A split-flow stretching screw element and screw assembly thereof

Abstract

The present invention discloses a diverter stretching screw element and a screw assembly thereof. The diverter stretching screw element is a hollow cylindrical stretching block as a whole. The core portion is a connecting hole connected to the screw core shaft. The outer surface is provided with a plurality of circumferentially parallel separating ribs. The separating ribs are provided with stretching grooves. The gap between the stretching grooves and the inner wall of the barrel forms a radial stretching channel. In addition, an inclined side surface can be provided at the top of the separating rib. The gap between the top of the separating rib with the inclined side surface and the inner wall of the barrel forms a circumferential stretching channel. When the screw is in operation, under the action of the stretching force field of the radial and axial stretching channels, the material is diverted and stretched to mix, thereby enhancing the mixing, plasticizing, and distributing and dispersing mixing effects. Compared with shear flow, stretching flow mixing has the characteristics of high energy efficiency, no viscosity ratio restrictions, and low temperature rise, resulting in better dispersion and distribution effects. The stretching block of the present invention can be docked with a traditional screw without the need for additional equipment or controls. It is easy to disassemble and assemble and is suitable for a variety of processing equipment.

Description

Technical Field

[0001] The invention relates to a polymer plasticizing and mixing device, in particular to a split-flow stretching screw element and a screw assembly thereof. Background Art

[0002] During the screw processing and plasticizing process, its ability to transport and distribute the material can be controlled by properly selecting the type and geometry of the screw elements. Most of the dispersive mixing action occurs in the kneading block dominated by the shear flow.

[0003] With the development of polymer materials science, traditional shear-based screw elements can no longer meet processing requirements. For some thermally unstable resins, such as PVC and PPC, excessive shear will generate a large amount of viscous heat dissipation, which may cause thermal degradation of the matrix. In addition, pure shear is not conducive to processing blends with relatively high viscosity. Therefore, how to ensure the reduction of shear heat while increasing the mixing effect has become an important issue in screw processing.

[0004] In recent years, in order to introduce tensile force fields or generate chaotic force fields in polymer plasticizing processing equipment, new processing equipment has emerged, such as differential screw extrusion technology - generating a chaotic force field through the speed difference between the two screws, hollow screw - introducing a tensile force field by using a convergent-divergent flow channel in the hollow part of the screw, and eccentric rotor extruder - achieving volume stretching through periodic changes in the cavity volume of the rotor and stator to generate a tensile dominant flow field. However, these devices often involve the modification of the entire screw or extruder equipment, have complex structures, are difficult to prepare, and are expensive. They are currently mainly used in laboratories, and it is difficult to achieve mass production of the equipment. Summary of the Invention

[0005] In order to solve the problems of poor mixing effect, temperature rise, and complex structure in the prior art, the present invention provides a split-flow stretching screw element, and the technical solution is as follows:

[0006] A split-flow stretching screw element is a hollow cylindrical stretching block as a whole. Its core is a connecting hole for connecting to the screw core shaft. Its outer surface is provided with a plurality of dividing ridges parallel to the circumference, and the dividing ridges are of consistent height along the radial direction of the stretching block; between each dividing ridge is a stretching groove, and the gap between the stretching groove and the inner wall of the barrel forms a stretching flow channel along the radial direction of the screw. The radial stretching flow channel is a semi-convergent-divergent stretching flow channel that is narrow in the middle and wide at both ends along the axial direction of the screw.

[0007] During the rotation of the screw, the material flows through the stretching block and is divided into several streams by the dividing edges, which disrupts the material flow and accelerates the homogenization of the material; the radial stretching flow channel formed by the stretching groove and the inner wall of the barrel produces a strong stretching force field, and the material flows are dispersed and merged to achieve excellent distribution, dispersion and mixing effects.

