Manufacturing equipment and method of large-diameter HDPE (High-Density Polyethylene) pipe

Abstract

The invention discloses equipment and a method for manufacturing a large-diameter HDPE (High-Density Polyethylene) pipe, and aims to solve the problems of uneven wall thickness caused by easy melting and sagging in extrusion molding, low ring stiffness and low efficiency in winding molding, large density difference in compaction molding, difficult utilization of recycled materials and poor control precision in the prior art. The equipment comprises seven integrated units: raw material pretreatment, inner layer extrusion, enhancement layer molding, outer layer coating, sizing cooling, traction and quality detection. The method comprises seven steps from raw material pretreatment to detection, and a maleic anhydride grafted HDPE compatilizer is added when the inner layer uses the recycled material. The pipe wall thickness deviation is smaller than or equal to + / -0.5%, the interlayer peel strength is larger than or equal to 5 N / mm, the recycled material mixing amount is 30-50%, the energy consumption is reduced by 20%, the product percent of pass is larger than or equal to 98%, and the municipal high-pressure conveying requirement is met.

Description

Technical Field

[0001] This invention relates to the field of polymer material pipe manufacturing technology, and in particular to a manufacturing equipment and method for large-diameter HDPE pipes. Background Technology

[0002] Currently, the mainstream manufacturing process for large-diameter HDPE pipes (DN≥800mm) is extrusion molding. However, this process faces insurmountable technical bottlenecks in the production of thick-walled pipes (wall thickness≥57mm): due to the weight of the melt, the pipe blank is prone to significant sag, resulting in an average reduction of 15-20% in the upper wall thickness and an abnormal increase in the lower wall thickness. Even with melt coolers to assist in temperature control, the wall thickness deviation cannot be eliminated, directly causing a product qualification rate of less than 85% and a decrease in pressure resistance of more than 30%. Furthermore, traditional single-screw extruders require a large-diameter screw of Φ200mm or more to achieve this. Producing Φ400mm pipes presents challenges such as insufficient torque and uneven mixing. While output can be improved using two-stage or barrier screw extruders, producing pipes larger than DN1600mm still requires multi-machine co-extrusion, increasing equipment investment by 35% and resulting in an energy consumption ratio as high as 1.8-2.2 kW・h / kg. More importantly, high shear forces during high-speed extrusion (linear speed >0.5m / min) can easily cause localized overheating of the melt (>220℃), leading to HDPE molecular chain breakage. This results in a 12-15% decrease in the tensile yield strength of the pipe and a 30% reduction in oxidation induction time, making it difficult to balance the contradiction between output and material performance. While spiral winding (such as the Krah tube process) can cover the production of pipes up to DN3000mm, its structural characteristics and material compatibility defects severely limit its application scenarios: The process of using PP skeleton pipe spiral winding + HDPE melt composite results in obvious weak interfacial bonding zones in the pipe wall, with ring stiffness only reaching SN8 level, far from meeting the SN16 level requirement for high-pressure transmission scenarios. Furthermore, during electrofusion welding, the porosity rate in the weld zone exceeds 15%, and the coaxiality deviation is >3mm / m, increasing the leakage risk by 40% compared to standard requirements. At the material level, this process mainly... It is compatible with PE80 grade raw materials but not with high-performance materials above PE100. Even if the cost is reduced by 30% by adding fly ash (ratio 1:1~1.85:1), the elastic modulus of the pipe will decrease by 25% and the hydraulic strength will decrease by 20%, making it only suitable for low-pressure sewage discharge scenarios. In addition, the winding speed is limited by the cooling time of the melt (3-5 min / layer), and the production cycle of DN2000mm pipe is as long as 8-10 hours. Moreover, the demolding process is prone to pipe wall deformation, with a roundness deviation of ≥2%, making it difficult to guarantee production efficiency and finished product quality. While compaction molding (such as patent CN201410047442) can produce pipes with a diameter of DN3000 and above, the radial stress gradient generated during roller compaction can lead to a 10-15% difference in pipe wall density distribution (1.35g / cm³ for the inner wall vs. 1.50g / cm³ for the outer wall), resulting in a serious lack of uniformity in ring stiffness. At the same time, when reinforced with steel mesh or carbon fiber, the HDPE melt penetration is insufficient, and the interfacial peel strength is only 3-5MPa, far below the theoretical requirement of ≥8MPa, which reduces the burst pressure of the pipe by 30%. Existing processes still suffer from common shortcomings in material utilization and process control: when the proportion of recycled HDPE exceeds 30%, the pipe's elongation at break drops sharply from 350% to 175%, and the ring flexibility test is prone to failure. Although compatibility can be improved by modifying the masterbatch with POE elastomer, the formulation of recycled materials for large-diameter pipes is still immature, resulting in high raw material costs and non-compliance with environmental protection requirements. In terms of process control, the vacuum shaping process generally adopts open-loop control, with vacuum fluctuations of ±15%, causing the pipe's outer diameter tolerance to reach ±1.5%, far exceeding the industry standard requirement of ±0.5%. The traction system's synchronization accuracy is insufficient, with a speed error >0.5%, further causing pipe wall thickness fluctuations of ±12%, which seriously affects the pipe's installation compatibility and long-term service stability.

