New developments in the manufacture of bearing steels are enabling SKF to make major advances in the performance and reliability of their industry-leading SKF Explorer class of bearings.
As a result, SKF is launching new versions of the self-aligning roller bearings, which now offer even longer operating life, especially in harsh or heavily contaminated applications, or where there is poor lubrication. In particular, SKF has improved wear resistance and increased the time that it takes for initial spalling to occur and reach through fracture. This means that once bearing damage has been detected, the bearing will continue to operate for longer so that customers have more time to plan, order parts and prepare for a shutdown.
Bearings are normally manufactured from steel alloys and the challenge is to produce a material that combines a number of characteristics: high levels of hardness, excellent wear, ductility and resistance to corrosion and contamination.
SKF pioneered the use of bainite steel hardening for large size bearing rings in the late 1950s and subsequently worked closely with steel producers to enhance the hardening processes. This led to the introduction of the first generation of advanced SKF Explorer bearings in 1999. These brought the benefits of toughness, dimensional stability, wear resistance, surface compressive residual stresses and long fatigue life to bearings in many different sizes for applications throughout industry.
In recent years, the challenge for SKF’s designers and engineers, working closely with scientists and metallurgists at leading universities, has been to develop a bearing steel that combines the traditional bainite properties with even greater robustness and reliability under the most demanding operating conditions.
For many years it was understood that the lower the temperature at which bainite steels are processed, the more their material properties are enhanced. However, it was believed that this could only be achieved by considerably extending the process time.
SKF’s research team found that once the bainite transformation develops to a certain degree at a low temperature, it then continues in exactly the same manner even if the temperature is significantly increased.
This breakthrough, combined with advances in manufacturing technology, has made it possible to develop a patented, commercially viable and extremely efficient heat treatment process that allows SKF to capitalise on the mechanical advantages of low temperature bainite without sacrificing any of the steel’s traditional benefits.
One of the key characteristics of the new bainite steel is its extremely low oxygen content; in essence, the lower the oxygen content the better the bearing life, and although oxygen content has been decreasing in bearing steels for many years SKF has now achieved almost 100% degassing.
In addition, the new material has a much finer microstructure than traditional bainite, which improves wear resistance – up to 60% better than that of the steels used in previous SKF Explorer bearings – and also gives exceptional dimensional stability and structural strength. These advantages are maintained even under conditions where there are high levels of contamination or where there is insufficient lubrication. In both cases, these tests have shown that operating life is typically doubled.
The new steel also has the ability to resist stress and fatigue cracks. Micro-fissures that do develop are able to penetrate to a far greater depth before a critical failure occurs, and take longer to develop from initial spall to through-fracture.
By comparison with conventional steels, the new bearing steel has a crack depth that, when measured as a percentage of ring wall thickness in a typical bearing, is up to 150% greater.
In an operational context, the far slower and more predictable rate at which micro-fissures occur provides an opportunity to schedule maintenance activities, thereby maximising mean time between failure (MTBF) and machine uptime.
The performance and reliability of the new bearings have been enhanced still further through careful redesign of the rolling elements, cages and guide rings.
For example, floating guide rings ensure that rolling elements are correctly aligned, with high load bearing strength, minimal friction and low temperature, while internal geometries and surface finishes are optimised to eliminate stress on moving parts and ensure efficient oil-film build up with long lubricant life
The new SKF Explorer bearings last longer, with predictable failure rates, and deliver smoother, lower temperature operation under the most demanding conditions. They are available in a full range of sizes and specification, making them ideal for applications in mining and quarrying, materials handling, marine, offshore and manufacturing.
For more information contact Samantha Joubert, SKF South Africa, +27 (0)11 821 3500, [email protected], www.skf.co.za
| Tel: | +27 11 821 3500 |
| Fax: | +27 11 821 3501 |
| Email: | [email protected] |
| www: | www.skf.co.za |
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