[0008] Furthermore, an inclined side surface can be provided at the top of the dividing edge. In this case, the gap between the top of the dividing edge with the inclined side surface and the inner wall of the barrel forms a circumferential stretching channel, so that the material is stretched and mixed not only in the original radial direction, but also in the circumferential direction. The material is subjected to strong stretching force fields in both radial and circumferential directions before being reunited. This repeated diversion, stretching, and converging of the material enhances the distribution, dispersion, mixing, and plasticization effects during the processing.

[0009] Furthermore, the semi-convergent-divergent stretching channel includes a middle convergent section L C , the first divergent section L1 and the second divergent section L2 at both ends, and the outer contour line of the semi-convergent-divergent stretching flow channel is a straight line, wherein the inlet angle of the first divergent section L1 is Φ1, and the inlet angle of the second divergent section L2 is Φ2. C The corresponding channel depth value is Wc, and the maximum channel depth value of the first divergent section L1 and the second divergent section L2 is Wu, and Wu is required to be greater than Wc; let a be the convergence ratio, then a=Wu / Wc>1; the larger a is, the greater the extrusion and stretching effect on the material when passing through the convergent-divergent channel. Usually, the extrusion and stretching effect is more obvious when the convergence ratio is greater than 2. The convergence ratio a and the inlet angles Φ1 and Φ2 are optimized according to the screw specifications and material properties to achieve the best effect, among which Φ1 and Φ2 can be optimized between 0°-90°.

[0010] Preferably, the first diverging section L1 and the second diverging section L2 are symmetrically distributed on both sides of the convergent section Lc. In this case, the first diverging section L1 and the second diverging section L2 are equal in length, and Φ1=Φ2.

[0011] Optionally, the cross section of the semi-convergent-divergent stretching channel along the axial direction of the screw has an outer shape curve on the side close to the stretching groove that is a semi-hyperbola.

[0012] Furthermore, the semi-hyperbola is given by the equation x = ((zL / 2) 2 -Vc) / k stipulates: where L is the length of the stretching block, Vc is the width of the stretching channel at the narrowest point along the axial section of the screw, z is the axial coordinate of a point on the inner wall of the barrel, x is the width of the stretching channel along the axial section of the screw corresponding to point z, and k is a constant; the length L of the stretching block varies according to the screw specifications and the number of grooves.

[0013] One advantage of using a hyperbolic converging flow channel is that it produces a constant strain rate along the centerline of the hyperbola, or the axis of the half-channel, close to the inner wall of the barrel. According to theoretical design, the above parameters are variable. Depending on the actual processing requirements, different parameter combinations can be optimized to achieve the best results.

[0014] Furthermore, the number of separating edges is not less than 4, and the edge thickness is 1 to 5 mm. The specific values ​​can be optimized in accordance with the specifications of the screw and the properties of the processed polymer material.

[0015] Furthermore, the length of the dividing ribs on the stretching block can be varied based on specific requirements and processing conditions. The portion of the stretching block with the dividing ribs is called the stretching section, while the portion without the dividing ribs is a hollow cylinder and is called the non-stretching section. The stretching block comprises both the stretching section and the non-stretching section. This configuration is primarily used in twin-screw or multi-screw extruders. Preferably, the length of the stretching section is equal to the length of the non-stretching section.

[0016] In twin-screw processing, the stretching section and non-stretching section of the stretching blocks installed on the left and right screws are staggered to ensure a certain meshing distance and the screw movement will not interfere; in multi-screw processing, the stretching section and non-stretching section of the stretching blocks installed on multiple screws are staggered to ensure a certain meshing distance and the screw movement will not interfere.

[0017] Another object of the present invention is to provide a screw assembly including the split-flow stretching screw element of the present invention, comprising a screw conveying section and a plurality of stretching blocks, wherein the plurality of stretching blocks are continuously mounted on the screw core shaft; preferably, the number of stretching blocks is three. With multiple stretching blocks continuously mounted on the screw core shaft, the material is repeatedly split, stretched, and merged, further enhancing the mixing, plasticizing, and distributing, dispersing, and mixing effects.