[0003] Therefore, it is necessary to provide a new manufacturing equipment and method for large-diameter HDPE pipes to solve the above-mentioned technical problems. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a manufacturing equipment and a supporting manufacturing method for large-diameter HDPE pipes, as detailed below: (a) Manufacturing equipment The equipment is an integrated production line, comprising a raw material pretreatment unit, an inner tube blank extrusion unit, a reinforcing layer forming unit, an outer co-extrusion coating unit, a sizing and cooling unit, a traction cutting unit, and a quality inspection unit connected in sequence. The structure and parameters of each unit are as follows: Raw material pretreatment unit: adopts a paddle-type mixing and drying integrated machine with a mixing speed of 800~1200r / min and a mixing temperature of 80~100℃ to ensure that the uniformity of mixing raw materials and additives is ≥95%; the drying temperature is 100~120℃ and the drying air volume is 1500~2000m³ / h, which can control the moisture content of the material to ≤0.05wt% and avoid the generation of air bubbles during extrusion. Inner tube preform extrusion unit: The core is a twin-screw extruder with a screw diameter ≥150mm and a length-to-diameter ratio of 36:1. A barrier section is set to improve the uniformity of melt plasticization. The discharge end is connected to a spiral distribution die head with a flow divider cone angle of 30°~45° (to ensure uniform melt distribution). The die orifice temperature control accuracy is ±2℃ to ensure uniform wall thickness of the inner tube preform. Reinforcing layer forming unit: It consists of a symmetrical double-rotor winding device and a hydraulic roller system; the double-rotor synchronously feeds the reinforcing strip (steel strip or glass fiber reinforced PP strip) to achieve uniform winding, with a winding angle of 30°~45° (to balance axial and circumferential strength); the hydraulic roller system compacts the winding layer with a pressure of 0.5~2.0MPa, and the roller temperature is 110℃ (to activate the adhesive and improve the bonding force). Outer co-extrusion coating unit: adopts a shielded screw extruder, which can accurately control the melt temperature of 185~190℃ to avoid overheating and degradation of the outer layer raw material; a cooling module is set before coating to reduce the temperature of the reinforcing layer to below 110℃ (to prevent poor bonding caused by excessive temperature difference between the outer layer and the reinforcing layer). Sizing and cooling unit: includes an internal pressure sizing sleeve and a segmented cooling water tank; the internal pressure sizing sleeve is supplied with 0.3~0.6MPa compressed air to make the tube blank fit tightly against the sizing sleeve to achieve accurate sizing; the segmented cooling water tank is provided with a 25~35℃ cooling water jacket (preliminary cooling and shaping) and a 5~8m / s normal temperature air cooling section in sequence, and a temperature transition zone (temperature difference ≤15℃) is provided between the two to avoid internal stress in the tube blank. Traction cutting unit: Three-jaw traction machine (traction wheel diameter ≥1200mm, symmetrically distributed at 120°, with wear-resistant rubber layer on the wheel surface), equipped with a closed-loop control system (real-time monitoring of pipe diameter deviation and adjustment of traction speed); ring cutting machine (speed 3000~5000r / min), equipped with a 50%~70% ethanol aqueous solution spraying component (cooling the cut and reducing burrs). Quality inspection unit: Uses ultrasonic scanning equipment (detection frequency 2~5MHz, defect detection accuracy ≤0.1mm) or laser speckle interferometry equipment to detect interlayer bonding strength online. (ii) Manufacturing method Based on the above-described equipment, the manufacturing method of the present invention includes the following steps: Raw material pretreatment: Weigh HDPE resin (density 0.941~0.965g / cm³, melt flow rate 0.2~1.5g / 10min) and additives (0.1~0.3wt% hindered phenolic antioxidant, 0.05~0.2wt% benzotriazole UV stabilizer, 5~10wt% calcium carbonate masterbatch with particle size ≤5μm) according to the formula, add them to the mixing and drying machine, mix for 10~15min at 800~1200r / min and 80~100℃, and then dry for 2~3h at 100~120℃ and 1500~2000m³ / h air volume, and control the moisture content ≤0.05wt%. Inner layer tube blank extrusion: If modified recycled material is used, add 2~5wt% maleic anhydride-grafted HDPE as a compatibilizer to the pretreated material; feed the material into a twin-screw extruder, set the feeding section temperature to 160~180℃, the compression section temperature to 180~200℃, the homogenization section temperature to 200~220℃, the die flange temperature to 210~230℃, and the die orifice temperature to 205~225℃, and extrude at a screw speed of 20~40r / min and an extrusion pressure of 15~25MPa. The inner layer tube blank is formed through the spiral distribution die head (melt temperature 190~195℃, thickness accounting for 40% of the total wall thickness, the wall thickness of the blank is 5%~10% larger than the target pipe material, leaving room for subsequent processing). Reinforcing layer winding and rolling: The reinforcing strip, pre-coated with HDPE adhesive (containing 2~5wt% maleic anhydride graft), is wound on the surface of the inner tube blank using a symmetrical double-rotor winding device (winding angle 30°~45°). Simultaneously, the hydraulic roller system is activated to compact the winding layer with a pressure of 0.5~2.0MPa (roller temperature 110℃) to ensure a tight bond between the reinforcing strip and the inner tube blank. Outer layer co-extrusion coating: After the reinforcing layer cools to below 110°C, the modified recycled material with added anti-aging agent (0.1~0.3wt% hindered phenolic antioxidant + 0.05~0.2wt% benzotriazole UV stabilizer) is fed into a shielded screw extruder and coated onto the outer surface of the reinforcing layer at a melt temperature of 185~190°C to form an outer layer accounting for 20% of the total wall thickness (the reinforcing layer accounts for 40% of the total wall thickness). Sizing and Cooling: The composite tube blank is introduced into the internal pressure sizing sleeve, and compressed air of 0.3~0.6MPa is introduced to make the outer wall of the blank adhere tightly to the sizing sleeve. At the same time, it is cooled by a cooling water jacket of 25~35℃ for 10~15s. Then it is sent to the normal temperature air cooling section of the segmented cooling water tank and cooled by a wind speed of 5~8m / s for 20~30s, so that the temperature of the tube blank drops to the ambient temperature ±5℃. Traction and Cutting: Start the three-jaw traction machine and pull at a speed of 0.5~1.5m / min. The closed-loop control system monitors the pipe diameter deviation in real time and maintains the deviation ≤±0.5% by adjusting the traction speed. When the pipe length reaches 6~12m, start the ring cutter to cut. During the cutting process, spray 50%~70% ethanol aqueous solution coolant to control the verticality deviation of the cut ≤0.5mm / m. Quality inspection: The interlayer bonding strength of the pipe is tested by the quality inspection unit to ensure that the peel strength is ≥5N / mm and the shear strength is ≥10MPa; at the same time, the pipe diameter deviation and wall thickness uniformity are tested. Qualified products are put into storage, and unqualified products are marked and reworked.

