Analyze the technology of NSK imported bearing high-speed spindle bearings
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1, NSK bearing high-speed spindle bearing development:
Generally, rigid and high-speed angular contact ball bearings are used, in order to meet the high-speed requirements of the Machine Tool spindle. Followed by the use of cylindrical roller bearings.
Under the condition of grease lubrication, the dmN value is below 50×104. After the development of oil-air lubrication, it gradually developed a suitable lubrication system. The dmN value representing the high-speed performance of the spindle bearing (dm is the diameter of the bearing pitch circle mm×N is the rotation speed r/min. The dmN value has reached 100×104 or more. Afterwards, the rolling element has been developed as a ceramic horn. Contact ball bearings achieve a dmN value of 200×104×90. After development of jet lubrication, the dmN value can reach 300×104.
2, high-speed spindle bearing technology:
(1) High-speed angular contact ball bearings:
Single-row, double-row cylindrical roller bearings are inferior to angular contact ball bearings in terms of high-speed performance. Angular contact bearings are bearings with contact angles. Tapered roller bearings can be seen. The greater the contact angle, the better the axial stiffness, but because the gyro slip and spin slip between the ball and the raceway are also large, heat generation also increases. In order to improve the speed performance, the method is to reduce the size (or mass) of the ball to change the curvature coefficient of the channel to reduce the centrifugal force of the ball, reduce the internal load generated during high-speed operation, and increase the number of balls to increase the rigidity.
(2) Ceramic ball angular contact ball bearings:
The hybrid ceramic ball bearing with silicon nitride (Si3N4) ceramics for rolling systems was introduced, in order to reduce the mass of the ball and increase the speed. Its performance is compared
As a high-speed spindle bearing material, ceramic (Si3N4) has the following advantages: The centrifugal force generated by the rolling elements at high speed rotation is small, and the weight is light. Because the density is less than the bearing steel. Rotational torque can be reduced, thus reducing temperature rise and increasing life. The good thermal conductivity makes it difficult for the rolling elements of the ceramic material to stick to the metal at high speeds. With good lubrication conditions, it is resistant to burns and burns. When the thermal expansion is small, the pre-tightening force does not easily increase when the rolling elements come into contact with the inner ring, resulting in reduced play. The deformation of the bearing is small due to its high hardness and good rigidity. The rigidity of the spindle is also improved. In summary, therefore, using ceramic materials (Si3N4) as rolling elements, the speed can be increased by about 25% and 35% compared with the rolling elements of the bearing steel, and the life can be increased by about 3 times.
(3) New Hybrid Angular Contact Ball Bearings:
The inner ring expands due to centrifugal force and rotates at high speed. The contact stress with the rolling body becomes larger, so that the internal preload increases, the clearance becomes smaller, and the heating increases. In response to this problem, a new hybrid ceramic ball bearing with a stainless steel inner ring has recently been developed. Since the coefficient of linear expansion of stainless steel is 20% smaller than that of the bearing steel, it is possible to further control the increase of the preload due to the expansion of the inner ring when the bearing rotates at a high speed. Adequate lubrication conditions, the dmN value can be increased by 1.2 times under fixed preload.
(4) Hybrid angular contact ball bearings with ceramic inner ring:
In the case of positioning preloading, information has recently been introduced. The inner ring also uses hybrid angular contact ball bearings made of ceramic material. Because the inner ring also uses ceramic materials, the bearing inner diameter or the raceway centrifugal expansion is small, the increase of pre-tightening is also small, and the rigidity is good, the contact area of ​​the ball and the raceway is small, so the heat and expansion are also smaller and can be smaller than only the ball. Ceramic bearings reach higher speeds. However, it is precisely because the centrifugal and the expansion are small at the time of high-speed rotation, and if the mating stress with the metal main shaft is too large, it may be damaged or even broken.
2. High speed spindle bearing lubrication:
Because of the ease of use and economical application, the trend of high-speed spindle bearings has placed higher demands on lubrication. Conservative grease lubrication with a dmN value of less than 50×104 is widely used due to its ease of use and economy. It requires no special maintenance and does not require follow-up replenishment. Most of them are lubricated for life. With the increase of the rotating speed, when the dmN value reaches 100×104 or more, it is lubricated with oil and gas and oil mist. Compared with the grease lubrication, the temperature rise is small and can be rotated at a higher speed, thus becoming the main lubrication method. The jet lubrication, although the dmN value can reach 250×104 but requires a lot of lubricating oil, the power loss due to the stirring resistance is large, and the complicated auxiliary equipment is needed, and the interest is higher, so this lubrication method is generally not used.