Technology transfer from low torque automotive bearings is bringing energy efficiency and size savings to other industrial sectors, reports bearings specialist NSK
Across the global automotive sector, NSK provides bearing solutions that achieve reduced weight and size and low torque for automobiles via its four core technologies: tribology, materials, analysis and mechatronics. These solutions 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.
However, the thrust of these developments, based upon core technologies, has not been limited solely to vehicles. NSK has used technology transfer to bring the same low torque, low power benefits to general purpose bearings used in all areas of industrial production, maintenance, repair and overhaul (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. NSK maintains that this is particularly important when customers are being audited for carbon footprint and for evidence of green credentials.
Results of this transfer initiative are evidenced by 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 when both are compared to conventional ball bearings of the same size. These major savings are helping to reduce energy use in high consumption equipment as electric motors, air conditioners and domestic appliances.
Improved bearing materials
The first focus area in the improvement process was bearing material. Through its developments in 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 acted upon these results, improving the steelmaking 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 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.
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 the greases. NSK says its 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, and this has led NSK to develop its V type seal.
Reducing bearing drag
The 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.
Benefits of NSK's bearing optimisation programme are not limited to standard ball bearings. The HPSTM series of spherical roller bearings now feature innovations in cage control, cage coating and lubrication, all of which help provide a synergy that delivers extended life, improved machine efficiency and reduced energy consumption.
With the HPS design, NSK clarified for the first time the mechanism that causes slippage and creates high friction on the bearing surface, leading 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 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.