Rolling elements
The Growing Importance of Hybrid Bearings in Rolling Bearing Applications
The use of hybrid bearings is becoming increasingly important in rolling bearing applications. In a hybrid bearing, the inner and outer rings are still made of steel, but the rolling elements are made of ceramic materials, such as Si₃N₄ (silicon nitride).
The ceramic rolling elements provide a significant reduction in weight, enabling higher rotational speeds and allowing the bearing to run at lower temperatures. This also benefits the lubricant, which experiences a longer service life.
As a result, the lifespan of a hybrid bearing can be up to ten times longer than that of comparable conventional steel bearings, since these bearings can continue to operate even under poor lubrication conditions.
Another advantage of hybrid bearings lies in the high corrosion resistance of the ceramic rolling elements, making them suitable for use in aggressive environments.
However, the use of currently available hybrid bearings is still limited to application areas where the advantages of ceramic rolling elements are absolutely essential, as hybrid bearings are significantly more expensive than steel bearings.
Additional issues with today’s ceramics include the very different thermal expansion coefficients between the Si₃N₄ rolling elements (3.5 ppm/K) and the steel rings (11.5 ppm/K) when bearings need to operate across varying temperature ranges. Furthermore, the high modulus of elasticity (E-modulus) of the ceramic rolling elements leads to smaller contact ellipses, resulting in higher contact pressure, which puts additional stress on the steel components of the bearing.
Ceramic rolling elements made from Metal-like Ceramic (MLC) now offer entirely new possibilities. By optimizing the material for use with steel, MLC is ideally suited for hybrid bearing applications. MLC provides a thermal expansion coefficient that is well-matched to steel, enabling reliable operation across a wide temperature range. Additionally, MLC rolling elements have a significantly lower E-modulus compared to Si₃N₄ ceramics, which results in larger contact ellipses and reduced contact pressure, thus reducing stress on the steel components. Moreover, due to the innovative manufacturing process, these rolling elements are significantly more cost-effective than traditional ceramic rolling elements. This means that the major advantages of hybrid bearings can be achieved at a much lower cost.