A method for the continuous production of composite pipes

Abstract

The application relates to a preparation method of continuous production of a composite material pipe, and belongs to the technical field of pipe production. The continuous production of the composite material pipe with synchronous improvement of axial strength and hoop strength, higher high-temperature strength retention rate, higher production efficiency, lower waste rate and lower cost is successfully realized by using specific traction speed, specific braiding angle, low impregnation tension, high-frequency preheating setting and gradient heating under the condition of pultrusion molding. The fibers are braided on a moving core mold to obtain a braided layer in a spiral line structure; the hybrid fibers are used as reinforced fiber bundles to realize balanced improvement of the axial and hoop strength of the product, solve the problem of unmatched strength in the traditional process, and reduce the manufacturing cost; the low-tension impregnation and high-frequency preheating are integrated, the independent low-tension control ensures uniform impregnation of the fibers, the core surface temperature difference is controlled by the high-frequency preheating to realize rapid and uniform gel setting of the resin, and the compactness and high-temperature performance retention rate of the product are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of pipe manufacturing technology, and in particular to a method for the continuous production of composite material pipes. Background Technology

[0002] The production of high-quality hybrid composite materials is still a challenge internationally because it involves multiple heterogeneous materials. The properties of each raw and auxiliary material, the process layup, the mold, temperature, humidity, worker skill level, and equipment performance all directly affect the product quality. To ensure the stability of product quality, meet the product's requirements for strength, temperature, and conductivity, and ensure product safety and reliability, hybrid composite pipes need to be produced continuously and stably.

[0003] To meet the high requirements for strength, temperature resistance, and conductivity of products, existing technologies mostly employ intermittent production or a simple combination of winding and pultrusion processes. These methods generally suffer from the following technical defects: low production efficiency, inability to achieve continuous and stable production, high scrap rate, especially during process transitions and shutdown restarts, mismatch between axial and circumferential strength of the product, resulting in redundant material design, increased use of expensive reinforcing fibers, large equipment footprint, and high energy consumption. All of these defects together lead to the high unit manufacturing cost of hybrid composite pipes.

[0004] Among existing published documents, patent CN102642316A discloses a continuous manufacturing method for composite material tubes. This technology involves alternating fiber winding and prepreg winding processes on the same equipment during layup, followed by curing and demolding to obtain the composite material tube. This patent, by alternating fiber winding and prepreg winding, can achieve fiber layup at any angle within the range of 0 to 90 degrees for fiber-reinforced composite material tubes, resulting in tubes with high circumferential strength, as well as excellent axial strength and bending stiffness. However, this manufacturing method requires alternating processes, necessitates process switching, and has a high scrap rate.

[0005] Therefore, it is essential to further research a process that can stably and continuously produce hybrid composite pipes, while simultaneously achieving both continuous production and improved overall pipe strength. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the continuous production of composite material pipes.

[0007] This invention employs a high-temperature polymerization pultrusion online weaving production process. During the weaving process, the fiber's movement trajectory is a spiral. By selecting appropriate fiber weaving angles and fiber tension, the product's density, axial strength, circumferential strength, and overall reliability are significantly improved, thereby ensuring safe and reliable performance under various stress conditions during operation.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for the continuous production of composite material pipes, wherein the continuous production line includes a braiding zone, an impregnation zone, a pre-forming zone, a pultrusion molding zone, and a cutting and stacking zone, and the preparation method includes the following steps: S1. In the weaving area, the reinforcing fiber bundles are woven onto the surface of the mandrel using a weaving machine to obtain a mandrel with a woven layer; the traction speed of the mandrel in the entire production line is 0.5~2.0 m / min; the mandrel is preheated before weaving and the absolute value of the axial temperature difference of the mandrel is not higher than 5℃; the weaving angle is 45°~75°; the fiber composition of the reinforcing fiber bundles is mixed fiber; S2. The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.05 MPa to -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each bundle of fibers in the braided layer is controlled to be 3N to 8N. S3. The preform enters the pre-forming area and uses high-frequency preheating to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature, forming a shaping layer on the surface of the preform, thus obtaining a surface-shaped preform; during the high-frequency preheating process, the temperature difference between the core layer and the surface layer of the preform is 5℃~10℃. S4. The surface-shaped preform enters the pultrusion die in the pultrusion molding zone. The pultrusion die includes a first heating zone, a second heating zone, and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion die through the first heating zone, the second heating zone, and the cooling zone to obtain the formed tube. The temperature of the first heating zone is 120℃~160℃, and the temperature of the second heating zone is 180℃~220℃. S5. The formed pipe separates from the pipe core mold and enters the cutting and stacking area. After cutting and stacking, the composite material pipe is obtained.

[0009] This invention utilizes specific traction speed, braiding angle, low impregnation tension, high-frequency preheating and shaping, and gradient heating conditions for pultrusion molding to successfully achieve continuous production of composite material pipes with simultaneous improvement in axial and circumferential strength, higher high-temperature strength retention, higher production efficiency, lower scrap rate, and lower cost.

[0010] The preparation method of this invention requires controlling the braiding angle to be between 45° and 75°. If the braiding angle exceeds this specific range, for example, 30° (close to the axial direction), although the axial strength of the prepared pipe is increased by as much as 130%, the circumferential strength is increased by a sharp drop to 35%, and it is impossible to achieve a simultaneous increase in axial strength and circumferential strength, resulting in poor pipe performance. If this braiding angle is used to prepare products that meet the usage requirements, the overall cost will increase significantly. For example, if the braiding angle is 80° (close to the circumferential direction), the circumferential strength is increased by 110%, but the axial strength is increased by only 40%, which also fails to achieve a simultaneous increase in axial strength and circumferential strength, resulting in poor pipe performance. When the pipe is subjected to axial tensile force, the braided layer undergoes large deformation, and the structure becomes unstable.

[0011] The preparation method of this invention also requires controlling the tension during impregnation to a low range of 3N to 8N. Traditional pultrusion processes typically use high tensions of 10N or more to prevent fiber wrinkling. This invention discovers that for hybrid fiber online weaving, excessive tension can flatten the fiber bundles, hindering resin impregnation and creating porosity. 3N to 8N is a "just right" window, ensuring both a stable weaving structure and perfect impregnation.

