A screw for an extruder

Abstract

This invention relates to the field of material forming equipment technology, addressing the shortcomings of existing extruder screws, which suffer from unreasonable structural design, inability to plasticize and extrude different raw materials, and poor mixing effects. The proposed solution is as follows: the screw is divided into a feeding section, a melting section, a mixing section, a venting section, and a homogenizing section from back to front. The screw length is L, and the nominal diameter is D. The feeding section length is 0.31L to 0.36L, the melting section length is 0.26L to 0.30L, the mixing section length is 0.074L to 0.10L, the venting section length is 0.12L to 0.15L, and the homogenizing section length is 0.15L to 0.18L. The mixing section includes at least two mixing elements, each of which has at least four mixing screw threads that rotate within 180° from back to front along the screw axis. The lead of the mixing screw threads gradually increases from back to front. This invention optimizes the structure of each segment, ensuring the plasticizing and extrusion efficiency of different materials while optimizing the structure of the mixing element to promote the mixing of molten materials and ensure the mixing and plasticizing effect of different types of materials.

Description

Technical Field

[0001] This invention relates to the field of molding equipment for plastic polymer materials, and more specifically to a screw for an extruder. Background Technology

[0002] Plastic polymer materials are widely used in various fields of production and daily life. Their molding and processing methods mainly include injection molding, extrusion molding, compression molding, blow molding, calendering, and foam molding. Among these, extrusion molding is highly efficient and continuous, suitable for large-scale continuous production and manufacturing, and helps reduce the molding cost of plastic polymer materials, thus its application is particularly widespread. The screw extruder is a key plasticizing equipment used in the extrusion molding process. It has a simple structure, stable operation, and good plasticizing effect, and is suitable for the extrusion molding of various plastic polymer materials such as PP, PA, PE, and PVC.

[0003] To improve the efficiency of extrusion plasticizing, optimizing and improving the extruder screw structure and its matching barrel structure is essential. Currently, most extruder barrels employ a groove structure with the grooves running in the opposite direction to the screw thread, utilizing the shearing effect of the coupled double grooves to improve material plasticizing efficiency. Extruder screws are generally divided into feeding, melting, mixing, venting, and homogenizing sections along their axial direction from back to front. Depending on the type of raw material being processed, the ratio of the length of each section to the total screw length, as well as the pitch and depth of the screw threads in each section, generally vary. This necessitates changing different screws when plasticizing and extruding different raw materials, affecting production continuity. Furthermore, the mixing element structure in the mixing section of existing extruder screws is relatively complex, for example, simultaneously possessing forward or reverse kneading blocks, or combining kneading blocks and large-lead threaded elements. This results in a large ratio of the mixing section length to the total screw length, affecting the optimized design of other sections. Consequently, the efficiency and effect of extrusion plasticizing different plastic polymers vary significantly, and the mixing effect is often poor. Summary of the Invention

[0004] In summary, the purpose of this invention is to solve the technical problems of existing extruder screws having unreasonable structural designs, being unsuitable for plasticizing and extruding different types of plastic polymer raw materials, and having complex mixing section structures, large length ratios, and significant differences in mixing effects for different materials, resulting in poor performance. The invention provides an improved extruder screw that is suitable for plasticizing and extruding a variety of plastic polymer materials, and has a simple mixing section structure, small length ratio, and excellent mixing effect.

[0005] To address the shortcomings of the technology proposed in this invention, the technical solution adopted is as follows: an extruder screw, coaxially rotatable within the barrel of a screw extruder, the screw being sequentially divided into a feeding section, a melting section, a mixing section, a venting section, and a homogenizing section from the rear feed end to the front extrusion end; the ratio of the screw length L to the nominal diameter D of the screw is 16-20; characterized in that: the length of the feeding section is 0.31L-0.36L, the length of the melting section is 0.26L-0.30L, the length of the mixing section is 0.074L-0.10L, the length of the venting section is 0.12L-0.15L, and the length of the homogenizing section is 0.15L-0.18L; the mixing section includes at least two identical mixing elements spaced apart front to back, each mixing element having at least four mixing screw ridges that rotate within 180° from back to front along the screw axis, the lead of the mixing screw ridges gradually increasing from back to front.

[0006] Furthermore, the groove depth of each mixing screw of the mixing element is consistent, ranging from 0.10D to 0.14D.

