A BFRP strip reinforced large-diameter thermoplastic pipe

Abstract

The present invention discloses a BFRP strip reinforced large-diameter thermoplastic pipe, which comprises, from the inside to the outside, an inner lining layer, a reinforcement layer, an outer cladding layer and stiffening ribs in sequence. The reinforcement layer is in the form of a strip and is wound around the surface of the inner lining layer, and the stiffening ribs are spaced apart on the surface of the outer cladding layer. The inner lining layer and the outer cladding layer are both made of short-fiber reinforced high-density polyethylene materials. The reinforcement layer is a BFRP strip; and the stiffening ribs are spaced apart on the surface of the outer cladding layer. This thermoplastic pipe can improve the stiffness, strength and durability of large-diameter (≥4000mm) water pipelines. The interface bonding performance between the short-fiber reinforced HDPE layer and the BFRP strip is excellent, which avoids interface peeling between the HDPE layer and the reinforcement layer during long-term use. In addition, the use of BFRP strips as a reinforcement skeleton fully utilizes the excellent creep resistance of basalt fiber composite materials, ensures the stability of the reinforcement layer during long-term use, and avoids safety hazards of the pipeline caused by failure of the reinforcement layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoplastic pipes, and in particular relates to a BFRP strip reinforced large-diameter thermoplastic pipe. Background Art

[0002] Currently, typical large-diameter water pipelines include cast iron pipes, prestressed reinforced concrete pipes, and glass fiber reinforced plastic sand-filled pipes. However, the maximum diameter of cast iron pipes is currently 2600mm, and they are prone to rust and corrosion over long periods of use, making them less safe and environmentally friendly. The inner wall of prestressed reinforced concrete pipes is a concrete structure, with a rough surface that is prone to scaling and microbial growth. Furthermore, during long-term use in actual projects, the prestressed high-strength steel wire corrodes and fractures, affecting the safety performance of the pipeline. Glass fiber reinforced plastic sand-filled pipes consist of an outer protective layer, an outer reinforcement layer, a sand-filled layer, an inner reinforcement layer, and an inner lining. The reinforcement layer is composed of radial and axial glass fibers. Under the long-term influence of internal water pressure, the glass fibers undergo creep fracture, causing accidents such as pipe wall cracking and structural delamination. Summary of the Invention

[0003] Purpose of the Invention: To address the shortcomings of the prior art, the present invention provides a BFRP strip-reinforced large-diameter thermoplastic pipe. This thermoplastic pipe utilizes chopped fiber-reinforced high-density polyethylene (HDPE) pipe as the base material, basalt fiber composite (BFRP) strips with excellent creep properties as the reinforcing framework, and high-density polyethylene box-sections as stiffening ribs. This improves the stiffness, strength, and durability of ultra-large-diameter water pipelines. The chopped fiber-reinforced high-density polyethylene improves the bond between the chopped fiber-reinforced high-density polyethylene and the framework BFRP strip layer. The reinforced pipe can reach diameters exceeding 4000 mm, and its physical and mechanical properties remain stable for over 50 years, effectively addressing the stiffness, strength, interface, and durability issues associated with large-diameter pipes.

[0004] Technical solution: To achieve the above-mentioned purpose, the present invention adopts the following technical solution:

[0005] A BFRP strip reinforced thermoplastic pipe, which comprises, from the inside out, an inner lining layer, a reinforcement layer, an outer cladding layer and stiffening ribs in sequence. The reinforcement layer is in the form of a strip and is wound around the surface of the inner lining layer. The stiffening ribs are distributed at intervals on the surface of the outer cladding layer. The inner lining layer and the outer cladding layer are both made of short fiber reinforced high-density polyethylene material. The reinforcement layer is a basalt fiber composite material.

[0006] The inner lining and outer covering are reinforced with high-density polyethylene through short-cut fibers, which improves the wear resistance and pressure resistance of the pipeline structure; at the same time, the short-cut fibers are randomly distributed in the HDPE layer, which increases the bonding performance between the HDPE layer and the BFRP strip layer.

[0007] As a preferred or specific embodiment:

[0008] The short fiber reinforced high-density polyethylene material is mainly made of dipped basalt fiber bundles and polyethylene. The fibers in the dipped basalt fiber bundles are high modulus basalt fibers with random fiber distribution. The fiber strength must be no less than 3500MPa and the elastic modulus must be no less than 90GPa. The volume fraction of basalt fibers in the entire fiber bundle is 50-60%. The resin is high-density polyethylene with a relative density of no less than 0.94g / cm 3 , the volume fraction of resin in the entire fiber bundle is 40-50%.

