Hard polyurethane spray polyethylene winding prefabricated direct-buried heat preservation pipe processing technology

Abstract

This application relates to the processing technology of rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes, covering the field of prefabricated direct-buried insulated pipe processing technology, including S1, precise inspection and three-level purification pretreatment of steel pipes upon arrival at the factory; S2, gradient temperature-controlled preheating to prevent rust recurrence; S3, dynamic layered gradient spraying and foaming with temperature and humidity linkage; S4, segmented constant temperature precise curing; S5, interlayer nano-modification and adhesion enhancement treatment; S6, closed-loop tension precise winding and forming; S7, synchronous gradient cooling and shaping; S8, graded constant temperature and humidity curing; and S9, full-item traceability quality inspection. This application utilizes dynamic proportioning technology linked to ambient temperature and humidity to achieve three-layer gradient layered atomized spraying and foaming, improving the uniformity and closed-cell rate of the insulation layer; it constructs a four-layer composite structure by adding a nano-rare earth adhesion-enhancing coating to solve the defect of interlayer layering and water seepage; and it combines closed-loop tension winding, three-stage synchronous gradient cooling, and graded curing processes according to pipe diameter to achieve precise product shaping and full curing.

Description

Technical Field

[0001] This application relates to the field of prefabricated direct-buried insulated pipe processing technology, and in particular to the processing technology of rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes. Background Technology

[0002] Pre-insulated direct-buried pipes are core components of urban centralized heating, industrial media transportation, and underground integrated pipe networks. Their structural integrity, insulation stability, and burial durability directly determine the energy consumption and service life of the pipeline network. With the upgrading of national standards GB / T34611-2017 and GB / T50538-2020, the industry has put forward stringent requirements for the interlayer composite strength, insulation uniformity, airtightness and waterproofness, and quality control level of large-scale production of insulation pipes.

[0003] The traditional "pipe-in-pipe" filling insulation process has been gradually phased out due to its poor overall molding and weak adaptability to large diameters. Currently, the industry mainstream adopts the polyurethane spraying and polyethylene winding integrated process. This process abandons the sleeve filling mode, can achieve continuous integrated molding, and has a wide range of pipe diameter adaptability. It has obvious advantages over the traditional process and has been widely used in the production of municipal and industrial insulation pipes.

[0004] Regarding the aforementioned technologies, the applicant believes that existing processes rely solely on the physical bonding of polyurethane insulation layers and polyethylene outer sheaths, lacking a transitional composite structure. Furthermore, each process lacks refined closed-loop control involving environmental linkage and pipe diameter adaptation. This leads to the formation of micro-gaps between layers and water vapor infiltration during the underground service of the insulated pipe, resulting in water absorption and powdering of the insulation layer, pipe corrosion, and a decline in insulation performance. Consequently, the pipeline network suffers from high long-term energy consumption and a significantly shortened service life, failing to meet the application requirements of high-standard, long-life pipeline network projects. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes.

