The wind turbine generator main shaft bearing is one of the core spare parts of the wind generator. Its life span is related to the life span of the whole wind turbine generator unit, and once it fails, replacement is very difficult and costly. At present, spindle bearings of megawatt wind turbines mostly use double-row spherical roller bearings. They also have to bear both axial and radial loads. Their advantage is that they are adaptable to the deflection of the main shaft and do not get stuck.
Whether the lubrication performance of the main shaft bearing of the wind turbine is good or bad is critical to its life. At present, there are mainly two kinds of lubrication methods for main shaft bearings of wind turbines in the market: grease lubrication and lubrication oil lubrication, in which the proportion of grease lubrication is relatively high, and it is applicable to a stand-alone main bearing seat installed on a machine base. Due to the difficult replacement of the grease in the main shaft bearing of the wind turbine, and the operation at extremely low ambient temperatures, the choice of grease is very important. In combination with the above lubrication requirements, the synthetic grease needs to be selected. It must have long life and good low temperature performance, and can provide good lubrication protection for the main shaft bearings of the wind turbine at -40°C.
(1) Composition of grease
Grease is made up of lubricating oil (base oil + additive) and thickening agent. The structure of the thickener is a three-dimensional fiber or granular network structure, with many pores, and the lubricant is flooded in this structure, so the grease can be seen as a sponge full of lubricating oil.
(2) Lubrication principle of grease
When the grease is subjected to external force, the lubricating oil will be released in the load point of the lubrication point, that is, precipitated, and play a role in lubrication; when the external force disappears, some of the precipitated lubricant will be reabsorbed back into the grease. There will also be some remaining in the lubrication point load area. Lubricants in greases that actually act as a lubricant, not the grease itself.
(3) Grease protection of bearings
Lubricating oil can form a thin layer of oil film between the rolling surface and the sliding surface of the bearing to prevent direct contact between metal and metal, thereby reducing the internal friction and wear of the bearing and preventing burn-in. Its main functions include the following: Friction and wear, fatigue life, cooling, sealing, rust prevention, etc.
(4) Grease flow characteristics (gap)
Grooving refers to the tendency of the grease to continuously work in the bearing to form a groove, so that a part of the grease that is not working beside the raceway forms the groove wall of the groove to form an oil pool, and also plays a certain sealing role.
The main shaft bearing works perpendicularly to the ground and has a diameter of 2.3m. The full-speed shaft rotates at 18rpm, so it has a very high line speed of 2.35m/s. During the continuous rotation of the roller, the grease is sheared by the high frequency. The lubricant oil is continuously deposited. The oil forms an oil film in the load surface area of ​​the roller and plays a major role in lubrication. This is the colorless oil film that we have touched; at the same time, the base oil will reduce the ability of grease to adhere to the roller. Under the effect of gravity, the grease on the roller surface will fall off.
Most of the grease in the main shaft bearing is relatively stationary with respect to the main shaft bearing, and the grease is replenished with the grease by the degrease of the grease and a small amount of the grease. In most cases, a certain consistency of grease can create a channeling state in the bearing, which facilitates the sealing of the bearing (greaser groove groove wall) and reduces the temperature rise of the bearing (the precipitated lubricant forms the oil pool) whenever the main bearing roller is used. When passing through the oil sump, the deposited lubricating oil will adhere to the surface of the roller, and the excessive adhesiveness of the grease will increase the bearing temperature rise and power consumption, which is not conducive to bearing lubrication.
The grease that slides down over the bearing is deposited in the lower half of the bearing. Opening the end face baffle at the bottom right of the bearing, the grease will fall into a block. The deposited grease also reflects the channeling characteristics of the grease, which is conducive to the formation of seals and oil pools, providing better lubrication protection for the bearings. 