Basalt fiber reinforced composite material pipeline and preparation method thereof

Abstract

The invention relates to the technical field of basalt fiber reinforced composite material pipelines and preparation methods thereof, and discloses a pipeline named as a basalt fiber reinforced composite material pipeline and a preparation method thereof and a preparation method thereof. The invention aims to overcome the defects of continuity, interface bonding and mechanical properties of the conventional basalt fiber reinforced composite material pipeline. The pipeline is composed of a lining layer, a basalt fiber winding reinforcing layer and an outer protective layer, the reinforcing layer is formed by compounding basalt fiber bundles subjected to surface treatment and a resin matrix, and the reinforcing layer is of a multi-layer structure with different winding angles. The preparation method comprises the following steps: roughening the inner lining layer, infiltrating and accurately winding the fiber bundles, performing multi-section curing and forming the outer protective layer. According to the scheme, the macroscopic mechanical property of the pipeline is remarkably improved, the interface combination of fibers and a matrix is optimized, the integrity of the fibers is kept, efficient preparation is achieved, and the pipeline has the advantages of being excellent in corrosion resistance and ultraviolet resistance, long in service life and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite materials, and in particular relates to a basalt fiber reinforced composite material pipeline and a preparation method thereof. BACKGROUND

[0002] With the continuous upgrading of the performance requirements of modern industry on materials, composite materials have been increasingly widely applied in many fields such as aerospace, automobile manufacturing, ocean engineering and infrastructure construction due to their significant advantages such as light weight, high strength, corrosion resistance and fatigue resistance. Especially in the field of fluid conveying pipelines, the problems such as corrosion, self-weight and maintenance cost of traditional metal pipelines are increasingly prominent, prompting the industry's increasingly urgent demand for high-performance, long-life new pipeline materials. Under this background, basalt fiber is gradually regarded as an ideal choice to replace glass fiber and part of carbon fiber application scenarios due to its excellent mechanical properties, excellent acid and alkali corrosion resistance, high temperature stability and green environmental protection characteristics, and has shown great application potential in the field of composite material pipelines. Basalt fiber reinforced composite material pipeline is gradually becoming the focus of the engineering and technical field due to its inherent characteristics such as light weight, high strength, pressure and wear resistance, insulation and magnetism, and longer service life, in order to provide more reliable fluid conveying solutions under harsh working conditions.

[0003] However, although basalt fiber has many excellent properties in theory, the existing composite material preparation technology still faces many bottlenecks and challenges when it is efficiently applied to the pipeline structure, thereby affecting the comprehensive performance, preparation efficiency and popularization and application of basalt fiber reinforced composite material pipeline in actual engineering. Specifically, the existing technical solutions are often difficult to effectively realize the optimized distribution of fibers in complex pipeline structures and the interface combination with the matrix while maintaining the basalt fiber reinforcement effect, and the complexity of the preparation process also restricts the economy of its large-scale production.

[0004] According to the search, the patent document with the publication number CN111844822B discloses a high-strength, high-impact non-continuous fiber-reinforced thermoplastic composite preform and its preparation method. The scheme finely cuts the continuous fiber-reinforced thermoplastic sheet into small pieces, then uniformly mixes them, and realizes the isotropic distribution of fibers with the help of low-shear mixing equipment, aiming to improve the overall strength and impact resistance of non-continuous fiber-reinforced thermoplastic composites. This method successfully alleviates the anisotropy problem of traditional short-cut fiber composites and improves their impact toughness to some extent when processing short-cut fiber systems. It provides a beneficial exploration for the design and preparation of non-continuous fiber-reinforced composites. However, the core of this technical solution is to handle "non-continuous fibers", and its fundamental principle relies on the shortening of fibers. Even if isotropic distribution is achieved, the load transfer between fibers is still limited by their length and end effect, which is fundamentally different from the efficiency of continuous fibers in transferring macroscopic stress. More importantly, the material system targeted by this patent is thermoplastic composites, and it does not explicitly involve the application of basalt fibers as a specific reinforcing material. Therefore, the process parameters and fiber-matrix interface optimization strategies cannot be directly applied to basalt fibers with different surface chemical activity and mechanical properties. In addition, directly applying this complex multi-step preparation process to continuous length pipe structures with extremely high strength and stiffness requirements will not only significantly increase the complexity and cost of production steps, but also due to the non-continuity of the fibers, the overall tensile strength, bending modulus, and pressure resistance of the material may not meet the stringent requirements of the pipe under high pressure, large span, or extreme working conditions. As a key structural component that bears internal and external pressure loads, the long-term service performance of the pipe has a very high requirement for the continuous load transfer capability of the material. Non-continuous fiber systems are theoretically difficult to provide the excellent macro-mechanical properties possessed by continuous fibers.

[0005] Correspondingly, patent document CN106626662B discloses a sandwich structure composite material and its preparation method. This patent focuses on cleverly injecting discontinuous fiber-reinforced thermoplastic core layers between the skin layers of a continuous fiber-reinforced thermoplastic composite material, thereby constructing a sandwich structure composite material with high strength, low density, and lightweight characteristics. The innovation of this solution lies in its effective improvement of the material's bending stiffness and shear resistance in specific structural applications through sandwich design, while also achieving structural weight reduction, making a significant technological contribution to applications in planar sheet or shell structures. However, this technical solution mainly focuses on the design of the sandwich structure, with its core objective being to optimize structural efficiency and reduce weight, rather than in-depth development of the mechanical properties of specific reinforcing fibers (such as basalt fiber) and their special synergistic effects with the matrix interface. A deeper contradiction lies in the inherent, unavoidable defect of the injection molding process used in this patent for the preparation of fiber-reinforced composite materials: under high-temperature, high-pressure shearing, the reinforcing fibers, especially the brittle basalt fibers, are prone to further shortening in length, severely weakening the reinforcing effect and ultimately leading to a significant decrease in the macroscopic mechanical properties of the composite material. This inherent defect is particularly prominent in complex geometric structures such as pipes, especially in basalt fiber-reinforced pipes that need to withstand high internal pressure and external loads. Because pipe structures have extremely stringent requirements for the overall stiffness, circumferential strength, and creep resistance of materials, the fiber degradation caused by injection molding makes it difficult for this solution to meet the high rigidity and pressure resistance requirements of basalt fiber-reinforced composite pipes at the principle level. Furthermore, the design concept of this sandwich structure and its injection molding process have low applicability to continuous, long-dimensional, and complex curvature pipe structures, making it difficult to achieve efficient, economical, and well-integrated pipe preparation.

[0006] In summary, existing technologies exhibit inherent limitations when applied to basalt fiber reinforced composite pipes. The discontinuous fiber characteristics and complex thermoplastic processing path of the CN111844822B scheme fundamentally restrict the potential of basalt fibers to provide continuous reinforcement in pipe structures, leading to secondary problems such as process complexity and insufficient performance. While the CN10662662B scheme offers innovation in sandwich structure design, the damage to basalt fiber length caused by its injection molding process, and the incompatibility between this structural design and pipe geometry, make it difficult to meet the comprehensive requirements of high-performance basalt fiber pipes for fiber integrity, structural integrity, and mechanical properties. Ultimately, existing technologies fail to effectively balance the deep-seated contradictions between fiber continuity and optimized distribution, the applicability and efficiency of the preparation process, and the inherent requirements of pipe structures for macroscopic mechanical properties. In the context of pursuing high-performance basalt fiber reinforced composite pipes, this contradiction manifests as: how to effectively resolve the inherent conflict between the fiber reinforcement effect and the maintenance of fiber integrity, optimized distribution, and efficient molding of complex pipe structures during the preparation process, while fully utilizing the excellent mechanical properties of basalt fibers, in order to achieve the best synergy between product performance and production efficiency. Therefore, overcoming the inherent limitations of existing technologies in maintaining basalt fiber continuity, optimizing the fiber-matrix interface, pipe structure molding processes, and the comprehensive mechanical properties of the final product, and developing a basalt fiber reinforced composite pipe and its preparation method that can fully utilize the potential of basalt fibers and possess high performance, high efficiency, and high reliability, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0007] This invention aims to overcome the inherent limitations of existing basalt fiber reinforced composite material pipes in terms of fiber continuity, fiber-matrix interface optimization, pipe structure forming process, and the comprehensive mechanical properties of the final product. It provides a basalt fiber reinforced composite material pipe and its preparation method that can fully utilize the potential of basalt fibers and has high performance, high efficiency, and high reliability.

