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NSK has achieved a 'world first' by combining carbides technology with a special alloy to develop a new super wear resistant (SWR) bearing steel for rolling bearing applications. Designed for use in the guide rolls of continuous casting machines, Super Wear-Resistant bearings have more than twice the life compared with conventional (SUJ2) bearing types. In field tests the SWR bearing has proven to be superior not only in wear resistance, but also in surface originated flaking life characteristics and core toughness.
As a result, NSK plans to develop SWR technology for use in other industries, in addition to steel, where low rotational speeds result in high levels of bearing wear.
The spherical roller bearings used in the guide rolls of continuous casting machines operate under some of the most severe conditions imaginable: heavy load, ultra-low-speed rolling (only a few rotations per minute), and an environment of water and dust contamination.
As a result of these conditions, the bearings often suffer from uneven wear on their outer ring raceways, leading to the development of cracks and flaking.
In some cases the flaking results in outer ring fracture, causing the bearing to fail, sometimes with very serious implications for continuous steel production.
To combat these conditions, NSK has developed a bearing whose life can be extended by means of the latest materials and heat treatment technologies.
Key to this development is a new type of steel, SWR; one that provides superior wear resistance under severe lubrication conditions, and also high resistance to surface originated flaking.
SWR is a synergy of materials (ie a special alloy), carbonitriding technology, unique heat treatment and surface hardening.
The special alloy is combined with NSK's carbonitriding technology to produce a material with large amounts of hard, fine-grained particles in the material surface.
The major benefit of this bearing material is that it provides superior resistance to wear: approximately seven times that of conventional AISI 52100 steel.
The second key element in the development of the new longer life SWR material is NSK's patented TF Technology.
This includes a special heat treatment process developed by NSK to optimise the level of retained Austenite in bearing steel.
The value of retained austenite is that it minimises stress concentrations around defects on the bearing surfaces, thus achieving extended flaking life performance under conditions of contaminated lubricant.
When compared on the basis of L10 life1, at which the cumulative damage probability becomes 10%; it can be said that the life of the newly developed SWR steel is about five times that of conventional AISI 52100 steel.
In addition to heat treatment, the newly developed SWR steel is also case hardened so that its core toughness is about five times as high as that of a SUJ2 through-hardened type steel.
The benefit of this process is that it allows the compressive residual stress in the surface layer of the SWR bearing material to function effectively, providing high resistance to flaking and helping to prevent outer ring fractures.
These qualities have been proven in core toughness tests, the SWR bearing steel exhibiting fracture toughness five times higher than that of conventional bearing material, making it more resistance to the development of cracks and fractures.
Following the excellent results obtained from its in-house testing programme, NSK has undertaken field evaluations of SWR bearings on continuous casting lines in co-operation with several major steelworks.
The results of these evaluations show that SWR bearings provide two or three times more life when compared with conventional bearings.
As a result of this success SWR bearings are set to make a real contribution to the extension of maintenance cycles on continuous casting machines, and to promote greater efficiency of production through the superior characteristics of flaking resistance and ultimate fracture resistance.
| Product Model | Inside Diameter | Outside Diameter | Thickness |
| GRAE40NPPB bearing | 40 | 80 | 30.2 |
| GE35KLLHB bearing | 35 | 72 | 37.7 |