As a kind of green energy, wind power is one of the most potential renewable energy sources. With the development and maturity of wind power technology, the model has reached 16MW, with a blade length of 123 meters. Blade is one of the key components of wind turbine, with large size, complex shape, high precision requirements, high requirements for strength, stiffness, and surface smoothness.
Composite materials have many advantages in the manufacturing of wind turbine blades. The manufacturing process mainly includes hand-lay-up molding, molding, prepreg molding, pultrusion molding, fiber winding, resin transfer molding and vacuum infusion molding.
1, wind turbine blades - hand lay-up process
Hand gluing is a traditional process for producing composite wind turbine rotor blades. In the hand-lay-up process, the fiber substrate is laid in a single mold, and then the glass cloth and resin are applied with a roller or brush, and then demolded after curing at room temperature. The hand lay-up method can be used to manufacture large, complex shapes at low cost. Because it does not have to be affected by heat and pressure. Simple equipment and molds can be used, plus it is less expensive than other viable options.
The main disadvantage of the hand-laying process to produce fan blades is that the product quality of the worker's proficiency and environmental conditions depend on a greater degree of production efficiency and product quality uniformity fluctuations, the product's static and dynamic balance of the guarantee is poor, the higher rate of scrap. Especially for high-performance complex aerodynamic shape and sandwich structure blade, also need to bonding and other secondary processing, bonding process need to bonding platform or type frame to ensure that the bonding surface of the adhesion, the production process is more complex and difficult.
Problems that occur during the use of wind turbine blades manufactured by the hand-lay-up process are often due to cracks, breaks and blade deformation caused by uneven glue content, poor fiber/resin infiltration and incomplete curing during the process.
The hand lay-up process is often accompanied by the release of a large number of hazardous substances and solvents, which has certain environmental pollution problems. Hand-laying is a proven method of producing composite blades, but due to its low yield and discontinuity of parts, as well as the difficulty of realizing large-scale products with complex structure and high mechanical property requirements, it has prompted people to shift the focus of research to other production methods.
2, wind turbine blades - molding
Molding process will first be reinforced materials and resins placed in a double-flap mold, and then close the mold, heating and pressure, and then demolding, after curing. The advantages of this process include high fiber content and low porosity, as well as short production cycles, precise dimensional tolerances and good surface finishes.
However, compression molding is suitable for the production of simple composite products such as skis, and it is difficult to manufacture complex shapes including skins, cores and blades for beams. Although it is possible to improve the molding process equipment, it requires a large capital investment to improve the heated molds that can withstand the pressure of a 20 to 40 meter span.
Compression molding produces parts with high fiber content and high strength/mass ratios, but it is difficult to manufacture blades with complex geometries in a cost-effective manner.
3. Wind Turbine Blades - Prepreg Placement Processes
The prepreg method is named after the prepreg reinforcement material used. In this process, partially cured resin and reinforcement are laid in a single mold and heated to cure. In order to avoid resin-rich zones and to exclude air storage voids, it is necessary that the resin in the prepreg consists of a sufficient amount of overflow, and at present, commercially available prepregs generally require high curing temperatures (90 to 110%). The main advantage of using prepregs is that the fiber reinforcement is well aligned during the production process, thus allowing for the manufacture of low fiber defects as well as high performance parts. Carbon fiber prepregs are widely used in the aerospace industry because they can be used to manufacture components with complex structures.
The main drawback of choosing prepregs for the production of wind turbine blades is the high cost. This material is typically 5 to 10 times more expensive than common resins and reinforcements. In addition, since prepregs are laid by hand, they are also labor-intensive and have a low throughput compared to hand lay-up.
Prepreg is an ideal process for producing complex shaped structural parts. Prepreg is widely used in foreign countries, and its process and equipment have been developed to a mature stage. In actual production, due to the blade of the skin, the main beam, the root and other parts of the mechanical properties and process requirements are different, and therefore, without affecting the performance of the conditions, in order to reduce costs, different parts of the use of different prepreg.
4, wind turbine blade - pultrusion process
Pultrusion molding process is generally used in the production of a certain cross-section, the production of continuous molding products. This continuous molding process, the reinforcing material through the resin dip tank, curing molding. Pultruded products have a high fiber content and stable quality, and are suitable for mass production due to the ease of automation in continuous molding. Moreover, the products do not need to be rested at a later stage, the quality is consistent, there is no need to test dynamic balance, and the yield is 95%. Costs can be reduced by up to 40% compared to other processes.
Although the pultrusion process has many advantages, there are also shortcomings in the manufacture of wind turbine blades. The pultrusion process has been successful in the manufacture of vertical axis fan blades and some small horizontal axis fan blades, but it is not possible to manufacture variable cross-section fan blade, I-beam and other solid cross-section for the pultrusion process is only a small challenge, while the hollow parts including beams and the core material is the difficult point.
