How to avoid oils that oxidise
When a substance reacts with oxygen, it turns into another compound altogether with a different molecular structure. This process is known as oxidation or oxidization and is widely known to occur in metals but can occur in fluids as well.
Vegetable-based metal cutting fluids are affected greatly by oxidation. The effect experienced is an increase in viscosity, varnish, sludge, and rust/corrosion. Fluids in this altered state begin to ‘gum up’ on the cutting tool, which reduces their effectiveness while cutting. These vegetable-based fluids are actually very good cutting fluids since they lubricate surfaces very well, take a while before they begin to vaporize (have a high flashpoint), and have a polar nature which causes them to adhere well to metal surfaces (wetting).
However, when they interact with oxygen they begin to change their form. These oils have bases in them and oxidation produces acids known as carboxylic acids. The bases become neutralized and the oil becomes more acidic. Increased acidity causes the formation of varnish and sludge. Other byproducts in this process such as hydro peroxides and carboxylic acids combine to form larger molecules. The larger the molecules of a liquid, the more viscous the liquid will be. Solids begin to form and eventually become sludge.
How then can you take advantage of the excellent lubrication properties of vegetable-based cutting fluids but avoid the problems caused by oxidization? The solution is to slightly alter these fluids’ composition. Unist Coolube® is actually derived from renewable plant-based oil, but its structure has been modified to make it resistant to oxidation. This modification keeps Coolube’s® environmentally friendly composition, but eliminates the sticky byproducts you may see with lesser vegetable-based fluids. Coolube’s® superior lubricating properties deliver improved cut-quality and tool life and have made it a favorite with metalworkers for over 30 years.