[0012] The preparation method of this invention also requires simultaneous high-frequency preheating to control the temperature difference between the core layer and the surface layer of the preform at 5-10°C. Traditional processes rely on mold conduction heating, which is slow and has a temperature gradient (cold core, hot surface), easily leading to premature or incomplete resin curing. This invention uses high-frequency dielectric heating to achieve volumetric heating "from the inside out." Its key advantage lies in controlling the "temperature difference between the core layer and the surface layer" within a very small range (5-10°C), which is the core of achieving rapid, stress-free gel setting.

[0013] The preparation method of this invention also requires simultaneous control of the traction speed (0.5~2.0 m / min) and the pultrusion curing heating temperature as a gradient temperature (120~160℃→180~220℃). The gradient temperature and traction speed of this invention are deeply coupled; if the initial temperature is too high and the traction speed is too slow, the resin will cure at the impregnation port (mold blockage), and if the initial temperature is too low and the traction speed is too fast, curing cannot be completed at the mold exit.

[0014] Only by synchronously controlling specific traction speed, braiding angle, low impregnation tension, high-frequency preheating and shaping, and gradient heating conditions can the continuous production of composite material pipes with better overall performance, higher production efficiency, and lower cost be achieved.

[0015] The braiding angle of this invention refers to the angle between the reinforcing fiber bundle and the mandrel axis.

[0016] The preparation method of the present invention allows for traction speeds including, but not limited to, 0.5 m / min, 0.6 m / min, 0.7 m / min, 0.8 m / min, 0.9 m / min, 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, 1.4 m / min, 1.5 m / min, 1.6 m / min, 1.7 m / min, 1.8 m / min, 1.9 m / min, 2.0 m / min, or a range of the above values.

[0017] The manufacturing method of the present invention allows for a weaving angle including, but not limited to, 45°, 45.3°, 47.8°, 50.2°, 52.6°, 55.1°, 57.4°, 59.9°, 62.3°, 64.7°, 67.0°, 69.2°, 71.5°, 73.1°, 74.0°, 74.9°, 75°, or a range of the above values.

[0018] In the preparation method of the present invention, the pressure of the resin tank includes, but is not limited to, -0.05 MPa, -0.04 MPa, -0.03 MPa, -0.02 MPa, -0.01 MPa, or a range of the above values.

[0019] The preparation method of the present invention uses tension including but not limited to 3N, 4N, 5N, 6N, 7N, 8N or a range of the above values.

[0020] The preparation method of the present invention uses a temperature difference between the core layer and the surface layer of the preform, including but not limited to 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, or a range of the above values.

[0021] The preparation method of the present invention includes a first heating zone with a temperature of not less than 120°C, 130°C, 140°C, 150°C, 160°C or a range of the above values, and a second heating zone with a temperature of not less than 180°C, 190°C, 200°C, 210°C, 220°C or a range of the above values.

[0022] In a preferred embodiment of the preparation method described in this invention, the preheating temperature in step S1 is 80℃~120℃, including but not limited to 80℃, 90℃, 100℃, 110℃, and 120℃.

[0023] In a preferred embodiment of the preparation method described in this invention, in step S1, the preheating is performed by induction heating for 5-15 minutes. This includes, but is not limited to, 5 minutes, 7 minutes, 9 minutes, 11 minutes, 13 minutes, and 15 minutes.

[0024] As a preferred embodiment of the preparation method of the present invention, in step S1, the fiber composition of the reinforcing fiber bundle includes a combination of at least two fibers selected from carbon fiber, glass fiber, or aramid fiber.

[0025] In a preferred embodiment of the preparation method described in this invention, in step S1, the fiber components of the reinforcing fiber bundle include carbon fiber and glass fiber, or carbon fiber and aramid fiber.

[0026] In a preferred embodiment of the preparation method described in this invention, in step S1, the weaving density of the braided layer is 10 to 20 weaving cross points per inch.

[0027] In a preferred embodiment of the preparation method described in this invention, during step S2, the viscosity of the resin is 300 mPa·s to 800 mPa·s during the impregnation process. In a preferred embodiment of the preparation method of the present invention, in step S2, the tension is controlled by a servo tension controller.

[0028] In a preferred embodiment of the preparation method described in this invention, during step S2, the tension fluctuation of each fiber bundle during impregnation does not exceed ±5% of the set tension value. During impregnation, monitoring is performed every 0.5 seconds to ensure that the tension fluctuation of each fiber bundle does not exceed ±5% of the set range, thus ensuring the stability of the impregnation tension, guaranteeing the uniformity of fiber impregnation, reducing porosity, and consequently reducing the scrap rate.

[0029] In a preferred embodiment of the preparation method described in this invention, the frequency of the high-frequency preheating in step S3 is 10~30MHz, including but not limited to 10 MHz, 20 MHz, and 30 MHz.

[0030] In a preferred embodiment of the preparation method described in this invention, the high-frequency preheating time in step S3 is 30s to 90s. This includes, but is not limited to, 30s, 40s, 50s, 60s, 70s, 80s, and 90s. Within 30s to 90s, the surface temperature of the preform is uniformly raised to the resin gelation initiation temperature.

[0031] As a preferred embodiment of the preparation method of the present invention, in step S4, the inner wall of the pultrusion die is coated with a wear-resistant and release-resistant nano-ceramic coating.

[0032] In a preferred embodiment of the preparation method described in this invention, the temperature of the cooling zone in step S4 is 40°C to 60°C, including but not limited to 40°C, 45°C, 50°C, 55°C, and 60°C.

[0033] In a preferred embodiment of the preparation method described in this invention, in step S5, the cutting is a fixed-length cutting; the precision of the fixed-length cutting is 1 mm to 1.5 mm, including but not limited to 1 mm, 1.2 mm, 1.3 mm, 1.4 mm, and 1.5 mm.

[0034] In a preferred embodiment of the preparation method described in this invention, in step S5, the stacking is performed using an automatic palletizer; the automatic palletizer is used to classify and stack the materials from bottom to top.

[0035] In a preferred embodiment of the preparation method of the present invention, in step S5, a traceability QR code is generated simultaneously after the formed pipes are stacked; the information in the traceability QR code includes production time, process parameter batch, and quality marking information.

