This paper analyzes the current status of wind turbine nacelle cover and hubcap, and introduces the mainstream composite material forming process currently applied in the nacelle cover and hubcap. At the same time, it has been continuously researched in the mainstream composite material forming process. , optimization and improvement, summed up some new experiences and new technologies to share.
1 Introduction
The wind turbine nacelle cover and hubcap cover are the outer casing protection structure of the large wind turbine (as shown in Figure 1). The wind turbine nacelle cover and hubcap cover are important components of the wind turbine, covering the equipment and electrical components inside the wind turbine. This enables wind turbines to work properly in harsh weather conditions, protecting internal equipment and personnel from external environmental factors such as wind, snow, rain, salt spray, and ultraviolet radiation.
Figure 1 Wind turbine hatch and hubcap
Because the nacelle cover and the hub cover have been attacked by nature and the external environment for a long time, the requirements for strength and rigidity are relatively high, and at the same time, weather resistance, corrosion resistance, temperature resistance, aging resistance, fatigue resistance, and UV resistance are required. In addition to the performance of radiation, in addition to the weight bearing of the entire wind turbine, the nacelle cover is required to be light in weight, high in strength, and large in carrying capacity. Therefore, the application of new composite materials capable of meeting the above requirements in the wind turbine nacelle cover and hub cover has begun to receive widespread attention.
2. Analysis of industry status
Due to the relatively transparent production technology of the nacelle cover and hubcap, the competition in the domestic nacelle cover and hubcap industry is relatively full, and there are about 30 manufacturers with large scale. The domestic foreign wind turbine manufacturers also purchase related products in China. The technical capabilities and quality levels of domestic brands have been generally recognized in the industry.
At present, the domestic engine room cover and hub cover manufacturers are roughly divided into three echelons. The first echelon is represented by Greed, Zhuzhite, Shandong Shuangyi, etc., with strong technical capability, high quality control standards and excellent product quality; the second echelon Represented by Tianjin Unicorna, the product quality standards are relatively strict, the product quality is relatively good, and the market share is high. The third echelon consists of other manufacturers with relatively single source and relatively small annual shipments. As wind power installations have entered a stage of low-speed growth in recent years, the overall profit rate of the wind power industry has continued to decline. The manufacture of aircraft cabin covers as a supporting industry has also been greatly affected. The prices of the first echelon manufacturers are higher than those of other manufacturers, but with their Excellent technical strength and strict quality management have won the recognition of more high-end customers, the order source is wider, the annual shipment is more secure, and the second echelon manufacturer's overall investment in the factory based on the quality of the products. The enthusiasm is not high, the price reduction strategy is adopted to win more orders; the third echelon manufacturers are keeping close to the intrinsic customers, developing new customers and expanding the re-production power shortage. Due to the unstable order, it is difficult to ensure the stable and continuous production of skilled workers. It often leads to poor product quality, increased after-sales service costs, and increasingly difficult to survive. At present, the nacelle cover and hubcap products independently designed, developed and produced by Guoneng United Power have also entered the research and development cycle and will enter the market during the year.
As can be seen from Chart 2, the main customers of the first echelon manufacturers are domestically owned market players with large market share, such as Goldwind, United Power, Huarui, etc., while foreign host brands also recognize and purchase. The second and third echelon's cabin cover manufacturers have relatively simple customers and a relatively small market share.
3. New technology research
Composite molding process is the basis and necessary condition for the development of composite materials industry. With the widening of the application field of composite materials, the composite material industry has developed rapidly. The molding processes commonly used in nacelle covers and hubcaps include hand lay-up process, spray forming process, vacuum bag forming process, LRTM forming process, etc., which are currently used by most manufacturers. The more mature vacuum bag forming process, and the light resin transfer molding process (LRTM) with double mold as the main design concept is also becoming mature. LRTM has become a future development due to its combination of high quality, environmental protection and protection of laborers. The mainstream direction.
