Preparation method of prestressed fiber reinforced wood-bamboo-based ship pressure pipeline

Abstract

The invention discloses a preparation method of a prestressed fiber reinforced wood-bamboo-based ship pressure pipeline, and relates to the technical field of ship engineering and composite material manufacturing. According to the method, firstly, wood-bamboo plates are machined into arc-shaped unit strips with mortise and tenon joint structures; preparing a corrosion-resistant anti-seepage lining layer on the core mold; then, the arc-shaped unit strips are spliced and buckled outside the lining layer in the annular direction to form a structural middle layer, and a pipe blank is formed through annular pressurizing and curing; after the surface of the pipe blank is treated, high-modulus continuous fibers are wound by adopting a variable tension and variable angle process to form a prestress reinforced outer layer; and finally, secondary curing, demolding and outer protection layer manufacturing and forming are carried out. Through the rigid-flexible structural design and the gradient tension winding process, the defects that a traditional biomass pipeline is poor in fire resistance, low in bearing pressure and prone to cracking are overcome, and the high-modulus biomass pipeline has excellent corrosion resistance, high specific strength and high modulus.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ship engineering and composite material manufacturing, and particularly relates to a preparation method of a four-layer structure ship pressure pipeline with fire resistance, seawater corrosion resistance, high specific strength, and using reconstituted wood, reconstituted bamboo or bamboo integrated material as a structural core layer and applying prestress through fiber winding. The present application is particularly suitable for the construction of grade III pressure pipelines of ship ballast systems, seawater systems, cooling water systems and bilge water systems, and aims to replace traditional metal pipelines, glass steel pipelines and ordinary plastic pipelines. BACKGROUND

[0002] With the increasing requirements of global shipping industry for energy saving and emission reduction, lightweight has become an important trend in ship design. Biomass composites with the concept of "bamboo instead of plastic" have gradually attracted the attention of the shipbuilding industry due to their renewable, low carbon emission and high specific strength characteristics. Ship pipeline system is known as the "blood vessels" of the ship, which is in a harsh marine environment of high salt mist and high humidity for a long time, and needs to withstand complex ship deformation stress and fluid pulsating pressure. At present, ship pressure pipelines mainly use the following two types of materials: (1) Metal pipelines (such as carbon steel, stainless steel, copper-nickel alloy). Carbon steel pipes have poor corrosion resistance and are prone to rust in seawater environment, which requires frequent coating of corrosion protection layer and regular replacement; although stainless steel and copper-nickel alloy pipes have excellent corrosion resistance, their density is high (7.8-8.9 g / cm 3 ), which significantly increases the self-weight of the ship, and the cost of raw materials is high.

[0003] (2) Non-metal pipelines, the typical representative of which is glass steel pipeline, which is a kind of fiber reinforced resin composite material and has the advantage of corrosion resistance, but the elastic modulus of ordinary glass steel pipeline is low (usually only 1 / 20 of that of steel), which is insufficient in rigidity when laid in long span, and is prone to excessive deflection. If high modulus carbon fiber is used, the cost will be extremely high. In addition, the density of glass steel is 1.8-2.3 g / cm 3 , which is also significantly higher than that of wood and bamboo, and the unit weight cost is high, and it is difficult to recycle after the end of service life.

[0004] In recent years, biomass materials represented by wood and bamboo have attracted attention due to their high specific strength and low carbon environmental properties. In the prior art, there has appeared a "bamboo winding composite pipe" (such as CN201434160Y), which is mainly composed of bamboo fillet curtain layers and resin adhesive spiral winding. It has been applied in land use fields such as municipal water supply and drainage, farmland irrigation, etc. However, the direct application of existing bamboo winding pipes in ship engineering faces insurmountable technical and regulatory barriers: (1) Insufficient fire resistance. The International Maritime Organization (IMO) Resolution A.753(18) and its amendments clearly stipulate that non-metallic pipes installed in high-risk areas such as engine rooms and pump rooms must meet the fire resistance requirements of L3 level (wet fire resistance for 30 minutes) or even L1 / L2 level (dry fire resistance). Ordinary bamboo and unsaturated polyester resin are extremely easy to burn, char and lose strength in a fire, and will release a large amount of dense smoke, which cannot pass the low flame spread, smoke and toxicity tests specified by the IMO FTP Code.

[0005] (2) Insufficient pressure bearing capacity. Ship piping systems need to withstand working pressures of up to 1.6 MPa or even higher, as well as dynamic stresses generated by the swaying of the hull. Existing bamboo spiral wound pipes mostly use low-tension winding, which makes it difficult to achieve high-density mechanical seals, resulting in insufficient compactness and low ring stiffness. In addition, bamboo is a typical unidirectional reinforcing material, with a tensile strength parallel to the grain that can reach over 200 MPa, but a tensile strength across the grain that is only 5%-10% of that parallel. Traditional bamboo spiral wound pipes are prone to longitudinal cracking along the direction of bamboo fibers when subjected to high pressure, resulting in numerous pores, making them unsuitable for ship pressure piping systems.

[0006] (3) Insufficient axial strength and uniformity. Existing bamboo-wound pipes are made by continuously winding bamboo strips in the circumferential direction, with discontinuous bamboo strips used for reinforcement in the axial direction. The reinforcement effect is limited, and the axial tensile strength is generally less than 50 MPa. In addition, due to the large bending radius of the bamboo strips, there are problems of uneven distribution of bamboo strips and resin in both the axial and circumferential directions, resulting in large performance variability.

