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Where is the gap between domestic bearings and imported bearings?
keywords: precision bearing, CNC machine tools, machine tool spindles
Bearings are almost everywhere in our life, from small shared bikes on the roadside and household appliances at home to spaceships in the sky and aircraft carriers in the water, all of which cannot exist without bearings.
However, the main bearing applied to high precision machinery is still in a blank in technology in China.
The precision of rolling bearings is generally divided into P0, P6, P5, P4 and P2 five grades. The precision of bearings used in precision machine tool spindles should be P5 and higher.
For CNC machine tools, machining centers and other high-speed, railway, aviation and other high-tech fields, it is necessary to choose P4 and superior ultra-precision bearings, P4 and superior ultra-precision bearings for technical performance and reliability requirements are very high, more than half of the domestic demand are dependent on imports.
The main reasons for the large quality gap between domestic bearings and imported bearings are as follows:
|Bearing quality difference of finished products
At home and abroad a large number of experiments show that keep the frame, ring, steel ball processing quality of bearing vibration with different degree of influence, one of the steel ball processing quality had evident effects on bearing vibration, the second is the ring of the processing quality, is the most important factors affecting the steel ball and ring roundness, surface roughness and surface waviness and knocked wounded, etc.
Steel ball products in China's most prominent problem is discrete vibration value is big, serious surface defect (single points, group, pits, etc.), although the surface roughness, size, shape, error is not lower than outside, but after close set of bearing vibration value is high, and even produce different sound, the main problem is a striation no control (top, without proper test and analysis instrument). At the same time, the vibration resistance of the machine tool is poor, the grinding wheel, grinding plate, coolant, process parameters are problematic; On the other hand, the management level should be improved to avoid random quality problems such as bump, scratch and burn.
For the ring, the most serious factors affecting bearing vibration are channel ripple and surface roughness. For example, when the roundness of inner and outer groove of small and medium-sized deep groove ball bearing is greater than 2μm, the bearing vibration will be significantly affected. When the corrugancy of inner and outer groove is greater than 0.7μm, the bearing vibration value increases with the increase of corrugancy, and the serious knock injury of groove can make the vibration rise more than 4dB, and even appear abnormal sound.
|Production process, talent, etc
1. Industrial technology gap.
The social status of bearing technical workers, and even engineers, is not properly respected (this situation has changed a lot in recent years). The unbalanced development of China's education industry, technical education has not received due attention, resulting in young people prefer to be white-collar idle, rather than work in the production line. At the same time, it also leads to everyone's entrepreneurship in China today, while most small and micro bearing factories and bearing companies do not have high-quality technical personnel, and can only produce some uncompetitive low-end bearing products.
2. The gap in materials.
World steel looks at China, China steel looks at Hebei, but this only refers to crude steel production, which is also in recent years, the world economy has declined, domestic steel overcapacity, steel prices have been depressed one reason. Alloy steel has always been the short board of the domestic iron and steel industry, high-end metallurgical technology is strictly confidential to us by developed countries, coupled with the deficiency of domestic steel enterprises in research and development, resulting in the congenital deficiency of bearings and industrial technology in China.
3, the gap in production technology.
Here, I'll just tell you what I think. Production technology is the most important link in industrial technology, is a cyclic, quantitative change produces qualitative change process. Take machine tools as an example, bearings have a huge impact on the accuracy of machine tools, and the big 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. Gap in production equipment.
Bearing manufacturers and application manufacturers are the relationship between fish and water. Without good bearings, good equipment can not be produced, and high quality bearings can not be processed without reliable machine tools. As far as I know, large machine processing manufacturers purchase basic imported machine tools. And some domestic smaller bearing manufacturers would rather purchase the old machine tool in the last century into bearing processing special machine tools, but also do not want to purchase domestic well-known brand machine tools. There is a price factor as well as a practical one.
5. There are no strong supporters.
In recent years, China's high-speed railway technology has developed rapidly, but high-speed railway bearings are purchased from Schaeffler Group in Germany. Investigate its fundamental reason, under the partial leadership of the northwest bearing plant Schaeffler began to cooperate. However, in the process of cooperation for several years, northwest bearing factory did not get due technical support, but also lost a lot of market share, leading to the decline of northwest bearing today.