[0007] Furthermore, the feeding section is provided with single spiral feeding screws of unequal width and depth. The pitch of the feeding screws gradually decreases from back to front along the screw axis, and the depth of the screw grooves gradually increases from back to front along the screw axis.

[0008] Furthermore, the melting section is provided with single spiral melting screw ribs of equal width but unequal depth. The screw groove depth of the melting screw ribs gradually decreases from back to front along the screw axis, and the screw groove depth of the last melting screw rib is the same as the screw groove depth of the first feed screw rib adjacent to it. The helix angle of the melting screw ribs and the feed screw ribs is the same.

[0009] Furthermore, the groove depth of the last feed screw is 0.12D to 0.13D, the groove depth of the first feed screw and the adjacent last molten screw are both 0.13D to 0.14D, and the groove depth of the first molten screw is 0.06D to 0.10D.

[0010] Furthermore, the compression ratio of the molten section is 1.6 to 2.

[0011] Furthermore, the exhaust section is provided with single spiral exhaust screw ridges of equal width and depth, and the screw groove depth of the exhaust screw ridge is 0.15D to 0.18D.

[0012] Furthermore, the pitch of the exhaust screw thread in the exhaust section is half the length of the mixing element.

[0013] Furthermore, the homogenization section is provided with single-helix homogenization spiral ridges of equal width and depth, and the spiral groove depth of the homogenization spiral ridges is 0.05D to 0.07D.

[0014] Compared with existing technologies, the beneficial effects of this invention are as follows: The functional segment structure of the screw has been optimized and improved. Specifically, the lengths of the feeding section, melting section, mixing section, venting section, and homogenizing section account for 31%–37%, 26%–30%, 7.5%–10%, 12%–15%, and 15%–18% of the total screw length, respectively. This design, while ensuring the plasticizing extrusion efficiency of different plastic polymer materials, minimizes the length of the mixing section, providing length space for the optimized design of other functional segments, and is applicable to the plasticizing extrusion of various materials. Furthermore, the screw structure design of this invention improves the plasticizing extrusion efficiency of different materials while optimizing the structure of the mixing element. The mixing screw threads on the mixing element promote the mixing of molten materials, and the gradually increasing lead of the mixing screw threads increases the shearing action of the material, promoting further plasticization. Simultaneously, it reduces the generation of coke and bubbles, reduces raw material waste and the difficulty of venting the exhaust section, and ensures the effective mixing and plasticizing of different types of materials. In addition, the screw for the extruder of this invention has a simple structure, reliable operation, strong applicability, and good plasticizing effect, making it suitable for widespread application in large-scale molding and processing enterprises of plastic polymer materials. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the screw of the present invention; Figure 2 This is an enlarged schematic diagram of a portion of the feed section of the screw of the present invention; Figure 3 This is an enlarged schematic diagram of a portion of the molten section of the screw of the present invention; Figure 4 This is an enlarged schematic diagram of a portion of the mixing section of the screw of the present invention; Figure 5 This is an enlarged schematic diagram of a portion of the exhaust section of the screw of the present invention; Figure 6 This is an enlarged schematic diagram of a portion of the homogenization section of the screw of the present invention.

[0016] In the diagram: 1. Feeding section, 11. Feeding screw, 2. Melting section, 21. Melting screw, 3. Mixing section, 31. Mixing element, 311. Mixing screw, 4. Exhausting section, 41. Exhausting screw, 5. Homogenizing section, 51. Homogenizing screw. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below through specific embodiments. The specific implementation methods used in the following embodiments are only some preferred implementation methods of the technical solution of the present invention and are not intended to limit the present invention.

[0018] Reference Figure 1 and Figure 4 As shown, the present invention discloses an extruder screw, which is coaxially rotatably disposed in the barrel of a screw extruder. The screw is sequentially divided into a feeding section 1, a melting section 2, a mixing section 3, a venting section 4, and a homogenizing section 5 from the rear feed end to the front extrusion end. The ratio of the screw length L to the nominal diameter D of the screw is 20, and the screw helix angle is preferably 17°40′.

[0019] Specifically, the length of the feed section 1 of the screw is L1=0.35L, the length of the melting section 2 is L2=0.3L, the length of the mixing section 3 is L3=0.08L, the length of the venting section 4 is L4=0.12L, and the length of the homogenization section 5 is L5=0.15L. The mixing section 3 includes two mixing elements 31 with identical structures arranged at intervals. Each mixing element 31 is provided with six mixing screw ridges 311 that rotate within 180° from back to front along the screw axis. The lead of the screw ridges 311 gradually increases from back to front.

