A double-walled hollow plastic pipe extrusion equipment

Abstract

This utility model discloses a double-walled hollow plastic pipe extrusion equipment, belonging to the field of plastic pipe extrusion technology. It includes: an extruder, a die, and a die head connected in sequence. The die has an outer spiral and an inner spiral, each having an outer extension channel and an inner extension channel extending into the die head, respectively. Multiple circumferentially arranged connecting channels are provided between the outer and inner extension channels. A mandrel between adjacent connecting channels is used to form the hollow layer between the inner and outer layers of the pipe. The mandrel has a hollow layer exhaust channel communicating with the hollow layer. An outer sizing sleeve and an inner sizing sleeve, each having an outer water cooling system and an inner water cooling system, respectively. A middle exhaust fan ring cools the hollow layer through the hollow layer exhaust channel. This "external cooling - internal cooling - hollow exhaust" three-in-one cooling system solves the problem of uneven cooling in traditional processes, improving the dimensional accuracy, surface quality, and structural stability of the pipe.

Description

Technical Field

[0001] This utility model belongs to the field of plastic pipe extrusion technology, specifically relating to a double-walled hollow plastic pipe extrusion equipment. Background Technology

[0002] Double-walled hollow plastic pipes typically consist of a thick outer wall, an inner wall, a hollow cavity between them, and connecting ribs. In existing extrusion molding processes, the outer diameter vacuum sizing method is commonly used to cool and shape the pipe. This method mainly achieves stable control of the outer diameter by applying vacuum adsorption and external water spray cooling to the outer surface of the pipe.

[0003] However, since the cooling effect is mainly concentrated on the outer wall, the inner wall of the pipe lacks an effective direct cooling method, resulting in an inconsistent cooling rate between the inner and outer walls: the outer layer cools and solidifies rapidly, while the inner layer cools slowly because the heat is difficult to dissipate in time.

[0004] This uneven cooling phenomenon causes significant differences in thermal shrinkage, generating large residual internal stress inside the pipe. This can easily lead to defects such as pipe deformation, inner wall collapse, or surface roughness, seriously affecting the product's dimensional stability, surface quality, and mechanical properties. Utility Model Content

[0005] This invention addresses the aforementioned problems in the existing technology by proposing a double-walled hollow plastic pipe extrusion device that can achieve simultaneous and efficient cooling of the inner and outer walls of the pipe.

[0006] This utility model can be achieved through the following technical solutions:

[0007] A double-walled hollow plastic pipe extrusion device, characterized in that it comprises:

[0008] The extruder, die, and orifice are connected in sequence.

[0009] The mold is provided with an outer spiral body and an inner spiral body arranged coaxially. The outer spiral body and the inner spiral body respectively have an outer extension flow channel and an inner extension flow channel extending into the die.

[0010] The outer extension channel and the inner extension channel are provided with multiple connecting channels at the outlet end near the mold, and the multiple connecting channels are arranged in a circumferential ring. The mandrel provided between adjacent connecting channels is used to form the hollow layer between the inner and outer layers of the tube. The mandrel is provided with a hollow layer air extraction channel, which is connected to the hollow layer.

[0011] An outer sizing sleeve and an outer water cooling system are provided. The outer sizing sleeve is located at the mold outlet end and is used for vacuum adsorption of the outer circumferential surface of the pipe. The outer water cooling system is positioned towards the outer sizing sleeve and the pipe.

[0012] The inner sizing sleeve and the inner water cooling system are provided. The inner sizing sleeve is located at the outlet end of the mold and fits against the inner wall of the pipe. The inner water cooling system is integrated into the inner sizing sleeve and is used to cool the inner wall of the pipe.

[0013] A middle-layer exhaust fan ring is disposed on the end face of the mold away from the outlet end. The middle-layer exhaust fan ring exhausts and cools the hollow layer through the hollow layer exhaust channel.

