Angular contact ball bearing manufacturers understand that the performance of the high-speed spindle of CNC metal cutting machine tools depends on the spindle bearing and its lubrication to a considerable extent. Machine tool bearings my country’s bearing industry is developing rapidly, bearing varieties from small to large, product quality and technical level from low to high, industry scale from small to large, and a professional production system with basically complete product categories and a more reasonable production layout has been formed. The tolerances of spindle bearings are limited. They are particularly suitable for bearing arrangements that require very high steering accuracy and speed capabilities. They are particularly suitable for the bearing arrangement of the shafts of machine tools. Because of its good rigidity, high precision, high load-bearing capacity and relatively simple structure, rolling bearings are not only used for spindles of general cutting machine tools, but also favored by high-speed cutting machine tools. From the perspective of high speed, angular contact ball bearings in rolling bearings, cylindrical roller bearings are the second, and tapered roller bearings are the worst.
The ball (that is, the ball) of the angular contact ball bearing revolves and rotates, and it generates centrifugal force Fc and gyro torque Mg. With the increase of the spindle speed, the centrifugal force Fc and the gyro torque Mg will also increase sharply, which will cause the bearing to produce a large contact stress, which will lead to increased friction of the bearing, increased temperature rise, decreased accuracy and shortened life. Therefore, in order to improve the high-speed performance of this bearing, every effort should be made to suppress the increase of its Fc and Mg. From the calculation formula of angular contact ball bearings Fc and Mg, it is known that reducing the density of the ball material, the diameter of the ball and the contact angle of the ball are beneficial to reduce the Fc and Mg, so now high-speed spindles often use contact angles of 15° or 20° Of small ball diameter bearings. However, the ball diameter cannot be reduced too much. Basically, it can only be 70% of the standard series ball diameter, so as not to weaken the rigidity of the bearing. The more important thing is to seek improvement in the material of the ball.
Compared with GCr15 bearing steel, the density of silicon nitride (Si3N4) ceramics is only 41% of its density. The ball made of silicon nitride is much lighter. Naturally, the centrifugal force and gyro torque generated during high-speed rotation are also small. many. At the same time, the elastic modulus and hardness of silicon nitride ceramics are 1.5 times and 2.3 times that of bearing steel, and the coefficient of thermal expansion is only 25% of bearing steel, which can improve the stiffness and life of the bearing, but also The matching clearance of the bearing changes little under different temperature rise conditions, and the work is reliable. In addition, the ceramic is resistant to high temperatures and does not stick to the metal. Obviously, the sphere made of silicon nitride ceramic is more suitable for high-speed rotation. Practice has shown that ceramic ball angular contact ball bearings can increase the speed by 25%~35% compared with the corresponding steel ball bearings, but the price is higher.
In foreign countries, bearings with steel inner and outer rings and ceramic rolling elements are collectively referred to as hybrid bearings. At present, hybrid bearings have new developments: one is that ceramic materials have been used to make the rollers of cylindrical roller bearings, and ceramic cylindrical hybrid bearings have appeared on the market; the other is to use stainless steel instead of bearing steel to make the inner and outer rings of the bearing, especially the inner ring. Since the coefficient of thermal expansion of stainless steel is 20% smaller than that of bearing steel, naturally, the increase in contact stress caused by the thermal expansion of the inner ring will be suppressed during high-speed rotation.
Post time: Apr-15-2021