[0020] The lengths of each functional segment of the screw have been optimized and improved to adapt to the extrusion molding of different types of raw materials. At the same time, the structure of the mixing element 31 has been optimized and improved. The adjacent mixing screw edges 311 form a flow channel for the flow and mixing of liquid phase materials. The liquid phase material flowing out from the outlet port (large lead) of the flow channel of the latter mixing element 31 passes through the gap between the two mixing elements 31 and is partially diverted at the inlet port (small lead) of the flow channel of the former mixing element 31, thus completing the flow channel conversion of liquid phase materials between the two mixing elements 31.

[0021] Furthermore, refer to Figure 4 As shown, the screw groove depth of each mixing screw ridge 311 of the two mixing elements 31 of the screw of the present invention is the same, which is 0.10D.

[0022] Furthermore, refer to Figures 2 to 3As shown, the feed section 1 of the screw of the present invention is provided with single spiral feed screw ridges 11 of unequal width and depth. The pitch of the feed screw ridges 11 gradually decreases from back to front along the screw axis, and the groove depth of the feed screw ridges 11 gradually increases from back to front along the screw axis. At the same time, the melting section 2 of the screw is provided with single spiral melting screw ridges 21 of equal width but unequal depth. The groove depth of the melting screw ridges 21 gradually decreases from back to front along the screw axis, and the groove depth of the last melting screw ridge 21 is the same as the groove depth of the first feed screw ridge 11 adjacent to it. The helix angle of the melting screw ridges 21 and the feed screw ridges 11 is the same.

[0023] Specifically, the groove depth of the last feed screw 11 is 0.12D, the groove depth of the first feed screw 11 and the adjacent last molten screw 21 is 0.14D, and the groove depth of the first molten screw 21 is 0.06D.

[0024] Preferably, the compression ratio of the melting section 2 of the screw is 1.8.

[0025] Furthermore, refer to Figure 5 As shown, the exhaust section 4 of the screw of the present invention is provided with a single spiral exhaust screw 41 of equal width and depth. The screw groove depth of the exhaust screw 41 is 0.16D, and the screw pitch of the exhaust screw 41 is half the length of the mixing element 31.

[0026] Furthermore, refer to Figure 6 As shown, the homogenization section 5 of the screw of the present invention is provided with a single helical homogenization screw ridge 51 of equal width and depth, and the screw groove depth of the homogenization screw ridge 51 is 0.06D.

[0027] During operation, the extruder drives the screw to rotate forward. The plastic polymer granules or powder continuously fed into the extruder through the feed screw ribs 11 of the feeding section 1 are conveyed forward to the melting section 2. Simultaneously, the progressively increasing groove depth of the feed screw ribs 11 improves material conveying efficiency, reduces friction between the material and the screw and barrel, promotes material mixing, increases the extrusion volume, and prevents premature plasticization. Furthermore, compared to the existing screw feed section 1's constant pitch and groove depth design, the feed screw ribs 11 of this invention have a gradually decreasing pitch from back to front, which can increase the pressure of continuous material feeding into the melting section 2, improve melting efficiency, and reduce bubble generation during the melting process.

[0028] After the material moves to the melting section 2, the gradually decreasing depth of the melting screw 21 continuously applies a certain amount of extrusion pressure to the material, increasing the friction and shearing action between the material and the screw and barrel, resulting in the formation of a molten film and a molten pool. In addition, a heating device on the outer wall of the barrel provides extra heat, prompting the material to gradually transform from a solid phase to a liquid phase, achieving the melting of the material, and the molten pool continuously grows.