[0007] In summary, there is an urgent need to develop a new method for preparing ship pressure pipelines that can leverage the advantages of biomass materials—low cost, low density, and high specific strength—while overcoming their shortcomings in fire resistance, pressure resistance, strength, and uniformity through structural design, in order to meet the special requirements of ship piping systems. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a prestressed fiber-reinforced wood-bamboo based marine pressure pipeline, so as to solve the technical problems of existing biomass pipelines such as poor fire resistance, low pressure bearing capacity, insufficient axial stiffness, as well as the low modulus of traditional fiberglass pipelines and the heavy weight and poor corrosion resistance of metal pipelines.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a prestressed fiber-reinforced wood-bamboo based marine pressure pipeline includes the following steps: 1) Processing of curved unit strips: The reconstituted wood, reconstituted bamboo or bamboo engineered wood boards are dried at 103℃ to a moisture content of ≤6%, processed into curved unit strips, and tenons and mortises are processed on the sides of the curved unit strips (interface agent can be sprayed or brushed on the surface and allowed to dry). The curved unit strips are then sealed and packaged. 2) Core mold preparation: Select a rigid cylindrical core mold as the molding mold, and evenly coat its surface with a release agent or cover it with a release film; 3) Inner lining layer laying: The reinforcing fiber material is laid in a spiral winding manner on a cylindrical core mold and impregnated with the first resin to prepare the corrosion-resistant and seepage-proof inner lining layer, and the corrosion-resistant and seepage-proof inner lining layer is kept in an ungelled and cured state. 4) Structural intermediate layer assembly: Apply the first resin to the surface of the tenon and the mortise of the arc-shaped unit strip, and assemble several arc-shaped unit strips in the circumferential direction using a tenon and mortise connection method to form multiple (e.g., 2 to 4) combined arc-shaped structural panels. Then, snap each combined arc-shaped structural panel together and fasten it to the outside of the uncured corrosion-resistant and seepage-proof inner lining layer to form the cylindrical structural intermediate layer. 5) Circumferential pressure curing: The intermediate layer of the structure covering the corrosion-resistant and seepage-proof inner lining is circumferentially pressure-cured using a fastening and pressure device, so that the excess first resin is squeezed out and the air is discharged. After curing, an integral tube blank is formed. 6) Surface treatment: Remove the fastening and pressurizing device, grind the outer surface of the integral tube blank to remove resin nodules and burrs, and expose the substrate surface of the reconstituted wood, reconstituted bamboo or bamboo laminated material. 7) Prestressed winding: On the outer surface of the integral tube blank, the high-modulus continuous fiber impregnated with a second resin (vinyl ester resin, unsaturated polyester or epoxy resin) is wound using a high-tension fiber winding process to form the prestressed reinforced outer layer. 8) Secondary curing and shaping: The integral tube blank and the wound prestressed reinforced outer layer are kept in rotation for curing. After complete curing, shaping and correction are performed. 9) Demolding: Using a special demolding machine, slowly eject the shaped pipe product from the mandrel along the axial direction from the end with the larger inner diameter; let the demolded pipe stand at room temperature to allow the resin to fully cure and eliminate internal stress. 10) Outer protective layer production: Apply weather-resistant gel coat or fire-retardant coating to form an outer protective layer. After the outer protective layer is cured, the final product can be formed.

[0010] Further, in step 1), the density of the reconstituted wood, reconstituted bamboo, or bamboo engineered wood panel is ≥0.8 g / cm³. 3The plate has a longitudinal bending strength ≥80MPa and an elastic modulus ≥10GPa, and a flame retardant rating of B1. If the plate length is insufficient, finger jointing is used for extension. The finger joints are bonded using one of the following: phenol-resorcinol-formaldehyde adhesive, structural phenol-resorcinol adhesive, or structural polyurethane adhesive. The finger joints are spaced apart along the length of the assembled pipe wall. In the circumferential direction, for two adjacent arc-shaped unit strips, their opposite sides are respectively provided with tenons and mortises that mate with the tenons. The cross-sectional shape of the mortise is selected from one of a semi-circular, trapezoidal, or wedge-shaped groove. When processing the mortise and tenon structure, the width of the tenon is 0.1–0.3 mm larger than the width of the mortise, and the depth of the mortise is 0.1–0.3 mm larger than the depth of the tenon. The tenon and mortise are interference-fitted.

[0011] Further, in step 3), the reinforcing fiber material is selected from glass fiber surface mat, glass fiber mesh, or chopped strand mat; the first resin is selected from unsaturated polyester resin, vinyl ester resin, or epoxy resin; the resin content of the corrosion-resistant and seepage-proof lining layer is 50% to 80%, and the thickness is 0.5 to 4 mm; the outer diameter of the uncured corrosion-resistant and seepage-proof lining layer is 0.1 to 0.5 mm larger than the inner diameter of the structural intermediate layer.

[0012] Furthermore, in step 4), pneumatic nails or staples are used for auxiliary fixing when assembling the combined arc-shaped structural plates to prevent the arc-shaped unit strips from spreading out. The spacing between the pneumatic nails or staples is preferably 600-1200mm along the length of the arc-shaped unit strips.

[0013] Further, in step 5), a segmented adjustable annular fastening and pressurizing device (mechanical hose clamp device or flexible pressurizing belt) is used to pressurize the assembled structural intermediate layer. The fastening and pressurizing device is preferably arranged at axial intervals of 100-600mm. During pressurization, the device is tightened evenly from the middle of the pipe section to both ends, gradually pressing the structural intermediate layer radially onto the cylindrical mandrel until the circumferential pressure of the fastening and pressurizing device reaches 0.5-1.5MPa. The curing method is selected from room temperature static curing, oven heating curing, infrared lamp heating curing, or a combination of the above curing methods.

[0014] Further, in step 6), the glue nodules, protrusions and burrs on the outer surface of the structural intermediate layer 2 are removed by mechanical grinding until the fresh substrate surface of reconstituted wood, reconstituted bamboo or bamboo laminated wood is exposed. The pits on the surface of the structural intermediate layer can be repaired with the first resin or the second resin, and an interface agent can be sprayed or brushed on the substrate surface.

[0015] Further, in step 7), the high-modulus continuous fiber is selected from continuous high-modulus glass fiber, basalt fiber, or carbon fiber, with a tensile strength greater than 2 GPa, a tensile modulus greater than 80 GPa, and a winding tension of 1% to 50% of the fiber breaking strength or 0.03 to 0.3 N / tex. A gradient tension control scheme decreasing from the inside out is adopted, with the high-modulus continuous fiber close to the intermediate layer of the structure using the highest tension and the high-modulus continuous fiber further away from the intermediate layer using a low tension, so that the intermediate layer of the structure is in a compressed state when not subjected to external pressure. The high-modulus continuous fiber is spirally wound at a winding angle of 55° to 89°, using a larger angle (85~89°) when close to the surface of the intermediate layer and a smaller angle (55~65°) when further away from the surface of the intermediate layer.

