A bimodal hdpe pipe biaxial orientation inflation molding device and process

Abstract

The application relates to the technical field of plastic pipe production, in particular to a bimodal HDPE pipe biaxial orientation expansion forming device and process, which comprises an extruder, an extrusion die and a gas supply mechanism, the outer side of the gas supply mechanism is connected with a fastening expansion assembly for primary expansion orientation, the outer side of one end of the fastening expansion assembly is provided with an auxiliary expansion assembly for secondary expansion orientation, one end of the extrusion die is connected with a cooling mechanism, and the cooling mechanism is connected with a blowing assembly on one side; the pipe embryo melt is extruded to the fastening expansion assembly through the extrusion die to complete the primary expansion orientation, then the outer side of the formed pipe embryo is circularly sprayed and cooled through a plurality of groups of circular spray heads in the cooling mechanism, so that the pipe embryo melt is transitioned from a high-temperature viscous flow state to a high-elasticity state, the blowing assembly simultaneously blows the residual water on the outer side of the pipe embryo to avoid the residual water on the outer side of the pipe embryo from causing the subsequent secondary expansion orientation effect to be reduced and the pipe embryo forming quality to be reduced.

Description

Technical Field

[0001] This invention relates to the field of plastic pipe manufacturing technology, specifically to a biaxial orientation expansion molding device and process for bimodal HDPE pipes. Background Technology

[0002] Plastic pipes, with their excellent properties such as lightweight, high strength, corrosion resistance, low flow resistance, and convenient construction, have promoted the replacement of steel with plastic in pipelines. They have not only become a key component of modern infrastructure systems, but also have urgent needs in transportation and aerospace fields where lightweighting and high performance are the core driving forces. The mechanical strength and pressure resistance of pipes are the core considerations for meeting the needs of pressurized fluid transportation. As the transportation distance and pressure increase, the requirements for the mechanical properties of pipes become higher and higher.

[0003] Chinese patent CN118990988A discloses a gas-assisted circumferentially reinforced pipe extrusion head, comprising a die assembly and a core die assembly. The die assembly includes a die, an expanding outer die, and an air inlet bolt. The die and the expanding outer die are coaxially arranged and detachably fixedly connected. The air inlet bolt is radially installed on the outer wall of the die, and an air inlet hole is formed along its own axial direction. The core die assembly includes a flow divider cone, a mandrel, and an expanding mandrel. This invention can circumferentially stretch the plastic melt during the pipe extrusion molding process, thereby enhancing the circumferential strength of the pipe and improving the product quality.

[0004] Traditional extruded pipes have higher axial strength than circumferential strength due to the orientation of molecular chains along the extrusion direction. However, in practical applications, the circumferential stress that fluid transport pipes bear is theoretically about twice that of the axial stress. This mismatch between material properties and actual needs results in a huge waste of material efficiency. Existing biaxial orientation molding technologies mostly adopt a two-step offline processing method, first extruding the pipe blank, cooling and shaping it, and then heating it a second time for expansion and orientation. This process is cumbersome, the production line occupies a large area, and the equipment investment and production energy consumption are high. Moreover, the secondary heating can easily lead to the thermal degradation of molecular chains, weakening the mechanical properties of the pipe.

[0005] Therefore, the present invention provides a biaxial orientation expansion molding device and process for bimodal HDPE pipes with low energy consumption and good circumferential reinforcement effect. Summary of the Invention

[0006] To address the issues of insufficient circumferential reinforcement in existing technologies, a biaxial orientation expansion molding device and process for bimodal HDPE pipes were designed.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a biaxial orientation expansion molding device and process for bimodal HDPE pipe, including an extruder and an extrusion die set at one end. An air supply mechanism is provided inside the extrusion die. A fastening expansion component for primary expansion orientation is connected to the outside of the air supply mechanism. An auxiliary expansion component for secondary expansion orientation is set on the outside of one end of the fastening expansion component. A cooling mechanism is connected to one end of the extrusion die. A purging component is connected to one side of the cooling mechanism.

[0008] The cooling mechanism includes a first mounting component and an annular spray chamber inside it. Several sets of spray heads are evenly arranged in the circumferential direction on the inner side of the water storage chamber for circumferential spray cooling of the primary expanded tube blank.

