Better bearings drive improved efficiency

Bearing optimisation could lead to a huge reduction in energy usage and emissions. Matt Bailey looks at some of the latest developments.

In the quest for energy efficiency, friction is the enemy. Bearings provide an obvious solution for overcoming the forces of friction and they can be found at the heart of pretty much any apparatus with moving parts. Although the standard practise of replacing worn or damaged bearings in existing equipment is still vital, the development of new, more efficient and thus energy-saving bearings has become a priority.

NSK's constant bearing improvement programme was designed to help equipment manufacturers meet energy targets. The programme, a synergy of materials, design, lubrication and sealing technology, has achieved a 30% improvement in efficiency for the company's standard deep groove ball bearings, and an even larger 47% saving for domestic appliance bearings: both compared to conventional ball bearings of the same size.

These savings are helping to reduce energy use in high consumption equipment like electric motors, air conditioners and domestic appliances. "Bearings are components that make a big contribution towards energy efficiency," states Kevin Delehanty, senior applications engineer at NSK. "We, as a bearings company, have an opportunity to drive up efficiency levels, reduce torque and reduce friction.

This is the main driver of our improvement programme. "There are a few different things we can address to achieve greater efficiency," says Delehanty. "There's the relative motion of the ball bearing on the raceway, which generates friction; there's the lubrication, grease, oil which has an effect on the torque and the efficiency; then there's the materials, the steel of the bearings and the cage. Optimising these three areas will increase efficiency.

There are benefits for the consumer in terms of less energy used and lower energy bills, but also the appliances will have longer lifetimes. Downtime is reduced, meantime between failures is increased and you can lengthen maintenance intervals." But there are certain limits to design. The basic ball bearing hasn't changed in a hundred years, although small tweaks to the surface finish of the raceway have been achieved and improved accuracy has resulted from better machining practices.

Improvements in the materials have also had an impact. Steel cleanliness has improved enormously over the last 20-30 years. NSK has improved the steel-making process and operating conditions to reduce impurities substantially, thereby achieving a decrease in oxides. The resulting long-life Z Steel is now the standard material for the company's bearings. Bearings manufactured from Z Steel have a significantly extended service life when compared to conventional vacuum degassed steel: up to 1.8 times longer.

In addition, Z Steel also benefits from more uniform response to heat treatment, a process that ensures good hardness and excellent wear resistance. And then there is the important question of lubrication. "Grease formulation and development is an on-going process," says Delehanty. "New, better greases come on the market all the time. We develop our own, so improvement is step-by step but we don't really anticipate and great leaps forward."

When it comes to producing better bearings for domestic goods, however, there are certain limitations in terms of design. "High capacity bearings for white goods have to fit into the same envelope as the existing bearings but have a higher capacity," says Delehanty. "We can put larger and more balls into the bearing giving longer lifetime and higher reliability. You can also downsize the equipment. If you're using, say, a standard 20mm bore inside diameter ball bearing at the moment, in the same application you could potentially put 15mm high-capacity bearings with the same load rating and the same lifetime, but you've reduced the size, so you can design your equipment to be more compact which is what everybody wants to do."

SKF is another organisation exploring energy-saving bearing technology. "Energy efficiency continues to sit at the top of the political agenda, with the introduction of ever tougher environmental and climate change legislation forcing all companies to cut their consumption of primary energy by 20% by 2020," says the company's Phil Burge. "Manufacturers need to take action, both to control costs and comply with legislation. The efficiency of electric motors is attracting more attention as this technology is responsible for consuming more than two thirds of all electricity in general industry, thus representing a large cost saving potential."

One solution is to replace the bearing units in existing motors with modern energy efficient equivalents. "This can be done both during initial manufacture and subsequent overhaul;" says Burge, "in each case, energy consumption can be cut by up to 50%. This technology makes it possible to reduce frictional losses by at least 30%, even when compared with the most efficient traditional bearings, and by as much as 50% or more, when the comparison is with older product designs."

Energy efficient bearings also run more smoothly and at lower temperatures than standard bearings at equivalent loads and speeds, generating less heat, and extending grease life and re-lubrication intervals to allow maintenance costs to be reduced further still. Also, bearing service life is extended significantly, with it being more than doubled in some cases, which in turn, can have a considerable positive impact on the operating life of the average motor.

SKF's energy efficient bearings feature optimised internal geometry and tough, lightweight polyamide ball cages, which are less susceptible to deformation, as well as featuring low friction lubricating greases, with each bearing being sealed for life to minimise the need for maintenance. Prevention is of course better than cure and there are a range of methods for detecting faulty bearings.

According to Dave Manning-Ohren, condition monitoring manager at Eriks, worn bearings often emit sound at frequencies between 20 and 100kHz, which is outside normal human hearing. "Detection, via fixed or hand-held meters which convert signals to the audible range and present them on a graphical display, can be a valuable method of isolating a faulty or worn system.

Although interpretation requires a degree of experience, the results can be remarkably accurate," he says. "In a few instances, vibration is a specified machine function. In most cases, however, it is an indicator of inefficiency, leading to heat, noise and energy losses. Most vibration occurs within rotating systems, often where it is hard to detect and where it only becomes obvious when components – typically bearings – fail," continues Manning-Ohren. "Measuring vibration can be achieved using small fixed accelerometers, permanently connected to plant-wide monitoring systems, or plugged into portable meters. Alternatively, hand held probes can be used where equipment is accessible. In each case, data is normally collected over time, so that deterioration in operating conditions can be identified and resolved before problems occur."

Reducing energy consumption is now a top priority for many companies to counter the effects of growing energy bills and increasing environmental responsibility. Thanks to developments in bearing technology and the introduction of energy efficient solutions, plant managers are now able to realise dramatic energy savings and increased productivity and reliability, leading to enhanced business performance at a time when it matters most.

Matt Bailey

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