[0014] As a further improvement of this utility model, the extruder is eccentrically disposed on the end face of the mold or disposed on the side of the mold. The extruder and the mold are connected by a connecting body. The connecting body has an independent outer feeding channel and an inner feeding channel. The outer feeding channel is connected to the flow channel of the outer spiral body, and the inner feeding channel is connected to the flow channel of the inner spiral body.

[0015] As a further improvement of this utility model, the connecting body is provided with two flow regulating valves, which are used to regulate the flow of the outer layer feed channel and the inner layer feed channel respectively.

[0016] As a further improvement of this utility model, it also includes a vacuum shaping machine, which is located at the outlet end of the mold, and the outer sizing sleeve and the inner sizing sleeve are both located inside the vacuum shaping machine.

[0017] As a further improvement of this utility model, the vacuum shaping machine is provided with a plurality of nozzles arranged in a ring along its length direction, and the nozzles are arranged toward the outer sizing sleeve and the pipe to form the outer water cooling system.

[0018] As a further improvement of this utility model, the mold has a channel along its central axis, and a central exhaust pipe extending outward is provided in the channel.

[0019] As a further improvement of this utility model, the inner sizing sleeve includes an inner sleeve and an outer sleeve, and a cooling channel is formed between the inner sleeve and the outer sleeve. The cooling channel is used to inject cooling water to form the inner water cooling system.

[0020] It also includes an inner fixed-sizing sleeve inlet pipe and an inner fixed-sizing sleeve outlet pipe, both of which are introduced inward from the channel and are respectively connected to the cooling flow channel.

[0021] As a further improvement of this utility model, a heat insulation pad is provided on the contact surface between the inner sizing sleeve and the mold.

[0022] As a further improvement of this utility model, it also includes a spray nozzle and a spray nozzle inlet pipe. The spray nozzle is located in the inner cavity of the pipe and is disposed facing the inner wall of the pipe. The spray nozzle inlet pipe is introduced into the pipe from the channel and connected to the spray nozzle.

[0023] As a further improvement of this utility model, the middle layer exhaust ring is connected to each of the hollow layer exhaust channels, and the external negative pressure system extracts the gas in the hollow layer through the middle layer exhaust ring and the hollow layer exhaust channels.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Achieve coordinated cooling of the inner and outer walls and the hollow layer to eliminate internal stress.

[0026] Through the synergistic effect of the outer sizing sleeve (in conjunction with the outer water cooling system), the inner sizing sleeve (in conjunction with the inner water cooling system), and the middle exhaust ring, a three-in-one cooling system of "external cooling - internal cooling - hollow exhaust" is formed, which effectively solves the problem of uneven cooling in traditional processes, significantly reduces internal stress, prevents deformation, and improves the dimensional accuracy and structural stability of the pipe.

[0027] 2. Simultaneous internal and external shaping ensures high precision and surface quality.

[0028] The inner and outer sizing sleeves are simultaneously fitted to the pipe wall, and with the help of vacuum shaping, the inner and outer diameters are accurately shaped. The outer surface of the inner sizing sleeve has a tapered design and a polished chrome-plated surface treatment to reduce frictional resistance, avoid scratches and collapse, and greatly improve the roundness, smoothness and production smoothness of the pipe.

[0029] 3. Structural integration and optimization enhance process flexibility and production efficiency.

[0030] The extruder features a lateral layout, integrated cooling and extraction piping in the central channel, independent feed belt flow regulation, and refrigeration design, achieving a high degree of functional integration and precise process control. This adapts to the production needs of multiple specifications, shortens the shaping and cooling length, and improves cooling efficiency and continuous production stability. Attached Figure Description

[0031] Figure 1 This is a cross-sectional view of the double-walled hollow plastic pipe extrusion equipment of this utility model (the extruder is installed on the side of the mold);

[0032] Figure 2 This is a cross-sectional view of the double-walled hollow plastic pipe extrusion equipment of this utility model (the extruder is eccentrically mounted at the end of the die);

[0033] Figure 3 This is a cross-sectional view of the pipe of this utility model.

