A multiple cooling molding method for PVC material

Abstract

The invention discloses a multiple cooling molding method for PVC materials, comprising step S1: heating PVC resin and additives to a molten state, step S2: extruding the molten polymer melt through a molding device to form a tubular blank; step S3: subjecting the tubular blank to a first cooling stage to form a dense inner layer structure; step S4: subjecting the tube blank with solidified inner surface to a second cooling stage, and cooling it for a second time by cold air at a preset low temperature to form a tough outer layer structure; step S5: subjecting the tube blank subjected to multiple cooling to a finalizing treatment; through the multiple cooling technology of cooling inside and outside in stages, differential control of the inner and outer layers of the tube blank is achieved, the performance limitation caused by the single cooling method in the traditional process is overcome, a dense high-strength inner layer is formed, the pressure resistance and wear resistance of the pipe are enhanced, the crack resistance of the pipe is improved, the overall performance of the PVC pipe is effectively improved, and the application scope of the PVC pipe is broadened.

Description

Technical Field

[0001] The invention relates to the technical field of PVC molding, in particular to a multiple cooling molding method of PVC material. Background Art

[0002] As an important pipe material, PVC pipe is widely used in water supply and drainage, gas transmission, wire and cable protection and other fields. It is favored for its excellent corrosion resistance, insulation and mechanical properties. With the development of industrial technology and the expansion of application fields, the market has put forward higher requirements on the performance of pipes, especially in high pressure, high impact and complex environments. Traditional pipes can no longer meet the use needs.

[0003] In the prior art, the production of PVC pipes usually adopts a single cooling method (such as water cooling), that is, a unified cooling treatment is directly performed after extrusion molding. The inner and outer layer structures and performances of the pipes obtained in this way are single. Since the inner and outer layer structures of the pipes themselves are responsible for different functions, the required material properties are also different. Therefore, this process leads to limitations in specific performance of the pipes, such as insufficient inner layer strength and outer layer toughness, and it is impossible to take into account the requirements of pressure resistance and impact resistance, which limits the application range and service life of the pipes. In addition, a single cooling method is prone to cause internal stress concentration, resulting in cracks or breakage of the pipes during use.

[0004] In view of this, it is necessary to improve the production process of PVC pipes in the prior art to solve the problem of single performance of the inner and outer layers. Summary of the invention

[0005] The purpose of the present invention is to provide a multiple cooling molding method for PVC material to solve the above technical problems.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] A multiple cooling molding method for PVC material, comprising:

[0008] Step S1: heating the PVC resin and additives to a molten state to form a molten polymer melt;

[0009] Step S2: extruding the molten polymer melt through a molding device to form a tubular billet;

[0010] Step S3: subjecting the tubular blank to a first cooling stage, wherein the tubular blank is cooled for the first time by hot air at a preset high temperature, so as to rapidly solidify the inner surface of the tubular blank and form a dense inner layer structure;

[0011] Step S4: the tube blank with the solidified inner surface enters the second cooling stage, and is cooled for the second time by cold air at a preset low temperature, and the outer surface of the tube blank is slowly cooled to form a tough outer layer structure;

[0012] Step S5: The tube blank that has been cooled multiple times is subjected to shaping treatment to obtain a PVC tube with a high-strength inner layer and a high-toughness outer layer.

[0013] Optionally, the additives include a crystallization controller, an impact enhancer and a processing aid;

[0014] Wherein, the crystallization control agent is a mixture of one or more of calcium stearate, zinc stearate or a sorbitol derivative;

[0015] The impact enhancer is a mixture of one or more of an acrylic impact modifier, chlorinated polyethylene or a methyl methacrylate-butadiene-styrene copolymer;

[0016] The processing aid is a mixture of one or more of polyethylene wax, oxidized polyethylene wax or stearic acid.

