A plastic recycling based pet sheet melt extrusion molding device and method

Abstract

The application relates to the technical field of hot melting and discloses a PET sheet melting extrusion forming device and method based on plastic recycling, which comprises a barrel mounted on a hot melting device, the inside of the barrel is provided with a rotatable screw, the barrel is sequentially divided into a front section, a middle section and a rear section along a material extrusion direction, the front section and the rear section of the barrel are both provided with heating devices, and the outer wall of the middle section of the barrel is covered with a heat preservation layer. By arranging external heating devices in the front section and the rear section of the barrel, arranging a heat preservation layer in the middle section, arranging internal heating devices in the middle section of the screw, and arranging internal cooling devices in the front section and the rear section, an axial heat source alternative layout of 'external heating and internal cooling -> external heat preservation and internal heating -> external heating and internal cooling' is formed.

Description

Technical Field

[0001] This invention relates to the field of hot melt technology, specifically to a PET sheet melt extrusion molding apparatus and method based on plastic recycling. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in beverage bottles, packaging sheets, and other fields due to its excellent mechanical and processing properties. With the development of the circular economy, the reuse of recycled PET (r-PET) is receiving increasing attention. However, r-PET undergoes molecular chain degradation to some extent during repeated thermal processing, significantly increasing its temperature sensitivity. It is highly susceptible to thermal degradation during processing, leading to defects such as black spots, crystal points, and scorched material in the sheets, severely limiting the reuse value of r-PET.

[0003] In the melt extrusion molding process of PET sheets, temperature control is one of the core factors determining product quality. Current technologies generally employ segmented heating of the barrel's outer wall, with heat conducted from the outside in. Due to PET's poor thermal conductivity, this unidirectional heat transfer results in extremely uneven radial temperature distribution of the material: material near the inner wall of the barrel remains in a high-temperature zone for extended periods, making it prone to overheating and degradation, producing black spots and scorched material; while material near the screw root has a lower temperature, resulting in insufficient plasticization and the formation of unmelted "crystal points" or "lumps." This radial temperature difference is persistent and cannot be completely eliminated through conventional temperature control methods.

[0004] To improve melt uniformity, some existing technologies install multiple heaters on the outer wall of the barrel and use multi-point temperature detection to achieve segmented temperature control. However, these measures are still limited to the basic framework of external barrel heating. The direction of heat conduction is always from the outside to the inside, and the radial temperature gradient of the material never reverses. Active radial convection and forced heat exchange cannot be formed between the inner and outer layers of material, and it is difficult to achieve rapid temperature homogenization by relying solely on slow heat conduction.

[0005] Regarding screw temperature control, existing technologies employ methods to achieve overall cooling by introducing a cooling medium into the screw core, thus maintaining a uniform screw temperature. However, this approach only cools the screw as a whole and cannot achieve independent temperature control in axial segments, nor can it create an alternating axial heat source layout with the barrel heating. Furthermore, existing screw geometries are mostly single designs with equal or gradually varying pitches, lacking a radial mixing structure that coordinates with the heat source layout. The melt flow within the screw channel remains predominantly laminar, making forced exchange of materials between the inner and outer layers difficult. Therefore, this invention provides a PET sheet melt extrusion molding apparatus and method based on plastic recycling. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a PET sheet melt extrusion molding apparatus and method based on plastic recycling, which solves the problems in existing technologies where heat is always conducted from the outside to the inside, the radial temperature gradient direction is never reversed, and the inner and outer layers of materials rely solely on slow heat conduction, making it impossible to form active radial circulation and forced heat exchange, resulting in low temperature homogenization efficiency.

[0007] The present invention provides the following technical solution: a PET sheet melt extrusion molding device based on plastic recycling, including a barrel installed on a hot melt equipment, and a rotatable screw is provided inside the barrel. The barrel is divided into a front section, a middle section and a rear section in sequence along the material extrusion direction. The front section and the rear section of the barrel are provided with heating devices, and the outer wall of the middle section of the barrel is covered with a heat insulation layer. The screw is divided into a front section, a middle section and a rear section along the material extrusion direction; the screw is equipped with a temperature control structure, which heats the middle section of the screw and cools the front and rear sections. The front, middle, and rear sections of the barrel correspond one-to-one with the front, middle, and rear sections of the screw in the axial direction, forming an alternating layout of axial heat sources along the extrusion direction. The melt in the front section of the barrel is subjected to external heating and internal cooling, resulting in heat transfer from the outside to the inside. The melt in the middle section is subjected to external insulation and internal heating, resulting in alternating heat transfer from the inside to the outside. The melt in the rear section resumes heat transfer from the outside to the inside. This causes the radial temperature gradient direction of the melt to be reversed twice during the extrusion process, inducing internal circulation and radial mixing of the melt to eliminate the risk of local overheating and coking, and to improve the uniformity of melt temperature and composition.

