Features and maintenance techniques of tilting bearing shells in steam turbines

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1 Structure and characteristics of tilting bearings Tilting bearings are usually composed of 3 to 5 or more arc-shaped babbitt blocks that can tilt freely at the pivot points. During operation, the tiles can swing freely depending on the rotational speed, load, and bearing temperature, thereby creating multiple oil wedges around the shaft diameter. Each tile is supported within the bearing sleeve by a spherical pin and a gasket on its back side, allowing it to swing around its spherical support pin ； Springs are installed on the upper bearing shell piece and the back side of the bearing, respectively; these springs exert pressure on one end of the bearing shell piece, thereby creating an oil wedge artificially. Lubricating oil enters the bearing through the gaps between the bearing pads, and exits from the openings in the oil seal rings at both ends of the bearing. If the inertia of the bearing pads, as well as the frictional forces at the pivot points and the shear internal friction forces within the oil film, are ignored, the force exerted by the oil film on the shaft diameter due to each bearing pad always passes through the center of the shaft diameter. This prevents the generation of unstable forces that could cause vibrations in the shaft diameter, resulting in high stability; theoretically, it is possible to completely avoid the occurrence of oil film oscillations. Furthermore, since the tiles can swing freely, this increases the flexibility of the support, and they also have the ability to absorb vibration energy from the rotating shafts, meaning they offer excellent vibration damping properties. Tilting pads have many advantages, but their disadvantages include complex structure, difficulty in installation and maintenance, and high costs. However, as the requirements for bearings in high-power units in terms of stability, power consumption, and load-bearing capacity become increasingly stringent, tilting pad bearings are being adopted by more and more high-power units. Tilting pad bearings rank first among all types of supporting bearings in terms of stability, load-bearing capacity, and power consumption; three-oil- wedge bearings and elliptical bearings come next, while cylindrical bearings perform the worst.