reflux groove (111) is opened at an angle along the spiral direction of the screw ridge (11), and the angle between the extension and through direction of the reflux groove (111) and the central axis of the screw element (1) is in the range of 10°-75°.

7. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1, characterized in that: The extension direction of the return groove (111) is parallel to the central axis of the screw element (1).

8. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1, characterized in that: The bottom of the reflux trough (111) is a flat surface / arc surface / multi-segment connected flat surface / multi-segment connected arc surface.

9. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1, characterized in that: The screw element (1) is engaged in a full engagement / partial engagement manner.

10. The twin-screw extruder screw element for efficient devolatilization of polymer solutions according to claim 1, characterized in that: The screw diameter D of the screw element (1) is 30-500mm, and the lead of the screw element (1) is 0.5-3D.

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