[0016] Furthermore, the secondary curing is carried out while the pipe is kept rotating to prevent the second resin from flowing and agglomerating due to gravity; after demolding, the pipe is left to stand at room temperature for 36 to 48 hours for post-curing to eliminate internal stress.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention utilizes the high flexural modulus of reconstituted wood, reconstituted bamboo, and bamboo laminated timber (15-25 GPa) as the structural intermediate layer, significantly improving the axial stiffness and bending resistance of the pipeline. Compared to ordinary fiberglass pipes, this reduces the number of support components required for ship pipelines. Simultaneously, high-tension winding of the prestressed outer layer introduces radial prestress into the structural intermediate layer. On one hand, this offsets the expansion stress that may arise from moisture absorption in the wood and bamboo materials; on the other hand, during pipeline pressure operation, it partially offsets the circumferential tensile stress caused by fluid pressure, effectively overcoming the weakness of low transverse tensile strength in wood and bamboo materials and significantly improving burst pressure. Testing shows that the burst pressure of the pipeline of this invention can be increased to over 8 MPa, significantly superior to existing non-metallic composite pipelines of the same size and specifications.

[0018] (2) The present invention adopts a circumferential interlocking structure of "mortise and tenon interference fit + adhesive bonding" combined with radial compression prestress applied by the external "prestressed fiber winding layer". This dual constraint mechanism not only achieves the tightness of the joint through mechanical interlocking and chemical adhesive bonding, but also uses the fastening force of the fiber layer to offset the circumferential and radial tension generated by the internal pressure of the pipe, effectively preventing joint cracking and leakage caused by moisture absorption and expansion or stress (especially circumferential and radial internal pressure) deformation of reconstituted wood, reconstituted bamboo or bamboo composite material, so that the pipe can withstand higher working internal pressure.

[0019] (3) The present invention uses reconstituted wood, reconstituted bamboo, or bamboo laminated timber as the structural intermediate layer, with a density ≥0.8g / cm³. 3Compared to natural wood and bamboo, reconstituted wood has a dense structure, very few pores (no macropores, very few micropores), no defects, and good uniformity. This allows for a dense middle layer in the pipe structure, providing inherent impermeability. Combined with a waterproof inner lining and prestressed fiber winding layer, which offer high hydrophobicity and airtightness, the pipe can operate under working pressures exceeding 1.6 MPa for extended periods. The density of reconstituted wood, reconstituted bamboo, or bamboo-laminated lumber is approximately 1 / 6 that of steel and 1 / 2 that of fiberglass. This high specific strength gives the pipes advantages such as light weight, easy installation, and good fatigue resistance.

[0020] (4) The arc-shaped unit of the intermediate layer of the structure of the present invention adopts a tenon-mortise interference fit in the circumferential direction. The width of the tenon is 0.1 to 0.3 mm greater than the width of the mortise. Since the width of the mortise is smaller than that of the tenon, the mortise applies a circumferential pressure to the tenon during assembly, causing the mortise and tenon to glue together under pressure, resulting in higher bonding strength and forming a mechanical interlocking effect. The depth of the mortise is 0.1 to 0.3 mm greater than that of the tenon, so that the tenon can be fully inserted into the mortise. The tiny gaps between the tenon and the mortise are sealed by filling with a first resin adhesive, which provides excellent sealing while ensuring bonding strength.

[0021] (5) The outer diameter of the uncured inner lining layer of this invention is 0.1~0.5 mm larger than the inner diameter of the structural intermediate layer. When the structural intermediate layer is pressurized by the fastening device, it will transmit the pressure to the inner lining layer, causing the resin in the inner lining layer to flow and expel air bubbles. The air bubbles and excess resin will be discharged through the tenon joint of the arc-shaped unit. As the structural intermediate layer is further tightened, the flowing resin will densely fill the gap between the inner lining layer and the tenon joint, further enhancing the tightness and sealing of the pipe and avoiding residual air bubbles and pores. In addition, because the excess first resin will seep out through the tenon groove, the bonding of the tenon groove also uses the first resin.

[0022] (6) The prestressed fiber winding layer of the present invention uses high-modulus continuous fibers (tensile strength ≥2GPa, tensile modulus ≥80GPa) for prestressed winding. When close to the surface of the intermediate layer of the structure, a large angle of 85~89° and high tension are used for winding, thereby forming a high-strength and high-modulus "hoop" to tighten the intermediate layer of the structure, giving the pipeline high ring stiffness (≥5kN / m²) and burst internal pressure (≥6.4MPa), making the pipeline suitable for Class III pressure pipeline application scenarios in ships. When far from the surface of the intermediate layer of the structure, a small angle of 55~65° and low tension are used for winding. According to the theory of composite material mechanics, small-angle winding can simultaneously reinforce the pipeline in both axial and circumferential directions, further improving the axial stiffness of the pipeline, making the pipeline suitable for large-span ship applications. In addition, the use of low tension for winding on the outer surface of the pipeline can increase the resin content of the surface layer and make the surface smooth.

[0023] (7) This invention employs a dual-sealing structure combining chemical adhesives and mechanical bonding. First, the corrosion-resistant and seepage-proof inner lining layer itself is dense, providing the first line of defense against leakage. Second, the tenon and mortise joints between the arc-shaped unit strips in the intermediate layer of the structure form a mechanical locking and adhesive seal under the action of the adhesive, eliminating any microscopic leakage channels that may exist between the pipe wall layers. The selected resin system has excellent resistance to seawater and chemical media corrosion, ensuring that the pipeline is not corroded or damaged during long-term use in a marine environment.

