Extrusion screw and extrusion device for producing PVC cast film

Abstract

The invention provides an extrusion screw for producing a PVC cast film and an extrusion device, and belongs to the technical field of extrudes.The extrusion screw comprises a screw body, the screw body comprises a feeding section, a compression homogenizing section, a plasticizing section and an extrusion section which are sequentially arranged in the axial direction of the screw body, first screw flights are distributed on the feeding section, the compression homogenizing section and the plasticizing section, and second screw flights are distributed on the extrusion section; the first screw flight is distributed on the feeding section, the second screw flight is distributed on the extrusion section, a barrier mixing head and a stirring mixing head are arranged on the extrusion section, the barrier mixing head is located between the first screw flight and the second screw flight, the feeding section, the plasticizing section and the extrusion section are all of an equal-diameter shaft structure, the diameter of the feeding section is smaller than that of the plasticizing section, and the compression homogenizing section is of a variable-diameter shaft structure. The diameter of the compression homogenizing section is gradually increased from one end close to the feeding section to one end close to the plasticizing section. The screw has the beneficial effects that the structural design of the screw is reasonable, the mixing and homogenizing effects of materials can be ensured, the materials cannot stay for a long time at high temperature, and meanwhile, the productivity efficiency is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of extruders and relates to an extrusion screw and an extrusion device for producing PVC cast film. Background Art

[0002] PVC cast film is a non-stretched, non-directional flat extruded film produced by quenching the melt. Cast film is widely used in the packaging of food, medical supplies, textiles, flowers, and daily necessities. PVC cast film can be used as a plastic wrap, which can fit tightly on the edge of the container and effectively isolate the air. In the production process of PVC cast film, PVC resin powder and additives such as plasticizers, stabilizers, and antioxidants must first be mixed evenly in a certain proportion to form a mixture suitable for processing. The mixed material is added to the extruder through the feed hopper. Inside the extruder, while the screw rotates, the material moves forward along the screw and gradually heats up to a molten state through external heating and screw shear heat. The molten PVC material is pushed by the pressure of the screw through a specific shape mold (such as a flat die head) in the die head to form a continuous film-like material.

[0003] The screw of the extruder is not only responsible for the transportation, heating and melting of materials, but also participates in the initial pressure establishment and the control of the mixing uniformity of materials, which has a direct impact on ensuring the quality of PVC cast film. Among them, if the extrusion speed of the screw is too fast, it will affect the mixing and homogenization effect of the material in the screw, resulting in uneven melt, which in turn affects the thickness uniformity and mechanical properties of the film. Especially when a variety of additives are added, sufficient mixing is particularly important. On the contrary, if the extrusion speed is too slow, the material stays at high temperature for too long, which is prone to thermal degradation, produces harmful gases, and reduces the performance of the product. And a slow extrusion speed will also affect the production capacity, but too high a speed will sacrifice the quality of the product. However, the existing general extrusion screw used for the production of PVC cast film cannot find an optimal balance point when extruding PVC cast film, which not only ensures the production efficiency of PVC cast film, but also ensures product quality. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems in the prior art and to provide an extrusion screw and an extrusion device for producing PVC cast film.

[0005] The object of the present invention can be achieved by the following technical scheme: an extrusion screw for producing PVC cast film, comprising: a screw body, the screw body comprising a feed section, a compression homogenizing section, a plasticizing section and an extrusion section arranged in sequence along its axial direction, the outer peripheral surface of the screw body is provided with a first screw rib and a second screw rib, the first screw rib is distributed on the feed section, the compression homogenizing section and the plasticizing section, the second screw rib is distributed on the extrusion section, a barrier mixing head and a stirring mixing head are provided on the extrusion section, the barrier mixing head is located between the first screw rib and the second screw rib, the plasticizing section and the extrusion section are both provided with a pin stirring part, the feed section, the plasticizing section and the extrusion section are all equal diameter shaft structures, the diameter of the feed section is smaller than the diameter of the plasticizing section, the compression homogenizing section is a variable diameter shaft structure, and the diameter of the compression homogenizing section gradually increases from one end close to the feed section to the end close to the plasticizing section.

[0006] Preferably, the first screw edge has a front R angle on a side facing the head of the screw body, and has a rear R angle on a side facing the tail of the screw body, and both the front R angle and the rear R angle are configured as a structure with a gradual angle change along the spiral direction of the first screw edge.

