In addition to the low-torque and low-noise demands placed upon rolling bearings used in electric motors, there is now the added requirement for longer service life to conserve energy and resources. NSK is meeting these requirements with a programme that delivers innovations in materials, production techniques and lubrication technologies. The programme has achieved 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.
An innovator in bearing steel, NSK has collaborated with steel makers to improve the steel-making process, reducing impurities substantially and achieving a decrease in AI2O3 alumina 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.
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.
Complementing the role of surface optimisation, improved bearing design, provided by the combination of cage and bearing balls, also contributes to improved efficiency.
Even distribution of lubricant
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 long service life.
In addition to 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 in 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. This experience has led to the introduction of a newly developed long-life, low-noise, and low-torque EAM urea grease for industrial motor bearings.
By adopting NSK ball bearings filled with EAM grease, electric motor manufacturers benefit from extended life against seizures, without sacrificing low-noise and low-torque performance. EAM grease offers a greater degree of low-torque performance than that of conventional lithium-soap grease. Such low-torque performance was achieved by selecting and blending the base oil and thickener using a special process that lowers friction and resistance, which thus lowers torque in the bearing.
With many of the applications for electric motors being in dirty or dusty environments, NSK offers several sealing options to protect motor bearings, and extend their life. The popular metal Z shields for high-speed applications protect against light contaminants, such as dust, and are coated with special anti-corrosion zinc. They provide superb performance across a wide temperature range.
In applications calling for even more protection, NSK’s patented non-contact labyrinth V seals are available. The V seal is a design innovation that seals effectively without an increase in torque or operating temperature.
The V seals have 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.
To learn more about energy efficient long life bearings for electric motors, please go to www.nskeurope.com.