Wind power tower bolt: some knowledge points of wind power tower bolt
Wind power tower bolt: wind power generation has the characteristics of mature technology, high reliability, low cost and remarkable scale benefit. It can operate on or off the power grid. It is a rapidly developing new energy technology in China. Tower is an important supporting structure of wind turbine. In the design, considering the economy of manufacturing, transportation and hoisting, the tower is usually divided into several parts, and the adjacent parts of the tower are connected with wind power tower bolts.
Wind power tower bolts generally use 10.9-grade high-strength bolts, which are formed by thread rolling. The high-strength bolt used for tower pipe connection is easy to produce high local strain and stress on the thread due to its bad working environment and the influence of alternating load, so that the bolt is in the state of fatigue stress.
The factors affecting the fatigue life of wind power tower bolts can generally be divided into three aspects: stress conditions, manufacturing conditions and service environment. The stress state can be attributed to the influence of stress concentration and average stress amplitude in the process of bolted connection. The manufacturing situation depends on the purity and strength of raw materials, the heat treatment process of bolts, the processing method of threads and the anti-corrosion measures of bolts. The influence of service environment on the fatigue life of bolts mainly includes corrosive medium and ambient temperature. These factors are interrelated and affect each other. When analyzing the fatigue life of bolts, we must comprehensively consider the influence of these factors.
Grade 10.9 high-strength wind power tower bolts are used for tower connection. Generally, 42CrMo is used as raw material. The thread is rolled after heat treatment, and the surface of the bolt is treated with Dacromet anti-corrosion treatment. The tower connecting bolt needs to bear alternating load during the operation of the unit, so the stress condition of the bolt is an important factor affecting its fatigue life.
In China, the tower flange is processed by CNC machine tool with very high precision, which can ensure that the bolt mounting hole of wind power tower on it can meet the design requirements of drawings, so as to effectively control the eccentricity and forced assembly in the process of bolt installation.
In addition, after the tower hoisting is completed, the bolts of the wind power tower shall be pre tightened in diagonal order to make the pre tightening force of the bolts evenly distributed during the installation of the tower bolts. In this way, under normal operation, the stress concentration factor of the tower connecting bolts can be controlled within the allowable range of the specification. At present, the height of the tower used by megawatt wind turbines is relatively high, generally about 80 m, the diameter of the tower section is relatively large, and the diameter of the bottom section is generally 4.2 M. however, when the tower section is welded with the connecting flange, the heat affected zone will affect the flatness of the flange to a certain extent, so in many projects, After the hoisting of tower sections, there will be a certain gap between the flange joint surfaces.
The root cause of fatigue failure of wind power tower bolts is damage accumulation. In order to ensure the fatigue life of bolts, the stress amplitude of bolts in use shall not exceed the allowable stress amplitude in bolt design. Taking the counter balanced flange used in a project as an example, the effect of flange clearance on the fatigue life of bolts is compared by calculating the stress amplitude of bolts.
Ningbo last Li High Strength Fastener Co., Ltd. is mainly engaged in wind power anchor plate, wind power high strength prestressed anchor bolt, wind power blade connecting bolt, wind power foundation anchor bolt cage, wind power tower bolt, etc. Since the establishment of the company, we have provided a large number of high-quality wind power anchor cage products for key new energy wind power projects, with thousands of supporting wind turbine units. The products are distributed in nearly 30 provinces, cities and autonomous regions across the country. Good product quality and excellent have won the trust of our customers. In China, many enterprises have established long-term friendly business relations with our company, It has established a good image in the domestic wind power high-strength fastener industry. Based on the enterprise tenet of "creating high-quality products and customer first", the company is willing to provide more customers with better products and better services.