The rotational speed of the spindle bearing of the machine tool is mainly limited by the temperature rise caused by the friction and heat inside the bearing. When the rotational speed exceeds a certain limit value, the bearing will sinter due to the rising temperature, so that it cannot be used continuously. 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 bear under certain working conditions. The limit speed of the spindle bearing of high-speed machine tools is related to the contact angle, tolerance level, working state, lubrication method, assembly type, preload and material type of the bearing. One: The contact angle of the high-speed machine tool spindle bearing with a contact angle of 25 is about 90% of that of the bearing with a contact angle of 15 with the same structure. 2: Tolerance grade The tolerance of high-speed machine tool spindle bearings is generally P4 grade. If the limit speed of the bearing under this precision is nm, the limit speed of the P4A and P2 grade bearings is about 1.1 nm, and the P5 grade bearing is about 0.9 nm. 3. Main shaft bearings of high-speed machine tools in working state generally rotate the inner ring and fix the outer ring. 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. 4. Lubrication method Different lubrication methods have a great influence on the limit speed of the bearing. Table 2 shows the limit speed coefficient of the bearing under different lubrication conditions. Five: Assembly type and preload The influence coefficient of assembly type and preload on the bearing limit speed is shown in Table 3. Table 2 Limiting speed coefficient of bearing under different lubrication conditions Lubricating mode Speed u200bu200bcoefficient grease lubrication 0.7 Oil mist lubrication 1.0 Oil-air lubrication 1.0 Oil spray lubrication 1.2 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