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21. How is a Lubricant made?
A lubricant is made in a blending plant. There, the base oils (which may constitute up to 99% of the lubricant, by volume) are mixed together with specially selected additives. Before blending, the base oil is purified by filtration and removal of water; after blending the finished product is subjected to quality control checks in the plant's laboratory before being approved for packing and dispatch.
Base Oil (sometimes also called base stock) is the name given to the main liquid component (or components) of a lubricant. It is. Base oils are mineral (or petroleum) or synthetic in origin, although vegetable oil-derived stocks may be used for specialised applications. The base stock provides the basic lubricating requirements of a lubricant.; i.e. the "oiliness"
However, in most modern lubricants a base oil mixture alone is insufficient to deliver the technical performance characteristics required and to keep the product from rapid degradation in use. Therefore the lubricant manufacturer will mix the base oils with a variety of different additives, each chosen to impart additional performance benefits to the finished oil.
Base oils are be classified by both viscosity and their generic chemical composition, itself a function of the original crude oil and/or the refining process. Depending on the proportions of hydrocarbon molecule type: base oils can be either paraffinic, naphthenic or aromatic in nature. There are several widely used viscosity classifications, of which the term ‘solvent neutral' is the most common, e.g. SN 150 and SN 500, where the number represents the SUS viscosity (measured in Saybolt Universal Seconds at 40 C). Base oils are also classified by their viscosity index (a calculated figure based on the viscosities measured at both 40 and 100 C). Thus oils are either Low Viscosity Index (LVIs) or Medium Viscosity Index (MVIs), High Viscosity Index (HVIs) or extra High Viscosity Index (XHVIs). The higher the viscosity index, the less the oil will ‘thin down' upon heating, and the less it will ‘thicken up' upon cooling.
Base oils are also be defined by the type of refining process used: solvent extraction (for solvent neutral oils) is widely used, but more highly refined oils can be made by a hydro-finishing process or by hydro-cracking.
Synthetic base oils are chemicals that have been made, or synthesised, by combining several smaller molecules together. There are several different types, each with its own suite of physical and chemical properties, and each ideal for a selected set of uses in lubrication. Because these are ‘made to design', and are usually quite pure in composition, the lubricants they are used in can have specific properties which cannot easily be achieved though the use of mineral base oils. This advantage, though, comes at a higher price.
In most cases the answer is "yes". Synthetic oils are man made lubricants which were originally created for jet aircraft engines. They have a wide range of performance and can protect engine at very high and very oil temperature conditions. In other words, they have exceptional thermal stability.
The main disadvantage of synthetic lubricants is that they are inherently more expensive than mineral oils. This restricts their use to speciality oils and greases which command premium prices. Coincidentally, oil marketers therefore ensure that their synthetic oils are also capable of the highest performance possible
The main advantages of the synthetic oils are in their high viscosity indexes, higher flash points, lower pour points and very low volatility (tendency to evaporate at higher temperatures) This makes them valuable blending components when compounding for extreme service at both high and low temperatures.
The list is extensive. Hydro-finished base oils are mineral oils that have been subjected to a light hydrogenation treatment to remove certain impurities that could affect the oil's chemical stability. There is a long list of synthetic fluids used to make lubricants; poly-alpha-olefins, long chain organic esters, phosphate esters, poly-glycols, poly-alkylbenzenes are the most common.
New refineries are being built in which natural gas (methane) is converted into liquid fuels (gasoline, diesel fuel), and a useful by-product will be heavier hydrocarbon molecules which can be used in lubricants. These gas-to-liquid base stocks are expected to have properties similar to some of the synthetic molecules now used, but be available at a much lower cost.
It is always best to follow the vehicle manufacturer's (the OEM's) recommendation for oil drain periods. Some OEMs do permit extended drain intervals when high quality, high performance synthetic oils are used. This is often done in combination with extended vehicle and engine service intervals, as it is in the OEM's interest to ensure the engine and the oil will require servicing after longer and longer intervals.
However, because most oil marketers ensure that their expensive, synthetic oils are also the best in terms of performance, when only a normal oil drain interval is observed the oil will give excellent protection to the engine and thus contribute to extended engine life.Additives are used in lubricating oil to change or alter or enhance its properties. Base oil as such cannot be used in most of the present-day lubricating applications. Their properties - like resistance to heat, oxygen, wear etc - have to be increased. This increment is done with the use of these additives. To increase the resistance to oxidation, we add 'antioxidants', to increase resistance to wear, we add 'anti-wear additives'
The list below covers most of the additives used. You can see that lubricant formulation is a real science as there are many components and variables, all of which must be balanced out to make a well-rounded product, which is then proven by a series of rigorous tests.
| ADDITIVE | WHAT IT DOES | HOW IT WORKS |
| Oxidation Inhibitor | Prevents varnish and sludge formation on bearings or in circulating systems. Retards aging of the oil. Lengthens service and storage life of oil. Protects oil itself directly (indirect protects metal parts - varnish and acids) | Reacts more readily with oxygen (from air) than does the oil itself, thereby retarding oxidation of the oil. Inhibits the formation of free radicals, an important chemical species in the oxidation process, thus slowing oxidation reactions |
| Rust Inhibitor | Prevents rusting of ferrous (iron or steel) machine parts | Forms a film on ferrous metallic parts thus protecting them from attack by water and air, or other destructive material. |
| Corrosion Inhibitor | Prevents corrosive attack on non-ferrous metallic surfaces | Forms a film on non-ferrous metallic parts thus protecting these parts from attack by contaminants in the oil. |
| Detergent | Prevents oxidation products (sludge) which have formed in oil from sticking to metal components. May also remove deposits already formed on metallic components. Usually combined with dispersant additive They are also used to neutralise acids which form in the oil, or are introduced as by-products of fuel combustion. | By chemical reaction, oxidation products (sludge) remain soluble in the oil and do not stick to the metal surfaces. Chemically neutralise acids. |
| Dispersant | Keeps oxidation products separated and suspended in the oil. Retards formation of sludge | By chemical reaction, oxidation product particles are kept small enough to allow them to float in the oil. |
| Foam Inhibitor | Causes foam to dissipate more rapidly | Protects combination of small bubbles into large bubbles which in turn burst more easily. |
| Viscosity Index (V.I.) Improver | Reduces rate of change of viscosity with temperature | Additive thickens with increasing temperature thereby preventing oil from thinning out too rapidly |
| Pour Depressant | Lowers the Pour Point | Keeps small wax crystals apart thus preventing the formation of large crystals which would stop the flow of oil. |
| Anti-wear agent | Minimizes wear caused by metal-to-metal contact during conditions of mild boundary lubrication e.g. starts and stops | Additive reacts chemically and forms a film on metal surfaces under normal operating conditions |
| Extreme Pressure (E.P.) Agent | Prevents welding and subsequent wear or seizure of contacting metal parts under extreme or shock load conditions. | When metal-to-metal contact occurs (as under extreme or shock load conditions), the heat generated at the point of contact causes the additive to react chemically with the metal. The new compound formed between the metal surfaces reduces friction and prevents welding or seizure. |
| Tackiness Agent | Increases the adhesive properties of a lubricant - improves retention and prevents dripping and spattering | High molecular weight compounds are added to the oil thereby increasing its viscosity and improving its adhesive properties. |
| Emulsifier | Promotes rapid mixing of water and oil resulting in the formation of a stable emulsion (e.g. water-soluble cutting oils) | Reduces interfacial tension and permits intimate mixing of oil and water. |