BEARINGS, SEALS & GASKETS
New production technologies are bringing the
many benefits of hybrid bearings to mass-market applications, as SKF explains
S
KF has been pioneering hybrid bearing technology for over two decades and is now bringing this cutting-edge solution
into mainstream applications. Charlotte Vieillard, a materials scientist, has played a pivotal role in this effort. With a background in non-metallic materials, she joined SKF’s R&D facility in the Netherlands as a graduate researcher, focusing on the development of hybrid bearings. While SKF is renowned for its high- quality steel bearings, Vieillard and her colleagues have turned their attention to the remarkable properties of ceramics. Hybrid bearings, which combine steel raceways with ceramic rolling elements made of silicon nitride, offer unique advantages. “This ceramic is 60% lighter
than steel,” comments Vieillard. “That weight reduction is especially valuable in larger bearings. Lightweight rolling elements also significantly minimise the centrifugal forces that typically burden bearings at high speeds, enabling hybrid bearings to operate successfully at much higher speeds.”
ENHANCED DURABILITY These attributes not only extend the life of the grease and bearing but also improve
Charlotte Vieillard, SKF senior ceramic technologist
HYBRID BEARING BENEFITS
performance at the contact points between ceramic and steel. “Silicon nitride is much harder and stiffer than steel, allowing it to handle contamination and imperfections in the raceway surface better,” explains Vieillard. Ceramic rolling elements can even flatten
raised portions of dents and imperfections in steel raceways, preventing damage from escalating. Additionally, because steel and ceramic resist seizing, hybrid bearings are exceptionally durable. The use of steel rings ensures hybrid bearings
have to ensure high toughness and strength by developing a specific microstructure.” Ceramic components are made through a
sintering process. Fine powders of silicon nitride and other additives are first milled together and compacted into a shape, then heated under high pressure until the material ‘fuses’ or sinters into a solid and dense ‘blank’. The blanks are then ground and superfinished into precision balls and rollers. Production requires tight control of multiple parameters at each manufacturing step to achieve the desired final structure and quality. “Many companies produce silicon nitride parts, but few today achieve the level of quality and consistency we need to produce bearing components,” says Vieillard. Costly processes may have been
Exploded view of a hybrid cylindrical roller bearing
remain user-friendly for both manufacturers and end users, as they can be installed like conventional steel bearings. This makes them a versatile ‘plug-and-play’ solution. Over the years, hybrid bearings have found their way into many other products – from the Thrust Supersonic Car or Space Shuttle, to widely used fans in hospitals, air conditioners in buildings, wind turbines, and industrial pumps and compressors. Currently, adds Vieillard, the biggest growth
area is in electric motors, which are replacing internal combustion engines in cars, motorcycles and other mobility applications. These applications benefit from another key advantage of ceramic materials: they are excellent electrical insulators, so the bearings are not susceptible to damage from the stray currents that can pass through them in high- frequency electrical machines.
MANUFACTURING CHALLENGES There’s only one thing standing in the way of wider adoption of hybrid bearings: ceramic rolling elements are difficult and expensive to manufacture. “It's a challenge to routinely and systematically produce high-quality silicon nitride rolling elements that can withstand the highly stressed point contacts of a bearing,” says Vieillard. “You need a really good material, and because ceramics are more brittle than steel, you
acceptable for successful and early adoption of hybrid bearings. Customers in the aerospace industry, for example, needed relatively small volumes of product and could absorb
the higher cost of hybrids in exchange for the performance benefits they offered. For Vieillard, a key focus from the earliest
years of working with hybrids was to ensure that customers received these benefits in every bearing SKF supplied – by understanding the performance of these materials and finished components, as well as the overall behaviour of the hybrid bearing, the associated detailed component specifications, and the inspection or characterisation processes. This required relentless attention to quality control and inspection processes to ensure that each batch of bearings met all specifications.
INTO THE MAINSTREAM To meet this challenge, SKF has invested in a fully integrated value chain, from raw materials to finished products, and developed advanced production systems. The company’s research and development efforts focus on optimising manufacturing processes and exploring cost- saving innovations, such as automation and improved sintering techniques. “Our goal is to unlock new performance
capabilities while ensuring cost-effective production,” explains Vieillard. SKF’s ceramics community is working to refine every stage of the process, from powder selection to final inspection, paving the way for hybrid bearings to become a mainstream solution.
SKF
www.skf.com DECEMBER/JANUARY 2025 DESIGN SOLUTIONS 37
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