[0036] As a preferred embodiment of the preparation method of the present invention, the production line further includes a detection marking area between the pultrusion molding area and the cutting and stacking area. The molded tube leaves the mandrel and enters the detection marking area. Through an online detection device, internal defects are monitored in real time and automatically marked according to the defect location. When the number of defects per unit length is lower than a preset threshold, the molded tube enters the cutting and stacking area.

[0037] Preferably, the line inspection device is an ultrasonic inspection device coupled with an image recognition module, used to identify the type and location coordinates of defects, and associate the location coordinates with the real-time position signal of the traction encoder in S1, thereby tracing the process parameters corresponding to the defect; when the number of defects per unit length exceeds a preset threshold of 3 to 5 defects per meter, the computing host performs at least one of the following adjustment operations based on a preset expert database: a. Adjustment for excessive porosity: If the defect type is determined to be porosity, the computer will gradually reduce the pressure of the resin tank in S2 by 0.005 MPa, until the lower limit of -0.05 MPa, and simultaneously slightly increase the heating power of the high-frequency preheating zone in S3 by 5%~15%; b: Adjustment for delamination defects: If the defect type is determined to be delamination, the computer first checks and fine-tunes the fiber tension in S2. The tension of each bundle is increased by 0.5N~1N, but not exceeding the upper limit of 8N~9N. At the same time, the temperature of the second heating zone in S4 is reduced by a step size of 5~15℃, with an adjustment range of 180℃~220℃. c: Adjustment for localized resin deficiency: If the defect type is determined to be resin deficiency, calculate the pressure at the resin tank injection port in S2 of the main unit, with an increase of 0.01 MPa to 0.03 MPa, and simultaneously reduce the traction speed in S1, with a reduction step of 0.1 to 0.5 m / min, but not lower than the lower limit of 0.5 to 0.8 m / min.

[0038] This invention constructs an online defect detection and closed-loop control system. It uses ultrasonic detection to identify defects such as porosity, delamination, and insufficient adhesive in real time, and automatically adjusts key process parameters based on an expert database. Simultaneously, it integrates a follow-up cutting, automatic stacking, and full-process traceability system, realizing continuous production throughout the entire process from automatic defect correction to finished product management. This significantly reduces scrap rate and energy consumption, and improves production efficiency and product stability.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes specific traction speeds, specific braiding angles, low impregnation tension, high-frequency preheating and shaping, and pultrusion molding under gradient heating conditions to successfully achieve continuous production of composite material pipes with simultaneous improvement in axial and circumferential strength, higher high-temperature strength retention, higher production efficiency, lower scrap rate, and lower cost.

[0040] This invention weaves fibers onto a traction-moving mandrel with precise control of the weaving angle, resulting in a helical fiber trajectory. Simultaneously, it incorporates hybrid fibers as reinforcing fiber bundles, achieving a balanced improvement in both axial and circumferential strength. This effectively solves the problem of material redundancy caused by strength mismatch in traditional processes, fully leveraging the performance advantages of different fibers and reducing manufacturing costs. Furthermore, this invention achieves gel setting by integrating low-tension impregnation and high-frequency preheating to control the core-surface temperature difference, enabling precise control of the temperature field and resin flowability. Vacuum-assisted impregnation combined with independent tension control ensures uniform fiber wetting, high-frequency preheating allows the resin to quickly and uniformly reach the gel point, and core-surface temperature difference control ensures gel uniformity, significantly improving the product's density and high-temperature performance retention. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the preparation method of continuous production of composite material pipes according to the present invention, wherein S1-S6 correspond to steps (1)-(6) in the embodiment. Detailed Implementation

[0042] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0043] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0044] This invention provides a method for the continuous production of composite material pipes. The continuous production line includes a braiding zone, an impregnation zone, a pre-forming zone, a pultrusion molding zone, and a cutting and stacking zone. The preparation method includes the following steps: S1. In the weaving area, the reinforcing fiber bundles are woven onto the surface of the mandrel using a weaving machine to obtain a mandrel with a woven layer; the traction speed of the mandrel in the entire production line is 0.5~2.0 m / min; the mandrel is preheated before weaving and the absolute value of the axial temperature difference of the mandrel is not higher than 5℃; the weaving angle is 45°~75°; the fiber composition of the reinforcing fiber bundles is mixed fiber; S2. The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.05 MPa to -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each bundle of fibers in the braided layer is controlled to be 3N to 8N. S3. The preform enters the pre-forming area and uses high-frequency preheating to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature, forming a shaping layer on the surface of the preform, thus obtaining a surface-shaped preform; during the high-frequency preheating process, the temperature difference between the core layer and the surface layer of the preform is 5℃~10℃. S4. The surface-shaped preform enters the pultrusion die in the pultrusion molding zone. The pultrusion die includes a first heating zone, a second heating zone, and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion die through the first heating zone, the second heating zone, and the cooling zone to obtain the formed tube. The temperature of the first heating zone is 120℃~160℃, and the temperature of the second heating zone is 180℃~220℃. S5. The formed pipe separates from the pipe core mold and enters the cutting and stacking area. After cutting and stacking, the composite material pipe is obtained.

[0045] As a preferred embodiment, in step S1, the preheating temperature is 80℃~120℃.

[0046] As a preferred embodiment, in step S1, the preheating is performed by induction heating for 5-15 minutes.

[0047] As a preferred embodiment, in step S1, the fiber composition of the reinforcing fiber bundle includes a combination of at least two fibers selected from carbon fiber, glass fiber, or aramid fiber.

[0048] As a preferred embodiment, in step S1, the fiber composition of the reinforcing fiber bundle includes carbon fiber and glass fiber, or carbon fiber and aramid fiber.

[0049] As a preferred embodiment, in step S1, the weave density of the braided layer is 10 to 20 weave intersections per inch.

[0050] As a preferred embodiment, in step S2, during the impregnation process, the viscosity of the resin is 300 mPa·s to 800 mPa·s; As a preferred embodiment, in step S2, the tension is controlled by a servo tension controller.

[0051] As a preferred embodiment, in step S2, during the impregnation process, the tension fluctuation of each fiber bundle does not exceed ±5% of the set tension value. During the impregnation process, monitoring is performed every 0.5 seconds to ensure that the tension fluctuation of each fiber bundle does not exceed ±5% of the set range, ensuring the stability of the impregnation tension, thereby ensuring the uniformity of fiber impregnation, reducing porosity, and thus reducing the scrap rate.

