NSK’s cost saving, asset improvement programme (AIP) has doubled the amount of throughput a major international manufacturer of wire is achieving from a cold rolling mill, from around 500,000 tons to 1,000,000 tonnes, as result of solving a problem of bearing contamination with Water Tough WTF bearings.
The wire manufacturer was experiencing costly unplanned shutdowns due to the poor performance of a four- row tapered roll neck roller bearing assembled into the bottom chock of a cold rolling mill. The roll neck bearing was failing prematurely due to the harsh operating conditions, including contamination from water and from solids, in the latter case, mainly steel powder coming from the production process itself.
NSK was called in to find a solution to the downtime problem. This involved engineers from the company in analysing the roll neck bearings, the lubricant used (grease) and the design of the mill line itself. At the conclusion of the analysis, NSK recommended using roll neck bearings manufactured from the company’s unique WTF steel, a material that is particularly suited for use in harsh conditions of solid and liquid (water) contamination.
Water Tough WTF® is one of the results of NSK’s partnerships with leading global steel makers to develop a package of high-performance bearings, matching specific application requirements to provide extended uptime and reduced maintenance costs, despite operating conditions of extreme heat, water ingress, and lubricant contaminated with water and scale.
WTF® has been developed following specific research by NSK into roll neck bearings for use in steel mills; the new steel effectively addressing the tough conditions under which roll neck bearings operate. These include water-infiltrated lubrication and the ingress of foreign particles, such as scale, which can cause flaking of the rolling contact surfaces of the bearings, reducing their service life and often resulting in premature failure.
Water-Tough WTF® steel addresses contamination problems, with a new super clean structure that benefits from tightly controlled levels of surface retained austenite, ensuring that bearing fatigue life is improved under debris-contaminated lubrication. Proof of this improved life has been provided both in stringent laboratory tests and in actual applications in cold rolling mills. These reveal that WTF®, consistently achieves a life up to three-times longer than that of bearings made from conventional case-hardened steel.
NSK’s recommendation of replacing the existing roll neck bearing with a unit manufactured from WTF was acted upon by the wire manufacturer, and this bearing substitution has subsequently brought dividends, in terms of longer life, and reduced maintenance and technical support. Previous to the fitting of the WTF bearing the average throughput before a bearing failed was 500,000 – 600,000 tonnes. Today, with the WTF roll neck bearing in place, throughput has reached 1,000,000 tonnes and counting.