[0008] To achieve the above-mentioned objectives, this invention provides a basalt fiber reinforced composite material pipe, comprising: an inner lining layer, a basalt fiber wound reinforcement layer, and an outer protective layer. The inner lining layer is composed of a polymer material possessing chemical corrosion resistance, a low coefficient of friction, and excellent gas barrier properties. The wall thickness of the inner lining layer ranges from 0.5 mm to 3.0 mm. The inner lining layer is disposed on the inner surface of the basalt fiber wound reinforcement layer and is fixedly bonded to it to form an integrated structure. The polymer material can be, for example, one or more composite materials selected from polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), or polytetrafluoroethylene (PTFE), the specific selection depending on the chemical properties and operating temperature of the medium transported by the pipe. When the pipeline is used to transport corrosive media, the inner lining is, for example, made of polyvinylidene fluoride (PVDF-HFP) material with a molecular weight distribution ranging from 100,000 to 300,000 and a melt index of 5.0 g / 10 min to 15.0 g / 10 min (at 230°C / 2.16 kg), exhibiting resistance to acid and alkali corrosion and high temperature resistance. The inner lining is prepared by extrusion molding or rotational casting. A micro-roughening structure is provided on the outer surface of the inner lining, such as an irregular array of depressions with a depth between 5 and 50 micrometers, to enhance the mechanical interlocking and bonding strength between the inner lining and the basalt fiber winding reinforcement layer. The micro-roughening structure is achieved through sandblasting, mechanical polishing, chemical etching, or plasma treatment. Exemplary parameters: Sandblasting uses 100-200 mesh alumina abrasive, pressure 0.3-0.6 MPa, distance 50-100 mm, time 10-30 s; mechanical grinding uses 180-400 mesh abrasive belt, linear speed 1-3 m / s; chemical etching uses 5-10 wt% NaOH solution (suitable for PVDF), temperature 40-60℃, time 1-5 min; plasma treatment power 300-500 W, oxygen atmosphere, treatment time 2-10 min. Preliminary experiments establish the correspondence between these parameters and Ra values ​​(5-20 μm).

[0009] The basalt fiber winding reinforcement layer is disposed on the outer surface of the inner lining layer and is composed of wound basalt fiber bundles and a cured resin matrix. The monofilament diameter of the basalt fiber bundles ranges from 9 micrometers to 16 micrometers, with a tensile strength of not less than 2800 MPa and a tensile modulus of not less than 85 GPa. The fiber volume content of the basalt fiber winding reinforcement layer ranges from 55% to 75%. The basalt fiber winding reinforcement layer comprises at least two layers of basalt fiber winding structures with different winding angles, and each winding structure is formed by a continuous basalt fiber bundle through a winding process. The at least two layers of winding structures with different winding angles include: an inner circumferential winding layer and an outer helical winding layer. The inner circumferential winding layer is composed of basalt fiber bundles with a winding angle of 85° to 90°, where the winding angle is defined as the angle between the fiber direction and the pipe axis direction. It is mainly used to withstand the internal circumferential pressure of the pipe and provide excellent anti-burst performance. The outer spiral winding layer consists of basalt fiber bundles with winding angles ranging from ±30° to ±70°, primarily used to withstand axial tensile loads, bending loads, and torsional loads on the pipeline. The basalt fiber bundles undergo surface treatment prior to winding, which includes applying a wetting agent containing a specific silane coupling agent. The silane coupling agent is, for example, γ-glycidoxypropyltrimethoxysilane (KH-560) or aminopropyltriethoxysilane (KH-550), with a mass percentage concentration in the wetting agent ranging from 0.5% to 2.0%. The sizing agent comprises water (50%-70% by mass), polyvinyl alcohol as a film-forming agent (5%-10% by mass), polyether-modified silicone oil as a surfactant (0.5%-2% by mass), and paraffin emulsion as a lubricant (1%-3% by mass). The specific proportions are optimized through sizing experiments: fibers are treated with sizing agents of different KH-560 concentrations (0.5%, 1.0%, 1.5%, 2.0%) to prepare unidirectional composite material samples. The interfacial shear strength (according to ASTM D2344) and the strength retention rate after damp heat aging (boiling in water at 100℃ for 1000h) are tested. A minimum interfacial shear strength of ≥30MPa and a strength retention rate of ≥85% are considered acceptable. The lowest effective concentration is selected as the optimal ratio. The silane coupling agent forms a layer of reactive silanol groups on the surface of basalt fibers, which undergo condensation reactions with the silanol groups on the surface of basalt fibers in the form of covalent bonds or hydrogen bonds, and undergo chemical cross-linking reactions with epoxy groups or amine groups in the resin matrix at the other end, thereby significantly improving the interfacial bonding strength and load transfer efficiency between basalt fibers and resin matrix.

[0010] The cured resin matrix is ​​composed of epoxy resin, curing agent, accelerator, and toughening agent, and is formed by chemical reaction. The epoxy resin is, for example, bisphenol A type epoxy resin (e.g., epoxy equivalent of 170-190 g / eq) or bisphenol F type epoxy resin (e.g., epoxy equivalent of 160-180 g / eq). The curing agent is, for example, an anhydride curing agent (e.g., methyltetrahydrophthalic anhydride) or an amine curing agent (e.g., diethylenetriamine or isophorone diamine). The accelerator is, for example, 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30). The toughening agent is, for example, polyurethane-modified epoxy resin or core-shell structured rubber particles. The optimized mass ratio of the epoxy resin, curing agent, accelerator, and toughening agent is: 100 parts epoxy resin, 70-90 parts curing agent, 0.5-2 parts accelerator, and 10-20 parts toughening agent. Formula optimization method: A four-factor, three-level orthogonal experiment (L9 array) was used, with variables being curing agent (75, 80, 85 parts), accelerator (1.0, 1.5, 2.0 parts), and toughening agent (12, 15, 18 parts). Viscosity at 25℃ (rotational viscometer, ASTM D2196), gel time at 120℃ (hot plate method, ASTM D2471), and DSC peak curing temperature were tested. With constraints of viscosity 300-800 mPa·s, gel time 30-60 min, and curing exothermic peak ≤150℃, the optimal formula ratio was selected (example: 80 parts curing agent, 1.5 parts accelerator, 15 parts toughening agent) to meet the requirements of continuous production and obtain excellent mechanical properties.

[0011] The outer protective layer is disposed on the outer surface of the basalt fiber wound reinforcement layer and is fixedly bonded to it to form an integrated structure. The outer protective layer is composed of a polymer composite material with excellent weather resistance, wear resistance, and UV resistance. The polymer composite material is, for example, modified polyester resin, polyurethane resin, or an epoxy resin system containing UV absorbers and antioxidants. The thickness of the outer protective layer ranges from 0.2 mm to 1.5 mm. The outer protective layer is formed by winding, spraying, or extrusion coating processes. The main function of the outer protective layer is to protect the internal basalt fiber reinforcement layer from external environmental factors (e.g., UV radiation, mechanical wear, chemical corrosion), thereby extending the service life of the pipeline.

[0012] The present invention also provides a method for preparing the above-mentioned basalt fiber reinforced composite material pipe, which includes the following steps:

[0013] First step: Inner lining layer forming.

[0014] A liner preform is provided, obtained by extrusion molding or rotational casting. The outer surface of the liner preform is roughened by sandblasting, mechanical grinding, or chemical etching. Sandblasting uses alumina abrasive with a particle size of 100-200 mesh, a blasting pressure of 0.3-0.6 MPa, a blasting distance of 50-100 mm, and a processing time of 10-30 seconds. The Ra value is monitored in real time using an online surface roughness meter, and parameters are adjusted until Ra is stable between 5-20 micrometers. For example, optimization methods include: determining the pressure-Ra correspondence curve through pre-experiments based on the liner material type to ensure uniformity.

[0015] Step 2: Preparation of basalt fiber winding reinforcement layer.

[0016] Basalt fiber bundles treated with sizing agent are drawn from multiple feeders and pass through a tension control device, a guide device, and a resin impregnation device. The tension control device includes multiple tension rollers driven by independent servo motors, each equipped with a high-precision strain gauge tension sensor (sampling frequency ≥100Hz) to detect tension values ​​in real time. A central control unit adjusts the servo motor speed based on a PID algorithm (proportional gain Kp = 0.8-1.2, integral time Ti = 0.5-1.0s), with a response time ≤50ms, ensuring tension fluctuations ≤±0.5N. The system uses closed-loop feedback to suppress disturbances caused by changes in fiber speed. The resin impregnation device includes a resin bath and a metering roller. The resin bath contains a pre-prepared and degassed resin matrix, maintained at a temperature between 20℃ and 40℃ and a viscosity between 300mPa·s and 800mPa·s. The metering roller precisely controls the resin content of the basalt fiber bundles, maintaining it between 30% and 45% (mass percentage). The impregnated basalt fiber bundles are precisely wound around the outer surface of the roughened inner liner preform prepared in the first step via guide nozzles. The winding process is performed on a CNC winding machine capable of at least three-axis linkage control for precise control of the winding angle, winding speed, and fiber tension. The basalt fiber winding reinforcement layer is achieved through layered winding, comprising: first, winding an inner circumferential winding layer with a winding angle of 85° to 90°, the thickness of which is controlled by the number of winding turns; subsequently, winding an outer spiral winding layer with a winding angle of ±30° to ±70°, achieved by changing the ratio of the winding machine head movement speed to the mandrel rotation speed. During the winding process, the inner liner preform is precisely mounted on a rotatable mandrel with a rotation speed ranging from 5 rpm to 50 rpm. The total thickness of the winding reinforcement layer is precisely calculated and controlled according to the pipeline's design pressure requirements.