[0024] (8) High fire resistance is achieved through material flame retardancy and structural design. The intermediate layer of reconstituted wood, reconstituted bamboo or bamboo laminated lumber is treated with flame retardant, and the prestressed reinforced outer layer and outer protective layer can be rapidly carbonized and foamed in a fire to form a solid "heat shield" protective layer, effectively blocking the transfer of heat to the inner layer. As verified by simulated fire test, under the condition of water medium (wet type), the pipeline of the present invention can still maintain internal pressure without leakage after being scorched by a flame at 1000°C for 30 minutes, meeting the L3 fire resistance standard requirements specified in IMO Resolution A.753(18).

[0025] (9) The density of the finished pipe is approximately 1.0–1.3 g / cm³. 3 It weighs only about 1 / 6 of conventional steel pipes and about 1 / 2 of ordinary fiberglass pipes, significantly reducing the empty weight of ships and helping to increase carrying capacity or reduce fuel consumption. In addition, the extensive use of renewable wood and bamboo biomass materials is a carbon storage material with low cost and low energy consumption in the manufacturing process, which is in line with the trend of green shipbuilding.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, embodiments of the present invention are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart illustrating the preparation method of a prestressed fiber-reinforced wood-bamboo based marine pressure pipeline according to the present invention. Figure 2 A schematic diagram of the DN150 ship ballast water pipe structure prepared according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the assembly and insertion of the intermediate layer of the structure in an embodiment of the present invention; Figure 4 This is an axial schematic diagram of the arc-shaped unit strip in an embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0030] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, this invention provides a method for preparing prestressed fiber-reinforced wood-bamboo based marine pressure pipes, comprising the following steps: S1. Processing of curved unit strips: Use prefabricated reconstituted wood, reconstituted bamboo, or bamboo engineered wood panels with a density of 0.8–1.3 g / cm³. 3 The sheet material has a longitudinal bending strength ≥80MPa, a bending modulus ≥10GPa, and a flame retardant rating of B1 (flame-retardant). It is dried at approximately 103℃ until the moisture content is ≤6%. The sheet material is processed into arc-shaped unit strips 21 with a width of 40–100mm and a thickness of 5–40mm. If the pipe length is greater than the sheet material length, finger-jointing is used. The finger joints are bonded using one of the following: phenol-resorcinol-formaldehyde adhesive, structural phenol-resorcinol adhesive, or structural polyurethane adhesive. The finger joints are ensured to be spaced apart along the length of the assembled pipe wall. After planing on all four sides, tenons 211 and mortises 212 are formed on the inner and outer curved surfaces and on both sides. The cross-sectional shape of the mortises is selected from one of the following: semi-circular, trapezoidal, or wedge-shaped. The width of the tenon is 0.1 to 0.3 mm larger than the width of the mortises, and the depth of the mortises is 0.1 to 0.3 mm larger than the depth of the tenons. The tenons and mortises are fitted with an interference fit. After processing, an interface agent (such as a polyurethane interface agent) can be sprayed or brushed onto the surface and allowed to dry. Then, the curved unit strip 21 is sealed (e.g., wrapped in plastic wrap) to prevent moisture absorption, deformation, or cracking.

[0031] S2, Core mold preparation Choose a rigid cylindrical mandrel as the molding die. Apply a release agent evenly to the surface of the mandrel, or cover it with a 0.1–0.15 mm thick release film (such as a polytetrafluoroethylene (PTFE) film). To facilitate demolding, the diameter of one end of the mandrel should be slightly smaller than the other end (0.5–1 mm smaller) to reduce friction between the product and the mold.

[0032] S3. Inner lining layer laying: A corrosion-resistant and seepage-proof inner liner 1 is prepared on the treated mandrel. Reinforcing fiber material (such as fiberglass surface mat, fiberglass mesh, or chopped strand mat) is spirally wound onto the mandrel and fully impregnated with a first resin (such as unsaturated polyester, vinyl ester resin, or epoxy resin) to prepare the corrosion-resistant and seepage-proof inner liner 1. The outer diameter of the uncured inner liner is 0.1–0.5 mm larger than the inner diameter of the structural intermediate layer, so that the structural intermediate layer can apply sufficient pressure to the inner liner to remove air bubbles and excess resin. Note that the corrosion-resistant and seepage-proof inner liner 1 must be kept in an ungelled and uncured state at this stage. The resin content of the corrosion-resistant and seepage-proof inner liner is 50%–80%, and the thickness is 0.5–4 mm.

[0033] S4. Assembly of intermediate structural layers: The same first resin as the inner lining layer is evenly applied to the surface of the tenon 211 and mortise 212 of the arc-shaped unit strip 21, and the mortise 212 is filled with resin to avoid insufficient glue. Several arc-shaped unit strips 21 are assembled circumferentially using mortise and tenon joints to form 2-4 combined arc-shaped structural plates (pneumatic nails or fasteners are used for auxiliary fixation when assembling the combined arc-shaped structural plates to prevent the arc-shaped unit strips from falling apart; the spacing of the pneumatic nails or fasteners along the length of the arc-shaped unit strips is preferably 600-1200mm). Then, the 2-4 combined arc-shaped structural plates are closed and fastened to the outside of the uncured corrosion-resistant and seepage-proof inner lining layer 1, with the mortise and tenon joints precisely aligned to form a complete cylindrical intermediate layer 2. This intermediate layer serves as the axial load-bearing skeleton of the pipeline and has a thickness of 5-40mm.

[0034] S5, Circumferential pressure curing: A segmented, adjustable annular fastening and pressurizing device (such as a stainless steel hose clamp) is used to circumferentially pressurize and tighten the structural intermediate layer 2 covering the corrosion-resistant and seepage-proof inner lining layer 1. The clamps are preferably spaced 100–600 mm apart axially, tightening evenly from the middle of the pipe section towards both ends until the circumferential pressure of the fastening and pressurizing device reaches 0.5–1.5 MPa. This process squeezes out excess first resin from the interface, expels air, and ensures a tight fit between each arc-shaped unit strip 21 and the corrosion-resistant and seepage-proof inner lining layer 1, as well as between the arc-shaped unit strips 21 themselves. Maintaining the clamped state, the curing method is selected according to the first resin system used: it can be cured at room temperature for a certain time, or the pipe blank can be moved into a curing oven and heated according to a staged temperature curve, or an infrared lamp can be used to heat and cure the outer surface of the structural intermediate layer 2, or a combination of the above curing methods can be used. During the curing process, the resin volume shrinkage further increases the clamping force between units and between units and the inner lining layer, thereby solidifying the corrosion-resistant and seepage-proof inner lining layer 1 and the structural intermediate layer 2 into a whole.