Different bearing noise size is different?
Compared with foreign countries, there is a big gap between domestic bearings in high-end and large bearings. The main industries are:
1. Aviation
As the key basic component of aero-engine, the second generation aero-engine 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 United States has developed the second-generation bearing steel for aero-engine, whose representative steel types are CSS-42L, a high strength corrosion resistant bearing steel with 500℃ resistance, and X30 (Cronidur30), a high nitrogen corrosion resistant bearing steel with 350℃ resistance. China is developing the second-generation bearing for aero-engine.
2. Cars
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 bearings are reliability, short payload spacing, easy installation, no adjustment, compact structure and so on. At present, most imported models in China use such lightweight and integrated structure hub bearings.
3. Railway rolling stock
At present, bearings used in China's railway heavy-haul trains are made of domestic electroslag remelting G20CrNi2MoA carburized steel. And foreign has the ultra high purity of bearing steel (EP) steel smelting and vacuum degassing inclusion homogenization technology (IQ) steel, long life steel technology (TF) steel, fine quality, and the heat treatment technology, surface hardening treatment technique and advanced sealing lubrication technology applied to the bearing production and manufacturing, thus greatly enhance the service life of bearing and reliability. The quality of Chinese electroslag bearing steel is not only low, but also the cost is 2000-3000 yuan/ton higher than that of vacuum degassing steel. In the future, China needs to develop vacuum degassing bearing steel with ultra-high purity, fine quality, homogenization and stable quality to replace the current use of electroslag bearing steel.
4. Wind power energy
For wind power bearings, China has not yet been able to produce high technical content of spindle bearings and turbocharger bearings, basically rely on imports, more than 3MW wind turbine supporting bearing localization problem has not been solved. In order to improve the strength, toughness and service life of wind turbine bearings abroad, a new special heat treatment steel SHX (40CrSiMo) is adopted. For yaw and slurry bearings, surface induction hardening heat treatment is used to control the depth of hardened layer, surface hardness, soft band width and surface cracks.
Carbonitriding is used for the speedup bearings and spindle bearings to obtain more stable residual austenite volume fraction (30%-35%) and a large number of fine carbides and carbonitrides on the surface of the parts, which improves the service life of the bearings under the pollution lubrication condition.
| Future domestic bearing improvement direction
The improvement is mainly reflected in four aspects:
1. Cleanliness of bearing steel
Under the premise of considering economy, the cleanliness of steel is further improved, the content of oxygen and titanium in steel is reduced, and the mass fraction 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.
2. Organization refinement and equalization
Through the application of alloying design and controlled rolling and controlled cooling process, the uniformity of inclusions and carbides is further improved, the reticulated 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 1μ m. The grain size of bearing steel is further refined by improving the grain size of matrix structure.
3, reduce low tissue defects
Further reduce the central porosity, central shrinkage cavity and central component segregation in bearing steel, improve the uniformity of low-power structure.
4. Toughness of bearing steel
The toughness of bearing steel was improved by new alloying, hot rolling process optimization and heat treatment process research.
Although domestic bearings and imported bearings have a lot of gap, but through the Chinese people's continuous development of more high-quality bearing products, there will be a lot of excellent bearing enterprises born.
In December 2013, "Yutu" successfully landed on the moon, which has been the dream of China for many years, bearing the painstaking efforts of many Chinese people. In our emotion and excitement at the same time, we can not forget the scientific research personnel and enterprises silently 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 bearings, not on imported bearings, which is very significant.
This means that the gap between domestic bearings and imported bearings is getting smaller and smaller, and domestic technology is getting closer to the high standard of the international level, and even in a leading position in some technologies. For some common machinery, may level requirements for the bearing is not high, but to the requirement of "moon" alive on the moon is very high, need to bear the bad environment of extreme cold pole hot, more flexible, it is really a great for domestic bearing test, but reassuring is entirely up to the domestic bearing, and finish very well.
Although domestic bearings have only developed for several decades, compared with the history of several hundred years in foreign countries, they do not have much advantage, but they can catch up in such a short time. We can only use an idiom to summarize, that is, the waves after the Yangtze River push the waves before.