3.1 Introduction to the main process
Introduction of vacuum bag film forming process
The vacuum bag forming process is a molding process in which the product is sealed between the mold and the vacuum bag, and the product is pressurized by vacuuming to make the product more compact and mechanically better. The vacuum bag film process is divided into dry process and wet process. The wet method is to put a hand lay-up or spray-formed uncured product, and a vacuum bag film is attached. The product is placed between the film and the mold, the periphery is sealed, and a vacuum is applied to remove bubbles and volatiles in the product. In the dry method, the reinforced glass fiber is placed on the mold, the vacuum bag film is sealed with the periphery of the mold, and the resin is introduced into the mold from the other end of the mold while the vacuum is being evacuated, so that the reinforced glass fiber is infiltrated. The difference between the two processes is that the dry glass content can be made higher, the molded product is better in quality and lighter in weight.
Figure 3 Vacuum bag film forming process vacuum infusion
The characteristics of vacuum flow forming technology: 1, can produce single-sided light products; 2, the molding efficiency is general, suitable for the production of medium-sized FRP products; 3, for closed mold operation, does not pollute the environment, does not harm the health of workers; 4 The reinforcing material can be laid in any direction, and it is easy to place the reinforcing material according to the stress state of the product; 5, the disposable consumables are more, the garbage recycling is a problem, and the cost is relatively high.
LRTM molding process
Lightweight resin transfer molding process (RTM-Light) is abbreviated as LRTM. It is a new type of composite material molding technology. Compared with the vacuum bag film single mold process, it is a double mold forming process. The mold has a rigid periphery with a width of about 100 mm. The double sealing tape forms a separate sealing zone. As soon as a vacuum mold is closed, the vacuum is applied to the cavity, and the negative pressure in the mold and the lower injection pressure are utilized. The resin is injected into the mold to allow the resin to penetrate into the pre-laid reinforcing fibers or preforms. The main principle is to first lay out a pre-formed body of reinforcing material designed according to performance and structural requirements in the cavity, and inject a special low-viscosity injection resin system into the closed cavity by using an injection device. The mold has peripheral sealing and fastening and injection. From the exhaust system to ensure the smooth flow of the resin and discharge all the gas in the cavity and thoroughly infiltrate the fiber, the gas in the fiber reinforcement is removed under vacuum, and the impregnation of the fiber and the fabric is achieved by the flow and penetration of the resin. And curing at room temperature to form a certain resin and fiber ratio process.
Figure 4 LRTM molding process vacuum infusion
Features of L-RTM process: 1. Due to the use of double abrasive tools, it can produce two-sided light products; 2. High molding efficiency, suitable for medium-sized production of FRP products; 3. L-RTM is closed mold operation, no pollution The environment does not harm the health of the workers; 4. The reinforcing materials can be laid in any direction, and it is easy to implement the reinforcement materials according to the example of the stress condition of the products; 5. The raw materials and energy consumption are small.
In the LRTM process, it is necessary to inject a resin into the cavity of the mold to have a certain pressure and flow rate, so that the structural strength and rigidity of the mold are large enough to not break or deform under the injection pressure. Usually, a sandwich composite material with steel tube support or an aluminum mold or a steel mold machined by a numerically controlled machine tool is used, which increases the manufacturing cost, and only the product with a large enough yield can offset the mold cost. In addition, in order to close the mold, it is necessary to have sufficient clamping force around the circumference or to use a pressure system that closes the mold. All of the above factors have led to difficulties in selecting materials for LRTM process molds, and the investment cost is expensive. The process has certain limitations in practical applications at the current stage.
3.2 Research on new processes and new technologies
With the continuous improvement of the customer demand for the nacelle cover and the hubcap product, the manufacturers have continuously optimized and improved on the basis of the original mature technology, and new technologies and new designs have emerged, which greatly enriched the product diversity and satisfied. Different customer customization needs.
