Extrusion screw and extrusion device for producing PVC cast film

Abstract

The utility model provides an extrusion screw rod and an extrusion device for producing a PVC (polyvinyl chloride) cast film, which belong to the technical field of extruders, and comprise a screw rod body, the screw rod body comprises a feeding section, a compression homogenizing section, a plasticizing section and an extrusion section which are sequentially arranged along the axial direction of the screw rod body, a first screw flight is distributed on the feeding section, the compression homogenizing section and the plasticizing section, and a second screw flight is 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, 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 equal-diameter shaft structures, 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 rod has the beneficial effects that the screw rod is reasonable in structural design, 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 utility model 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. It is widely used in packaging for food, medical supplies, textiles, flowers, and daily necessities. PVC cast film can also be used as plastic wrap, tightly fitting around the edges of containers while effectively sealing out air. During the PVC cast film production process, PVC resin powder is first mixed with additives such as plasticizers, stabilizers, and antioxidants in a specific proportion to form a suitable mixture. This mixture is then fed into an extruder through a hopper. Inside the extruder, the material moves forward along the rotating screw. External heating and shear heat from the screw gradually heat the material to a molten state. The molten PVC material, propelled by the screw's pressure, passes through a specially shaped die (such as a flat die) in the die head, forming a continuous film.

[0003] The screw of the extruder is not only responsible for conveying, heating and melting the material, but also participates in the initial pressure establishment and controlling the mixing uniformity of the material, 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 multiple 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, producing harmful gases and reducing the performance of the product. In addition, a slow extrusion speed will also affect production capacity, but too high a speed will sacrifice product quality. However, the existing extrusion screws commonly used in the production of PVC cast film cannot find an optimal balance when extruding PVC cast film to ensure both the production efficiency of PVC cast film and the quality of the product. Utility Model Content

[0004] The purpose of the utility model is to address the above-mentioned problems existing in the prior art and to propose an extrusion screw and an extrusion device for producing PVC cast film.

[0005] The purpose of the utility model can be achieved through the following technical solutions: An extrusion screw for producing PVC cast film, comprising: a screw body, the screw body comprising a feeding section, a compression and homogenizing section, a plasticizing section and an extrusion section arranged in sequence along its axial direction, the outer peripheral surface of the screw body being provided with a first screw fin and a second screw fin, the first screw fin being distributed on the feeding section, the compression and homogenizing section and the plasticizing section, the second screw fin being distributed on the extrusion section, a barrier mixing head and a stirring mixing head being provided on the extrusion section, the barrier mixing head being located between the first screw fin and the second screw fin, the plasticizing section and the extrusion section being provided with a pin stirring portion, the feeding section, the plasticizing section and the extrusion section being all of an equal-diameter shaft structure, the diameter of the feeding section being smaller than the diameter of the plasticizing section, the compression and homogenizing section being of a variable-diameter shaft structure, the diameter of the compression and homogenizing section gradually increasing from one end close to the feeding section to the end close to the plasticizing section.

[0006] Preferably, the first screw fin 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 to have a structure with a gradual angle change along the spiral direction of the first screw fin.

[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 pass over the closed end of the forward screw groove to flow 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 includes a plurality of kneading blocks, each of which is evenly spaced in the circumferential and axial directions of the extrusion section, and the kneading blocks are diamond-shaped protruding structures, and 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 mounted in the barrel, the barrel having a feed port, the feed port corresponding 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, the inner hole wall of the barrel near the feed port is set to a smooth wall structure without grooves; or the inner hole wall of the barrel near the feed port is provided with a plurality of straight grooves evenly arranged along its circumference; or the inner hole wall of the barrel near the feed port is provided with a plurality of spiral grooves evenly arranged along its circumference.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[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 production efficiency.

[0017] 2. The gradually changing compression ratio in the compression and homogenization section ensures a smooth transition from the feed section to the plasticizing section, reducing material shock and instability between sections. This ensures uniform heating of the material during the compression process, avoids localized overheating or uneven cooling, and improves the plasticizing effect. Furthermore, given the pyrolysis-prone nature of PVC cast film during production, the gradual compression in the compression and homogenization section better controls material temperature, avoiding localized high temperatures caused by sudden compression, reducing the risk of thermal degradation, and improving product performance and quality.

[0018] 3. The angles of the front and rear R angles gradually decrease toward the extrusion section, providing a smoother material flow path and reducing material stagnation and accumulation at the edges of the screw flights. This smooth transition promotes uniform material flow in the screw and reduces local pressure fluctuations. This gradual design also increases the shear force on the material at the edges of the screw flights, promoting material mixing and homogenization, increasing the interfacial contact area between different components, further improving the mixing effect, and ensuring better material performance during the subsequent plasticization and molding processes.

