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Blades and material

Blade is the most basic and key component of wind turbine. Its good design, reliable quality and superior performance are the decisive factors to ensure the normal and stable operation of the unit. In harsh environment and long-term non-stop operation, the requirements for blades are:

key word:Heat exchange element


Product description

1. Requirements for fan blades

Blade is the most basic and key component of wind turbine. Its good design, reliable quality and superior performance are the decisive factors to ensure the normal and stable operation of the unit. In harsh environment and long-term non-stop operation, the requirements for blades are:

1.1. The density is light and has the best fatigue strength and mechanical properties, and can withstand the test of extremely bad materials such as storm and random load;

1.2. The elasticity, inertia during rotation and vibration frequency characteristic curve of the blade are normal, and the load transmitted to the whole power generation system has good stability. It shall not break and fly out under the action of centrifugal force under the condition of out of control (flying car), nor break under the action of wind pressure, nor cause strong resonance of the whole wind turbine within the range below the speed of flying car;

1.3. The blade material must ensure that the surface is smooth to reduce wind resistance, and the rough surface will also be "torn" by the wind;

1.4. Strong electromagnetic wave interference and light reflection shall not be generated;

1.5. Excessive noise is not allowed;

1.6. Good corrosion resistance, ultraviolet radiation and lightning stroke resistance;

1.7. Low cost and lowest maintenance cost.

 

2. Material of fan blade

According to Bob bellemare, President of utilipoint, an international consulting firm, carbon fiber is the upcoming trend for wind turbines. Generally, smaller blades (e.g. 22m long) are made of E-glass fiber reinforced plastics with large amount and low price. The resin matrix is mainly unsaturated polyester, vinyl ester or epoxy resin can also be selected. While larger blades (e.g. more than 42m long) are generally made of CFRP or hybrid composites of CF and GF, and the resin matrix is mainly epoxy. Ramesh Gopalakrishnan, global manager of blade engineering of Ge wind energy, said that in the process of looking for lightweight and high-strength materials, designers chose carbon fiber to be used in blade design. Therefore, glass fiber and carbon fiber are the two most important materials in blade manufacturing.

In order to meet the above requirements and improve the economy of the unit, the increase of blade size can improve the economy of wind power generation and reduce the cost. The blade length has developed from 4.5m in 1980 to 61.5m today, and the capacity has developed from 55kW to 5MW today. In 1970, wind turbine blades were mainly made of steel, aluminum or wood. Today, E-glass fiber reinforced plastic (GFRP) is the most selected material. At present, carbon fiber composite (CFRP) has been adopted. The development of blade materials conforms to the direction of large-scale and lightweight of blades.

2.1. Wooden blade and cloth skin blade

Modern micro and small wind turbines also use wooden blades, but wooden blades are not easy to be twisted. Large and medium-sized wind turbines rarely use wooden blades. If wooden blades are used, the integral wooden square with good strength is also used as the blade longitudinal beam to bear the force and bending moment that the blades must bear when working.

2.2. Steel beam glass fiber skin blade

In recent years, the blades were made of steel tube or D shaped steel for longitudinal beam, steel plate as rib beam, and foam plastic covered with glass fiber reinforced plastic skin. The section of the steel pipe and D-section steel of the blade longitudinal beam from the blade root to the blade tip shall be gradually reduced to meet the requirements of twisting the blade and reduce the weight of the blade, that is, to make an equal strength beam.

2.3. Aluminum alloy equal chord extrusion blade

The equal chord blade extruded with aluminum alloy is easy to manufacture, can be produced continuously, and can be twisted according to the distortion required by the design. The shaft and flange connected between the blade root and the hub can be realized by welding or bolt connection. Aluminum alloy blades are light and easy to process, but they can't shrink gradually from blade root to blade tip, because this extrusion process has not been solved all over the world.

2.4. FRP blade

The so-called glass fiber reinforced plastic (GFRP) is a reinforced plastic made of epoxy resin, unsaturated resin and other plastics infiltrating glass fiber or carbon fiber with different lengths. Reinforced plastics have high strength, light weight and aging resistance. The surface can be wrapped around glass fiber and epoxy resin, and other parts are filled with foam plastics. The quality of glass fiber can also be improved by surface modification, sizing and coating. LM glass fiber company is now committed to developing all glass fiber blades up to 54m, with low cost per kWh.

2.5. FRP composite blade

At the end of last century, the blades of large and medium-sized wind turbine products in the world's industrial developed countries basically used profile steel longitudinal beam, laminated FRP rib beam and composite materials with metal structure for connecting blade root and hub. Different composite materials are selected for the rotor blades of wind power generation according to the blade length. At present, the most commonly used are glass fiber reinforced polyester resin, glass fiber reinforced epoxy resin and carbon fiber reinforced epoxy resin. Research in the United States shows that the tensile fatigue resistance of E-glass fiber coated by radio frequency plasma deposition can reach the level of carbon fiber, and the micro vibration wear between fibers that can actually cause damage can be reduced after this treatment. LM glass fiber company further develops 61m large blades mainly made of FRP and only a small amount of carbon fiber at the ends of beams and blades, so as to develop 5MW wind turbines.

2.6. Carbon fiber composite blade

With the increase of single generator power, the blade length is required to increase, and its application in wind power generation will also expand. For blades, stiffness is also a very important index. The research shows that the stiffness of carbon fiber (CF) composite blade is two to three times that of FRP composite blade. Although the performance of carbon fiber composites is much better than glass fiber composites, it is expensive, which affects its wide application in wind power generation. Therefore, major composite companies around the world are making in-depth research from the aspects of raw materials, process technology and quality control in order to reduce costs.