3040 – 03 – Using Straight Oil and Soluble Oil MWFs

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Metalworking fluids that are normal to use in metal forming are broken down into four major classes, which are straight oil, soluble oil, semi-synthetic fluids, and synthetic fluids. The majority of these MWF’s are combined with water or solvents. The age of the MWF and application will inform the user what sort of additives need to be added to the fluid for improved performance and life.

Straight oil is typically made up of vegetable oils or mineral oils that are used as a lubricant as opposed to a coolant. Petroleum oils usually get treated through a process of refining to remove any undesirable carcinogens present in crude oil. Straight oil may be mixed with marine or animal oils but never water. Straight oil requires special precautions and protective equipment.

Soluble oil, also known as emulsifiable oil, can have from 30 to 85% refined oil, emulsifiers which encourage water to mix with oil which, can improve fluid performance and improve fluid life. Soluble oil requires water because it begins as a concentrate. Soluble oils are both good lubricants and coolants. It can be contaminated leading to smoke and yielding poor mixture stability or decreased sump life.