Aero-bearing is one of the core components of aero-engine, which has the characteristics of high temperature, high speed, large load, complicated stress, harsh working environment and so on. Theoretically, the most direct way to improve the thrust and fuel efficiency of aeroengines at present is to increase the turbine inlet temperature and rotor speed, while increasing the speed on the limit speed performance, temperature resistance, lubricating performance and bearing capacity of aviation bearings are all proposed. More severe requirements.
Although China's bearing industry has developed rapidly for many years, it has become the world's third largest bearing country in terms of bearing production and sales, but the key technical areas need to be strengthened. In particular, the gap between aviation bearing technology and the world's strong bearing countries is relatively obvious It cannot meet the requirements of the rapid development of China's aviation equipment models and the substantial improvement of performance.
The life of international advanced aviation bearing products is generally more than 8 times the calculated life (up to more than 30 times), and the reliability is more than 98%, while the life of China's aviation bearings is generally 3 to 5 times the calculated life, and the reliability is About 96%.
For example, the service life of China's turbine engine main shaft bearings is generally about 500 to 1500 hours, the maximum temperature resistance does not exceed 200 ° C, the transmission device's oil-dry emergency dry operation capacity does not exceed half an hour, and the developed countries can achieve bearing life of 3000 to 6000 hours, the temperature resistance value is 350 ℃, the dry running capacity exceeds one and a half hours, and the actual performance is better than the above indicators. It is precisely because of the lack of high-end bearing technology in China that the domestic aviation bearings, high-speed rail bearings, robot bearings and other high-end bearing fields are basically mainly imported bearings, and there is an urgent need to improve in these key areas. Therefore, under the joint support of the National 863 Program, 973 Program, National Science and Technology Research Program, National Natural Science Foundation and other projects, China HE Bearing Manufacturing Co., Ltd. and a number of materials research institutes jointly carried out the research and Si3N4 silicon nitride ceramic hybrid bearing Industrial application work.
Hybrid ceramic bearing is composed of inner and outer ring bearing steel + silicon nitride ceramic ball + stainless steel retainer, etc. It combines the advantages of both metal and ceramic performance.
According to public information, in the field of bearing applications that require high performance, silicon nitride ceramic balls are considered to have the best comprehensive mechanical and physical properties. Bearing steel balls easily lose their hardness and strength under high temperature environment, and silicon nitride ceramic balls can completely maintain their original hardness at 400 ℃, only when it reaches 800 ℃, its hardness and strength begin to decline significantly. And even if a bearing failure occurs, it also occurs in a manner similar to the failure of the bearing steel ball, that is, local spalling, while other types of ceramic materials are damaged by catastrophic fragmentation. This situation is absolutely not in the field of aviation bearings. Allowed. And the ceramic ball in the bearing has oil-free self-lubricating properties, the friction coefficient is very small, and it can reach a very high speed, which is more than 1.5 times the speed of the general metal bearing, which can meet the needs of the engine to increase thrust and improve combustion efficiency.
Because the ceramic ball can make the bearing run normally even if the lubricating grease dries out, it avoids the premature bearing damage caused by the grease drying out in the ordinary metal bearings, which is extremely suitable for the extreme conditions when the aircraft engine is running. According to public information, it is speculated that the hybrid ceramic bearings may have been initially applied in the field of new turbofan 15 aero engine and transmission in China. In order to improve the long-range effective strike capability of our naval ships, a submarine-launched / ship-launched anti-ship missile proposed design requirements to increase range and speed. The rotor of its bomb turbine must reach a rated speed of more than 120,000 rpm. In the early stage of the project test, when a domestic-made metal aviation bearing was used for the engine operation test, when the test speed reached 40,000 rpm, the bearing quickly became hot and caused smoke to emanate from the surrounding area. After continuing to run for several minutes, the bearing made a strong noise, and then the shaft holding stopped, which seriously affected the development progress of the missile, and had to purchase foreign high-speed aviation bearings through special channels to meet the needs of the missile turbine engine rotor.
After switching to the hybrid ceramic bearing developed by Harbin Institute of Technology in the later period, the bearing passed the five-hour continuous running life assessment at a time. During the test, the bearing had no abnormalities except for the slight smoke generation. After the test, the bearing rotates flexibly without any abnormalities. With the continuous development of China's helicopter engine transmission technology, ceramic rolling element bearings are gradually used in high-speed input ends of transmission systems, clutches, tail drive shafts and tail reducer pitch control levers, planetary gear trains and other parts with their excellent performance. The dry running time of the main reducer is increased from the original half an hour to one hour, which meets the requirements for installation.
China's self-developed hybrid ceramic bearings will formally undertake the supporting requirements for high-performance bearings in the national aerospace field and high-end equipment, becoming the fifth after a few well-known bearing companies in Sweden, Germany, Japan, the United States, etc. The country of ceramic bearings for aerospace.