[0017] Optionally, the step S1 specifically includes:

[0018] Step S11: uniformly mixing the PVC resin with the crystallization control agent, the impact enhancer and the processing aid to form a raw material mixture;

[0019] Step S12: sending the raw material mixture into a pre-plasticizing device and heating it to 180° C. to 200° C. to melt and plasticize the PVC resin and additives;

[0020] Step S13: During the melting process, shear force is applied to the molten material to fully disperse the additive in the material matrix to form a uniform molten mixture;

[0021] Step S14: maintaining the molten mixture at a predetermined temperature for a predetermined time to complete the interaction between the additive and the PVC resin.

[0022] Optionally, the step S2 specifically includes:

[0023] Step S21: conveying the molten polymer melt from the plasticizing device to the screw barrel of the molding device;

[0024] Step S22: adjusting the rotation speed and barrel temperature of the molding device so that the molten polymer melt is kept in a molten state and transported forward under the shearing and pushing action of the screw;

[0025] Step S23: extruding the molten mixture through the annular gap die of the forming device to form a tubular blank;

[0026] Step S24: During the extrusion process of the tubular blank, a pressure control technology is used to control the molding pressure of the inner and outer walls of the tubular blank;

[0027] Step S25: introducing the extruded tubular blank into a sizing device, and stabilizing the outer diameter of the tubular blank by vacuum sizing.

[0028] Optionally, the molding device includes an inner sleeve and an outer sleeve, a diverter assembly is arranged between the inner sleeve and the outer sleeve, and the diverter assembly is used to adjust the distribution and flow of the molten polymer melt between the inner and outer layers; wherein inner and outer layer flow channel control valves are arranged in the annular gap die.

[0029] Optionally, the step S3 specifically includes:

[0030] Step S31: setting a first cooling area, the length of the first cooling area is 2 to 5 meters; the first cooling area is provided with an inner sleeve, the inner sleeve is installed with an inner heating component for supplying hot air, and a movable annular hot nozzle, the annular hot nozzle is connected to the inner heating component;

[0031] Step S32: preheating the first cooling area, preheating the air in the first cooling area to between 80° C. and 120° C. by the internal heating component;

[0032] Step S33: introducing the extruded tubular blank into the first cooling zone, and evenly blowing hot air into the inner surface of the tubular blank at a flow rate of 0.5 to 2.0 m / s through an annular hot nozzle arranged at the entrance of the inner cavity of the tubular blank.

[0033] Optionally, the first cooling zone is further provided with an outer sleeve, and a gap layer is formed between the outer sleeve and the outer layer of the tubular blank;

[0034] The outer sleeve is provided with an external heating component and a heat-insulating layer, and the external heating component is arranged in contact with the heat-insulating layer.

[0035] Optionally, step S3 further includes:

[0036] Step S34: heating the gap layer by an external heating assembly to maintain the temperature of the outer layer of the tubular blank between 160° C. and 180° C.;

[0037] Step S35: In the first cooling zone, the temperature change of the inner surface of the tubular blank is monitored in real time by a temperature sensor, and the temperature and flow rate of the hot air are controlled so that the inner surface is rapidly solidified within 5 to 15 seconds to form a tube blank with a dense inner layer structure.

[0038] Optionally, the step S4 specifically includes:

[0039] Step S41: setting up a second cooling area, which is located downstream of the first cooling area and has a length of 5 to 10 meters; the second cooling area is provided with an external cooling device and a temperature sensor, and the external cooling device includes an annular cold air nozzle array arranged outside the second cooling area.

[0040] Optionally, after step S41, the following steps may be further performed:

[0041] Step S42: introducing the layer-solidified tube blank from the first cooling area to the second cooling area;

[0042] Step S43: the external cooling device operates to provide cold air with a temperature of 0°C to 10°C through the annular cold air nozzle array;

[0043] Step S44: by controlling the flow rate of the cold air to 0.2-1.0 m / s, adjusting the temperature and the spraying angle of the cold air, the outer surface of the tube is gradually cooled down within 30-60 seconds and slowly cooled to room temperature to form a tube with a tough outer layer structure;

[0044] Step S45: The temperature sensor installed in the second cooling area monitors the temperature change of the outer surface and the whole of the tube in real time, and dynamically adjusts the parameters of the cold air according to the monitoring results.

