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Basic knowledge of the main bearings of a steam turbine ▲ What is the function of the main bearings? The main bearings are an important component of a steam turbine, and there are two types: support bearings and thrust bearings. They are used to bear the entire weight of the rotor and to determine its correct position within the cylinder ； As well as the additional force caused by partial steam injection that induces rotor vibration, the thrust bearing also bears a portion of the rotor’s axial thrust. ▲How is the lubricating oil film in bearings formed? The oil film inside the bearing is formed because the diameter of the bearing bush hole is slightly larger than that of the shaft journal. When at rest, the shaft journal is located below the bearing bush and comes into direct contact with its inner surface, creating a wedge-shaped gap between the bearing bush and the shaft journal. When the rotor first starts to rotate, direct friction occurs between the journal and the bearing shell. However, as the journal rotates, the lubricating oil adheres to the surface of the shaft due to its viscosity and is carried into the wedge-shaped gap between the journal and the bearing shell. The oil in this wedge-shaped gap can be considered to be divided into several layers; the velocity of the oil in each layer decreases as one moves further away from the surface of the bearing shell, with the velocity of the oil layer in direct contact with the bearing shell surface being zero. The flow velocity of the oil layer in direct contact with the journal surface is the same as the linear velocity of the journal. As the rotation speed increases, more oil is drawn in; since the exit area for the oil flow in the wedge-shaped gap continues to decrease, the oil pressure rises. When this pressure becomes high enough to balance all the forces exerted by the rotor on the bearing surfaces, the journal is lifted by the oil film and rotates suspended within it, thereby preventing direct metal-to-metal friction and establishing fluid friction. ▲Under what conditions do bearings experience dry friction? When the rotor is at rest, there is no oil film between the journal and the bearing; therefore, when the turbine rotor starts to rotate, dry friction occurs between the journal and the bearing bush. ▲Under what conditions does a bearing experience semi-friction? After the rotor starts rotating, as the speed increases, the oil attached to the journal is carried between the journal and the bearing; at this point, the journal and the bearing are in a state of semi-dry friction. ▲Under what conditions do bearings experience semi-liquid friction? Answer: As the rotational speed increases, most of the surface area between the journal and the bearing is separated by a layer of lubricating oil; at this point, the friction between the journal and the bearing is of a semi-liquid type. ▲Under what conditions does liquid friction occur in bearings? When the turbine speed reaches a certain level, a stable oil film of a certain thickness forms between the journal and the bearings; at this point, the friction is the friction between the oil layers, that is, fluid friction. ▲What are the conditions for the formation of a bearing oil film, and what factors affect changes in the oil film pressure? 1) The journal must maintain a certain linear velocity to form an oil film. 2) Lubricating oil must have a certain viscosity to form an oil film. 3) A wedge-shaped gap must be formed between the journal and the bearing shell in order to create an oil film. 4) The inner surface of the bearing bush must be carefully scraped to maintain a smooth surface. 5) The greater the load on the bearing, the more difficult it is to form an oil film. 6) The width of the bearing also has an impact. ▲What role do bearing shells play during operation? The functions of the bearing bush during operation are as follows: 1) By supplying oil to the bearing bush, it removes the heat generated during its operation, thereby cooling the bearing ； 2) A stable oil film with sufficient load-carrying capacity is formed between the bearing shell and the shaft journal to ensure liquid lubrication.