[0052] As a preferred embodiment, in step S3, the frequency of the high-frequency preheating is 10~30MHz.

[0053] As a preferred embodiment, in step S3, the high-frequency preheating time is 30s to 90s. Within 30s to 90s, the surface temperature of the preform is uniformly raised to the resin gelation initiation temperature.

[0054] As a preferred embodiment, in step S4, the inner wall of the pultrusion die is coated with a wear-resistant and release-resistant nano-ceramic coating.

[0055] As a preferred embodiment, in step S4, the temperature of the cooling zone is 40℃~60℃.

[0056] As a preferred embodiment, in step S5, the cutting is a fixed-length cutting; the accuracy of the fixed-length cutting is 1mm to 1.5mm.

[0057] As a preferred embodiment, in step S5, the stacking is performed using an automatic palletizer; the automatic palletizer is used to classify and stack the items from bottom to top.

[0058] As a preferred embodiment, in step S5, a traceability QR code is generated simultaneously after the formed pipes are stacked; the information in the traceability QR code includes production time, process parameter batch, and quality marking information.

[0059] As a preferred embodiment, the production line further includes a detection and marking area between the pultrusion molding area and the cutting and stacking area. The molded tube detaches from the mandrel and enters the detection and marking area. Through an online detection device, internal defects are monitored in real time and automatically marked according to the defect location. When the number of defects per unit length is lower than a preset threshold, the molded tube enters the cutting and stacking area.

[0060] As a preferred embodiment, the line inspection device is an ultrasonic inspection device coupled with an image recognition module for identifying the type and location coordinates of defects, and associating the location coordinates with the real-time position signal of the traction encoder in S1, thereby tracing the process parameters corresponding to the defect; when the number of defects per unit length exceeds a preset threshold of 3 to 5 defects per meter, the computing host performs at least one of the following adjustment operations based on a preset expert database: a. Adjustment for excessive porosity: If the defect type is determined to be porosity, the computer will gradually reduce the pressure of the resin tank in S2 by 0.005 MPa, until the lower limit of -0.05 MPa, and simultaneously slightly increase the heating power of the high-frequency preheating zone in S3 by 5%~15%; b: Adjustment for delamination defects: If the defect type is determined to be delamination, the computer first checks and fine-tunes the fiber tension in S2. The tension of each bundle is increased by 0.5N~1N, but not exceeding the upper limit of 8N~9N. At the same time, the temperature of the second heating zone in S4 is reduced by a step size of 5~15℃, with an adjustment range of 180℃~220℃. c: Adjustment for localized resin deficiency: If the defect type is determined to be resin deficiency, calculate the pressure at the resin tank injection port in S2 of the main unit, with an increase of 0.01 MPa to 0.03 MPa, and simultaneously reduce the traction speed in S1, with a reduction step of 0.1 to 0.5 m / min, but not lower than the lower limit of 0.5 to 0.8 m / min.

[0061] Example 1 An embodiment of the present invention provides a method for the continuous production of composite material pipes. The continuous production line includes a braiding zone, an impregnation zone, a pre-forming zone, a pultrusion molding zone, an inspection and marking zone, and a cutting and stacking zone. The preparation method includes the following steps: (1) In the braiding area, the reinforcing fiber bundles are braided onto the surface of the mandrel using a braiding machine to obtain a mandrel with a braided layer; the traction speed of the mandrel in the entire production line is 0.5 m / min; before braiding, the mandrel is heated to 80°C and preheated for 5 minutes by induction heating to control the temperature difference between the surface and near-surface of the mandrel within 5 minutes, and the axial temperature difference of the mandrel is -5°C; the braiding angle is 45°; the braiding density of the braided layer is 10 braiding intersections per inch, and the fiber composition of the reinforcing fiber bundles is carbon fiber and glass fiber; (2) The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin with a viscosity of 300 mPa·s is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.05 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each fiber bundle in the braided layer is controlled to be 3N by a servo tension controller. The tension is monitored every 0.5S to ensure that the tension fluctuation of each fiber bundle does not exceed -5% of the set value (3N in this embodiment). (3) The preform enters the pre-forming area and uses high-frequency preheating for 30 seconds to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature. The frequency of high-frequency preheating is 10MHz and the temperature difference between the core layer and the surface layer of the preform is 5℃. A shaping layer is formed on the surface of the preform to obtain a surface-shaped preform. (4) The surface-shaped preform enters the pultrusion mold in the pultrusion molding zone. The pultrusion mold includes a first heating zone, a second heating zone and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion mold through the first heating zone, the second heating zone and the cooling zone to obtain the formed pipe. The temperature of the first heating zone is 120°C, the temperature of the second heating zone is 180°C and the temperature of the cooling zone is 40°C. The inner wall of the pultrusion mold is coated with a wear-resistant and release-resistant nano-ceramic coating. (5) The formed pipe is removed from the pipe core mold and enters the inspection and marking area. The internal defects are monitored in real time by the online inspection device and automatically marked according to the defect location. When the number of defects per unit length is lower than the preset threshold, the formed pipe enters the cutting and stacking area. (6) The formed pipes that enter the cutting and stacking area are cut into fixed lengths using a follow-up cutting saw according to the preset length, and then automatically stacked. The precision of the fixed length cutting is 1mm. The cut pipes are sorted and stacked from bottom to top by an automatic palletizer, and a traceability QR code containing production time, process parameter batch, and quality mark information is generated simultaneously to obtain composite material pipes.

[0062] A schematic flow diagram of the preparation method for continuous production of composite material pipes according to the present invention is shown below. Figure 1 As shown, S1-S6 correspond to (1)-(6) in the embodiment.

