First. Tilting pad bearing structure and working principle
Tilting pad bearing is composed of five arc-shaped pads, the upper half bearing is 3 tilting pads, the lower half bearing is two tilting pads, the pads can be freely tilted on the fulcrum, and the pads can swing freely when working , A multi-oil wedge is formed around the journal. The lubricating oil of the bearing enters the annular channel of the bearing housing through the oil inlet at the bottom of the bearing. The lubricating oil enters the bearing pad through 5 oil holes from the annular channel, and the lubricating oil is distributed along the journal and discharged from both ends of the journal to complete the cooling and lubricating effect.
Second. The phenomenon of temperature rise of tilting pad bearing
During the start-up of the unit, the temperature of the tilting pad bearing rises slowly. After a fixed speed, the temperature of the tilting pad bearing reaches 78°C. After the unit is running at full load, the temperature of the tilting pad bearing reaches about 85°C and the oil return temperature is 56°C. , With the increase of the operating time of the unit, the temperature of the tilting pad bearing gradually increases, with an average increase of about 1°C per day, reaching a maximum of 92°C and a tendency to continue to rise. The return oil temperature of the tilting pad bearing reaches 65°C, which is higher than that of other bearings. The average oil return temperature is 54°C higher. Check the operating parameters of the unit, the bearing oil inlet pressure and temperature are normal, other bearing temperatures are within the standard range, only the tilting pad bearing pad temperature and the return oil temperature are too high, the on-site inspection found that the middle pressure rear shaft seal pipeline and tilting The foundation of the tile bearing box is tightly attached, the thickness of the insulation layer is thin, and the surface temperature of the foundation is detected up to 170°C.
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Third. The cause analysis of the high temperature of the tilting pad bearing
1. Factors that can be excluded
(1) During the installation process of the bearing, relevant inspections such as penetration and ultrasound were carried out, and the results were in line with the installation requirements, and the influence factors of the bearing bush itself, such as blackout, damage, etc., were excluded.
(2) The shafting center finding and bearing installation have passed multiple measurements and acceptance, and all meet the installation requirements, and the influence of this factor can be excluded.
(3) The temperature of other bearings is normal, only the temperature of the tilting pad bearing increases, so the influence of oil temperature, oil pressure, oil quality, etc. is excluded.
(4) On-site inspection eliminates the influence of temperature measuring element errors.
2. Reasons that can cause high temperature of tilting pad bearings
(1) The effect of steam leakage from the shaft seal after the medium pressure: this type of steam turbine adopts a high and medium pressure cylinder structure, the rotor length is shortened, the bearing is very close to the shaft seal after the medium pressure, and the amount of steam leakage from the shaft seal after the medium pressure during operation Thermal radiation has a greater impact.
(2) Uneven bearing load distribution. Although the center of the middle-pressure counter-wheel is 0.30mm lower than the center of the low-pressure counter-wheel when the wheel is centered, the upper limit height difference of the design value is reserved, but the temperature of the tilting pad bearing is still high after the unit is put into operation, indicating that the tilting pad The actual load of the bearing is too heavy, and the oil film is easy to rupture, resulting in local dry friction of the bearing bush and journal, which will increase the bearing temperature.
(3) The influence of cylinder heat radiation: the bearing box of the tile is very close to the medium pressure cylinder. The insulation construction at the rear of the medium pressure cylinder is limited by space and location, and the insulation quality is not good, causing the tilting tile bearing box and bearings to be radiated by the cylinder heat. , To increase the temperature of the tilting pad bearing.
(4) The design and installation of the medium-pressure steam seal steam supply pipeline is unreasonable. The distance between the vertical pipe section and the foundation of the tilting tile bearing box is very small. The insulation layer of the pipeline is tightly attached to the foundation. The thickness of the insulation layer is insufficient and the insulation effect is poor. Partially inserted thermal insulation material affects air circulation and heat dissipation. During the operation of the unit, the temperature of the base wall of the tilting-pad bearing box reaches 170°C, causing the foundation to expand due to heat, and the tilting-pad bearing box slowly rises, increasing the load of the tilting-pad bearing. , Causing the temperature of the tilting pad bearing to continue to rise.
(5) Influence of lubricating oil volume: Bearing lubricating oil has the function of lubricating and cooling. If the bearing oil inlet channel is narrow, insufficient oil inlet or poor oil drainage will occur, which will cause the bearing temperature to rise.