Speaking of bearings, it exists in almost every corner of our lives, and most of the mechanical equipment we can think of has its existence, vibrating motors in mobile phones, computer cooling fans, and even shared bicycles, washing machines, airplanes in the sky, ships in the sea... Bearings are required for any rotating part.
This small bearing seems inconspicuous, but it is also an important criterion for measuring a country's scientific and technological and industrial strength, and it is regarded as the "joint of high-end equipment". Like many fields, China has long been the world's largest production and sales base in the field of low-end bearings, but high-end bearings have only recently made a breakthrough.
(A) How harsh the working environment of the bearing is, you may not imagine
Bearings, as the name suggests, is to support the shaft, or the part of the part of the linear motion shaft, its role is to provide support for the rotating body or linear back and forth movement body in the machinery, when other parts produce relative motion on the shaft, the bearing can maintain the center of the shaft and control the movement.
Rolling bearing
Its types are extremely complex, simple to divide, can be divided into two types, rolling bearings and plain bearings. Regardless of the type of bearing, its main function is to support the rotating body in motion. In order to ensure mechanical efficiency and rotation accuracy, the rotating body is required to have a low coefficient of friction during movement, so the smaller the vibration between the shaft and the bearing, the less wear, and the lower the heat, the better.
Taking the rolling bearing as an example, when it starts to run, the bearing inside, the outer ring, the bearing rolling element will be subjected to high frequency, variable stress, the contact area between the rolling element and the ring is very small, and the unit area should be subjected to a lot of pressure, generally up to 1500-5000N/mm2. At the same time, rolling bearings are also subject to centrifugal force, and the centrifugal force will increase with the increase of rotational speed.
Under the action of this high frequency and variable stress, the surface of the ferrule or rolling element is easy to produce stress fatigue, and finally fatigue cracks are generated in the parts with low fatigue strength, forming fatigue spalling, so that the bearing is damaged and failed.
The load and speed at which the bearing is operating are important factors in determining the life of the bearing
In addition to the stress extrusion and friction caused by the high-speed rotation process, bearings that work under special conditions also have special requirements, such as high temperature resistance, low temperature resistance, corrosion resistance and anti-magnetic properties, etc. The working conditions of bearings are very complicated.
Full-section TBM with its main bearing
(2) To create high-end bearings that work under harsh conditions, it is necessary to have good steel
High-end equipment such as high-speed rail, large aircraft, and heavy-duty weapons have the needs for the use of high-end bearings, and to meet the requirements of high-end bearings in terms of accuracy, performance, life and reliability, the high quality and reliability of bearing materials are decisive factors.
Air Force ground crews are maintaining the F110 engine fan bearings for the F15 fighter jet
In the four components of rolling bearings, in addition to the retainer, the inner and outer rings, rolling elements (balls, rollers or rollers) are composed of bearing steel, and the bearing steel is known as the "king of steel" and is the most demanding steel in steel production.
There are also many types of bearing steel, according to the different requirements of use, the chemical composition is not the same, of which high carbon chromium bearing steel accounts for a large proportion, is the most commonly used steel for the manufacture of bearings and bearing parts.
The quality of bearing steel mainly depends on the following four factors: one is the content, form, distribution and size of inclusions in steel; the second is the carbide content, form, distribution and size of steel; the third is the central loose shrink hole and central segregation in steel; and the fourth is the consistency of the performance of bearing steel products. These four factors can be summarized as indicators of purity and uniformity.
Among them, purity requires that there are as few inclusions in the material as possible, and the quality of purity has a direct impact on the fatigue life of the bearing; while uniformity requires that the inclusions and carbide particles in the material be small and dispersed, which will affect the deformation and microstructure uniformity after heat treatment in bearing manufacturing.
Uniform fine carbide structure and evenly distributed fine carbide after heat treatment in high-end bearing steel
To improve the purity of bearing steel, the first thing to do is to control the oxygen content in the steel, steelmaking with ppm (per part of a million) as a unit of oxygen content, in general, 8 ppm steel is a good steel, and high-end bearings need 5 ppm of top steel. In addition, harmful elements such as titanium are easy to form multi-angular inclusions in the steel, which will cause local stress concentration and fatigue cracks, which should also be avoided as much as possible.
At present, with the improvement of the high purity smelting platform system of steel, the purity of bearing steel has been greatly improved, the level of inclusions has been effectively controlled, and the oxygen content in steel in foreign developed countries has been controlled below 5ppm, so the content, distribution, size, etc. of carbides in steel have gradually become the main factors restricting the quality of bearing steel.
(III) With bearing steel, China's bearing technology is one step closer to the world's top level
The demand for bearings in a country and the gross national product always maintain a certain relationship, and the production capacity and level of bearing steel is the key constraint on the development of the bearing industry, therefore, industrial developed countries have always attached great importance to the production, quality and research and development of bearing steel.
In the past, the research and development, manufacturing and sales of high-end bearing steel has been monopolized by the bearing giants in the United States, Sweden and other countries, how to obtain high purity and good uniformity of the top good steel, has been the core technology of these giants secretly, they even purchased low-end materials from China, and finally processed into high-end bearings, and then sold to the Chinese market at dozens of times the price.
Continuous casting machine for the production of continuously cast bearing steel
For a long time, China's bearing steel production is high, but the quality level is low, especially in high-end bearing steel, there is a big gap with the foreign advanced level, there are high content of trace impurities in steel, oxygen content level is two or three times higher than the international advanced level, and the uniformity of carbide forms in steel is poor.
After more than ten years of efforts, China has become a big producer of bearing steel, overcome many difficult problems in the production process of bearing steel, such as the oxygen content is controlled at the world's advanced level of ≤5ppm, and mastered the core technology of its inherent quality control.
In addition, the addition of rare earths in the steelmaking process makes the original high-quality steel more "strong", which is the technical direction to solve the high-end bearing steel, which was originally the core secret of the world's bearing giants, and now it has also been conquered by Chinese researchers, and Chinese scientists have reduced the number of large-size inclusions affecting fatigue life in rare earth bearing steel by 50%.
China's first batch of high-end rare earth bearing steels successfully rolled off the production line
Nowadays, China can not only produce high-end bearing steel, but also break through in the international market, China's bearing steel has been supplied to Sweden, Germany, Japan and other countries, while the fatigue life of high-end bearing steel has reached or even exceeded the same period of Japan and Europe.
With good steel, the next step to be solved is the problem of bearings, high-end bearing research and development involves materials, design, bearing manufacturing equipment, high-precision machining, testing and testing and a series of technical problems, but also need to contact mechanics, lubrication theory, tribology, fatigue and destruction, heat treatment and material organization and other basic research and interdisciplinary support, high-end bearing technology has extreme complexity, mastery is very difficult.
At present, domestic bearings, compared with imported high-end bearings, there is still a certain gap in precision, bearing vibration, noise and sound, reliability, and high-speed performance.
epilogue
High-end bearings, like chips, are the core technologies that China must master, although there is still a lot of distance to catch up, but China has a good industrial foundation in the field of bearings, and in the foreseeable future, it is fully capable of catching up with the world's advanced level.