In Focus

Energy efficiency of lubricated bearings

Energy efficiency of lubricated bearings

The energy efficiency of rolling bearings has increased significantly in recent years, mostly due to new bearing designs to reduce friction losses. What is the lubricant's role in this context? Klüber Lubrication developed a new test rig to gain insight into the influence of lubricants on energy efficiency in bearings, optimising the basis for its consulting.

Increasing the energy efficiency of lubricated bearings with expert consulting 

Energy efficiency is one of the big issues of our time. Operators do not only wish to save operating costs, but also to preserve valuable resources. Tailor-made lubricants for the respective application can contribute effectively to this aim: whenever friction is permanently reduced, downtime can be reduced while the operation becomes more efficient. Operators are often unaware of this hidden potential for energy savings. While it may be obvious that greases with low friction coefficients play an important role in very large bearings of wind power stations for instance, they can also bring along considerable savings when used for bearing lubrication in devices and components like electric motors and fans.

Comprehensive test bay for highly efficient lubricants

The first step of energy saving projects is to analyse the status quo, including the efficiency of the tribological system. Klüber Lubrication has a comprehensive test bay to make precise measurements of components' friction coefficients with different lubricants and uses it to develop and optimise highly efficient lubricants for specific customer applications. The efficiency of lubricants in specific applications can also be tested on the test rigs.

This is precisely what a customer requested Klüber Lubrication to do. The lubrication expert used a special test rig to conduct efficiency measurements of open bearings, which had only recently been added to the test bay. The test object were the deep groove ball bearings as used by the customer. The test result was expected to prove increased energy efficiency of open bearings with a lubricant having optimised friction values.

The test rig serves to determine the exact degree to which a grease reduces friction in a component. Positioned in a climate chamber, the bearings are arranged on a test head and driven by a motor. The temperature can be set to actual application temperature. The climate chamber is thermally sealed off from the load unit and the torsion meter. The load unit can be used to load the bearings both radially and axially, while the torsion meter is the central element of the test rig which measures the friction.

The test bearings were deep groove ball bearings type 6204, as used for example in fan motors. In accordance with standard motor design, the frictional moment was measured in two test bearings. It was found that the savings potential with a suitable grease is up to 480 kilowatt hours based on a component life of 20 years or 80 000 operating hours. In view of the number of components in use every day, the savings potential is enormous.

Customised consulting pays off

However, the measurements undertaken on the new test rig showed that the grease concepts do not bring along performance or energy efficiency increases in every case. At high temperatures, the greases' performance capacities were similar. Friction coefficients become more and more similar with increasing temperature. For this reason, the lubricant has to be selected according to application, requirements and objectives, e.g. energy savings.

The operating conditions must always be considered when selecting the lubricant. Beside the application temperature and ambient conditions like salty or dusty air, these include the place where the component is used and the loads it is subject to. Compatibility of all lubricants used is another important aspect, as incompatibility may cause component damage. Klüber Lubrication was able to recommend an alternative lubricant contributing to energy savings after a comprehensive analysis of the deep groove ball bearings, the lubricant and the operating conditions in the case described above.

In conclusion, it is always worthwhile for operators to consult a tribology expert, as effective energy savings can be obtained. Depending on the application, lubricant changeovers can contribute significantly to more energy-efficient operation.

By: Dieter Schuster, Manager Application Engineering (bearings, linear guides, electric motors) Klüber Lubrication München KG