[0018] Another object of the present invention is to provide another screw assembly comprising the split-flow stretching screw element of the present invention, comprising a reverse conveying element, a plurality of stretching blocks, a conveying element, a plurality of kneading blocks with a staggered angle of 90°, and a plurality of kneading blocks with a staggered angle of 60°, which are sequentially installed on the screw shaft core; wherein the stretching block includes a stretching section and a non-stretching section, and the reverse conveying element is located at the outlet of the screw mixing section.

[0019] It should be noted that the split-flow stretching screw element of the present invention can be docked with a traditional screw without interrupting its normal function or adding additional equipment systems or controls. Therefore, it is suitable for extrusion or injection molding equipment that uses a screw, including: single-screw extruders, twin-screw extruders, multi-screw extruders, and injection molding machines.

[0020] The present invention mainly has the following outstanding beneficial effects:

[0021] 1. This patent sets a separating edge and a stretching groove on the stretching block, and the gap between the stretching groove and the inner wall of the barrel forms a stretching flow channel along the radial direction of the screw; at the same time, an inclined side surface can be set at the top of the separating edge, and the gap between the top of the separating edge with the inclined surface and the inner wall of the barrel forms a stretching flow channel along the circumferential direction of the screw; when the screw is working, the material is diverted, stretched and mixed through the action of the stretching flow channels along the circumference and radial direction of the screw, thereby enhancing the mixing, plasticizing, distribution and dispersion mixing effects during the polymer plasticizing process.

[0022] 2. Compared with shear flow, extensional flow mixing has the following advantages: higher energy efficiency than shear flow; not limited by viscosity ratio; the temperature increase of extensional flow is only 1-3°C; and it produces better dispersion and distribution mixing.

[0023] 3. The stretching block used in the present invention can be used in a traditional screw system, and no additional equipment system or controls are required to achieve polymer extrusion processing or injection molding processing. It is easy to assemble and disassemble and is applicable to a variety of processing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the three-dimensional structure of Example 1 of a split-flow stretching screw element of the present invention.

[0025] Figure 2 This is a cross-sectional view of Example 1 of a split-flow stretching screw element of the present invention in a working state.

[0026] Figure 3 for Figure 2 Cross-section along the AA direction.

[0027] Figure 4 This is a schematic diagram of the three-dimensional structure of Example 2 of a split-flow stretching screw element of the present invention.

[0028] Figure 5 This is a cross-sectional view of Example 2 of a split-flow stretching screw element of the present invention in operation. (The enlarged portion in the lower right corner shows the circumferential stretching channel 8)

[0029] Figure 6 Schematic diagram of an embodiment of the semi-convergent-divergent stretching flow channel of the present invention.

[0030] Figure 7 Schematic diagram of another embodiment of the semi-convergent-divergent stretching flow channel of the present invention.

[0031] Figure 8 A three-dimensional structural diagram of a twin-screw rod using Example 3 of a split-flow stretching screw element of the present invention.

[0032] Figure 9 This is a schematic structural diagram of an implementable screw assembly 1 of a split-flow stretching screw element of the present invention.

[0033] Figure 10 This is a schematic structural diagram of an implementable screw assembly 2 of a split-flow stretching screw element of the present invention.

[0034] In the picture:

[0035] 1 is a stretching block, 2 is a connecting hole, 3 is a separating edge, 4 is a stretching groove, 5 is a radial stretching channel, 6 is a screw core shaft, 7 is a barrel, 8 is a circumferential stretching channel, 9 is an oblique side surface, 10 is a screw, 11 is a stretching section, 12 is a non-stretching section, 61 is a reverse conveying element, 62 is a conveying element, 63 is a kneading block with a staggered angle of 90°, and 64 is a kneading block with a staggered angle of 60°. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Figure 1-3 Example 1 of a split-flow stretching screw element of the present invention is shown, wherein Figure 1 Schematic diagram of the three-dimensional structure of Example 1. This embodiment is a hollow cylindrical stretching block 1. The outer surface of the stretching block 1 is provided with a plurality of parallel dividing edges 3 along the circumferential direction. The core of the stretching block 1 is a connecting hole 2 for connecting to the screw core shaft 6. Figure 2 The diagram shows this embodiment in use. The stretching block 1 is installed through the connecting hole 2 into the screw core shaft 6, which is then installed into the barrel 7. The separating ribs 3 have a uniform height along the radial direction of the stretching block. Stretching grooves 4 are located between the separating ribs 3. The gaps between the stretching grooves 4 and the inner wall of the barrel 7 form stretching channels 5 along the radial direction of the screw. These radial stretching channels 5 are semi-convergent and divergent stretching channels, narrow in the middle and wide at both ends, along the screw axis.