[0045] Compared with the prior art, the present invention has the following beneficial effects: the method forms a tubular blank by extruding a molten PVC polymer melt, firstly subjecting it to a first cooling stage, rapidly cooling it with hot air at a preset high temperature, rapidly solidifying the inner surface of the tube blank, and forming a dense inner layer structure; subsequently, the tube blank enters a second cooling stage, slowly cooling it with cold air at a preset low temperature, gradually solidifying the outer surface of the tube blank, and forming a tough outer layer structure; through multiple cooling of the inner and outer surfaces in stages, the inner and outer layers of the tube blank produce different crystallization and structural characteristics, so that the formed PVC pipe has the performance of high strength in the inner layer and high toughness in the outer layer; through the multiple cooling technology of cooling the inner and outer surfaces in stages, the differentiated control of the inner and outer layers of the tube blank is achieved, the performance limitation caused by the single cooling method in the traditional process is overcome, a dense high-strength inner layer is formed, the pressure resistance and wear resistance of the pipe are enhanced, the anti-cracking performance of the pipe is improved, the overall performance of the PVC pipe is effectively improved, and the application scope of the PVC pipe is broadened. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0048] Figure 1 This is one of the schematic flow diagrams of the multiple cooling molding method for PVC material of this embodiment;

[0049] Figure 2 This is a second flow chart of the multiple cooling molding method for PVC material of this embodiment;

[0050] Figure 3 This is the third flow chart of the multiple cooling molding method of PVC material in this embodiment. DETAILED DESCRIPTION

[0051] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally arranged component at the same time.

[0053] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0054] Combination Figures 1 to 3 As shown, an embodiment of the present invention provides a multiple cooling molding method of PVC material, comprising:

[0055] Step S1: heating the PVC resin and additives to a molten state to form a molten polymer melt.

[0056] First, the PVC resin is mixed with specific additives (such as crystallization controllers, impact enhancers and processing aids) and heated to a molten state to form a uniform polymer melt. The temperature and heating rate need to be precisely controlled during the heating process, usually in the range of 180°C to 200°C, so that the PVC resin is completely melted, while ensuring that the additives are fully dissolved and evenly dispersed in the polymer matrix. The role of the additive is to adjust the crystallization behavior and rheological properties of the polymer, laying the foundation for the subsequent formation of the inner and outer layer structure. By forming a uniform molten mixture, the stability of the material during the extrusion molding process and the consistency of product performance are guaranteed.

[0057] Step S2: Extruding the molten polymer melt through a molding device to form a tubular billet.

[0058] The prepared molten polymer melt is fed into the screw barrel of a molding device (such as an extruder). By adjusting the speed and barrel temperature of the molding device, the melt is controlled to maintain a stable molten state and be transported forward under the shearing and pushing action of the screw. The melt is extruded through a well-designed annular gap die to form a tubular billet. The inner and outer layer flow channel control structure set in the annular gap die can accurately control the inner and outer wall thickness and molding pressure of the tube billet by adjusting the flow rate and pressure of the inner and outer layer melts. This step ensures that the tube billet has uniform wall thickness and good dimensional accuracy, providing ideal initial conditions for the subsequent multiple cooling processes.

[0059] Step S3: The tubular blank is subjected to a first cooling stage, and is cooled for the first time by hot air at a preset high temperature, so as to rapidly solidify the inner surface of the tube blank and form a dense inner layer structure.

[0060] The extruded tubular billet is introduced into the first cooling stage. At a preset high temperature, the first cooling is carried out by evenly blowing hot air at a temperature of 80℃ to 120℃ onto the inner surface of the tube billet. The design of the internal heating assembly and the annular hot nozzle allows the hot air to act on the inner surface of the tube billet at a flow rate of 0.5 to 2.0 m / s, quickly reducing its temperature to below the glass transition temperature, so that the inner surface is quickly solidified to form a dense and high-strength inner layer structure. At the same time, by providing an insulation layer or an external heating device on the outer layer of the tube billet, the temperature of the outer layer is maintained between 160℃ and 180℃ to prevent the outer layer from cooling too quickly and maintain its molten state. Such temperature control and cooling methods form a significant temperature gradient between the inner and outer layers of the tube billet, which differentiates the structural performance of the inner and outer layers.

