Study On Lubricating And Load Bearing Performances Of Sliding Thrust Bearing In Vertical Pump Unit

The motor thrust bearing of a large vertical pump unit is not only an important component that guarantees the stable operation of the unit, but also the main controlling factor in the operating life, the overhaul period and the reliability of pump unit which bears the axial force of the pump unit. The study on the lubrication performance and carrying capacity will provide theoretical and reference base for the design and optimization of the thrust bearing.Hydrodynamic thrust bearings of the large vertical axial pump were studied in this paper. The 3 dimensional fluid model of the thrust bearing was built using CAD to build, the pressure boundary condition and meshed was established in Gambit, and then imported into Fluent to computing the lubrication stream field and pressure field. The factors influenced the bearing carrying capacity was analyzed, and some laws were found. Then the possible problems were studied which may occur in the actual process. The results are as follows:(1) The rotating mirror plate drives lubricating oil to move, gives dynamic pressure, forms high pressure areas on the surface of the thrust tile, and the pressure decreases gradually from the biggest pressure center to the tile surface.(2) In normal operation conditions, the oil film thickness of vertical pump unit is 0.0675mm for the example. The deformation of elastic metal plastic bearing shells is in general 2×10-4～9× 10-4mm, that is only 0.3%-1.3% of the oil film thickness, it is very little that can be ignored in calculation.(3) The oil film thickness has an obvious effect on the bearing capacity of thrust tiles, the smaller the oil film thickness, the greater bearing capacity is, especially under the condition of rather smaller oil film thickness, the small change of the oil film thickness will cause great change of bearing capacity.(4) Under the same oil film thickness of the supporting point, the greater eccentricity of loading bolt will cause greater tilt angle of the tile surface, high-pressure center is biased towards the direction of the oil outlet. The greater the rotational speed is, the larger the bearing capacity will be.(5) The height installed difference among a set of thrust bearings has a great influence on the load evenly distributed among a set of thrust bearings, the bigger the difference is, the larger the bearing load difference will be. When a bearing is 0.01-0.02mm higher than others, the load is 36%～75% above the average.(6)During the starting and stalling processes of the vertical pump unit, with low speed, the thrust bearing will bear the gravity of all rotating components and a small number of axial water thrust, the oil film thickness of tile surface is small, the lubrication performance is poor, the friction resistance is large, and the damage to the working face of the bearing is big. So the starting and stalling time of units should not be long and the pump unit should not be started and stopped frequently.(7)The viscosity of lubricating oil influences the bearing capacity of thrust bearings, the more viscosity, the greater bearing capacity. When the load of thrust bearing is constant, the more the viscosity is, the more the oil film thickness will be, and the better lubrication performances will be.