1, oil wedge of steam turbine bearing
Steam turbine radial support bearings generally consist of bearing sleeves + tilting pads. The rotor shaft diameter of the turbine is smaller than the inner diameter of the bearing. When stationary, the journal is located at the lower part of the bearing bush and is in direct contact with the inner surface of the bearing bush. A wedge-shaped gap is formed between the tilting pad and the journal (as shown in the figure 1), which is often called an oil wedge.
2, oil film formation
When the rotor starts turning, as shown below, direct friction occurs between the journal and bearing bush. As the journal rotates, oil adheres to the shaft through viscosity and is drawn into the oil wedge between the journal and bush. As speed increases, more oil enters. Because the outlet area of the wedge-shaped clearance progressively decreases, oil pressure rises. Once this pressure balances the rotor's entire load on the bush, the oil film lifts the journal, which rotates supported on the film. This avoids direct metal contact, establishes fluid friction and allows safe, stable turbine operation.
3, conditions for oil film formation
The small machines we use every day use oil and grease in the rotating parts to ensure flexible rotation and no friction between moving and static parts. The lubricating oil used in steam turbine bearings has strict requirements on oil quality, oil temperature, etc. In addition to these, the formation of oil film must also meet the following conditions:
(1) A wedge-shaped gap (oil wedge) should be formed between the inner surface of the bearing and the journal, which is the spatial condition for the formation of oil film;
(2) There must be sufficient lubricating oil between the inner surface of the bearing and the journal, and the lubricating oil should have a suitable viscosity, which is the material condition for the formation of oil film;
(3) There should be sufficient relative motion speed between the inner surface of the bearing and the journal to generate the required internal pressure in the oil wedge. An oil film is formed between the shaft and the bearing bush, which allows the shaft to float. This also organically unifies the formation and function of the oil film. The movement of the rotor forms an oil film which is beneficial to the movement of the rotor.
(Source: Qi Machinery Professional)