Properties of a Si3N4 ceramic bearing
Silicon nitride (Si3N4) is one of many ceramic materials. It’s an extremely hard but also remarkably light ceramic material. Si3N4 has excellent corrosion resistance and is well suited for use in water, salt water and in environments where certain acids and alkalis are present. This is why Si3N4 bearings are often used in marine applications, where they can be fully and permanently submerged without the material being affected.
These bearings also have a wide temperature range from -210°C to 800°C without a cage and up to 1200°C with reduced load capacity. They are suitable for use in high vacuum applications because of their very low outgassing. They are also non-magnetic and have electrically insulating properties.
Si3N4 is extremely hard but also brittle, so it's important to avoid shock or impact to prevent cracking. A Si3N4 bearing is only 40 percent of the weight of its steel equivalent.
Due to their greater brittleness, Si3N4 bearings have slightly lower load ratings than zirconia (ZrO2) bearings but will still cope with much higher loads and speeds than 316 marine grade bearings.
Ceramic Si3N4 bearings are hard, smooth, and can be used without lubrication. Because of this, they're commonly used when low turning resistance is needed.
Full ceramic bearings have an extremely low coefficient of friction compared to stainless steel bearings or even hybrid bearings. Si3N4 bearings have a coefficient of friction of 0.001 without lubrication at room temperature with a light load.
How does silicon nitride differ from zirconia?
Si3N4 differs from ZrO2 by having a low coefficient of expansion. Be careful when choosing shaft fits for high temperature use. A steel shaft expands more than the Si3N4 inner ring, which can lead to ring fracture. A steel housing expands more than a Si3N4 outer ring, causing a looser fit at high temperature.
Shaft sizes and temperature limits for ceramic bearings in silicon nitride
We supply ceramic bearings in Si3N4 for shaft sizes from 3mm up to 50mm. 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. Si3N4 bearings with a 316 stainless steel cage can be used up to 500°C.
Although Si3N4 expands much less than ZrO2, it is still advisable to specify greater internal clearance at high temperatures to avoid problems caused by radial play reduction. Our Si3N4 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.
Most of our range of Si3N4 ceramic bearings are supplied from stock in the UK.
The Si3N4 full ceramic ball bearings in the table below are available with cages (or retainers) made from PEEK and PTFE.
We can supply bearings with bore sizes from 8mm upwards with 316 stainless steel cages and GH4099 alloy cages. We also keep a stock of full complement silicon nitride bearings. These come without a cage and no extra balls. For full complement type, the load ratings are approximately 20 percent higher but the maximum speed is up to 70 percent lower.
For bearings with cages, PEEK cages are usually in stock because they are strong and durable. If PEEK cannot handle certain chemicals or extreme temperatures, we can offer a different cage material.
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 higher 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.
See product table below for dimensions and technical drawings
See products variants below for ZrO2 options
Have you still got questions about silicon nitride ceramic bearings? Get in contact with our experienced team today by emailing sales@smbbearings.com or fill in the contact form.
