Talking lubrication – the science of tribology
In his excellent book Which Oil, author and lubrication expert Richard Michell puts the basic problem of lubrication thus:
When one metal surface moves over another, friction occurs and energy is needed to overcome it. The amount of friction depends on how hard or forcefully the two surfaces are pushed or pressed together….Such movement and friction leads to very high rates of wear of the two surfaces.
Also, significant energy is needed to overcome it. However, if the two moving surfaces could be kept separate by a film of liquid (or gas), wear would be eliminated and the only friction involved would be that needed to move the fluid film. This is the simple concept behind lubrication.
While this is perhaps all too simple for professionals in the tribology field, it’s always worth bearing in mind the aim of lubricant oils and additives – to reduce wear and to reduce the energy needed to operate a mechanical device.
Reduced wear = longer machine life
Reduced energy = operating cost savings
These days a range of synthetic oils are available for the lubrication of vehicles and machines. Such synthetic oils are not made by physical separation from crude oil, but are manufactured using a chemical process. The original raw material is usually something derived from crude oil. Such hydrocarbon oils are the majority of lubricant oils now, but they often contain other elements added to the base oil to improve performance. There is also a variety of additives that one can use to enhance lubrication performance beyond what the base oil can provide. SOD-1 Plus, an ester-based lubricant, is one such additive.
Esters as lubricants
Esters have certain special qualities as lubricants or as additives to base oil lubricants. As the website Machinery Lubrication says:
Modern synthetic esters can be “tuned” to perform in nearly any environment and application. Whether you seek excellent hydrolytic stability, oxidative stability, biodegradability, lubricity, high viscosity index or low-temperature properties, all of these are possible with the right synthetic ester. Synthetic esters are manufactured from carboxylic acids and alcohols, which are very common chemical building blocks. They provide almost unlimited structural and performance possibilities.
The key benefits of an ester additive are:
- Thermo-oxidative (high temperature) stability
- Viscosity enhancement and extra lubricity
- Biodegradability and hydrolytic stability
- Lower volatility and high flashpoint
Machinery Lubrication adds:
Synthetic esters reduce varnish and other deposits because they have outstanding oxidative stability and do not form many radical decomposition products. Furthermore, they are good high-temperature solvents and tend to dissolve the varnish back into the liquid phase so it can be filtered out…..Esters are generally considered good boundary lubricants because they associate with metal surfaces and reduce the amount of metal-to-metal contact during sliding motion…..Esters are great for high-temperature hydrodynamic applications because they can survive in extreme environments where no other lubricant can.
Esters have been used successfully in lubrication for more than 60 years and are the preferred stock in many severe applications where their benefits solve problems or bring value. For example, esters have been used exclusively in jet engine lubricants worldwide for over 50 years due to their unique combination of low temperature flowability with clean high temperature operation….
“…esters are often used in combination with PAOs in full synthetic motor oils in order to balance the effect on seals, solubilize additives, reduce volatility, and improve energy efficiency through higher lubricity. The percentage of ester used can vary anywhere from 5 to 25% depending upon the desired properties and the type of ester employed.
“The new frontier for esters is the industrial marketplace where the number of products, applications, and operating conditions is enormous. In many cases, the very same equipment which operates satisfactorily on mineral oil in one plant could benefit greatly from the use of an ester lubricant in another plant where the equipment is operated under more severe conditions. This is a marketplace where old problems or new challenges can arise at any time or any location. The high performance properties and custom design versatility of esters is ideally suited to solve these problems.”