NSK´s expertise in solving issues for the worldwide steel industry is helping achieve savings of €372,555 per annum on a continuous annealing line thanks to the elimination of unplanned downtime resulting from failed bearings. On average, the steel strip annealing line was enduring unplanned downtime of 17 hours per year, which for a process intended to be continuous proved extremely costly. Adding up the costs of production stoppages, the need to hire heavy lifting gear and the requirement for additional maintenance personnel, meant each lost hour was costed at €21,915.
To help eliminate the annual average downtime cost of €372,555, the global steelmaker called upon the services of NSK. Applying the company´s AIP Added Value Programme, expert engineers performed analysis on the failed bearings and identified that both the bearing type and the sealing arrangement were inadequate for the application. Due to both contamination and lubrication issues, the ball bearings showed significant fatigue.
With the high load and low speed of the application in mind, it was recommended that the steel plant switch to NSK´s multi-row sealed cylindrical roller bearings (crane sheave bearings). As the name implies, this bearing type is often employed in crane sheaves found in quarries, ports and construction sites. However, the high load capacity and advanced sealing of crane sheave bearings means they are also ideal for use in the demanding conditions that prevail in steelmaking environments.
On the steel strip annealing line, NSK´s machine design support prompted a revision to the housing so it could better accommodate the crane sheave bearing unit. Importantly for the steelmaker, NSK´s full complement cylindrical roller bearings offer an advanced system of contact seals that minimises grease leakage and increases resistance to the entry of water and other foreign substances. In addition, the ability to provide reliable life in arduous environments is enhanced by machined holes that feature on the inner and outer rings of the bearings to allow the replenishment of lithium grease in situ. Re-lubrication holes facilitate easy maintenance and grease replenishment, while the provision of a phosphate surface treatment to improve corrosion resistance is a further benefit.
An initial trial of the bearings was undertaken on the annealing line to determine the effectiveness of NSK´s solution. Here, bearing condition analysis was performed mid-trial, revealing no signs of wear, while a post-trial review showed no significant bearing damage. In fact, the bearings were still in full operational condition after more than three years of service, completely eliminating the previous annual costs of €372,555.