[0007] Preferably, the barrier mixing head includes a plurality of forward screw grooves and reverse screw grooves alternately arranged along the circumference of the extrusion section, a barrier portion is formed between adjacent forward screw grooves and reverse screw grooves, the forward screw groove and the reverse screw groove are both configured as a single-opening inclined groove structure, the forward screw groove is an open end toward one end of the plasticizing section and the groove depth gradually decreases toward one end of the extrusion section to form a closed end, the reverse screw groove is a groove depth gradually decreases toward one end of the plasticizing section to form a closed end and is an open end toward one end of the extrusion section; the movement trajectory of the liquid phase material at the barrier mixing head is to enter the forward screw groove from the opening of the forward screw groove and flow over the closed end of the forward screw groove to the extrusion section, and at the same time, the liquid phase material in the forward screw groove passes over the barrier portion into the reverse screw groove and flows to the extrusion section through the opening of the reverse screw groove.

[0008] Preferably, each of the barrier parts is a first barrier and a second barrier, each of the first barriers and each of the second barriers are alternately arranged along the circumference of the extrusion section, and the height of the second barrier is lower than that of the first barrier.

[0009] Preferably, the stirring and kneading head comprises a plurality of kneading blocks, each of which is evenly spaced and distributed in the circumferential direction and the axial direction of the extrusion section, the kneading blocks are diamond-shaped protruding structures, and the kneading blocks are arranged obliquely.

[0010] Preferably, the screw body further comprises a screw head, and the screw head is threadedly connected to the end of the extrusion section via a thread structure.

[0011] Preferably, the screw body is provided with internal cooling and heat-conducting holes along its axial direction, and the internal cooling and heat-conducting holes are distributed in the feeding section, the compression and homogenization section, the plasticizing section and the extrusion section.

[0012] Preferably, the pin stirring portion is composed of a plurality of pins arranged in a circle at uniform intervals along the circumference of the screw body, and the pins are short cylindrical structures.

[0013] An extrusion device comprises the extrusion screw for producing PVC cast film and a barrel, wherein the screw body of the extrusion screw for producing PVC cast film is rotatably installed in the barrel, the barrel has a feed port, the feed port corresponds to the feed section of the screw body, the gap size between the feed section and the inner wall of the barrel, the gap size between the compression and homogenization section and the inner wall of the barrel, the gap size between the plasticizing section and the inner wall of the barrel, and the gap size between the extrusion section and the inner wall of the barrel are all different.

[0014] Preferably, a portion of the inner hole wall of the barrel near the feed port is arranged as a smooth wall structure without grooves; or a portion of the inner hole wall of the barrel near the feed port is arranged with a plurality of straight grooves evenly arranged along its circumference; or a portion of the inner hole wall of the barrel near the feed port is arranged with a plurality of spiral grooves evenly arranged along its circumference.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The screw has a reasonable structural design, which can ensure the mixing and homogenization effect of the materials, and will not cause the materials to stay at high temperature for too long, while ensuring the production efficiency.

[0017] 2. The gradually changing compression ratio of the compression homogenization section can achieve a smooth transition of the material from the feeding section to the plasticizing section, reduce the impact and instability of the material between different sections, ensure that the material is evenly heated during the compression process, avoid local overheating or uneven cooling, and improve the plasticizing effect of the material. In addition, in view of the easy pyrolysis of PCV materials in the production process of PVC cast film, the gradual compression of the compression homogenization section can better control the temperature of the material, avoid local high temperature caused by sudden compression, reduce the risk of thermal degradation of the material, and improve the performance and quality of the product.

[0018] 3. The angles of the front R angle and the rear R angle gradually decrease in the direction toward the extrusion section, thereby providing a smoother material flow path and reducing the stagnation and accumulation of materials at the edge of the screw ridge. This smooth transition helps the material to flow evenly in the screw and reduce local pressure fluctuations. This gradual design can increase the shear force of the material at the edge of the screw ridge, promote the mixing and homogenization of the material, increase the interface contact area between different components, further improve the mixing effect, and ensure that the material exhibits better performance in the subsequent plasticization and molding process.

[0019] 4. The gradual R angle design can reduce the retention time of powdered materials on the edge of the screw, avoid local overheating, and reduce the risk of thermal degradation. This helps to maintain the physical and chemical properties of the material and improve the quality and safety of the product. Moreover, this PVC material is generally powdery. This gradual R angle design is specifically designed for the processing characteristics of this powdery material. By optimizing the R angle design, it can ensure uniform heating of the powdered material in the screw, avoid local overheating or uneven cooling, and improve the plasticization effect of the material.

