Low-shear efficient mixing double-screw assembly and application thereof

Abstract

The invention relates to a low-shear efficient mixing twin-screw assembly and application thereof, the twin-screw assembly comprises a barrel and two screws meshed in the same direction, a groove is formed in the screw edge of each screw in the axial direction, and the radial gap between the two screws is 0.45-0.75 mm. Through cooperation of the axial grooves and the radial gaps of the screw flights, a low-shear macroscopic flow channel and an efficient particle distribution structure are constructed, the technical problem that high mixing efficiency of a traditional double-screw assembly depends on high shear is effectively solved, and the double-screw assembly can be widely applied to mixing processing in the fields of high polymer materials, bioactive materials and the like and has wide application prospects. The method has outstanding practical value and popularization prospect.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing machinery technology, and in particular to a low-shear, high-efficiency mixing twin-screw assembly and its applications. Background Technology

[0002] In polymer processing, the safe transport of high-solids-content sensitive materials has always been a serious challenge, such as solid propellants, solid battery electrode slurries, and highly filled thermoplastics. These materials typically have extremely high viscosity and are sensitive to shear heat. Traditional co-rotating twin-screw extruders use small-clearance screw elements (0.1mm~0.3mm) and high screw speeds to generate high shear to enhance mixing and transport. However, this design paradigm fundamentally contradicts the processing requirements of high-solids-content sensitive materials: while the small clearance can establish high pressure to promote transport, it also generates extremely high shear rates, leading to degradation or combustion and explosion of sensitive materials. Reducing the speed to protect the material weakens the transport capacity, resulting in material discharge or blockage. The flow and mixing of particles in high-solids-content systems in non-Newtonian fluids is extremely difficult. Traditional conveying elements at low screw speeds can only perform material transport, which greatly limits the particle distribution and mixing effect for high-viscosity, highly filled systems.

[0003] CN 115674638A discloses a mound-shaped stretching mixing element, which includes a barrel and a screw. The element has at least two continuous mound-shaped structures arranged along the screw, each mound containing several smaller hill-shaped structures evenly arranged axially, with adjacent mound structures staggered. The stretching flow field generated by the mound-shaped stretching mixing element effectively mixes materials uniformly, resulting in good mixing performance. The flow-diverting effect of the smaller hill-shaped structures allows for better material dispersion and distribution, preventing localized overheating. However, in practical applications, high screw speed and small screw clearance significantly increase the shear force on the material, leading to material degradation and combustion, making it impossible to ensure the safe extrusion of sensitive materials while improving the mixing effect.

[0004] CN 113557113A discloses a screw with undercut helical ribs for extruders or conveyors, the screw element having helical ribs that surround a core, the ribs being undercut along the conveying direction at least in one section of the screw on its active conveying side. The design of the screw rib profile provides advantages in feed performance through the undercut construction and results in efficient filling of the extruder. The undercut conveying side is particularly advantageous for lightweight materials such as foam materials or for materials with low bulk density. However, this screw element has limited application systems and can only be used to convey homogeneously mixed polymers, and cannot efficiently convey and mix solid-liquid mixtures in industrial production processes.

[0005] CN 120793455A discloses a conveying device for a solid-liquid mixture, including a frame with a conveying pipe on the frame. Inside the conveying pipe are a fixed shaft and auger blades. The fixed shaft is fixedly installed in the conveying pipe and extends along its length. The auger blades are coaxially rotatably installed outside the fixed shaft, with their inner circumferential surfaces in contact with the outer circumferential surface of the fixed shaft. A driving mechanism is also provided at one end of the conveying pipe, which drives the auger blades to rotate around the fixed shaft, causing the auger blades to convey the solid-liquid mixture from back to front. Simultaneously, the auger blades scrape off liquid material adhering to the fixed shaft. However, during the mixing of sensitive material systems, the scraping device is prone to causing the shear force on the material to exceed a safety threshold.