[0034] In the diagram, 100 is the extruder; 110 is the connector; 111 is the outer feed channel; 112 is the inner feed channel; and 113 is the flow regulating valve.

[0035] 200. Mold; 210. Die; 220. Outer spiral; 221. Outer extended flow channel; 230. Inner spiral; 231. Inner extended flow channel;

[0036] 300. Outer sizing sleeve;

[0037] 400, Inner sizing sleeve; 410, Inner sleeve; 420, Outer sleeve; 430, Cooling channel; 440, Inner sizing sleeve inlet pipe; 450, Inner sizing sleeve outlet pipe;

[0038] 500. Middle layer exhaust fan ring; 510. Hollow layer exhaust channel;

[0039] 600. Vacuum setting machine; 610. Nozzle;

[0040] 700. Central exhaust duct;

[0041] 800. Spray nozzle; 810. Spray nozzle inlet pipe;

[0042] 900. Thermal insulation gasket;

[0043] 1000, Pipe; 1100, Hollow layer. Detailed Implementation

[0044] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. The technical methods of the present invention will be further described, but the present invention is not limited to these embodiments.

[0045] like Figures 1-3 As shown, this utility model provides a double-walled hollow plastic pipe extrusion device, comprising:

[0046] The extruder 100, the die 200, and the orifice 210 are connected in sequence.

[0047] The mold 200 is provided with an outer spiral 220 and an inner spiral 230 arranged coaxially. The outer spiral 220 and the inner spiral 230 respectively have an outer extension flow channel 221 and an inner extension flow channel 231 extending into the die 210, and are used to form the melt channels of the outer layer and the inner layer of the tube 1000, respectively.

[0048] Multiple connecting channels (not shown in the figure) are provided between the flow channels of the outer spiral 220 and the inner spiral 230, and the multiple connecting channels are arranged in a ring around the circumference. The mandrel provided between two adjacent flow channels is used to form the hollow layer 1100 between the inner and outer layers of the tube 1000. The outer spiral 220 has a hollow layer air extraction channel 510 on the mandrel between two adjacent connecting channels, and the hollow layer air extraction channel 510 is connected to the hollow layer 1100.

[0049] The outer sizing sleeve 300 and the outer water cooling system are provided. The outer sizing sleeve 300 is located at the outlet end of the mold 200. The outer circumferential surface of the pipe 1000 is adsorbed onto the inner wall of the outer sizing sleeve 300 under vacuum. The outer water cooling system is located towards the outer sizing sleeve 300 and the pipe 1000 and is used to cool the outer wall of the pipe 1000.

[0050] The inner sizing sleeve 400 and the inner water cooling system are provided. The inner sizing sleeve 400 is set at the outlet end of the mold 200 and fits against the inner wall of the pipe 1000. The inner water cooling system is integrated into the inner sizing sleeve 400 and is used to cool the inner wall of the pipe 1000.

[0051] The middle layer exhaust fan ring 500 is set on the end face of the mold 200 away from the outlet end. The middle layer exhaust fan ring 500 exhausts and cools the hollow layer 1100 of the pipe 1000 through the hollow layer exhaust channel 510.

[0052] In other words, the double-walled hollow plastic pipe 1000 extrusion equipment provided in this embodiment can simultaneously and independently cool the outer wall, inner wall and hollow layer 1100 of the pipe 1000. The outer wall is cooled by the outer water cooling system, the inner wall is cooled by the inner water cooling system integrated in the inner sizing sleeve 400, and the hollow layer 1100 is cooled by negative pressure exhaust cooling by the middle exhaust fan ring 500, forming a three-in-one all-round cooling system.

[0053] This multi-dimensional synchronous cooling method effectively avoids the phenomenon of "external cold and internal heat" in traditional processes, significantly improves the uniformity and efficiency of cooling, thereby ensuring that the shrinkage of each part of the pipe 1000 tends to be consistent, reducing internal stress, preventing deformation, and greatly improving the dimensional accuracy, surface quality and structural stability of the pipe 1000.