[0006] The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes provided in this application adopts the following technical solution: The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes includes the following steps: S1. Precise inspection and three-level purification pretreatment of steel pipes upon arrival at the factory: The working steel pipes are inspected for appearance, size and wall thickness. Unqualified pipes are rejected. The pipes are then subjected to three-level purification in sequence, including high-temperature degreasing spray, high-pressure micro-dust blowing and closed-loop shot blasting. The rust removal grade reaches Sa2.5 near-white level. The pipes are then moved to the next process within 4 hours after rust removal, and the pipe openings are sealed. S2. Gradient temperature control preheating to prevent rust: Real-time monitoring of the workshop environment dew point temperature, using hot air circulation gradient preheating method to ensure that the steel pipe preheating temperature is always 3-5℃ higher than the ambient dew point temperature, and the preheating temperature is adjusted according to the ambient temperature in stages, so that the circumferential temperature difference of the pipe wall after preheating is ≤±2℃. S3, Temperature and Humidity Linked Dynamic Layered Gradient Spraying Foaming: The ratio of polyurethane black and white materials is dynamically adjusted according to the real-time temperature and humidity of the workshop. A three-layer gradient layered atomization spraying process is adopted to form the bottom bonding reinforcement layer, the middle insulation main layer, and the surface transition smoothing layer respectively. The spraying pressure, spray gun travel speed, steel pipe rotation speed and working environment parameters are controlled throughout the process. A waste recycling device is provided to realize the recycling of raw materials. S4. Segmented constant temperature precision curing: After spraying, the coating is transferred to a closed curing workshop. A segmented gradient curing mode is adopted, which uses high temperature reaction curing in the early stage and low temperature curing and shaping in the later stage. The curing time is matched according to the pipe diameter and specifications to prevent foam deformation and cracking. S5. Interlayer nano-modification and thickening treatment: A nano-rare earth composite thickening coating is sprayed onto the surface of the cured polyurethane insulation layer to form an interlayer transition composite structure. S6. Closed-loop tension precision winding molding: The melt-extruded polyethylene sheet is spirally wound onto the outside of the tackifying coating through a fully closed-loop tension control method, precisely controlling the winding pitch, sheet overlap width and constant tension. S7. Synchronous gradient cooling and shaping: During the winding process, a three-stage spray gradient cooling process is adopted simultaneously to gradually reduce the temperature and shape the winding process in accordance with the winding rhythm. S8. Graded constant temperature and humidity curing: The formed insulation pipe is transferred to the curing workshop, and the curing time is matched according to the pipe diameter specifications to complete the full curing of the interlayer structure in a constant temperature and humidity environment. S9. Full-item traceability quality inspection: Conduct full-item inspections on the appearance, dimensions, bonding strength, closed-cell rate, insulation coefficient, and airtightness of the cured insulation pipes, bind a unique number to realize full-process parameter traceability, and complete the finished product protection and warehousing after rejecting unqualified products.

[0007] Optionally, in the S1 three-level purification pretreatment, the high-temperature degreasing spray uses a neutral degreasing agent at 60-70℃, with a spraying pressure of 0.3-0.5MPa and a spraying time of 3-5min; the shot blasting rust removal uses 1.2-1.5mm alloy steel shot at a shot blasting speed of 70-80m / s. After rust removal, the steel pipe surface is free of oxide scale, oil stains, dust, and water stains, and presents a uniform matte metallic luster.

[0008] Optionally, during S2 gradient temperature control preheating, the preheating temperature is 55-60℃ when the ambient temperature is ≤15℃, 45-55℃ when the ambient temperature is 15-25℃, and 40-45℃ when the ambient temperature is ≥25℃. After preheating, the temperature is kept constant for 5 minutes.

[0009] Optionally, in the S3 dynamic layered gradient spraying foaming process, the basic ratio of polyurethane black and white materials is 1:1, which is slightly adjusted to 1.02:1 when the humidity is 50%-70% and the temperature is 15-25℃, with a total ratio error of ≤±2%; the thickness of the three spraying layers is 8-10mm, 10-12mm, and 6-8mm respectively, with an interval of 2-3min between layers; the spraying pressure is 0.45-0.55MPa, the spray gun travel speed is 0.8-1.2m / s, the steel pipe rotation speed is 12-15r / min, and the working environment has an air speed ≤5m / s, a temperature of 15-35℃, and a humidity of 40%-70%.

[0010] Optionally, in the S4 segmented constant temperature precision curing process, the reaction curing temperature is 30-35℃ for 0-4h and the curing and shaping temperature is 25-30℃ for 4-12h; the curing time is 12h for pipes of DN100 and below, 16h for pipes of DN100-DN500, and 20h for pipes of DN500 and above. Pipe movement and vibration are prohibited throughout the curing process.

[0011] Optionally, in the S5 interlayer nano-modification and adhesion enhancement treatment, the nano-rare earth composite adhesion enhancement coating is composed of nano-silica, rare earth oxides, and polyurethane adhesion enhancement resin. The coating thickness is 0.2-0.5 mm, penetrating and interlocking the micropores of the polyurethane surface, and then thermally fused with the subsequent polyethylene layer.

[0012] Optional, S6 closed-loop tension precision winding, polyethylene sheet thickness 2-5mm, width 200-400mm, constant winding tension 80-120N, tension fluctuation ≤±3N, winding pitch 50-150mm, sheet overlap width ≥15%, overlap joints are heat-pressed seamlessly bonded.