[0009] The auxiliary expansion assembly includes an expansion mandrel with a tapered end, used for secondary expansion and orientation through the tapered section. After the melt completes the initial expansion and orientation through the fastening expansion assembly, the spray head performs circumferential spray cooling on the outside of the formed tube blank, causing the tube blank melt to transition from a high-temperature viscous flow state to a high-elastic state. The purging assembly simultaneously purges the residual water on the outside of the tube blank. The expansion mandrel, in conjunction with the gas supply mechanism, discharges gas from the fastening expansion assembly to the expansion mandrel, so that an air film is formed between the tube blank and the expansion mandrel to assist the tube blank in secondary expansion and orientation.

[0010] Furthermore, the auxiliary expansion assembly also includes a temperature control device at one end of the expansion mandrel to control the temperature of the blowing gas. The expansion mandrel consists of a conical section and a sizing section. The interior of the expansion mandrel is a hollow structure. After installation, both ends are connected to and sealed with the gas supply mechanism to prevent gas leakage.

[0011] Furthermore, the cooling mechanism also includes an annular water storage chamber inside the first mounting component, a first protrusion on one side of the spray chamber for forming an airflow channel with the purging assembly, and symmetrical water collection tanks at the bottom of the inner side of the spray chamber for collecting the cooling water splashed during spraying. A drain pipe is connected to the bottom of the water collection tank, one end of the spray head is connected to the inside of the water storage chamber for absorbing cooling water, and the other end of the spray head is located inside the spray chamber.

[0012] Furthermore, the purging assembly includes a second mounting component and multiple evenly distributed second air inlets on its outer side. The second mounting component has several sets of second air inlets and an annular air storage chamber inside. A second protrusion is provided on one side inside the second mounting component. The second protrusion cooperates with the first protrusion to form an exhaust channel for discharging gas to purge the outer side of the tube blank. A shielding component is provided inside the air storage chamber for sealing the air storage chamber by sliding adjustment. A telescopic component is connected to one side of the shielding component, and an evenly distributed elastic component is connected to the inner side of one end of the shielding component.

[0013] Furthermore, the two ends of the second air intake channel are respectively connected to the second air intake end and the air storage chamber, one side of the second mounting part is connected to the first mounting part, and one side of the first mounting part is connected to the extrusion die. The first mounting part, the second mounting part and the extrusion die are coaxially arranged.

[0014] Furthermore, the extrusion die includes an extrusion die and a pressure ring fixedly connected to one side. The extrusion die is provided with a flow divider cone and an inner core. The flow divider cone works with the inner core to divide the extruded tube preform melt. The inner side of the inner core is fixedly connected to the gas supply mechanism.

[0015] Furthermore, the gas supply mechanism includes a first air inlet symmetrically arranged outside the extrusion die, a first air inlet channel symmetrically opened inside the extrusion die, an air inlet pipe connected to the outside of the symmetrically arranged air inlet channel, and a number of exhaust ports opened at the part of the air inlet pipe where a fastening expansion component is provided, for discharging gas into the fastening expansion component.

[0016] Furthermore, the fastening expansion assembly includes an expansion member fixedly installed on the outside of the intake pipe, and an exhaust chamber is provided inside the expansion member.

[0017] Furthermore, a vacuum cooling sizing device is provided on the outside of the auxiliary expansion assembly to cool and sizing the tube blank after it has undergone two expansion orientations. A traction machine is provided on one side of the vacuum cooling sizing device to drive the tube blank to move smoothly.

[0018] The beneficial effects of this invention are:

[0019] The present invention discloses a biaxial orientation expansion molding device and process for bimodal HDPE pipes. The pipe blank melt is extruded through an extrusion die to the fastening expansion component to complete the initial expansion orientation. Then, several sets of circumferential spray heads inside the cooling mechanism perform circumferential spray cooling on the outside of the formed pipe blank, so that the pipe blank melt transitions from a high-temperature viscous flow state to a high-elastic state. At the same time, as the pipe blank moves, the purging component simultaneously blows away the residual water on the outside of the pipe blank to avoid the residual water on the outside of the pipe blank causing a decrease in the subsequent secondary expansion orientation effect and a decrease in the pipe blank forming quality.