[0035] S6. Surface treatment: After removing the fastening and pressurizing device, the solidified "corrosion-resistant and seepage-proof inner lining layer - structural intermediate layer" integral tube blank is obtained. The outer surface of the tube blank is then ground (e.g., with a sander) to remove residual resin nodules and burrs, exposing the fresh surface of the reconstituted wood, reconstituted bamboo, or bamboo engineered wood substrate. Pits on the surface of the structural intermediate layer can be repaired using the first or second resin. An interface agent can be sprayed or brushed onto the surface and allowed to dry (this operation is generally performed when the interfacial bonding performance between the structural intermediate layer and the second resin is poor) to improve the interfacial bonding strength of subsequent winding layers.

[0036] S7, Prestressed winding: High-tension fibers are wound with varying tension and angle on the outer surface of the integral tube blank. Specifically, continuous high-modulus glass fibers, basalt fibers, or carbon fibers with a tensile strength greater than 2 GPa and a tensile modulus greater than 80 GPa are selected. After impregnation with a second resin (vinyl ester resin, unsaturated polyester, or epoxy resin), the fibers are wound in multiple axes using a fiber winding machine at a set tension and winding angle. The winding tension is 1% to 50% of the fiber breaking strength or 0.03 to 0.3 N / tex. A gradient tension control scheme that decreases from the inside out is adopted. The high-modulus continuous fibers close to the middle layer of the structure are subjected to the highest tension, while the high-modulus continuous fibers further away from the middle layer are subjected to a low tension, so that the middle layer of the structure is in a compressed state when not subjected to external pressure. The high-modulus continuous fibers are spirally interlaced with a winding angle of 55° to 89°, with a larger winding angle (85~89°) near the surface of the middle layer and a smaller winding angle (55~65°) further away from the surface of the middle layer. This ensures that sufficient radial compressive prestress is applied to the intermediate layer 2 of the structure, while maintaining a smooth and dense outer layer surface. The resin content of the prestress-reinforced outer layer 3 formed by winding is preferably 30% to 40%, and the thickness is preferably 1 to 5 mm.

[0037] S8. Secondary curing and shaping: A second curing process is performed while the pipe blank is kept rotating, allowing the prestressed reinforced outer layer 3 to solidify and bond firmly with the internal structural intermediate layer 2. The pipe body is continuously rotated before the resin initially sets to prevent the second resin from flowing and agglomerating, ensuring uniform resin content throughout the pipe wall. After curing, the three layers of the pipe – the corrosion-resistant and seepage-proof inner lining, the structural intermediate layer, and the prestressed reinforced outer layer – form a tightly bonded whole, i.e., the pipe blank after secondary curing. A roundness shaping machine is used to shape and correct the pipe blank, ensuring that the roundness and surface flatness of the pipe's outer circumference meet the requirements.

[0038] S9, Demolding: Using a specialized demolding machine, the shaped pipe product is slowly ejected axially from the larger inner diameter end of the mandrel. The demolded pipe is then left to stand at room temperature for 36–48 hours to allow the resin to fully cure and eliminate internal stress.

[0039] S10. Outer protective layer fabrication: A weather-resistant gel coat or fire-retardant coating is applied to form an outer protective layer 4. After the outer protective layer 4 cures, the final product is formed. Depending on the application requirements, a weather-resistant gel coat layer containing UV absorbers, anti-aging agents, and flame retardants can be applied, or an intumescent marine fire-retardant coating can be applied. This outer protective layer further improves the pipe's weather resistance and UV aging resistance, and enables the pipe to meet the L3 or even higher fire resistance requirements specified in IMO Resolution A.753(18), with a thickness of 0.5~5mm.

[0040] This invention provides six embodiments, each illustrating the preparation of prestressed fiber-reinforced wood-bamboo based marine pressure pipes: a DN150 reconstituted wood marine ballast water pipe, a DN150 bamboo-laminated marine ballast water pipe, a DN300 reconstituted wood marine seawater cooling pipe, a DN300 reconstituted bamboo marine bilge water pipe, a DN600 reconstituted wood marine ventilation pipe, and a DN600 reconstituted bamboo marine water supply pipe.

[0041] Example 1 This embodiment uses the above 10 preparation steps to prepare DN150 reconstituted wood ship ballast water pipe, and: The first and second resins selected are both vinyl ester resins.

[0042] In step S1, a density of 1.0 g / cm³ is selected. 3 Reconstituted wood panels (with a bending strength parallel to the grain of 170 MPa and a modulus of elasticity parallel to the grain of 20 GPa) were used as the structural intermediate layer 2 material and dried at 103℃ to a moisture content of 5%. Ten arc-shaped unit strips 21, each 3000 mm long, were processed to obtain the following: the inner arc of each arc-shaped unit strip 21 corresponds to the inner diameter of the pipe, which is 154 mm, and the thickness is 10 mm. Trapezoidal mortises, each 4 mm wide and deep, were machined on the sides, with the tenon width 0.1 mm larger than the mortise opening and the tenon depth 0.1 mm smaller than the mortise opening. A polyurethane surface agent was sprayed onto the surface of the arc-shaped units and allowed to dry.

[0043] In step S2, a release agent is first applied to a stainless steel core mold with a diameter of 150 mm, and then a 0.1 mm thick self-adhesive PTFE release film is wrapped and laid.

