Ceramic bearings in silicon nitride for shaft sizes from 0.125” up to 1.0”
See product table below for dimensions and technical drawings
See Products Variants below for zirconia options
Si3N4, or silicon nitride, is a very hard but lightweight ceramic material. Si3N4 has excellent resistance to water, salt water and many acids and alkalis. It also has a very wide temperature range and is suitable for use in high vacuum applications.
The extreme hardness of silicon nitride also means greater brittleness so shock/impact loads should be minimised to avoid the risk of cracking. Si3N4 bearings are only about 40% of the weight of steel bearings.
Silicon nitride ceramic bearings have high hardness, very smooth wear surfaces and can run without lubrication so they are frequently used where very low turning resistance is important. They have a very low coefficient of friction compared to steel bearings or even hybrid bearings. The coefficient of friction for Si3N4 bearings at ambient temperature in air with a light load is approximately 0.001.
Unlike zirconia, silicon nitride has a low coefficient of expansion so care should be exercised when choosing shaft fits for higher temperature applications as a steel shaft will expand much more than the silicon nitride inner ring which could lead to ring fracture. In the same way, a steel housing will expand much more than a silicon nitride outer ring, leading to a looser fit at high temperatures.
The Si3N4 full ceramic ball bearings in the table below are available with cages (or retainers) made from PEEK, PTFE. Bearings with bore sizes from 8mm upwards can also be fitted with 316 stainless steel cages or, for temperatures of 500°C and over, GH4099 nickel-based alloy cages.
In addition, we keep stock of full complement silicon nitride bearings. These have no cage and extra balls. For full complement type, the load ratings are approximately 20% higher but the maximum speed is up to 70% lower.
As for bearings with cages, PEEK cages are generally the option available from stock due to the strength and durability of PEEK. If an alternative cage material is required to cope with particular chemicals or temperature extremes beyond the range of PEEK, these can be produced to order.
Si3N4 bearings are not magnetic and they are highly corrosion 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 fully and permanently submerged without the material being affected.
Due to their greater brittleness, Si3N4 bearings have slightly lower load ratings than ZrO2 bearings but will still support much higher loads and speeds than 316 marine grade bearings.
Full complement Si3N4 bearings can be used up to 1200°C at low speeds and with very low axial loads. For higher speeds and axial loads, bearings with a PEEK cage are rated up to 250°C while silicon nitride bearings with a 316 stainless steel cage can be used up to 500°C. From 500°C to 900°C, GH4099 nickel-based alloy cages are recommended. Although silicon nitride expands much less than ZrO2, it is still advisable to specify greater internal clearance at high temperatures to ensure sufficient radial play. Our silicon nitride bearings are supplied with a C3 loose radial play as standard.
For temperatures below -70°C it is worth considering PTFE or 316 stainless steel cages due to their better low temperature performance. For an overview of the pros and cons of silicon nitride bearings, you can click HERE to see our ceramic bearing selection guide.
Most of the range of Si3N4 ceramic bearings are supplied from stock in the UK. We also keep ZrO2 full ceramic bearings in stock. See Products Variants below for the ZrO2 versions.
Click on INFO in the rows below to display technical drawings of the bearings with load and speed data. Please note that the maximum loads and speeds are used in theoretical life calculations. It is recommended to use bearings at significantly less than the maximum load and speed ratings to ensure reasonable bearing life. Si3N4 full ceramic bearings are best used with low to medium speeds and loads due to their greater brittleness.
