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Analysis of domestic and imported bearing technology and application gap

2019-12-09

Bearing applied in industrial production in our country plays an important role, for bearing production, while bearing industry of our country has been in the world of economy of scale bearing total third, but the accuracy on technology and products and imported bearing has very big disparity, small make up to analyze the technology and application on what distance...




The quality difference of domestic bearing


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 of machine tool vibration resistance is poor, grinding wheel, grinding disc, cooling liquid, the process parameters all problems; On the other hand, management level should be improved to avoid accidental quality problems such as knock, scratch and burn.


For the ring, it is the channel waviness and surface roughness that affect the bearing vibration most seriously. For example, when the roundness of internal and external grooves of small and medium-sized deep groove ball bearings is greater than 2 ° m, the bearing vibration will be significantly affected. When the corrugation of internal and external grooves is greater than 0.7 ° m, the bearing vibration value will increase with the increase of corrugation.




Bearing industry caused by the gap in many aspects


1. Material gap.


The world steel looks at China, China steel looks at hebei, but this only refers to crude steel production, which is why the world economic downturn in recent years, domestic steel overcapacity, steel prices have been depressed for a generation. Alloy steel has always been the short board of the domestic steel industry, the high-end metallurgical technology is developed countries to us strictly confidential, plus the domestic steel enterprise research and development deficiencies, resulting in China's bearing and industrial technology congenital deficiencies. The gap in industrial technology.


2. Production equipment gap.


Bearing manufacturers and application manufacturers is the relationship between fish and water. Without good bearings, the production of good equipment, no reliable machine can not produce high-quality bearings. As far as I know, the major machine manufacturers are basically imported machine tools. And the bearing manufacturer of a few lesser strength of the home would rather buy the old machine tool of last century to transform into bearing processing special machine tool, also do not wish to buy the machine tool of domestic well-known brand. There is a price factor as well as a practical one.


3. The gap of production technology.


Here, I just want to share my thoughts. The production technology is the most important link in the industrial technology, is a cycle to and fro, the quantity change produces the quality change process. Taking machine tools as an example, bearing has a great impact on the accuracy of machine tools, and the large customer group of high-end precision bearing is machine tool spindle bearing. However, there is a huge gap between the life and precision of domestic and foreign precision bearings.


4. Gaps in industrial technology.


The status of skilled workers, and even engineers, is not respected (much has changed in recent years). The development of China's education industry is not balanced, and technical education has not received due attention. As a result, young people prefer to do white-collar jobs and do nothing but work in the production line. At the same time, it has also led to the fact that everyone is starting his own business in China. However, most small micro-bearing factories and bearing companies have no high-quality technical personnel and can only produce some uncompetitive low-end bearing products. Production equipment gap.




High end bearing application blank


Compared with foreign countries, domestic bearings have a big gap in high-end and large bearings, the main industries are:


(1) automobile


For automotive hub bearings, China is currently widely used in the first and second generation of hub bearings (ball bearings), while Europe has widely adopted the third generation of hub bearings. The main advantages of the third generation of hub bearings are reliability, short payload spacing, ease of installation, no adjustment, and compact structure. At present, most models introduced in China adopt such lightweight and integrated structure hub bearing.


(2) railway rolling stock


At present, China railway heavy-duty train bearing adopt domestic esr G20CrNi2MoA carburizing steel manufacturing, 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. Chinese electroslag bearing steel is not only of low quality, but also costs 2000-3000 yuan/ton more than vacuum degassified steel. In the future, China needs to develop ultra-high purity, fine quality, homogenization and stable quality vacuum degassified bearing steel to replace the current electroslag bearing steel.


(3) aviation


As a key basic component of the aero engine, the 2nd generation aero engine bearing with a thrust ratio of 15-20 is being developed abroad and is ready to be assembled into the 5th generation aircraft around 2020. In the past 10 years, the United States has developed the bearing steel for the 2nd generation aeroengine. The representative steel is css-42l, a high-strength corrosion-resistant bearing steel resistant to 500℃, and X30 (Cronidur30), a high-nitrogen stainless bearing steel resistant to 350℃. China is developing the bearing for the 2nd generation aeroengine.


(4) wind power energy


As for wind power bearing, China is still unable to produce spindle bearing and speeder bearing with high technical content, and basically relies on imports. The problem of localization of supporting bearing for wind power units above 3MW has not been solved. In order to improve the strength, toughness and service life of wind power bearings, a new type of special heat-treated steel SHX (40CrSiMo) is adopted in foreign countries. For yaw and variable slurry bearings, the depth of hardened layer, surface hardness, width of soft belt and surface crack are controlled by surface induction quenching heat treatment.




For the speed-increaser bearing and the spindle bearing, carbonitriding is adopted, so that more stable residual austenite volume fraction (30%-35%) and a large number of fine carbides and carbonitrides can be obtained on the surface of the parts, which improves the service life of the bearing under the condition of polluted lubrication.


Future direction of home-made bearing improvement


The improvement is mainly reflected in the following four aspects:


(1) economic cleanliness


On the premise of considering economy, further improve the cleanliness of steel, reduce the content of oxygen and titanium in steel, and achieve the mass fraction of oxygen and titanium in bearing steel is less than 6×10-6 and 15×10-6 respectively, reduce the content and size of inclusions in steel, and improve the distribution uniformity.


(2) organization refinement and balance


Through alloying design and application of controlled rolling and controlled cooling process, the uniformity of inclusions and carbides is further improved, mesh 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 1 cm. The grain size of bearing steel is further refined by increasing the grain size of matrix.


(3) reduce low-fold tissue defects


Further reduce the center porosity, center shrinkage and center component segregation in bearing steel, and improve the uniformity of low-fold structure.


(4) high toughness of bearing steel


The toughness of bearing steel was improved through the study of new alloying, hot rolling and heat treatment.