[0020] Then, by expanding the mandrel in conjunction with the air supply mechanism, high-pressure gas is discharged through the air holes, so that an air film is formed between the tube blank and the expanding mandrel to assist the tube blank in secondary expansion and orientation. This air film is like an air cushion bearing, realizing frictionless contact between the tube blank and the mold. This not only greatly reduces the solid-phase stretching resistance and avoids scratches on the inner surface of the pipe, but also ensures the uniformity of the stretching process. Under the action of the traction machine, the tube blank can smoothly complete the deep circumferential expansion and axial stretching, realizing the secondary orientation and crystallization of molecular chains. Finally, after vacuum cooling and sizing, it is sent to the traction machine to obtain a high circumferential strength and high pressure resistance bimodal HDPE pipe product. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a schematic diagram of the main structure of the present invention;

[0023] Figure 2 This is a three-dimensional structural diagram of the extrusion die of the present invention;

[0024] Figure 3 This is a front view of the extrusion die structure of the present invention;

[0025] Figure 4 This is a partial sectional view of the extrusion die structure of the present invention;

[0026] Figure 5 This is a schematic diagram of the gas supply mechanism of the present invention;

[0027] Figure 6 The present invention Figure 5 Enlarged section view at point A

[0028] Figure 7 This is a cross-sectional view of the extrusion die structure of the present invention;

[0029] Figure 8 This is a schematic diagram of the cooling mechanism structure of the present invention;

[0030] Figure 9 For the present invention Figure 8 A partially enlarged sectional view at point B;

[0031] Figure 10 This is a cross-sectional view of the first mounting component structure of the present invention;

[0032] Figure 11 This is a cross-sectional view of the expanded core mold structure of the present invention.

[0033] In the diagram: 1. Extruder; 2. Extrusion die; 21. Extrusion orifice; 22. Pressure ring; 23. Diverter cone; 24. Inner core; 3. Air supply mechanism; 31. First air inlet end; 32. First air inlet channel; 33. Air inlet pipe; 34. Exhaust port; 4. Cooling mechanism; 41. First mounting component; 42. Water storage chamber; 43. Spray chamber; 44. Spray head; 45. Water collection tank; 46. Drainage pipe; 47. First protrusion; 5. Blowing assembly; 51. Second mounting component; 52. Second air inlet end; 53. Second air inlet channel; 54. Air storage chamber; 55. Second protrusion; 56. Exhaust channel; 57. Shielding component; 58. Telescopic component; 59. Elastic component; 6. Fastening expansion assembly; 61. Expansion component; 62. Exhaust chamber; 7. Auxiliary expansion assembly; 71. Expansion core mold; 72. Temperature control equipment. Detailed Implementation

[0034] To make the technical means, technical features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0035] Example: Figure 1 - Figure 11 As shown, the present invention discloses a biaxial orientation expansion molding device and process for bimodal HDPE pipes, comprising an extruder 1 and an extrusion die 2 at one end. The extrusion die 2 is provided with an air supply mechanism 3 inside. A fastening expansion component 6 for primary expansion orientation is connected to the outside of the air supply mechanism 3. An auxiliary expansion component 7 for secondary expansion orientation is provided on the outside of one end of the fastening expansion component 6. A cooling mechanism 4 is connected to one end of the extrusion die 2. A blowing component 5 is connected to one side of the cooling mechanism 4. The cooling mechanism 4 includes a first mounting component 41 and an annular spray chamber 43 inside it. Several sets of spray heads 44 for circumferential spray cooling of the primary expanded pipe blank are uniformly arranged on the inner side of the water storage chamber 42. The auxiliary expansion component 7 includes an expansion mandrel 71 with a conical end.

[0036] Specifically, the high-temperature viscous HDPE melt enters the extrusion die 2 through the extruder head and undergoes initial expansion and orientation at the fastening expansion assembly 6. Then, several sets of circumferential spray nozzles 44 inside the cooling mechanism 4 provide circumferential cooling to the outside of the preform, causing the melt to transition from a high-temperature viscous state to a highly elastic state. Simultaneously, as the preform moves, the purging assembly 5 blows away any residual water on the outside of the preform to prevent it from reducing the effectiveness of subsequent secondary expansion and orientation and the overall quality of the preform. Then, high-pressure gas is discharged from the fastening expansion assembly 6 to the expansion mandrel 71 through the air supply mechanism 3, forming an air film between the preform and the expansion mandrel 71 to assist in secondary expansion and orientation. This air film acts like an air cushion bearing, facilitating the connection between the preform and the die. The frictionless contact significantly reduces solid-phase tensile resistance, avoids scratches on the inner surface of the pipe, and ensures the uniformity of the stretching process. This allows the pipe blank to smoothly complete deep circumferential expansion and axial stretching under the action of the traction machine, achieving secondary orientation and crystallization of the molecular chains. Finally, after vacuum cooling and sizing, the pipe is sent to the traction machine to obtain a high-circumferential-strength, high-pressure-resistant bimodal HDPE pipe. The bimodal HDPE secondary biaxial orientation self-reinforcement meets the requirements for high-strength pressure resistance, high circumferential strength, high impact resistance, and smooth inner surface quality of the bimodal HDPE pipe. PE100 grade commercial bimodal HDPE is selected, with a weight-average molecular weight of less than 300,000 for the high molecular weight component and 15,000-75,000 for the low molecular weight component, with a mass ratio of low molecular weight component to high molecular weight component of 3:7-7:3.

