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30 April 2012

NSK’s asset improvement programme is saving the operator of a Cold Rolling Mill €16,300 annually as a result of solving a problem of bearing failure that was occurring three/four times per year, resulting in unplanned shutdowns and serious loss of production at the mill.

The mill operator was being forced to change bearings up to four times a year due to the harsh working environment in which the bearings operated. The bearings were failing prematurely due to contamination; ingress from dirt, debris and liquids that were affecting the bearing lubricant and shortening bearing life.

NSK was called in to find a solution to the failure problem. This involved engineers from the company in analysing the mill bearings, and taking samples of the lubricant used (grease) to determine the actual operating conditions. At the conclusion of the analysis, NSK recommended using spherical roller bearings manufactured from the company’s Super -TF steel, a material particularly suited for use in environments subject to contamination from debris.

A unique bearing material developed by NSK, Super-TF provides up to ten- times longer life in conditions of contaminated lubricant, in comparison with bearings made of ordinary carburised steel. Where the problem is related to insufficient lubrication, the life of Super TF bearings is still impressive at around 5.5 times that of ordinary carburised steel.

In addition to extending service life under conditions of contaminated or boundary lubrication, Super TF bearings also offer increased resistance to wear and seizure. In comparative tests with bearings made of conventional materials, such as AISI 52100 steel, the Super TF has shown less than one third the rate of wear and a 40% increase in seizure resistance.

Following NSK’s recommendation, Super-TF spherical roller bearings were installed in the cold rolling mill. After 4-months in operation the bearings were disassembled & sent back to factory. The laboratory results found that the minimum residual life was between 29-50 months, compared to less than 4-months previously. To date the customer has replaced the bearings once, and that as part of a planned annual shutdown for scheduled maintenance.

More about Super-TF Steel
Super-TF steel provides an answer to the problem of premature bearing failures resulting from contaminated or insufficient lubricant. These failures occur because, under arduous and dirty operating conditions, bearing lubricant is easily contaminated with debris. The debris particles are then indented on the bearing raceways causing stress concentrations at the indentation edges. This results in cracks forming at the stress concentration points, leading to accelerated rates of fatigue damage and, ultimately, shorter bearing life.

Super-TF overcomes these problems with a unique microstructure which is able to relax the stress concentrations on the edges of indentations. This microstructure - a material with a high volume of retained austenite and a high hardness - produces a longer life even under conditions where there is an insufficient oil film and surface damage, such as peeling, easily occurs.

New Free Publication for the Steel Industry
NSK has detailed its innovative bearing products for the steel industry in a new publication. Running to 40 pages the free booklet provides a wealth of information regarding the choice of bearings for plant and equipment used in steelmaking processes. Free copies of the publication are available via NSK’s Freephone service Tel: 0500 2327464. Callers should quote the catalogue reference Cat STE/B/E/03.11 (English), and also the title of the publication: ‘Bearings for the Steel Industry’.

For further information, please contact Mary Fletcher:

, Northern Road, Newark, Nottinghamshire, NG24 2JF Tel: 0500 2327464 Fax: 01636 643075 Web: www.nskeurope.com  Email: info-uk@nsk.com
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