Which is better? Soluble or mineral oil?

Which is better? Soluble or mineral oil?

The advantages of an emulsion of soluble oil are:

• no risk of fire. This point can be decisive if there is no efficient fire brigade or protection.

• easy filtration, except for fine, light particles, which float at the top of the tank.

• easy wiping

• excellent cooling power

The drawbacks are:

• the risk of damage to the bearings. In the case of oil mist failure, all the bearings are destroyed (multi-high mills).

• risk of preventing high surface finish (which is usually required for stainless steels)

• risk of proliferation of bacteria. The workers may be allergic to so much bacteria, and it also shortens the life of the emulsion. The smell is bad too. The oil supplier should add an antibacterial agent and give relevant instructions for minimizing environmental pollution from the discharge of used emulsion (the emulsion has to be broken back down into oil and water).

The supplier should also indicate how frequently the oil quality should be checked, the expected life of the emulsion, the recommended water quality (demineralized), and the risk of rust on the strip after rolling (the next process should occur within a few days at the most).

If everything is taken into consideration, soluble oil is not as economical as one might think. The real advantages are no risk of fire and excellent cooling, which allows high rolling speeds (800, 1000, 1200 m/min, and so on) when temperature would otherwise limit performance.

For many 2-high, 4-high, and 6-high mills, soluble oil is used, but it is rarely used on multi-high mills. Soluble oil is used on multi-high mills rolling soft materials (mild steel, silicon steels) with high reductions, needing good cooling effects.