Bearings are almost everywhere in our lives, ranging from shared bicycles on the side of the road, household appliances at home, to spaceships in the sky, and aircraft carriers launched into the water, all of which cannot exist without bearings.
However, the main bearing used in high-precision machinery is still in a blank in our country.
The precision of rolling bearings is generally divided into five grades: P0, P6, P5, P4 and P2. The precision of bearings used on precision machine tool spindles should be P5 and above. For CNC machine tools, machining centers and other high-speed, railway, aviation and other high-tech fields, it is necessary to use P4 and above ultra-precision bearings. P4 and above ultra-precision bearings have high requirements for technical performance and reliability, half of the domestic demand All of the above are dependent on imports.
Video: Experts analyze the gap between domestic and foreign bearings
As a result, there is a large quality gap between domestic bearings and imported bearings. The main reasons are as follows:
Differences in quality of finished bearings
A large number of tests at home and abroad have shown that the processing quality of cages, rings, and steel balls have varying degrees of influence on bearing vibration, among which the processing quality of steel balls has the most obvious impact on bearing vibration, followed by the processing quality of rings, the most important influence Factors are the roundness, waviness, surface roughness, surface bumps, etc. of steel balls and ferrules.
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The most prominent problem of my country's steel ball products is the large dispersion of vibration values and serious surface defects (single point, group point, pit, etc.). Although the surface roughness, size, shape, and error are not lower than the level outside the circle, the combination The vibration value of the rear bearing is high, and even produces abnormal sound. The main problem is that the waviness is not controlled (no standard, no suitable test and analysis instrument). At the same time, it shows that the vibration resistance of the machine tool is poor, and there are problems with the grinding wheel, grinding disc, coolant, and process parameters. ; On the other hand, it is necessary to improve the management level to avoid random quality problems such as bumps, scratches, and burns.
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For the ring, the channel waviness and surface roughness are the most serious factors that affect the vibration of the bearing. For example, when the roundness of the inner and outer grooves of small and medium-sized deep groove ball bearings is greater than 2 μm, it will have a significant impact on the vibration of the bearing. It can increase the vibration by more than 4dB, and even produce abnormal sound.
Production process, talents, etc. widen the distance
1. The gap in industrial technology. The social status of bearing technical workers and even engineers is not respected as it should be (this situation has changed a lot in recent years). The development of my country's education industry is unbalanced, and technical education has not received due attention. As a result, young people would rather be white-collar workers with nothing to do than work on the production line. At the same time, it has also led to everyone starting a business in China today, and most small and micro bearing factories and bearing companies do not have high-quality technical personnel, so they can only produce some uncompetitive low-end bearing products.
2. The gap in material. The world's steel depends on China, and China's steel depends on Hebei, but this only refers to the output of crude steel. This is also one of the reasons why the world economy has declined in recent years, domestic steel production capacity has been excessive, and steel prices have been sluggish. Alloy steel has always been the shortcoming of the domestic steel industry, and the high-end metallurgical technology is strictly kept secret by developed countries. In addition, the lack of research and development of domestic steel enterprises has caused the congenital deficiency of bearings and even industrial technology in our country.
3. The gap in the production process. Here, I just tell my thoughts. The production process is the most important link in industrial technology. It is a process in which quantitative changes produce qualitative changes. Taking machine tools as an example, bearings have a huge impact on the accuracy of machine tools. The major customer group of high-end precision bearings is machine tool spindle bearings. However, there is a huge gap between the life and precision of domestic precision bearings and foreign bearings.
4. Production equipment gap. Bearing manufacturers and application manufacturers are the relationship between fish and water. Without good bearings, good equipment cannot be produced, and high-quality bearings cannot be processed without reliable machine tools. As far as I know, large-scale machining manufacturers basically purchase imported machine tools. However, some smaller domestic bearing manufacturers would rather purchase old-fashioned machine tools from the last century and transform them into special machine tools for bearing processing than purchase machine tools of well-known domestic brands. There are price factors as well as practical factors.
