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Ceramic balls

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Ceramic balls
Bearing is a kind of basic product in mechanical industry. It is a mass production and widely used. In whole bearing production, the ball bearing occupies a biggest proportion.
The Speciality of Ceramic Ball
Compared with steel, ceramic materials are noted for their better or particular characters, such as wearability, corrosion resistance, high temperature resistance, electrical insulation (except SiC), non-magnetic, high strength, high rigidity, and low specific gravity. These properties qualify them for replacing steel to make bearings serve in conditions of higher speed, harsh environment and less lube, and decrease wear, noise, vibration and maintenance time of bearings, and eventually increase performance, reliability and life of bearings.

Ceramic materials, which can be used in making bearings, include mainly silicon nitride, zirconia, alumina (Al2O3), and silicon carbide . Si3N4 is first choice within the above mentioned ceramic materials due to its excellent characters (Table 1). And a properly engineered silicon nitride bearing ball fails in the same manner as a steel ball, spalling of the ball surface. But ZrO2 , Al2O3 and SiC fail in a crush form, a catastrophic failure.
Field of Application
The transmit device of high temperature furnaces
Si3N4ceramic retains strength and hardness nearly up to 800 ? , but bearing steel hardness drops above 120°C .
High-speed rotation field
Such as high speed motor spindle bearings, main shaft bearings of machine tools, dental drill bearings, computer hard disk drive bearing and precise instrument bearings.

The specific gravity of Si3N4 is 3.20g/cm3 and that of bearing steel is 7.85g/cm3 . We can see the former is much lower than the latter, therefore the ceramic rolling elements can effectively restrain the centrifugal force, which appears in high speed rotation, and reduce the load of rolling elements. At the same time the effect of turning slide between rolling elements and raceway corresponding reduces. This is good to prevent surfaces from damage.
Aviation and airspace fields
The coefficient of thermal expiation of Si3N4 is 3.2×10-6 /K /K but that of bearing steel is 10×10-6 /K /K. Therefore Si3N4 ceramic bearings are more stable and reliable in a temperature changeable condition.
The main shaft of machine tools
The Si3N4 ceramic has much higher hardness than bearing steel, and 1/3 modulus of elasticity larger than that of bearing steel. We can found that the elastic deformation of Si3N4 is small under an identical loading. Therefore the ceramic bearing has better machining precision.
Chemical machinery, food industry and marine industry
The ceramic bearings can solve corrosion problems.
High vacuum field
In high vacuum field people take the advantage of self-lubrication of ceramic bearings to replace the bearing steel bearing in order to prevent vacuum pollution from lubrication contamination.
Strong magnetic environment
In a strong magnetic environment the metal powder which is produced from wear of steel bearing, adheres the surfaces of rolling element and raceway and causes flanking in advance and increasing noise. The solution to this problem is also using ceramic bearing.
Roller skates, aeromodellings and motor-driven toys, etc in civil use
It is the price factor of ceramic bearing that limits its wide use in the world. So up to now most application of ceramic bearing are merely in high speed, high precision mechanism, in addition the hybrid construction of ceramic bearing, that is ceramic ball with steel inner ring and outer ring, is most adopted. Owing to adopting near net shaping technology, the using of ceramic bearing can be applied not only in the above mentioned industry spheres but also in civil fields such as roller skates, aeromodellings and motor-driven toys, etc.
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