Product category:
Bearings
News Release from: NSK UK | Subject: EA Series spherical roller bearings
Edited by the Engineeringtalk Editorial
Team on 04 June 2001
State of the art package for gearbox
bearings
For gearboxes, NSK now allies the most state of the art design of any spherical roller bearing with a unique bearing material, Super-TF, which provides up to ten times longer life
Today, in all types of industries, designers are seeking to reduce the size and weight of their products, to improve market competitiveness without any loss of reliability or life For crucial components such as bearings this invariably means a tougher working regime of increased loads, higher working temperatures and longer "fit-and-forget" operating intervals
This article was originally published on Engineeringtalk on 4 Jul 2008 at 8.00am (UK)
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Nowhere is this more pronounced than in gearboxes used in automotive, industrial and power generation (in particular wind energy) applications.
As critical components in any gearbox, bearings can be subjected to a very demanding regime, not only from raised operating temperatures, as a result of high loads and operating speeds, but also from severe ambient conditions and lubricant which will feature inherent contamination.
Yet despite these operating conditions, the requirement on the bearing manufacturer is still to provide longer operating life, in some cases, with gearboxes used on wind turbines, as much as 15 to 25 years.
Meeting such demands has meant that bearings have moved from being ordinary support and load bearing components to actual performance enhancers in their own right.
What is making this possible is the bringing together of materials, software, mechanical design and lubrication technologies to produce synergy's of operation that one discipline on its own cannot.
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With this approach, each technology is basically an "element" which, when combined with another, moves the boundaries of technology forward to a new and higher level, enabling optimised machine and equipment performance to be achieved in terms of reliability, speed of operation, size, efficiency and safety.
NSK developed this unique "solutions based" technology approach as a means of meeting the ever changing and increasingly demanding performance specifications required by its customers in the first half of the 21st century.
The advantages and scope of the technology extend to all market segments, providing customer benefits in everything from gearboxes to machine tool spindles, pumps to compressors and steel mills.
In respect of gearboxes, the solutions technology is epitomised with the package of NSK's new EA Series spherical roller bearings, Super-TF steel and the New Life Theory for determining bearing life.
The package allies the most state of the art design of any spherical roller bearing with a unique bearing material, Super-TF, which provides up to ten times longer life in conditions of contaminated lubricant.
Completing the package, The New Life Theory determines much more accurately, based upon empirical data gathered over a wide range of applications over many years, the estimated fatigue life of bearings under various operating conditions.
NSK's development of Super-TF steel is an answer to the problem of premature bearing failures resulting from insufficient or contaminated lubricant.
These failures occur because, under arduous and dirty operating conditions, bearing lubricant is easily contaminated with debris.
The debris particles cause indentations on the bearing raceways.
These give rise to stress concentrations at the indentation edges.
The result is that cracks form from the surface of the material at these stress concentration points, leading to an accelerated rate of fatigue damage and, ultimately, marked shorter bearing life.
The whole process is accelerated in conditions of insufficient lubricant viscosity.
Super-TF overcomes these problems with special materials and heat treatment, which creates a stress relaxation mechanism due to a high retained austenite level at the surface and a high surface hardness due to carbonitriding.
This provides for a longer life even under adverse operating conditions like high contamination and low film thicknesses where surface damage would normally result.
In comparison with bearings made of ordinary carburised steel, Super-TF material offers up to 10 times the life with contaminated lubrication and up to twice the life where the lubricant is clean.
Where the problem is related to insufficient lubrication, the life of Super-TF is still impressive at several times that of ordinary carburised steel.
Besides extending service life under conditions of boundary or contaminated lubrication, Super-TF bearing steel also offer increased resistance to wear and seizure as a result of the dispersion of large number of fine carbides and carbo-nitrides in the bearing material.
In comparative tests with bearings made of conventional materials, such as SUJ2 steel, the Super-TF material structure has shown less than one third the rate of wear and a 40% increase in seizure resistance.
Unique materials technology is the first element in the package which NSK is producing to revolutionise the performance of spherical roller bearings used in gearboxes - especially heavy duty types.
The second element is optimised mechanical design.
This is exemplified in the EA Series, which offers the advantages of longer life, through reduced heat generation and low wear, plus high strength, and improved heat resistance for operation at high temperatures.
A unique feature of the EA bearings is that the EA cage incorporates a roller guide function in place of a guide ring.
Together with other detailed design initiatives, this facilitates the integration of a greater number or larger rollers than is possible with conventional spherical roller bearings.
As a result, the load capacity of the EA Series exceeds that of the conventional bearings by between 10 to 20% In addition, the operational life of the EA bearings is significantly extended by between 30 to 80%.
In user terms these twin improvements mean that in many applications bearings can be downsized, leading to savings in both equipment size, weight and cost.
Another major benefit of the "Next Generation" design is that the guide surfaces within the EA bearings ensure that minimal sliding occurs between the symmetrical rollers and the cage.
Consequently, frictional heat and torque produced within the bearing is substantially reduced and the limiting operating speed increased.
Moreover, the provision of heat stabilised inner and outer rings and cages of pressed steel enable EA Series bearings to operate at temperatures as high as 200øC.
The radical improvements in operating performance and life that can be realised with the package of the Super-TF and EA series have helped bring about a revolution in the way that manufacturers and users estimate the fatigue life of bearings.
For the last 50 years the mechanism for estimating bearing fatigue life has been the ISO standard.
The use of this theory is adequate for most applications, it does not, however, take into account the development of new steels or the vast improvements in steel quality and surface finish achieved over recent years, or enable allowances to be made for contamination of lubricant.
Because of these deficiencies a new model was called for.
This has been supplied by NSK with its "New Life Theory", a new life equation that is particularly relevant to manufacturers of such "infinite life" equipment as gearboxes and pumps.
The value of NSK's New Life Theory is that it enables greater accuracy in predicting equipment failure or required service intervals for applications where operating and lubrication conditions are well understood.
The equation, which is the central core of the Theory, offers advantages of being familiar, as it closely resembles the format of the current ISO calculation, enabling engineers to compare and quantify life improvements.
In some applications the theory enables the use of more compact bearings with a high degree of confidence in their suitability, thus reducing costs. Request a free brochure from NSK UK ...
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