[0013] Optionally, in the S7 synchronous gradient cooling and shaping process, the three-stage spray cooling temperatures are 35-40℃, 20-25℃, and 15-20℃ respectively, and the cooling action and the sheet winding action are linked and synchronized in real time.

[0014] Optionally, in the S8 grade constant temperature and humidity curing, the curing environment temperature is 25±2℃ and the humidity is 55±5%; DN100 and below pipelines are cured for 24 hours, DN100-DN500 pipelines are cured for 30 hours, and DN500 and above pipelines are cured for 36 hours.

[0015] Optionally, the waste recycling device in S3 collects, filters, and purifies the polyurethane raw materials splashed by spraying and atomization in real time for recycling, thereby improving the utilization rate of raw materials; in S9, the entire process of production, maintenance, and testing parameters are entered into the system in real time and bound to the unique number of the pipeline to achieve process traceability of the entire life cycle of a single pipeline.

[0016] In summary, this application includes at least one of the following beneficial technical effects: This invention employs a three-stage purification + gradient temperature control preheating technology to thoroughly remove hidden impurities and moisture from steel pipes, precisely match environmental conditions to eliminate the risk of rust recurrence, and increase the bonding strength between polyurethane and the steel pipe substrate by more than 35%, thereby fundamentally solving the problems of delamination, hollowing, and cracking, and achieving a qualitative improvement in the stability of the pipeline base layer. Dynamic mixing ratio and layered gradient spraying process make the polyurethane foaming reaction more complete, the foam cells are fine and uniform, the closed cell rate is stable, the circumferential and axial insulation thickness deviation of the pipeline is controlled within ±1mm, there is no problem of local heat loss concentration, the overall insulation and energy-saving efficiency is improved by more than 25%, and the long-term pipeline operation energy consumption is significantly reduced. A new nano-rare earth adhesive transition layer is added to construct a four-layer integrated composite structure with no micro-gaps between the layers, improving the adhesion and effectively blocking the penetration of water vapor and corrosive media. This completely solves the problems of water seepage between layers, insulation layer failure, and steel pipe corrosion in traditional processes, and increases the service life of the finished product buried underground from the traditional 20 years to more than 30 years. The closed-loop tension control + synchronous gradient cooling process solves the problems of edge warping, gaps and deformation caused by unstable winding tension and delayed cooling in the existing winding process. The outer protective layer overlap airtightness meets the standards, and the impact strength, tensile strength and anti-aging performance are significantly improved. It can be adapted to complex and harsh working conditions such as saline-alkali land, heavy-load road surface and high humidity. The entire process parameter linkage closed-loop control and intelligent traceability quality control eliminate human operation errors and arbitrary parameter adjustment problems, improve the finished product qualification rate, improve production efficiency, significantly reduce rework costs and schedule pressure, and adapt to the large-scale project supply needs; Specialized waste recycling equipment enables the recycling of coating raw materials, improves raw material utilization, significantly reduces emissions of fugitive waste gas and dust, ensures that the workshop production environment meets standards, and further reduces production costs. This process is compatible with pipe diameters from DN50 to DN1200 and can process straight pipes, bends, tees, reducers and other irregular pipe fittings. It is suitable for various pipeline network conditions such as high temperature, low temperature, high corrosion and high load. Its customization capabilities and engineering adaptability far exceed those of existing traditional processes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0018] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0019] This application discloses a processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes. (Refer to...) Figure 1 The processing technology of rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipe includes the following steps: S1. Precise inspection and three-level purification pretreatment of steel pipes upon arrival at the factory: The working steel pipes are inspected for appearance, size and wall thickness. Unqualified pipes are rejected. The pipes are then subjected to three-level purification in sequence, including high-temperature degreasing spray, high-pressure micro-dust blowing and closed-loop shot blasting. The rust removal grade reaches Sa2.5 near-white level. The pipes are then moved to the next process within 4 hours after rust removal, and the pipe openings are sealed. S2. Gradient temperature control preheating to prevent rust: Real-time monitoring of the workshop environment dew point temperature, using hot air circulation gradient preheating method to ensure that the steel pipe preheating temperature is always 3-5℃ higher than the ambient dew point temperature, and the preheating temperature is adjusted according to the ambient temperature in stages, so that the circumferential temperature difference of the pipe wall after preheating is ≤±2℃. S3, Temperature and Humidity Linked Dynamic Layered Gradient Spraying Foaming: The ratio of polyurethane black and white materials is dynamically adjusted according to the real-time temperature and humidity of the workshop. A three-layer gradient layered atomization spraying process is adopted to form the bottom bonding reinforcement layer, the middle insulation main layer, and the surface transition smoothing layer respectively. The spraying pressure, spray gun travel speed, steel pipe rotation speed and working environment parameters are controlled throughout the process. A waste recycling device is provided to realize the recycling of raw materials. S4. Segmented constant temperature precision curing: After spraying, the coating is transferred to a closed curing workshop. A segmented gradient curing mode is adopted, which uses high temperature reaction curing in the early stage and low temperature curing and shaping in the later stage. The curing time is matched according to the pipe diameter and specifications to prevent foam deformation and cracking. S5. Interlayer nano-modification and thickening treatment: A nano-rare earth composite thickening coating is sprayed onto the surface of the cured polyurethane insulation layer to form an interlayer transition composite structure. S6. Closed-loop tension precision winding molding: The melt-extruded polyethylene sheet is spirally wound onto the outside of the tackifying coating through a fully closed-loop tension control method, precisely controlling the winding pitch, sheet overlap width and constant tension. S7. Synchronous gradient cooling and shaping: During the winding process, a three-stage spray gradient cooling process is adopted simultaneously to gradually reduce the temperature and shape the winding process in accordance with the winding rhythm. S8. Graded constant temperature and humidity curing: The formed insulation pipe is transferred to the curing workshop, and the curing time is matched according to the pipe diameter specifications to complete the full curing of the interlayer structure in a constant temperature and humidity environment. S9. Full-item traceability quality inspection: Conduct full-item inspections on the appearance, dimensions, bonding strength, closed-cell rate, insulation coefficient, and airtightness of the cured insulation pipes, bind a unique number to realize full-process parameter traceability, and complete the finished product protection and warehousing after rejecting unqualified products.

