The impressive lifespan offered by sealed spherical roller bearings is reducing total operational costs for engineering companies across industry, especially in applications such as metals and quarrying, where bearings are often subjected to a high amount of contamination.
Even in the harshest environments, the best of today’s sealed spherical roller bearings meet the need for industrial companies to improve machine reliability, avoid unplanned downtime and reduce operating costs.
One reason for this enhanced performance is that integral seals have enabled spherical roller bearings to be re-lubrication-free. When provided with integral seals, spherical roller bearings are protected against both particle and moisture contamination, negating the need for re-lubrication in most applications.
As the bearings do not require external seals in all but the most aggressive environments, installation is simplified, further reducing downtime and maintenance costs. The extended lifespan, reduced lubricant use, and capability to run machinery faster and cooler has delivered an excellent return on investment for users of spherical roller bearings with integral seals.
Sealed spherical roller bearings are also helping OEMs optimise equipment design. A sealed spherical roller bearing can, in many applications, last as long as four open bearings. The extended service life of sealed bearings can help OEM manufacturers to optimise their equipment by selecting smaller bearings providing the same or better performance. This, of course, saves weight and cost, and reduces environmental impact.
The sealed bearings also enable quicker mounting and decreased need for external seals - making machines cheaper to manufacture. Sealed spherical roller bearings increase the cleanliness inside the bearings - making it possible to downsize the bearing arrangement without negatively affecting service life or performance.
The bearings can therefore help to lower the weight, cost and environmental impact of machinery. For example, sealed spherical roller bearings have the same load carrying capacity, and in most cases, the same ISO boundary dimensions as corresponding open bearings, enabling applications to be upgraded simply and cost effectively.
Spherical roller bearings are used across industry, but the high availability of sealed bearings within the range has especially benefitted industries such as metals and mining that operate under aggressive conditions. Sealed spherical roller bearings keep contaminants out of the bearing, reducing maintenance costs and lubricant consumption while increasing bearing service life.
For example, SKF’s Explorer sealed spherical roller bearings feature acrylonitrile-butadiene (NBR) double lip seals and high quality grease. The seals virtually eliminate the risk of lubricant leakage associated with conventional open bearings, minimising their environmental impact.
A history lesson
The spherical roller bearing was introduced in 1919 and has since been enhanced to meet customer needs. In 2011, an upgrade was introduced, offering increased lifespan. Tests conducted in SKF laboratories have shown that upgraded spherical roller bearings can last up to twice as long as previous bearings under contaminated or poor lubrication conditions.
The company’s Explorer bearings provide higher dynamic load carrying capacity than previous designs, enabling design engineers to downsize their applications. In addition to being high-capacity the sealed variants generally also provide longer service life and improved operational reliability due to the built-in high degree of cleanliness. Their self-aligning properties enable the bearings to accommodate misalignment of up to 0.5 degrees between the shaft and housing without increasing friction or reducing bearing service life.
The development of bearing steels has greatly influenced major advances in the reliability of bearings. SKF pioneered the use of Bainite hardening for large size bearing rings in the late 1950s and subsequently worked closely with steel producers to enhance hardening processes.
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.
One of the key characteristics of the latest 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 engineers have now achieved almost 100 percent degassing.
In addition, the new material has a much finer microstructure than traditional Bainite, which improves wear resistance 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, 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, when measured as a percentage of ring wall thickness, in a typical bearing, that is up to 150 percent.
Sealed spherical roller bearings withstand extremely harsh environments with a three-barrier method. The first barrier is a non-contact labyrinth seal containing grease that acts as the second barrier by effectively preventing contaminants from moving towards the bearing. The third barrier is the integrated bearing seal that seals the rolling elements inside the bearing and keeps the high performance grease inside where it belongs.
Where uptime and reliability matter, sealed spherical roller bearings will reduce the total cost of ownership. The range of sealed spherical roller bearings on the market continues to grow, offering increased uptime and machine availability, reduced maintenance, resistance to contamination and poor lubrication, reduced noise and vibration levels, and superior reliability to an increasing number of applications.
Phil Burge is with SKF in the UK