[0038] Figure 4-5 Example 2 of a split-flow stretching screw element of the present invention is shown, wherein Figure 4 is a schematic diagram of the three-dimensional structure, Figure 5 The diagram of the embodiment in use shows a diagram of a state in which an inclined side surface 9 is provided at the top of the separating edge 3. In the diagram, the stretching block 1 is installed into the screw core shaft 6 through the connecting hole 2 and then into the barrel 7. At this time, the gap between the top of the separating edge 3 with the inclined side surface 9 and the inner wall of the barrel forms a circumferential stretching channel 8. ( Figure 5 The lower right corner shows the enlarged separation edge 3 and the circumferential stretching channel 8), so that the material is not only stretched and mixed in the original radial direction, but also stretched and mixed in the circumferential direction. The material is repeatedly divided, stretched and merged, which enhances the distribution, dispersion, mixing and plasticization effect during the processing.

[0039] The semi-convergent-divergent stretching channel can have various forms, and two embodiments are provided here.

[0040] Figure 6 This is a cross-sectional view of an embodiment of a semi-convergent-divergent stretching channel of a split-flow stretching screw element of the present invention along the screw axial direction. The semi-convergent-divergent stretching channel includes a middle convergent section L C , the first divergent section L1 and the second divergent section L2 at both ends; in this embodiment, the outer contour line of the semi-convergent-divergent stretching flow channel is a straight line, wherein the inlet angle of the first divergent section L1 is Φ1, and the inlet angle of the second divergent section L2 is Φ2. C The corresponding channel depth value is Wc, and the maximum channel depth value of the first divergent section L1 and the second divergent section L2 is Wu, and Wu is required to be greater than Wc; let a be the convergence ratio, then a=Wu / Wc>1; the larger a is, the greater the extrusion and stretching effect on the material when passing through the convergent-divergent channel. Usually, the extrusion and stretching effect is more obvious when the convergence ratio is greater than 2. The convergence ratio a and the inlet angles Φ1 and Φ2 are optimized according to the screw specifications and material properties to achieve the best effect, among which Φ1 and Φ2 can be optimized between 0°-90°.

[0041] Preferably, the first diverging section L1 and the second diverging section L2 are symmetrically distributed on both sides of the convergent section Lc. In this case, the first diverging section L1 and the second diverging section L2 are equal in length, and Φ1=Φ2.

[0042] Furthermore, when the above semi-convergent-divergent stretching flow channel is selected, the outer contour line of the flow channel is a straight line, and fillets can be set at each inflection point formed therein to reduce the resistance of the material flow and prevent the material flow from staying there for too long and overheating and burning.

[0043] Figure 7 This is an axial cross-sectional view of another embodiment of a semi-convergent-divergent stretching channel of a split stretching screw element of the present invention. The outer shape curve of the cross-section along the axial direction of the screw near the stretching groove 4 is a semi-hyperbola. Further, the semi-hyperbola is given by the equation x = ((zL / 2) 2 -Vc) / k stipulates: where L is the length of the stretching block 1, Vc is the width of the stretching channel at the narrowest point along the axial cross-section of the screw, z is the axial coordinate of a point on the inner wall of the barrel 7, x is the width of the stretching channel along the axial cross-section of the screw corresponding to point z, and k is a constant; the length L of the stretching block varies according to the screw specifications and the number of grooves.