[0008] Preferably, the outer diameter of the front and middle sections of the screw is consistent, and the pitch of the spiral blades decreases sequentially along the extrusion direction, which is used to achieve gradual compression and plasticization of the material in the feeding section and the compression section, thereby improving the solid conveying efficiency and melting rate. The outer diameter of the rear section of the screw gradually decreases and becomes conical along the extrusion direction, which is adapted to the conical inner wall of the rear section of the barrel. The pitch of the spiral blades in the rear section of the screw remains unchanged while the depth of the screw groove gradually becomes shallower. This is used to force shearing and pressurize the molten plastic in the metering section, thereby improving the uniformity of melt mixing and the stability of extrusion.

[0009] Preferably, the front section of the screw has a mixing element that spans the screw groove in the screw groove between two adjacent helical blades; when the screw rotates, the mixing element guides the material layer near the inner wall of the barrel toward the screw axis, causing the molten plastic to undergo radial tumbling.

[0010] Preferably, the mixing element has a triangular cross-section that extends along the axial and radial directions of the screw. Its outer side is flush with the arc surface of the screw's outer diameter, and its inner sides are symmetrical arc surfaces. The arc surfaces guide the molten plastic, thus introducing the molten plastic from the inner wall of the barrel inward.

[0011] Preferably, the middle section of the screw is provided with a conical protrusion located between two helical blades. The conical protrusion is disposed on the axial surface of the screw and consists of two symmetrically designed arc surfaces, which guide the molten plastic near the axial surface of the screw outward.

[0012] Preferably, the temperature control structure includes a front cavity, a middle cavity, and a rear cavity arranged sequentially along the screw axis, with each cavity being independent or interconnected; two front insulation pipes are provided in the front cavity of the screw, with the ends of the two front insulation pipes extending to both ends of the front cavity respectively, for introducing cooling medium to cool the front section of the screw; the two front insulation pipes extend rearward from the front cavity of the screw, sequentially passing through the middle cavity and the rear cavity of the screw, and are led out from the tail end of the screw; Two mid-section heat-insulating pipes are provided in the cavity of the middle section of the screw, which are used to introduce heating medium to heat the middle section of the screw. The two heating heat-insulating pipes also extend backward, pass through the rear cavity and are led out from the tail end of the screw. Two rear section insulation pipes are provided in the cavity of the screw section to allow cooling medium to be introduced to cool the rear section of the screw, and the two rear section insulation pipes are led out from the tail end of the screw. The front cavity, middle cavity, and rear cavity have the same internal structure, but are circulated with media of different temperatures to achieve segmented temperature control; the insulation pipe is isolated from the media in the corresponding cavity when it passes through the rear cavity.

[0013] A method for melt extrusion molding of PET sheets based on plastic recycling, the specific operation is as follows: Step 1: Preheating and Temperature Setting The heating devices of the front and rear sections of the barrel are started. At the same time, the cooling medium is introduced into the front and rear cavities and the heating medium is introduced into the middle cavity through the temperature control structure, so that the front and rear sections of the barrel reach the state of external heat and internal cold. The middle section of the barrel forms an external heat insulation and internal heat state through the internal heating of the middle section of the screw. Along the extrusion direction, an axial heat source alternating layout of "external heat and internal cold → external heat insulation and internal heat → external heat and internal cold" is formed. Step 2: Feeding and Solid Conveying Plastic granules are added to the feed inlet of the barrel, and the screw rotates to drive the material forward. In the front section of the screw, the pitch of the spiral blades gradually decreases, compressing the material step by step. At the same time, the external heat and internal cooling of the front section of the barrel softens the surface of the material and keeps the core at a low temperature, preventing it from sticking to the screw too early. Step 3: Metering and Extrusion The material enters the rear section of the barrel. The outer diameter of the rear section of the screw is conical, and the pitch of the spiral blades remains unchanged while the depth of the screw groove becomes shallower. It cooperates with the conical inner wall of the rear section of the barrel to force shearing and pressurize the melt. At the same time, the external heat and internal cooling of the rear section of the barrel maintains the surface temperature of the melt, so that the melt is extruded from the die head at a uniform temperature and pressure.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) By setting external heating devices in the front and rear sections of the barrel and a heat insulation layer in the middle section, and setting internal heating devices in the middle section of the screw and internal cooling devices in the front and rear sections, an alternating axial heat source layout of "external heat and internal cooling → external heat insulation and internal heat → external heat and internal cooling" is formed. During the extrusion process, the material undergoes three different heat transfer modes: from the outside to the inside, from the inside to the outside, and then from the outside to the inside again. The radial temperature gradient direction is reversed twice, inducing natural convection and forced circulation inside the melt. This design fundamentally solves the problems of local overheating, coking, black spots, and degradation caused by the material near the inner wall of the barrel being in a high-temperature state for a long time in traditional extruders, and significantly improves the processing quality and product qualification rate of recycled PET sheets.

