Application of silicon nitride ceramics in new energy vehicles

Bearings are the soul of all rotating machinery and are known as the "chip" of the machinery industry. Their main function is to support the rotating body of the machine, reduce the friction coefficient during its movement, and ensure its rotation accuracy. The density of silicon nitride material is about 42% of that of bearing steel, the elastic modulus is as high as 320GPa, the tensile strength is 1600MPa, the compressive strength is as high as 3600MPa, and the mechanical properties are almost unchanged below 900℃, so it is one of the ideal materials for rolling elements of rolling bearings. At present, bearings with silicon nitride balls as rolling elements are the most popular, most performance-oriented and most widely used high-end ceramic bearings in the world.

① Compared with traditional bearings, motor bearings have a higher rotation speed and require materials with lower density and relatively higher wear resistance;

② Since the alternating current of the motor causes changes in the surrounding electromagnetic field, better insulation is needed to reduce the electrical corrosion caused by bearing discharge;

③ The surface of the bearing ball is required to be smoother and less worn. Ceramic balls have the characteristics of low density, high hardness, and friction resistance, and are suitable for high-speed rotation conditions. Ceramic balls are irreplaceable in the fields of high temperature, strong magnetism, and high vacuum.

At present, in the field of new energy vehicles, it is a trend for ceramic bearings to replace steel ball bearings. For example, the output shaft of the motor used by Tesla uses ceramic bearings, hybrid ceramic bearings designed by NSK, and the bearing balls are composed of 50 silicon nitride balls; the two rotor bearings inside the Audi ATA250 motor are made of ceramic material.

The preparation of ultra-precision silicon nitride ceramic balls is the prerequisite for manufacturing ultra-precision high-end silicon nitride ball bearings. High-end ceramic balls generally need to achieve three key technical indicators at the same time: high precision, long fatigue life, and good surface quality.

Thanks to the continuous development and maturity of "hot isostatic pressing" high temperature and high pressure sintering technology, the preparation technology of silicon nitride blank balls with long fatigue life ceramic ball blanks has made a breakthrough. However, in order to ensure the ultra-precision large-scale production of silicon nitride balls, the following points should be noted:

① The surface of the silicon nitride ball is ground with equal probability, which means that each particle on the sphere has the same grinding probability;

② The grinding efficiency has automatic size selectivity, that is, the large ball or long axis direction is automatically given priority grinding;

③ Grinding technology can easily achieve large-scale industrialized and low-cost production.