To understand what lubrication is, you first need to understand why we use it. Friction is the force that resists relative motion between two bodies in contact. If friction didn't exist, nothing would ever stop moving. We need friction to function, but there are instances where you want to be able to reduce the amount of friction present. When you rub your hands together, you create heat because of the friction between the sliding surfaces of your hands. Now imagine rubbing your hands together 3600 times a minute – your hands would be on fire! Similar heat is generated by friction in your machinery. If the lubricant in your equipment has not been appropriately selected with standard operating temperatures, load, speed, etc., in mind, catastrophic failure may result.

You could wipe your bearings or if you stop your motor, for example, and the machine is too hot, you could seize the bearings. Either way, both are costly when you consider time lost, manpower used, and new equipment purchased. In order to avoid failures of this nature, we lubricate our machinery to minimize the resistance to movement, and as a result, minimize the amount of heat produced. The heat that is produced by the equipment is transferred to the oil so that it may be removed by a lube oil cooler. There are a lot of considerations that must be applied when selecting the type of lubricant we need to use: viscosity, additives needed, properties, etc.

Reducing friction and reducing heat are only a couple of the reasons we use lubricants. If you look under a microscope at two surfaces moving across each other, you would see something that looks like two mountain ranges rubbing against one another. As this happens, pieces of the weaker material break off and create smaller abrasive particles, resulting in more broken off pieces, which go on to create more abrasion. It's a vicious cycle, and the way we prevent this from occurring is by creating a lubrication film. Two of the preferred and most common types of fluid related lubricant films are hydrodynamic and elastohydrodynamic. Hydrodynamic films are present between sliding contacts. The most common example would be a journal bearing.

When a shaft is still, it sits on the bottom of the bearing, but when it starts to move, it tries to “climb” up the side of the bearing. Microscopic layer upon layer of the lubricant create friction with each other and form an oil wedge between the shaft and the bearing, protecting both surfaces. Elastohydrodynamic films are present in rolling contacts, such as ball bearings or roller bearings. In this situation, the softer material makes up the rolling element which actually deforms for a split second to enlarge the contact area between mating surfaces. Here, the oil film thickness is one micron or less, which brings me to another reason for lubrication. We need to minimize foreign particles that may cause damage to this area.

Now in situations where the film layer is only one micron thick, you could imagine that any contaminants that are present can create major damage, so we try to eliminate as many as possible. While we can control the amount of contamination that enters a system by using seals, filters, and other quality controls, it's impossible to completely eliminate machinery wear, even with the best lubricant films. So what do we do with the wear particles we can't avoid? Certain additives in lubrication will be attracted to these contaminants , suspend them in the lubricant, and transfer them to filters or other separators installed in the system where they will be removed.

Finally, most places aren't completely unaffected by humidity. So what does it mean when water and air come into contact with metal? Corrosion, and as we all know, that's not good for machine operation. So how does a lubricant help with this problem? There are different additives, similar in operation to the additives used for contamination control, which prevent metal surfaces from coming in contact with water. This prevents the production of rust, therefore preventing damage to the metal machine surfaces.

So a lubricant is a substance that reduces friction, heat, and wear when introduced as a film between solid surfaces. Using the correct lubricant helps maximize the life of your bearings and machinery, therefore saving money, time, and manpower, thus making operations more efficient and more reliable.