FEATURE TEST & MEASUREMENT
TESTING LARGE BEARINGS under operational conditions
Phil Burge, marketing and communications manager at SKF, describes how the
company overcame the current limitations of simulation and modelling software for large bearing design using the facilities of a new test centre in Germany, which, in turn, are contributing to the improvement of these models
F
or small to medium sized bearings, modern computer simulation has
allowed designers to refine the geometries and discover in minute detail the dynamics and the load distributions within these components well before they enter production. Computer simulation has enabled the release of ‘right first time’ products and significantly reduced incidences of premature wear or failure thanks to the software model's ability to provide realistic ‘cause-and-effect’ analyses in the virtual world that can be accounted for in the design prior to prototyping. But when it comes to much larger
bearings - typically those installed in the drives of large wind turbines or supporting ship propulsion systems - simulation tends not to work quite so well. Indeed, there is no simulation platform in the world today that is able to reproduce the dynamic behaviour of large-size bearings in a truly realistic manner. Subsequently, some large-size bearings that have been placed in service are prone to premature damage and failure, despite being manufactured to the highest standards while also incorporating additional ‘safety margins’ within their design. Marine propulsion shaft bearings and
wind turbine main shaft bearings are subject to enormous forces, such as the shocks and surges associated with storm sea conditions, or the veering, gale-force winds encountered in remote, offshore wind farms. In these real-world applications, something is happening within these large bearings that is defeating the cause-and-effect algorithms of current simulation models, and design engineers are having to resort to more traditional methods in order to assess their robustness – i.e. physical testing. But how do you subject a bearing of
more than six meters in diameter and weighing several tonnes to the forces that it is likely to encounter out in the field, in a laboratory environment? SKF’s own portfolio of simulation software tools, including SimPro Expert
30 SEPTEMBER 2017 | INSTRUMENTATION
Test data will be used to improve the accuracy and effectiveness of current simulation models for large bearing developments
rams that are capable of producing several megaNewtons of dynamic load. The rams act on a 7m diameter, 125 tonne steel disc rotating within the rig, which transfers the forces via an adapter, to which the tested bearing is attached. This arrangement ensures that the forces acting on the test specimen are not limited by the inherent stability of a bearing exerting the load, while ensuring that the loads are applied over all axes. Accelerated testing allows a 20-year expected lifecycle to be condensed to just a couple of weeks. The smaller rig is additionally fitted with
and Beast, have proved to be effective design aids for the company's small to medium sized bearing developments, but have hitherto proved of limited use when trying to determine the dynamics and life expectancy of large bearings such as those outlined above. In a major project designed to reveal the unpredictable ‘hidden’ root causes of damage to large scale bearings, SKF has invested some €40m in a large-size bearing test centre capable of physically simulating real world conditions and testing large-size bearings to their absolute limits within a controlled environment. Located in Schweinfurt, Germany, the new Sven Wingquist Test Centre was officially opened in June of this year and houses two rigs – the largest designed for the testing of wind turbine main shaft arrangements, and a smaller one dedicated to the testing of bearings used in other heavy industrial sectors, including mining, construction, steel manufacturing and marine transport. The larger rig, isolated from the
building’s main foundations and weighing in at around 700 tonnes, can test a single wind turbine main shaft bearing with an outside diameter of up to six metres, or a complete bearing assembly with customer components attached. It comprises 64 radially and axially arranged hydraulic
lubrication equipment from SKF Lubrication Systems, which, contrary to its normal mode of operation, can drive a bearing under test to its boundaries in terms of lubricant deficiency and elevated lubricant temperatures. Lubricant is metered and distributed via a number of conduits to the bearing under test, enabling internal flows to be examined in close detail. Multiple sensors are installed to measure local temperatures, as well as vibration, loads and the positions of critical bearing components. In this way, it is possible to relate dynamic phenomena to specific operating conditions. While these new test rigs are set to
deliver deeper insights into the behaviour of large bearings under real-world load conditions, ultimately leading to improvements in the robustness of future generation products, their test data will also be used to improve the accuracy and effectiveness of current simulation models for large bearing developments.
SKF
www.skf.co.uk
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