The rotation speed of the machine tool spindle bearing is mainly limited by the temperature rise caused by the internal friction and heating of the bearing. When the rotation speed exceeds a certain limit value, the bearing will sinter due to the continuous increase in temperature and cannot continue to be used. The limit speed of the bearing is the limit value of the speed when the bearing reaches the highest thermal equilibrium temperature that the bearing can withstand under certain working conditions. The limit speed of high-speed machine tool spindle bearings is related to the contact angle, tolerance level, working status, lubrication method, assembly type, preload, and material type of the bearing. One: For high-speed machine tool spindle bearings with a contact angle of 25°, the limit speed is about 90% of that of the same structure with a contact angle of 15°. Two: Tolerance class The tolerance of high-speed machine tool spindle bearings is generally P4. If the limit speed of the bearing under this accuracy is nm, the limit speed of the P4A and P2 bearings is about 1.1 nm, and the P5 bearing is about 0.9 nm. 3: Working state High-speed machine tool spindle bearings generally have inner ring rotating and outer ring fixed. If the limit speed of the bearing is nm at this time, when the outer ring rotates and the inner ring is fixed, the limit speed of the bearing is about 0.6 nm. Four: Lubrication methods Different lubrication methods also have a greater impact on the limiting speed of the bearing. Table 2 shows the limiting speed coefficient of the bearing under different lubrication conditions. Five: Assemble type and preload 　 Assemble type and preload have influence coefficient on bearing limit speed as shown in Table 3. Table 2 　Limit speed coefficient of bearing under different lubrication conditions Lubrication method Speed u200bu200bcoefficient Grease lubrication 0.7 Oil mist lubrication 1.0 Oil-air lubrication 1.0 Oil injection lubrication 1.2 　　　　 Table 3 　 The limiting speed when the combination type and preload are different Coefficient combination type preload light medium heavy DB 0.85 0.75 0.60TBT 0.75 0.60 0.40QBC 0.70 0.50 0.25QBT 0.70 0.50 0.25