[0020] 5. When passing through the barrier mixing head, the material needs to go through a complex flow path, including entering from the open end of the forward screw groove, passing through the closed end and flowing to the extrusion section. At the same time, part of the material will pass through the barrier part and enter the reverse screw groove, and then flow out from the open end of the reverse screw groove. This complex flow path helps to fully mix and homogenize the material. Through this complex flow path, the material undergoes multiple shearing and mixing in the barrier mixing head, ensuring that the components are more evenly distributed in the material. This design helps to reduce bubbles and voids in the material, improve the thickness uniformity and mechanical properties of the film, and the design of the barrier mixing head can optimize the pressure distribution of the material in the screw, ensuring that the pressure of the material in different sections is more uniform and reducing pressure fluctuations.

[0021] 6. The height of the first barrier is relatively high, which mainly plays a strong blocking and shearing role. The height of the second barrier is relatively low, which mainly plays a role in assisting mixing and guiding the flow of materials. The height of the first barrier is slightly higher, which can increase the plasticizing pressure, and the height of the second barrier is slightly lower, which helps the material to pass through. This design improves the smoothness and production capacity of extrusion while ensuring the plasticizing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of an extrusion screw for producing PVC cast film according to the present invention.

[0023] Figure 2 It is a schematic structural diagram of the barrier mixing head of the present invention.

[0024] Figure 3 It is a schematic structural diagram of the stirring and kneading head of the present invention.

[0025] Figure 4 It is a schematic diagram of the front R angle and the rear R angle of the first screw edge of the present invention.

[0026] Figure 5 It is a schematic structural diagram of the extrusion device of the present invention.

[0027] Figure 6 It is a schematic diagram of the barrel structure in Example 1 of the present invention.

[0028] Figure 7 It is a schematic diagram of the barrel structure in the second embodiment of the present invention.

[0029] Figure 8 This is a schematic diagram of the barrel structure in Example 3 of the present invention.

[0030] Fig. 9 It is a schematic diagram of the position of the internal cooling heat conduction hole in the screw body of the present invention.

[0031] In the figure, 100, screw body; 110, feed section; 120, compression and homogenization section; 130, plasticizing section; 140, extrusion section; 150, screw head; 160, internal cooling and heat conduction hole; 200, first screw fin; 210, front R angle; 220, rear R angle; 300, second screw fin; 400, barrier mixing head; 410, forward screw groove; 420, reverse screw groove; 430, first barrier; 440, second barrier; 500, stirring and mixing head; 510, mixing block; 600, pin stirring part; 610, pin; 700, barrel; 710, straight groove; 720, spiral groove; 730, copper tube. DETAILED DESCRIPTION

[0032] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0033] like Figure 1-4As shown, an extrusion screw for producing PVC cast film comprises: a screw body 100, the screw body 100 comprises a feed section 110, a compression homogenization section 120, a plasticization section 130 and an extrusion section 140 arranged in sequence along its axial direction, the outer peripheral surface of the screw body 100 is provided with a first screw fin 200 and a second screw fin 300, the first screw fin 200 is distributed on the feed section 110, the compression homogenization section 120 and the plasticization section 130, the second screw fin 300 is distributed on the extrusion section 140, and the extrusion section 140 is provided with a screen The barrier kneading head 400 and the stirring kneading head 500, the barrier kneading head 400 is located between the first screw 200 and the second screw 300, the plasticizing section 130 and the extrusion section 140 are both provided with a pin stirring portion 600, the feeding section 110, the plasticizing section 130 and the extrusion section 140 are all equal-diameter shaft structures, the diameter of the feeding section 110 is smaller than the diameter of the plasticizing section 130, the compression homogenizing section 120 is a variable-diameter shaft structure, and the diameter of the compression homogenizing section 120 gradually increases from one end close to the feeding section 110 to the end close to the plasticizing section 130.

[0034] The extrusion screw for producing PVC cast film is specially designed for the production of PVC cast film, and the cast film produced by the extrusion screw can be used as a fresh-keeping film. The screw body 100 is divided into four main parts along the axial direction, namely the feeding section 110, the compression homogenization section 120, the plasticizing section 130 and the extrusion section 140. The design of the screw ribs is crucial for the transportation and mixing of materials. The screw ribs on the screw body 100 can be divided into two sections, wherein the first screw rib 200 is distributed in the feeding section 110, the compression homogenization section 120 and the plasticizing section 130, and is responsible for material transportation, shearing and mixing; and the second screw rib 300 is only distributed in the extrusion section 140, and the second screw rib 300 is used to control the flow speed and pressure of the material. The barrier kneading head 400 and the stirring kneading head 500 are located in the extrusion section 140, and are used to enhance the mixing effect of the materials and ensure that the various components are evenly dispersed. On the screw body 100, the barrier kneading head 400 can effectively disperse and mix the materials of different components through its unique geometric shape and arrangement, and can generate strong shear force when the materials pass through, further refine and mix the materials, ensure that the interface contact between the components is more sufficient, and greatly improve the plasticization effect. The stirring kneading head 500 can provide additional shear force when the materials pass through, further promoting the mixing of the materials.