[0037] In this embodiment, the extrusion die 2 includes an extrusion die 21 and a pressure ring 22 fixedly connected to one side thereof. The extrusion die 21 has a flow divider cone 23 and an inner core 24 inside; specifically, as shown... Figure 2 - Figure 4 As shown, the flow divider cone 23, in conjunction with the inner core 24, divides the extruded tube preform melt. The inner side of the inner core 24 is fixedly connected to the air supply mechanism 3. The extrusion die 2 adopts a modular, interlocking structure, which makes it easier to ensure the machining accuracy and assembly coaxiality of the extrusion die 21, pressure ring 22, flow divider cone 23, and inner core 24. This effectively reduces the wall thickness deviation of the tube, improves the roundness and dimensional stability of the tube, and ensures the consistency of product quality. At the same time, the interlocking structure of the die facilitates disassembly, cleaning, and maintenance. Furthermore, by replacing different specifications of interlocking components, the die can be adjusted relatively flexibly to adapt to the production of tubes of different sizes or specifications, enhancing the adaptability of the production line and the controllability of the process.

[0038] In this embodiment, the air supply mechanism 3 includes a first air inlet end 31 symmetrically arranged on the outside of the extrusion die 21, a first air inlet channel 32 symmetrically opened inside the extrusion die 21, an air inlet pipe 33 connected to the outside of the connection of the symmetrically arranged first air inlet channel 32, and a plurality of exhaust ports 34 opened at the part on the outside of the air inlet pipe 33 where a fastening expansion component 6 is provided. The fastening expansion component 6 includes an expansion member 61 fixedly installed on the outside of the air inlet pipe 33, and an exhaust chamber 62 is opened inside the expansion member 61.

[0039] Specifically, such as Figure 4 - Figure 8 As shown, the exhaust port 34 is located on the outside of the air intake pipe 33 and connected to the fastening expansion assembly 6. It is used to discharge gas into the fastening expansion assembly 6 and out to the outside of the auxiliary expansion assembly 7, so that an air film is formed between the tube blank and the expansion core mold 71. The air supply mechanism 3 also includes a pressure or temperature controller, an air tank and an air compressor set on the outside, which are used to control the gas temperature and pressure. The high-pressure gas after heating and stabilizing is injected into the first air intake channel 32 through the stainless steel threaded high-pressure air nozzle joint set at the first air intake end 31, and then transported to the fastening expansion assembly 6 through the air intake pipe 33 and the exhaust port 34.

[0040] The inside of the fastening expansion assembly 6 is fixedly connected to the outside of the air inlet pipe 33, and the expansion member 61 is fixedly connected to the air inlet pipe 33. The exhaust chamber 62 opened inside the expansion member 61 is used to collect the high-pressure gas discharged from the exhaust port 34. The end of the fastening expansion assembly 6 away from the extrusion die 2 is set as the exhaust part, which is used to discharge the gas inside the exhaust chamber 62 to the outside of the auxiliary expansion assembly 7. Its outside is the expansion part, which is used for the initial expansion and orientation of the bimodal HDPE melt. The end of the fastening expansion assembly 6 close to the extrusion die 2 is designed with a tapered shape, which is used for the initial expansion and orientation of the extruded tube preform melt.

[0041] In this embodiment, the cooling mechanism 4 also includes an annular water storage cavity 42 inside the first mounting member 41, a first protrusion 47 on one side inside the spray cavity 43 for forming an airflow channel with the blowing assembly 5, a water collection tank 45 symmetrically opened at the bottom inside the spray cavity 43 for collecting the cooling water splashed during spraying, a drain pipe 46 connected to the bottom of the water collection tank 45, one end of the spray head 44 connected to the inside of the water storage cavity 42 for absorbing cooling water, and the other end of the spray head 44 located inside the spray cavity 43.