[0017] Third step: online curing or offline curing.

[0018] After the basalt fiber winding reinforcement layer is completed, it is sent to a continuous curing oven for online curing, or transferred to an offline curing oven for curing. The curing process employs multi-stage temperature control to optimize the curing reaction of the resin matrix and reduce internal stress. The multi-stage temperature control includes:

[0019] The first stage is the pre-curing stage, which involves maintaining a temperature of 80°C to 100°C for 30 to 60 minutes to allow the resin matrix to undergo initial gelation and form a stable shape.

[0020] The second stage is the main curing stage, which involves maintaining a temperature of 120°C to 150°C for 2 to 4 hours to allow the resin matrix to fully cross-link and cure, achieving the designed mechanical properties.

[0021] The third stage: post-curing stage, held at 160℃ to 180℃ for 1 to 2 hours (optional), is used to eliminate residual internal stress and improve the thermal stability and durability of the material. The temperature uniformity inside the curing oven is controlled within ±3℃.

[0022] Fourth step: Formation of the outer protective layer.

[0023] After the basalt fiber winding reinforcement layer has fully cured, an outer protective layer is formed on its outer surface through extrusion coating, spraying, or rewinding processes. If extrusion coating is used, the pipe is passed through an annular extrusion die, which extrudes a pre-prepared melt of weather-resistant polymer composite material. This melt cools and solidifies on the outer surface of the pipe to form a uniform protective layer. If spraying is used, the weather-resistant polymer composite material is uniformly sprayed onto the outer surface of the pipe in an atomized form and then cured by heat. The thickness of the outer protective layer is controlled between 0.2 mm and 1.5 mm.

[0024] Step 5: Demolding and cutting of the pipes.

[0025] After the entire composite pipe structure has fully cured and cooled to room temperature, demolding is performed. If a permanent mandrel is used, it is removed hydraulically or mechanically; if an expandable / shrinkable mandrel is used, it is removed after shrinking the mandrel. Subsequently, according to design requirements, the pipe is precisely cut using a diamond saw to form a pipe product of the specified length.

[0026] In a preferred embodiment of the present invention, the basalt fiber bundles pass through a preheating unit before entering the impregnation device. The preheating unit raises the temperature of the basalt fiber bundles to 30°C to 60°C to improve the wettability of the fibers with the resin matrix and accelerate resin penetration. The preheating unit employs infrared heating or hot air circulation heating.

[0027] In a preferred embodiment of the present invention, the CNC winding equipment is equipped with an online tension sensing and feedback system. This system monitors the tension of each basalt fiber bundle in real time and transmits the data to a central control unit. Based on a preset tension curve and real-time feedback data, the central control unit adjusts the servo motor speed of each tension unwinding unit using a PID control algorithm, thereby controlling the deviation between the actual tension and the set tension within ±0.2 Newtons.

[0028] In a preferred embodiment of the present invention, the impregnation apparatus is equipped with an ultrasonic-assisted impregnation module. The ultrasonic-assisted impregnation module is disposed within a resin bath, and the ultrasonic parameters are optimized according to the fiber bundle specifications (e.g., 600 tex): frequency 28-35 kHz, power 100-150 W (power density ≥ 0.5 W / cm²). 2 The resin penetration depth was observed using high-speed imaging, with a single filament wetting rate of ≥95% as the benchmark. Verification method: The resin filling rate of the fiber bundle cross-section before and after treatment was compared (microscopic image analysis), requiring that the bubble area ratio be ≤2%, thereby reducing bubble entrainment and increasing the effective wetting area of ​​the fiber.

[0029] In a preferred embodiment of the present invention, the curing furnace is equipped with an internal air circulation system, which includes multiple fans and baffles to ensure a uniform temperature distribution within the furnace. The air velocity of the air circulation system is controlled between 0.5 m / s and 2.0 m / s. The curing furnace is also equipped with a waste gas collection and treatment system to collect volatile organic compounds (VOCs) generated during the curing process and treat them through activated carbon adsorption or catalytic oxidation. In another preferred embodiment of the present invention, the basalt fiber reinforced composite material pipe is subjected to online non-destructive testing after preparation. The non-destructive testing system includes an ultrasonic testing module and an infrared thermal imaging testing module. The ultrasonic testing module is used to detect defects such as delamination, pores, and unwetted areas inside the pipe, using a probe with a frequency of 1 MHz to 5 MHz. The infrared thermal imaging testing module is used to detect cracks, bubbles, or localized overheating areas on and near the surface of the pipe, with a resolution of 640x480 pixels and a temperature resolution of 0.05℃. The test results are analyzed using specialized software to ensure that the quality of the pipe product meets design standards.

[0030] The basalt fiber reinforced composite pipe provided by this invention features a basalt fiber winding reinforcement layer formed by a precisely controlled winding process using continuous basalt fiber bundles. This structure ensures high continuity and optimized distribution of basalt fibers within the pipe structure, significantly improving the macroscopic mechanical properties of the composite material, including tensile strength, flexural strength, and circumferential compressive strength. The multi-angle composite design of the inner circumferential winding layer and the outer helical winding layer achieves synergistic reinforcement of the pipe under internal and external pressure, axial tension, bending, and torsional loads. Simultaneously, the preparation method optimizes the interfacial bonding between the basalt fiber and the resin matrix through specialized surface treatment of the basalt fiber bundles and the introduction of specific components into the resin matrix, effectively solving the problem of poor interfacial bonding between basalt fiber and matrix in existing technologies. Furthermore, the preparation method of this invention avoids damage to the length of basalt fibers caused by traditional high-shear processes such as injection molding. Through precise tension control, temperature control, and impregnation control, the integrity of the basalt fibers is maintained to the greatest extent, thereby fully utilizing the high strength and high modulus characteristics of basalt fibers. The preparation method described in this invention enables continuous production, significantly improving production efficiency and reducing manufacturing costs, thus giving it broad application prospects in the field of large-diameter, long-distance fluid transportation pipelines. Specifically, the basalt fiber reinforced composite material pipeline of this invention has a circumferential tensile strength of not less than 300 MPa, an axial tensile strength of not less than 200 MPa, and an internal pressure burst strength of not less than 30 MPa, and maintains its excellent mechanical properties within a working temperature range of -40℃ to 120℃. Its long-term service life exceeds 50 years.

[0031] The basalt fiber reinforced composite material pipe and its preparation method provided by this invention exhibit the following significant improvements in technical performance:

[0032] This invention solves the fundamental defect of traditional discontinuous fiber reinforced composite materials in terms of macroscopic load transfer efficiency by using continuous basalt fiber bundles for multi-layer and multi-angle winding. It ensures that basalt fibers can play their continuous reinforcement effect in high-strength composite pipe structures, and significantly improves the overall strength, stiffness and impact resistance of the pipes.

[0033] This invention achieves efficient interfacial bonding between basalt fibers and resin matrix by impregnating basalt fibers with a specific silane coupling agent and precisely proportioning each component in the resin matrix. This effectively improves the anti-delamination performance and damp heat aging performance of the composite material and overcomes the problem of insufficient interfacial adhesion caused by the relatively low surface chemical activity of basalt fibers.

[0034] The preparation method provided by this invention, by introducing a precisely controlled tension feeding unit, an optimized resin impregnation device, and a multi-stage temperature curing process, effectively avoids the problem of fiber length shortening caused by excessive shear force during processing, thus preserving the original mechanical properties of basalt fiber to the maximum extent, while ensuring sufficient resin impregnation of the fiber bundle.

[0035] The basalt fiber winding reinforcement layer structure design described in this invention includes the synergistic effect of the inner circumferential winding layer and the outer helical winding layer, which enables the pipeline to achieve optimized load distribution and efficient transmission when subjected to internal and external pressure, axial, bending and torsional loads under complex working conditions, significantly improving the pipeline's comprehensive load-bearing capacity and reliability.