[0020] Example 1: Small diameter pipe processing (DN100, low temperature environment production, ambient temperature 10℃, humidity 45%) S1. Steel pipe pretreatment: Select qualified seamless steel pipes and sequentially spray them with 65℃ neutral degreasing agent for 4 minutes, clean air micro-dust blowing at 0.6MPa, and variable frequency closed-loop shot blasting to remove rust. The steel shot particle size is 1.3mm and the shot blasting speed is 75m / s. After rust removal, the steel pipes are free of impurities, water stains, and oxide scale. They are transferred to the next process within 4 hours and the pipe ends are sealed.

[0021] S2. Gradient preheating: Real-time detection of ambient dew point, steel pipe preheating temperature set at 58℃, 4℃ higher than ambient dew point, full-area hot air circulation preheating, pipe wall circumferential temperature difference ≤±2℃, constant temperature and stand for 5 minutes after preheating.

[0022] S3. Dynamic layered spraying: Low temperature and low humidity environment, black and white material ratio 1:1, ratio error ≤±1%; Three-layer gradient spraying is adopted, with a bottom bonding layer of 9mm, a middle insulation layer of 11mm, and a surface transition layer of 7mm, with an interval of 2min between layers; Spraying pressure 0.5MPa, spray gun travel speed 1.0m / s, steel pipe rotation speed 13r / min, working environment wind speed ≤5m / s, and waste material recycling device is turned on.

[0023] S4. Segmented curing: Curing at 32℃ for 4 hours in the early stage, and at 28℃ for 8 hours in the later stage, with a total curing time of 12 hours. Pipe movement and vibration are prohibited throughout the process.

[0024] S5. Interlayer adhesion modification: A 0.3mm nano-rare earth composite adhesion coating is sprayed onto the surface of the polyurethane insulation layer and allowed to cure naturally for 3 minutes to form a microporous interlocking transition structure.

[0025] S6, Closed-loop tension winding: Extruded polyethylene sheet with a width of 300mm and a thickness of 3mm, with a constant winding tension of 90N, a pitch of 80mm, an overlap width of 16%, and hot-pressed fusion at the overlap.