[0005] Compared with related technologies, the manufacturing equipment and method for large-diameter HDPE pipes provided by this invention have the following advantages: Excellent interlayer bonding performance: Through the design of pre-coating the reinforcing belt with HDPE adhesive containing maleic anhydride grafts, hydraulic roller compaction (110℃ activation of adhesive), and cooling the reinforcing layer to below 110℃ before covering the outer layer, the interlayer peel strength is ≥5N / mm and the shear strength is ≥10MPa, which is more than 60% higher than the traditional technology.

[0006] High molding precision: The twin-screw extruder is equipped with a barrier section and a spiral distribution die (30°~45° flow divider cone) to ensure uniform plasticization of the inner tube blank; the three-jaw traction machine is equipped with closed-loop control, and the tube diameter deviation is ≤±0.5%; the ring cutter is cooled with ethanol aqueous solution, and the cut perpendicularity deviation is ≤0.5mm / m. High utilization rate of recycled materials: When the inner layer uses modified recycled materials, 2-5 wt% maleic anhydride grafted HDPE compatibilizer is added, and the outer layer uses modified recycled materials containing anti-aging agents. Under the premise of ensuring the mechanical properties of the pipe, the amount of recycled materials can reach 30%-50%, reducing the raw material cost by 20%-30%. High production stability: The equipment is designed with integrated features and the parameters of each unit are controlled in a coordinated manner; the segmented cooling system has a temperature transition zone to prevent internal stress cracking; the quality inspection unit provides online monitoring, increasing the product qualification rate to over 98% and improving production efficiency by 15% to 20%. Excellent anti-aging properties: Both the inner and outer layers are enriched with hindered phenolic antioxidants and benzotriazole UV stabilizers. Accelerated aging tests have verified that after 5 years of outdoor exposure, the mechanical properties of the pipes have a degradation rate of ≤10%, and the service life is extended to more than 50 years. Detailed Implementation

[0007] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely for explaining the invention and are not intended to limit the invention.

[0008] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0009] I. Overall Overview of the Implementation Examples This section uses three examples to verify the feasibility and superiority of the manufacturing equipment and method of the present invention under different raw material types (virgin / recycled), reinforcing strip types (steel strip / glass fiber reinforced PP strip), and pipe wall thickness specifications: Example 1: Using virgin HDPE as raw material and steel strip as reinforcement layer, the production stability and interlayer bonding performance of conventional large-diameter HDPE pipes (total wall thickness ≤10mm) were verified. Example 2: Using HDPE modified recycled material (40%~50% content) as raw material and glass fiber reinforced PP tape as reinforcement layer, the mechanical properties and molding accuracy of the pipe when the recycled material is used efficiently were verified. Example 3: Using virgin HDPE material as raw material and double steel strips as reinforcement layers, the production process adaptability and high strength performance of pipes with large wall thickness (total wall thickness ≥ 20 mm) were verified. All embodiments are based on the integrated equipment described in this invention, strictly control the core process parameters, and the final test results all meet the requirements of the invention's purpose of "peel strength ≥5N / mm, shear strength ≥10MPa, and pipe diameter deviation ≤±0.5%". II. Detailed Implementation Examples Example 1 (Produced from virgin material, reinforced with steel strip, total wall thickness 7.5mm) Equipment preparation and parameter calibration Raw material pretreatment unit: adopts SHR-1000 paddle-type mixing and drying integrated machine, and pre-calibrates the speed sensor (to ensure 800~1200r / min error ≤±10r / min), temperature sensor (80~100℃ error ≤±1℃), and drying fan air volume meter (1500~2000m³ / h error ≤±50m³ / h). Inner tube preform extrusion unit: Twin-screw extruder model SHJ-160 (screw diameter 160mm, length-to-diameter ratio 36:1), barrier section length is 1 / 5 of the total screw length, spiral distribution die head flow divider cone angle is 35°, and the temperature of each heating section (feeding section 160~180℃, compression section 180~200℃, etc.) is calibrated in advance with thermocouples, and the error is controlled within ±2℃; Reinforcing layer forming unit: The symmetrical double turntable winding device is model CW-2000, with a turntable diameter of 1.2m. The synchronization accuracy of the double turntables is adjusted in advance (speed difference ≤ ±1r / min), the pressure sensor of the hydraulic roller system is calibrated (0.5~2.0MPa error ≤ ±0.05MPa), and the roller heating tube temperature is set to 110℃ (temperature control error ±3℃). Other units: The internal pressure sizing sleeve pressure valve of the sizing cooling unit is calibrated (0.3~0.6MPa, error ≤ ±0.02MPa); the water temperature sensor of the segmented cooling water tank is 25~35℃, error ±1℃; the anemometer is 5~8m / s, error ±0.2m / s; the traction wheel speed sensor of the traction cutting unit is 0.5~1.5m / min, error ±0.05m / min; the tachometer of the ring cutting machine is 3000~5000r / min, error ±50r / min; the concentration of the ethanol aqueous solution is calibrated to 50%~70% using a refractometer. Raw material preparation and pretreatment Raw material selection: The new HDPE material is Yanshan Petrochemical 6100M (density 0.952g / cm³, melt flow rate 0.8g / 10min, density measured according to GB / T1033.1-2008, melt flow rate measured according to GB / T3682.1-2018). Additives: Hindered phenolic antioxidant 1010 (BASF), benzotriazole UV stabilizer UV-327 (Ciba), and calcium carbonate masterbatch in nanoscale (particle size ≤5μm, whiteness ≥95%, Zhejiang Chuanhua). Pretreatment process: Weigh the materials according to the ratio (94.6wt% HDPE virgin material, 0.2wt% antioxidant, 0.1wt% UV stabilizer, and 5.1wt% calcium carbonate masterbatch). First, put the HDPE virgin material into the mixing and drying machine and start stirring (800r / min). After 1 minute, slowly add the antioxidant and UV stabilizer (avoid dust). After 3 minutes, add the calcium carbonate masterbatch and heat to 90℃ and mix for 12 minutes. Then, turn off the stirring and turn on the drying fan (air volume 1800m³ / h). Heat to 110℃ and dry for 2.5 hours. During this period, take samples every 30 minutes to measure the moisture content (according to GB / T2914-2008, measured with a Karl Fischer moisture analyzer). The final moisture content is controlled at 0.03wt%.