[0036] The preparation method provided by this invention has high potential for automated and continuous production. Its process flow is simple and easy to control, which not only improves production efficiency and reduces manufacturing costs, but also ensures the uniformity and stability of product quality, which is conducive to the large-scale promotion and application of basalt fiber reinforced composite material pipes.

[0037] The inner lining and outer protective layer design proposed in this invention endows the pipeline with excellent corrosion resistance, low flow resistance, UV resistance, and wear resistance, thereby comprehensively improving the pipeline's environmental adaptability and long-term service performance, extending the pipeline's service life, and reducing maintenance costs. Attached Figure Description

[0038] Figure 1 This is a cross-sectional view of the overall structure of the basalt fiber reinforced composite material pipe of the present invention.

[0039] Figure 2 This is a schematic flowchart of the method for preparing basalt fiber reinforced composite material pipes according to the present invention.

[0040] Figure 3 This is a schematic diagram of the winding equipment used in the preparation process of the basalt fiber winding reinforcement layer of the present invention.

[0041] The attached figures are labeled as follows:

[0042] 1. Inner lining layer; 2. Basalt fiber winding reinforcement layer; 3. Outer protective layer; 4. Inner circumferential winding layer; 5. Outer spiral winding layer; 6. Basalt fiber bundle; 7. Pay-off frame; 8. Tension control device; 9. Impregnation device; 10. Resin bath; 11. Metering roller; 12. Guide nozzle; 13. Mandrel; 14. CNC winding equipment; 15. Preheating unit; 16. Ultrasonic-assisted impregnation module. Detailed Implementation

[0043] This invention provides a basalt fiber reinforced composite material pipe and its preparation method. The technical solution aims to provide a pipe product with optimized structure, superior performance, and high manufacturing efficiency. This invention will fully disclose its technical content through a detailed description of each core layer constituting the pipe and its preparation method, supplemented by specific engineering parameters, material specifications, and experimental data, to ensure that those skilled in the art can understand and implement this invention.

[0044] like Figure 1As shown, the basalt fiber reinforced composite material pipe of the present invention comprises, from the inside out, an inner liner 1, a basalt fiber wound reinforcement layer 2, and an outer protective layer 3. Through precise design and coordinated manufacturing processes, these layers form a tightly bonded integrated structure, thereby endowing the pipe with excellent comprehensive mechanical properties and durability. Specifically, the inner liner 1, as the inner surface of the pipe, is in direct contact with the transported medium. The inner liner 1 is composed of carefully selected high-molecular polymer materials, whose material properties are strictly controlled to ensure that the pipe can meet the performance requirements under specific operating conditions. The high-molecular polymer material is designed to possess excellent chemical corrosion resistance, an extremely low coefficient of friction, and excellent gas barrier properties. Its wall thickness is precisely defined, typically between 0.5 mm and 3.0 mm, aiming to balance structural strength, material consumption, and fluid resistance. The high-molecular polymer material used in the inner liner 1 can be optimized according to the specific application environment, the chemical properties of the transported medium, and the operating temperature. For example, one or more composite materials selected from polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), or polytetrafluoroethylene (PTFE) can be used. When the pipeline is used to transport highly corrosive media or operates at high temperatures, for example in the field of chemical acid and alkali transportation, the inner lining 1 is preferably composed of polyvinylidene fluoride co-polymer (PVDF-HFP). The molecular weight distribution of this PVDF-HFP material is typically controlled between 100,000 and 300,000 to ensure its excellent mechanical properties and processing fluidity; its melt index (at 230°C / 2.16 kg) ranges from 5.0 g / 10 min to 15.0 g / 10 min, ensuring its processability in extrusion molding or rotational casting processes, while also taking into account the material's heat resistance and chemical corrosion resistance. The preparation process of the inner lining 1 typically employs extrusion molding or rotational casting, both of which can produce inner lining preforms with uniform wall thickness and smooth surfaces. To significantly enhance the interfacial bonding strength between the inner liner 1 and the outer basalt fiber-wound reinforcing layer 2, especially to resist shear stress caused by internal and external pressure differences and temperature cycles during long-term service, the outer surface of the inner liner 1 is designed and subjected to a micro-roughening structure. This micro-roughening structure manifests, for example, as an irregular array of depressions with depths ranging from 5 to 50 micrometers. These depression arrays, by providing mechanical interlocking points, greatly enhance the physical anchoring and chemical bonding strength between the inner liner 1 and the subsequently wound basalt fiber reinforcing layer 2. This micro-roughening structure can be achieved through various refined processes such as mechanical polishing, chemical etching, or plasma treatment. The parameters of each process must be rigorously optimized to ensure the uniformity and controllability of the roughening effect.

[0045] The basalt fiber winding reinforcement layer 2 is disposed on the outer surface of the inner lining layer 1 and forms a firm bond with it. This reinforcement layer is the core structure of the pipeline that bears the main mechanical loads, and is composed of a continuous basalt fiber bundle 6 wound into shape and a cured resin matrix. The basalt fiber bundle 6 used is strictly controlled in terms of the diameter of the single filaments within the range of 9 to 16 micrometers to ensure the flexibility and wettability of the fiber bundles, while maximizing their mechanical properties. The tensile strength of these basalt fiber single filaments is not less than 2800 MPa, and the tensile modulus is not less than 85 GPa, demonstrating the excellent mechanical properties of basalt fiber. In the basalt fiber winding reinforcement layer 2, the volume content of basalt fiber is precisely controlled within an optimized range of 55% to 75% to ensure fiber continuity and effective load transfer while maintaining sufficient wetting and protection of the fibers by the resin matrix. The basalt fiber winding reinforcement layer 2 comprises at least two layers of basalt fiber winding structures with different winding angles. Each winding structure is formed by continuous basalt fiber bundles 6 through an automated winding process, ensuring the continuity and integrity of the fibers throughout the pipeline structure and avoiding load transfer efficiency loss caused by chopped fibers. These at least two winding structures with different winding angles typically include an inner circumferential winding layer 4 and an outer helical winding layer 5. The inner circumferential winding layer 4 is composed of basalt fiber bundles with winding angles of 85° to 90°, where the winding angle is defined as the angle between the fiber direction and the pipeline axis. This near-pure circumferential winding method allows it to efficiently withstand the circumferential pressure inside the pipeline and provide excellent burst resistance. The outer helical winding layer 5 is composed of basalt fiber bundles with winding angles of ±30° to ±70°, achieved through positive and negative bidirectional helical winding, designed to effectively withstand the axial tensile loads, bending loads, and torsional loads faced by the pipeline, thereby providing comprehensive structural support for the pipeline. To further optimize the interfacial bonding between basalt fibers and the resin matrix and ensure efficient load transfer from the matrix to the fibers, the basalt fiber bundles 6 undergo rigorous surface treatment before entering the winding process. The core of this surface treatment lies in applying a wetting agent containing a specific silane coupling agent. The selected silane coupling agent is, for example, γ-glycidoxypropyltrimethoxysilane (KH-560) or aminopropyltriethoxysilane (KH-550), and its mass percentage concentration in the wetting agent is optimized to a range of 0.5% to 2.0%. The mechanism of action of this silane coupling agent is that one end of its molecule can form reactive silanol groups through hydrolysis. These silanol groups can then undergo condensation reactions with the silanol groups on the surface of the basalt fibers in the form of covalent bonds or strong hydrogen bonds, forming strong chemical bonds. Meanwhile, the other end of the silane coupling agent molecule contains an epoxy group (such as KH-560) or an amine group (such as KH-550), which can undergo a chemical cross-linking reaction with the corresponding functional groups in the cured resin matrix.Through this "molecular bridge" effect, the silane coupling agent significantly enhances the interfacial bonding strength between basalt fibers and the resin matrix, optimizes load transfer efficiency, and effectively improves the composite material's resistance to damp heat and fatigue. Furthermore, in addition to the silane coupling agent, the wetting agent also includes water as a solvent, a film-forming agent to provide fiber integrity, a surfactant to improve wetting properties, and a lubricant to reduce frictional damage between fibers.

