The Importance of Wind Tower Anchor Bolt
Chinese wind power industry have developed from the stage of digesting and introducing overseas technologies to the stage of independent technological innovation, which compared with other countries, has advantages in terms of both technology and price. In recent years, China’s wind power industry, especially large-capacity megawatt-scale large-scale wind power generators, has developed rapidly. Wind power fasteners are the main connector of wind power generators. In power generators, high-strength anchor bolts are used in large numbers. It accounts for about 22% of the total number of wind turbine components. Pitch bearing and blade, hub and pitch bearing, hub and main shaft, main frame and yaw bearing, main frame and generator frame, main bearing and main frame, gear box elastic support and main frame, tower and offset high-strength anchor bolts are used to tighten the brake discs, the connection between tower parts, and locking discs used to connect main shaft to gearbox planet carrier. It can be seen that almost all key components are connected by high-strength anchor bolts. The cost of a wind turbine’s fasteners accounts for about 3.5% to 6.0% of the total equipment cost. Although the parts are small, they have a great effect. High-strength anchor bolt for wind power require strong fan stability due to long-term field service, harsh environments, and poor maintenance conditions. Under normal continuous working conditions, wind power fasteners must guarantee a service life of more than 15 years.
Due to randomness of its power source, harshness of operating conditions, particularity of manufacturing and installation, and high cost of maintenance, wind turbines have set extremely high requirements for anchor bolted connections. It is necessary to start from its characteristics in structural design and manufacturing. Necessary measures must also be taken on the process, workshop and on-site production assembly to ensure that anchor bolt connection is foolproof. Most of high-strength anchor bolts for wind power use 10.9 grades, and a few are 8.8 or 12.9 grades. High-strength anchor bolt quality for wind turbines is greatly affected by raw materials. From a series of aspects such as appearance quality, chemical composition, low magnification structure, depth of decarburized layer, non-metallic inclusions, microstructure (grain size) and upset test, all have a significant impact on anchor cage foundation bolt quality . For high strength anchor bolt fastener industry, wind power fasteners will undoubtedly be a huge market. Opportunities and risks coexist in the wind power fastener market.
Classification of Wind Tower Anchor Bolt
At present, there are roughly 3 types of fasteners used in domestic wind turbines and foundations:
- Tower bolts. High strength bolts used on the wind turbine tower are mainly GB / T 1228 ～ 1231, DIN6914 ～ 6916 and DAST.
- Bolts of wind turbine. Or foundation bolt, onshore anchor cage bolt, high strength anchor bolts used on wind turbines are mainly hexagonal head bolts such as GB / T 5782, GB / T 5783, GB / T 70.1, GB / T 6170, and GB / T 97, hexagon bolts, hexagon nuts and washers.
- Blade bolts. That is, anchor bolts connecting wind turbine blades are mainly non-standard double-headed studs and T-round nuts, blade bolts, T-nuts and morse washers, etc.
Steel Material Used for Wind Tower Bolts
High-strength anchor bolt for wind power are widely used in medium-carbon steel and medium-carbon alloy steel with a carbon content of 0.25% to 0.55%. For products ≤ M24, the material is 20MnTiB steel; for M27 and M30 bolts, 35VB steel is used; a small number of products are also allowed to use 30 CrMnSiA steel; ≥ M 3 3 are all 42CrMoA, B7, 40CrNiMoA steel.
Generally, 45 and 35 steels are used for wind power nuts, and some products are specified with 35CrMoA steel; gasket material is 45 steel. The elemental composition of the materials used for bolts, screws, studs, nuts, and washers is directly related to the mechanical properties of the fasteners, so it must not be lower than the requirements of the recommended materials.