[0006] In response to the shortcomings of existing technologies, there is an urgent need in the field for a novel screw design that can synergistically optimize the transport, mixing and shearing history in order to overcome the processing bottleneck of high solids content sensitive materials. Summary of the Invention

[0007] To solve the above-mentioned technical problems, this invention achieves the goals of eliminating material conveying dead zones, distributive mixing efficiency far exceeding that of traditional components, and gentle shearing of materials by improving the screw structure and clearance. This overcomes the problem of the incompatibility between conveying and mixing and low shearing encountered by high solids content sensitive materials during extrusion. Thus, while improving the material conveying and mixing effect, it achieves low shearing action on sensitive materials, realizing stable conveying of high solids content sensitive materials with synergistic optimization of mixing and shearing history.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-shear, high-efficiency mixing twin-screw assembly, the twin-screw assembly comprising a cylinder and two screws meshing in the same direction, wherein the screws have axial grooves on their threaded edges, and the radial gap between the two screws is 0.45~0.75mm, for example, it can be 0.45mm, 0.50mm, 0.55mm, 0.60mm, 0.70mm or 0.75mm, etc.

[0009] This invention provides a low-resistance conveying channel for the continuous dynamic mixing of high-viscosity, high-solids-content materials by synergistically optimizing the screw spacing and screw ridge slotted structure in the twin-screw assembly, thereby avoiding severe shearing and particle compression wear. The flowing material is subjected to repeated low-shear cutting, diversion, merging and reorientation, which greatly improves the distributed mixing efficiency without significantly increasing the shear force.

[0010] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0011] The screw of the present invention includes a double-ended screw, wherein the long and short diameters of the cross section of the double-ended screw are perpendicular to each other, so that the screw edge and the screw groove maintain stable engagement and uniform gap during rotation.

[0012] As a preferred embodiment of the present invention, the gap between the screw and the cylinder is the same as the radial gap between the two screws.

[0013] As a preferred embodiment of the present invention, the groove includes a double-arc groove, wherein the double arc is formed by combining two arcs with the same radius of curvature.

[0014] Preferably, the depth of the groove is 0.48 to 0.58 times the height of the screw thread, for example, it can be 0.48, 0.50, 0.52, 0.54, 0.56 or 0.58, etc.

[0015] As a preferred technical solution of the present invention, the radius of curvature of the arc is 4.55~4.75mm, for example, it can be 4.55mm, 4.60mm, 4.65mm, 4.70mm or 4.75mm, etc.

[0016] As a preferred technical solution of the present invention, the circumferential interval angle between the two arc centers of the double arc groove is 9.2~10.8°, for example, it can be 9.2°, 9.4°, 9.6°, 9.8°, 10.0°, 10.2°, 10.4°, 10.6° or 10.8°, etc.

[0017] As a preferred technical solution of the present invention, each turn of the screw thread has 6 to 8 grooves, for example, 6, 7 or 8, and the grooves are evenly distributed along the circumference of the screw.

[0018] Preferably, the groove is arranged in a reverse spiral, and the spiral angle of the reverse spiral is 1.2~1.8°, for example, it can be 1.2°, 1.3°, 1.4°, 1.5°, 1.6°, 1.7° or 1.8°, etc.

[0019] As a preferred embodiment of the present invention, the grooves of two adjacent turns of the screw thread are aligned.

[0020] The present invention preferably features a spiral groove structure and distribution to prevent the material from being suddenly cut off from its flow path when it reaches the groove during the extrusion process as the screw rotates. This forces the material to turn and compress, squeezing it out from the radial gap, which would hinder axial conveying, reduce conveying efficiency, cause material accumulation, and generate violent and irregular pressure fluctuations. The material is subjected to sudden and high local shear, generating a large amount of instantaneous mechanical heat. Some materials are repeatedly subjected to high-intensity shear, which can easily lead to a sharp increase in local temperature.

[0021] As a preferred embodiment of the present invention, the outer diameter of the screw thread is 34.5~35.1mm, for example, it can be 34.5mm, 34.7mm, 34.8mm, 34.9mm, 35.0mm or 35.1mm, etc.; the bottom diameter of the screw groove is 23.50~24.00mm, for example, it can be 23.5mm, 23.6mm, 23.7mm, 23.8mm, 23.9mm or 24mm, etc.

[0022] The twin-screw assembly of the present invention adopts a double-headed screw rib structure, and the screw rib height is (outer circumferential diameter of screw rib minus bottom diameter of screw groove) / 2.

