One of the reasons for the gap between domestic bearings and imported bearings: the difference in quality of finished bearings

The accuracy of rolling bearings is generally divided into five levels: P0, P6, P5, P4 and P2. The accuracy 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, P4 and above super-precision bearings need to be selected. P4 and above super-precision bearings have very high requirements for technical performance and reliability, accounting for half of domestic demand. All of the above rely on imports.

In recent years, my country's bearing development has continued to progress and has gradually become industrialized. At present, my country accounts for about 10% of the world's bearing market, and its sales volume ranks third in the world. However, compared with the world's leading bearing industry powers, there is still a certain gap in my country's bearing industry. The main manifestation is that the proportion of high-tech, high-precision, and high-value-added products is low, and the stability of the products needs to be further improved.

There are many reasons for the large quality gap between domestic bearings and imported bearings. One of the reasons is: the quality difference of finished bearings.

A large number of tests at home and abroad have shown that the processing quality of cages, ferrules and steel balls has varying degrees of impact on bearing vibration. Among them, the processing quality of steel balls has the most obvious impact on bearing vibration, followed by the processing quality of ferrules, which has the most important impact. The factors are the roundness, waviness, surface roughness, surface bumps, etc. of the steel balls and ferrules.

Double row full complement roller bearing without outer ring

The most prominent problems of my country's steel ball products are the large dispersion of vibration values ​​and serious surface defects (single points, group points, pits, etc.). Although the surface roughness, size, shape, and error are not lower than those outside the circle, the fit is not The vibration value of the rear bearing is high, and even abnormal noise is produced. The main problem is that the waviness is not controlled (no standards, no suitable testing and analysis instruments). It also 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, management level must be improved to avoid random quality problems such as bumps, scratches, and burns.

For ferrules, the most serious effects on bearing vibration are channel waviness and surface roughness. 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 bearing vibration. When the waviness of the inner and outer grooves is greater than 0.7 μm, the bearing vibration value increases with the increase of the waviness, and the grooves are seriously damaged. It can increase the vibration by more than 4dB and even cause abnormal noise.