[0044] In step S3, a 2.2 mm thick corrosion-resistant and seepage-proof inner lining layer 1 is formed by spirally winding a glass fiber surface felt with a unit area of ​​50 g and impregnated with flame-retardant vinyl ester resin onto the core mold, at which point the resin has not gelled and cured.

[0045] In step S4, vinyl ester resin adhesive is applied to the interface of the arc-shaped unit strip 21. First, five pieces are assembled into a semi-cylinder and fixed with staples (staple spacing 600mm). Then, two semi-cylinders are fastened to the uncured inner lining layer.

[0046] In step S5, a steel hose clamp is fitted every 200mm along the axial direction and tightened to a clamping pressure of 1.5MPa. Curing is then carried out at room temperature for 6 hours.

[0047] In step S7, 2400tex high-modulus E-grade glass fiber roving is selected as the high-modulus continuous fiber (tensile strength of 2190MPa, tensile modulus of 82GPa), and impregnated with flame-retardant vinyl ester resin. Four layers are interleaved at an 89° circumferential angle, followed by layers interleaved at a 55° angle. Gradient tension winding is implemented, with the tension of the first four layers at 960N, decreasing sequentially to 480N and 360N, and the outermost two layers at 120N.

[0048] In step S8, the mixture is rotated and cured at room temperature for 6 hours, then moved to a curing station and heated to 110°C for 2 hours for curing.

[0049] In step S9, the product is left at room temperature for 48 hours after demolding.

[0050] In step S10, 120g / ㎡ marine fire retardant coating is applied as the outer protective layer 4.

[0051] The final DN150 reconstituted wood ship ballast water pipe prepared in this embodiment has an inner diameter of 150mm, a corrosion-resistant and seepage-proof inner lining layer 1 with a thickness of 2mm, a structural intermediate layer 2 with a thickness of 10mm, and a prestressed reinforced outer layer 3 with a thickness of 4mm.

[0052] Example 2 This embodiment prepares a DN150 bamboo laminated timber ship ballast water pipe, which differs from Embodiment 1 in that: In step S1, the selected structural intermediate layer material is bamboo engineered wood panel with a density of 0.8 g / cm³. 3 The flexural strength parallel to the grain is 120MPa, and the elastic modulus parallel to the grain is 11GPa; the inner arc of the processed arc-shaped unit strip 21 corresponds to the inner diameter of the pipe of 150mm and the thickness of 10mm.

[0053] In step S3, the thickness of the prepared corrosion-resistant and seepage-proof inner lining 1 is 2 mm.

[0054] In step S7, four layers are interleaved at an 89° circumferential angle, followed by interleaved layers at a 55° angle. Gradient tension winding is performed, with a tension of 0.3 N / tex for layers 1-4, 0.15 N / tex for layers 5-6, and 0.03 N / tex for the remaining layers.

[0055] The final DN150 bamboo laminated marine ballast water pipe prepared in this embodiment has an inner diameter of 150mm, a corrosion-resistant and seepage-proof inner lining layer 1 with a thickness of 2mm, a structural intermediate layer 2 with a thickness of 10mm, and a prestressed reinforced outer layer 3 with a thickness of 4mm.

[0056] Example 3 This embodiment prepares a DN300 reconstituted wooden ship seawater cooling pipe, which differs from Embodiment 1 in that: In step S1, although the material is still reconstituted wood, the inner arc of the processed arc-shaped unit strip 21 corresponds to the inner diameter of the pipe of 304mm to adapt to the DN300 pipe size.

[0057] In step S2, a stainless steel core mold with a diameter of 300 mm is selected.

[0058] In steps S3, S4 and S7, the first resin and the second resin selected are both unsaturated polyester resins (isophthalic UPR).

[0059] In step S7, four layers are interleaved at an 89° circumferential angle, followed by interleaved layers at a 55° angle. Gradient tension winding is performed, with a tension of 0.3 N / tex for layers 1-4, 0.15 N / tex for layers 5-6, and 0.03 N / tex for the remaining layers.

[0060] The DN300 reconstituted wood ship seawater cooling pipe finally prepared in this embodiment has an inner diameter of 300mm, a corrosion-resistant and seepage-proof inner lining layer 1 with a thickness of 2mm, a structural intermediate layer 2 with a thickness of 10mm, and a prestressed reinforced outer layer 3 with a thickness of 4mm.

[0061] Example 4 This embodiment prepares DN300 reconstituted bamboo ship bilge water pipes, which differs from Embodiment 1 in that: In step S1, the selected structural intermediate layer material is reconstituted bamboo board with a density of 1.2 g / cm³. 3 The flexural strength parallel to the grain is 200MPa, and the elastic modulus parallel to the grain is 28GPa; the inner arc of the processed arc unit strip 21 corresponds to the inner diameter of the pipe of 304mm.

[0062] In step S2, a stainless steel core mold with a diameter of 300 mm is selected.

[0063] In step S7, the selected high-modulus continuous fiber is basalt fiber, which has a tensile strength of 2130 MPa and a tensile modulus of 90 GPa.

[0064] In step S7, four layers are interleaved at an 89° circumferential angle, followed by interleaved layers at a 55° angle. Gradient tension winding is performed, with a tension of 0.3 N / tex for layers 1-4, 0.15 N / tex for layers 5-6, and 0.03 N / tex for the remaining layers.

[0065] The DN300 reconstituted bamboo ship bilge water pipe finally prepared in this embodiment has an inner diameter of 300mm, a corrosion-resistant and seepage-proof inner lining layer 1 with a thickness of 2mm, a structural intermediate layer 2 with a thickness of 10mm, and a prestressed reinforced outer layer 3 with a thickness of 4mm.

[0066] Example 5 This embodiment prepares a DN600 reconstituted wooden ship ventilation pipe, which differs from Example 1 in that: In step S1, although the material is still reconstituted wood, the thickness of the processed arc-shaped unit strip 21 is increased to 12mm, and the inner arc corresponds to the inner diameter of the pipe of 606mm.

[0067] In step S2, a stainless steel core mold with a diameter of 600 mm is selected.