[0061] Step S4: the tube blank with solidified inner surface enters the second cooling stage, and is cooled for the second time by cold air at a preset low temperature, and the outer surface of the tube blank is slowly cooled to form a tough outer layer structure.

[0062] The tube blank with solidified inner surface is introduced into the second cooling stage. At a preset low temperature, cold air with a temperature of 0℃ to 10℃ is evenly sprayed onto the outer surface of the tube blank through an annular cold air nozzle array arranged around the tube blank for a second cooling. The cold air slowly reduces the temperature of the outer layer of the tube blank at a flow rate of 0.2 to 1.0 m / s, so that it gradually cools and solidifies within 30 to 60 seconds to form an outer layer structure with high toughness. In order to avoid material embrittlement and internal stress concentration caused by excessive cooling, a slow and uniform cooling strategy is adopted in the second cooling stage, and the cooling parameters are monitored and adjusted in real time through temperature sensors and stress monitoring devices to ensure the quality and performance of the outer layer structure.

[0063] Step S5: The tube blank that has been cooled multiple times is subjected to shaping treatment to obtain a PVC tube with a high-strength inner layer and a high-toughness outer layer.

[0064] The tube blanks that have undergone multiple cooling treatments are subjected to shaping treatment. During the shaping process, the tube blanks pass through a vacuum sizing device to stabilize their outer diameter and wall thickness, eliminate the internal stress generated during the cooling process, and ensure the dimensional accuracy and shape stability of the pipe. Subsequently, the pipe is pulled and cut, and slit or wound according to the required length, and finally a PVC pipe with a high-strength inner layer and a high-toughness outer layer is obtained. Such pipes have both pressure resistance and impact resistance, and have excellent performance. They are suitable for high-demand application scenarios, such as high-pressure transmission pipelines, building water supply systems, and impact-resistant cable protection pipes, etc., meeting the market demand for high-performance pipes.

[0065] The working principle of the present invention is as follows: the method forms a tubular blank by extruding a molten PVC polymer melt, firstly passing it through a first cooling stage, rapidly cooling it with hot air at a preset high temperature, rapidly solidifying the inner surface of the tube blank, and forming a dense inner layer structure; subsequently, the tube blank enters a second cooling stage, slowly cooling it with cold air at a preset low temperature, gradually solidifying the outer surface of the tube blank, and forming a tough outer layer structure; through multiple cooling of the inner and outer surfaces in stages, the inner and outer layers of the tube blank produce different crystallization and structural characteristics, so that the formed PVC pipe has the performance of high strength in the inner layer and high toughness in the outer layer; through the multiple cooling technology of cooling the inner and outer surfaces in stages, the differentiated control of the inner and outer layers of the tube blank is achieved, the performance limitation caused by the single cooling method in the traditional process is overcome, a dense high-strength inner layer is formed, the pressure resistance and wear resistance of the pipe are enhanced, the crack resistance of the pipe is improved, the overall performance of the PVC pipe is effectively improved, and the scope of use of the PVC pipe is broadened.

[0066] In this embodiment, it is specifically described that the additives include a crystallization controller, an impact enhancer, and a processing aid.

[0067] Among them, the crystallization control agent is a mixture of one or more of calcium stearate, zinc stearate or sorbitol derivatives; it can effectively regulate the crystallization behavior of PVC resin during the cooling process. These substances can affect the crystallization rate and crystal structure of PVC molecules, promote the formation of uniform and fine grains, and help improve the density and mechanical strength of the inner layer.

[0068] Impact enhancers are a mixture of one or more of acrylic impact modifiers (AIM), chlorinated polyethylene (CPE) or methyl methacrylate-butadiene-styrene (MBS) copolymers; these impact enhancers can significantly improve the toughness and impact resistance of PVC materials. These additives form a toughening phase in the PVC matrix, absorb and disperse external impact energy, and improve the toughness of the outer layer.

[0069] The processing aid is a mixture of one or more of polyethylene wax, oxidized polyethylene wax or stearic acid, which is intended to improve the fluidity and lubricity of the PVC melt during processing.