[0054] Compared to existing technologies, this design has at least the following advantages:

[0055] 1. Achieve simultaneous cooling of the inner and outer walls, significantly reducing internal stress and improving surface quality and dimensional accuracy.

[0056] By setting up an inner sizing sleeve 400 with an integrated inner water cooling system, in conjunction with an outer sizing sleeve 300 and an outer water cooling system, synchronous and symmetrical cooling of the inner and outer walls of the pipe 1000 is achieved. This effectively solves the problem of uneven cooling caused by the rapid cooling of the outer wall and the slow cooling of the inner wall in traditional processes. It significantly reduces the residual internal stress caused by differences in thermal shrinkage, preventing the pipe 1000 from bending and deforming. At the same time, the synergistic effect of the inner sizing sleeve 400 and the cooling system enables the inner wall to solidify quickly and uniformly, resulting in a tight fit. This significantly improves the smoothness of the inner wall, avoids defects such as collapse and wrinkling, and improves the overall surface quality and geometric shaping accuracy of the pipe 1000.

[0057] 2. The hollow layer has independent exhaust cooling to enhance structural stability.

[0058] The middle-layer exhaust fan ring 500 is connected to the external negative pressure system, which can directionally exhaust air from the hollow layer 1100 between the inner and outer layers of the pipe 1000. On the one hand, it can promptly discharge the hot air in the hollow cavity and accelerate the cooling of the hollow area; on the other hand, under the action of negative pressure, it can make the inner and outer layer walls adhere tightly to the sizing sleeve, enhance the pipe wall fit and structural rigidity, prevent the hollow layer 1100 from collapsing or bubbling, and ensure the integrity and stability of the hollow structure.

[0059] 3. The multi-channel design ensures uniform molding of the hollow layer at 1100mm.

[0060] The mold 200 is provided with multiple interconnected flow channels distributed in a ring along the circumference, connecting the flow channels of the outer spiral 220 and the inner spiral 230, so that the molten material is evenly distributed in the mold 200 and smoothly merges to form multiple independent hollow cavities, ensuring that the circumferential wall thickness of the hollow layer 1100 is consistent, and improving the overall symmetry and mechanical properties of the pipe 1000.

[0061] 4. Synergistic cooling and shaping improves production efficiency and product qualification rate.

[0062] The outer water cooling, inner liquid cooling, and hollow 1100 exhaust cooling work together to form a highly efficient cooling and shaping system that integrates "external cooling - internal cooling - hollow exhaust". This significantly shortens the cooling and shaping length and production cycle, while reducing the scrap rate and improving the stability and product consistency of continuous production.

[0063] Preferably, the extruder 100 is eccentrically positioned on the end face of the die 200 or on the side of the die 200. The extruder 100 and the die 200 are connected by a connector 110. The connector 110 has an independent outer feed channel 111 and an inner feed channel 112. The outer feed channel 111 is connected to the flow channel of the outer spiral 220, and the inner feed channel 112 is connected to the flow channel of the inner spiral 230. This structure enables independent conveying and precise distribution of the outer and inner molten materials, avoids mutual interference between materials, and ensures the stability of the double-layer co-extrusion process.

[0064] It should be noted that both of the above-mentioned arrangements of the extruder 100 can provide sufficient installation space for the axial end face of the die 200, so as to centrally arrange the water inlet pipe and water outlet pipe for cooling the inner sizing sleeve 400, as well as the central exhaust pipe 700, the middle exhaust ring 500 and other internal components at the front end (axial direction) of the die 200.

[0065] In this arrangement, the extruder 100 is eccentrically positioned on the end face of the die 200 compared to the lateral arrangement. Since the extruder 100 and the die 200 form a parallel axis feeding method, the material path when entering the die 200 is smoother. Furthermore, this arrangement can reduce the space occupied by the machine, and therefore can be considered a better implementation method.

