Over the last few decades, the design of bearings has advanced significantly bringing new material uses, advanced lubrication techniques and sophisticated computer analysis. Chris Johnson reflects on the developments
Bearings are used in virtually all types of rotating machinery. From defence and aerospace equipment to food and beverage production lines, the demand for these components is rising. Crucially, design engineers are increasingly demanding smaller, lighter and more durable solutions to satisfy even the most testing of environmental conditions.
Reducing friction is a key area of research for manufacturers. Many factors affect friction such as dimensional tolerances, surface finish, temperature, operational load and speed. Significant advancements have been made in bearing steel over the years. Modern, ultra-clean bearing steels contain fewer and smaller non-metallic particles, giving ball bearings greater resistance to contact fatigue.
Modern steel-making and de-gassing techniques produce steel with lower levels of oxides, sulphides and other dissolved gases while better hardening techniques produce harder and more wear-resistant steels. Advances in manufacturing machinery enable manufacturers of precision bearings to maintain closer tolerances in bearing components and produce more highly polished contact surfaces, all of which reduce friction and improve life ratings.
New 400-grade stainless steels (X65Cr13) have been developed to improve bearing noise levels as well as high nitrogen steels for greater corrosion resistance. For highly corrosive environments or temperature extremes, customers can now choose from a range of 316-grade stainless steel bearings, full ceramic bearings or plastic bearings made from acetal resin, PEEK, PVDF or PTFE. As 3D printing becomes more widely used, and therefore more cost-effective, we see increasing possibilities for production of non-standard bearing retainers in small quantities, something that will be useful for low volume requirements of specialist bearings.
Lubrication may have garnered the most attention. With 13% of bearing failure attributed to lubrication factors, bearing lubrication is a fast-evolving area of research, supported by academics and industry alike. There are now many more specialist lubricants thanks to a number of factors: a wider range of high-quality synthetic oils, a greater choice of the thickeners used in grease manufacture and a greater variety of lubricant additives to provide, for example, higher load capabilities or greater corrosion resistance. Customers can specify highly-filtered low noise greases, high-speed greases, lubricants for extreme temperatures, waterproof and chemically-resistant lubricants, high-vacuum lubricants and cleanroom lubricants.
Another area where the bearing industry has made great strides is through the use of bearing simulation software. Now, bearing performance, life and reliability can be extended beyond what was achieved a decade ago without undertaking expensive time-consuming laboratory or field tests. Advanced, integrated analysis of rolling element bearings can give unrivalled insight into bearing performance, enable optimal bearing selection and avoid premature bearing failure.
Advanced fatigue life methods can allow the accurate prediction of element and raceway stresses, rib contact, edge stress, and contact truncation. They also allow full system deflection, load analysis and bearing misalignment analysis. This will give engineers the information to modify the bearing design to better accommodate the stresses resulting from the specific application.
Another clear advantage is that simulation software can reduce the amount of time and resources spent on the testing phase. This not only speeds up the development process but also reduces the expenses in the process.
It’s clear that new materials science developments along with advanced bearing simulation tools will provide engineers with the insight required to design and select bearings for optimum performance and durability, as part of a whole system model. Continued research and development in these fields will be crucial in ensuring bearings continue to push the boundaries in the years to come.
Source: Controls, Drives & Automation