When SKF first launched the SKF Explorer performance class in 1999, it set new standards for bear­ing performance.
By combining material, design and manufacturing improvements, SKF engineers and scientists were able to maximize the effect of lubri­cation and minimize the effects of friction, wear and contamination. The result: a performance class of bearings that provided higher load carrying capacity and extended bearing service life. The superior behaviour of this performance class has been confirmed and validated by leading certification bodies, certificate 72736 dated 10/05/2006 from Germanischer Lloyd and CPN-1441-1 dated 10/05/2006 from Det Norske Veritas.
From a materials perspective, SKF Explorer self-aligning roller bearings were characterized by an extremely clean and homogenous bearing steel that underwent a unique heat treatment process. The purity of the steel gave SKF Explorer bearings their exceptional strength and durability. The heat treatment created the optimal com­bination of hardness and dimen­sional stability.
These improvements in material performance were built into a new bearing concept with improved surface structures and refined internal geometry tolerances. SKF also made signifi­cant investments in its manufac­turing processes.
The result was a highly reli­able range of self-aligning roller bearings, with low friction, high load carrying capacity and minimized stresses.
Since the introduction of SKF Explorer spherical roller bearings, the SKF Explorer performance class has expanded to include other bearing types including tapered roller bearings, cylindrical roller bearings, deep groove ball bearings and angular contact ball bearings. Today, all standard spherical roller bearings, CARB toroidal roller bearings and most spherical roller thrust bearings are manufactured to SKF Explorer performance class specifications.

Heat treatment adds performance

Now, SKF has further improved the heat treatment for self-aligning roller bearings (fig. 1), so that they are even more wear resistant. Though this upgraded heat treatment can improve uptime for virtually any application where reliability and long service life are key operational parameters, the benefits are most apparent in industrial applications where there are high levels of contamination or poor lubrication conditions. Typical examples include the metals, mining, mineral and cement processing industries, wind power and marine, industrial transmission and material han­d-ling applications.
To reach this new level of performance, SKF engineers were able to adjust the heat treatment process and increase hardness by up to 2 HRC (depending on bearing size) while maintaining or improving toughness.
This is particularly important for medium- and large-size bearings used in process equipment.
The improved toughness pro­vides more time from when the first signs of damage are identified, until the bearing becomes unservice­able. This additional time enables end-users an opportunity to track the condition of the bearing as they prepare for repairs, virtually eliminating unplanned downtime and reducing the additional costs typically associated with it.

Validation testing

The upgraded heat treatment process results in significantly improved wear resistance for upgraded SKF Explorer bearings when compared with original SKF Explorer bearings. Validation testing was carried out at testing centres within SKF and at KTH University (Royal Insti­tute of Technology) in Stockholm, Sweden, to validate the perfor­mance improvements. The test results (fig. 2) show the improved wear resistance that upgraded SKF Explorer self-aligning roller bear­ings provide.
Other tests, conducted at the SKF Engineering and Research Centre, to verify the service life gain of upgraded SKF Explorer self-aligning roller bearings under poor lubrication conditions (fig. 3), indicate that these bearings can last up to twice as long as original SKF Explorer bearings. For contamin­­ated conditions, endurance tests (fig. 4) similarly indi­cate a possible doubling in service life for upgraded SKF Explorer bearings, when compared with the original SKF Explorer bearings.
To verify the extended failure mode of upgraded SKF Explorer self-aligning roller bearings, through-fracture tests were per­formed on the rings. In these tests, upgraded SKF Explorer bearings were compared with original SKF Explorer bearings.
The results shown in fig. 5 indi­cate that the average radial crack depth at through-fracture, for rings in upgraded SKF Explorer bear­ings, is deeper than for original SKF Explorer bearings. This shows that medium- and large-size upgraded SKF Explorer bearings can further extend the time from initial spalling to through-fracture. The extended failure mode, when part of a proactive maintenance programme, can virtually eliminate unplanned downtime.
The flange strength of upgraded SKF Explorer spherical roller thrust bearings was tested against original SKF Explorer bearings (fig. 6). After the flanges on origin­al SKF Explorer fractured, the upgraded SKF Explorer bearings ran twice as long and had only developed spalls.
Even though bearings in process equipment are not run to through-fracture, these tests show that once bearing damage has been detected, upgraded SKF Explorer bear­ings continue to operate longer, providing more time to plan, order parts and prepare for a shut­down; thereby reducing downtime and its related costs.

Conclusion

The contribution that the improved heat treatment pro­vides, to extend the service life of upgraded SKF Explorer self-align­ing roller bearings, is significantly improved wear-resistance, which can result in up to twice the bearing service life under poor lubrica­tion or severe contamination conditions. This opens the oppor­tunity for end users to increase equipment uptime in some of the harshest and most challenging industries, from wind power to metals processing.

CARB is a registered trademark of the SKF Group. SKF EXPLORER is a trademark of the SKF Group.