[0029] After the molten material moves to the mixing section 3, it undergoes continuous flow channel switching sequentially within the flow channels formed by the mixing screw ridges 311 of the two mixing elements 31. The molten material first enters the mixing flow channel through the feed port formed by the rear of the next mixing screw ridge 311, and is discharged through the discharge port formed by its front. Then, it enters the mixing flow channel through the gap between the two mixing elements 31, through the feed port formed by the rear of the previous mixing screw ridge 311, and is sent to the exhaust section 4 through the discharge port formed by its front. This flow channel switching of the molten material promotes mixing and further plasticization, significantly improving the mixing effect of the molten material. It further refines and homogenizes the components in the material, improving the dispersion and uniformity of the material components, ensuring the homogeneity of the product after molding, and achieving a better mixing effect. Furthermore, the structural design of the mixing section 3 of this invention is relatively simple, and the length of this section accounts for a small proportion of the total screw length, which facilitates the optimized design of other sections. This allows the screw of this invention to be applicable to the extrusion molding of various plasticizable polymer materials.

[0030] After the molten liquid material moves to the exhaust section 4, the gaseous components, moisture and volatile impurities in the material are discharged through the exhaust screw 41, which reduces the impurity content of the material, further improves the homogeneity of the product after molding, and ensures the quality of the molded product.

[0031] After the liquid material is discharged from the exhaust section 4, the gas phase components, moisture and volatile impurities are discharged. Then it is pushed by the screw to the homogenization section 5 (metering and verification). Under the action of the homogenization screw ribs 51 of equal width and depth in the homogenization section 5, it is extruded from the front end of the screw and barrel at a constant pressure and temperature, so that it enters the molding container in a stable state for molding.

[0032] By adopting the above technical solution, the present invention has the following beneficial effects: First, this invention optimizes and improves the functional segment structure of the screw. The lengths of the feeding section 1, melting section 2, mixing section 3, venting section 4, and homogenizing section 5 account for 31%–37%, 26%–30%, 7.5%–10%, 12%–15%, and 15%–18% of the total screw length, respectively. This design ensures the plasticizing and extrusion efficiency of polymers with different plasticity while minimizing the length of the mixing section 3, providing length space for the optimized design of other functional segments, and is applicable to the plasticizing and extrusion of various materials.

[0033] In addition, the screw structure design of this invention improves the plasticizing and extrusion efficiency of different materials while optimizing the structure of the mixing element, promoting the mixing of molten materials, and ensuring the mixing and plasticizing effect of different types of materials.

[0034] The above embodiments are merely for illustrating the technical solutions of the present invention and are not intended to limit the implementation of the present invention. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention.

Claims

1. A screw for an extruder, which is coaxially rotatably arranged in a barrel of a screw extruder, and which is sequentially divided into a feeding section, a melting section, a mixing section, a degassing section and a homogenizing section from a rear feeding end to a front extruding end, the ratio of the length L of the screw to the nominal diameter D of the screw being 16-20; characterized in that: The length of the feeding section is 0.31L to 0.36L, the length of the melting section is 0.26L to 0.30L, the length of the mixing section is 0.074L to 0.10L, the length of the venting section is 0.12L to 0.15L, and the length of the homogenization section is 0.15L to 0.18L. The mixing section includes at least two mixing elements with identical structures arranged at intervals. Each mixing element is provided with at least four mixing screw threads that rotate within 180° from back to front along the screw axis. The screw thread lead between the mixing screw threads gradually increases from back to front. ​ The groove depth of each mixing screw of the mixing element is consistent, ranging from 0.10D to 0.14D. The feeding section is provided with single spiral feeding screws of unequal width and depth. The pitch of the feeding screws gradually decreases from back to front along the screw axis, and the depth of the screw grooves gradually increases from back to front along the screw axis. The melting section is provided with single spiral melting screw ribs of equal width but unequal depth. The screw groove depth of the melting screw ribs gradually decreases from back to front along the screw axis, and the screw groove depth of the last melting screw rib is the same as the screw groove depth of the first feed screw rib adjacent to it. The helix angle of the melting screw ribs and the feed screw ribs is the same. The groove depth of the last feed screw is 0.12D to 0.13D, the groove depth of the first feed screw and the last adjacent molten screw is 0.13D to 0.14D, and the groove depth of the first molten screw is 0.06D to 0.10D. The compression ratio of the molten section is 1.6 to 2; The exhaust section is provided with single spiral exhaust screw ridges of equal width and depth, and the screw groove depth of the exhaust screw ridge is 0.15D to 0.18D; The homogenization section is provided with single spiral homogenization ridges of equal width and depth, and the groove depth of the homogenization ridges is 0.05D to 0.07D.

2. The screw for an extruder according to claim 1, characterized in that: The pitch of the exhaust screw thread in the exhaust section is half the length of the mixing element.

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