[0019] 4. The gradual R-angle design reduces the time powdered materials spend at the screw edge, preventing local overheating and reducing the risk of thermal degradation. This helps maintain the material's physical and chemical properties, improving product quality and safety. PVC materials are typically powdered, and this gradual R-angle design specifically addresses the processing characteristics of these powders. By optimizing the R-angle design, the powdered material is evenly heated in the screw, avoiding local overheating or uneven cooling, and improving the material's plasticization.

[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 channel, flowing across the closed end to the extrusion section, and at the same time, some of the material will cross the barrier part and enter the reverse screw channel, and then flow out from the open end of the reverse screw channel. 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 various 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 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 the role of assisting mixing and guiding material flow. The height of the first barrier is slightly higher, which can play a role in increasing the plasticizing pressure. The height of the second barrier is slightly lower, which helps the material 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 This is a schematic structural diagram of an extrusion screw for producing PVC cast film according to the present invention.

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

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

[0025] Figure 4 Schematic diagram of the front R angle and rear R angle of the first screw flight of the present invention.

[0026] Figure 5 This is a schematic structural diagram of the extrusion device of the present utility model.

[0027] Figure 6 This is a schematic diagram of the barrel structure in Example 1 of the present utility model.

[0028] Figure 7 This is a schematic diagram of the barrel structure in Example 2 of the present utility model.

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

[0030] Figure 9 This is a schematic diagram of the position of the internal cooling and heat conduction holes in the screw body of the present invention.

[0031] In the figure, 100, screw body; 110, feeding 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 flight; 210, front R angle; 220, rear R angle; 300, second screw flight; 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 includes: a screw body 100, the screw body 100 includes a feed section 110, a compression and homogenization section 120, a plasticizing section 130 and an extrusion section 140 arranged in sequence along its axial direction, and the outer peripheral surface of the screw body 100 is provided with a first screw wing 200 and a second screw wing 300, the first screw wing 200 is distributed on the feed section 110, the compression and homogenization section 120 and the plasticizing section 130, the second screw wing 300 is distributed on the extrusion section 140, and the extrusion section 140 is provided with a screen The barrier mixing head 400 and the stirring mixing head 500, 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 and homogenization section 120 is a variable-diameter shaft structure, and the diameter of the compression and homogenization 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 plastic wrap. The screw body 100 is divided into four main parts along the axial direction, namely the feed section 110, the compression and homogenization section 120, the plasticizing section 130 and the extrusion section 140. The design of the screw fins is crucial for the transportation and mixing of materials. The screw fins on the screw body 100 can be divided into two sections, of which the first screw fins 200 are distributed in the feed section 110, the compression and homogenization section 120 and the plasticizing section 130, and are responsible for material transportation, shearing and mixing; while the second screw fins 300 are only distributed in the extrusion section 140, and the second screw fins 300 are used to control the flow rate and pressure of the material. The barrier mixing head 400 and the stirring mixing head 500 are located in the extrusion section 140 and are used to enhance material mixing and ensure uniform dispersion of the various components. On the screw body 100, the barrier mixing head 400, through its unique geometry and arrangement, effectively disperses and mixes the different components. It generates strong shear forces as the materials pass through, further refining and mixing the materials, ensuring more complete interfacial contact between the components and significantly improving the plasticizing effect. The stirring mixing head 500 also provides additional shear forces as the materials pass through, further promoting material mixing.

[0035] The barrier mixing head 400 is located between the first screw flight 200 and the second screw flight 300. The first screw flight 200 is distributed between the feed section 110, the compression and homogenization section 120, and the plasticizing section 130, primarily responsible for conveying, shearing, and initially mixing the material. During this stage, the material gradually transitions from a solid state to a molten state. The barrier mixing head 400 is located between the first screw flight 200 and the second screw flight 300, meaning it is in a stage where the material is partially melted but not yet fully homogenized. At this stage, the material's viscosity is higher, making it easier to achieve thorough mixing and dispersion through the shearing action of the barrier mixing head 400. When the material is partially melted, the barrier mixing head 400 can provide stronger shear forces, helping to thoroughly mix the different components of the material (such as PVC resin, plasticizer, stabilizer, etc.). If the barrier mixing head 400 is located in an area where the material is fully melted, the shearing effect may be less pronounced due to the lower viscosity of the material. If the barrier mixing head 400 is located after the second screw flight 300, that is, the material has completely melted and begun 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 regulatory role between the two, ensuring that the material has appropriate pressure and flow characteristics when entering the second screw flight 300 area.