[0035] The barrier mixing head 400 is located between the first screw 200 and the second screw 300. The first screw 200 is distributed in the feeding section 110, the compression homogenization section 120 and the plasticization section 130, and is mainly responsible for the transportation, shearing and preliminary mixing of the material. At this stage, the material gradually changes from a solid state to a molten state. The barrier mixing head 400 is located between the first screw 200 and the second screw 300, which means that it is in a stage where the material has been partially melted but not yet completely homogenized. At this time, the viscosity of the material is high, and it is easier to achieve full mixing and dispersion through the shearing action of the barrier mixing head 400. In the state where the material is partially melted, the barrier mixing head 400 can provide stronger shearing force to help the different components in the material (such as PVC resin, plasticizer, stabilizer, etc.) to be fully mixed. If the barrier mixing head 400 is located in the area after the material is completely melted, the effect of the shearing force may be weakened because the viscosity of the material is low at this time and the shearing effect is not so obvious. If the barrier mixing head 400 is located after the second screw flight 300, that is, the material has been completely melted and begins to form a stable flow state, excessive shear force may cause excessive shearing of the material, generate unnecessary heat, and increase the risk of thermal degradation of the material. Therefore, the barrier mixing head 400 is located between the first screw flight 200 and the second screw flight 300, which can help establish and control the pressure gradient of the material. The first screw flight 200 is mainly responsible for the transportation and preliminary mixing of the material, while the second screw flight 300 mainly controls the flow rate and pressure of the material. The barrier mixing head 400 can play a transition and adjustment role between the two, ensuring that the material has appropriate pressure and flow characteristics when entering the second screw flight 300 area.

[0036] The feeding section 110, the plasticizing section 130 and the extrusion section 140 are all equal-diameter shaft structures, which can ensure that the material is evenly transported in these sections, help maintain a stable material pressure, and ensure that the material flows more smoothly in these sections. The compression homogenization section 120 gradually increases in diameter from one end close to the feeding section 110 to the end close to the plasticizing section 130. This design can achieve gradual compression of the material. Gradual compression can gradually increase the density of the material, making the material more compact before entering the plasticizing section 130, which is helpful for the subsequent plasticizing process. Gradual compression can reduce the air and bubbles in the material, improve the homogeneity of the material, and avoid bubbles or voids in the finished product, which affects the product quality. More importantly, gradual compression can increase the shear force of the material, promote the mixing and homogenization of the material, and ensure that the components are more evenly distributed in the material. The gradually changing compression ratio of the compression homogenization section 120 can achieve a smooth transition of the material from the feeding section 110 to the plasticizing section 130, reduce the impact and instability of the material between different sections, ensure that the material is evenly heated during the compression process, avoid local overheating or uneven cooling, and improve the plasticizing effect of the material. In addition, in view of the characteristic that PCV material is easy to pyrolyze during the production process of PVC cast film, the gradual compression feature of the compression homogenization section 120 can better control the temperature of the material, avoid local high temperature caused by sudden compression, reduce the risk of thermal degradation of the material, and improve the performance and quality of the product.

[0037] This extrusion screw for the production of PVC cast film is specially designed for the production of PVC cast film. By designing a reasonable screw structure, the mixing and homogenization effect of the material in the screw can be significantly improved. This helps to ensure that various components (such as PVC resin, plasticizer, stabilizer, etc.) are evenly distributed in the material, thereby improving the quality of the final product. By optimizing the design of the screw, the residence time of the material at high temperature can be controlled to reduce the risk of thermal degradation. This helps to avoid the generation of harmful gases and improve the performance and safety of the product. Increase the production speed without sacrificing product quality, thereby improving overall production efficiency and capacity.

[0038] It should be additionally explained here that tungsten carbide is sprayed on the bottom groove of the screw body 100. Tungsten carbide can increase the roughness of the bottom groove and thus increase the shear force, making the feeding more stable.

[0039] like Figure 1 , Figure 4 As shown, based on the above embodiment, the side of the first screw flight 200 facing the head of the screw body 100 has a front R angle 210, and the side of the first screw flight 200 facing the tail of the screw body 100 has a rear R angle 220, and the front R angle 210 and the rear R angle 220 are both arranged to be a structure with a gradual angle change along the spiral direction of the first screw flight 200.