[0023] The screw of this invention adopts a modular structure and can be mounted on a twelve-tooth mandrel, making it easy to combine with other functional components such as kneading blocks.

[0024] In a second aspect, the present invention provides an application of the twin-screw assembly as described in the first aspect, characterized in that the application includes using the twin-screw assembly for conveying and mixing heat-sensitive materials with high solids content.

[0025] As a preferred technical solution of the present invention, the solid content of the high solid content heat-sensitive material is 40~65 vol%, for example, it can be 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, or 65 vol%. The high solid content heat-sensitive material includes any one of solid propellant, solid battery electrode slurry, or highly filled thermoplastic. Preferably, the continuous phase of the high solid content heat-sensitive material includes a non-Newtonian fluid.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention enables the twin-screw extruder to have a low-shear macro-flow channel and efficient particle distribution capability through optimized screw element structure design, which ensures safe material transportation while improving solid-liquid mixing efficiency, and improves mixing efficiency by more than 4% under the same conveying capacity. (2) The conveying screw element structure provided by the present invention has special adaptability to high solid content sensitive systems. The loose flow channel provides a mild shear environment to match the processing window of shear heat sensitive materials. The efficient distribution mixing ensures the uniform dispersion of high content fillers. While improving the mixing efficiency, the peak shear stress is reduced by more than 60%. Attached Figure Description

[0027] Figure 1 This is a three-dimensional structural schematic diagram of the twin-screw assembly provided in Embodiment 1 of the present invention; Among them, 1-cylinder, 2-screw, 3-slotted screw, 4-center hole; Figure 2This is a schematic diagram of the three-dimensional structure of the screw of the twin-screw assembly provided in Embodiment 1 of the present invention; Figure 3 This is a three-dimensional structural diagram of the slotted twin-screw assembly provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the three-dimensional structure of the screw of the twin-screw assembly provided in Embodiment 4 of the present invention. Detailed Implementation

[0028] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0029] Example 1 This embodiment provides a low-shear, high-efficiency mixing twin-screw assembly, such as... Figure 1 As shown, the twin-screw assembly includes a cylinder 1 and a... Figure 2 The two screws 2 shown are meshing in the same direction. The inner diameter of the cylinder is 36mm and the length is 32mm. The center distance between the two conveying screws is 30mm. The outer diameter of the screw ridge is 35mm, the bottom diameter of the screw groove is 24mm, and the screw length is 32mm. The radial clearance between the two screws is 0.5mm. The screw ridge slotted structure 3 is as shown. Figure 3 As shown, the spiral grooves are uniformly distributed θ along the circumference. a =60°; circumferential spacing angle θ of the double circular arc structure s =9.6°; Radius R from the bottom of the screw groove to the center of the screw rod s =14.62mm; Radius R from the center of the double arc of the screw groove to the center of the screw rod s1 =18.62mm; radius of curvature R of the arc s2 =4.55mm, the depth of the groove on the screw edge is 2.88mm, and the screw rod adopts a modular structure with a central hole 4.

[0030] Example 2 This embodiment provides a low-shear, high-efficiency mixing twin-screw assembly. The twin-screw assembly includes a cylinder and two co-rotating screws. The cylinder has an inner diameter of 36 mm and a length of 32 mm. The center distance between the two conveying screws is 29.75 mm, the outer diameter of the screw ridge is 35.1 mm, the bottom diameter of the screw groove is 23.5 mm, the screw length is 32 mm, and the radial clearance between the two screws is 0.45 mm. The screw ridges of the screws have axial grooves with a depth of 2.78 mm. The shape and distribution of the grooves are the same as in Embodiment 1. The screws adopt a modular structure with a central hole.

[0031] Example 3 This embodiment provides a low-shear, high-efficiency mixing twin-screw assembly. The twin-screw assembly includes a cylinder and two co-rotating screws. The cylinder has an inner diameter of 36 mm and a length of 32 mm. The center distance between the two conveying screws is 30 mm, the outer diameter of the screw ridge is 34.5 mm, the bottom diameter of the screw groove is 24 mm, the screw length is 32 mm, and the radial clearance between the two screws is 0.75 mm. The screw ridges of the screws have axial grooves with a depth of 3.10 mm. The shape and distribution of the grooves are the same as in Embodiment 1. The screws adopt a modular structure with a central hole.