[0010] Inner tube blank extrusion (3mm thick, accounting for 40% of the total wall thickness) Material conveying: The pretreated material is fed into the twin-screw extruder through a loss-in-weight feeder (feeding accuracy ±0.5%), with the feeding rate set at 500 kg / h; Temperature and speed control: feeding section 170℃, compression section 190℃, homogenization section 210℃, die flange 220℃, die orifice 215℃, screw speed 30r / min, extrusion pressure is monitored in real time by pressure sensor (maintained at 18~20MPa, automatic speed reduction when exceeding 25MPa). Melt quality control: Take a sample of the melt temperature at the die opening every 5 minutes (using a contact thermometer, 190~195℃). If the temperature exceeds the tolerance, adjust the homogenization section temperature (±5℃). The billet wall thickness is detected by a laser thickness gauge (accuracy ±0.01mm). Set the billet wall thickness to 3.24mm (8% larger than the target 3mm, leaving machining allowance). If the deviation exceeds ±0.05mm, adjust the die head clearance. Reinforcing layer winding and roll forming (3mm thickness, accounting for 40% of the total wall thickness) Reinforcing strip preparation: The steel strip is hot-dip galvanized steel strip (thickness 1.5mm, width 50mm, tensile strength ≥300MPa), pre-coated with HDPE adhesive (containing 3wt% maleic anhydride grafted HDPE, adhesive thickness 50μm, peel strength tested according to GB / T2790-1995), preheated in a 60℃ oven for 30min in advance (to avoid adhesive clumping); Winding process: The inner tube blank is pulled into the double turntable winding device and the winding angle is adjusted to 40° (monitored in real time by the angle sensor, with a deviation of ±1°). The speed of the double turntable is set to 15r / min to ensure that the overlap of the reinforcing tape is 1 / 3 of the bandwidth (to avoid gaps). Roller pressure control: The hydraulic roller starts synchronously during winding, with the pressure set at 1.2MPa and the roller temperature at 110℃. Samples are taken every 10m to check the adhesion of the reinforcing layer (visual inspection shows no bubbles or wrinkles, and the adhesion rate is ≥99%). If the adhesion is poor, the roller pressure (±0.1MPa) or temperature (±5℃) is adjusted. Outer co-extruded coating (1.5mm thick, accounting for 20% of the total wall thickness) Raw material preparation: The ratio of new HDPE material for the outer layer is the same as that for the inner layer, the amount of anti-aging agent added is the same, and the material pretreatment is the same as in step 2 (moisture content ≤0.05wt%). Reinforcement layer cooling: After the reinforcement layer is wound, it is cooled to 105℃ by an air-cooling module (wind speed 4m / s) (detected with an infrared thermometer to avoid exceeding 110℃). Coating process: Shielded screw extruder (model SJ-90) temperature settings: feeding section 160℃, compression section 175℃, homogenization section 185℃, melt temperature 188℃ (error ±2℃), extrusion rate set to 200kg / h. During coating, the outer layer thickness is monitored by a visual inspection system (1.5mm, deviation ±0.05mm). If the deviation exceeds the limit, the extruder speed is adjusted (±2r / min). Sizing and Cooling Internal pressure sizing: The composite tube blank is introduced into an internal pressure sizing sleeve (500mm in diameter, corresponding to large diameter specifications), and 0.4MPa compressed air is introduced (pressure fluctuation ±0.02MPa). At the same time, it is cooled by a 30℃ cooling water jacket for 12s (water temperature fluctuation ±1℃). The fit between the outer wall of the tube blank and the sizing sleeve is fed back by a pressure sensor (fitting pressure ≥0.3MPa). Segmented cooling: The tube blank is first cooled by 30℃ cooling water for 35 seconds (water depth 1.5m, tube blank is completely submerged), and then cooled by 6m / s ambient temperature air for 25 seconds (air temperature 25℃). After cooling, the tube blank temperature is detected by infrared thermometer (28℃, ±3℃ of ambient temperature) to avoid stress caused by excessive temperature difference. Traction and Cutting Traction control: The three-jaw traction machine has a traction speed of 1.0 m / min and the pressure of the three traction wheels is set to 0.8 MPa (to ensure that the tube blank does not slip). The closed-loop control system collects tube diameter data every 2 seconds (laser diameter measuring instrument, accuracy ±0.1 mm). If the tube diameter deviation exceeds ±2.5 mm (corresponding to ±0.5%), the traction speed is automatically adjusted (±0.05 m / min). Cutting process: When the pipe length reaches 10m (encoder count, error ±0.05m), the ring cutter is started (speed 4000r / min), and 60% ethanol aqueous solution is sprayed at the same time (flow rate 100mL / min, evenly covering the cut). The cutting time is controlled at 10s. After cutting, the perpendicularity of the cut is checked with a right angle ruler (deviation 0.3mm / m, if the deviation exceeds the tolerance, adjust the positioning device of the cutter). Quality Inspection and Results Mechanical properties: According to GB / T18477.1-2019, one sample was taken from every 20 pipes to measure the interlayer peel strength (5.8 N / mm) and shear strength (11.5 MPa). Dimensional accuracy: Pipe diameter deviation ±1.5mm (±0.3%), wall thickness uniformity ±0.08mm; Appearance and pass rate: The tube surface is free of scratches and bubbles, and the cut is free of burrs. The pass rate is 99.2% when 100 tubes are produced continuously. Example 2 (produced from recycled materials, reinforced with glass fiber reinforced PP tape, total wall thickness 10mm) Core differences and supplementary details Raw materials: HDPE modified recycled material is pipe crushed material (extruded by twin screw extrusion, melt flow rate 0.6g / 10min), with a dosage of 40% (inner layer) and 50% (outer layer), and 3wt% maleic anhydride grafted HDPE compatibilizer (model CMG9801, Shanghai Rizhisheng) is added. The compatibilizer and recycled material are premixed in a high-speed mixer (1000r / min, 80℃) for 5min. Reinforcing tape: Glass fiber reinforced PP tape (glass fiber content 40%, thickness 2mm, width 60mm, tensile modulus ≥5GPa), HDPE adhesive contains 2.5wt% maleic anhydride grafts, and the adhesive is cured in an oven at 80℃ for 1h after coating; Key parameter adjustments: inner layer extrusion screw speed 25r / min (recycled material melt has slightly poor fluidity, reduce speed to prevent overload), reinforcing layer winding angle 35° (glass fiber tape has high rigidity, reduce angle to prevent breakage), hydraulic roller pressure 0.8MPa (glass fiber tape is easily damaged, reduce pressure), traction speed 0.8m / min (recycled material cools slowly, reduce traction speed to ensure sufficient cooling). Quality inspection results Mechanical properties: peel strength 5.2 N / mm, shear strength 10.8 MPa (although lower than Example 1, it still meets the requirements of ≥5 N / mm and ≥10 MPa). Dimensional accuracy: Pipe diameter deviation ±2mm (±0.4%), cut perpendicularity deviation 0.4mm / m; Economic efficiency: With 40%~50% recycled material, raw material costs are reduced by 25%, and the pass rate is 98.5% when producing 100 pieces continuously. Example 3 (Production of thick-walled pipes, reinforced with double steel strips, total wall thickness 20mm) Core differences and supplementary details Equipment compatibility: Twin-screw extruder model SHJ-180 (screw diameter 180mm, feed rate 1000kg / h), spiral distribution die head with a 45° cone angle (larger distribution angle is required for thick-walled tube blanks to ensure uniform melt), and an internal pressure sizing sleeve with a diameter of 800mm (for large diameter specifications). Reinforcing layer: Double steel strips (each layer is 4mm thick, totaling 8mm, accounting for 40% of the total wall thickness), the first layer of steel strips is wound at a 45° angle (to enhance circumferential strength), the second layer is wound at a 30° angle (to enhance axial strength), and HDPE adhesive (containing 5wt% maleic anhydride grafts to improve interlayer bonding) is applied between the two layers. Process adjustments: Inner layer extrusion temperature increased by 5℃ (homogenization section 215℃, die 220℃, higher temperature required for thicker walls to ensure plasticization), extrusion pressure 22~24MPa, hydraulic roller pressure 1.8MPa (double steel strip is thicker, requiring greater pressure for compaction), cooling time extended (cooling water jacket 15s, air cooling 30s, to ensure thorough cooling of thicker billets), traction speed 0.6m / min. Quality inspection results Mechanical properties: peel strength 6.5 N / mm, shear strength 12.8 MPa (double steel strip reinforcement significantly improves strength); Dimensional accuracy: Pipe diameter deviation ±1.6mm (±0.2%), wall thickness uniformity ±0.1mm, cut perpendicularity deviation 0.2mm / m; Application compatibility: The ring stiffness is measured according to GB / T19472.1-2019 and reaches SN16 level (≥16kN / m²), meeting the requirements of municipal high-pressure water transmission, with a pass rate of 99.5%.