[0040] It should be noted here that the R angle (front R angle 210 or rear R angle 220) is actually the arc chamfer between the side of the screw ridge and the outer peripheral surface of the screw body 100. The angles of the front R angle 210 and the rear R angle 220 gradually decrease in the direction toward the extrusion section 140, thereby providing a smoother material flow path and reducing the stagnation and accumulation of materials at the edge of the screw ridge. This smooth transition helps the material to flow evenly in the screw and reduce local pressure fluctuations. And this gradual design can increase the shear force of the material at the edge of the screw ridge, promote the mixing and homogenization of the material, increase the interface contact area between different components, further improve the mixing effect, and ensure that the material exhibits better performance in the subsequent plasticization and molding process. It helps to control the pressure distribution of the material in the screw and establish and optimize the pressure gradient of the material, ensuring that the material has appropriate pressure and flow characteristics when entering the subsequent processing section.

[0041] In general screws, the R angle is fixed, but in the PVC cast film production process, since PVC materials are very sensitive to temperature and temperature changes, some tiny features on the screw have a great impact on the quality of the finished product. The gradual R angle design can reduce the residence time of powdered materials on the edge of the screw, avoid local overheating, and reduce the risk of thermal degradation. This helps to maintain the physical and chemical properties of the material and improve the quality and safety of the product. Moreover, this kind of PVC material is generally powdery, and this gradual R angle design is specifically designed for the processing characteristics of this powdery material. By optimizing the R angle design, it can ensure uniform heating of the powdery material in the screw, avoid local overheating or uneven cooling, and improve the plasticization effect of the material.

[0042] like Figure 1-2 As shown, on the basis of the above-mentioned embodiment, the barrier mixing head 400 includes a plurality of forward screw grooves 410 and reverse screw grooves 420 alternately arranged along the circumference of the extrusion section 140, a barrier portion is formed between adjacent forward screw grooves 410 and reverse screw grooves 420, and the forward screw grooves 410 and reverse screw grooves 420 are both configured as single-opening inclined groove structures, the end of the forward screw groove 410 facing the plasticizing section 130 is an open end and the groove depth gradually decreases toward the end of the extrusion section 140 to form a closed end, and the reverse screw grooves 410 are arranged in a plurality of positions. The groove depth of the groove 420 gradually decreases at one end toward the plasticizing section 130 to form a closed end, and the end toward the extrusion section 140 is an open end; the movement trajectory of the liquid phase material at the barrier mixing head 400 is to enter the forward screw groove 410 from the opening of the forward screw groove 410 and flow over the closed end of the forward screw groove 410 to the extrusion section 140, and at the same time, the liquid phase material in the forward screw groove 410 passes over the barrier part and enters the reverse screw groove 420 and flows to the extrusion section 140 through the opening of the reverse screw groove 420.

[0043] The alternating arrangement of the forward screw groove 410 and the reverse screw groove 420 can significantly increase the shear force of the material when passing through the barrier mixing head 400. This shear force helps to refine the material and improve the mixing uniformity of the material. When passing through the barrier mixing head 400, the material needs to pass through a complex flow path, including entering from the open end of the forward screw groove 410, passing through the closed end to flow to the extrusion section 140, and at the same time, part of the material will pass through the barrier part to enter the reverse screw groove 420, and then flow out from the open end of the reverse screw groove 420. This complex flow path helps to fully mix and homogenize the material. Through this complex flow path, the material undergoes multiple shearing and mixing in the barrier mixing head 400, ensuring that the components are more evenly distributed in the material, and this design helps to reduce bubbles and voids in the material, and improve the thickness uniformity and mechanical properties of the film. The design of the barrier mixing head 400 can optimize the pressure distribution of the material in the screw, ensure that the pressure of the material in different sections is more uniform, and reduce pressure fluctuations.

[0044] In the actual extrusion process, the molten (liquid phase) material needs to pass through the barrier mixing head 400 when entering the extrusion section 140 from the plasticizing section 130. The liquid phase material first enters each forward screw groove 410, and then a part of the material flows over the closed end of the forward screw groove 410 to the area where the second screw rib 300 is located. In this process, the material is mixed and subjected to high pressure and shearing. Another part of the material passes through the barrier part and enters the reverse screw groove 420. At this time, this part of the material is mixed and subjected to high pressure and shearing, and then enters the area where the second screw rib 300 is located from the opening of the reverse screw groove 420. This design significantly improves the mixing uniformity of the material, promotes the full mixing and homogenization of the material, reduces the residence time of the material in the screw groove, avoids local overheating and thermal degradation, ensures that each component is more evenly distributed in the material, improves the thickness uniformity and mechanical properties of the film, and makes pressure and temperature easier to control.

