In the last issue of Fundamentals of Lubrication Series, I discussed the three lubrication types, namely boundary, mixed, and hydrodynamic lubrication. Boundary lubrication is the least preferred as there is still surface contact between moving parts that leads to wear.
Thankfully, there are substances that can be added to the oil that can, not only minimise wear during boundary lubrication but provide a vast range of additional benefits. Those substances are better known as additives.
Additives are chemical mixtures, which when added to base oils make up a finished lubricant. Nowadays, almost all lubricants have some form of additives because base oil alone is not adequate to meet the demands of modern machinery.
The way additives modify base oils can be categorised into three. First, they enhance existing base oil properties. Second, they overcome base oil undesirable properties, and third, they impart new properties that base oil does not have in the first place.
Additives boost existing base oil properties such as lubricity, anti-wear, corrosion protection, friction reduction and demulsibility. These are properties that are usually responsible for lubricating oil’s primary functions.
The physical and chemical properties in base oil that are undesirable to perform well as lubricants can be improved by additives. The physical properties include viscosity index, pour point, and anti-foam while chemical properties are oxidation resistance and extreme pressure load-carrying abilities.
Properties that are not inherent in base oils can be introduced with additives. Examples of this are detergency and dispersancy. Engine oils are very much dependent on these properties due to the need to handle carbon and soot. For water-soluble metalworking fluids, emulsibility is a new property that must be provided by additives because it is against the base oil’s natural tendency to demulsify.
While the improved properties served by additives are many, the actual number of additives required can sometimes be minimal. That is because some additives can deliver multiple properties, known as multifunctional additives.
I will go deeper into additives in the future, but before we get there, in the next issue I will discuss mineral and synthetic base oils.
About the Author:
Aaron Said is ILD/Sinopec’s National Technical Manager. He is responsible for developing and delivering value-added lubricant technical services to client for reliability improvement, lubricant optimization, and cost-savings. Among his professional credentials are Certified Lubricant Specialist (CLS) and Oil Monitoring Analyst I (OMA) from Society of Tribology & Lubrication Engineers (STLE) and the International Council of Machine Lubrication (ICML)’s Machine Lubricant Analysist I.