Low-torque bearings bring energy, efficiency & size savings

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Across the global automotive sector, NSK is known for providing bearings that achieve reduced weight and size and low torque for automobiles, via its four core technologies: tribology, materials, analysis and mechatronics. These meet all the needs of the automotive sector in reducing power consumption and emissions, and in enabling more efficient integration of the engine and electrical system, or engine and electric motors in the case of hybrid vehicles.

Low-torque bearings bring energy, efficiency & size savingsThe thrust of these developments, based upon core technologies, has not been limited solely to vehicles. NSK has used technology transfer to effectively bring the same low-torque, low-power benefits to general-purpose bearings used in all areas of industrial production, MRO, construction, quarrying, mining and domestic appliances. In addition, NSK is also working on calculations to quantify savings in energy and cost when low-torque bearings are applied over standard. This will be used to quantify cost and energy contributions for a whole site or even series of sites. This is particularly important when customers are being audited for carbon footprint and for evidence of green credentials.

This transfer initiative has resulted in a 30 per cent improvement in efficiency for NSK’s standard deep groove ball bearings, and an even larger 47 per cent saving for domestic appliance bearings, both compared with conventional ball bearings of the same size. These major savings are helping to reduce energy use in high-consumption equipment such as electric motors, air conditioners and domestic appliances.

A first area of focus in the improvement process was bearing material. Through its developments in materials technology for ball bearings, NSK has proven that improvements in steel cleanliness (principally reducing the number of non-metallic inclusions in a steel) strongly correlates with an improved fatigue limit of bearing steel.

NSK acted upon these results, improving 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 NSK’s ball bearings.

Bearings manufactured from Z steel have a significantly extended service life when compared with 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.

High resistance to abrasion

Building upon the life and wear improvements achieved through new materials technology, NSK developed its surface optimisation process – a key factor in achieving increased efficiency. However, surface optimisation goes further by reducing the energy-consuming friction that impairs efficiency and ultimately leads to wear. A good surface geometry aids optimum oil film formation, while the machining processes ensure good compressive stress levels and high resistance to abrasion and excessive wear. The raceways of NSK’s ball bearings are specially honed to reduce operating friction and to reduce noise. In addition, the better lubricant distribution that results from this operation also ensures longer operating life.

In addition to new materials technology and surface optimisation, NSK has also achieved incremental improvement in the efficiency of its ball bearings with improved low-torque seals and lubricants – in particular, greases. NSK’s experience with electrical motors, and the automotive industry, which has had a historic requirement for low-torque bearings to ensure efficient cold starts, has proved pivotal in the lubrication area.

Grease, of course, is retained within bearings by seals or shields, and these units also play a role in energy conservation; a seal that is too tight a fit will lead to friction in a bearing and consequent energy loss. The challenge in the bearing market has been to develop high-speed seals, which minimise bearing friction. This has led NSK to develop its V-type seal.

NSK’s V seal is a design innovation that seals effectively without an increase in torque or operating temperature. It has better sealing capability than a shield, and a speed capability comparable to that of a shielded bearing. The non-contact lip of the V design reduces drag in the bearing – an important advantage where power loss is critical, as in small electrical motors.

The benefits of NSK’s bearing optimisation programme are not limited to standard ball bearings. The HPSTM series of spherical roller bearings underlines this fact with innovations in cage control, cage coating and lubrication, all of which provide a synergy that delivers extended life, improved machine efficiency and reduced energy consumption.

Slippage minimised

With the HPS design, NSK clarified for the first time the mechanism that causes slippage and creates high friction on the bearing surface, leading to high levels of energy consumption and, eventually, damage due to surface fatigue. NSK verified, by theoretical analysis and bench testing, that the friction can be reduced by controlling the motion of rotating rollers, and that a special surface treatment of the outer ring is effective in achieving this. Based upon these findings, NSK developed mass-production technology and bearings which can minimise slippage to prolong running life by more than twice that of conventional products. As a result of these design initiatives – plus a 20 per cent increase in maximum limiting running speed – the HPS Series provides users in diverse industries such as steel, pulp and paper, transportation, extraction and construction, with significant benefits by reducing maintenance costs, energy costs, and enabling downscaling of product designs.

Products such as the HPS series are increasingly being quantitatively assessed by NSK in respect of their eco-efficiency indicators. This is achieved via set of indicators that NSK introduced in 2008 to measure the ecological friendliness of all NSK products using its own calculation formulas. These indicators enable NSK to quantitatively measure how much an individual NSK-developed product can contribute to the environment. They do so by demonstrating how much better the product can perform than its predecessor in terms of ecological efficiency using numerical values obtained by dividing product value (life and performance of the product) by the environmental burden it creates (weight and power consumption of the product).

The effectiveness of this approach has been recognised in Japan with the Award of the Director-General of the Industrial Science and Technology Policy and Environment Bureau, Ministry of Economy, Trade and Industry (METI). The award, the top prize, was given in recognition of the Neco (NSK Eco-efficiency Indicators) developed by NSK.

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