| The wind power bearing is the core component of the wind turbine and is applied to the main shaft,blades,pitch and yaw.The main types are pitch bearings,yaw bearings,main shaft bearings,generator bearings,and gearbox bearings.The pitch bearing is a member that connects the blade and the hub,and also plays the role of transferring the blade load to the hub.The pitch bearing is installed on the tower of the wind turbine,and the height is about 50 to 100 m.The maintenance of the shutdown caused by the bearing damage is very difficult and the cost is extremely expensive.The economic loss caused by the shutdown will far exceed the value of the bearing itself.Therefore,wind power equipment has strict requirements on the service life and reliability of the bearing.Generally,it requires a service life of 20 years.Some wind turbines in some wind farms have cracks in the mounting hole of the outer ring of the bearing after two years of use.For bearing removal inspection,it is found that the crack width of the mounting hole of the bearing ring is about 5mm,and the fixing bolts of the outer ring part are for relaxation,the relaxation angle is about 15° to 20°.In this paper,the pitch bearing is studied in the following aspects.(1)This paper gives an overview of the working conditions,operating characteristics,structural characteristics,pitch bearing materials and heat treatment of pitch bearings.The physical force model of the pitch bearing is established and solved.The load distribution of the bearing of the pitch bearing under different working conditions and the check of the bearing capacity of the bearing are analyzed.(2)Using the finite element to establish the model of the pitch bearing outer ring,the rolling body transmission load is loaded to the contact position in the form of force using a parametric method,and the constraint condition is changed to calculate the bearing ring in the presence of the fixed bolt looseness installation hole the location of stress distribution.The fatigue properties of the material,the cumulative fatigue damage theory,and the fatigue life analysis method of the material are described.The fatigue analysis of the bearing ring results in the cracking of the bearing ring.(3)The bolts of the pitch bearing were analyzed and the bolts with the highest load were calculated.The theoretical and finite element simulations of the strength of the bolts were used.Compare the results and analyze the causes of bolt relaxation.Through the above studies,the following conclusions have been drawn:(1)When the pitch bearing is subjected to the combined load,the effect of the overturning torque is most obvious.The more the rolling elements that are farther away from the action line of the overturning moment,the greater the bearing load.The rolling element transmission load presents a more regular sine distribution according to the position angle.To solve the maximum contact stress of the bearing,it is considered that the bearing capacity of the pitch bearing meets the working requirement.(2)Using the finite element to change the constraint conditions,it is found that the relaxation of the fixing bolt has a significant effect on the position stress of the mounting hole of the bearing outer ring,and the first principal stress of the mounting hole reaches 415.35 MPa when the symmetrical two bolts are loose near the mounting hole.Use the ASME Fatigue Design Curve to verify the fatigue life of bearing rings at this stress level.Qualitatively,it is believed that the sudden increase in the stress on the ferrule caused by loose bolts near the mounting hole is the cause of the cracking of the pitch bearing ferrule.(3)The calculation of the theoretical strength and the finite element simulation of the pitch bearing bolts were performed.The results showed that the static strength and fatigue strength of the bolts and rods satisfied the working requirements,and the threaded part of the bolt root exceeded the yield limit of the material and was plastically deformed.Accumulation may cause loose bolts. |
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