[0032] Example 4 This embodiment provides a low-shear, high-efficiency mixing twin-screw assembly, wherein the twin-screw assembly is arranged in a reverse spiral configuration with slotted screw edges, such as... Figure 4 As shown, except for the helix angle distributed along the spiral line being 1.6°, everything else is the same as in Implementation 1.

[0033] Example 5 This embodiment provides a low-shear, high-efficiency mixing twin-screw assembly, wherein the radius R from the bottom of the screw groove to the center of the screw is... s =13.65mm; radius of curvature R of the arc s2 =5.40mm, the depth of the screw groove is 3.85mm, and the rest are the same as in Example 1.

[0034] Example 6 This embodiment provides a low-shear, high-efficiency mixing twin-screw assembly, wherein the radius R from the bottom of the screw groove to the center of the screw is... s =15.3mm; radius of curvature R of the arc s2 =4.17mm, the depth of the screw groove is 2.20mm, and the rest are the same as in Example 1.

[0035] Comparative Example 1 This comparative example provides a twin-screw assembly, which includes a cylinder and two co-rotating screws. The cylinder has an inner diameter of 36 mm and a length of 32 mm. The center distance between the two screws is 30 mm, the outer diameter of the screw thread is 35.6 mm, the bottom diameter of the screw groove is 24 mm, the screw length is 32 mm, and the radial clearance between the two screws is 0.20 mm.

[0036] Application Example 1 In this application example, a non-Newtonian flow is used as the continuous phase, with a feed mass flow rate of 0.002778 kg / s and a density of 1372 kg / m³. 3 Solid particles were used as the dispersed phase, with an initial dispersed phase content of 50 vol% and a density of 1980 kg / m³. 3The continuous phase and the dispersed phase were mechanically mixed using the twin-screw assembly of Example 1 and Comparative Example 1 at screw speeds of 10 rpm, 20 rpm, and 30 rpm. During the mechanical mixing process, the mass flow rate, shear stress, and mixing effect at the outlet were monitored. The material conveying capacity and solid-liquid mixing efficiency are compared in Table 1, and the maximum shear stress and volume average shear stress are compared in Table 2.

[0037] Application Example 2 In this application example, a non-Newtonian flow is used as the continuous phase, with a feed mass flow rate of 0.002778 kg / s and a density of 1372 kg / m³. 3 Solid particles were used as the dispersed phase, with an initial dispersed phase content of 40 vol% and a density of 1980 kg / m³. 3 The continuous phase and the dispersed phase were mechanically mixed using a twin-screw assembly as described in Example 2 at a screw speed of 10 rpm. During the mechanical mixing process, the mass flow rate, shear stress, and mixing effect at the outlet were monitored. The material conveying capacity and solid-liquid mixing efficiency are compared in Table 3, and the maximum shear stress and volume average shear stress are compared in Table 4.

[0038] Application Example 3 In this application example, a non-Newtonian flow is used as the continuous phase, with a feed mass flow rate of 0.002778 kg / s and a density of 1372 kg / m³. 3 Solid particles were used as the dispersed phase, with an initial dispersed phase content of 65 vol% and a density of 1980 kg / m³. 3 The continuous phase and the dispersed phase were mechanically mixed using a twin-screw assembly as described in Example 3 at a screw speed of 10 rpm. During the mechanical mixing process, the mass flow rate, shear stress, and mixing effect at the outlet were monitored. The material conveying capacity and solid-liquid mixing efficiency are compared in Table 3, and the maximum shear stress and volume average shear stress are compared in Table 4.

[0039] Application Example 4 In this application example, a non-Newtonian flow is used as the continuous phase, with a feed mass flow rate of 0.002778 kg / s and a density of 1372 kg / m³. 3 Solid particles were used as the dispersed phase, with an initial dispersed phase content of 50 vol% and a density of 1980 kg / m³. 3 The continuous phase and the dispersed phase were mechanically mixed using twin-screw assemblies from Examples 4, 5, and 6 at a screw speed of 10 rpm. During the mechanical mixing process, the mass flow rate, shear stress, and mixing effect at the outlet were monitored. The material conveying capacity and solid-liquid mixing efficiency are compared in Table 3, and the maximum shear stress and volume average shear stress are compared in Table 4.