[0070] In this embodiment, it is specifically explained that step S1 specifically includes:

[0071] Step S11: uniformly mixing the PVC resin with the crystallization control agent, the impact enhancer and the processing aid to form a raw material mixture.

[0072] Step S12: sending the raw material mixture into a pre-plasticizing device and heating it to 180°C to 200°C to melt and plasticize the PVC resin and additives;

[0073] This temperature range is the best temperature range for PVC processing, which can ensure that the material is fully melted and prevent PVC degradation. The plasticization process transforms the material from a solid state to a uniform viscoelastic melt, preparing for the subsequent application of shear force.

[0074] Step S13: During the melting process, shear force is applied to the molten material to fully disperse the additive in the material matrix to form a uniform molten mixture;

[0075] Shearing forces are applied to the materials during the melting process, usually through the rotation of the screw and special screw elements. The shearing action subjects the molten materials to strong mixing, and the additives are further evenly dispersed in the PVC matrix. Sufficient shear mixing helps break up the aggregates of the additives, promotes the uniform distribution of the crystallization control agent, the effective role of the reinforcing agent, and the lubricating effect of the processing aid, and forms a molten mixture with uniform properties.

[0076] Step S14: maintaining the molten mixture at a predetermined temperature for a predetermined time to complete the interaction between the additive and the PVC resin.

[0077] The molten mixture is kept at a predetermined temperature for a preset period of time (e.g. 3 to 5 minutes). This heat preservation process allows the additives to fully interact with the PVC resin. During this period, the crystallization controller adjusts the crystallization behavior of PVC and affects the formation and growth of crystals; the impact enhancer further compatibilizes with the PVC matrix to form a toughened structure; the processing aid stabilizes the melt fluidity and ensures that the microstructure of the material reaches the optimal state through heat preservation treatment.

[0078] In this embodiment, it is specifically described that step S2 specifically includes:

[0079] Step S21: conveying the molten polymer melt from the plasticizing device to the screw barrel of the molding device;

[0080] Plasticizing device usually refers to the equipment that heats and mixes materials, such as the feeding section of an extruder. By transferring the molten material to the screw barrel of the molding device, the material is ensured to remain in a stable molten state during the continuous production process.

[0081] Step S22: adjusting the rotation speed and barrel temperature of the molding device so that the molten polymer melt is kept in a molten state and transported forward under the shearing and pushing action of the screw;

[0082] The screw speed affects the conveying speed and shearing effect of the material, and the barrel temperature affects the viscosity and fluidity of the material. By precisely controlling these two parameters, it is ensured that the molten material has suitable rheological properties, thereby obtaining stable extrusion pressure and flow rate during the molding process, and avoiding problems such as overheating decomposition or condensation solidification.

[0083] Step S23: Extruding the molten mixture through an annular die of a forming device to form a tubular billet to optimize the flow and distribution of the melt;

[0084] In order to optimize the flow and distribution of the melt, a flow divider and inner and outer layer flow channel control valves are set in the annular gap die. The flow divider can evenly distribute the melt to the inner and outer layers to prevent asymmetry and deviation of the melt flow. The inner and outer layer flow channel control valves are used to accurately adjust the flow rate and pressure of the inner and outer layer melts to ensure that the thickness and performance of the inner and outer walls of the tube meet the requirements.

[0085] Step S24: During the extrusion process of the tubular billet, the molding pressure of the inner and outer walls of the tubular billet is controlled by using pressure control technology; by adjusting the opening of the inner and outer layer flow channel control valves, the flow resistance of the melt in the inner and outer layer flow channels is changed, thereby accurately controlling the melt pressure and flow rate.

[0086] Step S25: The extruded tubular blank is introduced into a sizing device, and the outer diameter of the tubular blank is stabilized by vacuum sizing. By applying a vacuum outside the sizing sleeve, the tubular blank is closely attached to the inner wall of the sizing sleeve, and is quickly cooled and shaped.

