Steel plate rolling mill achieves €46k savings thanks to NSK bearings

Faced with high maintenance costs relating to bearings on a plate rolling mill, a major steel manufacturer has witnessed significant benefits following an application specific product replacement from NSK. Until recently, a daily maintenance routine was required on the rolling mill’s existing open roll bearings to ensure sufficient lubrication. However, analysis by NSK led to the proposal, and subsequent installation, of advanced Sealed-Clean bearings, which are designed specifically for use in heavily contaminated environments and offer 2.7 times longer life than conventional roll neck bearings.

The iron and steel industry is among the most demanding environments in which power transmission equipment is expected to operate. The bearings used on rolling mills have to cope with a multitude of extreme operating conditions, which include high temperature variations, both fast and slow rotational speeds, and heavy loads. In addition, they are expected to withstand exposure to moisture, corrosive contaminants and damaging particulates.

At this particular steel manufacturer, the team of maintenance engineers was having to spend valuable time every day re-lubricating its bearings. The arrival of the NSK application engineers, with their extensive experience of the iron and steel industry, signalled a change of technology, namely the deployment of a bearing with enhanced sealing protection and better bearing steel technology. Through NSK’s Added Value Programme – AIP, the additional benefits of the Sealed-Clean range could be ably demonstrated.

The solution centred on the adoption of four-row, sealed tapered roller bearings on the roll necks of the steel manufacturer’s rolling mills. Here, they are expected to offer long life despite extreme operating conditions such as high loads, severe shock loads and the presence of high pressure water and scale debris. However, in comparison with conventional sealed roll neck bearings, advanced seal technology developed by NSK means the customer is now enjoying both longer service life and greater reliability, as well as the potential for higher load capacity.

NSK’s four-row, sealed tapered roller bearings are manufactured from the company’s patented Super-TF bearing steel. This unique innovation was derived from NSK research that set about tackling the problem of bearing life in conditions of contaminated or inadequate lubrication – two major causes of premature bearing failure in rolling mills.

The research revealed that bearing life in such conditions could be improved by altering the bearing steel’s microstructure, thus enhancing its ability to relax stress concentrations on the edges of indentations. The microstructure, featuring a high quantity of retained austenite and high hardness, is able to deliver extended life, even where there is an insufficient oil film to protect the bearing’s surfaces from damage.

In reality, the most impressive results are seen when both retained austenite and hardness are increased together, rather than in isolation, as is the case with Super-TF steel. Compared with bearings manufactured from ordinary carburised steel, tests show that NSK bearings made from Super-TF demonstrate up to 10 times greater life with contaminated lubrication and up to double the life where the lubricant is clean. In cases where insufficient lubrication is the issue, bearings produced from Super-TF still offer an impressive 5.5 times greater life (on average) over ordinary carburised steel bearings.

A major feature of NSK’s latest design of Sealed-Clean bearings is the inclusion of the cage flange within the seal space of the bearing, which permits the use of longer rollers. In addition, the cage diameter is now bigger to accommodate more and larger rollers without any detriment to cage strength. From a performance perspective, these enhancements elevate the basic dynamic load rating capacity by up to 34 percent when compared with NSK's conventional roll neck bearings. In short, this equates to an impressive 2.7 times longer life.

For the steel manufacturer, the introduction of Sealed-Clean bearings from NSK saved over €46,000 thanks to the elimination of daily maintenance operations in combination with the cost of grease (and the cost of disposing of used grease). What’s more, the environmental cost of production has also been reduced significantly.

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