[0009] The impregnated basalt fiber bundle has a fiber bundle length of 3-6 mm, a diameter of 2-4 mm, and a circular or quasi-circular cross-section.

[0010] The volume fraction of the impregnated basalt fiber bundles in the entire inner lining layer (1) is 30-40%; the volume fraction of the impregnated basalt fiber bundles in the entire outer cladding layer (3) is 30-40%.

[0011] The impregnated basalt fiber bundles are mixed with ordinary polyethylene particles to form the inner lining and outer cladding of the pipeline, without changing the original molding process, while ensuring the uniformity of the pipeline.

[0012] The basalt fiber composite material is mainly made of basalt fiber, thermoplastic resin and curing agent.

[0013] Further preferably, the basalt fiber angle is 0°, the tensile strength must be no less than 3500 MPa, the elastic modulus must be no less than 85 GPa, the creep rupture stress must be no less than 50% fu, and the volume fraction of basalt fiber in the entire reinforcement layer strip is 60-65%; the thermoplastic resin is high-density polyethylene, the tensile strength must be no less than 30 MPa, the elastic modulus must be no less than 20 MPa, and the volume fraction of the resin in the entire reinforcement layer strip is 35-40%; the curing agent is hexamethylenetetramine, and the volume fraction of the curing agent in the entire reinforcement layer strip does not exceed 5%.

[0014] The creep rupture stress of the basalt fiber in the BFRP strip is not less than 50%fu, and it has excellent resistance to wear, which avoids the breakage of the reinforcement layer during long-term use.

[0015] The reinforcement strips are 600mm-1000mm wide and 0.25-0.35mm thick. They are spirally wound around the pipe in both forward and reverse directions at an angle of 60-90°, with an overlap length of 5-10% of the strip width. The BFRP strip winding angle ensures good rigidity and strength in both the circumferential and axial directions.

[0016] The cross section of the stiffening rib is box-shaped and is filled with compression-resistant material.

[0017] Further preferably, the cross-section of the stiffening rib is made of chopped fiber reinforced high-density polyethylene material, which is made of basalt fiber and high-density polyethylene, and the volume fraction of basalt fiber in the box section is 35-50%; the compression material is a mixture of quartz sand and waste plastic, and the quartz sand accounts for 40-60% of the volume fraction of the mixture, and the waste plastic accounts for 40-60% of the volume fraction of the mixture. The waste plastic can be recycled polyethylene particles. The design of the box section keeps the material away from the inertia axis, improves the bending moment of inertia of the section, and makes full use of the material properties. The inner cavity of the box chamber uses a mixture of quartz sand and waste plastic as the filler, which increases the compression resistance of the stiffening rib and can also realize the recycling of waste plastic.

[0018] The height-to-width ratio of the box section of the stiffening rib is 1.5-2, the height-to-width ratio of the box cavity is 1.5-2, and the ratio of the box cavity width to the rib width is 0.5-0.75.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] 1. The inner lining and outer cladding are reinforced with high-density polyethylene (HDPE) using short-cut fibers, improving the pipe structure's abrasion resistance and pressure resistance. The inner lining and outer cladding are formed by mixing impregnated basalt fiber bundles with ordinary polyethylene particles. This maintains the original molding process while ensuring the dispersion of the fiber bundles during production, improving the uniformity of the pipe.

[0021] 2. The chopped fibers are randomly distributed in the inner lining and outer cladding. At the interface between HDPE and BFRP strips, the chopped fibers are randomly embedded in the BFRP strips like rivets, which increases the mechanical bonding properties of the interface and thus improves the interface bonding strength and integrity.

[0022] 3. The BFRP strips used in the reinforcement layer fully utilize the excellent creep resistance of basalt fiber, with a creep rupture stress of 50% fu. Compared with the creep rupture stress of glass fiber (29% fu), basalt fiber's creep performance is improved by 72%. This ensures the mechanical properties of the reinforcement layer during long-term use and avoids safety hazards caused by pipeline reinforcement failure.

[0023] 4. The BFRP strips are spirally wound in the forward and reverse directions along the pipe with a winding angle of 45-60°. The winding angle can ensure that the pipe has good rigidity and strength in both the circumferential and axial directions, avoiding the defects of low axial strength and easy leakage of the wound pipe.

[0024] 5. The box-section design distances the material from the axis of inertia, increasing the cross-section's bending moment of inertia and fully utilizing the material's properties. The interior of the box is filled with a mixture of quartz sand and waste plastic, which increases the stiffening rib's compressive strength and enables the recycling of waste plastic.

