By David R. Mikalonis
Every innovation in the design, engineering, and materials for rolling element bearings ultimately expands options for design engineers to specify the right bearing for the right application and, in turn, elevate equipment performance to new levels. While bearings in rotating equipment primarily serve to support shaft loads, reduce friction with rolling elements, and provide shaft location and system rigidity, these precision components can contribute so much more. Recent trends certainly bear this out.
1. MATERIAL UPGRADES
Every feature of a rolling bearing will play a vital role in success or failure in service. This includes the bearing material and, from this perspective, unconventional materials are making inroads as alternatives to standard bearing steels for those applications where a switch would be appropriate.
Example: Bearings routinely exposed to highly corrosive elements and/or repeated chemical wash downs typically will be unable to withstand the constant attacks from corrosive media over time (especially without proper sealing or shielding). This dilemma has led to the breakthrough development of highly corrosion-resistant steel – shown to outperform conventional grades of stainless steel – and has expanded the material world of bearings.
High Nitrogen Corrosion Resistant (HNCR) steel exhibits superior corrosion and wear resistance compared with 440C Series stainless steel and superior corrosion resistance and equal wear characteristics compared with 52100 Series stainless. Bearings featuring inner and outer rings made from HNCR steel can deliver unequaled protection in extreme corrosive environments without sacrificing hardness and fatigue life.
Specifically, the combined presence of nitrogen and high chromium in HNCR steel imparts superior corrosion resistance. HNCR steel also offers greater material “cleanliness” than 440C and 52100 steels and almost no presence of sulfides, aluminates, silicates, or globular oxides. The lack of these non-metallic contaminants contributes to enhanced bearing life, as does the extremely homogeneous structure of HNCR steel.
In terms of hardness and fatigue life, HNCR steel further outperforms, especially since HNCR steel is a martensitic through-hardened steel capable of being case- or induction hardened. Hardened and tempered HNCR steel exhibits hardness comparable to the hardness of 52100 stainless. And, based on fatigue test data, HNCR steel can yield a significantly longer fatigue life – up to three times greater – than conventional stainless steels.