Bearings are almost everywhere in our life, from shared bicycles on the side of the road, household appliances at home, to spaceships in the sky, aircraft carriers in the water, all of which can’t exist without bearings. However, the main bearing used in high-precision machinery is still in a blank in technology in China. The accuracy of rolling bearing is generally divided into P0, P6, P5, P4 and P2. The accuracy of bearing used on the spindle of precision machine tool shall be P5 or higher.
For high-speed, railway, aviation and other high-tech fields such as CNC machine tools and machining centers, P4 and above ultra precision bearings are required to be selected. P4 and above ultra precision bearings have high requirements for technical performance and reliability, and more than half of domestic demand depends on SKF,FAG, NSK,NTN,GRW,HQW,TIMKEN Etc.
The main reasons for the large quality gap between China’s bearing and the world’s top bearing are as follows:
1.. Quality difference of bearing finished products
A large number of tests at home and abroad show that: the machining quality of cage, ferrule and ball has different degrees of influence on bearing vibration, of which the machining quality of ball has the most obvious influence on bearing vibration, followed by the machining quality of ferrule, and the main influencing factors are the roundness, waviness, surface roughness, surface bruise, etc. of ball and ferrule.
The most prominent problem of steel ball products in China is that the vibration value is discrete, and the surface defects are serious (single point, group point, pit, etc.). Although the surface roughness, size, shape, and error are not lower than the level outside the circle, the vibration value of the bearing after the sleeve is high and even produces abnormal noise. The main problem is that the waviness is not controlled (no standard, no suitable test and analysis instrument). At the same time, the machine tool’s On the other hand, the management level should be improved to avoid random quality problems such as bump, scratch and burn. For the rings, the most serious influence on bearing vibration is the channel waviness and surface roughness. For example, when the roundness of the inner and outer raceways of medium and small deep groove ball bearings is greater than 2 μm, it will have a significant impact on the bearing vibration. When the waviness of the inner and outer raceways is greater than 0.7 μm, the vibration value of the bearing increases with the increase of the waviness. Serious gouges can increase the vibration by more than 4dB, or even cause abnormal noise.
Distance between production process and talents
- Industrial technology gap.
The social status of bearing technicians and even engineers is not respected as they should be (this situation has changed a lot in recent years). China’s education industry is developing unevenly, and technical education has not been given due attention, which leads to young people prefer to be white-collar workers and not willing to work in the production line. At the same time, it has also led to the entrepreneurship of everyone in China. Most of the small micro bearing factories and bearing companies have no high-quality technical personnel and can only produce some low-end bearing products without competitiveness.
- Material gap.
The world steel looks at China, the Chinese steel looks at Hebei, but this only refers to the crude steel production, which is also a reason why the world economy has declined in recent years, the domestic steel production capacity is over, and the steel price has been depressed. Alloy steel has always been the short plate of domestic steel industry, high-end metallurgical technology is strictly confidential to us in developed countries, coupled with the lack of research and development of domestic steel enterprises, resulting in the congenital shortage of bearing and even industrial technology in China.
- Production process gap.
Here, I will only talk about my own ideas. Production technology is the most important link in industrial technology, which is a process of cyclic, quantitative change and qualitative change. Taking machine tools as an example, bearings have a huge impact on the accuracy of machine tools. The main customer group of high-end precision bearings is machine tool spindle bearings. However, there is a huge gap between the life and accuracy of China precision bearings and world class top quality bearings.
- Production equipment gap.
Bearing manufacturers and application manufacturers are the relationship between fish and water. Without good bearings, no good equipment can be produced, and no reliable machine tool can produce high-quality bearings. As far as I know, most of the large-scale machining manufacturers purchase imported machine tools. However, some smaller domestic bearing manufacturers prefer to purchase the old-fashioned machine tools of the last century to transform them into special machine tools for bearing processing, rather than purchase the machine tools of domestic famous brands. There are price factors and practical factors.
- There are no strong supporters.
In recent years, China’s high-speed rail technology has developed rapidly, but high-speed railway bearings are purchased from Schaeffler Group. The basic reason is that under the control of some leaders, the northwest bearing factory began to cooperate with Schaeffler. However, in the course of several years’ cooperation, the northwest bearing factory has not received the technical support and lost a lot of market share, resulting in the decline of the northwest bearing today.