[0045] On the basis of the above embodiment, each barrier part is a first barrier 430 and a second barrier 440 , each first barrier 430 and each second barrier 440 are alternately arranged along the circumference of the extrusion section 140 , and the height of the second barrier 440 is lower than that of the first barrier 430 .

[0046] The first barrier 430 and the second barrier 440 actually both play a blocking and shearing role. The difference between the two lies in the height of the protrusions. The first barrier 430 is higher and mainly plays a stronger blocking and shearing role. The second barrier 440 is lower and mainly plays a role of assisting mixing and guiding the flow of materials. The height of the first barrier 430 is slightly higher, which can increase the plasticizing pressure. The height of the second barrier 440 is slightly lower, which helps the material to pass through. This design improves the smoothness and production capacity of extrusion while ensuring the plasticizing effect.

[0047] In addition, the main reason why the heights of the first barrier 430 and the second barrier 440 are not designed to be equally low is to ensure the maximum size of the outer circumference of the barrier kneading head 400, which directly affects the gap between the screw and the barrel 700. If the heights of the first barrier 430 and the second barrier 440 are equally low, the outer circumference of the barrier kneading head 400 is equivalent to being reduced by one circle, which will cause the gap between the screw and the barrel 700 to become larger. Appropriate gaps are essential for the conveying, shearing and mixing of materials. If the gap is too large, the material conveying efficiency will be reduced, and the shear force will also be weakened, affecting the mixing effect. If the gap is too small, the flow of materials will be hindered, increasing energy consumption and causing a decrease in production capacity.

[0048] like Figure 1 , Figure 3 As shown, based on the above embodiment, the stirring and kneading head 500 includes a plurality of kneading blocks 510, each of which is evenly spaced in the circumferential and axial directions of the extrusion section 140, and the kneading blocks 510 are diamond-shaped protruding structures, and the kneading blocks 510 are inclined.

[0049] The evenly distributed mixing blocks 510 can ensure that the material is evenly sheared and mixed when passing through the stirring and mixing head 500, avoiding local insufficient mixing or excessive mixing. Each mixing block 510 is a diamond-shaped protrusion structure, which can provide more shear surfaces and increase the shear force of the material when passing through the mixing block 510. The tilted mixing blocks 510 can increase the shearing effect of the material when passing through, which helps to refine the material and improve the mixing uniformity of the material. The diamond-shaped protrusion structure can promote smoother passage of the material, reduce the retention time of the material at the mixing block 510, avoid local overheating and thermal degradation, improve the thermal stability of the material, and further increase production capacity.

[0050] like Figure 1 As shown, based on the above embodiment, the bottom groove depth of the second screw flight 300 is greater than the bottom groove depth of the first screw flight 200. That is, the height of the second screw flight 300 is greater than the height of the first screw flight 200. Since the bottom groove depth of the second screw flight 300 is larger, the shear force is reduced and the flow speed is controlled, so that the production capacity can be increased, the extrusion pressure is released, and it is helpful to reduce the risk of thermal degradation of the material and improve the thermal stability of the material.

[0051] Specifically, the area where the second screw fin 300 is located is called the releasing extrusion section, and its main function is to release the material from the screw in a stable and controllable manner after the material is fully mixed, plasticized and homogenized, and enter the subsequent molding device (such as the die head).

[0052] like Figure 1 , Figure 3As shown, based on the above embodiment, the screw body 100 further includes a screw head 150, which is threadedly connected to the end of the extrusion section 140 through a thread structure. The axial position of the screw head 150 can be changed by rotating the screw head 150, and this design can better cooperate with the barrel.

[0053] like Figure 1 , Fig. 9 As shown, based on the above embodiment, internal cooling and heat-conducting holes 160 are opened in the screw body 100, and the internal cooling and heat-conducting holes 160 are distributed in the feeding section 110, the compression and homogenization section 120, the plasticizing section 130 and the extrusion section 140.

[0054] The inner cooling heat conduction hole 160 is usually used to pass a cooling medium (such as water or cooling oil) to remove the heat inside the screw through the circulation of the cooling medium. This design can make the temperature of the screw body 100 uniform after heating, ensuring that the screw is in a constant temperature state.

[0055] like Figure 1 As shown, based on the above embodiment, the pin stirring portion 600 is composed of a plurality of pins 610 evenly spaced and arranged in a circle along the circumference of the screw body 100, and the pins 610 are short cylindrical structures.

[0056] The pin stirring section 600 mainly plays the role of stirring and dispersing uniformly, further promoting the mixing and homogenization of materials. When the material passes through the pin stirring section 600, the pin 610 can cut and disperse the material to ensure that the components are more evenly distributed in the material. The pins 610 are evenly arranged along the circumference, and the material can be sheared and mixed at multiple points to improve the mixing effect. The short cylindrical structure of the pin 610 can increase the contact area between the material and the screw surface, improve the heat exchange efficiency, ensure that the material is evenly heated when passing through, and avoid local overheating or uneven cooling.