[0066] Furthermore, the connector 110 is equipped with two flow regulating valves 113, which correspond to and regulate the melt flow of the outer feed channel 111 and the inner feed channel 112 respectively. The flow regulating valves 113 can flexibly adjust the ratio of inner and outer wall thicknesses according to the process requirements of the pipe 1000 to meet the production needs of different specifications of products. At the same time, the flow rate of inner and outer materials is balanced in real time during the extrusion process to avoid problems such as wall thickness deviation, core eccentricity or poor melt convergence caused by uneven material supply. This effectively improves the wall thickness uniformity, structural symmetry and co-extrusion interface bonding quality of the pipe 1000, and further ensures the dimensional accuracy and overall performance stability of the product.

[0067] In addition, a melt temperature regulating device (not shown in the figure) can be installed on the flow channel connected to the die 200 of the extruder 100, near the screw barrel side, to reduce melt problems entering the die 200 and facilitate the cooling and shaping of the tube 1000.

[0068] Preferably, it also includes a vacuum setting machine 600, which is located at the exit end of the mold 200. The outer sizing sleeve 300 is installed inside the vacuum setting machine 600, while the inner sizing sleeve 400 is also located in the inner cavity of the vacuum setting machine 600. The end of the inner sizing sleeve 400 is connected to the die 210. This design integrates the inner and outer sizing with vacuum adsorption and cooling functions to form a complete setting environment.

[0069] The vacuum sizing machine 600 is provided with a number of nozzles 610 arranged in a ring along its length. The nozzles 610 spray cooling water or atomized water toward the outer sizing sleeve 300 and the outer surface of the pipe 1000, forming an efficient and uniform outer water cooling system. The ring-arranged nozzles 610 ensure that the cooling water acts uniformly on the outer wall of the pipe 1000 from all directions, avoiding deformation or stress concentration caused by uneven local cooling, and significantly improving cooling efficiency and sizing quality.

[0070] Preferably, the mold 200 has a channel along its central axis, and a central exhaust pipe 700 extends outward from the channel. The central exhaust pipe 700 continuously draws high-temperature air from the inner cavity of the pipe 1000 and the inner sizing sleeve, thereby accelerating the cooling of the inner wall of the pipe 1000 and reducing the temperature of the inner sizing sleeve 400, and stabilizing the dimensions of the pipe 1000.

[0071] Preferably, the inner sizing sleeve 400 includes an inner sleeve 410 and an outer sleeve 420, with a cooling channel 430 formed between the inner sleeve 410 and the outer sleeve 420 for introducing cooling water to form a high-efficiency inner water cooling system. At the same time, an inner sizing sleeve inlet pipe 440 and an inner sizing sleeve outlet pipe 450 are provided, which are introduced into the mold 200 from the central axial channel and are respectively connected to the inlet and outlet of the cooling channel 430 to realize the circulation and transportation of cooling water.

[0072] By constructing a circulating cooling channel 430 inside the inner sizing sleeve 400 and introducing inlet and outlet water pipes through the axial channel, direct and continuous liquid cooling of the inner wall area of ​​the pipe 1000 is achieved, which greatly improves the cooling efficiency and uniformity of the inner wall and effectively avoids problems such as deformation, collapse or surface roughness caused by insufficient cooling of the inner wall.

[0073] Meanwhile, the cooling channel 430 is close to the inner surface of the pipe 1000, with a short heat exchange path and high heat transfer efficiency. It can quickly remove heat, stabilize the temperature of the inner sizing sleeve 400, and ensure the accuracy of the inner diameter and the process stability of long-term operation.

[0074] In addition, to improve the cooling effect on the inner wall of the pipe 1000, refrigerated cooling water is used. All cooling water supply pipes installed in the mold 200 and the inner water-cooled sizing sleeve are covered with heat insulation material. This can effectively reduce the heat absorption and cold loss of the low-temperature medium during transportation, maintain the temperature stability of the cooling system, and avoid the reduction of cooling efficiency due to the intrusion of ambient heat.