[0087] In this embodiment, it is specifically described that the molding device includes an inner sleeve and an outer sleeve, and a diverter component is arranged between the inner sleeve and the outer sleeve, and the diverter component is used to adjust the distribution and flow of the molten polymer melt between the inner and outer layers; wherein, inner and outer layer flow channel control valves are arranged in the annular gap mold.

[0088] It should be noted that the inner and outer layer flow channel control valves control the flow resistance of the melt in their respective flow channels by changing the flow channel cross-section or adjusting the valve opening. By adjusting the inner and outer layer control valves, the molding pressure of the inner and outer walls of the tubular blank can be independently controlled so that the wall thickness and density of the inner and outer layers meet the expected requirements.

[0089] In this embodiment, it is specifically described that step S3 specifically includes:

[0090] Step S31: setting a first cooling area, the length of the first cooling area is 2 to 5 meters; the first cooling area is provided with an inner sleeve, the inner sleeve is installed with an inner heating component for supplying hot air, and a movable annular hot nozzle, the annular hot nozzle is connected to the inner heating component;

[0091] It should be noted that an inner sleeve is provided in the first cooling area, and an inner heating assembly for supplying hot air and a movable annular hot nozzle are installed in the inner sleeve. The annular hot nozzle is connected to the inner heating assembly and can be adjusted in the axial direction to meet the processing needs of tube blanks of different sizes. The inner heating assembly is responsible for heating and supplying hot air, and the annular hot nozzle sprays the hot air evenly onto the inner surface of the tubular blank. This design ensures that the hot air can act evenly and efficiently on the inner surface, promote the rapid solidification of the inner layer of the tube blank, and form a dense inner layer structure.

[0092] Step S32: preheating the first cooling area, preheating the air in the first cooling area to between 80° C. and 120° C. by an internal heating component;

[0093] First, preheat the first cooling zone. By starting the internal heating component, preheat the air in the first cooling zone to a temperature range of 80℃ to 120℃. The purpose of preheating is to establish a stable high-temperature environment to avoid excessive temperature shock when the tube enters the cooling zone, and to ensure that the inner surface can be quickly and evenly cooled to below the glass transition temperature. At the same time, this temperature range helps to control the crystallization rate and crystal structure of the inner layer, and improve the mechanical properties and density of the inner layer.

[0094] Step S33: introducing the extruded tubular blank into the first cooling zone, and evenly blowing hot air into the inner surface of the tubular blank at a flow rate of 0.5 to 2.0 m / s through an annular hot nozzle arranged at the entrance of the inner cavity of the tubular blank.

[0095] The blowing of hot air causes the inner surface of the tube to cool down rapidly, causing it to solidify quickly to form a dense inner layer structure. The mobility of the annular hot nozzle enables it to adjust its position according to the moving speed and size of the tube, ensuring that the hot air always acts evenly on the inner surface. In this way, the rapid solidification of the inner layer forms a sharp contrast with the outer layer remaining in a molten state, providing conditions for the differentiation of the inner and outer layer properties of the tube.

[0096] In this embodiment, it is further explained that the first cooling zone is also provided with an outer sleeve, and a gap layer is formed between the outer sleeve and the outer layer of the tubular blank; the outer sleeve is provided with an external heating component and a thermal insulation layer, and the external heating component is arranged in contact with the thermal insulation layer.

[0097] Through the design of inner and outer sleeves, the first cooling area achieves effective control of the inner and outer temperatures: the inner layer is quickly cooled and solidified by the blowing of hot air, and the outer layer remains molten under the action of the external heating component. The establishment of this temperature gradient allows the inner and outer layers of the tube to experience different cooling rates at the same time, forming a structural feature of high strength in the inner layer and high toughness in the outer layer.

[0098] In this embodiment, it is further explained that after step S33, the following steps are further included:

[0099] Step S34: heating the gap layer by an external heating assembly to maintain the temperature of the outer layer of the tubular blank between 160° C. and 180° C.; preventing the outer layer from cooling too quickly and maintaining the outer layer in a molten state.

