The Blending of Oils

Base Oils 

Crude oil is the term for "unprocessed" oil, the stuff that comes out of the ground. It is also known as petroleum. Crude oil is a fossil fuel, meaning that it was made naturally from decaying plants and animals living in ancient seas millions of years ago -- anywhere you find crude oil was once a sea bed. Crude oils vary in color from clear to tar-black and in viscosity from water to almost solid.
Crude Oil supplies many different products including hexane, toluene, diesel, petrol and most plastics. However the most important product supplied is “base oil” in our industry.

Oils are made up of several different components, however fundamentally they share a common thread. Most oils are comprised of base oils and require specific additives.

The base oils used in lubricant formulations are selected on a number of criteria, with the main one being the required oxidation stability. Manufacturers produce oils that can be categorised into groups which gives an indication of its oxidation characteristics. Group I oils, the type generally manufactured in Australian refineries, provide the least amount of oxidation protection due to the presence of unsaturated hydrocarbon compounds in the product. In applications where the lubricant is not overly exposed to conditions that cause oxidation e.g. enclosed gear boxes etc and, to some extent, normal spark ignition/compression ignition engines where change intervals are not extended beyond manufacturer’s recommendations. Where long life is required, the use of Group II, Group III and Group IV base oils are employed. Group II and Group III are more highly refined than the Group I oils resulting in the reduction of unsaturated oil components which make the oils more oxidation stable. Group IV are also known as Poly Alpha Olefins and are synthetically manufactured oils that are 100% saturated and very oxidation stable. This group of oils is not produced in conventional refineries and are called synthetic oils. They can by the nature of their manufacture, be tailor made to suit the end use of the oil.

The majority of oils are derived from crude oil with the exception of synthetic oils. The shorter the refinement process the more impurities are left in the oil. This leaves the lower group oils susceptible to poor oxidation stability. Oxidation stability is the ability to withstand harsh environmental pressures. Key indicators of oil oxidation are thickening, bad odour and an increase in acidity with a tendency to “varish” and once the oil displays these characteristics, the life of the oil is considered to be unsuitable for further use.

The grade is an indicator of the viscosity of the oil and and the higher the grade, the thicker the oil.

Additives

To counteract the majority of ill effects that contaminants cause, additives are incorporated in the oil formulations.

Detergent additives clean deposits from inside engines while the dispersant additive keeps what is cleaned separated to avoid “sludging”, particularly when moisture is present. 

Anti-foaming additives prevent bubble persistence that may cause lack of lubricant to critical locations. 

Anti-wear additives chemically treat the metal surfaces and make them “slippery”. 

In some instances, cold temperatures can be experienced that could freeze lubricants, consequently an additive is incorporated that enables the oil to pour at low temperatures. 

Corrosion inhibitors are added to counter acidic effects on metals.  In engine oils, reserve alkalinity is included in the formulation to neutralise acids formed by combustion.  This is reflected by the Total Base Number (TBN) of an engine oil.  Oxidation inhibitors are also necessary to prevent deterioration of the lubricant due to the action of moisture, air and temperature on it. 

In short, the modern lubricant has been designed and formulated to meet the harsh environment of modern equipment.  Contaminants can “Unbalance” the lubricant and can result in less than optimum performance in its duty.

How does it protect and lubricate

Friction

Friction is an accumulation of forces that tend to prevent motion between surfaces that are designed to move relative to each other. The extent of these frictional forces directly relates to the load placed on the surfaces. The smaller the area of contact , the greater the effect of the load per square millimetre on rough surfaces.

For example, consider the bearings in an internal combustion engine, mating gear teeth in a gearbox or the piston of a hydraulic ram. In each of these cases, surface roughness is a critical factor. A simple example of the effect of surface roughness on motion is to place two files, one on top of the other on a bench with a load on top of them. Try to slide the top file out from beneath the load. It is difficult to achieve the desired motion.

If you take a very close look at even the “smoothest” surfaces that would be encountered in engineering applications, each surface would consist of microscopic high and low spots. The metal-to-metal contact would only be on these high spots (called asperities) with the consequent point loading similar to the “files example”. Point loading leads to a High Coefficient Of Friction.

By adding motion, the high spots (asperities) on the surfaces would generate enough heat to weld. The continued application of the force would cause the weld to stretch and break leaving new, similar high spots (asperities) generated on the surfaces. Metal particles can also break off which can then act as an abrasive leading to an accelerated process of “wear”. It is obvious that the effects of these surface peaks must be reduced. Lubrication choice is critical to avoid high spots (asperities) coming into contact with each other, hence lowering friction and WEAR.

How is the lubricant forced between surfaces?

A lubricant film will adhere to surfaces upon which it comes in contact. This is referred to as Boundary or Thin Film lubrication. It is the main source of lubrication in equipment upon starting from rest. In this case the asperities can and will make contact and wear occurs. As the relative motion between the surfaces increases, particularly rotational motion, the boundary lubrication film is increased as the lubricant is forced between the surfaces. This process is known as Hydrodynamic Lubrication.

The fluid film which develops pressures sufficient to carry the load and hence permit motion, is increased due to the “wetted” surfaces dragging more oil molecules between the surfaces when these commence rotating.

A situation will be arrived at where the maximum film thickness is achieved. The oil molecules can be considered as a wedge that continually supplies replacement lubricant to maintain this film thickness. The faster the rotation, the greater the separation. Conversely, as the rotation slows down the film diminishes. The same principle applies to meshing gears.