[0015] (2) A triangular cross-section mixing element spanning the screw groove is set at the front section of the screw, and a conical protrusion is set at the middle section of the screw. The two are staggered in the axial direction and complement each other in function. The mixing element scoops up and guides the high-temperature melt near the inner wall of the barrel towards the screw axis, while the conical protrusion guides the lower-temperature melt near the axis to the outer periphery. The two work together to form a complete radial circulation loop in the screw groove. This structure enables forced exchange between the inner and outer layers of melt, greatly improves radial temperature uniformity and component dispersion, and effectively avoids melt viscosity differences and internal stress in the product caused by temperature inhomogeneity.

[0016] (3) The front and middle sections of the screw have the same diameter and the pitch gradually decreases, which implements gradual mechanical compression of the material. This, combined with the externally heated and internally cooled heat source layout, achieves a smooth transition from cold to hot melting in the feeding section. The rear section of the screw is conical with a constant pitch and a gradually shallower screw groove depth, which matches the conical inner wall of the rear section of the barrel. This allows for forced shearing and pressurization of the melt in the metering section. This geometric structure and the alternating layout of the heat source complement each other functionally, forming a dual synergistic effect of mechanical compression and thermal field control. This not only improves the solid conveying efficiency and melting rate but also ensures the stability of extrusion pressure and flow rate. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the specific structure of the present invention; Figure 2 This is a schematic diagram of the screw structure of the present invention; Figure 3 This is a schematic diagram of the temperature control structure of the present invention.

[0018] In the diagram: 1. Barrel; 2. Screw; 3. Heating device; 4. Insulation layer; 5. Temperature control structure; 6. Mixing element; 7. Conical protrusion; 51. Front insulation pipe; 52. Middle insulation pipe; 53. Rear insulation pipe. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. In order to keep the following description of the embodiments of this disclosure clear and concise, detailed descriptions of known functions and known components are omitted to avoid unnecessarily obscuring the concept of the present invention.

[0020] Please see Figure 1 This embodiment provides a PET sheet melt extrusion molding apparatus based on plastic recycling, including a barrel 1 arranged horizontally along the axial direction and a screw 2 coaxially disposed within the barrel. The barrel 1 is divided into a front section, a middle section, and a rear section along the material extrusion direction. Heating devices 3 are installed on the outer walls of the front and rear sections of the barrel for external heating of the front and rear sections, respectively. The outer wall of the middle section of the barrel is covered with an insulation layer 4, and this section is not equipped with an active heating or cooling device. The screw 2 is divided into a front section, a middle section, and a rear section along the extrusion direction, and has a temperature control structure 5 inside. This temperature control structure heats the middle section of the screw and cools the front and rear sections of the screw, thereby forming an alternating heat source layout of the barrel and screw in the axial direction: the front section is externally heated and internally cooled, the middle section is externally insulated and internally heated, and the rear section is externally heated and internally cooled.

