Big Dimensions Require Expertise


As big size rolling bearings are going to play an essential role in proper operation of complex machinery, their design and production call for wise quality-oriented decisions by the manufacturer, under pain of unexpected faults or, still worse, machine downtimes.

Big size rolling bearings for heavy industry are costly and require long production times and therefore long delivery times. As a result, users are generally anxious about having at their disposal the spare to be used in case of unexpected faults or damages which can lead to extremely long and burdensome ma- chine downtimes when the backup part is not immediately available. For this reason, it is a matter of primary importance to know the data of the application where the bearing will be mounted on (specifications, exploitation, technical diagram, load, speed, operating temperature, misalignments, lubrication type, etc.) in order to select the adequate product, mainly in terms of total cost of ownership, thus reducing at the minimum the risk of unsuitable parameters, which can cause serious drawbacks. In the light of the fact that big size bearings are going to carry out a critical function for proper operation of complex expensive machinery, nothing can be left to chance and selections should be made with highest level of awareness and information.

RKB Bearing Industries, the Swiss bearing manufacturer, has always been a specialist in all four main classes of radial and axial bearings (self-aligning, cylindrical roller, tapered roller and spherical roller bearings), with outside diameter up to 1,925 mm and mass of more than 4,000 kg. RKB defines as «T3» the segment containing its range of big size bearings, i.e. technological bearings. For this bearing range, in fact, the technology is at the root of the whole production chain, which must be strictly inspected at every step in order to guarantee the consistency of all processes.

Design and Research & Development

Knowledge and experience that were acquired in the field of design and manufacture solutions, both general and related to internal geometry, and appropriately sup- ported by innovative advanced calculation and simulation methods allow to optimize various bearing parameters and many expedients to secure proper operative functioning and life, with regard to the technical features of the application where the product will be mounted on.

                            Figure 2 – Dimensional inspections at RKB metrology laboratory in Switzerland

After the above preliminary remarks, the RKB Group Advanced Software Engineering Unit developed a proprietary software (RRLC ver. 9.1) that is used to estimate the life expectancy of a bear- ing as it is able to consider the very large number of variables that can affect bearing performance. Furthermore, in case of particularly complex and/or unusual con- figurations, RKB Technical Department is also exploiting the capacity of an application software which is based on evolutionary algorithms for design optimization (REABO ver. 2.0).

Strictly connected to engineering stage, there are the R&D activities for materials, heat and surface treatments, executions, topography, contacts, profiles and calculation and simulation software, which lead to higher levels of knowledge for constant updating of technological solutions to be included in the end product. In or- der to meet the more and more sophisticated requirements of the market effectively, as this requires to update one’s know- how according to unceasing evolutions of the field, RKB is yearly devolving more than 10% of the turnover to Research & Development department and has also undertaken cooperative relations with eminent university centres in Europe.

                                                      Figure 1 – Big size RKB technological bearings

Material selection

Material selection is extremely important for bearing end quality, as this is largely depending on the technology used to produce steel. The conformity to com- position, purity, hardenability and stability requirements recommended by International Reference Standards, is significantly more complex and critical for bars with diameter higher than 200-220 mm and ingots. For this reason, at RKB the procurement process of raw mate- rials required by the production activity is following strict specific protocols assuring the compliance with highest quality levels and full operation traceability. Moreover, a sub-specification of the general protocol is applied to each bearing typology, based on the class it belongs to, geometry parameters and related heat treatments.

                                       Figure 3 – Forging processes at RKB T3 Plant

Advanced machine tools and processing

Normally, technological bearings are manufactured in short-medium runs, and this involves the need to use a flexible enough production technology which is also precise and qualified in order to keep up with engineering and R&D constant progress and assure time repeatibility of production batches, through an effective procedure of traceability and upgrading.

The huge capital investments made by RKB to constantly update the CNC ma- chine tools necessary to meet the requirements of big size technological bearing users, which are more and more sophisticated and demanding, such as the players of the wind industry, certainly are an important barrier to the entrance of this specific production sector.

Quality control and service

Big size bearings are intrinsically more inclined to show nonconformity over each production process step. For quality controls RKB is using a multilevel platform. This means online controls of the different transformation and machining processes, particularly during forging, he- at treatments, turning, grinding and assembling as well as final inspections and approvals on assembled bearing, being all these performed at RKB metrology analysis laboratories.

Based on continuing updating and time gained experience, RKB Group implemented a set of more restrictive control procedures including additional steps to locate possible defects before these are spreading into subsequent working cycles. For instance, the ultrasonic inspection of internal material structure is performed both after forging and heat treatments and rough-grinding, while MPI (magnetic inspection) is performed after finish- grinding. Furthermore, these procedures are assuring the Company Wide Quality Control, that is the constant real upgrading of each production cycle activity. Often customers ask the manufacturer of big size technological bearings for support during machinery design. This starts with technical analysis for the selection of the most suitable bearing type, coupling and lubrication to arrive at a real co-engineering activity that is performed by their respective technical departments synergistically. The services offered to end customers can be extended to aids for bearing installation, dismounting and maintenance, as these activities are risking of com- promising the performance of the whole application if not performed by qualified personnel.

At RKB, creating real collaborations with customer technical departments is a customary routine, in order to be able to offer complete support during project discussion. Moreover, RKB Group can pro- vide the services of its own application engineer team for mounting, dismounting and preventive maintenance processes that are properly performed according to accurate instructions and practices. To conclude, given the crucial importance that a big size bearing has on heavy machinery or plant operation as well as the complexity present in all stages of bearing productive cycle, from engineering and design to machining and after-sale service, it can be said that it’s all a matter of company consistency.

In fact, a properly manufactured techno- logical bearing is a peculiarity of organized qualified structures which are vertically integrated and adequately consistent throughout the whole value chain. Moreover, the company consistency of a bearing manufacturer is at the root of a reliable product and the bearing reliability becomes a crucial part of customer reputation whether it is an OEM, a distributor or an ultimate consumer.

check RKB website for more information