A large number of experiments have proved that the "ball" in the precision bearing operating at high speed (speed above 4×104r/min) is the weakest part in the bearing, and about 60%-70% of the high-speed bearing failure is caused by the steel ball. Produced by varying degrees of fatigue. Many domestic high-speed bearings have problems such as bearing steel balls with different degrees of fatigue damage. In order to improve the performance of high-speed bearings to prolong their fatigue life, the application of structural ceramics at home and abroad to manufacture spheres or other bearing parts can significantly improve the performance and life of "high-speed bearings". There are many kinds of ceramics, and silicon nitride is not the hardest in industrial ceramics, and the toughness is not the highest. However, in high-performance bearing applications, silicon nitride is considered to have the best mechanical and physical properties. What is this? The important reason is that other ceramics are damaged by catastrophic rupture, while silicon nitride ceramics occur in a manner similar to the failure of bearing steel, ie, partial spalling. Therefore, as a material for rolling bearings, only silicon nitride can be used from the viewpoint of rolling fatigue life and reliability! The characteristics of the silicon nitride bearing material will be briefly analyzed below, and the molding process of the rolling element (silicon nitride ball) will be briefly introduced.
What are the advantages of silicon nitride bearing materials? 1 Smaller density and less centrifugal force - more convenient for high-speed operation. The density of silicon nitride ceramic materials is about 3.2×103kg/m3, while the density of bearing steel is about 7.8×103kg/m3. . The density of silicon nitride ceramics is only about 40% of the density of bearing steel. Therefore, when the rolling element is made of a silicon nitride ceramic, the bearing can effectively suppress an increase in the rolling element load caused by the centrifugal force at a high speed rotation. Therefore, the use of low-density silicon nitride balls is more conducive to the development of high rotational speed of bearings.
2 Heat-resistant - can adapt to higher temperature working conditions When the steel bearing temperature exceeds 120 °C, the hardness will decrease and the rolling life will decrease. For example, the temperature limit of the M50 high-temperature bearing steel is about 400 ° C. At this temperature, the hardness of the steel is greatly reduced, and the silicon nitride completely maintains the original hardness in this temperature range, only at about 800 ° C. Its hardness and strength began to decline. Therefore, silicon nitride materials are very suitable for bearings used in high temperature environments. For example: aviation jet engines, gas turbines, nuclear reactor systems, X-ray tube tungsten disks, and rockets and spacecraft. 3 Linear expansion coefficient is small - can be used in the field of ambient temperature change The linear expansion coefficient of silicon nitride is about 1/4 of that of bearing steel, so the dimensional change of silicon nitride bearing material with temperature changes is small. Anti-lock: Therefore, the bearing prepared by the silicon nitride ceramic material can effectively prevent the bearing material from being "locked" due to dimensional changes caused by temperature changes. This ensures stable operation of the equipment and reduces losses due to equipment failure. 4 Excellent self-lubricating properties Silicon nitride ceramic materials have anti-friction, anti-wear and lubrication functions. Under poor lubrication conditions, such as lean lubrication and oil-free dry friction, they show superior friction reduction. Lubrication performance, with a good emergency state, can effectively avoid the loss caused by sudden equipment failure.
Silicon nitride, the strongest "bearing ball" material
2019 11/04