[0046] The cured resin matrix is ​​another key component of the basalt fiber winding reinforcement layer 2, and its performance directly affects the final mechanical properties and durability of the composite material pipe. This resin matrix is ​​composed of epoxy resin, curing agent, accelerator, and toughening agent, and has undergone precise formulation optimization. The selected epoxy resin can be, for example, bisphenol A type epoxy resin (e.g., epoxy equivalent of 170-190 g / eq) or bisphenol F type epoxy resin (e.g., epoxy equivalent of 160-180 g / eq), which have moderate viscosity, good mechanical properties, and chemical stability. As a curing agent, anhydride curing agents (e.g., methyltetrahydrophthalic anhydride) or amine curing agents (e.g., diethylenetriamine or isophorone diamine) can be selected; their type and amount determine the curing reaction rate and final crosslinking density of the resin system. To accelerate the curing reaction, an accelerator, such as 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), is also introduced into the resin matrix. To improve the toughness and impact resistance of the composite material, the resin matrix also contains toughening agents, such as polyurethane-modified epoxy resin or core-shell structured rubber particles. These agents can improve the fracture toughness of the material by introducing a micro-toughening mechanism without significantly sacrificing strength and modulus. The mass ratios of epoxy resin, curing agent, accelerator, and toughening agent have been extensively verified and precisely optimized through experiments to ensure that the resin system has a suitable viscosity of 300 mPa·s to 800 mPa·s at 25°C. This viscosity range allows for sufficient and uniform wetting of the basalt fiber bundles during winding, minimizing the generation of air bubbles and unwetted areas. Simultaneously, this optimized ratio also ensures that the resin system has a reasonable gel time and curing cycle. For example, at 120°C, the gel time is controlled between 30 and 60 minutes, and the curing time is between 2 and 4 hours. This not only meets the process window requirements for continuous production but also ensures that the resin matrix can be fully cross-linked and cured, thereby enabling the composite material pipe to acquire excellent mechanical properties and thermal stability. The outer protective layer 3 is the outermost structure of the pipeline, which is disposed on the outer surface of the basalt fiber wound reinforcement layer 2 and integrally bonded to it. The main function of this layer is to act as the "skin" of the pipeline, providing environmental protection for the internal structure. Therefore, the outer protective layer 3 is composed of a polymer composite material with excellent weather resistance, abrasion resistance, and UV resistance. Typically, modified polyester resin, polyurethane resin, or epoxy resin systems containing UV absorbers and antioxidants can be used. These materials can effectively resist UV radiation, oxidation, mechanical wear, and mild chemical corrosion in the outdoor environment, thereby significantly extending the overall service life of the pipeline. The thickness of the outer protective layer 3 is typically controlled between 0.2 mm and 1.5 mm, designed to provide sufficient protection without significantly increasing the overall weight and manufacturing cost of the pipeline. The formation process of the outer protective layer 3 is flexible and can be achieved through winding, spraying, or extrusion coating processes, depending on material properties, pipeline size, and production efficiency requirements.

[0047] This invention also provides a method for preparing the above-mentioned basalt fiber reinforced composite material pipe. This method integrates advanced technologies such as automation, precision control, and multi-stage curing, ensuring high product quality and production efficiency. The preparation method includes the following key steps:

[0048] First step: Inner lining layer forming.

[0049] This step first requires providing a pre-formed inner liner. This pre-formed inner liner can be obtained through a precise extrusion molding process or rotational casting process, depending on the designed diameter and length of the pipe. Extrusion molding is typically used to produce continuous inner liner tubes, and its process parameters, such as screw speed, zone temperature, die temperature, and traction speed, must be precisely controlled to ensure the uniformity of the inner liner wall thickness and dimensional stability. Rotational casting is suitable for inner liners of specific sizes or shapes. It involves injecting liquid polymer material into a rotating die, using centrifugal force to distribute it evenly and solidify it. After obtaining the pre-formed inner liner, its outer surface undergoes a fine roughening treatment to form a micro-roughened structure. This roughening treatment aims to increase the specific surface area and mechanical anchoring points of the inner liner's outer surface, thereby significantly improving its interfacial bonding strength with the subsequent basalt fiber-wound reinforcement layer 2. Roughening can be achieved through various processes, such as sandblasting, mechanical polishing, or chemical etching. If sandblasting is used, the process parameters need to be strictly optimized. For example, alumina abrasive with a particle size of 100 to 200 mesh should be selected, the blasting pressure should be controlled at 0.3 MPa to 0.6 MPa, the blasting distance should be maintained at 50 mm to 100 mm, and the processing time should be 10 to 30 seconds. Precise control of these parameters aims to ensure the uniformity and controllability of the roughened structure, so that the average roughness Ra value of the micro-roughened structure can stably reach 5 to 20 micrometers. Mechanical grinding can physically grind the surface of the liner layer using tools such as abrasive belts and grinding wheels to remove the surface layer and form micro-grooves. Chemical etching selectively dissolves or modifies the surface of the liner layer using specific chemical reagents (e.g., solutions containing strong alkalis or organic amines can be used for PVDF liner layers) to form micropores or irregular surface morphologies. Regardless of the method used, the core objective is to obtain a roughened surface with good wettability and mechanical interlocking ability.

[0050] Step 2: Preparation of basalt fiber winding reinforcement layer.

[0051] This step is the core of the preparation method of this invention, such as Figure 3As shown, this process is performed on a highly automated CNC winding machine 14. First, a continuous basalt fiber bundle 6, pre-treated (including surface treatment, i.e., application of a wetting agent), is drawn from multiple pay-off frames 7. Each pay-off frame 7 is equipped with an independent tension control device 8. The tension control device 8 consists of multiple tension rollers driven by independent servo motors, capable of applying precisely controlled tension to each basalt fiber bundle 6, ranging from 5 Newtons to 20 Newtons, with tension fluctuations strictly controlled within ±0.5 Newtons. This precise tension control is crucial for ensuring uniform fiber bundle arrangement during winding, preventing fiber buckling, and ensuring proper pre-stress distribution. Subsequently, the basalt fiber bundle 6 enters the impregnation device 9 via a guide device. The impregnation device 9 mainly consists of a resin bath 10 and a metering roller 11. The resin bath 10 contains a pre-prepared and rigorously degassed resin matrix. To ensure the resin matrix has suitable fluidity and sufficient wetting ability for the fibers, its temperature is maintained constant between 20°C and 40°C during the winding process, and its viscosity is controlled between 300 mPa·s and 800 mPa·s. The function of the metering roller 11 is to precisely control the resin content of the basalt fiber bundle. By adjusting the contact pressure between the metering roller and the fiber bundle or the rotation speed of the metering roller, the resin content can be stably controlled between 30% and 45% (mass percentage). The resin-impregnated basalt fiber bundle 6 is then precisely wound through the guide nozzle 12 onto the outer surface of the roughened inner lining preform prepared in the first step. The inner lining preform is precisely mounted on a rotatable mandrel 13, the rotation speed of which ranges from 5 rpm to 50 rpm and can be dynamically adjusted according to the winding speed and angle requirements. The CNC winding equipment 14 can achieve at least three-axis linkage control (including the mandrel rotation axis, the guide head lateral movement axis, and the longitudinal movement axis), thereby precisely controlling the winding angle, winding speed, and fiber tension to achieve the fiber arrangement required by the design. The formation of the basalt fiber winding reinforcement layer 2 is a layered winding process. First, an inner circumferential winding layer 4 is wound, with its winding angle strictly controlled between 85° and 90°. The thickness of this layer is precisely controlled by the number of winding turns to enable it to efficiently withstand internal pressure. Subsequently, an outer spiral winding layer 5 is wound, with its winding angle between ±30° and ±70°. This spiral winding is achieved by changing the ratio of the winding equipment head movement speed to the mandrel rotation speed to ensure that the fiber can effectively withstand axial, bending, and torsional loads. The total thickness of the winding reinforcement layer 2 is precisely calculated and controlled according to the specific design pressure requirements and target mechanical properties of the pipeline.

[0052] Furthermore, in a preferred embodiment of the present invention, the basalt fiber bundle 6 passes through a preheating unit 15 before entering the impregnation device 9. The preheating unit 15 uses infrared heating or hot air circulation heating to raise the temperature of the basalt fiber bundle to 30°C to 60°C. This preheating treatment effectively reduces the surface tension of the fiber surface, improves the wettability of the fiber to the resin matrix, and accelerates the penetration of the resin into the fiber bundle, thereby further reducing bubbles and improving impregnation quality.

[0053] Furthermore, as a preferred embodiment of the present invention, the CNC winding equipment 14 is equipped with an online tension sensing and feedback system. This system can monitor the tension of each basalt fiber bundle in real time with high precision and transmit the collected data to the central control unit immediately. Based on a preset tension curve and real-time feedback data, the central control unit precisely adjusts the servo motor speed of each tension unwinding unit using an advanced PID (proportional-integral-derivative) control algorithm. This feedback control system can strictly control the deviation between the actual tension and the set tension within ±0.2 Newtons, thereby ensuring the tension uniformity of the fibers during the winding process and further improving the mechanical properties of the composite material.