[0036] The feed section 110, the plasticizing section 130, and the extrusion section 140 all have an equal-diameter shaft structure. The equal-diameter shaft structure can ensure that the material is evenly transported in these sections, helps maintain a stable material pressure, and ensures that the material flows more smoothly in these sections. The compression and homogenization section 120 gradually increases in diameter from the end close to the feed 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 air and bubbles in the material, improve the homogeneity of the material, and avoid bubbles or voids in the finished product that affect 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 various components are more evenly distributed in the material. The gradually changing compression ratio of the compression and homogenization section 120 ensures a smooth transition of the material from the feed section 110 to the plasticizing section 130, reducing material shock and instability between sections. This ensures uniform heating of the material during the compression process, avoids localized overheating or uneven cooling, and improves the plasticization of the material. Furthermore, given the pyrolysis-prone nature of PVC cast film during production, the gradual compression of the compression and homogenization section 120 better controls the material's temperature, avoiding localized high temperatures caused by sudden compression, reducing the risk of thermal degradation, and improving product performance and quality.

[0037] This extrusion screw for PVC cast film production is specifically designed for this purpose. Through a well-designed screw structure, material mixing and homogenization within the screw are significantly improved. This helps ensure uniform distribution of various components (such as PVC resin, plasticizer, stabilizer, etc.) throughout the material, thereby improving the quality of the final product. By optimizing the screw design, the residence time of the material at high temperatures can be controlled, reducing the risk of thermal degradation. This helps prevent the generation of harmful gases and improves product performance and safety. This increases production speed without sacrificing product quality, thereby improving overall production efficiency and capacity.

[0038] It should be noted 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, on the basis of 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 set to 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 reduces local pressure fluctuations. And this gradient 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 plasticizing 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 conventional screws, the radius (R) angle is fixed. However, in the production of PVC cast film, because PVC is extremely sensitive to temperature and temperature fluctuations, even small screw features can significantly impact the quality of the finished product. A gradual R angle design can reduce the time that powdered material spends at the screw edge, preventing localized overheating and reducing the risk of thermal degradation. This helps maintain the material's physical and chemical properties, improving product quality and safety. Furthermore, this type of PVC material is typically in powder form, and this gradual R angle design specifically addresses the processing characteristics of this powdery material. By optimizing the R angle design, the powdered material is evenly heated in the screw, avoiding localized overheating or uneven cooling, and improving the material's plasticization.

[0042] like Figure 1-2 As shown, on the basis of the above 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, and 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 end of the forward screw groove 410 toward 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. The reverse screw grooves 410 are arranged in a circumferential direction of the extrusion section 140. The groove 420 has a groove depth that gradually decreases toward one end of 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 through the opening of the reverse screw groove 420 to the extrusion section 140.

[0043] The alternating arrangement of the forward groove 410 and the reverse groove 420 can significantly increase the shear force of the material as it passes through the barrier mixing head 400. This shear force helps to refine the material and improve the uniformity of material mixing. 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 groove 410, flowing across the closed end to the extrusion section 140, and at the same time, some of the material will pass through the barrier portion and enter the reverse groove 420, and then flow out from the open end of the reverse 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 various components are more evenly distributed in the material. This design also helps to reduce bubbles and voids in the material, improving 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, ensuring that the pressure of the material in different sections is more uniform and reducing pressure fluctuations.

[0044] During 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 portion of the material flows over the closed end of the forward screw groove 410 to the area where the second screw fin 300 is located. During this process, the material is mixed and subjected to high pressure and shearing. The other portion of the material passes through the barrier portion and enters the reverse screw groove 420. At this time, this portion of the material is mixed and subjected to high pressure and shearing, and then enters the area where the second screw fin 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 the various components are 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] Based on the above embodiment, each barrier portion is a first barrier 430 and a second barrier 440 , and 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 in assisting mixing and guiding material flow. 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 pass through. This design improves the smoothness and production capacity of extrusion while ensuring the plasticizing effect.

[0047] Furthermore, the main reason for not designing the first barrier 430 and the second barrier 440 to be of equal height is to ensure the maximum outer circumference of the barrier mixing head 400. This maximum outer circumference directly affects the clearance between the screw and barrel 700. If the first barrier 430 and the second barrier 440 were of equal height, the outer circumference of the barrier mixing head 400 would be reduced by one circle, which would increase the clearance between the screw and barrel 700. Proper clearance is crucial for material conveying, shearing, and mixing. If the clearance is too large, material conveying efficiency will be reduced, shearing forces will be weakened, and mixing will be affected. If the clearance is too small, material flow will be impeded, increasing energy consumption and reducing 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, and each kneading block 510 is evenly spaced in the circumferential direction and the axial direction of the extrusion section 140. The kneading blocks 510 are diamond-shaped protruding structures, and the kneading blocks 510 are arranged at an angle.

