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Improving Rolling Mill Lube Oil Performance and Useful Life - Part 1: Quality

Fri, Feb. 15, 2013

steel mill equipment and lube oil

Premium oils keep steel mills running. It's crucial to protect their quality in order to keep the mills fully functioning. 

In both hot and cold steel mill production, high-demulsibility lubricant is used for backup roller bearing lubrication. Some of these oils are referred to as SD, which stands for super-demulsibility. Not surprisingly, these SD oils are a premium product and come at a premium price. If a manufacturer wants to invest in these big-ticket oils, they obviously want to go to great lengths in order to keep them clean and fully functioning.

Join us for this three-part series as we take an in-depth look at improving rolling mill lube oil performance and useful life.

Steel Mill Equipment and Lube Oil 

Manufacturers of steel mill equipment often specify fluid brands that are recommended for use; think of this as your car mechanic recommending the best oil for your certain car. This is because steel mills encounter very high amounts of water and particulates in lube applications.

A mill might have a single tank for oil return - or it might have a second tank as a settling tank connected to a supply tank. Water is regularly drained from these tanks. And I'm not talking just a few drops here. Hundreds of gallons of water are often removed daily - sometimes multiple times a day - depending on the condition of the seals and chocks. That's a LOT of water!

Some specified oils are formulated for super demulsibility, as we mentioned previously. These oils have the ability to shed water in the presence of gross free water. This is because of quality base stock and the oil's ability to remain chemically stable. 

In the field, it's not surprising to find some rolling mill oils that look like chocolate milk. As appetizing as that sounds, it's not a pleasing state with water levels from 3000 ppm (.3%) up to 150,000 (15%). Keep in mind that one blender suggests a maximum suitable water level of 500 ppm (0.05%). 

Loss of Demulsibility and Roller Bearing Failure 

Once the oil loses demulsibility, the oil can stay in the tank, but it may cause bearing failures, which can cost $30,000 each. When viscosity drops, the lubricating film is compromised. This thin film can lead to particulate contamination damage and metal to metal between bearing and bearing housings.

This friction creates heat that can vaporize the water, causing further damage to the bearings and the oil. The combination of the highly emulsified water and the high particulate levels create a perfect storm for bearing failure and reduced oil life.

Tune in next week to see how to weather this storm in Part 2.

Read Part 2: Prevention 

Written by Aaron Hoeg


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