NUCOR Steel Arkansas is a flat rolled steel mill in Blytheville, Ark., producing in excess of 2.4 million tons of steel annually, with a market value of more than $1.4 billion. It is a state-of-the-art facility with a turnkey comprehensive condition-monitoring program for the mill that includes remote machinery monitoring. Azima DLI has operated programs for NUCOR for more than 12 years, and the solution for its gearboxes was no different.
NUCOR Steel Arkansas is one of the largest remotely monitored machine sites in the world. In 2009, NUCOR Steel Arkansas undertook a major upgrade to its gearboxes driving the F1 and F2 mill stands. The upgrade represented a capital investment of nearly $24 million. Due to the low speeds of these very large machines, traditional vibration monitoring was of questionable value. However, monitoring of the bearing temperatures in these massive gearboxes was recommended by the gearbox OEM. The company used Azima DLI’s 1600 network-based temperature monitoring technology to all 16 bearings in the gearboxes. This technology allowed for trending, alarming and immediate notification of off-site support and plant personnel. The system was commissioned in July 2009, along with the startup of improved mill stand drives.
The remote monitoring system immediately identified two anomalous bearing temperatures that were well above expected limits due to excessive mill loads and speeds. The data was exported to the hosted web portal where vibration analysts with knowledge of mill stands were able to review it and confirm that the mill speeds and loads were directly correlated with the temperature data.
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The company also applied thermal imaging technology to the gearboxes to confirm the data from the temperature monitoring systems. The thermal imaging results revealed that the lubrication feed oil piping temperature was much higher than anticipated, suggesting a malfunction in the lubricating system. Further thermal imaging tests discovered a fault in a large water-cooled heat exchanger used to regulate lubricant temperatures.
The findings revealed a leaking bypass valve that was allowing hot oil to cross over into the cooled lubricant stream to the gearboxes, with the effect of overheating the bearing. A simple correction to this valve promptly lowered lubricant temperatures. The application of multiple condition-monitoring technologies provided a quick and simple solution that greatly improved the mill’s equipment performance and reliability, and it mitigated the risk of costly damage to a new $24 million gearbox.
