Si3N4, or silicon nitride, is a very hard yet lightweight ceramic material. Si3N4 has excellent resistance to water, salt water and many acids and bases. It also has a very wide temperature range and is suitable for high vacuum applications. The extreme hardness of silicon nitride also means greater brittleness, so impact/impact loading should be minimized to avoid the risk of cracking. The weight of Si3N4 bearings is only about 40% of that of steel bearings. Silicon nitride ceramic bearings have high hardness, very smooth wear surfaces and can run without lubrication, so they are often used where very low rotational resistance is important. Their coefficient of friction is very low compared to steel bearings or even hybrid bearings. Si3N4 bearings have a coefficient of friction of approximately 0.001 in lightly loaded air at ambient temperature.
Unlike zirconia, silicon nitride has a low coefficient of expansion, so care should be taken when selecting a suitable shaft for high temperature applications, as steel shafts expand much more than silicon nitride inner rings, which can lead to ring fracture. Also, the steel housing expands much more than the silicon nitride outer ring, resulting in a looser fit at high temperatures.
Si3N4 bearings are non-magnetic and highly resistant to most chemicals. They are also electrically insulating. Like ZrO2 bearings, they are also extremely water resistant, which is why they are often used in marine applications. They can be completely and permanently submerged without affecting the material. Due to greater brittleness, Si3N4 bearings have slightly lower load ratings than ZrO2 bearings, but can still withstand much higher loads and speeds than 316 marine grade bearings.
Si3N4 full ceramic ball bearings are available with cages (or cages) made of PEEK, PTFE. Bearings with a bore diameter above 8mm can also be fitted with 316 stainless steel cages. Silicon Nitride Ceramic Bearing Laminate Seals We also stock full complement silicon nitride bearings in stock. These come without cages and extra balls. For full complement types, the rated load is approximately 20% higher, but the maximum speed can be reduced by up to 70%. For bearings with cages, PEEK cages are often the off-the-shelf choice due to PEEK's strength and durability. If alternative cage materials are required to handle specific chemicals or extreme temperatures beyond the range of PEEK, these can be manufactured to order. For temperatures below -70°C it is worth considering PTFE or 316 stainless steel cages due to their better low temperature performance.
Si3N4 Ceramic Bearings Sealed full complement Si3N4 bearings can be used at temperatures up to 800°C. Bearings with PEEK cages are only rated up to 250°C, while silicon nitride bearings with 316 stainless steel cages are rated up to 500°C. Although silicon nitride expands much less than ZrO2, it is still recommended to specify larger internal clearances at high temperatures to ensure adequate radial clearance. Our silicon nitride bearings come standard with C3 loose radial clearance.
Silicon nitride ball bearings have the following advanced features:
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