The most dominant obstacles preventing the full use of High Speed Cutting (HSC) are currently the performance limits of spindle bearing systems due to the speed and service limitations of conventional rolling bearings. Since angular contact ball bearings are most suitable for high speed applications the Brite EuRam project EuroBearing aimed to increase the speed and lifetime of this bearing type by combining ceramic balls with coated races.
As a result of this project, the speed characteristic has been increased by a factor of 1.4. However, cylindrical roller bearings show several advantages in comparison with angular contact ball bearings: apart from the higher radial stiffness and the lack of boring, cylindrical roller bearings are excellent movable bearings because both the inner and the outer ring can be mounted tightly. Due to the high friction between rollers and rim and because of lubrication problems at very high speeds, the speed characteristic is limited to approx. 1.0 106 mm/min, which is about 60% of the speed characteristic achievable with conventional angular contact ball bearings. For this reason, cylindrical roller bearings are rarely used for high speed applications. Nevertheless, the advantages of this bearing type has been realized by Far East and American competitors resulting in significant higher market share due to their intensive R&D work carried out in recent years.
In order to compensate for this delay in European bearing development, the REFINE project aims to develop reliable environmentally friendly spindle bearings for high speed applications. The experience of EUROBEARING will be exploited in REFINE to further optimise the tribological systems of angular contact ball bearings and to develop PVD coatings for cylindrical roller bearings. The combination of wear resistant hard coatings and solid lubricant coatings (e.g. diamond like carbon DLC) is a new approach which offers the capability to change the tribological characteristics. Simultaneously, new environmentally friendly lubricants will be developed and adapted to the new tribological system. High speed spindles and high frequency spindles with angular contact ball bearings as non movable front bearings and cylindrical roller bearings as movable rear bearings will be built and tested. This configuration combines high radial stiffness and the capability to compensate for thermal deformations with an optimal movable bearing.
As a main result the speed limit and service life of this kind of spindle bearing system will be increased by a factor of about two so that it will become a preferable system not only for medium but also for high speed application. The consortium comprises experts in the field of coatings, tribology, roller bearings, spindle bearing design and machine tools. 6 industrial companies and 3 research organisations coming form 5 different member states are involved.
Funding SchemeCSC - Cost-sharing contracts
40069 Zola Predosa Bologna
3439 MT Nieuwegein