Ceramic Bearing Designs

Ceramic microstructures engage in the covalent bonding inherit between non-metal elements. This means they share electrons. This atomic cooperation presents a strong attraction force and because of this, ceramics offer a set of advantages that cannot be offered by metals.

High Hardness

Ceramic bearings typically have a very high hardness (70-90 HRc) and elastic, or Young’s, modulus, meaning they are resistant to shape change when loads are applied along with improved wear characteristics.

Lubrication Free

Ceramic bearings provide the ability to run lubrication free, this benefit derives from the fact that ceramic materials do not micro-weld. Micro-welding occurs commonly with metals, when surface imperfections on the rolling element and raceway interact with each other via an electric arc. This process degrades the surface, sustainability, and life of the bearing. Ceramic materials do not have this issue, making these bearings ideal for applications that operate within a lubrication-free environment.

Extreme Temperatures

Ceramic bearings behave in a stable and consistent manner at high temperature, causing less thermal expansion. A significantly higher amount of energy is need to increase the bond length of a covalent bond in comparison to a metallic ionic bond.

Corrosion Resistance

Ceramic is a nonferrous, non-metallic material. They do not corrode in the same manner as metals do when exposed to hazardous chemicals and water. Their corrosion-resistant properties allow them to perform exceptionally in chemically-corrosive and wet conditions.

Lightweight

Engineering ceramics have a low density, leading to enhancements in the bearings’ operational speeds, which is due to low centripetal forces and reduced friction.

Non-magnetic

Ceramic bearings are non-magnetic and excellent insulators due to their lack of free electrons.

Although all those advantages portray a somewhat perfect bearing, there is potentially bad news that emerges with their disadvantages.

Higher Cost

The initial disadvantage that you may encounter when researching ceramic bearings is that they are substantially more expensive than their metal counterparts. The sintering process of high-grade raw materials requires extremely high energy and processing combined with the mass energy needed to reach the required temperature is what drives the cost of these bearings so high. As ceramics are so hard, the grinding and machining costs also add up rapidly when manufacturing precision bearings. Further costs are accumulated because all of these processes have to be conducted in a clean environment by only the most skilled employees. The material is also highly sensitive to impurities in their pores, meaning that any contaminates could cause permanent failure.

Higher Cost at Larger Sizes

Larger sized bearings only increase costs further, this is due to the need for high-cost processing methods. This includes a slower sintering process to overcome the green body temperature gradient, the amount evenly applied pressure over a larger volume and the resulting machine costs.

Sensitive to Thermal Shock

This material has lower load capacities compared to metals and is sensitive to thermal shock. Thermal shock occurs when the temperature gradient within the material causes an adverse expansion, resulting in internal stress. The stress has the capability to exceed the strength of the material, forming cracks.

Market of Poor Quality

As the popularity of ceramic bearings increase, the market has become exposed to poor-quality products with little to no traceability. The material composition is critical for the success of the bearing, and recent failures have impacted their credibility. Ceramic bearings from UNASIS are the highest possible quality, and provided alongside top knowledge and excellent quality and support.

This table summarises aforementioned advantages and disadvantages in a clear, easy-to-read format.

The retention of high-strength and creep resistance with oxidation resistance are what silicon nitride combine to provide it with its unique properties. It has more enhanced high-temperature capabilities than the majority of metal and its low thermal expansion coefficients provide it with better thermal-shock resistance compared to most ceramic materials.

This material is black in colour and is the ideal choice for vacuum and high-speed applications. It’s 50% lighter than traditional steel, which causes a reduction in centripetal force generated by the rolling elements, significantly increasing fatigue lifetime.

Zirconia (ZrO₂) was initially developed during the 1960s and ‘70s, it was developed to produce a thermal barrier on the external tiles of a space shuttle which allowed the shuttle to re-enter the earth’s atmosphere without disintegrating. Since the ‘70s, Zirconia has become the material of choice for high-temperature and corrosive applications. Unlike ceramic, the density and thermal expansion of Zirconia is similar to that of steel. This means that this material does not have the same weight saving and thermal-shock resistance that other ceramic materials enjoy. Although this is the case, compared with Silicon Nitride and Silicon Carbide, Zirconia has a high fracture toughness. Zirconia is white in colour.

Despite offering the best heat and corrosion resistance of all ceramic materials, Silicon Carbide is less frequently used due to the raw material costs and difficulties in machining. This material is best used under low loads and within highly corrosive environments.

Space and Satellites

The majority of modern materials discover their origins in pioneering space technology. Many of the ceramic bearings that have been developed and used throughout industries globally were originally created for space use. Space environments tend to exhibit consistent extreme loads and turbulent environments, which demand strict weight constrains and vacuum requirements. Ceramic bearings are able to fulfil these requirements as the material is vacuum-compatible and lightweight. Dissimilar to their steel counterparts, ceramic bearings are able to run unlubricated which not only stops possible contamination of delicate components, but also reduces weight as there is no need to utilise heavy greases. Also, ceramic bearings do not experience cold-welding unlike conventional steel bearings.

Chemical and Medical

As many applications pose a threat to bearings due to contamination reasons, ceramic bearings offer the best solution. Whether it is mixing chemicals or for use in medical equipment, steel bearings are susceptible to corrosion and other damage from strong acids, water and alkalis. Standard steels (including stainless), can rust when washed with solutions and result in particulate contamination. Ceramic bearings do not have the same reaction as standard steels as they are chemically inert compounds. They are not chemically reactive to corrosive materials, and never release any harmful by-products. Standard steel bearings require a form of lubrication; either grease or oil, which can be notoriously difficult to clean. This can then lead to the breeding of bacteria that is unsuitable for sanitary applications. As ceramic bearing is lubrication free, there is no need to be concerned about additional microbiology.

Scientific Instrumentation

The magneto-optical phenomenon named the ‘Faraday Effect’, showcases the interaction between light and a magnetic field in a medium, meaning that some instruments may require a fully non-magnetic system. If an instrument is designed to measure or utilise light, a standard steel bearing must be avoided. Ceramic bearings will offer the perfect solution when magnetic resonance is an issue.

Ceramic bearings provide a vast array of advantages for many different applications that operate well in extreme environments. However they also present disadvantages that must be considered. The bearings are extremely hard, corrosion-resistant, and have a high elastic modulus. A core advantage is that they are able to run without any lubrication, have low thermal expansion, are low-density, and have excellent non-magnetic qualities. This comes at a cost though, as bearings have low load capacities, are sensitive to thermal shock, are expensive, and are difficult to achieve a superior high-quality surface finish on.

Ceramic bearings are available for a wide variety of industries and applications such as space, chemical, medical, and scientific instrumentation.

If you believe that your application would benefit from a ceramic bearing or just want to speak to an expert, then contact UNASIS today and speak to one of our team.