[0026] S7. Synchronous gradient cooling: The winding process starts with three-stage spray cooling. The first stage is 38℃ for shaping, the second stage is 22℃ for curing, and the third stage is 18℃ for stress relief. The cooling rhythm is matched with the winding speed in real time.

[0027] S8. Graded curing: Place in a curing workshop at 25℃ and 55% humidity for 24 hours under constant temperature and humidity.

[0028] S9. Full-item inspection: Complete full-item inspection of appearance, size, closed-cell rate, bonding strength, and thermal conductivity, bind a unique number for traceability, and seal the pipe opening and flexibly stack it into the warehouse after passing the inspection.

[0029] Example 2: Medium-diameter pipe processing (DN300, production in a normal temperature environment, ambient temperature 22℃, humidity 55%) S1. Steel pipe pretreatment: The same three-level purification process as in Example 1 is adopted to ensure that rust removal meets the standards and the surface is clean, and the 4-hour time control is strictly implemented.

[0030] S2. Gradient preheating: Ambient temperature 22℃, preheating temperature set to 50℃, 3.5℃ higher than the ambient dew point, pipe wall temperature difference ≤ ±2℃, constant temperature and stand for 5 minutes.

[0031] S3. Dynamic layered spraying: The environment is moderately humid and the ratio of black and white materials is finely adjusted to 1.02:1 with a ratio error of ≤±1.5%; the thickness of the three layers of spraying is 9mm, 12mm and 7mm respectively, the spraying pressure is 0.5MPa, the spray gun travel speed is 1.1m / s and the steel pipe rotation speed is 14r / min.

[0032] S4. Segmented curing: initial curing at 33℃ for 4 hours, subsequent curing at 27℃ for 12 hours, total curing time 16 hours.

[0033] S5. Interlayer thickening modification: Spray a 0.4mm nano rare earth thickening coating to ensure full interlayer composite.

[0034] S6, Closed-loop tension winding: Polyethylene sheet thickness 4mm, width 350mm, winding tension 100N, pitch 100mm, overlap width 17%.

[0035] S7. Synchronous gradient cooling: The three cooling temperatures are 36℃, 23℃ and 17℃ respectively, with synchronous linkage cooling.

[0036] S8. Graded maintenance: Constant temperature and humidity maintenance for 30 hours.

[0037] S9. Full-item traceability testing: full-indicator quantitative testing, data binding and archiving, and classified storage and protection of qualified products.

[0038] Example 3: Large-diameter pipe processing (DN600, produced in a high-temperature and high-humidity environment, ambient temperature 30℃, humidity 65%) S1. Steel pipe pretreatment: Adopting a standardized three-level purification process, strengthening the micro-dust blowing process, eliminating moisture residue in high temperature and high humidity environment, and completing preheating spraying within 4 hours.

[0039] S2, Gradient preheating: Ambient temperature 30℃, preheating temperature set to 42℃, 3℃ higher than the ambient dew point, uniform preheating, constant temperature standing.

[0040] S3, Dynamic Layered Spraying: High temperature and high humidity conditions, black and white material ratio 1.02:1, error strictly ≤±2%; three-layer spraying thickness 10mm, 12mm, 8mm, spraying pressure 0.55MPa, spray gun travel speed 1.2m / s, steel pipe rotation speed 15r / min, strictly control ambient humidity ≤70%.

[0041] S4. Segmented curing: initial curing at 35℃ for 4 hours, followed by curing at 26℃ for 16 hours, for a total curing time of 20 hours, ensuring that the foam in large-diameter pipes is fully set.

[0042] S5. Interlayer thickening modification: Spray a 0.5mm thick nano-rare earth thickening coating to improve the interlayer composite stability of large-diameter pipes.

[0043] S6. Closed-loop tension winding: Polyethylene sheet thickness 5mm, width 400mm, winding tension 110N, pitch 120mm, overlap width 18%, ensuring the airtightness of large-diameter outer protective layer.

[0044] S7. Synchronous gradient cooling: The three-stage cooling temperatures are 35℃, 25℃, and 20℃ respectively, with slow gradient cooling to prevent deformation of large-diameter pipes.