Application of colored resin
The colored resin is a new type of raw material. The resin is the same as the ordinary resin component. A certain amount of toner is added according to the requirements of the finished product. After the vacuum infusion is cured, the inner surface directly reaches the finished color requirement. The inner surface of this type of resin product is beautiful in color, which can effectively avoid wall hanging and uneven color caused by spraying paint on the inner surface of the later stage, and can effectively improve the apparent quality. The use of colored resin for the overall infusion of the nacelle cover, the post-spray treatment of the overall infusion with respect to the conventional resin reduces some of the processes, but requires an increase in the infusion process. As shown in Figs. 5 and 6, the use of the colored resin relative to the ordinary resin can effectively avoid the defects such as wall hanging, uneven color difference, inner wall leakage and flaking of the paint surface caused by post-treatment such as painting, thereby improving the appearance quality of the product and reducing the appearance. cost.
At present, the technology is generally applied to foreign wind turbine brands such as Vestas, Siemens, and Gemei.
Figure 5 using colored resin effect
Figure 6: Post-treatment effect using ordinary resin painting
Optimization of internal reinforcement methods
The reinforcement method of the strength of the traditional nacelle cover glass reinforced plastic is generally carried out by using a cabin cover layer and a pre-buried polyurethane foam slat for the resin infusion, and a grid-shaped rib is formed inside the nacelle cover for reinforcement. The new process ensures that the nacelle cover does not reduce the strength, and in order to achieve the purpose of reducing the weight of the nacelle cover, the internal layer of PVC core material is used for reinforcement. The core material reinforcement method is mainly to lay the core material in a large area when the nacelle cover and the hub cover layer are laid, and correspondingly reduce the number of layers of the fiberglass cloth, and at the same time cancel the reinforcing ribs to achieve the purpose of weight reduction, and the comparison by Table 7 can be Clearly see this change. (The table data is derived from a 2MW nacelle cover of a major domestic OEM):
From the data point of view, the thickness of the product is reduced by changing the internal strength enhancement of the nacelle cover, thereby reducing the weight of the product. Comprehensive comparative analysis shows that the inner reinforcement of the nacelle cover by the core material laying method is lower than that of the polyurethane reinforcing rib reinforcement method, the operation is simple, the process is simple, easy to implement, and the cost is slightly increased, but the weight is greatly reduced. Due to the larger internal space, the finished product becomes easier during the installation of the fan and reduces the occurrence of internal interference.
Figure 8 Using polyurethane reinforcement reinforcement
Figure 9 using core reinforcement
The emergence of split design
Due to the large size of the nacelle cover product, the large-area large-area FRP products have high deformation probability and inconvenient transportation. In order to solve the above problems, a unit split design (shown in Figure 10) appears, and the nacelle cover is reasonably designed into multiple The unit is manufactured, stacked and transported. Its outstanding features are as follows:
(1) The small unit can effectively control the production process and better guarantee the product quality;
(2) The production of the split unit is less deformed, fully reflecting the compatibility and interchangeability;
(3) Reasonable compression of transportation space, convenient and convenient transportation, improved transportation efficiency, and greatly reduced transportation costs;
However, the split design also has shortcomings. On the one hand, the unit area is reduced, the absolute quantity is increased, and the overall area is increased. On the other hand, the combination of different units puts higher requirements on the sealing performance, and the combined production leads to the production cost and the detection cost. Increase by about 40%. The two factors of increasing production cost and transportation cost savings are comprehensively calculated. At present, the design is applied more in overseas transportation of ultra-long distance.
Figure 10 A well-known manufacturer's nacelle cover split production
4. Conclusions and prospects
With the continuous development of the wind turbine cover and hubcap industry and the increasingly fierce domestic and international competition, the nacelle cover and hubcap products are required to have the advantages of new design, high performance, excellent quality and low cost. In order to produce high-precision, high-quality and high-efficiency products, the technology of the nacelle cover and hubcap forming process needs constant innovation, improvement and optimization. From the traditional single type to the composite type and multi-functional type, it gradually becomes integrated. Diversified and scientific, the application of new materials will continue to be enriched and exerted higher value. Accelerating the development of the nacelle cover and hubcap molding technology is an inevitable requirement for adapting to the domestic market and participating in global competition.
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