[0057] like Figure 1-8 As shown, an extrusion device includes an extrusion screw for producing PVC cast film, and also includes a barrel 700. The screw body 100 of the extrusion screw for producing PVC cast film is rotatably installed in the barrel 700. The barrel 700 has a feed port, which corresponds to a feed section 110 of the screw body 100. The gap size between the feed section 110 and the inner wall of the barrel 700, the gap size between the compression and homogenization section 120 and the inner wall of the barrel 700, the gap size between the plasticizing section 130 and the inner wall of the barrel 700, and the gap size between the extrusion section 140 and the inner wall of the barrel 700 are all different.

[0058] The barrel 700 is also provided with an external cooling circulation device, which includes a copper tube 730 spirally wound around the outer circumference of the barrel 700, so as to assist the barrel 700 in heat dissipation and thus control the temperature.

[0059] It should be noted here that in conventional extrusion devices, there is only one gap size between the screw and the barrel 700, that is, the gap between the two is uniformly fixed, while in this device, there are at least four different matching gaps between the extrusion screw and the barrel 700 used to produce PVC cast film. The material enters from the feed port and is transported forward through the first screw 200 of the feed section 110. The gap between the feed section 110 and the inner wall of the barrel 700 is relatively large. The larger gap can reduce the resistance when the material enters, ensuring the smooth entry and initial transportation of the material. The gap between the compression and homogenization section 120 and the inner wall of the barrel 700 gradually decreases. The gradually decreasing gap can gradually compress the material, increase the pressure and temperature of the material, and enhance the mixing effect. The gap size between the plasticizing section 130 and the inner wall of the barrel 700 is specifically designed to ensure that the material is evenly heated during the plasticizing process, avoid local overheating or uneven cooling, and provide appropriate shear force to ensure that the material is fully mixed and homogenized in this section.

[0060] The gap design of different sections can adjust the flow speed and pressure of materials, optimize the entire production process, improve production efficiency, significantly improve the mixing uniformity of materials, control the flow speed and pressure of materials, and optimize heat exchange.

[0061] Embodiment 1:

[0062] like Figure 6 As shown, part of the inner hole wall of the barrel 700 near the feed port is configured as a smooth wall structure without grooves.

[0063] In this embodiment, this groove-free design is suitable for low-yield and low-energy production requirements. The smooth inner hole wall can reduce the friction resistance between the material and the inner wall of the barrel 700, reduce the energy required to drive the screw, and thus reduce energy consumption. In addition, reducing friction resistance can improve the feeding efficiency of the material, ensure that the material enters the screw smoothly, and reduce losses during the feeding process.

[0064] Embodiment 2:

[0065] like Figure 7 As shown, a portion of the inner hole wall of the barrel 700 close to the feed port is provided with a plurality of straight grooves 710 evenly arranged along its circumference.

[0066] The design of the straight groove 710 is suitable for medium and high production capacity. The straight groove 710 can increase the shear force between the material and the inner wall of the barrel 700, which is helpful for the crushing and refinement of the material. Especially when feeding the material, it can ensure that the material quickly enters the screw. The increased shear force can promote the initial mixing of the material and improve the uniformity of the material.

[0067] Embodiment three:

[0068] like Figure 8As shown, a portion of the inner wall of the barrel 700 close to the feed port is provided with a plurality of spiral grooves 720 evenly arranged along its circumference.

[0069] The design of the spiral groove 720 is suitable for high production capacity. The spiral groove 720 can greatly increase the shear force. The increased shear force can effectively crush the material, improve the fineness and uniformity of the material, and thus increase the production capacity.

[0070] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0071] In addition, in the present invention, descriptions such as "first", "second", "one", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0072] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0073] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. An extrusion screw for producing PVC cast film, characterized in that: include: A screw body (100), the screw body (100) comprising a feed section (110), a compression homogenization section (120), a plasticization section (130) and an extrusion section (140) arranged in sequence along the axial direction thereof, the outer peripheral surface of the screw body (100) being provided with a first screw fin (200) and a second screw fin (300), the first screw fin (200) being distributed on the feed section (110), the compression homogenization section (120) and the plasticization section (130), the second screw fin (300) being distributed on the extrusion section (140), the extrusion section (140) being provided with a barrier kneading head (400) and a stirring kneading head (500), 00), the barrier mixing head (400) is located between the first screw flight (200) and the second screw flight (300), the plasticizing section (130) and the extrusion section (140) are both provided with a pin stirring portion (600), the feeding section (110), the plasticizing section (130) and the extrusion section (140) are all equal-diameter shaft structures, the diameter of the feeding section (110) is smaller than the diameter of the plasticizing section (130), the compression homogenizing section (120) is a variable-diameter shaft structure, and the diameter of the compression homogenizing section (120) gradually increases from one end close to the feeding section (110) to one end close to the plasticizing section (130).