[0021] The heating devices 3 at the front and rear sections of the barrel generate external heating, while the corresponding front and rear sections of the screw are cooled, forming a "heated outside, cooled inside" heat source layout. The middle section of the barrel relies on the insulation layer 4 to reduce heat loss, while the corresponding middle section of the screw is heated, forming a "heated outside, cooled inside" heat source layout. Thus, along the extrusion direction, an alternating axial heat source layout of "heated outside, cooled inside → heated outside, cooled inside → heated outside, cooled inside" is formed sequentially. When the material enters the barrel from the feed port, it passes through the front, middle, and rear sections sequentially under the push of the screw, experiencing three different heat transfer modes: heating from the outside in, heating from the inside out, and heating from the outside in again. The radial temperature gradient direction is reversed twice, inducing natural convection and forced circulation within the melt, significantly improving the radial mixing effect and effectively eliminating the risk of local overheating and material coking.

[0022] See Figure 2 and Figure 3The temperature control structure 5 is specifically configured as follows: A front cavity, a middle cavity, and a rear cavity are arranged sequentially along the axial direction of the screw 2. Two front insulation pipes 51 are installed in the front cavity, with their ends extending to both ends of the front cavity for introducing cooling medium to cool the front section of the screw. The two front insulation pipes 51 extend rearward from the front cavity, passing through the middle cavity and the rear cavity sequentially, and exiting from the tail end of the screw, maintaining isolation from the medium in the corresponding rear cavity. Two middle insulation pipes 52 are installed in the middle cavity for introducing heating medium to heat the middle section of the screw. These two insulation pipes also extend rearward through the rear cavity and exit from the tail end of the screw. Two rear insulation pipes 53 are installed in the rear cavity for introducing cooling medium to cool the rear section of the screw. These two insulation pipes exit directly from the tail end of the screw. The three cavities have the same internal structure, but are circulated with media of different temperatures, thereby achieving independent temperature control of the screw in three axial sections.

[0023] The front cavity of screw 2 is cooled to reduce the temperature of the molten plastic, effectively suppressing premature melting in the feeding section and ensuring stable operation of the solid conveying zone. The moderate cooling of the front section can prevent the melt from adhering excessively to the surface of screw 2, making the melt more inclined to adhere to the inner wall of the barrel, thereby forming a good molten "cushion" and promoting subsequent melting and mixing. The rear cavity of the screw is cooled to prevent degradation caused by localized overheating. Thermal degradation can easily occur over a long period or at excessively high temperatures, leading to a decrease in the mechanical properties of the product. Appropriate cooling can appropriately increase the apparent viscosity of the melt, which is beneficial for pressure build-up and stable discharge, avoiding pressure fluctuations and extrusion instability caused by excessively low melt viscosity.

[0024] Based on the alternating axial heat source layout, the geometry of screw 2 further enhances the plasticizing and mixing effect of the material. The outer diameter of the front and middle sections of the screw remains consistent, and the pitch of the helical blades gradually decreases along the extrusion direction, causing the material to undergo progressively stronger mechanical compression during its advancement, compacting the solid bed and rapidly melting it. The outer diameter of the rear section of the screw gradually decreases along the extrusion direction, forming a conical shape that matches the conical design of the inner wall of the rear section of the barrel 1. At the same time, the pitch of the helical blades in the rear section of the screw remains constant, while the screw groove depth gradually becomes shallower, thereby subjecting the molten PET material to forced shearing and pressurization in the metering section, improving the uniformity of melt mixing and extrusion stability.

[0025] To further enhance the forced mixing of the melt in the radial direction and avoid local overheating and charring, a mixing element 6 is installed across the screw groove between two adjacent helical blades at the front section of the screw. The mixing element 6 has a triangular cross-section, extending along the screw's axial and radial directions. Its outer side is flush with the arc surface of the screw's outer diameter, and its inner sides are symmetrical arc surfaces. There is a gap between the mixing element 6 and the screw's axial surface, allowing material to pass through. When the screw rotates, the mixing element scoops up and guides the high-temperature material layer near the inner wall of the barrel towards the screw axis, causing the molten plastic to undergo radial tumbling, thereby achieving forced exchange between the outer high-temperature melt and the inner lower-temperature melt.

[0026] Meanwhile, a conical protrusion 7 is provided on the axial surface between two adjacent helical blades in the middle section of the screw. This conical protrusion has two symmetrically designed arc surfaces. Contrary to the function of the mixing element, the conical protrusion 7 guides the molten plastic near the screw axial surface outwards, causing the inner layer material to move towards the outer periphery. The mixing element 6 and the conical protrusion 7 are arranged in a staggered axial direction, and together they form a complete radial circulation loop within the screw groove: the high-temperature melt is pushed towards the axis by the mixing element, and the low-temperature melt is pushed towards the outer periphery by the conical protrusion, thereby significantly improving the heat exchange efficiency of the inner and outer layers and making the temperature distribution of the entire melt system more uniform.