[0011] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for manufacturing a large-diameter HDPE pipe, characterized in that, It includes a raw material pretreatment unit, an inner tube blank extrusion unit, a reinforcing layer forming unit, an outer co-extrusion coating unit, a sizing and cooling unit, a traction cutting unit, and a quality inspection unit connected in sequence. The raw material pretreatment unit is a mixing and drying device. This device has a mixing speed of 800~1200 r / min, a mixing temperature of 80~100℃, a drying temperature of 100~120℃, and a drying air volume of 1500~2000 m³ / h, and can control the material moisture content to ≤0.05wt%. The inner tube preform extrusion unit is a twin-screw extruder with a screw diameter ≥150mm, a length-to-diameter ratio of 36:1, and a barrier section for improving the uniformity of melt plasticization. The discharge end of the twin-screw extruder is connected to a spiral distribution die head with a flow divider cone angle of 30°~45°. The reinforcing layer forming unit includes a symmetrical double-rotor winding device and a hydraulic roller system. The compaction pressure of the hydraulic roller system is 0.5~2.0MPa and the roller temperature is 110℃. The outer co-extrusion coating unit is a shielded screw extruder; The sizing and cooling unit includes an internal pressure sizing sleeve and a segmented cooling water tank. The segmented cooling water tank is provided with a cooling water jacket with a water temperature of 25~35℃ and a normal temperature air cooling section with a wind speed of 5~8m / s. The traction cutting unit includes a three-jaw traction machine and a ring cutter. The traction wheel diameter of the three-jaw traction machine is ≥1200mm and it is equipped with a closed-loop control system. The rotation speed of the ring cutter is 3000~5000r / min and it is equipped with a 50%~70% ethanol aqueous solution spraying component. The quality inspection unit is an ultrasonic scanning device.

