First, the rolling bearing is composed of a ring, a rolling body and a retainer.
Because the contact point between the ferrule and the rolling element is subject to external load and rotation, contact pressure and deformation are repeatedly generated.
Due to the material characteristics of steel bearings, the main form of bearing failure is fatigue spalling, short fatigue life, and the application range is greatly limited. Ceramic materials (Si3N4) have the advantages of low density, medium elastic modulus, small thermal expansion coefficient, high hardness, high temperature resistance, corrosion resistance, non-magnetism, etc. Ceramic ball bearings with silicon nitride ceramic balls as rolling elements can significantly improve the bearings The contact fatigue life has greatly expanded the application field of rolling bearings, and has been widely used in various high-precision, high-speed machine tools, automobiles, racing cars, subways, motors, aero engines, petrochemical machinery, metallurgical machinery and other fields. At present, silicon nitride ceramic balls and ceramic ball bearings have begun to enter the stage of mass production, especially in high-speed precision spindle bearings for machine tools and high-temperature and corrosion-resistant bearings and other fields with broad application prospects.
Second, the performance of silicon nitride ceramic materials 1. Low density: Due to the low density of the ceramic rolling body material and the small centrifugal load, it can work at higher speeds and generate less heat.
2. Medium elastic modulus: The elastic modulus of the ceramic rolling element is higher than that of the steel rolling element, the dynamic stiffness of the bearing will be increased, but the too large elastic modulus will reduce the bearing capacity of the bearing due to stress concentration.
3. Low coefficient of thermal expansion: A small coefficient of thermal expansion helps reduce sensitivity to temperature changes, thereby preventing seizures. For hybrid roller bearings, the applicable operating speed range is wider.
4. High compressive strength: High compressive strength is required for rolling bearings to withstand high contact stress (for ceramic materials, its strength is usually determined by the modulus of rupture measured by a three-point or four-point bending test).
5. High hardness and high toughness: The combination of these two characteristics can obtain better surface roughness, and can prevent damage from external hard particles and impact.
6. Good anti-rolling contact fatigue characteristics: This performance is very important for the requirements of bearing rolling elements.
7. Flaking failure form: If the rolling element fails during work, it should be fatigue spalling. This effective form has an omen before it dies. It is a practical form that causes the least harm. In some application areas where the application conditions are relatively high, ceramic materials also have some special properties.
8. High temperature resistance and stability: It can stably maintain its mechanical properties in high temperature environment up to 800 ℃.
9. Corrosion resistance: In the oxidation and corrosive environment, especially in the contact area where the surface oil film is squeezed out after repeated rolling, it should have oxidation resistance and corrosion stability.