[0027] This embodiment provides an operating method for a PET sheet melt extrusion molding apparatus based on plastic recycling, comprising the following steps: Step 1: Preheating and Temperature Setting The heating devices 3 for the front and rear sections of the barrel are activated. Simultaneously, cooling medium is introduced into the front and rear cavities and heating medium is introduced into the middle cavity through the temperature control structure 5. This achieves an externally heated and internally cooled state for the front and rear sections of the barrel. The middle section of the barrel, relying on the insulation layer 4 and the internal heating of the screw section, forms an externally insulated and internally heated state. Along the extrusion direction, an alternating axial heat source layout of "external heat and internal cooling → external insulation and internal heating → external heat and internal cooling" is formed. Preheating is completed after the temperature of each section stabilizes.

[0028] Step 2: Feeding and Solid Conveying The recycled PET sheets are added to the feed inlet of the barrel, and the screw 2 is started to rotate. The material is mechanically compressed by the gradually decreasing pitch of the helical blades at the front of the screw. At the same time, the external heat and internal cooling of the front section of the barrel softens the surface of the material while keeping the core at a lower temperature, preventing the material from sticking to the screw too early and achieving stable solid conveying.

[0029] Step 3: Melting and Radial Mixing After the material enters the middle section of the barrel, the internal heating of the screw section heats the material from the inside out, forming an "external insulation and internal heating" state. At this time, the mixing element 6 scoops up and guides the high-temperature melt near the inner wall of the barrel towards the screw axis, while the conical protrusion 7 discharges the lower-temperature melt near the screw axis to the outside. The two work together to cause the melt to generate forced radial tumbling and circulation, which, together with the insulation layer in the middle section of the barrel, achieves internal heat exchange and temperature homogenization of the melt.

[0030] Step 4: Metering and Extrusion After the material enters the rear section of the barrel, the external heating of the rear section of the barrel and the cooling of the rear section of the screw return to the "external heat and internal cold" state, and the radial temperature gradient of the melt reverses again. At the same time, the conical outer diameter of the rear section of the screw matches the conical inner wall of the rear section of the barrel, the screw pitch of the helical blades remains unchanged while the screw groove depth gradually becomes shallower, which applies forced shearing and pressure to the melt, so that the melt is extruded from the die head with uniform temperature and pressure.

[0031] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A PET sheet melt extrusion molding apparatus based on plastic recycling, comprising a barrel (1) installed on a hot melt equipment, wherein a rotatable screw (2) is provided inside the barrel (1), characterized in that: The barrel (1) is divided into a front section, a middle section and a rear section in sequence along the material extrusion direction. The front section and the rear section of the barrel (1) are equipped with heating devices (3), and the outer wall of the middle section of the barrel (1) is covered with a heat insulation layer (4). The screw (2) is divided into a front section, a middle section and a rear section in sequence along the material extrusion direction; the screw (2) is provided with a temperature control structure (5), and the temperature control structure (5) heats the middle section of the screw (2) while cooling the front and rear sections; The front, middle, and rear sections of the barrel (1) correspond one-to-one with the front, middle, and rear sections of the screw (2) in the axial direction, forming an alternating layout of axial heat sources along the extrusion direction. The melt in the front section of the barrel (1) is subjected to external heat and internal cooling, forming heat transfer from the outside to the inside. The melt in the middle section is subjected to external insulation and internal heat, forming alternating heat transfer from the inside to the outside. The melt in the rear section resumes heat transfer from the outside to the inside, causing the radial temperature gradient direction of the melt to be reversed twice during the extrusion process, inducing internal circulation and radial mixing of the melt to eliminate the risk of local overheating and coking, and improve the uniformity of melt temperature and composition.

2. The PET sheet melt extrusion molding apparatus based on plastic recycling according to claim 1, characterized in that: The outer diameter of the front and middle sections of the screw (2) is consistent, and the pitch of the spiral blades along the extrusion direction gradually decreases, which is used to realize the gradual compression and plasticization of the material in the feeding section and the compression section, thereby improving the solid conveying efficiency and melting rate. The outer diameter of the rear section of the screw (2) gradually decreases along the extrusion direction and becomes conical, which is compatible with the conical inner wall of the rear section of the barrel (1). The pitch of the spiral blades in the rear section of the screw (2) remains unchanged while the depth of the spiral groove gradually becomes shallower. This is used to force shearing and pressurize the molten plastic in the metering section to improve the uniformity of melt mixing and the stability of extrusion.