2. A method for manufacturing large-diameter HDPE pipes based on the manufacturing equipment described in claim 1, characterized in that, Includes the following steps: (1) Raw material pretreatment: HDPE resin and additives are added to a mixing and drying device, mixed for 10-15 min and then dried for 2-3 h; the density of the HDPE resin is 0.941-0.965 g / cm³, the melt flow rate (190℃, 2.16 kg) is 0.2-1.5 g / 10 min, and the additives include 0.1-0.3 wt% hindered phenolic antioxidant, 0.05-0.2 wt% benzotriazole UV stabilizer and 5-10 wt% calcium carbonate masterbatch with a particle size ≤5 μm; (2) Inner layer tube blank extrusion: The pretreated modified recycled material is fed into a twin-screw extruder. The feeding section is set to 160~180℃, the compression section to 180~200℃, the homogenization section to 200~220℃, the die flange to 210~230℃, and the die orifice to 205~225℃. The extrusion is carried out at a screw speed of 20~40r / min and an extrusion pressure of 15~25MPa. The inner layer tube blank is formed through the spiral distribution die head. The melt temperature is controlled at 190–195℃. The thickness of the inner layer tube blank accounts for 40% of the total wall thickness of the tube, and the wall thickness of the blank is 5%~10% larger than that of the target tube. (3) Reinforcing layer winding and rolling: The reinforcing tape pre-coated with HDPE adhesive is wound on the surface of the inner tube blank by a symmetrical double-rotor winding device. The reinforcing tape is glass fiber reinforced PP tape, and the winding angle is 30°–45°. At the same time, a hydraulic roller system is used to compact the winding layer with a pressure of 0.5–2.0MPa. (4) Co-extrusion coating of outer layer: After cooling the reinforcing layer to below 110°C, the modified recycled material with added anti-aging agent is coated on the outer surface of the reinforcing layer through a shielded screw extruder to form an outer layer accounting for 20% of the total wall thickness. The melt temperature is controlled at 185–190°C. (5) Sizing and cooling: The composite tube blank is introduced into the internal pressure sizing sleeve, and compressed air of 0.3~0.6MPa is introduced to make the outer wall of the blank adhere to the sizing sleeve. At the same time, it is cooled by the cooling water jacket for 10~15s; then it is sent to the normal temperature air cooling section of the segmented cooling water tank and cooled by normal temperature air of 5~8m / s for 20~30s. (6) Traction and cutting: A three-jaw traction machine is used to pull at a speed of 0.5~1.5m / min. The traction speed is monitored and adjusted in real time through a closed-loop control system to control the pipe diameter deviation ≤±0.5%; when the pipe length reaches 6~12m, a ring cutter is used to cut it. During cutting, 50%~70% ethanol aqueous solution is sprayed as coolant to control the verticality deviation of the cut ≤0.5mm / m. (7) Quality inspection: The interlayer bonding strength is tested by the quality inspection unit to ensure that the peel strength is ≥5N / mm and the shear strength is ≥10MPa.