[0042] Specifically, such as Figure 8 - Figure 10 As shown, the cooling mechanism 4 also includes several sets of water injection joints provided on the outside of the first mounting part 41, which are used to connect the outer water injection pipe to inject the cooling water required for spraying into the water storage chamber 42. The first mounting part 41 is installed close to the outlet flange of the extrusion die 21. By adjusting the pressure and flow rate, the spray head 44 can spray the extruded pipe blank in a uniform and controllable circumferential manner, so as to achieve rapid and gentle cooling to a temperature range suitable for crystallization development. In a short time, the pipe blank is reduced from the extrusion temperature to the expansion temperature, and the melt is precisely transitioned from the high temperature viscous flow state to the high elastic state, thereby providing a melt with suitable rheological properties and molecular orientation potential for the subsequent biaxial self-reinforcement of the bimodal HDPE pipe.

[0043] The spray angle of the spray head 44 is 30°-45° with the outer wall of the tube blank to prevent water mist from flowing back into the inlet mold. The cooling medium temperature is 60°C-80°C to prevent rapid cooling and cracking, and to control the crystallization rate. By measuring the tube blank temperature during expansion with infrared thermography, a closed loop is formed to achieve effective cooling control. The tube blank temperature is reduced from nearly 200°C to 110°C-125°C expansion temperature in a short time. The water collection tank 45 is symmetrically opened at the bottom of the spray chamber 43 and located on both sides of the spray head 44. The water collection tank 45 is arc-shaped and is used to collect the cooling water splashed and dripped during spraying, as well as the cooling water remaining on the outside of the tube blank blown off by the blowing component 5. The collected water can be discharged through the bottom drain pipe 46. It can be filtered and cooled and then recycled for reuse, saving water resources. The first protrusion 47 is an annular protrusion that can block the cooling water during spraying and prevent it from flowing into the exhaust channel 56. The first protrusion 47 is inclined and its angle with the tube blank is set between 15° and 25°.

[0044] In this embodiment, the purging assembly 5 includes a second mounting member 51 and a plurality of evenly distributed second air inlet ends 52 disposed on its outer side. The second mounting member 51 has a plurality of second air inlet channels 53 and an annular air storage cavity 54 inside. A second protrusion 55 is provided on one side inside the second mounting member 51. The second protrusion 55 cooperates with the first protrusion 47 to form an exhaust channel 56 for discharging gas to purge the outer side of the tube blank. A shielding member 57 is disposed inside the air storage cavity 54 for sealing the air storage cavity 54 by sliding adjustment. A telescopic member 58 is connected to one side of the shielding member 57, and an evenly distributed elastic member 59 is connected to the inner side of one end of the shielding member 57.

[0045] Specifically, such as Figure 8 and Figure 9 As shown, the purging assembly 5 also includes an externally mounted pressure or temperature controller, an air tank, and an air compressor for controlling gas temperature and pressure. High-pressure gas, after being heated and stabilized, is injected into the second air intake channel 53 through a stainless steel threaded high-pressure air nozzle connector located at the second air intake end 52. The telescopic member 58 is not connected to the shielding member 57. The shielding member 57 is used to shield the air storage chamber 54 when not in operation, preventing moisture from entering the air storage chamber 54. After the telescopic member 58 extends or retracts a certain distance, it pushes the shielding member 57 to move and compress the elastic member 59, shielding one side of the bottom of the air storage chamber 54, blocking the connection between the air storage chamber 54 and the exhaust channel 56, thus keeping the air storage chamber 54 in a sealed state. During operation, the telescopic member 58 retracts, and the shielding member 57 is positioned relative to the elastic member 59. The springback action of 9 resets the tube blank, allowing airflow to flow out through the exhaust channel 56 to purge the outside of the tube blank. The two ends of the second air inlet channel 53 are connected to the second air inlet end 52 and the air storage chamber 54 respectively. One side of the second mounting part 51 is connected to the first mounting part 41, and one side of the first mounting part 41 is connected to the extrusion mold 2. The first mounting part 41, the second mounting part 51 and the extrusion mold 2 are coaxially arranged. The elastic part 59 is set as a spring, and the parameters of the spring are set according to common knowledge. It can drive the blocking part 57 to reset and move. The telescopic part 58 is set as a telescopic rod that can be telescopically adjusted and has a self-locking function, such as an electric telescopic rod. At the same time, the elastic part 59 and the telescopic part 58 can also be set as any other structure that can achieve the same effect.

