• Products

In this article, Dr. Eng. Alberto Barili of the RKB Technical Team Unit (RKB TTU) presents a recent technological development in the field of rolling bearings, focusing on a demanding application in which both rotational accuracy and a low moment of friction were critical performance requirements.

Recently, RKB was approached by a customer seeking a solution for a complex application involving a special rotating roll operating at low speed in the following configuration: an outer ring fitted to the roll bore and a shaft-mounted inner ring. Initially, the application appeared relatively straightforward; however, two specific requirements made the bearing design particularly demanding.

The first requirement concerned rotational accuracy. The application required a level of rotational precision exceeding standard specifications. This represented a significant manufacturing challenge, particularly because the bearing was a thin-section design. To address this issue, RKB implemented significant improvements to the manufacturing and inspection processes for the rolling elements and bearing rings.

The second, and considerably more challenging, requirement was a low moment of friction during rotation. Minimizing the moment of friction was essential to maximizing the overall efficiency of the customer’s application. The conventional bearing configuration using a brass cage, although reliable and well established, could not meet the required performance level.

For this specific application, the brass-cage configuration generated excessive sliding friction between the rolling elements and the cage pockets. Furthermore, the relatively high density of brass resulted in high cage rotational inertia, which was also undesirable, particularly in terms of sensitivity to speed changes.

A different approach was therefore required. To meet the customer’s demanding requirements, RKB developed a new cage design specifically for thin-section ball bearings, with the primary objective of reducing friction while maintaining the required mechanical and tribological performance.

The selected solution was based on a carbon-fiber-reinforced polymer material. This material was selected for its combination of high mechanical strength, low density, compatibility with a wide range of lubricants, and high operating-temperature capability.

This development was made possible through close collaboration between Jiří Andrle from the RKB Additive Manufacturing department and Petar Petrov, Riccardo Sarcone, and Alberto Barili from RKB TTU. Their collaboration enabled the rapid production of prototype cages using 3D printing technology, significantly accelerating the development and validation process.

The new cage was developed for the CSB 060 T9 thin-section ball bearing. Following the manufacture of the prototypes, extensive friction-torque measurements and running tests were conducted to verify the design and confirm its suitability for the application.

The test results demonstrated a significant improvement over the conventional brass-cage configuration. The breakaway friction torque achieved with the new carbon-fiber-reinforced polymer cage was approximately one-third to one-fifth of that of the corresponding standard brass-cage design.

Following successful validation, the new cage design was qualified for production, and the first batch of bearings was supplied to the customer. The results were satisfactory, confirming that the combination of advanced polymer materials and additive manufacturing can provide an effective solution for demanding bearing applications in which conventional cage designs reach their performance limits.

This development represents a significant example of how RKB can innovate and provide customers with premium, competitive, and application-optimized bearing solutions, including for the most demanding applications.