3. The manufacturing method according to claim 2, characterized in that, In step (2), if modified recycled material is used for the inner layer, 2-5 wt% of maleic anhydride-grafted HDPE is added as a compatibilizer.

4. The manufacturing method according to claim 2, characterized in that, In step (4), the anti-aging agent added to the outer modified recycled material is 0.1~0.3wt% hindered phenolic antioxidant and 0.05~0.2wt% benzotriazole UV stabilizer.

5. The manufacturing method according to claim 2, characterized in that, The HDPE adhesive in step (3) contains 2-5 wt% maleic anhydride graft.

6. The manufacturing equipment according to claim 1, characterized in that, The die temperature control accuracy of the twin-screw extruder is ±2℃, ensuring the stability of the inner tube blank forming.

7. The manufacturing equipment according to claim 1, characterized in that, The segmented cooling water tank has a temperature transition zone between the cooling water jacket and the ambient temperature air cooling section to prevent stress cracking of the tube blank due to excessive temperature difference.

8. The manufacturing method according to claim 2, characterized in that, In step (1), the mixing and drying device adopts a paddle-type stirring structure to ensure that the mixing uniformity of raw materials and additives is ≥95%.

9. The manufacturing method according to claim 2, characterized in that, In step (7), if ultrasonic scanning is used, the detection frequency is set to 2~5MHz to ensure that the detection accuracy of interlayer defects is ≤0.1mm.

10. The manufacturing equipment according to claim 1, characterized in that, The three traction wheels of the three-jaw traction machine are symmetrically distributed at 120°, and the surface of the traction wheels is provided with a wear-resistant rubber layer to avoid scratching the surface of the pipe.