Silicon nitride balls have the characteristics of low density, high hardness, low friction coefficient, wear resistance, self-lubrication and good rigidity. Thus the Si3N4 balls are especially suitable for rolling elements of high-speed, high-precision and long-life hybrid ceramic ball bearings. ZYS Si3N4 ceramic ball adopts spray drying granulating, cold isostatic pressure,net size molding, GPS HIP sintering process, high efficiency grinding and processing of composite abrasives. The accuracy of silicon nitride bearing balls can acheive G5 (GB/T308 2002) and the accuracy of material can achieve grade 1.

The sintering process of silicon nitride ceramics generally has three types: hot isostatic pressing (HIP), hot pressing (HP) and atmospheric pressure sintering.

The hot isostatic pressing (HIP) process is to place the product in a closed container, apply equal pressure to the product in all directions, and apply high temperature at the same time. Under the action of high temperature and high pressure, the product can be sintered and densified. Hot isostatic pressing can directly shape the powder and the powder is loaded into the mold, and then nitrogen and argon are used as the pressurizing medium, so that the powder is directly heated and pressed to sinter, and the sintering pressure is 150MPa ~ 200MPa.

Hot press sintering is a kind of sintering method which fills the dry powder into the model, and then heats while pressurizing from the uniaxial direction. The pressure is about 70Mpa, so that the forming and sintering can be completed at the same time. The hot press sintering method has the advantages of reducing the sintering temperature, shortening the sintering time, resisting the growth of grains, and obtaining products with fine grains, high density and good mechanical and electrical properties. However, hot press sintering also has some disadvantages, such as high sintering pressure, complicated sintering process, strict production control requirements, large energy consumption, the low production efficiency, and high production cost.

Atmospheric sintering is a method of sintering a ceramic body in a furnace where a certain gas is passed, and its sintering pressure is 5 to 10 MPa.

The preparation method of silicon nitride ceramic includes the following process steps:

① Ceramic raw material preparation: mix the dried ceramic raw materials uniformly according to the proportion, pass through 80~200 mesh sieve, put the sieved powder in a ball mill for grinding at a speed of 300~360r/min for 6h~10h;

② Press forming: Place the powder obtained in step 1 in an abrasive tool and press into a ball shape by cold isostatic pressing;

③ Sintering: Put the powder into the mold under normal pressure, and heat it up to 1600℃~1650℃ at a rate of 60~80℃/min in the sintering furnace, keep the heat for 0.5h~2h, and then cool down to room temperature in the furnace after heating is stopped ;

④Grinding and polishing: Ground the ceramic ball, and then polish the workpiece after grinding. The sphericity of the ceramic ball does not exceed 0.07 microns, and the surface roughness does not exceed 0.008 microns.