[0054] Furthermore, in a preferred embodiment of the present invention, the impregnation device 9 is further equipped with an ultrasonic-assisted impregnation module 16. The ultrasonic-assisted impregnation module 16 is disposed inside the resin bath 10, and its emission frequency is typically set between 20 kHz and 40 kHz, with a power range of 50 W to 200 W. The cavitation effect generated by ultrasound in the resin matrix can effectively open the monofilaments in the basalt fiber bundles, promoting more uniform and thorough penetration of the resin matrix into the internal microstructure of the fiber bundles, thereby significantly reducing bubble entrainment and greatly increasing the effective wetting area of ​​the fibers, thus improving the interfacial bonding quality. Third step: Online curing or offline curing.

[0055] After the basalt fiber reinforcing layer 2 is wound, the entire pipe structure needs to undergo curing to allow the resin matrix to crosslink and form a robust composite material. This curing process can be performed online in a continuous curing oven, or the wound pipe can be moved to an offline curing oven for curing. To optimize the curing reaction kinetics of the resin matrix and minimize internal stress generated during curing, this invention employs a multi-stage temperature-controlled curing scheme. This scheme typically includes:

[0056] Phase 1: Pre-curing stage. Maintain a temperature of 80°C to 100°C for 30 to 60 minutes. The main purpose of this stage is to allow the resin matrix to undergo initial gelation, forming a stable shape and preventing the pipe from deforming or the fibers from slipping during the subsequent high-temperature stages.

[0057] The second stage: the primary curing stage. Maintain a temperature of 120°C to 150°C for 2 to 4 hours. This stage is crucial for the full cross-linking and curing of the resin matrix, aiming to achieve a high degree of cross-linking in the resin network structure, thereby imparting the mechanical properties (such as high strength and high modulus) to the composite material's pipe design.

[0058] The third stage: Post-curing stage. This stage is optional and can be maintained at a temperature of 160°C to 180°C for 1 to 2 hours. Its main purpose is to further improve the crosslinking degree and glass transition temperature of the resin matrix, eliminate any residual internal stress that may remain during the curing process, thereby improving the thermal stability, long-term durability, and environmental adaptability of the material.

[0059] Throughout the curing process, the temperature uniformity inside the curing oven is strictly controlled within ±3℃ to ensure that the curing degree of each part of the pipeline is consistent.

[0060] Furthermore, in a preferred embodiment of the present invention, the curing oven is equipped with an advanced air circulation system. This system includes multiple high-efficiency fans and precisely designed baffles to ensure a uniform temperature distribution within the oven, avoiding areas of localized overheating or insufficient curing. The air velocity of the air circulation system is typically controlled between 0.5 m / s and 2.0 m / s. Simultaneously, the curing oven is also equipped with a waste gas collection and treatment system to efficiently collect volatile organic compounds (VOCs) that may be generated during the curing process, and treat them using environmentally friendly methods such as activated carbon adsorption or catalytic oxidation to meet industrial environmental standards.

[0061] Step 4: Formation of the outer protective layer. After the basalt fiber-wound reinforcement layer 2 has fully cured and cooled to room temperature, the outer protective layer 3 is formed on its outer surface through extrusion coating, spraying, or rewinding processes. If extrusion coating is used, the cured pipe is passed through an annular extrusion die. The die extrudes a pre-formulated melt of weather-resistant polymer composite material, which rapidly cools and solidifies on the outer surface of the pipe, forming a uniform, dense, and precisely thick (0.2 mm to 1.5 mm) outer protective layer. If spraying is used, the weather-resistant polymer composite material (typically a liquid resin system) is uniformly sprayed onto the outer surface of the pipe in a highly atomized form, and then cured by external heating or room temperature self-curing to form the protective layer. If rewinding is used, fibers or films containing weather-resistant resin are used for winding. Regardless of the process, the goal is to ensure the uniformity, density, and thickness precision of the outer protective layer 3 to fully exert its protective function.

[0062] Step 5: Pipe Demolding and Cutting. After the entire composite pipe structure has completely cured and cooled to room temperature, demolding is performed. The demolding method depends on the type of mandrel: if a permanent metal mandrel is used, it is removed smoothly using hydraulic or mechanical means; if an expandable / shrinkable mandrel (e.g., a removable or inflatable mandrel) is used, it is easily removed by shrinking the mandrel, avoiding damage to the pipe structure. Subsequently, according to design requirements and customer needs, the pipe is precisely cut using high-precision cutting equipment equipped with a diamond saw to form pipe products of the specified length. The cutting process must ensure that the cut is smooth, burr-free, and dimensionally accurate.

[0063] Furthermore, as a preferred embodiment of the present invention, the basalt fiber reinforced composite material pipeline of the present invention undergoes rigorous online non-destructive testing after preparation. The non-destructive testing system integrates multiple testing technologies, including an ultrasonic testing module and an infrared thermal imaging testing module. The ultrasonic testing module uses a probe with a frequency of 1 MHz to 5 MHz to perform omnidirectional scanning of the pipeline, accurately detecting hidden defects such as delamination, porosity, unwetted areas, and fiber bundle defects within the pipeline. Its principle is to identify defects by analyzing changes in the propagation characteristics of ultrasonic waves in the material. The infrared thermal imaging testing module utilizes a high-resolution (e.g., 640x480 pixels) and high temperature resolution (e.g., 0.05℃) infrared thermal imager to perform non-contact scanning of the pipeline surface and near-surface, detecting cracks, bubbles, localized overheating areas, or other surface and near-surface defects. The test results are analyzed and visualized in real time using dedicated image processing and data analysis software to ensure that the quality of each pipeline product strictly meets design standards and industry specifications, thereby guaranteeing its long-term service reliability.

[0064] The basalt fiber reinforced composite pipe and its preparation method provided by this invention achieve significant technical improvements through the detailed technical parameters and process optimizations described above. The basalt fiber winding reinforcement layer 2 is formed using a precisely controlled winding process with continuous basalt fiber bundles 6. This structure ensures high continuity and optimized distribution of the basalt fibers within the pipe structure, significantly improving the macroscopic mechanical properties of the composite material. The multi-angle composite design of the inner circumferential winding layer 4 and the outer helical winding layer 5 achieves synergistic reinforcement of the pipe under internal and external pressure, axial tension, bending, and torsional loads, optimizing load distribution. Simultaneously, the preparation method, through specialized silane coupling agent surface treatment of the basalt fiber bundles 6 and the introduction of specific components into the resin matrix with optimized proportions, solves the problem of poor interfacial bonding between basalt fibers and the matrix in existing technologies, significantly improving interfacial bonding strength and resistance to damp heat aging. Furthermore, the preparation method described in this invention, such as online tension control, preheating, and ultrasonic-assisted impregnation, effectively avoids damage to the length of basalt fibers during traditional processing, maximizing the integrity of the basalt fibers and fully utilizing their high strength and high modulus characteristics. These technological advancements enable the pipe products prepared by this invention to achieve, for example, a stable circumferential tensile strength of over 300 MPa, an axial tensile strength exceeding 200 MPa, and an internal pressure burst strength of no less than 30 MPa. Simultaneously, they maintain excellent mechanical properties within a wide operating temperature range of -40℃ to 120℃ and have a long service life exceeding 50 years, significantly surpassing the performance level of existing similar products.

[0065] Example 1:

[0066] Preparation and properties of high-performance basalt fiber reinforced composite pipes.

[0067] This embodiment aims to illustrate in detail the preparation process and final performance indicators of a basalt fiber reinforced composite material pipe with a diameter of DN200 (outer diameter 220 mm).

[0068] In the first step of liner molding, a PVDF-HFP (molecular weight 150,000, melt index 9.0 g / 10 min) liner with a wall thickness of 1.5 mm was prepared using an extrusion molding process. The extruder temperature was set at 180℃-210℃ in each zone, the die temperature at 220℃, and the traction speed at 1.5 m / min. The outer surface of the liner preform was then roughened by sandblasting using 150-mesh alumina abrasive, a blasting pressure of 0.45 MPa, a blasting distance of 75 mm, and a processing time of 20 seconds, resulting in an average roughness Ra value of 12 micrometers.