[0046] The second protrusion 55, together with the first protrusion 47, forms an exhaust channel 56. The second protrusion 55 is inclined, and the inclination angle is the same as that of the first protrusion 47. This allows the airflow to be blown out obliquely along the direction of tube blank travel, preventing direct impact on the tube blank and causing radial vibration and eccentricity. The oblique airflow also peels off water droplets and prevents water vapor from flowing back into the spray area. This avoids residual cooling water on the outside of the tube blank. Local temperature differences caused by moisture will directly damage the consistency of orientation and crystallization, resulting in a significant decrease in the mechanical properties of the tube. At the same time, residual moisture may form water spots or watermarks on the outside of the tube blank. Because the cooling rate and crystallinity are different in different areas, the gloss and color difference of the tube surface will be significantly different, forming watermarks of varying depths. The annular air knife of the blowing assembly 5 blows away the residual cooling water on the outside of the tube blank, further improving the expansion orientation stability and expansion orientation effect of the tube blank.

[0047] In this embodiment, the auxiliary expansion assembly 7 also includes a temperature control device 72 at one end of the expansion mandrel 71, which is used to control the temperature of the blowing gas. The expansion mandrel 71 is composed of a conical section and a sizing section. The interior of the expansion mandrel 71 is a hollow structure. After installation, both ends are connected to and sealed with the gas supply mechanism 3. A vacuum cooling sizing device is provided on the outside of the auxiliary expansion assembly 7, which is used to cool and sizing the tube blank after two expansion orientations. A traction machine is provided on one side of the vacuum cooling sizing device, which is used to drive the tube blank to move smoothly.

[0048] Specifically, such as Figure 3 , Figure 4 and Figure 11 As shown, the expansion mandrel 71 is designed with a hollow splicing structure to reduce the influence of gravity and facilitate replacement. At the same time, expansion mandrels 71 with different expansion angles can be replaced according to needs. The angle of the conical section of the expansion mandrel 71 is the expansion angle. The expansion mandrel 71 is divided into a conical section and a sizing section. The conical section is the part between the end near the fastening expansion component 6 and the sizing section. After cooling, the tube blank melt undergoes secondary expansion and orientation through the conical section. Gas is discharged into the exhaust chamber 62 through the exhaust port 34 and discharged to the outside of the expansion mandrel 71, so that an air film layer is formed between the tube blank and the conical section of the expansion mandrel 71. The air film layer plays a lubricating and drag-reducing role, so that the melt and the mold have no frictional contact, improving the smoothness of the inner surface of the bimodal HDPE pipe. The air film temperature for auxiliary expansion is close to the orientation temperature of bimodal HDPE, about 120℃, and the air pressure can reach 0.6MPa-0.8MPa.

[0049] The vacuum cooling sizing device is used to tightly adhere the outer wall of the pipe to the inner wall of the sizing sleeve under vacuum negative pressure, while uniform and thorough cooling is achieved through circulating cooling water. This process not only precisely fixes the outer diameter of the pipe, but more importantly, it permanently locks the excellent molecular orientation and crystal structure formed after two expansions into the microstructure of the pipe. The traction machine consists of multiple sets of synchronously operating rubber rollers or tracks, which clamp and pull the pipe forward at a constant and precise speed. Stable traction is a key link to ensure uniform pipe wall thickness, consistent outer diameter, and continuous and stable operation of the production line.

[0050] A biaxial orientation expansion molding process for bimodal HDPE pipes includes the following steps:

[0051] S1: Raw material pretreatment and plasticizing extrusion. Strictly screened bimodal high-density polyethylene (HDPE) granules are fed into a high-speed mixer for uniform mixing to ensure the consistency of material properties. Subsequently, the dried granules are fed into the hopper of extruder 1. Under the continuous rotation of the screw, the granules are forced to be transported into the heated barrel. Through the synergistic effect of the external heating coil of the barrel and the shear heat of the screw, the solid granules are gradually heated, melted and homogenized, and finally transformed into a viscous melt with uniform temperature and viscosity, laying the foundation for subsequent precision molding.

