Design News: New technology developments like SKF's Explorer Bearing have brought about an astonishing increase in bearing life and performance. What has made these developments possible?

Ioannides: Bearing performance has been steadily increasing throughout the second half of the 20th century as a result of improvements in steel cleanliness, bearing manufacturing, bearing design, and quality assurance. What makes the Explorer Spherical Roller Bearings unique is the simultaneous improvement of material, design, and manufacturing processes that results in this astonishing increase in bearing life. The exceptionally clean steel used for these bearings was further exploited using a new heat treatment, the manufacturing tolerances were tightened, surface finishes re-fined, and the roller guidance was improved through sophisticated modeling.

Q: Can we expect to see further increases in bearing performance in the future?

A: We are far from the physical barriers that are absolute limits to bearing performance. I therefore expect that the further increases of bearing performance are ahead as the state of the art technologies are implemented in design and manufacturing. However, it is worth noting that bearing performance has many attributes. The most commonly discussed is bearing life, but in many cases the bearing friction, torque, or the bearing contribution to noise, vibrations, high running speeds, or corrosion resistance are the important criterion of bearing performance. For each of these criteria different technologies are required. Surface engineering, where the surface and the near surface area are modified with coatings or special diffusion heat treatments are examples of this. Special coatings, for example our NoWear coating, can extend the bearing life many fold in adverse lubrication conditions.

Q: How important are the roles of modeling and simulation in the development and application of bearings?

A: Modeling and simulation are already important in mechanical engineering and their importance continues to rise in computing power. Moreover, as the realism and complexity of the modeling increases, it competes and displaces testing, which is costlier and slower. This trend is also evident in the world of rolling bearings, where computer models are routinely used to design bearings on the basis of quasi-static stress calculations. However, at the top end, very complex dynamic computer bearing models exist that can be used to design internal bearing geometries and cages for optimum performance. The de-tailed information obtained from such models makes them irreplaceable as tools in product development because it is almost impossible to obtain this information through testing.

Q: What role do bearings play in drive-by-wire systems?

A: The main interest in the electromechanical actuating unit for all by-wire systems is the conversion of the rotational movement of an electric motor to a linear motion. This is done by the means of a ball screw-a screw mechanism in which the screw and the nut are connected with each other by means of rolling elements, in this case balls. For these elements, the same technologies apply as for rolling bearings. In order to take up any axial loads that are applied to the ball screw and to disconnect the rotating movement from the static part, a support bearing is necessary. The other integrated parts (like sensors, sealing, and electric motor) will also benefit from the bearing/ball screw precision tolerances for running accuracy. In the case of brake-by-wire systems, the axial loads that have to be accommodated can be as high as 50 kN. The bearing solution is dedicated to the electromechanical actuating unit so that the electronics and the electric motor are integrated efficiently in this application.

Q: Can you give us a sneak preview of new technologies?

A: Many exciting products and technologies are in the pipeline. For example, one can expect additional Explorer-like bearings, and the adaptation of the electromechanical actuating unit in more drive-by-wire applications. On the technology side, the use of the SKF NoWear coating will be extended to non-bearing applications and other coatings will be used to minimize, or even eliminate, the use of lubricants in bearings in certain applications.