[0063] Example 2 An embodiment of the present invention provides a method for the continuous production of composite material pipes. The continuous production line includes a braiding zone, an impregnation zone, a pre-forming zone, a pultrusion molding zone, an inspection and marking zone, and a cutting and stacking zone. The preparation method includes the following steps: (1) In the braiding area, the reinforcing fiber bundles are braided onto the surface of the mandrel using a braiding machine to obtain a mandrel with a braided layer; the traction speed of the mandrel in the entire production line is 1.5 m / min; before braiding, the mandrel is heated to 110°C and preheated for 10 minutes by induction heating to control the temperature difference between the surface and near-surface of the mandrel within 8 minutes, and the axial temperature difference of the mandrel is 3°C; the braiding angle is 65°; the braiding density of the braided layer is 15 braiding intersections per inch, and the fiber composition of the reinforcing fiber bundles is carbon fiber and aramid fiber; (2) The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin with a viscosity of 500 mPa·s is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.05 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each fiber bundle in the braided layer is controlled to be 8N by a servo tension controller. The tension is monitored every 0.5S to ensure that the tension fluctuation of each fiber bundle does not exceed 5% of the set value (8N in this embodiment). (3) The preform enters the pre-forming area and uses high-frequency preheating for 50 seconds to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature. The frequency of high-frequency preheating is 20MHz and the temperature difference between the core layer and the surface layer of the preform is 8℃. A shaping layer is formed on the surface of the preform to obtain a surface-shaped preform. (4) The surface-shaped preform enters the pultrusion mold in the pultrusion molding zone. The pultrusion mold includes a first heating zone, a second heating zone and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion mold through the first heating zone, the second heating zone and the cooling zone to obtain the formed pipe. The temperature of the first heating zone is 150°C, the temperature of the second heating zone is 190°C and the temperature of the cooling zone is 50°C. The inner wall of the pultrusion mold is coated with a wear-resistant and release-resistant nano-ceramic coating. (5) The formed pipe is removed from the pipe core mold and enters the inspection and marking area. The internal defects are monitored in real time by the online inspection device and automatically marked according to the defect location. When the number of defects per unit length is lower than the preset threshold, the formed pipe enters the cutting and stacking area. (6) The formed pipes that enter the cutting and stacking area are cut into fixed lengths using a follow-up cutting saw according to the preset length, and then automatically stacked. The precision of the fixed length cutting is 1.2mm. The cut pipes are sorted and stacked from bottom to top by an automatic palletizer, and a traceability QR code containing production time, process parameter batch, and quality mark information is generated simultaneously to obtain composite material pipes.

[0064] Example 3 An embodiment of the present invention provides a method for the continuous production of composite material pipes. The continuous production line includes a braiding zone, an impregnation zone, a pre-forming zone, a pultrusion molding zone, an inspection and marking zone, and a cutting and stacking zone. The preparation method includes the following steps: (1) In the braiding area, the reinforcing fiber bundles are braided onto the surface of the mandrel using a braiding machine to obtain a mandrel with a braided layer; the traction speed of the mandrel in the entire production line is 2.0 m / min; before braiding, the mandrel is heated to 120°C and preheated by induction heating for 15 minutes to control the temperature difference between the surface and near-surface of the mandrel within 10 minutes, and the axial temperature difference of the mandrel is 5°C; the braiding angle is 75°; the braiding density of the braided layer is 20 braiding cross points per inch, and the fiber composition of the reinforcing fiber bundles is carbon fiber and glass fiber; (2) The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin with a viscosity of 800 mPa·s is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each fiber bundle in the braided layer is controlled to be 8N by a servo tension controller. The tension is monitored every 0.5S to ensure that the tension fluctuation of each fiber bundle does not exceed -5% of the set value (8N in this embodiment). (3) The preform enters the pre-forming area and uses high-frequency preheating for 90 seconds to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature. The frequency of high-frequency preheating is 30MHz and the temperature difference between the core layer and the surface layer of the preform is 10℃. A shaping layer is formed on the surface of the preform to obtain a surface-shaped preform. (4) The surface-shaped preform enters the pultrusion mold in the pultrusion molding zone. The pultrusion mold includes a first heating zone, a second heating zone and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion mold through the first heating zone, the second heating zone and the cooling zone to obtain the formed pipe. The temperature of the first heating zone is 160°C, the temperature of the second heating zone is 220°C and the temperature of the cooling zone is 60°C. The inner wall of the pultrusion mold is coated with a wear-resistant and release-resistant nano-ceramic coating. (5) The formed pipe is removed from the pipe core mold and enters the inspection and marking area. The internal defects are monitored in real time by the online inspection device and automatically marked according to the defect location. When the number of defects per unit length is lower than the preset threshold, the formed pipe enters the cutting and stacking area. (6) The formed pipes that enter the cutting and stacking area are cut into fixed lengths using a follow-up cutting saw according to the preset length, and then automatically stacked. The precision of the fixed length cutting is 1.5mm. The cut pipes are sorted and stacked from bottom to top by an automatic palletizer, and a traceability QR code containing production time, process parameter batch, and quality mark information is generated simultaneously to obtain composite material pipes.

[0065] Comparative Example 1 This invention provides a comparative example of a method for continuous production of composite material pipes. The only difference between this comparative example and Example 3 is the tension in step (2) of the preparation method. Compared with Example 3, the tension of each bundle of fibers in the braided layer in step (2) of Example 3 is adjusted from 8N ​​to 12N.

[0066] The preparation method described in this comparative example includes the following steps: (1) In the braiding area, the reinforcing fiber bundles are braided onto the surface of the mandrel using a braiding machine to obtain a mandrel with a braided layer; the traction speed of the mandrel in the entire production line is 2.0 m / min; before braiding, the mandrel is heated to 120°C and preheated by induction heating for 15 minutes to control the temperature difference between the surface and near-surface of the mandrel within 10 minutes, and the axial temperature difference of the mandrel is 5°C; the braiding angle is 75°; the braiding density of the braided layer is 20 braiding cross points per inch, and the fiber composition of the reinforcing fiber bundles is carbon fiber and glass fiber; (2) The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin with a viscosity of 800 mPa·s is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each fiber bundle in the braided layer is controlled to be 12N by a servo tension controller. The tension is monitored every 0.5S to ensure that the tension fluctuation of each fiber bundle does not exceed -5% of the set value (8N in this embodiment). (3) The preform enters the pre-forming area and uses high-frequency preheating for 90 seconds to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature. The frequency of high-frequency preheating is 30MHz and the temperature difference between the core layer and the surface layer of the preform is 10℃. A shaping layer is formed on the surface of the preform to obtain a surface-shaped preform. (4) The surface-shaped preform enters the pultrusion mold in the pultrusion molding zone. The pultrusion mold includes a first heating zone, a second heating zone and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion mold through the first heating zone, the second heating zone and the cooling zone to obtain the formed pipe. The temperature of the first heating zone is 160°C, the temperature of the second heating zone is 220°C and the temperature of the cooling zone is 60°C. The inner wall of the pultrusion mold is coated with a wear-resistant and release-resistant nano-ceramic coating. (5) The formed pipe is removed from the pipe core mold and enters the inspection and marking area. The internal defects are monitored in real time by the online inspection device and automatically marked according to the defect location. When the number of defects per unit length is lower than the preset threshold, the formed pipe enters the cutting and stacking area. (6) The formed pipes that enter the cutting and stacking area are cut into fixed lengths using a follow-up cutting saw according to the preset length, and then automatically stacked. The precision of the fixed length cutting is 1.5mm. The cut pipes are sorted and stacked from bottom to top by an automatic palletizer, and a traceability QR code containing production time, process parameter batch, and quality mark information is generated simultaneously to obtain composite material pipes.