3. The PET sheet melt extrusion molding apparatus based on plastic recycling according to claim 1, characterized in that: The front section of the screw (2) is provided with a mixing element (6) that spans the screw groove between two adjacent spiral blades; when the screw rotates, the mixing element (6) guides the material layer near the inner wall of the barrel toward the screw axis, causing the molten plastic to undergo radial flipping.

4. The PET sheet melt extrusion molding apparatus based on plastic recycling according to claim 3, characterized in that: The mixing element (6) has a triangular cross section and extends along the axial and radial directions of the screw. Its outer side is flush with the arc surface of the screw's outer diameter, and its inner sides are symmetrical arc surfaces. The arc surfaces guide the molten plastic and introduce the molten plastic from the inner wall of the barrel inward.

5. The PET sheet melt extrusion molding apparatus based on plastic recycling according to claim 1, characterized in that: The screw (2) has a conical protrusion (7) located between two helical blades in the middle section. The conical protrusion (7) is set on the axial surface of the screw (2) and has two symmetrically designed arc surfaces to guide the molten plastic near the axial surface of the screw (2) outward.

6. The PET sheet melt extrusion molding apparatus based on plastic recycling according to claim 1, characterized in that: The temperature control structure (5) includes a front cavity, a middle cavity and a rear cavity arranged sequentially along the axial direction of the screw (2), and each cavity is independent or connected to each other; the front cavity of the screw (2) is provided with two front insulation pipes (51), the ends of the two front insulation pipes (51) extend to both ends of the front cavity respectively, and are used to introduce cooling medium to cool the front section of the screw; the two front insulation pipes (51) extend backward from the front cavity of the screw, pass through the middle cavity and the rear cavity of the screw in sequence, and are led out from the tail end of the screw; Two middle section heat insulation pipes (52) are provided in the middle section cavity of the screw (2) for introducing heating medium to heat the middle section of the screw. The two heating heat insulation pipes also extend backward, pass through the rear section cavity and are led out from the tail end of the screw. Two rear section insulation pipes (53) are provided in the cavity of the rear section of the screw (2) for cooling medium to be introduced to cool the rear section of the screw, and the two rear section insulation pipes (53) are led out from the tail end of the screw; The front cavity, middle cavity, and rear cavity have the same internal structure, but are circulated with media of different temperatures to achieve segmented temperature control. When the insulation pipe passes through the rear cavity, it remains isolated from the medium inside the corresponding cavity.

7. A method for melt extrusion molding of PET sheets based on plastic recycling, characterized in that, The specific operation of the PET sheet melt extrusion molding apparatus based on plastic recycling as described in any one of claims 1-6 is as follows: Step 1: Preheating and Temperature Setting Start the heating devices (3) of the front and rear sections of the barrel, and at the same time, through the temperature control structure (5), the cooling medium is introduced into the front cavity and the rear cavity, and the heating medium is introduced into the middle cavity, so that the front and rear sections of the barrel reach the state of external heat and internal cold. The middle section of the barrel forms an external heat insulation and internal heat state through the heat insulation layer (4) and the internal heating of the middle section of the screw. Along the extrusion direction, an axial heat source alternating layout of "external heat and internal cold → external heat insulation and internal heat → external heat and internal cold" is formed. Step 2: Feeding and Solid Conveying Plastic granules are added to the feed inlet of the barrel (1), and the screw (2) rotates to drive the material forward. In the front section of the screw, the pitch of the spiral blades gradually decreases, compressing the material gradually. At the same time, the external heat and internal cold of the front section of the barrel cause the surface of the material to soften and the core to maintain a low temperature, preventing premature adhesion to the screw. Step 3: Metering and Extrusion The material enters the rear section of the barrel. The outer diameter of the rear section of the screw is conical, and the pitch of the spiral blades remains unchanged while the depth of the screw groove becomes shallower. It cooperates with the conical inner wall of the rear section of the barrel to force shearing and pressurize the melt. At the same time, the external heat and internal cooling of the rear section of the barrel maintains the surface temperature of the melt, so that the melt is extruded from the die head at a uniform temperature and pressure.

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