5. No strong supporters. In recent years, my country's high-speed rail technology has developed rapidly, but high-speed rail bearings are purchased from Schaeffler Group in Germany. The fundamental reason is that under the control of some leaders, Schaeffler, the Northwest Bearing Factory, began to cooperate. However, during several years of cooperation, Northwest Bearing Factory did not receive proper technical support and lost a large amount of market share, leading to the decline of Northwest Bearing today.
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Blanks for high-end bearing applications
Compared with foreign countries, there is a big gap between domestic bearings in high-end and large bearings. The main industries are:
01
aviation
As a key basic component of aero-engines, foreign countries are developing second-generation aero-engine bearings with a thrust ratio of 15-20, which will be assembled into fifth-generation fighters around 2020. In the past 10 years, the United States has developed the second-generation bearing steel for aero-engines. The representative steel types are high-strength corrosion-resistant bearing steel CSS-42L resistant to 500°C and high-nitrogen stainless bearing steel X30 (Cronidur30) resistant to 350°C. China The research and development of bearings for second-generation aero-engines is underway.
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02
car
For automobile wheel bearings, the first and second generation wheel bearings (ball bearings) are widely used in China, while the third generation wheel bearings have been widely used in Europe. The main advantages of the 3rd generation hub bearings are reliability, short payload distance, easy installation, no need for adjustment, compact structure, etc. At present, most of the models imported from China use this lightweight and integrated structure hub bearing.
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03
railway vehicles
At present, bearings for heavy-duty trains in China's railways are made of domestically produced electroslag remelting G20CrNi2MoA carburizing steel, while foreign countries have adopted the vacuum degassing smelting technology of ultra-high-purity bearing steel (EP steel) and the technology of homogenizing inclusions (IQ steel) , ultra-long-life steel technology (TF steel), fine-grained heat treatment technology, surface superhardening treatment technology and advanced sealing lubrication technology are applied to the production and manufacture of bearings, thus greatly improving the life and reliability of bearings. China's electroslag bearing steel is not only low in quality, but also costs 2,000-3,000 yuan/ton higher than vacuum degassed steel. Electroslag bearing steel used.
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Wind energy
As for wind power bearings, China is currently unable to produce high-tech main shaft bearings and speed reducer bearings, basically relying on imports, and the localization of supporting bearings for wind turbines above 3MW has not yet been resolved. In order to improve the strength, toughness and service life of wind power bearings abroad, a new type of special heat treatment steel SHX (40CrSiMo) is adopted. For yaw and pitch bearings, the depth of hardened layer, surface hardness, soft belt width and surface cracks.
Carbonitriding is used for speed reducer bearings and spindle bearings, so that the surface of the parts can get more stable residual austenite volume fraction (30%-35%) and a large number of fine carbides and carbonitrides, which improves the bearing's resistance to pollution and lubrication. Service life under working conditions.
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Improvement direction of domestic bearings in the future
Mainly reflected in four aspects of improvement:
01. Bearing steel cleanliness
Under the premise of considering the economy, further improve the cleanliness of the steel, reduce the content of oxygen and titanium in the steel, and reach the level that the mass fractions of oxygen and titanium in the bearing steel are less than 6×10-6 and 15×10-6 respectively , reduce the content and size of inclusions in steel, and improve the uniformity of distribution.
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02 Organization refinement and balance
Through the application of alloying design and controlled rolling and controlled cooling process, the uniformity of inclusions and carbides is further improved, the network and banded carbides are reduced and eliminated, the average size and maximum particle size are reduced, and the average size of carbides is less than The goal of 1μm; further increase the grain size of the matrix structure, so that the grain size of the bearing steel is further refined.
03 Reduce low-magnification tissue defects
Further reduce the central porosity, central shrinkage cavity and central component segregation in the bearing steel, and improve the uniformity of the low-magnification structure.
04. Toughness of bearing steel
Through new alloying, hot rolling process optimization and heat treatment process research, the toughness of bearing steel is improved.
