On a roll

Swedish bearings manufacturer SKF has redesigned its two most popular types of bearing to be more energy efficient. It says that design changes to its deep groove ball bearings and tapered roller bearings will make them at least 30% more energy efficient. The energy saving refers to the friction torque of the bearing itself, and not to the system – such as an electric motor – in which it is being used. The main factors are behind the improved efficiency of the ball bearings are: use of a new low-friction grease; a redesigned internal geometry; and the use of a polymer cage. As well as industrial electric motors – the first likely application – SKF believes the deep groove ball bearings will find use in gearboxes, compressors and fans. For the tapered roller bearings, the company has managed to reduce the number of rollers – and therefore, total weight – without affecting performance. In addition to increased energy efficiency, there is less intertia (leading to less skidding), the ability to run at higher speeds and a reduction in working temperature. The first application will probably be in wind turbines, though other medium to large sized applications such as industrial transmissions, hydraulic pumps and railway applications are expected to follow. The products will initially be available with outside diameters of 220-600mm. While the energy saved by each bearing is relatively small, SKF says the cumulative effect of replacing standard bearings with these new ones could be significant. “Bearings account for 0.6% of losses from an electric motor – so this is where savings could be made,” says Stathis Ioannades, product R&D director at SKF. If each bearing is 30% more efficient, this means that each replacement of a ‘standard’ bearing could increase motor efficiency by 0.18%. The calculation is not this simple – because factors such as balancing and alignment also have to be taken into consideration – but is a guide to the level of potential savings. The company claims that replacing five pairs of bearings in the gearbox of a 2MW wind turbine could lead to a 0.5% increase in energy efficiency. SKF has tried to maximise ease of replacement by producing the new designs in standard ISO dimensions. Production will begin in the second half of the year, with product available towards the end of 2007 – though SKF already has prototype samples to take to selected customers. The new bearings have been tested through simulation – using SKF’s Bearing Simulation Tool, or ‘Beast’ – and physical testing. “If we didn’t have the software, the physical testing would be more extensive,” says Johnstone. “The correlation between model and test is very good.” He also said that SKF will be extending the re-design to products beyond deep groove ball bearings and tapered roller bearings. These two were chosen first because they are produced in the highest volume. “We are already working on other product areas. Some of this will be influenced by customers,” said Johnstone. However, he would not speculate on which type of bearing might be redesigned next – but confirmed that there would be no announcement this year. “We are working with customers already, to determine the order in which we introduce the new products,” said Johnstone. POINTERS Re-designed ball bearings and roller bearings could be at least 30% more efficient in terms of friction torque Replacing five pairs of bearings in a 2MW wind turbine could lead to a 0.5% increase in turbine efficiency Similar redesigns of other types of bearing are planned – but none have yet been confirmed