[0044] One advantage of using this hyperbolic converging channel is that it produces a constant strain rate along the centerline of the hyperbola, or the axis of the half-channel, close to the inner wall of the barrel. According to theoretical design, the above parameters are variable, and depending on actual processing requirements, different parameter combinations can be optimized to achieve the best results.

[0045] Typically, the length of the stretching block is determined by the screw specifications and the number of grooves. The number of separating ribs 3 is no less than 4, and the rib thickness is 1 to 5 mm. These parameters are variable and can be optimized based on the specific screw specifications and processing requirements.

[0046] Figure 8 The three-dimensional structural diagram of Example 3 of a diversion stretching screw element of the present invention is shown. In this embodiment, the stretching block 1 includes a stretching section 11 and a non-stretching section 12, wherein the stretching section 11 is provided with a separating rib 3 and a stretching groove 4, and the non-stretching section 12 is a hollow cylinder without a separating rib 3 and a stretching groove 4. The lengths of the stretching section 11 and the non-stretching section 12 can be equal. Usually, this embodiment is used in a twin-screw extruder. In order to ensure the circumferential meshing gap between the left and right screws, when the screw is working, the stretching section 11 and the non-stretching section 12 of the left and right screws are staggered, while ensuring a certain axial meshing distance so that the screw movement will not interfere. Similarly, the stretching block of Example 3 can also be used in a multi-screw extruder.

[0047] The stretching block 1 of the present invention can be adapted to different screw combinations by installing different screws and screw elements, and two combinations are provided here.

[0048] Figure 9 A screw assembly 1 comprising a diverter stretching screw element of the present invention is shown, comprising a screw conveying section 10 and a stretching block 1 of Example 2, wherein the top of the stretching block 1 has an oblique side surface, wherein there are three stretching blocks 1, which are continuously mounted on the screw core shaft 6, and when the material flows through the stretching block 1, it is divided into multiple streams by the dividing edge 3, and the pressure from the extruder conveying forward forces the material to pass through the semi-convergent-divergent flow channel formed by the stretching groove 4 and the inner wall of the barrel as a radial stretching flow channel, while undergoing a circumferential stretching flow channel formed by the top of the dividing edge 3 with the oblique side surface and the inner wall of the barrel 7 during the screw rotation process, and is subjected to a strong stretching force field in the radial and circumferential directions, and then merges again. The material undergoes repeated diversion, stretching and converging effects to enhance the distribution, dispersion, mixing and plasticizing effects of the processing process. Of course, the stretching block 1 in this embodiment combination can also be selected as a stretching block such as Example 1. In addition, the number of stretching blocks 1 is not limited to three, and 2-4, for example, is also optional.

[0049] Figure 10 Another screw assembly 2 comprising the split-flow stretching screw element of the present invention is shown, comprising a reverse conveying element 61, several stretching blocks 1, a conveying element 62, several kneading blocks 63 with a staggered angle of 90°, and several kneading blocks 64 with a staggered angle of 60°, which are sequentially installed on the screw shaft core; wherein the stretching block 1 includes a stretching section 11 and a non-stretching section 12, and the reverse conveying element 61 is located at the outlet of the screw mixing section.

[0050] The material enters the extruder barrel through the hopper and is conveyed forward by the rotating screw. At this point, the material remains in a solid state. Although the plastic in contact with the inner wall of barrel 7 nears or reaches its viscosity temperature due to intense frictional heat near the end, causing the surface of the solid particles to become sticky, melting has not yet begun. Through repeated shear mixing by kneading blocks 64 (staggered at 60°) and kneading blocks 63 (staggered at 90°), the material undergoes significant frictional shear and barrel heat transfer, fully melting and plasticizing. The solid particles are essentially melted, and the material is now in a fluid state. It is conveyed into the mixing section by conveying element 62. The fluid undergoes repeated diversion, stretching, and converging action by the diverting and stretching screw elements, further refining and uniforming the sizes of the components, enhancing the mixing, plasticizing, and distributing and dispersing mixing effects. The reverse conveying element 61 located at the outlet of the mixing section generates back pressure, ensuring sufficient pressure to fill the stretching channel, increasing the particle residence time and distribution time in the diverting and stretching screw elements, and strengthening the stretching and mixing effect.

