They’ve been around since the 16th century; can bearings continue to evolve?
The basic mechanical principles behind bearings are essentially the same. The design, construction and applications can be as varied and unique as a single snowflake.
Determining the best overall bearings would be impossible because bearing selection depends both on the application and the operating parameters. Why would you choose the same bearing for a pair of roller skates and a precision machine tool?
The most common bearings on the market include plain (sleeve) bushings, ball/roller, ceramic hybrid and radial contact (Conrad style) — each offered in a vast array of size and design configurations — but custom-made bearings developed for unique applications also play a key role in the bearing manufacturing industry.
ADVERTISEMENT
According to Maria Brill, marketing manager with Graphite Metallizing, “All bearings must do one job well, reduce friction. It takes a comprehensive design manual to review all of the design variables available when selecting a bearing, but important features to consider include application suitability, materials, lubrication method, level of manufacturing tolerances, cage design and housing configurations.”
The demand for basic material principles has increased, driven by the large availability from Chinese and Eastern European market steel suppliers that have not been as reliable.
“We have noticed an increase in care for raw material purity,” says Pietro Prosino, director and sales manager at PROSINO S.r.l. “For all of our customers, the material purity is the main factor in determining the life and performance of the bearings.”
With increased reliability and performance, bearing selection can become an unnecessarily complicated and overpriced process.
“The best bearings on the market are the ones that are not overdesigned, and thus overpriced for the application,” says Jim Hammer, ART Technologies operations and engineering manager. “Quite often, bearings with inexpensive stamped races could be used instead of more expensive turned and ground races.”
Harsh Environments
Leonardo da Vinci developed an early model for ball bearings in the 16th century; bearing functionality has not changed significantly in the 500 years since. New materials, lubrication and coatings are the variables under constant development to improve bearing life and the ability to hold up in harsh environments.
Bearings are also protected by isolation from the harsh system (contaminants, electric charges, high temperatures, shock loads, etc.) by adding external components, such as seals, compensating rings and special housings. A careful heat treatment can also contribute to extend the lifetime of the bearings.
“Various types of lubrication have been developed for different environments like food-grade solid lubes, ultra-high temperature greases and super-slick dry lubrication,” says Jay Flanzbaum with Boca Bearing. “The materials used for the bearing enclosures and retainers have also changed as advanced polymers are developed. Materials like Torlon, Viton, Ploymide and Phenolic have exceptional characteristics.”
Adaptive bearings that transform to better handle changes to the conditions are not the status quo. Quite a bit of work has been done to provide compliant structures that enable bearings to handle high loads, and installation and/or surface preparation errors or imperfections.
“Linear motion bearings are selected or accessorized specifically to be able to function and perform in the design environment,” says Alison Ng, Thomson Industries’ director of engineering – rails, guides and components. “Certain types of bearings are better capable of handling extreme temperatures, such as bearings with all steel construction or special high-temperature range materials."
Material selection is a primary aspect in a bearing’s ability to survive environments.
“Bearing design is a highly customized process. The material for each of the components used in a bearing (balls, cage, races, etc.) are selected to meet the requirements of the application,” says Bob Stanko, executive vice president and general manager of Harford Technologies. “Temperature, operating environment, speed, load, duty cycle and cost are all considered during bearing development.”
“52100 chrome steel is the ‘workhorse’ of the bearing industry due to good performance in hardenability, wear resistance, toughness and fatigue strength,” adds Stanko. “Many common applications can be met with 52100 or the case-hardened steels. Tool steels were developed to provide even greater endurance. Process improvements in the production of raw material, such as vacuum degassing and vacuum induction melting, further improved the quality and purity of the steel. Ceramics, nickel-based super alloys and precipitation-hardened stainless steels have been developed to meet extremely demanding applications involving high temperatures, high speeds, corrosive environments, etc.”
Room To Grow
Since the bearing industry and the technologies associated with bearing manufacture are considered mature, it is difficult to predict where bearing design is headed. Certainly, improvements in materials, manufacturing tolerances and price will continue.
“There will be more emphasis on manufacturing location in order to provide the most economical price to customers, while still maintaining consistent quality,” says Stanko. “When component manufacturing is done in low-cost countries, the facilities must have strict, traceable quality standards — a huge consideration for many bearing applications.
New technology (integrated sensors, special coatings, surface treatments, etc.) will continue to become cost effective going from R&D to select applications, eventually to standard product lines, according to Scott Hart, manager of advanced industrial development, Schaeffler Group USA. “Bearings and systems will become more integrated and the separation between supplier and customer will continue to become less defined as each party becomes more integrated with the other in the development process,” says Hart.
With the global economy and manufacturing in their current states, the changes to bearings could continue to be value focused and incremental to be oriented for special applications.
“Motion systems designers [will not] only look at price, but rather at the overall installed end user cost,” says Thomson’s Ng. “This will mean demands for improved reliability, ease of installation, ease of maintenance, low operating cost and low power consumption without a reduction in performance. This will in turn drive the desire for better sealing and lubrication accessories, better quality products that are more consistent, downsizing bearings, alternative materials for demanding environments. Perhaps even hybrid bearings”.