The Complete Handbook of Lubricants

Chapter 1: Understanding Lubricants

A lubricant is a fluid or semi-solid substance engineered to reduce friction, dissipate heat, and prevent wear between moving surfaces. But this definition, stripped of context, misses what makes lubricants matter in practice. To understand lubricants, you need to understand what happens when two solid surfaces try to move past each other, what goes wrong when they do, and how the right fluid, with the right chemistry, stops that from happening.

When two metal surfaces—a journal bearing spinning in its race, a gear tooth meshing with another, a piston sliding inside a cylinder—come into contact under load, they do not actually touch smoothly. At magnification, both surfaces are rough. Their peaks and valleys create points of contact (called asperities) that generate enormous localized pressure. Without intervention, friction at these contact points generates heat, metal particles tear free, and equipment fails.

A lubricant's first job is to prevent this failure by creating a film between the surfaces—a separating layer that keeps the peaks of one surface from colliding with the peaks of the other. The thickness and stability of that film determine whether your equipment runs for 10,000 hours or 1,000.

How Film Formation Works

The most common lubricants—mineral oils, synthetic hydrocarbons, and synthetic esters—work by exploiting a property called hydrodynamic film formation. When a surface moves through the oil, it drags the fluid with it. The oil clings more strongly to the metal than it does to itself, so as the moving surface pulls it