[0025] Through the above technical solution, the diameter of the enhanced pipeline can reach 4m-6m, and the physical, chemical and mechanical properties can be stable for more than 50 years. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of a large-diameter thermoplastic pipe reinforced with BFRP strips;

[0027] Figure 2 Schematic diagram of chopped fiber distribution at the interface of HDPE and BFRP strips;

[0028] Figure 3 Schematic diagram of bidirectional spiral winding of BFRP strips;

[0029] Figure 4 This is a schematic diagram of the box section stiffener; DETAILED DESCRIPTION

[0030] The following is a comprehensive description of the present invention. The implementation cases described are the most preferred implementation methods of the present invention, but the present invention is not limited to the following examples.

[0031] Example 1

[0032] This embodiment provides a BFRP strip reinforced large diameter thermoplastic pipe, the measured diameter of the pipe is 6m. Figure 1 As shown, it includes an inner lining layer 1, a reinforcement layer 2, an outer cladding layer 3, and a stiffening rib 4; the inner lining layer is short fiber reinforced high-density polyethylene; the reinforcement layer is a BFRP strip; the outer cladding layer is short fiber reinforced high-density polyethylene; the BFRP strip is spirally wound around the pipe, and the stiffening rib 4 has a box-shaped cross-section and is filled with pressure-resistant material.

[0033] The chopped fibers are impregnated basalt fiber bundles, which are high modulus basalt fibers with a fiber strength of 3500 MPa and an elastic modulus of 92 GPa. The volume fraction of basalt fibers in the entire fiber bundle is 55%. The resin is high-density polyethylene with a relative density of 0.945 g / cm 3 The volume fraction of the resin in the entire fiber bundle is 45%; the fiber bundle is 4 mm long, 3 mm in diameter, and the cross-section can be quasi-circular.

[0034] The volume fraction of the rubber-impregnated basalt fiber bundles in the entire inner lining layer is 30%, and the volume fraction of the rubber-impregnated basalt fiber bundles in the entire outer cladding layer is 35%.

[0035] The BFRP strip comprises basalt fiber, a thermoplastic resin, and a curing agent. The basalt fiber has a 0° angle, a tensile strength of 3550 MPa, and an elastic modulus of 85 GPa, with the basalt fiber accounting for 60% of the total BFRP strip. The thermoplastic resin is high-density polyethylene (HDPE), with a tensile strength of 30 MPa and an elastic modulus of 22 MPa, accounting for 35% of the total BFRP strip. The curing agent is hexamethylenetetramine (HMT), accounting for 3% of the total BFRP strip. The basalt fiber, HDPE, and HMT are extruded in the aforementioned proportions to form the BFRP strip. Tensile tests show that the resulting BFRP strip has a tensile strength (f) of 1050 MPa.

[0036] Furthermore, the BFRP strip has a width of 800 mm and a thickness of 0.3 mm. The BFRP strip is spirally wound in forward and reverse directions along the pipeline, with a winding angle of 45° and an overlap length of 5% of the strip width.

[0037] The cross section 5 of the stiffening rib 4 is box-shaped, with a height of 400 mm and a width of 200 mm. The box-shaped section material is short-cut fiber reinforced high-density polyethylene, and the short-cut fibers are impregnated basalt fiber bundles, with the volume fraction of basalt fibers in the box-shaped section being 45%.

[0038] The inner cavity 6 of the stiffening rib has a width of 200 mm and a height of 100 mm. The filling material of the inner cavity 6 of the box chamber is a mixture of quartz sand and waste plastics, wherein the quartz sand accounts for 50% of the volume fraction of the mixture and the waste plastics account for 50% of the volume fraction of the mixture.

[0039] The preparation method of the above pipeline is as follows:

[0040] The pipe lining layer 1 is prepared by mixing the impregnated basalt fiber bundles with ordinary polyethylene particles, feeding the mixture into an extruder for extrusion molding, and hot-melt molding at a high temperature of 180°C.

[0041] The reinforcement layer 2 is bidirectionally wound by BFRP strips and is welded to the inner lining layer 1 by a hot melt forming process.

[0042] The outer layer 3 is formed by mixing the impregnated basalt fiber bundle with ordinary polyethylene particles, feeding the mixture into an extruder, and extruding the mixture through high-temperature hot-melt molding at a temperature of 220°C.

[0043] The stiffening ribs 4 are formed by compression molding and then spirally wound around the outer cladding 3, and the two are tightly connected by welding.

[0044] Creep tests were conducted on the BFRP strips used in Example 1. The test method followed the American standard ACI 440.3R, with creep tests conducted at two stress levels (30% FU and 50% FU) and a holding time of 1000 hours. Furthermore, for comparative purposes, a control group of GFRP strips (glass fiber reinforced thermoplastic strips) was added at the same stress level and holding time. The measured tensile strength of the GFRP strips was 618 MPa.

