The sliding bearing is an important part of the shafting of the steam turbine unit. In addition to supporting the rotor, it also plays a very important role in the vibration of the rotor, which largely determines the safety of the rotor system. Oil-lubricated sliding bearings are widely used because of their high bearing capacity, long service life and convenient processing and maintenance.
There are two ways for oil-lubricated sliding bearings to maintain lubricating oil pressure:
1.The oil pump is used outside the bearing to input pressure oil into the bearing to produce a pressure oil film between the journal and the bearing surface, which is called hydrostatic bearing. This bearing can maintain oil film even when the journal does not rotate.
2. Relying on the rotation of the journal itself to make the lubricating oil layer generate pressure, establish the oil film, and support the rotor, which is the dynamic pressure bearing.
Hydrodynamic bearings are generally used for steam turbines. The oil film pressure of the hydrodynamic bearings is generated by the rotation of the shaft itself. In the hydrodynamic bearings, there is a certain gap between the journal and the bearing hole, and the gap is filled with lubricating oil.
When the machine is stopped, the journal sinks at the bottom of the bearing.
When the shaft starts to start, the journal crawls up along the inner surface of the bearing depending on the friction force. When it reaches a certain position, the friction force cannot support the weight of the rotor and starts to slip, which is semi-liquid friction.
As the speed continues to rise, the journal will bring viscous lubricating oil into the wedge clearance (oil wedge) between the bearing and the bearing. Because the wedge clearance is convergent, its inlet section is larger than the outlet section, so a certain oil pressure will be generated in the oil wedge, and the journal will be squeezed to the other side by the oil pressure. If the flow of lubricating oil into the wedge gap is continuous, the oil pressure in the oil will increase, which will reduce the average flow rate at the inlet and increase the average flow rate at the outlet. The oil layer accumulated in the gap is called oil film, and the oil film pressure can lift the rotor journal. When the oil film pressure is balanced with the external load, the journal runs stably without contact with the inner surface of the bearing.
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