| The development of hydraulic turbines,one of the important equipments for hydropower projects,has a major impact on the hydropower industry.At present,the main shaft of the turbine mainly adopts the form of contact seal such as packing seal,rubber flat seal,blade seal and end seal.However,due to the easy wear of the main shaft and the large amount of leakage,the turbine will not work in serious cases and the main shaft needs to be shut down for maintenance.Life is shortened and there will be a certain economic loss.The magnetic fluid sealing technology is applied to the main shaft seal of the hydraulic turbine to study the hydrophobic magnetic fluid.The magnetic fluid sealing device suitable for the main shaft of the hydraulic turbine is designed,so that there is no rigid contact between the moving part and the stationary part,no wear,and it can be repaired by itself.It can also work reliably for a long time and solve the sealing problem of the turbine shaft effectively.As a new type of functional material,magnetic fluid has been widely used in the field of application due to its unique properties.Compared with traditional mechanical seals,magnetic fluid seals have the advantages of tight seal,low leakage rate,high reliability,no pollution and high speed.In this paper,the finite element method is used to analyze the magnetic field of the magnetic fluid seal structure of the turbine main shaft,and the analysis results are verified by experiments.The main research contents and results are as follows:1)The main shaft seal structure of the turbine is designed,and the materials in the structure are selected: the magnetic fluid is fluoroether oil base,the magnetic source is NdFeB permanent magnet,the pole shoe material is made of No.10 steel,and the outer shell is made of 1Cr18Ni9 Ti alloy.In order to meet the requirements of turbine shaft seals with different shaft diameters and different application heads,the above structure has been improved and the structural parameters are explained.2)The finite element simulation software is used to simulate the above structure and the effects of magnetic fluid’s own performance,sealing gap,pole piece magnetic pole angle,sealing gap and spindle speed on the sealing pressure bearing capacity are verified by experiments.The pressure resistance of the magnetic fluid seal of the turbine main shaft gradually decreases with the increase of the sealing clearance.When the sealing clearance is 0.2~0.6mm,it can meet the requirements of various working conditions.In the double-inclined trapezoidal tooth structure,the sealing is increased with the increase of the inclination angle.The pressure resistance first increases and then decreases.The sealing capacity is the strongest when the sealing angle is between 40° and 70°.With the increase of the number of sealing stages,the sealing pressure capacity is gradually increased until stable;Under dynamic conditions,the sealing capacity decreases with increasing Rotating speed.3)In the magnetic fluid seal device,the maximum magnetic induction intensity ΔBsum corresponding to the tooth gap(valley)and the tooth tip(crest)has a great influence on the unbalanced rotation.The larger the ΔBsum,the more obviously the nano magnetic fluid unbalance rotation will be.The nano magnetic fluid unbalance torque is large,sealing pressure difference is larger,the sealing ability is better and the friction power consumption will be larger,and vice versa. |
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