[0075] Preferably, the contact surface between the inner sizing sleeve 400 and the mold 200 is provided with a heat insulation pad 900, which effectively blocks the heat conduction path between the mold 200 and the inner sizing sleeve 400. This not only protects the cooling capacity of the inner sizing sleeve 400, enabling it to continuously and uniformly cool the pipe 1000 efficiently, but also helps maintain the thermal stability of the mold 200 outlet area, preventing the melt from generating stress or flow defects due to excessive temperature difference in the early stage of molding.

[0076] Preferably, it also includes a spray nozzle 800 and a spray nozzle inlet pipe 810. The spray nozzle 800 is located in the inner cavity of the pipe 1000 and is disposed towards the inner wall of the pipe 1000. The spray nozzle inlet pipe 810 is introduced into the pipe from the channel and connected to the spray nozzle 800 to achieve a stable supply of coolant.

[0077] By installing a spray nozzle 800 inside the pipe 1000, cooling water is sprayed directly onto the inner wall in an atomized form, significantly enhancing the heat exchange efficiency with the inner wall surface, achieving efficient and uniform enhanced cooling of the inner wall, and further shortening the cooling and setting time; combined with the negative pressure suction effect of the central exhaust pipe 700, the steam and hot air generated by the spray can be discharged in time, preventing air blockage and improving the cooling effect.

[0078] Preferably, the middle layer exhaust fan ring 500 is connected to each hollow layer exhaust channel 510. The external negative pressure system extracts gas from the hollow layer 1000 through the middle layer exhaust fan ring 500 and the hollow layer exhaust channels 510, which significantly accelerates the cooling and solidification speed of the hollow structure, improves the structural integrity and dimensional stability of the pipe 1000, strengthens the shaping control of the hollow layer 1100, avoids defects such as bubbling and deformation, and is especially suitable for high-quality, high-speed continuous production of multi-cavity hollow pipes 1000, further improving product consistency and production efficiency.

[0079] In addition, the inner sizing sleeve 400 has a tapered surface, with the side closer to the mold 200 being the larger end and the side farther from the mold 200 being the smaller end. The tapered value should be slightly larger than the cooling shrinkage value. The tapered design of the inner sizing sleeve 400 matches the cooling shrinkage trend of the tube 1000. When the tube 1000 is extruded from the mold 200, it is initially in a high-temperature softened state. The larger end of the inner sizing sleeve 400 can provide good guidance and initial sizing.

[0080] As the pipe 1000 moves forward along the axial direction and gradually cools and shrinks, its inner diameter naturally tends to decrease. The conical structure of the sizing sleeve, whose outer diameter decreases from large to small, is just right to adapt to this shrinkage process, avoiding excessive frictional resistance or "jamming" caused by rigid straight cylinder sizing.

[0081] Furthermore, in order to reduce the friction between the inner sizing sleeve 400 and the inner wall of the pipe 1000, the outer surface of the inner sizing sleeve 400 is polished and chrome-plated. The polishing process significantly reduces the surface roughness of the sizing sleeve. Combined with the high hardness and low friction coefficient surface formed by the chrome plating layer, it effectively reduces the sliding resistance between the pipe 1000 and the inner sizing sleeve 400 during the traction process, and prevents surface defects such as scratches and roughening of the inner wall.

[0082] Meanwhile, the chrome plating layer possesses excellent wear resistance and corrosion resistance, maintaining surface smoothness for a long time, extending the service life of the inner sizing sleeve 400, and ensuring the stability of continuous production. This treatment process further improves the shaping quality of the inner wall of the 1000 pipe and is particularly suitable for long-cycle, high-speed extrusion processes.

[0083] The technical means disclosed in this utility model are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above are specific embodiments of this utility model. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of this utility model, and these improvements and modifications are also considered within the scope of protection of this utility model.