Blank of high end bearing application
Compared with foreign countries, there is a big gap between domestic bearings in high-end and large-scale bearings. The main industries are:
As a key basic component of aeroengine, the second generation aeroengine bearing with thrust ratio of 15-20 is being developed abroad, which is ready to be assembled into the fifth generation fighter around 2020. In the past 10 years, the second generation of bearing steel for Aeroengine has been developed in the United States. The representative steel types are css-42l bearing steel with high strength and corrosion resistance at 500 ℃ and x30 bearing steel with high nitrogen and rust resistance at 350 ℃ (cronidur30). China is developing the second generation of bearing for aeroengine.
For automobile hub bearings, the first and second generation hub bearings (ball bearings) are widely used in China, while the third generation hub bearings have been widely used in Europe. The main advantages of the third generation hub bearing are reliability, short payload spacing, easy installation, no adjustment, compact structure, etc. At present, most of the imported models in China use this lightweight and integrated structure hub bearing.
- Railway vehicles
At present, the bearings for heavy-duty trains in China are made of domestic electroslag remelting G20 crni2moa carburizing steel, while foreign countries have applied the vacuum degassing smelting technology, inclusion homogenization technology (IQ steel), ultra long life Steel Technology (TF steel), fine heat treatment technology, surface super hardening treatment technology and advanced seal lubrication technology to bearings Therefore, the service life and reliability of the bearing are greatly improved. China’s electroslag bearing steel is not only of low quality, but also has a higher cost of 2000-3000 yuan / ton than the vacuum degassing steel. In the future, China needs to develop ultra-high purity, fine quality, homogenization and stable quality vacuum degassing bearing steel to replace the current electroslag bearing steel.
- Wind power energy
For wind turbine bearings, at present, China is unable to produce spindle bearings and booster bearings with high technology content, which are basically imported. The localization of supporting bearings for wind turbine units above 3MW has not been solved. In order to improve the strength, toughness and service life of wind power bearing, a new type of special heat treatment steel SHX (40crsimo) is used in foreign countries. For yaw and variable slurry bearing, the depth of hardened layer, surface hardness, soft band width and surface crack are controlled by surface induction quenching heat treatment.
For the speed increaser bearing and the main shaft bearing, the use of Carbonitriding makes the surface of the parts get more stable retained austenite volume fraction (30% – 35%) and a large number of fine carbides and carbonitrides, which improves the service life of the bearing under the condition of polluted lubrication.
Improvement direction of China bearings in the future
The improvement is mainly reflected in four aspects:
- Cleanliness of bearing steel
On the premise of economy, the cleanliness of steel is further improved, the content of oxygen and titanium in steel is reduced, the content of oxygen and titanium in bearing steel is less than 6 × 10-6 and 15 × 10-6 respectively, the content and size of inclusions in steel are reduced, and the distribution uniformity is improved.
- Organization refinement and equalization
Through the application of alloying design and controlled rolling and controlled cooling process, the homogeneity of inclusions and carbides can be further improved, the network and ribbon carbides can be reduced and eliminated, the average size and maximum particle size can be reduced, and the average size of carbides can be less than 1 μ m; the grain size of matrix structure can be further improved, and the grain size of bearing steel can be further refined.
- Reduce macrostructure defects
Furthermore, the center porosity, center shrinkage and center component segregation in bearing steel are further reduced, and the uniformity of low power structure is improved.
- Toughness of bearing steel
The toughness of bearing steel is improved through the study of new alloying, hot rolling process optimization and heat treatment process.
Although domestic bearings and imported bearings have many gaps, but after the continuous development of the Chinese people are sure to develop more high-quality bearing products, there will be many excellent bearing enterprises.
In December 2013, “Jade Rabbit” successfully landed on the moon, which is the dream of China for many years and carries the painstaking efforts of many Chinese people. While we are feeling and excited, we can not forget the scientific researchers and enterprises who are quietly dedicated to the development of national science and technology. We may not know that the successful development and operation of the “Jade Rabbit” depends on our domestic Luoyang bearing, not imported bearing, which is of great significance. This means that the gap between domestic and imported bearings is becoming smaller and smaller, and the domestic technology is getting closer to the international high standard level, even in some technologies, it is still in a leading position. For some ordinary machines, the level of bearing may not be high, but the requirement for “Yutu” to jump on the moon is very high, it needs to bear the extremely cold and hot environment, and it also needs to operate flexibly, which is really a great test for domestic bearings, but it is gratifying that the domestic bearings are fully competent and completed very well Color. Although domestic bearings have only developed for several decades and have little advantage over foreign ones in the history of hundreds of years, they can catch up with each other in such a short time. We can only use one idiom to summarize, that is, the waves behind the Yangtze River push the waves ahead.