[0068] In steps S3, S4, and S7, both the first and second resins used are epoxy resins. The prepared corrosion-resistant and seepage-proof inner lining layer 1 has a thickness of 3 mm.

[0069] In step S5, the curing method is adjusted to: rotating and curing at 90°C in the curing station for 2 hours.

[0070] In step S7, the selected high-modulus continuous fiber is basalt fiber, with a tensile strength of 2130 MPa and a tensile modulus of 90 GPa. Four layers are interleaved at an 89° circumferential angle, followed by layers interleaved at a 55° angle. Gradient tension winding is implemented, with a tension of 0.3 N / tex for layers 1-4, 0.15 N / tex for layers 5-6, and 0.03 N / tex for the remaining layers.

[0071] In step S8, the curing method is adjusted to: rotary curing at 90°C for 2 hours in the curing station, followed by rotary curing at 110°C for 2 hours.

[0072] The final DN600 reconstituted wood ship ventilation pipe prepared in this embodiment has an inner diameter of 600mm, a corrosion-resistant and seepage-proof inner lining layer 1 with a thickness of 3mm, a structural intermediate layer 2 with a thickness of 12mm, and a prestressed reinforced outer layer 3 with a thickness of 4mm.

[0073] Example 6 This embodiment prepares a DN600 reconstituted bamboo ship water supply pipe, which differs from Embodiment 1 in that: In step S1, the selected structural intermediate layer material is reconstituted bamboo board with a density of 1.2 g / cm³.3 The flexural strength parallel to the grain is 200MPa, and the elastic modulus parallel to the grain is 28GPa; the thickness of the processed arc-shaped unit strip 21 is 12mm, and the inner arc corresponds to the inner diameter of the pipe of 606mm.

[0074] In step S2, a stainless steel core mold with a diameter of 600 mm is selected.

[0075] In steps S3, S4, and S7, both the first and second resins used are epoxy resins. The prepared corrosion-resistant and seepage-proof inner lining layer 1 has a thickness of approximately 3 mm.

[0076] In step S5, the curing method is adjusted to: rotating and curing at 90°C in the curing station for 2 hours.

[0077] In step S7, the selected high-modulus continuous fiber is carbon fiber (T300), with a tensile strength of 3530 MPa and a tensile modulus of 230 GPa. Four layers are interleaved at an 89° circumferential angle, followed by layers interleaved at a 55° angle. Gradient tension winding is implemented, with a tension of 0.3 N / tex for layers 1-4, 0.15 N / tex for layers 5-6, and 0.03 N / tex for the remaining layers.

[0078] In step S8, the secondary curing is adjusted as follows: rotary curing at 90°C for 2 hours in the curing station, followed by rotary curing at 110°C for 2 hours.

[0079] The DN600 reconstituted bamboo marine water supply pipe finally prepared in this embodiment has an inner diameter of 600mm, a corrosion-resistant and seepage-proof inner lining layer 1 with a thickness of 3mm, a structural intermediate layer 2 with a thickness of 12mm, and a prestressed reinforced outer layer 3 with a thickness of 4mm.

[0080] The prestressed fiber-reinforced wood-bamboo based marine pressure pipelines prepared in Examples 1-6 underwent a 30-minute fire resistance test (simulating a fire) in a water-filled state. The pipelines remained leak-free, meeting the IMO L3 fire resistance standard requirements. Table 1 shows the main mechanical properties of the prestressed fiber-reinforced wood-bamboo based marine pressure pipelines prepared in Examples 1-6, with the corresponding test environment temperature being 21℃. As can be seen from Table 1, compared with existing common Class III marine fiberglass pressure pipelines (which serve as a comparative example of the pipeline products prepared in Examples 1-6 of this invention), Examples 1-6 exhibit higher axial tensile strength, axial tensile modulus, axial bending strength, and burst pressure. The axial tensile strength and axial bending strength are approximately twice that of the comparative example, giving the pipelines of this invention better axial mechanical properties, enabling larger span arrangements and installations in ships. The burst pressure of Examples 1-6 is approximately 2-3 times that of the comparative example, indicating a higher working pressure and a wider range of applications. Furthermore, the density of the comparative example is approximately 2.1 g / cm³. 3In these examples 1-6, the density is 1.0-1.3 g / cm³. 3 Its density is about half that of the comparative version, making it lighter and more in line with the concept of lightweight ship design.

[0081] Table 1

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a prestressed fiber-reinforced wood-bamboo based marine pressure pipeline, characterized in that, Includes the following steps: 1) Processing of curved unit strips: The reconstituted wood, reconstituted bamboo or bamboo engineered wood boards are dried and then processed into curved unit strips. Tenons and mortises are processed on the side of the curved unit strips. The curved unit strips are then sealed and packaged. 2) Core mold preparation: Select a rigid cylindrical core mold as the molding mold, and evenly coat its surface with a release agent or cover it with a release film; 3) Inner lining layer laying: On the cylindrical core mold, the reinforcing fiber material is laid in a spiral winding manner and impregnated with the first resin to prepare a corrosion-resistant and seepage-proof inner lining layer, and the corrosion-resistant and seepage-proof inner lining layer is kept in an ungelled and cured state. 4) Assembly of the intermediate structural layer: Apply the first resin to the tenon and mortise surfaces of the arc-shaped unit strips, and assemble several arc-shaped unit strips in the circumferential direction using a tenon and mortise connection method to form multiple combined arc-shaped structural panels. Then, snap each combined arc-shaped structural panel together and fasten it to the outside of the uncured corrosion-resistant and seepage-proof inner lining layer to form a cylindrical intermediate structural layer. 5) Circumferential pressure curing: The intermediate layer of the structure covering the corrosion-resistant and seepage-proof inner lining is circumferentially pressure-cured using a fastening and pressure device, so that the excess first resin is squeezed out and the air is discharged. After curing, an integral tube blank is formed. 6) Surface treatment: Remove the fastening and pressurizing device, grind the outer surface of the integral tube blank to remove resin nodules and burrs, and expose the substrate surface of the reconstituted wood, reconstituted bamboo or bamboo laminated material. 7) Prestressed winding: On the outer surface of the integral tube blank, a fiber winding process with variable tension and variable angle is used to wind the high modulus continuous fibers impregnated with the second resin to form a prestressed reinforced outer layer. 8) Secondary curing and shaping: The integral tube blank and the wound prestressed reinforced outer layer are kept in rotation for curing. After complete curing, shaping and correction are performed. 9) Demolding: Use a special demolding machine to eject the shaped pipe product axially from the end with the larger inner diameter; let the demolded pipe stand at room temperature to allow the resin to fully cure and eliminate internal stress. 10) Outer protective layer production: Apply weather-resistant gel coat or fire-retardant coating to form an outer protective layer. After the outer protective layer is cured, the final product is formed.