[0051] Similarly, in the embodiment of the present screw assembly, the number of stretching blocks and the number and type of the two kneading blocks can be optimized according to the specific requirements of the screw processing.

[0052] The embodiments listed above are merely preferred implementation methods for the convenience of explaining and illustrating the technical solutions and working principles of the present invention. In fact, there are many forms and combinations of implementation methods of the present invention, which are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A split-flow stretching screw element, which is a hollow cylindrical stretching block (1) as a whole; characterized in that: The core of the stretching block (1) is a connecting hole (2) connected to the screw core shaft (6); the outer surface of the stretching block (1) is provided with a plurality of dividing ridges (3) in parallel along the circumferential direction; the dividing ridges (3) are at the same height along the radial direction of the stretching block (1); between the dividing ridges are stretching grooves (4); the gap between the stretching grooves (4) and the inner wall surface of the barrel (7) forms a radial stretching flow channel (5); the radial stretching flow channel is a semi-convergent-divergent stretching flow channel that is narrow in the middle and wide at both ends; The top end of the separating edge (3) is provided with an oblique side surface (9); The semi-convergent-divergent stretching channel includes a middle convergent section L C , the first divergent section L1 and the second divergent section L2 at both ends, and the outer contour line of the semi-convergent-divergent stretching flow channel is a straight line; let the convergent section L C The channel depth is Wc, and the maximum channel depth of the first divergent section L1 and the second divergent section L2 is Wu, which is required to be greater than Wc. Let a be the convergence ratio, then a=Wu / Wc, a>2; The inlet angle of the first divergent section L1 is Φ1, and the inlet angle of the second divergent section L2 is Φ2. The convergence ratio a and the inlet angles Φ1 and Φ2 are optimized according to the screw specifications and material properties. Φ1 and Φ2 can be optimized between 0° and 90°.

2. A split-flow stretching screw element according to claim 1, characterized in that: The first diverging section L1 and the second diverging section L2 of the semi-converging-diverging stretching flow channel are equal in length.

3. A split-flow stretching screw element according to claim 1, characterized in that: The cross section of the semi-convergent-divergent stretching channel along the axial direction of the screw has an outer shape curve close to the stretching groove (4) on the side thereof that is a semi-hyperbola.

4. A split-flow stretching screw element according to claim 3, characterized in that: The semi-hyperbola is given by the equation x=((zL / 2) 2 -Vc) / k is specified as follows: where L is the length of the stretching block (1), Vc is the width of the stretching channel at the narrowest point along the axial section of the screw, z is the axial coordinate of a point on the inner wall of the barrel (7), x is the width of the stretching channel corresponding to point z along the axial section of the screw, and k is a constant.

5. The split-flow stretching screw element according to claim 1, characterized in that: The number of the separating edges (3) is not less than 4, and the thickness of the edges is 1 to 5 mm.

6. A split-flow stretching screw element according to claim 1, characterized in that: The stretching block (1) comprises a stretching section (11) and a non-stretching section (12); wherein the stretching section (11) is provided with a separating edge (3) and a stretching groove (4), and the non-stretching section (12) is a hollow cylinder.

7. A screw assembly comprising the split-flow stretching screw element according to any one of claims 1 to 6, characterized in that: It comprises a screw conveying section (10) and no less than two stretching blocks (1), wherein the stretching blocks (1) are continuously mounted on the screw core shaft (6) of the screw conveying section (10).

8. A screw assembly comprising the split-flow stretching screw element according to claim 6, characterized in that: The invention comprises a reverse conveying element (61) sequentially mounted on the screw shaft core, a plurality of stretching blocks (1), a conveying element (62), a plurality of kneading blocks (63) with a staggered angle of 90 degrees, and a plurality of kneading blocks (64) with a staggered angle of 60 degrees.

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