[0049] The evenly distributed mixing blocks 510 ensure that the material is uniformly sheared and mixed as it passes through the mixing and kneading head 500, avoiding localized under-mixing or over-mixing. Each mixing block 510 has a diamond-shaped raised structure, which provides more shear surfaces and increases the shear force on the material as it passes through the mixing blocks 510. The tilted arrangement of the mixing blocks 510 also increases the shearing effect on the material as it passes through, helping to refine the material and improve the uniformity of its mixing. The diamond-shaped raised structure promotes smoother material flow, reduces the material's residence time at the mixing blocks 510, avoids localized overheating and thermal degradation, improves the thermal stability of the material, and further increases 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. Due to the greater bottom groove depth of the second screw flight 300, shear force is reduced and flow velocity is controlled, thereby increasing production capacity, releasing extrusion pressure, helping to reduce the risk of thermal degradation of the material, and improving the thermal stability of the material.

[0051] Specifically, the area where the second screw flight 300 is located is called the releasing extrusion section. 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 、 Figure 9 As shown, based on the above embodiment, internal cooling and heat conduction holes 160 are opened in the screw body 100, and the internal cooling and heat conduction 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 internal cooling holes 160 are generally used to pass a cooling medium (such as water or cooling oil) to remove heat from 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 kept at a constant temperature.

[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 along the circumference of the screw body 100 and arranged in a circle, 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 pins 610 can cut and disperse the material, ensuring that the various components are more evenly distributed in the material. The pins 610 are evenly arranged along the circumference, and can shear and mix the material at multiple points to improve the mixing effect. The short cylindrical structure of the pins 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 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 the 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 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 uniform and fixed. However, in this device, there are at least four different fitting 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 flight 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 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, avoiding 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 rate and pressure of materials, optimize the entire production process, improve production efficiency, significantly improve the mixing uniformity of materials, control the flow rate and pressure of materials, and optimize heat exchange.

[0061] Example 1:

[0062] like Figure 6 As shown, the inner 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-volume, low-energy production requirements. The smooth inner bore reduces friction between the material and the inner wall of barrel 700, lowering the energy required to drive the screw and thus reducing energy consumption. Furthermore, reduced friction improves material feeding efficiency, ensuring smooth material entry into the screw and minimizing losses during the feeding process.

[0064] Example 2:

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

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

[0067] Example 3:

[0068] like Figure 8As shown, a portion of the inner wall of the barrel 700 near the feed port is provided with a plurality of spiral grooves 720 evenly distributed 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 (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the various 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, terms such as "first," "second," and "an" in this utility model are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this utility model, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0072] In this utility model, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. For those skilled in the art, the specific meanings of the above terms in this utility model 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 this field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this utility model.

Claims

1. An extrusion screw for producing PVC cast film, characterized in that, include: A screw body (100) includes a feed section (110), a compression and homogenization section (120), a plasticizing 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 and homogenization section (120), and the plasticizing section (130). The second screw fin (300) is distributed on the extrusion section (140). The extrusion section (140) is provided with a barrier mixing head (400) and a stirring mixing head (5 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 of equal-diameter shaft structure, the diameter of the feeding section (110) is smaller than the diameter of the plasticizing section (130), the compression homogenizing section (120) is of 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 according to claim 1, characterized in that: The side surface of the first screw flight (200) facing the head of the screw body (100) has a front R angle (210), and the side surface 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 configured to have a structure with a gradually changing angle along the spiral direction of the first screw flight (200).

3. An extrusion screw for producing PVC cast film according to claim 1, characterized in that: The barrier mixing head (400) includes a plurality of forward screw grooves (410) and reverse screw grooves (420) arranged alternately 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 the reverse screw grooves (420) are both configured as single-opening inclined groove structures, the forward screw groove (410) is open at one end toward the plasticizing section (130) and the groove depth gradually decreases toward one end of the extrusion section (140) to form a closed end, and the reverse screw groove (420) is closed at one end toward 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 pass through the closed end of the forward screw groove (410) to flow to the extrusion section (140), and at the same time, the liquid phase material in the forward screw groove (410) passes through the barrier part and enters the reverse screw groove (420) and flows through the opening of the reverse screw groove (420) to the extrusion section (140).

4. An extrusion screw for producing PVC cast film according to 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 barrier (440) is lower than the height of the first barrier (430).

5. An extrusion screw for producing PVC cast film according to claim 4, characterized in that: 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). The kneading blocks (510) are diamond-shaped protruding structures, and the kneading blocks (510) are arranged obliquely.

6. The 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 conduction holes (160) along its axial direction, and the internal cooling and heat conduction 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 according to any one of claims 1 to 8, and also comprises a barrel (700), wherein the screw body (100) of the extrusion screw for producing PVC cast film is rotatably mounted in the barrel (700), and the barrel (700) has a feed port, which corresponds to the feed section (110) of the screw body (100), and 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.

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

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