Two SKF scientists, two very different careers, and one common goal: transforming the efficiency, performance, and reliability of modern machines.
Thanks to advances in manufacturing technology, modern bearings don’t fail like they used to. Years ago, the main issue was sub-surface fatigue, explains SKF principal scientist Guillermo Morales-Espejel. Today, most failures are triggered by surface-related problems, such as poor lubrication, contamination, frictional heat, or electrical damage.
With degrees in mechanical engineering from Mexico and a Ph.D. in tribology from Cambridge, Morales joined SKF’s research lab in 2000 to study surface issues in bearings. One early project simulated bearing performance in mixed lubrication environments, where contamination or a lack of lubricant creates areas of direct metal-to-metal contact within a bearing. Another study evaluated the effect on bearing life of small indentations that can occur if a bearing is mishandled during manufacturing, shipping, or assembly.
Life, in general
In 2012, a new technical director approached Morales with a bigger challenge. “He said our bearing life models were useful, but they were too rigid,” recalls Morales. “It takes too much effort to adapt the model to different problems or to integrate new knowledge.”
The technical director’s request was simple but daunting. Could Morales and his team take what they had learned about the effect of surface conditions on bearing life and build a general-purpose model that would better predict bearing life in the real world?
Their answer to this challenge took two years to develop. “We already had some of the key ingredients,” says Morales. “To build a general-purpose bearing life prediction model, you have to simulate the operation of different bearings under various conditions, over millions of cycles.”
Other parts of the model required the team to break new ground. In particular, Morales explains, they had to develop an approach that combined new surface damage models with traditional methods for estimating subsurface fatigue.
The first iteration of the SKF Generalized Bearing Life Model (GBLM) for conventional steel bearings was introduced as a concept to customers at the 2015 Hannover Messe. It offered the promise of an immediate solution to many challenges faced by design engineers every day.
“With a better life prediction model, you can design better machines,” says Morales. “Our model helps designers select the optimal size and type of bearing for their application and allows companies to provide more reliable advice on maintenance and replacement intervals.” The result is more efficient use of resources, with fewer breakdowns and less premature replacement of parts that still have life left in them.
Beyond metal
Over the past decade, Morales and his colleagues have expanded the GBLM to include new types of bearings, notably adding models for hybrid bearings that combine ceramic rolling elements with conventional steel rings. Surface-related issues are a key challenge in hybrid bearing design, since the extreme stiffness of the ceramic components leads to higher contact pressures under load. There are other challenges as well.
For Charlotte Vieillard, a materials scientist, the intricacies of ceramics have been a career-long focus. Joining SKF’s R&D facility in the Netherlands as a graduate researcher, Vieillard brought her expertise in non-metallic materials to the development of hybrid bearings.
Hybrid bearings offer many advantages over conventional steel designs, especially in high-performance applications. Early adopters of the technology used hybrids to the extreme. Examples included spindles for machine lathes or machining centers with very high speeds, as well as wheels and gearboxes in F1 racing cars.
Over the years, says Vieillard, hybrid bearings have found their way into many more products, from fans for air conditioning units to wind turbines, industrial pumps, and compressors. Currently, 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, making bearings resistant to damage from stray currents in high-frequency electrical machines.
Hard materials, harder to make
One factor limits the wider adoption of hybrid bearings: ceramic rolling elements are difficult and costly to manufacture. “It’s a challenge to produce high-quality silicon nitride rolling elements that can withstand the highly loaded point contacts of a bearing,” says Vieillard. “You need a very high-quality material, and because ceramics are more brittle than steel, it’s essential to secure high toughness and strength by developing a specific microstructure.”
Ceramic components are made by a sintering process similar to powder metallurgy. 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, dense “blank.” These blanks are then ground and super-finished into precision balls and rollers. Production requires tight control over multiple parameters at each manufacturing step to achieve the desired final structure and quality.
“Many companies produce silicon nitride parts, but few achieve the level of quality and consistency we need for bearing components,” says Vieillard.
From niche to mainstream
While costly processes were acceptable for early hybrid bearing implementations, such as in the aerospace industry, demand has expanded as customers across industries seek performance benefits.
For Vieillard, maintaining stringent quality control and inspection processes has been a key focus since her early work with hybrids. Each batch of bearings must meet all the specifications required by demanding customers.
As hybrid bearings move into mainstream applications, such as automotive powertrains, SKF has invested in a full in-house production chain, from powder to finished product, alongside strategic suppliers and has developed larger production systems.
Today, SKF’s expertise across the company enables customers to benefit from this new generation of bearings. Morales and his team continue to refine their life prediction models, guiding design and specification decisions, while Vieillard and her colleagues ensure that customers receive the full benefit of hybrid technology in every bearing SKF delivers.
