DNV-GL certifies NSK Super Tough upgrade material
"Such is the effect of the higher load rating that bearing service life is effectively doubled in wind turbine applications."
NSK Tough Steels are a family of exclusive materials with patented heat treatment processes.
Originally developed to combat the cause of 80% of bearing failures due to contamination and marginal lubrication, NSK Tough Steels have also been proven to drastically improve life in Wind Turbine Gearboxes. In addition NSK's proprietary Tough Steels have proven to prevent White Etching Cracking failures.
Wind Turbines experience bearing failures as a result of subsurface formation of white structure. Tough Steels resist the microstructural changes that cause white structure flakes and axial cracks.
The STF and AWS-TF materials contain increased percentages of chromium and retained austenite to slow the microstructural change of steel that leads to the formation of white structure. NSK’s patented processing of Tough Steels results in increased compressive residual stress to resist crack initiation. Higher levels of retained austenite increase material toughness. Specially developed heat treatments create higher surface hardness for debris, wear and smearing resistance.
White Etch Cracking failures have plagued Wind for several years. Hydrogen ions penetrate the bearing race and weaken the bonds allowing a crack to form.
Compressive Residual Stress
The compressive residual stress found in Super Tough case hardened bearings makes crack initiation and propagation much harder to achieve than in the traditional through hard bearings supplied by the OEM. Through hard bearings have a neutral residual stress allowing for easier cracking and shorter fatigue life.
High Retained Austenite
NSK Tough Steel materials have a high level of retained austenite at the raceway surface. This drastically increases the toughness of the bearing also resisting bearing crack formation.
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High Hardness Raceway
The Carbonitride heat treatment on Super Tough bearings gives the bearing a case hardened profile. This provides the bearing with a higher surface hardness than either through hardening or case carburizing heat treat methods would. This higher hardness reduces the effect of debris on the bearing surfaces increasing bearing life.
High Retained Austenite
NSK Tough Steel materials have a high level of retained austenite at the raceway surface. This drastically increases the toughness of the bearing also reducing the effects of debris on the life of the bearing.
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Smearing damage occurs when the rollers are not traveling the same speed as the bearing race and lubrication is insufficent. This can happen when a roller bearing is too lightly loaded for example during startup or idling. This can also happen when there are sudden speed changes potentially caused by wind gusts, grid connection issues, or braking events.
Black Oxide
Black Oxide surface treatments increase the oil adhesion properties of the bearing. With a more reliable lubrication film the bearing is less likely to experience metal to metal contact even with some bearing slip caused by the above conditions.
High Hardness Raceway
The Carbonitride heat treatment on Super Tough bearings gives the bearing a case hardened profile. This provides the bearing with a higher surface hardness than either through hardening or case carburizing heat treat methods would. Harder surfaces are less like to have the localized adhesion during bearing slip that causes smearing damage.
Better Carbide Distribution
Super Tough bearings have a carbide distribution that is much more uniform in size, and evenly distributed than standard bearings. This distribution helps the bearing carry the load more evenly across the bearing surface minimizing the possability of localized adhesive and smearing wear.
High Retained Austenite
NSK Tough Steel materials have a high level of retained austenite at the raceway surface. This drastically increases the toughness of the bearing also reducing the effects of debris on the life of the bearing.
Related Links
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