[0045] Creep performance test results show that after 1000 hours, the BFRP strips remained intact at a stress level of 50%, while the GFRP strips fractured at a stress level of 30% fu. Based on the analysis of the experimental data presented in this study and a prediction model developed by domestic and international scholars, the 200-year creep rupture stress of the BFRP strips is predicted to be 54% fu. This indicates that BFRP strips have excellent creep performance (>50% fu), which can improve the physical, chemical and mechanical properties of pipelines.

[0046] The pipe prepared in Example 1 was subjected to a ring stiffness mechanical property test. The test loading was based on GB / T9647 "Determination of Ring Stiffness of Thermoplastic Plastic Pipes", with a 3% deformation in the vertical direction of the pipe inner diameter. The pipe diameter was 6m. The measured ring stiffness was 5.3kN / m. 2 Compared with the ring stiffness of ordinary polyethylene pipe (1.1kN / m 2 ) compared to the embodiment, the stiffness is increased by 380%.

[0047] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. According to the technical essence of the present invention, any simple modification, equivalent changes and modifications made to the above embodiment should be included in the scope of protection of the present invention.

Claims

1. A BFRP strip reinforced thermoplastic pipe, characterized in that: The thermoplastic pipe comprises, from the inside to the outside, an inner lining layer (1), a reinforcement layer (2), an outer cladding layer (3) and stiffening ribs (4) in sequence; the reinforcement layer (2) is in the form of a strip and is wound around the surface of the inner lining layer (1); the stiffening ribs (4) are spaced apart and distributed on the surface of the outer cladding layer (3); the inner lining layer (1) and the outer cladding layer (3) are both made of short-cut fiber reinforced high-density polyethylene materials; the reinforcement layer (2) is a basalt fiber composite material; The short fiber reinforced high-density polyethylene material is mainly made of dipped basalt fiber bundles and polyethylene. The fibers in the dipped basalt fiber bundles are high-modulus basalt fibers with random fiber distribution. The fiber strength must be no less than 3500 MPa and the elastic modulus must be no less than 90 GPa. The volume fraction of basalt fibers in the entire fiber bundle is 50-60%. The dipped basalt fiber bundles have a fiber bundle length of 3-6 mm, a diameter of 2-4 mm, and a circular or quasi-circular cross-section. The basalt fiber composite material is mainly made of basalt fiber, thermoplastic resin and curing agent; the basalt fiber angle is 0°, the tensile strength must be not less than 3500MPa, the elastic modulus must be not less than 85GPa, the creep rupture stress must be not less than 50%fu, and the volume fraction of the basalt fiber in the entire reinforcement layer (2) strip is 60-65%; The cross section of the stiffening rib (4) is box-shaped and filled with a pressure-resistant material; the cross section of the stiffening rib (4) is short-cut fiber reinforced high-density polyethylene material, which is made of basalt fiber and high-density polyethylene, and the volume fraction of the basalt fiber in the box section is 35-50%; the pressure-resistant material is a mixture of quartz sand and waste plastic, the quartz sand accounts for 40-60% of the volume fraction of the mixture, and the waste plastic accounts for 40-60% of the volume fraction of the mixture; the height-to-width ratio of the box section of the stiffening rib (4) is 1.5-2, the height-to-width ratio of the box cavity is 1.5-2, and the ratio of the box cavity width to the rib width is 0.5-0.

75.

2. The BFRP strip reinforced thermoplastic pipe according to claim 1, characterized in that: The resin in the impregnated basalt fiber bundle is high-density polyethylene with a relative density of not less than 0.94g / cm 3 , the volume fraction of resin in the entire fiber bundle is 40-50%.

3. The BFRP strip reinforced thermoplastic pipe according to claim 1, characterized in that: The volume fraction of the impregnated basalt fiber bundles in the entire inner lining layer (1) is 30-40%; the volume fraction of the impregnated basalt fiber bundles in the entire outer cladding layer (3) is 30-40%.

4. The BFRP strip reinforced thermoplastic pipe according to claim 1, characterized in that: The thermoplastic resin is high-density polyethylene, the tensile strength must be no less than 30 MPa, the elastic modulus must be no less than 20 MPa, and the volume fraction of the resin in the entire reinforcement layer (2) strip is 35-40%; the curing agent is hexamethylenetetramine, and the volume fraction of the curing agent in the entire reinforcement layer (2) strip does not exceed 5%.

5. The BFRP strip reinforced thermoplastic pipe according to claim 1, characterized in that: The strip of the reinforcement layer (2) has a width of 600mm-1000mm and a thickness of 0.25-0.35mm. The strip is spirally wound in forward and reverse directions along the pipeline, with a forward and reverse winding angle of 60-90° and an overlap length of 5-10% of the strip width.

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