1. Types of Lubrication
Liquid (Mineral Oils, Synthetic Oils, and Vegetable Oils)
Semi-Solid (Grease)
Solid ( Graphite, Molybdenum Disulphide, Polytetrafluoroethylene PTFE)
Gas (Air, Nitrogen, Helium)

2. Mineral Oil
Mineral Oils are made up of Hydrocarbons, basically these are complex molecules of Hydrogen and Carbon such as Paraffin's, Naphthenes and Aromatics which are distilled from Crude Oil, they also contain additives to modify performance and to prevent them from degrading.
Mineral oils are generally cheap to purchase, the manufacturing process is not environmentally friendly, they tend to degrade more rapidly than other types of oils.
As with all oils they come in a range of different viscosities such as light, medium and heavy oils.
The lighter the oil the more Aromatics they contain (lower Viscosity)
The heavier the oil the more Paraffin’s they contain (higher viscosity
Mineral oils are suitable for lubricating plain journal bearings, gears, and slide- ways on machines or for pumps and compressors where the operating temperature is reasonably low

3. Synthetic Oils
Semi-Synthetic oils contain a mixture of mineral oil and synthetic oil which contains man made substances such as Ester, Silicone and other polymers, these are added to enhance the performance over different operating temperatures and to stabilise the Viscosity so it does not change too much at higher temperatures.
Fully Synthetic oils are completely man made from esters, silicones, polymers and other additive which enhance the performance over wide operating temperatures and provide more effective wear resistance.
These oils are more expensive and are considered to be more environmentally friendly than basic Mineral oil.
The viscosity of these oils is generally lower than that of the mineral oil but it does not change as much with greater temperature change unlike mineral oil where the viscosity becomes lower at higher temperatures.
This type of oil is usually used for high performance internal combustion engines where temperature change covers a larger range and also protects the parts better from cold starts and at lower temperatures.

4. Vegetable Oils
Soluble Vegetable oils are used extensively on machine tools as coolant and cutting tool lubrication.
Their purpose is to keep the tool and work-piece cool, aid the cutting process/improve surface finish, wash away swarf/material particles and prolong the life of the tool.
Two common vegetable oils used are extracted from sunflower seeds and Rapeseeds.
The oils are soluble in water and form a milky liquid when mixed with water.
Depending on the application machine tool lubricants consist of between 1% - 10% soluble oil with the remainder being water.
They are generally applied to the process by a pumped recirculating method.
Vegetable oils are bio-degradable so better for the environment.

5. Viscosity Viscosity Index Group Viscosity Index Low Viscosity Index
Viscosity is a term used to the describe a substances resistance to flow.
Lubricants with a low viscosity are thinner and will flow relatively easily (light oils)
Lubricants with a high viscosity are thicker and will flow much more slowly (heavy oils)
Lubricants are also classified by their viscosity Index this is a measure of how much the viscosity changes when the temperature increases.
Viscosity Index Group
Viscosity Index
Low Viscosity Index
Below 35
Medium Viscosity Index
35-80
High Viscosity Index
80-110
Very High Viscosity Index
Above 110

6. Oil Additives

7. Semi Solid
Grease is the most common semi-solid lubricant, it is a mixture of oil and thickening agents such as mineral oil and soap.
Grease or semi-solid lubricants have an number of advantages over liquid lubricants in the fact that they do not flow freely, so when applied they remain in place and are resistant to being displaced by centrifugal force, they form a seal against water and other contaminants from entering the component/system.
Disadvantages are they do not dissipate heat as well as oils, also because of the high viscosity they create a certain resistance to motion.
The table below shows typical thickening agents, operating temperatures and applications.
Lubricating Fluid
Soap/thickener
Temperature Range
Use
Mineral Oil
Calcium
-20°C to 80°C
General purpose ball and roller bearings
Sodium
0°c to 175°C
Glands, Seals and medium speed ball and roller bearings
Calcium and Sodium
-40°C to 150°C
High speed ball and roller bearings
Lithium
Clay
-30°C to 200°C
Slide-ways
Ester Polymer
-75°C to 120°C
Silicone Polymer
-55°C to 205°C
Silicone Soap
-75°C to 260°C
Miniature bearings

8. Solid Lubricants
The three most commonly used solid lubricants are Graphite, Molybdenum Disulphide and Polytetrafluoroethylene (PTFE).
Solid lubricants are used where components are subject to very high or very low operating temperatures where oils and grease would be ineffective.
Also used in environments where oil and grease would become contaminated and ineffective
The methods of applying solid lubricant are applying with a brush in powder form, spraying it on to the surface using a spray can or adding it to molten metal in the manufacturing process, with this method when the metal cools the lubricant is impregnated into the material, a typical example is where graphite is added to Phosphor-Bronze which is commonly used for plain bearings.
Cast Iron also contains graphite flakes and is often referred to as a self lubricating material, also the reason it is used for the bed and slide-way construction on machine tools.

9. Gas Lubrication
Compressed gas lubrication works the same as oil lubrication in forming a thin cushion between mating components to separate them hence reduce friction and wear, typical gasses used are Natural Air and inert gasses such as Carbon Dioxide.
Gas lubrication has a number of advantages over oil and grease, it can be used for high speed applications rotating at speeds of up to 300,000rpm, can be used over much greater temperature ranges, has very little resistance to motion and is much cleaner.
One major disadvantage of gas lubrication is that it needs a constant supply of gas to operate which is costly due to use of compressors, the parts also need to be machined more accurately to tighter tolerances.
Typical operating pressures range from 2 bar (30 psi) to 10 bar (140 psi)
Components are usually sprayed with a solid lubrication on assembly to protect them should the compressed gas supply fail.
Gas bearings have many applications such as air tools, dental drills and other medical equipment.