The performance of CNC high-speed spindles for CNC cutting machines depends to a large extent on the spindle bearings and their lubrication. Rolling bearings are not only the first choice for general cutting machine spindles, but also favored by high-speed cutting machine tools because of their high rigidity, high precision, high load carrying capacity and relatively simple structure. From the perspective of high speed, the angular contact ball bearings in the rolling bearings are the best, the cylindrical roller bearings are the second, and the tapered high speed bearing are the worst.
The ball of the angular contact ball bearing (ie, the ball) revolves and rotates, and generates a centrifugal force Fc and a gyro moment Mg. As the spindle speed increases, the centrifugal force Fc and the gyro moment Mg also increase sharply, causing the bearing to generate a large contact stress, resulting in increased bearing friction, increased temperature rise, reduced accuracy, and reduced life. Therefore, in order to improve the high-speed performance of such bearings, efforts should be made to suppress the increase in 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 all beneficial to reduce Fc and Mg, so now the high-speed spindle uses a contact angle of 15° or 20°. Small ball diameter bearings. However, the ball diameter can not be reduced too much, basically only 70% of the standard series ball diameter, so as not to weaken the rigidity of the bearing, it is more important to seek improvement on the ball material.
Compared with GCr15 bearing steel, the density of tantalum nitride (Si3N4) ceramic is only 41%. The ball made of tantalum nitride is much lighter. Naturally, the centrifugal force and gyro moment generated during high-speed rotation are also small. many. At the same time, the elastic modulus and hardness of tantalum nitride ceramics are 1.5 times and 2.3 times that of bearing steel, and the thermal expansion coefficient is only 25% of bearing steel, which can improve the rigidity and life of the bearing, and make the bearing fit. The gap has small change under different temperature rise conditions, and the work is reliable. In addition, the ceramic is resistant to high temperature and does not bite with the metal. It is obvious that the ball made of tantalum nitride ceramic is more suitable for high-speed rotation. Practice has shown that the ceramic ball angular contact ball bearing can increase the speed by 25%~35% compared with the corresponding steel ball bearing, but the price is also higher.