Bearings - 2013-02-25
NSK has developed spherical roller bearings especially for steel-industry applications. Made from extra tough, wear-resistant steel, they also feature highly efficient seals. Field experience shows that these bearings can significantly reduce downtime for continuous casting machines.
The bearings used for guide rollers in continuous casting machines have limited service life due to their adverse operating conditions. Contamination from mill scale and water spray both have a negative impact on the components’ useful lives, as do very low speeds and high mechanical loads.
At one company in the steel industry, the bearings’ life expectancy was so low – just one to two months – that downtime was seriously impairing productivity. Part of the problem was that continuous casting machines have a complicated coolant and lubricant supply system which had to be reconnected every time the machinery was serviced. This was a lengthy process.
The plant managers contacted NSK’s industry experts, who visited the site to analyse the use of bearings as part of NSK’s Asset Improvement Programme (AIP). They found that the premature wear and tear was attributable to contamination and the fact that the existing cylindrical roller bearings were unable to compensate for the deflection of the guide rollers. NSK therefore suggested replacing the bearings with special sealed spherical roller bearings from the SWR series (Super Wear Resistant). The plant operator acted on NSK’s recommendation.
The material used to make the outer rings of these bearings was specially developed by NSK for applications of this kind – i.e. bearings subject to low speeds, high mechanical loads and a contaminated environment. Its resistance to wear is higher than that of conventional bearing steel by a factor of three. When it comes to protection from fatigue damage, it performs better by an impressive factor of five. The material also has five times more core toughness.
By using spherical roller bearings rather than cylindrical roller bearings, it is also possible to compensate for the misalignment caused by shaft deflection. In addition, the bearings are subject to more even loading. On top of all this, there is no need to connect the bearings to the central lubricant supply system because they are pre-lubricated and sealed for life. This makes replacing them quicker.
The change of bearings suggested by NSK led to a substantial improvement in bearing performance, extended the bearings’ average service lives to four months, and cut the cost of lubricant, spare parts and servicing. All in all, the operator now saves approximately €14,850 a year by using SWR spherical roller bearings.
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