Managing hybrid spindle bearings

Hybrid spindle bearings are provided with steel races and ceramic balls, typically silicon nitride and are significantly more expensive than all-steel bearings offering advantages in high-speed applications. Si₃N ₄ balls are about 50 percent stiffer than steel balls, which exhibits that the spindle is stiffer, and less heat is generated during stress cycling of the balls. Centrifugal force is proportional to ball density, to the distance from the spindle axis and to the square of the spindle speed. Si ₃N₄ balls are beneficial in high-speed applications because they are about 40 percent less dense than steel balls. Ceramic balls have a lower coefficient of friction on steel races than steel balls. Spindle designers are forced to use expensive measures of controlling preload while allowing thermal expansion of the shaft or providing supplemental cooling to remove the heat, such as chilled oil through the spindle shaft.