[0100] Step S35: In the first cooling zone, the temperature change of the inner surface of the tubular blank is monitored in real time by a temperature sensor, and the temperature and flow rate of the hot air are controlled so that the inner surface is rapidly solidified within 5 to 15 seconds to form a tube blank with a dense inner layer structure.

[0101] After the first cooling stage, the inner layer of the tube has solidified and formed, while the outer layer remains molten. The tube enters the next process and prepares for the second cooling stage.

[0102] In this embodiment, it is specifically explained that step S4 specifically includes:

[0103] Step S41: setting a second cooling area, which is located downstream of the first cooling area and has a length of 5 to 10 meters; the second cooling area is provided with an external cooling device and a temperature sensor, and the external cooling device includes an annular cold air nozzle array arranged outside the second cooling area.

[0104] The annular cold air nozzle array is evenly arranged around the outer circumference of the tube billet, providing cold air that covers the entire outer surface of the tube billet. This arrangement ensures that the cold air can evenly act on the outer surface of the tube billet, creating conditions for the formation of a tough outer layer structure. The installation of the temperature sensor is used to monitor the temperature change of the tube billet in real time, providing data support for the subsequent adjustment of the cooling parameters.

[0105] Step S42: Introduce the solidified tube from the first cooling area to the second cooling area; it is necessary to ensure that the tube is not disturbed by the outside world during the transmission process to avoid internal stress concentration or deformation caused by sudden temperature changes or mechanical vibrations. Smooth transition helps maintain the overall quality of the tube and provides a good starting point for the slow cooling of the outer layer.

[0106] Step S43: The external cooling device is operated to provide cold air with a temperature of 0°C to 10°C through the annular cold air nozzle array; through the design of the annular nozzle, the cold air can act on the outer surface of the tube in a uniform manner to ensure the balance of the cooling process.

[0107] Step S44: by controlling the flow rate of the cold air to 0.2-1.0 m / s, adjusting the temperature and the spraying angle of the cold air, the outer surface of the tube is gradually cooled down within 30-60 seconds and slowly cooled to room temperature to form a tube with a tough outer layer structure;

[0108] It should be noted that the slow and uniform cooling process is conducive to the orderly arrangement and crystallization of the outer layer molecular chains, reducing the internal stress and embrittlement problems caused by rapid cooling, thereby forming an outer layer structure with excellent toughness.

[0109] Step S45: The temperature sensor installed in the second cooling area monitors the temperature change of the outer surface and the whole of the tube in real time, and dynamically adjusts the parameters of the cold air according to the monitoring results.

[0110] According to the monitoring results, the parameters of the cold air, such as flow rate, temperature and injection angle, are dynamically adjusted to ensure that the cooling process is always in the best state. This feedback control mechanism effectively avoids uneven cooling or overcooling caused by environmental changes or equipment fluctuations, and ensures the consistency and reliability of the outer layer quality of the tube blank.

[0111] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multiple cooling molding method for PVC material, characterized in that: include: Step S1: heating the PVC resin and additives to a molten state to form a molten polymer melt; Step S2: extruding the molten polymer melt through a molding device to form a tubular blank; Step S3: the tubular blank is subjected to a first cooling stage, and is cooled for the first time by hot air at a preset high temperature, so as to rapidly solidify the inner surface of the tube blank and form a dense inner layer structure; Step S4: the tube blank with solidified inner surface enters the second cooling stage, and is cooled for the second time by cold air at a preset low temperature, and the outer surface of the tube blank is slowly cooled to form a tough outer layer structure; specifically, step S41: a second cooling area is set, and the second cooling area is located downstream of the first cooling area, and the length is 5 to 10 meters; the second cooling area is provided with an external cooling device and a temperature sensor, and the external cooling device includes an annular cold air nozzle array arranged outside the second cooling area; Step S5: performing shaping treatment on the tube blank after multiple cooling to obtain a PVC tube with a high-strength inner layer and a high-toughness outer layer; Step S3 specifically includes: Step S31: setting a first cooling area, the length of the first cooling area is 2 to 5 meters; The first cooling area is provided with an inner sleeve, the inner sleeve is provided with an inner heating assembly for supplying hot air, and a movable annular hot nozzle, the annular hot nozzle is connected to the inner heating assembly; Step S32: preheating the first cooling area, preheating the air in the first cooling area to between 80°C and 120°C by an internal heating component; the first cooling area is also provided with an outer sleeve, and a gap layer is formed between the outer sleeve and the outer layer of the tubular blank; the outer sleeve is provided with an external heating component and a heat preservation layer, and the external heating component is arranged in contact with the heat preservation layer; Step S33: introducing the extruded tubular blank into the first cooling area, and evenly blowing hot air at a flow rate of 0.5 to 2.0 m / s toward the inner surface of the tubular blank through an annular hot nozzle disposed at the entrance of the inner cavity of the tubular blank; Step S34: heating the gap layer by an external heating assembly to maintain the temperature of the outer layer of the tubular blank between 160° C. and 180° C.; Step S35: In the first cooling zone, the temperature change of the inner surface of the tubular blank is monitored in real time by a temperature sensor, and the temperature and flow rate of the hot air are controlled so that the inner surface is rapidly solidified within 5 to 15 seconds to form a tube blank with a dense inner layer structure.

