Ceramic Ball Bearings
Use of Ceramic Materials in Ball Bearings
Today's engineers have many options available to them when faced with extreme, or demanding operating conditions. This includes the use of ceramic materials that have many benefits in a variety of applications. This includes the use of ceramic materials that have many benefits in a variety of applications. The most common use is producing the rolling elements- the balls, from a ceramic material with the inner and outer rings made from traditional, heat-treated, chrome or stainless steel. These bearings are commonly referred to as Hybrid Bearings. With improvements in manufacturing technology, Full Ceramic Bearings are also readily available. These bearings have both the inner and outer rings in addition to the rolling elements manufactured from ceramic material. While hybrid and full ceramic bearings demand a premium price, they are often the most economical solution when considering the cost of a failure and the total cost of ownership for the end-user.
The most common configuration is with chrome or stainless steel rings, and ceramic balls. Nitrogen enhanced stainless steel ring material is also available.
The most common ceramic material for the balls is silicon nitride, Si3N4. Compared to traditional steel balls, this material has desirable properties for rolling bearings, such as,
- lightweight (approximately 60% lighter than bearing steel)
- high hardness - over 75 HRc
- higher elastic modulus - stiffer
- lower coefficient of thermal expansion
- higher maximum operating temperature - 1000°C
- highly polished surface finish resulting in lower friction
Balls made of zirconia, ZrO2, are also available. This ceramic material has some properties similar to those of silicon nitride but differs in that it has some mechanical and thermal properties much closer to that of the alloy steel that the rings are made from. This can be desirable in maintaining the preload and contact angle over a broad range of operating temperatures.
|Characteristics||Unit||Chrome Steel||Stainless Steel||Nitrogen Enhanced Stainless Steel||Si3N4||ZrO2|
|Expansion Coefficient||x 10-6°C||10,9||10,1||10,1||2,9||10|
|Top Temperature Limit||°C||170||260||500||1000||600|
|Corrosion Resistance||limited||good||very good||very good||good|
|Magnetism||magnetic||magnetic||magnetic||not magnetic||not magnetic|
An AST Applications Engineer should be consulted for a full analysis of the operating conditions and potential failure modes.
Benefits of Hybrid Ceramic Bearings:
- higher stiffness and rigidity reduces deflection
- increased the limiting speed, RPM
- less adhesive wear, there is no cold welding
- better lubricant life
- lower noise levels and vibration
- no electrical arcing through the balls
Applications for Hybrid Ceramic Bearings:
- machine tool spindle
- pumps - submersible, fuel, vacuum
- dental drills
- optical scanner
- electric motors
- aerospace applications
- laboratory equipment
- applications that requre higher speeds, longer life, and lower friction
Full Ceramic Bearings
Full Ceramic Bearings are often the answer for extreme environments, such as high temperatures, corrosive chemicals, steam, and hard vacuum. These bearings have both the inner and outer rings in addition to the rolling elements manufactured from ceramic material. Like the balls in hybrid bearings, the rings in full ceramic bearings are typically manufactured from silicon nitride, Si3N4, or zirconia, ZrO2. Retainers in full ceramic bearings are typically made from high-performance plastics such as PEEK or PTFE. Full complement versions are also available.
Benefits of Full Ceramic Bearings:
- resistant to acid, salt and water, and blood
- lower coefficient of friction
- resistant to electricity
- lighter, smoother and stiffer
Applications for Full Ceramic Bearings:
- MRI equipment
- vacuum environments
- semiconductor manufacturing
- food processing industrie
- any extreme environment requiring non-corrosive, non-conductive or non-magnetic bearings
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