2. An extrusion screw for producing PVC cast film as claimed in claim 1, characterized in that: A side surface of the first screw flight (200) facing the head of the screw body (100) has a front R angle (210), and a side surface of the first screw flight (200) facing the tail of the screw body (100) has a rear R angle (220), and both the front R angle (210) and the rear R angle (220) are configured as structures with gradually changing angles along the spiral direction of the first screw flight (200).

3. An extrusion screw for producing PVC cast film as claimed in claim 1, characterized in that: The barrier mixing head (400) comprises a plurality of forward screw grooves (410) and reverse screw grooves (420) which are alternately arranged along the circumference of the extrusion section (140), a barrier portion is formed between adjacent forward screw grooves (410) and reverse screw grooves (420), the forward screw grooves (410) and reverse screw grooves (420) are both configured as single-opening inclined groove structures, the forward screw groove (410) is an open end at one end facing the plasticizing section (130) and the groove depth gradually decreases towards one end of the extrusion section (140) to form a closed end, and the reverse screw groove (420) is a closed end at one end facing the plasticizing section (130). The groove depth at one end of the plasticizing section (130) gradually decreases to form a closed end, and the end facing the extrusion section (140) is an open end; the movement trajectory of the liquid phase material at the barrier mixing head (400) is to enter the forward screw groove (410) from the opening of the forward screw groove (410) and flow over the closed end of the forward screw groove (410) to the extrusion section (140), and at the same time, the liquid phase material in the forward screw groove (410) passes over the barrier part and enters the reverse screw groove (420) and flows to the extrusion section (140) through the opening of the reverse screw groove (420).

4. An extrusion screw for producing PVC cast film as claimed in claim 3, characterized in that: Each of the barrier parts is a first barrier (430) and a second barrier (440), and each of the first barriers (430) and each of the second barriers (440) are alternately arranged along the circumference of the extrusion section (140), and the height of the second barriers (440) is lower than the height of the first barriers (430).

5. An extrusion screw for producing PVC cast film as claimed in claim 4, characterized in that: The stirring and kneading head (500) comprises a plurality of kneading blocks (510), each of which is evenly spaced and distributed in the circumferential and axial directions of the extrusion section (140); the kneading blocks (510) are diamond-shaped protruding structures, and the kneading blocks (510) are arranged at an inclination.

6. An extrusion screw for producing PVC cast film according to claim 1, characterized in that: The screw body (100) further comprises a screw head (150), and the screw head (150) is threadedly connected to the end of the extrusion section (140) via a thread structure.

7. An extrusion screw for producing PVC cast film according to claim 1, characterized in that: The screw body (100) is provided with internal cooling and heat-conducting holes (160) along its axial direction, and the internal cooling and heat-conducting holes (160) are distributed in the feeding section (110), the compression and homogenization section (120), the plasticizing section (130) and the extrusion section (140).

8. An extrusion screw for producing PVC cast film according to claim 1, characterized in that: The pin stirring portion (600) is composed of a plurality of pins (610) arranged in a circle at even intervals along the circumference of the screw body (100), and the pins (610) are short cylindrical structures.

9. An extrusion device, characterized in that: It comprises an extrusion screw for producing PVC cast film as described in any one of claims 1 to 8, and also comprises a barrel (700), wherein a screw body (100) of the extrusion screw for producing PVC cast film is rotatably installed in the barrel (700), and the barrel (700) has a feed port, which corresponds to a feed section (110) of the screw body (100), and a gap size between the feed section (110) and the inner wall of the barrel (700), a gap size between a compression and homogenization section (120) and the inner wall of the barrel (700), a gap size between a plasticizing section (130) and the inner wall of the barrel (700), and a gap size between an extrusion section (140) and the inner wall of the barrel (700) are all different.

10. An extrusion device according to claim 9, characterized in that: The inner hole wall of the barrel (700) near the feed port is configured as a smooth wall structure without grooves; or the inner hole wall of the barrel (700) near the feed port is configured with a plurality of straight grooves (710) evenly arranged along its circumference; or the inner hole wall of the barrel (700) near the feed port is configured with a plurality of spiral grooves (720) evenly arranged along its circumference.

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