Rolling up the energy savings

Since lower frictional torque means less energy loss, this represents a major contribution to reducing energy usage in industry.
Since lower frictional torque means less energy loss, this represents a major contribution to reducing energy usage in industry.
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The need to save energy means it’s essential to look everywhere for ways to reduce consumption. Since rolling bearings are crucial to the transfer of rotational energy, are there opportunities to reduce the energy losses involved in the process?

Since bearings are designed to reduce friction and resulting energy loss, you may think that they already go as far as they can in saving energy. However, research and development by NSK has led to new advances in materials and design, which have led to reduced energy consumption, longer bearing life, and therefore less impact on the environment.

Reducing the frictional resistance of rolling bearings is a never-ending task. However, NSK has developed a theory for frictional resistance, for tapered roller bearings that run in rolling and sliding contact at their ribs and roller ends. By applying this theory to bearing designs for electric motors, NSK has achieved a reduction in frictional torque of as much as 50%, without any adverse effect on bearing life or rigidity.

Since lower frictional torque means less energy loss, this represents a major contribution to reducing energy usage in industry.

Hand-in-hand with improved bearing design is the need for surface optimisation: reducing even further the friction that leads to unnecessary energy consumption, bearing wear and – potentially – bearing failure. Improving the surface geometry with machining processes such as barrelling and honing leads to optimum oil film formation, good compressive stress levels, and high resistance to abrasion and excessive wear. So the surface not only creates less friction, but also remains in this state for longer.

What usually limits rolling bearing life is the fatigue phenomenon of ‘flaking’, where some of the bearing surface peels off in small flakes as a result of repeated stress loads. This can be caused by internal defects in the bearing – such as nonmetallic inclusions in the bearing material – or bearing raceway surface defects: usually dents caused by foreign particles in the bearing lubricant. To overcome the former problem, NSK has developed extra-pure, cleaner steels, known as Z steel and EP steel, to reduce non-metallic inclusions and extend bearing life. At the same time, optimising the retained austenite content in bearing raceway surfaces – through the use of NSK’s TF, HTF, RTF and STF steels – leads to reduced stress concentration from dents and again lengthens bearing life.

The immediate and direct energy saving effect may be limited, but a longer bearing life means less frequent replacement, which in turn means less use of natural resources in manufacturing and transporting new bearings. If that sounds too far removed from your own bottom line, consider instead the reduced overall cost of bearings resulting from fewer replacements, and the reduced downtime from longer replacement intervals.

Lubrication is also an important factor in achieving low torque in bearings. Calling on its experience in the automotive industry, where ensuring efficient cold starts means there has always been a demand for low torque bearings, NSK has long been at the forefront of grease research and development.

NSK EA3 grease is a prime example, having been developed for use on commutator motor shafts, but now available to reduce torque in the operation of rolling bearings. A poly-alpha-olefine type of grease, EA3 maximises energy efficiency by effectively minimising torque. But NSK’s energy-saving innovations don’t stop there.

However effective the grease, it has to be retained within the bearing by seals and shields, which also have a role to play in energy conservation. A too tightly-fitting seal or shield leads to friction in the bearing, and that, as we have seen, leads to energy loss. NSK’s V-type seal is a design innovation which seals effectively with no increase in torque or operating temperature. Not only does the V-type seal have a better sealing capability than a shield, it also has a speed capability comparable to a shielded bearing. Its non-contact lip reduces drag in the bearing, and therefore reduces power loss: a critical consideration in a small electric motor, for example.

Of course, talking about energy-saving is all very well, but the obvious question is how that translates into what matters – saving money. For NSK bearing technology, the answer is: exceptionally well.

For example, NSK recently reviewed a micro wind turbine project which was in danger of being shut down due to the prohibitive cost of its bearings. NSK not only reduced the unit build cost but also improved the unit’s performance, increased its reliability, simplified assembly procedures and increased bearing life from 200,000 to 224,400 hours, resulting in an overall cost saving of €337,600 per annum. Which shows in cold hard figures that rolling bearings have an important role to play in reducing your energy usage.

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