2. The preparation method according to claim 1, characterized in that, In step 1), the drying is carried out at 103°C, and the reconstituted wood, reconstituted bamboo, or bamboo laminated board is dried to a moisture content of no more than 6%; the density of the reconstituted wood, reconstituted bamboo, or bamboo laminated board is ≥0.8 g / cm³. 3 The flexural strength parallel to the grain is ≥80MPa and the elastic modulus is ≥10GPa, and the flame retardant rating reaches B1.

3. The preparation method according to claim 1, characterized in that, In step 1), after the arc-shaped unit strip is processed, an interface agent is sprayed or brushed onto its surface and allowed to dry.

4. The preparation method according to claim 1, characterized in that, In step 1), if the length of the board is insufficient, a finger-jointing process is used to extend it. The finger joints are glued with one of the following: phenol-resorcinol-formaldehyde adhesive, structural phenol-resorcinol adhesive, or structural polyurethane adhesive, and the finger joints are ensured to be spaced apart in the length direction of the assembled pipe wall.

5. The preparation method according to claim 1, characterized in that, In step 1), in the circumferential direction, for two of the arc-shaped unit strips that need to be arranged adjacently, their opposite sides are respectively provided with the tenon and the mortise that mates with the tenon, and the cross-sectional shape of the mortise is selected from one of the following: semi-circular, trapezoidal or wedge-shaped groove.

6. The preparation method according to claim 5, characterized in that, The width of the tenon is 0.1 to 0.3 mm larger than the width of the mortise, and the depth of the mortise is 0.1 to 0.3 mm larger than the depth of the tenon. The tenon and the mortise are interference fit.

7. The preparation method according to claim 1, characterized in that, In step 3), the reinforcing fiber material is selected from glass fiber surface mat, glass fiber mesh, or chopped strand mat; the first resin is selected from unsaturated polyester resin, vinyl ester resin, or epoxy resin.

8. The preparation method according to claim 1, characterized in that, The corrosion-resistant and seepage-proof inner lining has a resin content of 50% to 80% and a thickness of 0.5 to 4 mm.

9. The preparation method according to claim 1, characterized in that, The outer diameter of the uncured corrosion-resistant and seepage-proof inner lining is 0.1 to 0.5 mm larger than the inner diameter of the intermediate layer of the structure.

10. The preparation method according to claim 1, characterized in that, In step 4), pneumatic nails or staples are used to assist in fixing the assembled arc-shaped structural panels to prevent the arc-shaped unit strips from falling apart. The spacing between the pneumatic nails or staples is 600-1200mm along the length of the arc-shaped unit strips.

11. The preparation method according to claim 1, characterized in that, In step 5), a segmented adjustable annular fastening and pressurizing device is used to pressurize the assembled structural intermediate layer. The fastening and pressurizing device is arranged at axial intervals of 100 to 600 mm. During pressurization, the device is tightened evenly from the middle of the pipe section to both ends, gradually pressing the structural intermediate layer radially onto the cylindrical mandrel until the circumferential pressure of the fastening and pressurizing device reaches 0.5 to 1.5 MPa.

12. The preparation method according to claim 1, characterized in that, In step 5), the curing method is selected from one or more combinations of room temperature static curing, oven heating curing, and infrared lamp heating curing.

13. The preparation method according to claim 1, characterized in that, In step 6), the glue nodules and burrs on the outer surface of the structural intermediate layer are removed by mechanical grinding until the fresh substrate surface of the reconstituted wood, reconstituted bamboo or bamboo laminated wood is exposed. If there are pits on the surface of the structural intermediate layer, the pits are repaired with the first resin or the second resin, and an interface agent is sprayed or brushed on the substrate surface.

14. The preparation method according to claim 1, characterized in that, In step 7), the second resin is selected from vinyl ester resin, unsaturated polyester resin or epoxy resin; the high modulus continuous fiber is selected from continuous high modulus glass fiber, basalt fiber or carbon fiber, with a tensile strength greater than 2 GPa and a tensile modulus greater than 80 GPa.

15. The preparation method according to claim 1, characterized in that, In step 7), the winding tension of the prestressed winding is 1% to 50% of the fiber breaking strength or 0.03 to 0.3 N / tex, and a gradient tension control scheme that decreases from the inside to the outside is adopted. The high modulus continuous fiber close to the middle layer of the structure is subjected to the highest tension, and the high modulus continuous fiber far from the middle layer of the structure is subjected to low tension, so that the middle layer of the structure is in a compressed state when not subjected to external pressure.

16. The preparation method according to claim 1 or 15, characterized in that, In step 7), the prestressed winding adopts a spiral staggered winding with a winding angle of 55° to 89°. When the winding is close to the surface of the intermediate layer of the structure, a large angle of 85° to 89° is used for winding, and a small angle of 55° to 65° is used for winding away from the surface of the intermediate layer of the structure.

17. The preparation method according to claim 1, characterized in that, In step 9), the demolded pipe is left to stand at room temperature for 36 to 48 hours for post-curing to eliminate internal stress.

18. The preparation method according to claim 1, characterized in that, In step 10), a weather-resistant gel coat layer containing ultraviolet absorbers, anti-aging agents, and flame retardants is applied, or an intumescent marine fire-retardant coating is brushed on to form an outer protective layer, the thickness of which is 0.5~5mm.

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