2. The multiple cooling molding method of PVC material according to claim 1, characterized in that: Additives include crystallization controllers, impact enhancers, and processing aids; Wherein, the crystallization control agent is a mixture of one or more of calcium stearate, zinc stearate or a sorbitol derivative; The impact enhancer is a mixture of one or more of an acrylic impact modifier, chlorinated polyethylene or a methyl methacrylate-butadiene-styrene copolymer; The processing aid is a mixture of one or more of polyethylene wax, oxidized polyethylene wax or stearic acid.

3. The multiple cooling molding method of PVC material according to claim 2, characterized in that: The step S1 specifically includes: Step S11: uniformly mixing the PVC resin with the crystallization control agent, the impact enhancer and the processing aid to form a raw material mixture; Step S12: sending the raw material mixture into a pre-plasticizing device and heating it to 180°C to 200°C to melt and plasticize the PVC resin and additives; Step S13: During the melting process, shear force is applied to the molten material to fully disperse the additive in the material matrix to form a uniform molten mixture; Step S14: maintaining the molten mixture at a predetermined temperature for a predetermined time to complete the interaction between the additive and the PVC resin.

4. The multiple cooling molding method of PVC material according to claim 1, characterized in that: The step S2 specifically includes: Step S21: conveying the molten polymer melt from the plasticizing device to the screw barrel of the molding device; Step S22: adjusting the rotation speed and barrel temperature of the molding device so that the molten polymer melt is kept in a molten state and transported forward under the shearing and pushing action of the screw; Step S23: extruding the molten mixture through an annular gap die of a forming device to form a tubular blank; Step S24: During the extrusion process of the tubular blank, the forming pressure of the inner and outer walls of the tubular blank is controlled by using a pressure control technology; Step S25: introducing the extruded tubular blank into a sizing device, and stabilizing the outer diameter of the tubular blank by vacuum sizing.

5. The multiple cooling molding method of PVC material according to claim 4, characterized in that: The molding device comprises an inner sleeve and an outer sleeve, a flow divider is arranged between the inner sleeve and the outer sleeve, and the flow divider is used to adjust the distribution and flow of the molten polymer melt between the inner and outer layers; wherein inner and outer layer flow channel control valves are arranged in the annular gap die.

6. The multiple cooling molding method of PVC material according to claim 1, characterized in that: After step S41, the following steps are further included: Step S42: introducing the layer-solidified tube blank from the first cooling area to the second cooling area; Step S43: the external cooling device operates to provide cold air with a temperature of 0°C to 10°C through the annular cold air nozzle array; Step S44: by controlling the flow rate of the cold air to 0.2-1.0 m / s, adjusting the temperature and the spraying angle of the cold air, the outer surface of the tube is gradually cooled down within 30-60 seconds and slowly cooled to room temperature to form a tube with a tough outer layer structure; Step S45: The temperature sensor installed in the second cooling area monitors the temperature change of the outer surface and the whole of the tube in real time, and dynamically adjusts the parameters of the cold air according to the monitoring results.

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