[0045] S8. Graded curing: Constant temperature and humidity sealed curing for 36 hours to completely eliminate the internal stress of molding.

[0046] S9. Full-item testing: Focus on testing the uniformity of the insulation layer, the interlayer bonding strength, and the overall airtightness, and retain all data for traceability.

[0047] Comparative Example The traditional spraying and winding process disclosed in CN111234677B is used to process DN100, DN300 and DN600 pipes respectively. The process flow is as follows: simple shot blasting rust removal → natural preheating at room temperature → fixed 1:1 ratio single-layer spraying foaming → natural curing at room temperature → open-loop tension winding → natural cooling → appearance inspection before leaving the factory. The whole process has no dynamic parameter adjustment, no layered spraying, no interlayer adhesion enhancement, no gradient cooling and no graded precision maintenance. Implementation effect

[0048] Testing revealed that, compared to existing comparative processes, the performance of the products in the three sets of embodiments of this invention is significantly improved: 1. The bonding strength between the steel pipe and the insulation layer is increased by 35%-42%, with no delamination or hollow defects; 2. The polyurethane closed-cell rate is stable at 92%-95%, far exceeding the 82%-85% of the comparative example, reducing heat loss from insulation by more than 25%; 3. The polyethylene outer sheath has no issues with curling edges, gaps, or bulges, and the overlap sealing pass rate is 100%; 4. There are no water seepage gaps between layers, significantly improving the corrosion resistance and aging resistance when buried underground, with an estimated service life of more than 30 years; 5. The raw material utilization rate is increased by 15%, with no unorganized pollution in the workshop, and the finished product qualification rate is increased to more than 99%; 6. It has extremely strong adaptability to different pipe diameters and different environmental conditions, and the product quality stability is far superior to traditional processes.

[0049] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A rigid polyurethane spray polyethylene winding prefabricated direct-buried thermal insulation pipe processing technology, characterized in that, Includes the following steps: S1. Precise inspection and three-level purification pretreatment of steel pipes upon arrival at the factory: The working steel pipes are inspected for appearance, size and wall thickness. Unqualified pipes are rejected. The pipes are then subjected to three-level purification in sequence, including high-temperature degreasing spray, high-pressure micro-dust blowing and closed-loop shot blasting. The rust removal grade reaches Sa2.5 near-white level. The pipes are then moved to the next process within 4 hours after rust removal, and the pipe openings are sealed. S2. Gradient temperature control preheating to prevent rust: Real-time monitoring of the workshop environment dew point temperature, using hot air circulation gradient preheating method to ensure that the steel pipe preheating temperature is always 3-5℃ higher than the ambient dew point temperature, and the preheating temperature is adjusted according to the ambient temperature in stages, so that the circumferential temperature difference of the pipe wall after preheating is ≤±2℃. S3, Temperature and Humidity Linked Dynamic Layered Gradient Spraying Foaming: The ratio of polyurethane black and white materials is dynamically adjusted according to the real-time temperature and humidity of the workshop. A three-layer gradient layered atomization spraying process is adopted to form the bottom bonding reinforcement layer, the middle insulation main layer, and the surface transition smoothing layer respectively. The spraying pressure, spray gun travel speed, steel pipe rotation speed and working environment parameters are controlled throughout the process. A waste recycling device is provided to realize the recycling of raw materials. S4. Segmented constant temperature precision curing: After spraying, the coating is transferred to a closed curing workshop. A segmented gradient curing mode is adopted, which uses high temperature reaction curing in the early stage and low temperature curing and shaping in the later stage. The curing time is matched according to the pipe diameter and specifications to prevent foam deformation and cracking. S5. Interlayer nano-modification and thickening treatment: A nano-rare earth composite thickening coating is sprayed onto the surface of the cured polyurethane insulation layer to form an interlayer transition composite structure. S6. Closed-loop tension precision winding molding: The melt-extruded polyethylene sheet is spirally wound onto the outside of the tackifying coating through a fully closed-loop tension control method, precisely controlling the winding pitch, sheet overlap width and constant tension. S7. Synchronous gradient cooling and shaping: During the winding process, a three-stage spray gradient cooling process is adopted simultaneously to gradually reduce the temperature and shape the winding process in accordance with the winding rhythm. S8. Graded constant temperature and humidity curing: The formed insulation pipe is transferred to the curing workshop, and the curing time is matched according to the pipe diameter specifications to complete the full curing of the interlayer structure in a constant temperature and humidity environment. S9. Full-item traceability quality inspection: Conduct full-item inspections on the appearance, dimensions, bonding strength, closed-cell rate, insulation coefficient, and airtightness of the cured insulation pipes, bind a unique number to realize full-process parameter traceability, and complete the finished product protection and warehousing after rejecting unqualified products.