[0040] Test methods The flow rate was monitored at a cross-section (fully developed) 5 mm from the material inlet using numerical simulation to characterize the conveying capacity. Shear stress data was obtained by multiplying the shear rate by the corresponding apparent viscosity of the liquid phase at that shear rate, and the distribution of peak shear stress and volume average shear stress of the entire fluid was statistically analyzed. A specific monitoring area was set up, and the mixing uniformity was statistically analyzed based on the solid volume fraction of different conveying elements to characterize the mixing efficiency.

[0041] Test Results Table 1 Table 2 Table 3 Table 4 The test results show that: (1) As can be seen from Examples 1 to 3, the present invention achieves the technical effects of stable and controllable conveying capacity, high mixing efficiency and reduced shear stress by adjusting the synergistic effect of screw clearance and screw groove. This enables the twin-screw assembly to adapt to the mixing requirements of non-Newtonian fluids with high solid content, and reduces shear stress to make it suitable for heat-sensitive materials while maintaining conveying stability. (2) As can be seen from Examples 1 and 4-6, the present invention can achieve better synergy by further optimizing the depth and distribution of the spiral grooves, so as to improve the mixing efficiency and reduce the shear force. When the reverse spiral grooves are used, the mixing efficiency of the material is further optimized. When the spiral grooves are too deep, the peak shear stress increases. When the spiral grooves are too shallow, the disturbance and mixing of the material are insufficient.

[0042] (3) As can be seen from Example 1 and Comparative Example 1, the present invention can achieve the technical effect of high mixing efficiency under low shear stress by setting a groove structure with specific parameters on the screw edge and cooperating with a reasonable screw radial clearance design. However, when the screw edge groove structure is not adopted and only the radial clearance is reduced, it is impossible to achieve the technical requirements of conveying stability, mixing efficiency and low shear.

[0043] This invention achieves the technical effects of low shear stress, high mixing efficiency, and stable conveying capacity through the synergistic optimization of screw size parameters and screw rib slotting. It adapts to the mixing requirements of materials with different dispersed phase contents and significantly improves the process adaptability of twin-screw assembly in heat-sensitive materials with high solid content.

[0044] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A low-shear, high-efficiency mixing twin-screw assembly, characterized in that, The twin-screw assembly includes a cylinder and two screws meshing in the same direction. The screws have grooves along the axial direction on their threaded edges, and the radial gap between the two screws is 0.45~0.75mm.

2. The twin-screw assembly according to claim 1, characterized in that, The gap between the screw and the cylinder is the same as the radial gap between the two screws.

3. The twin-screw assembly according to claim 1 or 2, characterized in that, The groove includes a double-arc groove, wherein the double arc is formed by combining two arcs with the same radius of curvature; Preferably, the depth of the groove is 0.48 to 0.58 times the height of the screw thread.

4. The twin-screw assembly according to claim 3, characterized in that, The radius of curvature of the arc is 4.55~4.75mm.

5. The twin-screw assembly according to claim 3, characterized in that, The circumferential spacing angle between the two arc centers of the double circular arc groove is 9.2~10.8°.

6. The twin-screw assembly according to any one of claims 1 to 5, characterized in that, The screw thread has 6 to 8 grooves per turn, and the grooves are evenly distributed along the circumference of the screw. Preferably, the groove is arranged in a reverse spiral, and the spiral helix angle of the reverse spiral is 1.2~1.8°.

7. The twin-screw assembly according to any one of claims 1 to 6, characterized in that, The grooves on two adjacent turns of the screw thread are aligned.

8. The twin-screw assembly according to any one of claims 1 to 7, characterized in that, The outer diameter of the screw thread is 34.5~35.1mm, and the bottom diameter of the screw groove is 23.50~24.00mm.

9. An application of the twin-screw assembly according to any one of claims 1 to 8, characterized in that, The applications include using the twin-screw assembly for conveying and mixing heat-sensitive materials with high solids content.

10. The application according to claim 9, characterized in that, The high solids content heat-sensitive material has a solids content of 40-65 vol, and the high solids content heat-sensitive material includes any one of solid propellants, solid battery electrode slurries, or highly filled thermoplastics.

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