[0069] In the second step of preparing the basalt fiber winding reinforcement layer, basalt fiber bundles with a single filament diameter of 12 micrometers, a tensile strength of 3000 MPa, and a tensile modulus of 90 GPa were selected. The impregnating agent contained 1.0% KH-560 silane coupling agent by mass percentage and also included polyvinyl alcohol (film-forming agent), polyether-modified silicone oil (surfactant), and paraffin emulsion (lubricant). Before entering the impregnation device, the basalt fiber bundles were preheated to 45°C using an infrared preheating unit. The resin matrix was composed of bisphenol A type epoxy resin (epoxy equivalent 185 g / eq), methyltetrahydrophthalic anhydride (curing agent), DMP-30 (accelerator), and polyurethane-modified epoxy resin (toughening agent), with a mass ratio of 100 parts epoxy resin, 80 parts curing agent, 1 part accelerator, and 15 parts toughening agent. The viscosity of this resin system at 25°C was 550 mPa·s. The resin bath temperature in the impregnation unit is maintained at 30°C, and it is equipped with an ultrasonic-assisted impregnation module with a frequency of 30 kHz and a power of 100 watts. Metering rollers precisely control the resin content of the basalt fiber bundles to 38% (by mass). The CNC winding equipment uses four-axis linkage, with a mandrel rotation speed of 20 rpm. The winding tension is controlled at 10 Newtons ± 0.2 Newtons via an online tension sensing and feedback system. First, an inner circumferential winding layer (angle 88°) is wound, for a total of 8 layers, with a layer thickness of 2.0 mm. Then, an outer spiral winding layer (angle ± 45°) is wound, for a total of 12 layers, with a layer thickness of 3.0 mm. Finally, the total thickness of the basalt fiber winding reinforcement layer is 5.0 mm, and the fiber volume content is 65%.

[0070] In the third curing step, the pipes enter a continuous curing oven. The curing process employs a three-stage temperature control: the pre-curing stage is maintained at 90℃ for 45 minutes; the main curing stage is maintained at 135℃ for 3 hours; and the post-curing stage is maintained at 170℃ for 1.5 hours. The internal temperature uniformity of the curing oven is controlled within ±2℃, and an air circulation system with a wind speed of 1.2 m / s is continuously running.

[0071] In the fourth step, the outer protective layer is formed using an extrusion coating process to create a 0.8 mm thick polyurethane resin outer protective layer. Finally, demolding and cutting are performed. After preparation, the pipe undergoes online non-destructive testing using an ultrasonic testing probe at a frequency of 3 MHz and infrared thermal imaging at a resolution of 640x480 pixels. The test results show no defects such as delamination, porosity, or unwetted areas inside the pipe. Subsequently, the cut sample is subjected to performance testing. The test results show that the pipe's circumferential tensile strength reaches 350 MPa, its axial tensile strength reaches 230 MPa, and its internal pressure burst strength reaches 38 MPa. After immersion in water at 100°C for 1000 hours, the circumferential tensile strength retention rate is 92%, indicating its excellent damp heat aging performance.

[0072] Comparative Example 1: Preparation and performance of traditional basalt fiber reinforced composite pipes.

[0073] The pipe prepared in this comparative example has a structure that is basically the same as that in Example 1, but there are differences in key process parameters and material selection. The inner lining is made of PE material with a wall thickness of 1.5 mm, and its outer surface is not roughened and remains smooth.

[0074] The basalt fiber bundles used in the basalt fiber winding reinforcement layer are the same as in Example 1, but their surfaces are not treated with silane coupling agent; instead, they are treated with ordinary water-based film-forming agents. The resin matrix formulation consists of bisphenol A type epoxy resin (epoxy equivalent 185 g / eq) and diethylenetriamine (curing agent) in a mass ratio of 100:12, without the addition of accelerators or toughening agents. The viscosity of this resin system is 1200 mPa·s at 25°C. No fiber bundle preheating was performed during the winding process, and the impregnation device did not include an ultrasonic-assisted impregnation module. The winding tension was controlled by a mechanical friction tensioner, with a relatively large fluctuation range (±1.5 Newtons). The winding structure remains an inner circumferential winding layer (angle 88°) and an outer spiral winding layer (angle ±45°), with the thickness of each layer and the total thickness being the same as in Example 1, and the fiber volume content being 65%.

[0075] The curing process employed a single-stage curing method, maintaining a temperature of 120℃ for 4 hours without pre-curing or post-curing. The curing oven lacked an air circulation system, maintaining a temperature uniformity of ±5℃. The outer protective layer was a 0.8 mm thick modified polyester resin. After preparation, the cut samples underwent performance testing. Test results showed that the comparative pipe exhibited a circumferential tensile strength of 240 MPa, an axial tensile strength of 150 MPa, and an internal pressure burst strength of 22 MPa. After immersion in water at 100℃ for 1000 hours, the circumferential tensile strength retention rate was only 65%, indicating significant interfacial delamination.

[0076] Experimental data and performance comparison

[0077] Table 1 below compares in detail the key performance indicators of the basalt fiber reinforced composite material pipes prepared in Example 1 and Comparative Example 1, intuitively demonstrating the technical superiority of the present invention.

[0078] Table 1: Comparison of pipeline performance between Example 1 and Comparative Example 1 As can be clearly seen from the comparative data in Table 1, the basalt fiber reinforced composite material pipe prepared in Example 1 of the present invention is significantly better than Comparative Example 1 in many key performance indicators.

[0079] Specifically, the pipe of the present invention exhibits improvements of 45.8%, 53.3%, and 72.7% in circumferential tensile strength, axial tensile strength, and internal pressure burst strength, respectively. This comprehensive improvement in mechanical properties is primarily attributed to the fine roughening treatment of the inner lining layer, which enhances interfacial interlocking; the silane coupling agent impregnation treatment of the basalt fiber bundles, which effectively improves the interfacial bonding strength between the fibers and the resin matrix; and the optimized resin formulation (containing toughening agents) and precise winding processes (such as preheating, ultrasonic-assisted impregnation, and high-precision tension control), which ensure full impregnation and undamaged arrangement of the fibers.

[0080] The significant improvement in strength retention after humid heat aging (from 65% to 92%) is particularly noteworthy, directly reflecting the remarkable success of this invention in optimizing interfacial bonding. The molecular bridging effect of the silane coupling agent effectively prevents the accumulation and penetration of water molecules at the fiber-resin interface, greatly improving the durability and long-term stability of the composite material under humid heat conditions. Furthermore, the multi-stage temperature-controlled curing process further ensures sufficient cross-linking of the resin matrix, reducing internal residual stress and thus comprehensively improving the pipe's fatigue resistance and environmental resistance. In Comparative Example 1, due to issues such as the lack of inner lining roughening, insufficient fiber surface treatment, inadequate resin matrix properties, and imperfect curing process, its mechanical properties and durability are far lower than those of Example 1.

[0081] In summary, the basalt fiber reinforced composite pipe and its preparation method provided by this invention, through a series of refined structural designs and process optimizations, achieve a continuous reinforcement effect of basalt fiber in a high-strength composite pipe structure, significantly improving the overall strength, stiffness, and impact resistance of the pipe. By subjecting the basalt fiber to specific silane coupling agent impregnation treatment and precisely proportioning each component in the resin matrix, efficient interfacial bonding between the basalt fiber and the resin matrix is ​​achieved, effectively improving the composite material's anti-delamination and damp heat aging performance. The preparation method provided by this invention, by introducing a precisely controlled tension pay-off unit, an optimized impregnation device, and a multi-stage temperature curing process, effectively avoids the problem of fiber length shortening due to excessive shear force during processing, maximizing the preservation of the original mechanical properties of the basalt fiber while ensuring sufficient resin impregnation of the fiber bundle. The basalt fiber winding reinforcement layer structure design, including the synergistic effect of the inner circumferential winding layer and the outer helical winding layer, enables the pipeline to achieve optimized load distribution and efficient transmission when subjected to complex internal and external pressure, axial, bending, and torsional loads, significantly improving the pipeline's overall load-bearing capacity and reliability. Furthermore, the manufacturing method provided by this invention has high potential for automated and continuous production. Its process flow is simple and easy to control, not only improving production efficiency and reducing manufacturing costs, but also ensuring the uniformity and stability of product quality. The inner lining and outer protective layer designs respectively endow the pipeline with excellent corrosion resistance, low flow resistance, and UV resistance and wear resistance, comprehensively improving the pipeline's environmental adaptability and long-term service performance, extending its service life, and reducing maintenance costs, making it a promising candidate for large-diameter, long-distance fluid transportation pipelines.

Claims

1. A basalt fiber reinforced composite material pipe, characterized in that, include: An inner liner (1) is composed of a polymer material that is resistant to chemical corrosion, has a low coefficient of friction, and excellent gas barrier properties. The wall thickness of the inner liner (1) ranges from 0.5 mm to 3.0 mm. A basalt fiber winding reinforcement layer (2) is disposed on and fixed to the outer surface of the inner liner (1). The basalt fiber winding reinforcement layer (2) is composed of a basalt fiber bundle (6) wound and a cured resin matrix. The monofilament diameter of the basalt fiber bundle (6) ranges from 9 μm to 16 μm, and the tensile strength is not less than 2800 MPa. The tensile modulus is not less than 85 gigapascals, the fiber volume content of the basalt fiber winding reinforcement layer (2) ranges from 55% to 75%, and the basalt fiber winding reinforcement layer (2) includes at least two layers of basalt fiber winding structures with different winding angles, the winding angle being defined as the angle between the fiber direction and the pipe axis direction; and an outer protective layer (3) is disposed on the outer surface of the basalt fiber winding reinforcement layer (2) and fixed thereto, the outer protective layer (3) being composed of a high-molecular composite material with excellent weather resistance, wear resistance and UV resistance, and the thickness of the outer protective layer (3) ranges from 0.2 mm to 1.5 mm.