2. The process for manufacturing rigid polyurethane spray polyethylene wound prefabricated direct-burial thermal insulation pipe according to claim 1, characterized in that, In the S1 three-level purification pretreatment, the high-temperature degreasing spray uses a neutral degreasing agent at 60-70℃, with a spraying pressure of 0.3-0.5MPa and a spraying time of 3-5min; the shot blasting rust removal uses 1.2-1.5mm alloy steel shot at a shot blasting speed of 70-80m / s. After rust removal, the steel pipe surface is free of oxide scale, oil stains, dust, and water stains, and presents a uniform matte metallic luster.

3. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, During S2 gradient temperature control preheating, the preheating temperature is 55-60℃ when the ambient temperature is ≤15℃, 45-55℃ when the ambient temperature is 15-25℃, and 40-45℃ when the ambient temperature is ≥25℃. After preheating, maintain the temperature and let it stand for 5 minutes.

4. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, In S3 dynamic layered gradient spraying foaming, the basic ratio of polyurethane black and white materials is 1:1, which is slightly adjusted to 1.02:1 when the humidity is 50%-70% and the temperature is 15-25℃, with a total ratio error of ≤±2%. The thickness of the three spraying layers is 8-10mm, 10-12mm, and 6-8mm respectively, with an interval of 2-3 minutes between layers. The spraying pressure is 0.45-0.55MPa, the spray gun travel speed is 0.8-1.2m / s, the steel pipe rotation speed is 12-15r / min, and the working environment has an air speed ≤5m / s, a temperature of 15-35℃, and a humidity of 40%-70%.

5. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, During the S4 segmented constant temperature precision curing process, the reaction curing temperature is 30-35℃ for 0-4 hours, and the curing and shaping temperature is 25-30℃ for 4-12 hours. Pipes with diameters of DN100 and below are cured for 12 hours, pipes with diameters of DN100-DN500 are cured for 16 hours, and pipes with diameters of DN500 and above are cured for 20 hours. Pipe movement and vibration are prohibited throughout the curing process.

6. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, In the S5 interlayer nano-modification and thickening treatment, the nano-rare earth composite thickening coating is composed of nano-silica, rare earth oxides and polyurethane thickening resin. The coating thickness is 0.2-0.5mm, which penetrates and interlocks with the micropores of the polyurethane surface and is then thermally fused with the subsequent polyethylene layer.

7. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, In S6 closed-loop tension precision winding, the polyethylene sheet thickness is 2-5mm, the width is 200-400mm, the winding tension is constant at 80-120N, the tension fluctuation is ≤±3N, the winding pitch is 50-150mm, the sheet overlap width is ≥15%, and the overlap is seamlessly bonded by heat pressing.

8. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, During the S7 synchronous gradient cooling and shaping process, the three-stage spray cooling temperatures are 35-40℃, 20-25℃, and 15-20℃ respectively, and the cooling action and the sheet winding action are carried out in real time and synchronously.

9. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, In the S8 grade constant temperature and humidity curing process, the curing environment temperature is 25±2℃ and the humidity is 55±5%; the curing time for pipelines of DN100 and below is 24 hours, the curing time for pipelines of DN100-DN500 is 30 hours, and the curing time for pipelines of DN500 and above is 36 hours.

10. The processing technology for rigid polyurethane sprayed polyethylene wound prefabricated direct-buried insulated pipes according to claim 1, characterized in that, In S3, the waste recycling device collects, filters, purifies, and recycles the polyurethane raw materials splashed during spraying and atomization. In S9, the entire process of production, maintenance, and testing parameters are entered into the system in real time and bound to the unique pipeline number to achieve process traceability throughout the entire life cycle of a single pipeline.

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