[0052] S2: First circumferential expansion and initial orientation. The high-temperature melt in the viscous flow state enters smoothly into the extrusion die 21 and fastening expansion component 6 through the specially designed extruder head under the action of extrusion pressure. The circumferential expansion of the extruded melt causes the first circumferential expansion. This process causes the polymer chains to be initially stretched and oriented in the circumferential and axial directions, forming a preliminary biaxial orientation structure, which significantly improves the circumferential strength of the pipe.

[0053] S3: Rapid cooling and structural locking. The tube blank, after completing the first expansion, immediately enters the circumferential water mist spray cooling zone. The uniform and fine water mist formed by the high-precision spray head 44 rapidly and gently cools the outer surface of the tube blank. This step aims to quickly reduce the melt temperature to a specific "high elasticity" temperature window. Rapid cooling can effectively "freeze" and retain some of the molecular orientation structures formed in the first expansion, while inducing moderate and controlled crystallization of the polymer, creating an ideal material state for the next deep processing. The purging component 5 uses an annular air knife to simultaneously circumferentially purge the residual cooling water on the outside of the tube blank, avoiding water residue that would reduce the orientation effect of subsequent secondary expansion.

[0054] S4: Secondary circumferential expansion and melt-solid continuous molding. When the tube blank cools to the visco-plastic transition state (i.e., high elasticity), it has both rigidity and ductility. At this time, a high-pressure gas film is introduced between the expansion mandrel 71 and the inner wall of the tube blank to play a lubricating and isolating role. Under the action of traction force, the tube blank is stretched smoothly and passes through the expansion mandrel 71 to carry out the second, more intense circumferential expansion. This step enables the polymer chains to achieve further deep orientation and arrangement in the circumferential direction, accompanied by secondary crystallization, which greatly enhances the mechanical properties of the tube. The whole process realizes continuous and integrated expansion molding from the molten state to the solid state, namely "melt-solid continuous expansion".

[0055] S5: Vacuum sizing and structural fixation. Although the tubes after secondary expansion have ideal orientation and crystal structure, they are still in a highly elastic state and their dimensions are unstable. Therefore, the tubes are immediately sent to the vacuum cooling sizing device. Under the action of vacuum negative pressure, the outer wall of the tube is tightly adsorbed onto the inner wall of the sizing sleeve. At the same time, it is cooled evenly and thoroughly by circulating cooling water. This process not only accurately fixes the outer diameter of the tube, but more importantly, it permanently "locks" the excellent molecular orientation and crystal structure formed after the two expansions into the microstructure of the tube.

[0056] S6: Stable traction and conveying. The pipes that have completed sizing and cooling are smoothly drawn out of the vacuum sizing box and enter the traction machine. The traction machine consists of multiple sets of synchronously operating rubber rollers or tracks. They clamp and pull the pipes forward at a constant and precise speed. Stable traction is the key to ensuring uniform pipe wall thickness, consistent outer diameter, and continuous and stable operation of the production line.

[0057] S7: Fixed-length cutting and finished product output. After the pipe is pulled to the set length, the automatic cutting device (usually a planetary cutter or chipless cutter) is activated to quickly and smoothly cut the pipe to a fixed length. After the pipe is cut, it is inspected and packaged to finally obtain HDPE pipe finished product with excellent ring stiffness, impact resistance and pressure resistance, and biaxial orientation self-reinforcing structure.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A biaxial orientation expansion molding apparatus for bimodal HDPE pipes, comprising an extruder and an extrusion die at one end, wherein an air supply mechanism is provided inside the extrusion die, characterized in that: The gas supply mechanism is connected to a fastening expansion assembly for initial expansion orientation on the outside. An auxiliary expansion assembly for secondary expansion orientation is provided on the outside of one end of the fastening expansion assembly. A cooling mechanism is connected to one end of the extrusion die, and a purging assembly is connected to one side of the cooling mechanism. The cooling mechanism includes a first mounting component and an annular spray chamber inside it. Several sets of spray heads are evenly arranged in the circumferential direction on the inner side of the water storage chamber for circumferential spray cooling of the initial expansion tube blank. The auxiliary expansion assembly includes an expansion mandrel with a tapered end, used for secondary expansion and orientation through the tapered section. After the melt completes the initial expansion and orientation through the fastening expansion assembly, the spray head performs circumferential spray cooling on the outside of the formed tube blank, causing the tube blank melt to transition from a high-temperature viscous flow state to a high-elastic state. The purging assembly simultaneously purges the residual water on the outside of the tube blank. The expansion mandrel, in conjunction with the gas supply mechanism, discharges gas from the fastening expansion assembly to the expansion mandrel, so that an air film is formed between the tube blank and the expansion mandrel to assist the tube blank in secondary expansion and orientation.

2. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 1, characterized in that: The auxiliary expansion assembly also includes a temperature control device at one end of the expansion mandrel for controlling the temperature of the blowing gas. The expansion mandrel is composed of a conical section and a sizing section, and the interior of the expansion mandrel is a hollow structure.

3. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 1, characterized in that: The cooling mechanism also includes an annular water storage chamber inside the first mounting component. A first protrusion is provided on one side of the spray chamber to form an airflow channel with the purging component. A water collection tank is symmetrically provided at the bottom of the inner side of the spray chamber to collect the cooling water splashed during spraying. A drain pipe is connected to the bottom of the water collection tank. One end of the spray head is connected to the inside of the water storage chamber to draw in cooling water, and the other end of the spray head is located inside the spray chamber.

4. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 3, characterized in that: The purging assembly includes a second mounting component and multiple evenly distributed second air inlets on its outer side. The second mounting component has several sets of second air inlets and an annular air storage chamber inside. A second protrusion is provided on one side of the second mounting component. The second protrusion, together with the first protrusion, forms an exhaust channel for discharging gas to purge the outer side of the tube blank. A shielding component is provided inside the air storage chamber for sealing the air storage chamber by sliding adjustment. A telescopic component is connected to one side of the shielding component, and an evenly distributed elastic component is connected to the inner side of one end of the shielding component.

5. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 4, characterized in that: The second air intake channel is connected to the second air intake end and the air storage chamber at both ends, the second mounting part is connected to the first mounting part on one side, the first mounting part is connected to the extrusion die on one side, and the first mounting part, the second mounting part and the extrusion die are coaxially arranged.

6. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 5, characterized in that: The extrusion die includes an extrusion die and a pressure ring fixedly connected to one side. The extrusion die is provided with a flow divider cone and an inner core. The flow divider cone works with the inner core to divide the extruded tube blank melt. The inner side of the inner core is fixedly connected to the gas supply mechanism.

7. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 6, characterized in that: The gas supply mechanism includes a first air inlet symmetrically arranged outside the extrusion die, a first air inlet channel symmetrically opened inside the extrusion die, an air inlet pipe connected to the outside of the symmetrically arranged air inlet channel, and a number of exhaust ports opened at the part of the air inlet pipe where a fastening expansion component is provided, for discharging gas into the fastening expansion component.

8. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 7, characterized in that: The fastening expansion assembly includes an expansion member fixedly installed on the outside of the intake pipe, and an exhaust chamber is opened inside the expansion member.

9. The biaxial orientation expansion molding device for bimodal HDPE pipes according to claim 8, characterized in that: A vacuum cooling sizing device is provided on the outside of the auxiliary expansion assembly to cool and sizing the tube blank after it has undergone two expansion orientations. A traction machine is provided on one side of the vacuum cooling sizing device to drive the tube blank to move smoothly.

10. A biaxial orientation expansion molding process for bimodal HDPE pipes, characterized in that: The biaxial orientation expansion molding apparatus for bimodal HDPE pipes as described in any one of claims 1-9 includes the following steps: S1: The bimodal HDPE granules are evenly mixed and placed into the hopper. As the screw rotates, the granules are conveyed to the barrel and heated to a viscous flow state. S2: The viscous melt is diverted through the extrusion die and into the fastening expansion assembly via the diversion cone, where it undergoes one circumferential expansion to obtain a biaxial orientation structure; S3: After the melt is expanded circumferentially, it is rapidly cooled to a suitable temperature by circumferential water mist spraying. At the same time, the residual cooling water on the outside of the tube blank is blown away, so that the melt retains part of the orientation structure and crystallizes appropriately. S4: When the tube blank is in the transition state, it is stretched and pulled under the action of gas film lubrication, and then undergoes secondary circumferential expansion through the expansion mandrel to further orient and crystallize, thus completing the one-time molding of melt solidification continuous expansion. S5: The expanded pipe is in a highly elastic state and needs to be cooled and sized by a vacuum cooling and sizing device to fix its orientation and crystal structure. S6: After the pipe comes out of the vacuum cooling sizing device, it is pulled forward evenly by the rollers of the traction machine; S7: Pipe to cutting device, cuts the pipe to obtain HDPE pipe with biaxial orientation self-reinforcing structure.

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