[0067] Comparative Example 2 This invention provides a comparative example of a method for continuous production of composite material pipes. The difference between this comparative example and Example 3 is only that the heating and shaping method in step (3) of the preparation method is different. This comparative example uses traditional conduction heating and directly utilizes the conduction preheating of the first heating zone of the pultrusion die integrated in step (4). The preform is placed in the pultrusion die and heated to 150°C for 90s by the first heating zone of the pultrusion die to form a shaping layer and obtain a surface-shaped preform. Then, the temperature of the first heating zone of the pultrusion die is adjusted to 160°C and pultruded according to the conditions of step (4) of Example 3.

[0068] The preparation method described in this comparative example includes the following steps: (1) In the braiding area, the reinforcing fiber bundles are braided onto the surface of the mandrel using a braiding machine to obtain a mandrel with a braided layer; the traction speed of the mandrel in the entire production line is 2.0 m / min; before braiding, the mandrel is heated to 120°C and preheated by induction heating for 15 minutes to control the temperature difference between the surface and near-surface of the mandrel within 10 minutes, and the axial temperature difference of the mandrel is 5°C; the braiding angle is 75°; the braiding density of the braided layer is 20 braiding cross points per inch, and the fiber composition of the reinforcing fiber bundles is carbon fiber and glass fiber; (2) The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin with a viscosity of 800 mPa·s is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each fiber bundle in the braided layer is controlled to be 8N by a servo tension controller. The tension is monitored every 0.5S to ensure that the tension fluctuation of each fiber bundle does not exceed -5% of the set value (8N in this embodiment). (3) In the pultrusion die of the preform pultrusion molding zone, the pultrusion die includes a first heating zone, a second heating zone and a cooling zone. The preform is heated in the first heating zone of the pultrusion die for 150°C and 90s to form a shaping layer on the surface of the preform, thereby obtaining a surface-shaped preform. (4) The surface-shaped preform continues to be pultruded. Under the continuous traction of the production line, the surface-shaped preform is solidified in the pultrusion die through the first heating zone, the second heating zone and the cooling zone to obtain the shaped pipe. The temperature of the first heating zone is adjusted to 160°C, the temperature of the second heating zone is 220°C and the temperature of the cooling zone is 60°C. The inner wall of the pultrusion die is coated with a wear-resistant and release-resistant nano-ceramic coating. (5) The formed pipe is removed from the pipe core mold and enters the inspection and marking area. The internal defects are monitored in real time by the online inspection device and automatically marked according to the defect location. When the number of defects per unit length is lower than the preset threshold, the formed pipe enters the cutting and stacking area. (6) The formed pipes that enter the cutting and stacking area are cut into fixed lengths using a follow-up cutting saw according to the preset length, and then automatically stacked. The precision of the fixed length cutting is 1.5mm. The cut pipes are sorted and stacked from bottom to top by an automatic palletizer, and a traceability QR code containing production time, process parameter batch, and quality mark information is generated simultaneously to obtain composite material pipes.

[0069] Comparative Examples 3-4 Two comparative examples of a method for continuous production of composite material pipes according to the present invention are provided. The difference between comparative examples 3-4 and example 3 lies only in the weaving angle in step (1) of the preparation method. Specifically, Comparative Example 3: Compared with Example 3, the weaving angle in step (1) of Example 3 was adjusted from 75° to 30°; Comparative Example 4: Compared with Example 3, the weaving angle in step (1) of Example 3 was adjusted from 75° to 80°.

[0070] Comparative Example 5 This invention provides a comparative example of a method for continuous production of composite material pipes. The only difference between this comparative example and Example 3 is the temperature difference between the preform core layer and the surface layer in step (3) of the preparation method. Compared with Example 3, this comparative example adjusts the temperature difference between the preform core layer and the surface layer in step (3) of Example 3 from 10°C to 25°C.

[0071] The preparation method described in this comparative example includes the following steps: (1) In the braiding area, the reinforcing fiber bundles are braided onto the surface of the mandrel using a braiding machine to obtain a mandrel with a braided layer; the traction speed of the mandrel in the entire production line is 2.0 m / min; before braiding, the mandrel is heated to 120°C and preheated by induction heating for 15 minutes to control the temperature difference between the surface and near-surface of the mandrel within 10 minutes, and the axial temperature difference of the mandrel is 5°C; the braiding angle is 75°; the braiding density of the braided layer is 20 braiding cross points per inch, and the fiber composition of the reinforcing fiber bundles is carbon fiber and glass fiber; (2) The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin with a viscosity of 800 mPa·s is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each fiber bundle in the braided layer is controlled to be 8N by a servo tension controller. The tension is monitored every 0.5S to ensure that the tension fluctuation of each fiber bundle does not exceed -5% of the set value (8N in this embodiment). (3) The preform enters the pre-forming area and uses high-frequency preheating for 90 seconds to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature. The frequency of high-frequency preheating is 30MHz and the temperature difference between the core layer and the surface layer of the preform is 25℃. A shaping layer is formed on the surface of the preform to obtain a surface-shaped preform. (4) The surface-shaped preform enters the pultrusion mold in the pultrusion molding zone. The pultrusion mold includes a first heating zone, a second heating zone and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion mold through the first heating zone, the second heating zone and the cooling zone to obtain the formed pipe. The temperature of the first heating zone is 160°C, the temperature of the second heating zone is 220°C and the temperature of the cooling zone is 60°C. The inner wall of the pultrusion mold is coated with a wear-resistant and release-resistant nano-ceramic coating. (5) The formed pipe is removed from the pipe core mold and enters the inspection and marking area. The internal defects are monitored in real time by the online inspection device and automatically marked according to the defect location. When the number of defects per unit length is lower than the preset threshold, the formed pipe enters the cutting and stacking area. (6) The formed pipes that enter the cutting and stacking area are cut into fixed lengths using a follow-up cutting saw according to the preset length, and then automatically stacked. The precision of the fixed length cutting is 1.5mm. The cut pipes are sorted and stacked from bottom to top by an automatic palletizer, and a traceability QR code containing production time, process parameter batch, and quality mark information is generated simultaneously to obtain composite material pipes.

