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High- performance ceramics


CEROBEAR hybrid and ceramic rolling bearings exclusively use silicon nitride (Si3N4). The combination zirconium oxide (ZrO2), used as a ring material, and spheres made of Si3N4 seldom occurs. Hardness, compression strength, wear resistance, and corrosion resistance are considerably higher than in rolling bearing steel. A high E-module decreases deformation under stress. A bearing containing ceramic spheres is stiffer than a steel bearing one. In addition, a smaller contact surface develops (hertzian contact ellipse). A decrease in friction is the result. Although a smaller contact surface leads to higher hertzian pressure this proves to be unproblematic for ceramic.

 

The material characteristics listed in the table below apply to ceramic materials and qualify for the use in rolling bearings. For example, this occurs in rig testing under defined test conditions which are verified to special requirements of the customer. Important for the handling and manufacturing of ceramic is the consistent quality of the basic raw material, the powder, and the proceeding finishing steps.

 

 



Material characteristics   Si3N4 ZrO2 100 Cr 6 
Density ρ g/cm³ 3,2 6,1 7,85 
Heat expansion coefficient  α 10-6/K 2,8 9,6 11,5 
Elasticity modulus GPa 320 200 210 
Poisson number μ  0,27 0,30 0,30 
Hardness  HV10 N/mm² 1 600 1 200 700 
Bending strength  σB N/mm² 700 1 000 > 2 500 
Fracture toughness KIC MPa m1/2 10 > 20 
Temperature limit  °C 800 … 1000 400 180 
Heat conductivity λ W/m • K 30 … 35 40 … 45 
spec. electrical resistance  Ω • mm²/m 1018 109 10-1 



For today’s standard is Si3N4, of all the ceramics, the best material to use for rolling bearings and bearing rings. Especially the low weight of Si3N4 makes it an ideal material for rolling bearings that are under high rotational stress. The minimal dilation is favourable for ceramic bearings. The reason for this is that the warming in ceramic bearings does not lead to such severe decreases in bearing play as found in steel spheres and is therefore an important safety aspect. Greater temperature fluctuations lead to problems of fit when trying to connect metallic modification parts. In this case, ZrO2 provides a friendly alternative for application and assemblage instead of Si3N4.


 
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