Since the pultrusion process is not currently able to manufacture complex shaped parts with large variations in cross-section, the cost of large automated equipment is another consideration for the application of the pultrusion process. Therefore, pultrusion molding process in the production of small wind turbine blade has a greater potential for application.
5, wind turbine blades - fiber winding
Fiber winding is mainly used in the manufacture of containers and pipes, the process of continuous fiber immersed in the dip tank in the machine-controlled mandrel winding. The winding process controls variables such as fiber tension, production speed and winding angle.
Fiber winding is capable of producing parts of different sizes and thicknesses. One drawback of the winding process as applied to blade production is that it cannot be wound in the longitudinal direction of the blade, and the lack of lengthwise fibers makes the blade susceptible to problems under high tensile and bending loads. In addition, the rough outer surface produced by fiber winding may affect the aerodynamic performance of the blade, so a surface treatment is necessary.
Finally, the core mold and computer control costs are significant. Obviously, the characteristics of fiber winding are suitable for containers and pipes, and additional costs are incurred in blade production.
6. Wind Turbine Blades - Resin Transfer Molding (RTM)
Resin transfer molding process belongs to semi-mechanized composite molding process, workers only need to put the designed dry fiber preform into the mold and close the mold, the subsequent process is completely rely on the mold and injection system to complete and ensure that there is no any resin exposure, and therefore, the technical and environmental requirements of the workers are much lower than the hand lay-up process and can effectively control the quality of the product.
The RTM process is a closed-mold molding process, especially suitable for molding wind turbine blades in one piece (fibers, cores and joints can be co-molded in one mold cavity) without the need for secondary bonding. Compared with the hand-laying process, it not only saves all kinds of tooling and equipment of the bonding process, but also saves working time, improves the production efficiency and reduces the production cost. At the same time, due to the use of low-viscosity resin impregnated fibers as well as the use of heating curing process, greatly improve the quality of composite materials and production efficiency.
The RTM process is less dependent on the skill level of the workers, the quality of the process is only dependent on the defined process parameters, the quality of the product is easy to guarantee, and the rejection rate of the product is lower than that of the hand-lay-up process.The limitations of the RTM process in the production of blades are, first of all, the cost.The RTM mold equipment is very expensive. In addition, because RTM is a closed mold process, it is difficult to predict the resin flow condition, and it is easy to produce unqualified products.
7、Wind turbine blade-Vacuum infusion molding process
Vacuum infusion molding process is the fiber reinforced material directly on the mold, in the fiber reinforced material on top of a layer of stripping layer, stripping layer is usually a very thin layer of low porosity, low permeability of the fiber fabrics, stripping layer on the high permeability medium, and then wrapped and sealed with a vacuum film. Vacuum pump pumping to negative pressure state, the resin through the feed tube into the whole system, through the guide tube to guide the main direction of resin flow.
The guide cloth distributes the resin to every corner of the layup, and the release cloth is peeled off after curing, resulting in a dense layup with low glue content. The vacuum infusion molding process is ideal for manufacturers of wind turbine blades. Compared with standard RTM, it saves time, has very low machine volatiles, improves labor conditions, reduces operator exposure to hazardous substances, meets people's demands for environmental protection, improves the working environment, and the process is simple to operate. At the same time, the vacuum assistance can fully eliminate air bubbles, reduce product porosity, and effectively control the product glue content.
High stability of product quality and good repeatability. Good apparent quality of the product, the same layup and thin thickness, high strength, relative to the hand-layup molding tensile strength increased by more than 20%, the process does not require high molds, mold making is simple, compared with the traditional RTM process, its mold cost can be reduced by 50 to 70%.
With the vigorous development of wind power business, composite wind turbine blade to the complexity of the direction of large-scale development. Various processes are applied in the manufacture of wind turbine blades. According to the characteristics of different wind turbine blades, the suitable process is reasonably adopted to obtain low-cost and high-quality wind turbine blades.
شركة بولاند للطاقة المتجددة المحدودة، شركة متكاملة للطاقة الجديدة، تُقدم لكم حلولاً متكاملة عالية الجودة لطاقة الرياح والطاقة الشمسية وأنظمة تخزين الطاقة. بولاند الآن شركة تابعة لشركة CRRC، وهي مسؤولة عن التوسع الخارجي لأعمال CRRC في مجال طاقة الرياح والطاقة الشمسية. نمتلك سلسلة توريد داخلية متكاملة نسبيًا، وشبكة خدمات، وجودة منتجات وتقنيات ممتازة.
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