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Increased efficiency for ball bearings
NSK says its constant bearing improvement programme has achieved a 30% improvement in efficiency for its greased sealed-for-life deep groove ball bearings, compared to conventional ball bearings of the same size. This major saving is helping to reduce energy use in high consumption equipment as electric motors, air conditioners and domestic appliances.
The 30% improvement in efficiency is the result of a synergy of materials, design, lubrication and sealing technology. Through its developments in the materials technology for ball bearings, NSK has shown 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 has acted upon these results, improving the steel making process and operating conditions to reduce impurities substantially, thereby achieving a decrease in oxide non-metallic inclusions. The resulting long-life steel is Z Steel, which is now the standard material for NSK's ball 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.
Like new materials technology, surface optimisation plays a key role in achieving increased efficiency. However, surface optimisation goes further by reducing the energy-consuming friction that impairs efficiency and ultimately leads to wear. For a surface design to ensure reduced friction and longer bearing life, machining processes (barrelling and honing) as well as surface roughness play important roles.
A good surface geometry leads to 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.
Complementing the role of surface optimisation, improved bearing design, provided by a unique combination of cage and bearing balls, also contributes greatly to improved efficiency. The pressed steel cages used on NSK's ball bearings have close coined pockets and tightly controlled clearances to reduce friction and ensure even distribution of lubricant. The balls optimise this combination with their almost perfect levels of sphericity, minimising friction with their precision surface finish. They are ground on machines designed and manufactured by NSK specifically for the purpose, hence the consistent super-precision finish that also helps the bearings deliver maximum service life.
In addition to materials technology and design, NSK has also achieved incremental improvement in the efficiency of its ball bearings with improved low torque seals and lubricants - in particular, greases. Originally developed for use on induction motor bearings, NSK's NS7 grease is a Polyolester diester type, which is superior in low-torque characteristics to maximise energy efficiency in the operation of ball bearings used in motors, pumps, air conditioners and compressors.
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