2. The basalt fiber reinforced composite material pipe according to claim 1, characterized in that, The polymer material of the inner lining layer (1) includes polyvinylidene fluoride (PVDF-HFP) material with a molecular weight distribution range of 100,000 to 300,000 and a melt index of 5.0 g / 10 min to 15.0 g / 10 min (at 230℃ / 2.16 kg). The PVDF-HFP material has the characteristics of acid and alkali corrosion resistance and high temperature resistance. The outer surface of the inner lining layer (1) is provided with a micro-roughened structure, which is an irregular array of depressions with a depth between 5 micrometers and 50 micrometers, used to enhance the mechanical interlocking effect and bonding strength between the inner lining layer (1) and the basalt fiber winding reinforcement layer (2).

3. The basalt fiber reinforced composite material pipe according to claim 1, characterized in that, In the basalt fiber winding reinforcement layer (2), the at least two layers of basalt fiber winding structure with different winding angles include an inner circumferential winding layer (4) and an outer spiral winding layer (5); the inner circumferential winding layer (4) is composed of basalt fiber bundles (6) with winding angles of 85° to 90°, mainly used to bear the internal circumferential pressure of the pipeline and provide excellent anti-burst performance; the outer spiral winding layer (5) is composed of basalt fiber bundles (6) with winding angles of ±30° to ±70°, mainly used to bear the axial tensile load, bending load and torsional load of the pipeline.

4. The basalt fiber reinforced composite material pipe according to claim 1 or 3, characterized in that, The basalt fiber bundle (6) undergoes surface treatment before winding, the surface treatment including the application of a wetting agent containing a specific silane coupling agent; the silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane (KH-560), aminopropyltriethoxysilane (KH-550) or a combination thereof, and its mass percentage concentration in the wetting agent ranges from 0.5% to 2.0%; the silane coupling agent forms a layer of reactive silanol groups on the surface of the basalt fiber, which undergoes a condensation reaction with the silanol groups on the surface of the basalt fiber in the form of covalent bonds or hydrogen bonds, and undergoes a chemical crosslinking reaction with the epoxy groups or amine groups in the cured resin matrix at the other end.

5. The basalt fiber reinforced composite material pipe according to claim 1, characterized in that, The cured resin matrix is ​​composed of epoxy resin, curing agent, accelerator, and toughening agent; the epoxy resin is selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, or a combination thereof; the curing agent is selected from acid anhydride curing agents, amine curing agents, or a combination thereof; the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) or its analogues; the toughening agent is selected from polyurethane modified epoxy resin, core-shell structured rubber particles, or a combination thereof; the viscosity of the cured resin matrix at 25°C is in the range of 300 mPa·s to 800 mPa·s, and it has a reasonable gel time and curing cycle, wherein the gel time at 120°C is 30 minutes to 60 minutes, and the curing time at 120°C is 2 hours to 4 hours.

6. A method for preparing a basalt fiber reinforced composite material pipe, the pipe comprising an inner lining layer (1), a basalt fiber winding reinforcement layer (2), and an outer protective layer (3), characterized in that, Includes the following steps: a. Liner Forming: A liner preform is provided, which is obtained by extrusion molding or rotational casting. The outer surface of the liner preform is roughened to form a micro-roughened structure. b. Basalt Fiber Wrapping Reinforcement Layer Preparation: Basalt fiber bundles (6) treated with sizing agent are drawn from multiple feeders (7), and after passing through a tension control device (8), a guide device, and an impregnation device (9), the impregnated basalt fiber bundles (6) are precisely wound around the roughened liner through a guide nozzle (12). c. Curing: After the basalt fiber winding reinforcement layer (2) is wound, it is cured in a multi-stage temperature-controlled manner; d. Formation of outer protective layer: After the basalt fiber winding reinforcement layer (2) is completely cured, the outer protective layer (3) is formed on its outer surface by extrusion coating, spraying or rewinding process; and e. Demolding and cutting of pipe: After the entire composite material pipe structure is completely cured and cooled to room temperature, demolding and cutting are performed to form pipe products of a specified length.

7. The preparation method according to claim 6, characterized in that, In step a of the inner lining layer forming process, the roughening treatment is achieved by sandblasting, mechanical grinding, or chemical etching. The process parameters of the roughening treatment are optimized so that the average roughness Ra of the micro-roughened structure reaches 5 micrometers to 20 micrometers. In step b of the basalt fiber winding reinforcement layer preparation process, the tension control device (8) includes multiple tension rollers driven by independent servo motors. The tension applied by each tension roller to a single basalt fiber bundle (6) can be precisely controlled between 5 Newtons and 20 Newtons. Between, the tension fluctuation range is controlled within ±0.5 Newtons; the impregnation device (9) includes a resin bath (10) and a metering roller (11). The resin bath (10) contains a pre-prepared and degassed resin matrix. The temperature of the resin matrix is ​​maintained between 20°C and 40°C, and the viscosity is between 300 mPa·s and 800 mPa·s. The metering roller (11) is used to precisely control the glue content of the basalt fiber bundle (6) to be between 30% and 45% (mass percentage).

8. The preparation method according to claim 6 or 7, characterized in that, In step b of the preparation of the basalt fiber winding reinforcement layer, the basalt fiber bundle (6) passes through a preheating unit (15) before entering the impregnation device (9). The preheating unit (15) uses infrared heating or hot air circulation heating to raise the temperature of the basalt fiber bundle (6) to 30°C to 60°C to improve the wettability of the fiber and the resin matrix. The impregnation device (9) is equipped with an ultrasonic-assisted impregnation module (16), which is set in the resin bath (10). Its emission frequency is 20 kHz to 40 kHz and its power is 50 watts to 200 watts. The cavitation effect of the ultrasonic waves helps to promote the resin matrix to penetrate into the fiber bundle (6) more uniformly and thoroughly.

9. The preparation method according to claim 6 or 7, characterized in that, Step b of the basalt fiber winding reinforcement layer preparation is performed on a CNC winding machine (14). The CNC winding machine (14) can achieve at least three-axis linkage control to precisely control the winding angle, winding speed and fiber tension. The inner lining preform is precisely mounted on a rotatable mandrel (13). The rotation speed of the mandrel (13) is from 5 rpm to 50 rpm. The basalt fiber winding reinforcement layer (2) is achieved by layer winding, including first winding an inner circumferential winding with a winding angle of 85° to 90°. The winding layer (4) is followed by an outer spiral winding layer (5) with a winding angle of ±30° to ±70°; and the CNC winding equipment (14) is equipped with an online tension sensing and feedback system. The system monitors the tension of each basalt fiber bundle (6) in real time and transmits the data to the central control unit. The central control unit adjusts the servo motor speed of each tension release unit according to the preset tension curve and real-time feedback data through a PID control algorithm, thereby controlling the deviation between the actual tension and the set tension within ±0.2 Newtons.

10. The preparation method according to claim 6, characterized in that, In the curing step c, the multi-stage temperature control includes: a first stage, a pre-curing stage, maintaining a temperature of 80°C to 100°C for 30 to 60 minutes; a second stage, a main curing stage, maintaining a temperature of 120°C to 150°C for 2 to 4 hours; and a third stage, a post-curing stage, maintaining a temperature of 160°C to 180°C for 1 to 2 hours; the curing oven is equipped with a temperature sensor array (such as a K-type thermocouple) and a PID controller, which adjusts the heating element power and fan speed to control the temperature uniformity within ±3°C; the air circulation system includes... The system includes 6-8 fans and baffles, with the airflow speed controlled by a frequency converter between 0.5 m / s and 2.0 m / s. The baffle angle is adjustable to ensure uniform hot air distribution. After the pipeline is manufactured, online non-destructive testing is performed. The non-destructive testing system includes an ultrasonic testing module and an infrared thermal imaging module. The ultrasonic testing module uses a probe with a frequency of 1 MHz to 5 MHz for scanning. The infrared thermal imaging module is used to detect whether there are cracks, bubbles, or localized overheating areas on and near the surface of the pipeline. Its resolution is 640x480 pixels, and its temperature resolution is 0.05℃.

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