Tribology and Lubrication Technology April 2012 : Page 43‘The main disadvantage is that self-lubricating bearings have speed and temperature limitations that must be respected to avoid bearing damage.’ —Dr. Ryan Evans, The Timken Co. for low-speed applications where relu-brication or external water contamina-tion causing lubricant washout are present. Possible examples are over-head cranes, food conveyors and ski lifts.” Two disadvantages are speed limi-tations and concern about the poten-tial for longer term wear. Snyder says, “Self-lubricating bearings are limited in speed capabilities because of the surface interactions and lack of lubri-cation cooling. Longer term wear may be an issue because lubrication is not provided by an elastohydrodynamic lubricating film.” fUTURE TYPES Of BEARInGS Each of our industry experts was asked about what new types of bearings will emerge over the next 10 years and what lubrication challenges they will present. Miller says, “I expect the im-mediate and midterm future will see a great deal more development of spe-cial materials and coatings. In particu-lar, I believe there will be even greater utilization of ceramic materials. As the cost factor improves due to greater general usage, more and more applica-tions become economically viable.” Snyder anticipates that bearings development will become more appli-cation-specific. “The emphasis will be on lower friction bearings and, of course, lubricants that provide low friction in bearings while still giving the film thickness and life required for the application,” Snyder says. “Bear-ings will become matched to a specific application and the application’s an-ticipated environment. This means bearings will move from off-the-shelf items to being more application-spe-cific. I expect to see greater use of nan-otechnology to develop lubricant sur-face films for bearing use. Finally, I will not be surprised to see high-tem-perature thermoplastics being used in bearings more frequently.” Evans also predicts the greater use of new materials in bearings with an emphasis on not just boosting perfor-mance but also improving efficiency. “Rolling element bearing development trajectory continues to be toward in-creased energy efficiency, continued performance optimization and the in-corporation of modern materials,” Ev-ans says. “These goals may be met by optimizing the wear resistance of bear-ing surfaces, incorporating low-viscos-ity or minimum quantity lubrication systems, improving thermal manage-ment in bearing systems, increasing bearing power density and further op-timizing bearing designs. Hybrid ce-ramic-steel rolling element bearings have already emerged, but additional incorporation of nonferrous materials in bearings is expected in the future.” Zaretsky believes that the use of new bearing materials could extend to removing all metal from the bearing. He says, “Depending on costs and reli-ability, there will be greater use of non-metallic, rolling element bearing com-ponents such as—or similar to—today’s hybrid bearings. However, the entire bearing may be made from nonmetal-lic materials. This will challenge the chemist to develop additive packages that will function in a similar manner to those used in today’s oils and greas-es that lubricate steel rolling element bearings.” Bakolas feels that bearing develop-ment will progress to the point that sensors will be incorporated so that they can detect and adjust to changes in operating conditions. “We will see a shift towards ‘smart’ bearings, i.e., bearings that have temperature or force sensors integrated in them. The trend towards minimum lubrication also will continue, thus requiring more intelligent lubrication systems. Hybrid bearings and the use of all sorts of sur-face coatings such as diamond-like carbon coatings will remain in focus. All this will require the need for new lubricants that conform to these new systems and provide for good lubrica-tion, even in minimum quantities,” Bakolas says. “Finally, the chemical in-teraction between the surface and the lubricant will become more important and, thus, influence the design of the new generation of lubricants.” Development efforts are becoming more specialized with a growing em-phasis placed on tailoring the bearing for a specific application. With the use of new materials and even the move-ment toward the use of sensors, new lubricants and lubrication systems will need to be developed to ensure that the new types of bearings will operate at an optimum level. Additional information on bearings can be found in The Tribology Data Handbook 2 . Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. You can reach him at neilcanter@comcast.net. REfEREncES 1. Evans, R., Doll, G., Hager, C. and Howe, J. (2010), “Influence of Steel Type on the Propensity for Tribochemical Wear in Boundary Lubrication with a Wind Turbine Gear Oil,” Tribology Letters , 38 (1), pp. 25-32. 2. Jendzurski, T. and Moyer, C. (1997), “Rolling Bearings Per-formance and Design Data,” in Booser, E. editor, Tribology Data Handbook , pp. 645-668. (Presenter: Paul Michael, Milwaukee School of Engineering), April 18. Details at www.stle.org . 43 Publication List Using a screen reader? Click Here |
