On the independent safety and controllability of my country's major technical equipment bearings (3) - CNC machine tool bearings

3 CNC Machine Tool Bearings 3.1 CNC Machine Tool Bearing System CNC machine tool bearings include high-speed spindle-bearing system (including motorized spindle bearings, dynamic and static pressure bearings), linear guide bearings, ball screws and other functional components (Figure 5-Figure 7). 1-sheath; 2-front compression ring; 3-front bearing; 4-bearing seat; 5-rear bearing; 6-rear locking nut; 7-rear end cover; 8-drive pulley; 9-pulley Lock nut; 10- encoder pulley; 11- rear set nut; 12- rear gland; 13- rear compression ring; 14- rear adjustment ring; 15- front set nut; 16- angular contact bearing set ;17-Front adjusting ring;18-Spindle. Fig.5 Typical machine tool spindle-bearing systemFig.5 Typical machine tool spindle-bearing systemFig.6 Typical structure diagram of high speed motorized spindle-bearing systemFig.6 Typical structure diagram of high speed motorized spindle-bearing systemFig.7 Ball screw and Linear guide bearings Fig.7 Ball screws and linear guide bearings3.2 Bearing types and their diagrams are shown in Figure 8. Pair or multi-group angular contact ball bearings are shown in Figure 8, and a certain preload must be applied during application and installation. Selecting an appropriate preload can improve the rigidity of the spindle system, reduce the temperature rise, and improve the machining accuracy of the system. The bearing preload is usually divided into three grades: light (A), medium (B), and heavy (C), which can be selected by the user according to the actual working conditions of the spindle system. The structure of single and double row cylindrical roller bearings is shown in Figure 9. Two-way thrust angular contact ball bearings are shown in Figure 10, and usually require SP grade tolerances, and UP grade tolerances can also be required if necessary. Fig.8 Matched angular contact ball bearing sets for machinetool spindlesFig.8 Matched angular contact ball bearing sets for machinetool spindlesFig.9 Single and double row cylindrical roller bearingsFig.9 Single and double row cylindrical roller bearingsFig.10 Bidirectional thrust angle Contact ball bearing Fig.10 Bidirectional thrust angular contact ball bearing3.3 Key technical indicators 1) Accuracy class P2 or P4; 2) Accuracy life up to 30 000 h; 3) Temperature rise less than 20 ℃; 4) Stable improvement in high-speed performance, dmn The value will reach 3.0 × 106 mm r/min in 2020 and 4.0 × 106 mm r/min in 2025; 5) The mean time between failure (MTBF) is increased from 500 h to 2 000 h; 6) Silicon nitride ceramic ball bearings adopt After hot isostatic pressing, the bending strength is not less than 900 MPa, the Weibull modulus is not less than 12, the porosity is not more than 0.02%, the crushing load is not less than 50%, and the accuracy level is higher than the requirements of G5. 3.4 Market Analysis There are nearly 100 enterprises producing machine tool bearings in my country's bearing industry, and more than 20 enterprises above designated size. At present, domestic machine tool bearings are mainly used in the maintenance market, and are mainly used in low-end machine tools. Most of the precision bearings used in high-end CNC machine tools rely on imports, and this market is monopolized by foreign companies such as NTN, NSK, and SKF. According to the statistics of the National Bureau of Statistics and China Machine Tool Association, a total of 420x104 metal cutting machine tools were produced nationwide in 2019. There are many types of machine tool bearings. Here, only the spindle bearings and wire bearings with high technical content and wide application are representative. Take the screw bearing as an example to analyze the market capacity: each machine tool needs to be equipped with 4~6 sets of main shaft bearings and 4~8 sets of screw bearings, then a total of 252 × 104 sets of main shaft bearings and 336 × 104 sets of screw bearings are required for new machine tools every year. ;According to the depreciation period of the machine tool is 8 years, the service life of the main shaft bearing is 0.5 years, and the service life of the screw bearing is 2 years, 3 528 × 104 sets of main shaft bearings and 1 176 × 104 sets of screw bearings are required; comprehensive consideration of new machine tools According to the needs of the market and maintenance market, the market size of domestic machine tool bearings is about 4 500x104 sets each year, and the sales volume is about 6 billion to 10 billion yuan. 3.5 Independence At present, due to the large gap between the accuracy retention and the mean time between failures of domestic bearings and foreign products, the cost of bearings accounts for a small proportion of the cost of machine tools, and machine tool enterprises lack the pressure and power of localization. Users do not recognize domestic bearing brands and require foreign brand bearings to be configured in machine tool manufacturing, so that all bearings of high-end CNC machine tools and most of the bearings of mid-range CNC machine tools still rely on imports. Therefore, we need to integrate the fragmented research and development achievements of the bearing industry on CNC machine tool bearings for decades, and on this basis, combine production, education and research, increase research and development and engineering efforts, and strive to make bearings in a relatively short time. Performance, life and reliability, especially precision retention and mean time between failures have reached the international advanced level. (References omitted) Source: 'Bearing' 2022-1 issue (excerpt)