[0084] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in this utility model embodiment are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0085] Furthermore, in this utility model, the use of terms such as "first," "second," and "a" is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. The terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly specified. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0086] The technical solutions of the various embodiments of this utility model can be combined with each other, but only if they are based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the protection scope claimed by this utility model.

[0087] The specific embodiments described herein are merely illustrative examples illustrating the spirit of this utility model. Those skilled in the art to which this utility model pertains may make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of this utility model or exceeding the scope defined by the appended claims.

Claims

1. A double-walled hollow plastic pipe extrusion device, characterized in that, include: The extruder, die, and orifice are connected in sequence. The mold is provided with an outer spiral body and an inner spiral body arranged coaxially. The outer spiral body and the inner spiral body respectively have an outer extension flow channel and an inner extension flow channel extending into the die. The outer extension channel and the inner extension channel are provided with multiple connecting channels at the outlet end near the mold, and the multiple connecting channels are arranged in a circumferential ring. The mandrel provided between adjacent connecting channels is used to form the hollow layer between the inner and outer layers of the tube. The mandrel is provided with a hollow layer air extraction channel, which is connected to the hollow layer. An outer sizing sleeve and an outer water cooling system are provided. The outer sizing sleeve is located at the mold outlet end and is used for vacuum adsorption of the outer circumferential surface of the pipe. The outer water cooling system is positioned towards the outer sizing sleeve and the pipe. The inner sizing sleeve and the inner water cooling system are provided. The inner sizing sleeve is located at the outlet end of the mold and fits against the inner wall of the pipe. The inner water cooling system is integrated into the inner sizing sleeve and is used to cool the inner wall of the pipe. A middle-layer exhaust fan ring is disposed on the end face of the mold away from the outlet end. The middle-layer exhaust fan ring exhausts and cools the hollow layer through the hollow layer exhaust channel.

2. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, The extruder is eccentrically positioned on the end face of the mold or on the side of the mold. The extruder and the mold are connected by a connector. The connector has an independent outer feed channel and an inner feed channel. The outer feed channel is connected to the flow channel of the outer spiral body, and the inner feed channel is connected to the flow channel of the inner spiral body.

3. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, The connector is equipped with two flow regulating valves, which are used to regulate the flow rates of the outer feed channel and the inner feed channel, respectively.

4. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, It also includes a vacuum setting machine, which is located at the outlet end of the mold, and the outer sizing sleeve is installed inside the vacuum setting machine.

5. The double-walled hollow plastic pipe extrusion equipment according to claim 4, characterized in that, The vacuum shaping machine is provided with a plurality of nozzles arranged in a ring along its length, and the nozzles are positioned toward the outer sizing sleeve and the pipe to form the outer water cooling system.

6. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, The mold has a channel along its central axis, and a central exhaust pipe extending outward is provided in the channel.

7. The double-walled hollow plastic pipe extrusion equipment according to claim 6, characterized in that, The inner sizing sleeve includes an inner sleeve and an outer sleeve, and a cooling channel is formed between the inner sleeve and the outer sleeve. The cooling channel is used to inject cooling water to form the inner water cooling system. It also includes an inner fixed-sizing sleeve inlet pipe and an inner fixed-sizing sleeve outlet pipe, both of which are introduced inward from the channel and are respectively connected to the cooling flow channel.

8. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, The contact surface between the inner sizing sleeve and the mold is provided with a heat insulation pad.

9. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, It also includes a spray nozzle and a spray nozzle inlet pipe. The spray nozzle is located in the inner cavity of the pipe and is positioned towards the inner wall of the pipe. The spray nozzle inlet pipe is introduced into the pipe from the channel and connected to the spray nozzle.

10. The double-walled hollow plastic pipe extrusion equipment according to claim 1, characterized in that, The middle layer exhaust ring is connected to each of the hollow layer exhaust channels, and the external negative pressure system extracts gas from the hollow layer through the middle layer exhaust ring and the hollow layer exhaust channels.

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