[0072] Comparative Examples 6-7 The present invention provides two comparative examples of a method for continuous production of composite material pipes. Comparative Examples 6-7 differ from Example 3 only in the traction speed of the entire production line. Specifically, Comparative Example 6: Compared with Example 3, the traction speed of the entire production line in Example 3 was adjusted from 2.0 m / min to 0.3 m / min; Comparative Example 7: Compared with Example 3, the traction speed of the entire production line in Example 3 was adjusted from 2.0 m / min to 2.5 m / min.

[0073] Comparative Example 8 This invention provides a comparative example of a method for continuous production of composite material pipes. The only difference between this comparative example and Example 3 is the heating method of the pultrusion die in step (4) of the preparation method. This comparative example uses isothermal heating, and the first heating zone and the second heating zone are heated at the same temperature of 200°C.

[0074] This comparative model cannot achieve continuous production. The resin cures prematurely near the impregnation port, completely clogging the mold and preventing production from starting.

[0075] Comparative Example 9 This invention provides a comparative example of a method for the continuous production of composite material pipes. This comparative example employs a common, traditional "winding + pultrusion" combined discontinuous production process, and the specific steps are as follows: (1) Core preparation and winding: First, on an independent winding machine, one of the reinforcing fibers (glass fiber) is impregnated with resin and then wound around the core surface at a large angle close to the circumferential direction to form a circumferential reinforcing layer; then, the equipment is changed and another of the reinforcing fibers (carbon fiber prepreg tape) is wound at a smaller longitudinal angle to form an axial reinforcing layer; during the winding process, the fiber tension is controlled manually or semi-automatically (without precise closed-loop adjustment). (2) Curing and molding: The core mold with completed layup is hoisted into a large oven and cured using a stepped heating process; the entire curing process takes several hours, and then it is naturally cooled to a certain temperature; (3) Demolding and cutting: After curing, the mold and the pipe are moved to the demolding equipment and the core mold is pushed mechanically to separate it from the pipe; the demolded pipe is cut to a fixed length using ordinary cutting equipment; (4) Post-processing and inspection: The ends of the cut pipes are manually trimmed and random inspections are carried out using an offline flaw detector. Any defects found are manually marked and repaired.

[0076] This comparative example uses a combination of winding and pultrusion, which cannot achieve continuous production.

[0077] Test Example 1 Composite material pipes were produced according to the preparation methods of Examples 1-3 and Comparative Examples 1-9, respectively, and the continuous production time was tested. Comparative Examples 8 and 9 could not be produced continuously, therefore, the continuous production time was not tested.

[0078] The continuous production times for the preparation methods of Examples 1-3 and Comparative Examples 1-7 are shown in Table 1. Table 1 The results in Table 1 show that the continuous production time for composite material pipes produced by the preparation method of the present invention can reach more than 6 hours.

[0079] According to Comparative Example 2, continuous production cannot be achieved by using conductive preheating and shaping (continuous production time is less than 4 hours).

[0080] According to Comparative Example 5, even with high-frequency preheating, the temperature difference between the core layer and the surface layer of the preform is higher than 10°C, which makes continuous production impossible (continuous production time is less than 4 hours).

[0081] According to Comparative Examples 6 and 7, if the traction speed of the production line is lower or higher than 0.5~2 m / min, continuous production cannot be achieved (continuous production time is less than 4 hours).

[0082] Test Example 2 The performance of the composite pipes of Examples 1-3 and Comparative Examples 1-9 was tested. Comparative Examples 2, 5, 6, 7, 8, and 9 could not be produced continuously, therefore their performance was not tested.

[0083] 1. Strength Axial strength improvement rate: Tested according to GB / T 5349-2005 "Test method for axial tensile properties of fiber reinforced thermosetting plastic pipes"; Circumferential strength improvement rate: Tested in accordance with GB / T 5351-2005 "Test method for short-time water pressure failure of fiber reinforced thermosetting plastic pipes".

[0084] High-temperature strength retention rate: The test was conducted in accordance with GB / T 5349-2005 "Test method for axial tensile properties of fiber reinforced thermosetting plastic pipes". The strength of the pipe was tested at room temperature (25℃) and 120℃ respectively, and the high-temperature strength retention rate was calculated. High-temperature strength retention rate = [strength (120℃) / strength (room temperature)] × 100%.

[0085] The results of axial strength improvement rate, circumferential strength improvement rate, and high-temperature strength retention rate of the composite material pipes of Examples 1-3 and Comparative Examples 1 and 3-4 are shown in Table 2. Table 2 2. Production efficiency Production efficiency was compared with the traditional "winding + pultrusion" combined discontinuous production process of Comparative Example 9. Examples 1-3 and Comparative Examples 1, 3, and 4 were used as experimental groups, and Comparative Example 9 was used as the control group.

[0086] Using 8 consecutive hours as the unit of time, the total length of qualified finished pipes that finally passed the inspection and entered the stacking area in the experimental group and the control group within the unit of time was recorded as the qualified output length per unit time. The total production length per unit of time of the experimental group and the control group, as well as the proportion of scrapped products due to defects (porosity, delamination, and insufficient glue), were recorded to obtain the scrap rate.

[0087] Production efficiency improvement rate = [(experimental group's qualified output length per unit time - control group's qualified output length per unit time) / control group's qualified output length per unit time] × 100%.

[0088] The reduction in scrap rate = [(Scrap rate of control group - scrap rate of experimental group) / scrap rate of control group] × 100%.

[0089] Table 3 shows the results of the production efficiency improvement rate and scrap rate reduction of the preparation methods in Examples 1-3 and Comparative Examples 1 and 3-4. Table 3 3. Cost Costs were compared to those of Comparative Example 9, which uses a traditional "winding + pultrusion" combined discontinuous production process. Examples 1-3 and Comparative Examples 1, 3, and 4 were used as the experimental groups, while Comparative Example 9 served as the control group.

[0090] Fiber material saving rate: The total mass of reinforcing fibers required for the experimental group and the control group to achieve the same circumferential / axial strength design index; denoted as the total mass of the experimental group and the total mass of the control group, respectively.

[0091] Fiber material saving rate = [(total mass of control group - total mass of experimental group) / total mass of control group] × 100%.

[0092] Energy consumption reduction rate: The electrical energy consumed by the experimental group and the control group in producing one kilogram of qualified pipe is recorded as the electrical energy of the experimental group and the electrical energy of the control group, respectively.

[0093] Energy consumption reduction rate = [(Electric energy of control group - Electric energy of experimental group) / Electric energy of control group] × 100%.

[0094] Overall cost reduction rate: The total cost per meter of pipe (raw materials + energy consumption + labor + equipment depreciation + scrap loss) for the experimental group and the control group is recorded as the total cost of the experimental group and the total cost of the control group, respectively.

[0095] Overall cost reduction rate = [(total cost of control group - total cost of experimental group) / total cost of control group] × 100%.

[0096] Table 4 shows the fiber material saving rate, energy consumption reduction rate, and overall cost reduction rate of the preparation methods of Examples 1-3 and Comparative Examples 1 and 3-4. Table 4 Table 2-4 shows that Example 3 outperforms Examples 1 and 2 in key indicators such as strength, temperature resistance, production efficiency, and economy. Its axial strength improvement rate is 105%, circumferential strength improvement rate is 102%, and high-temperature strength retention rate is 93%, resulting in superior mechanical properties. Production efficiency is increased by 280%, scrap rate is reduced by 82%, fiber is saved by 27%, energy consumption is reduced by 35%, and overall cost is reduced by 43%, demonstrating significantly better overall performance than the previous two groups. Example 3, through better process parameter matching and closed-loop control, achieves continuous production with higher performance, lower defects, and lower costs, making it the preferred solution for this invention.

[0097] The tension of Comparative Example 1 is higher than the range of 3N to 8N. Although it can be continuously produced for 4 hours, its strength, temperature resistance, production efficiency and economy are significantly lower than those of the Example.

[0098] The weaving angles of Comparative Examples 3 and 4 exceed 45°~75°. Although they can be continuously produced for 5~6 hours, their strength, temperature resistance, production efficiency and economy are significantly lower than those of the Example.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for continuous production of composite material pipes, characterized in that, The continuous production line includes a weaving zone, an impregnation zone, a pre-forming zone, a pultrusion molding zone, and a cutting and stacking zone. The preparation method includes the following steps: S1. In the weaving area, the reinforcing fiber bundles are woven onto the surface of the mandrel using a weaving machine to obtain a mandrel with a woven layer; the traction speed of the mandrel in the entire production line is 0.5~2.0 m / min; the mandrel is preheated before weaving and the absolute value of the axial temperature difference of the mandrel is not higher than 5℃; the weaving angle is 45°~75°; the fiber composition of the reinforcing fiber bundles is mixed fiber; S2. The core mold with the braided layer enters the impregnation mold in the impregnation zone. Resin is injected into the impregnation mold through the resin tank. The pressure of the resin tank is -0.05 MPa to -0.01 MPa. The resin impregnates the braided layer to obtain a preform. During the impregnation process, the tension of each bundle of fibers in the braided layer is controlled to be 3N to 8N. S3. The preform enters the pre-forming area and uses high-frequency preheating to uniformly raise the surface temperature of the preform to the resin gelation initiation temperature, forming a shaping layer on the surface of the preform, thus obtaining a surface-shaped preform; during the high-frequency preheating process, the temperature difference between the core layer and the surface layer of the preform is 5℃~10℃. S4. The surface-shaped preform enters the pultrusion die in the pultrusion molding zone. The pultrusion die includes a first heating zone, a second heating zone, and a cooling zone. Under the continuous traction of the production line, the surface-shaped preform is solidified and formed in the pultrusion die through the first heating zone, the second heating zone, and the cooling zone to obtain the molded pipe. S5. The formed pipe separates from the pipe core mold and enters the cutting and stacking area. After cutting and stacking, the composite material pipe is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the preheating temperature is 80℃~120℃; And / or, in step S1, the preheating is performed by induction heating for 5-15 minutes.

3. The preparation method according to claim 1, characterized in that, In step S1, the fiber composition of the reinforcing fiber bundle includes a combination of at least two fibers selected from carbon fiber, glass fiber, or aramid fiber.

4. The preparation method according to claim 1, characterized in that, In step S1, the weaving density of the braided layer is 10 to 20 weaving cross points per inch.

5. The preparation method according to claim 1, characterized in that, In step S2, during the impregnation process, the viscosity of the resin is 300 mPa·s to 800 mPa·s.

6. The preparation method according to claim 1, characterized in that, In step S2, the tension is controlled by a servo tension controller; And / or, in step S2, during the impregnation process, the tension fluctuation of each fiber bundle does not exceed ±5% of the tension setting value.

7. The preparation method according to claim 1, characterized in that, In step S3, the frequency of the high-frequency preheating is 10~30MHz; And / or, in step S3, the high-frequency preheating time is 30s~90s.

8. The preparation method according to claim 1, characterized in that, In step S4, the temperature of the first heating zone is 120℃~160℃, and the temperature of the second heating zone is 180℃~220℃; And / or, in step S4, the inner wall of the pultrusion die is coated with a wear-resistant and release-resistant nano-ceramic coating; And / or, in step S4, the temperature of the cooling zone is 40℃~60℃.

9. The preparation method according to claim 1, characterized in that, In step S5, the cutting is a fixed-length cutting; the accuracy of the fixed-length cutting is 1~1.5mm; And / or, in step S5, the stacking is performed using an automatic palletizer; And / or, in step S5, a traceability QR code is generated simultaneously after the formed pipes are stacked.

10. The preparation method according to claim 1, characterized in that, The production line also includes a detection and marking area between the pultrusion molding area and the cutting and stacking area. The molded tube leaves the mandrel and enters the detection and marking area. Through an online detection device, internal defects are monitored in real time and automatically marked according to the defect location. When the number of defects per unit length is lower than a preset threshold, the molded tube enters the cutting and stacking area.

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