TYPES OF LUBRICANT ADDITIVES
There are many types of chemical additives mixed into base oils to enhance the properties, additives typically make up about 0.1 to 30 percent of finished lubricating oil, depending upon the target application of the lubricant, many lubricant additives are available and selected for use based upon their ability to perform their intended function, they are chosen for their ability to mix easily with the selected base oil to be compatible with other additives in the formulation and to be cost effective, some additives perform their function within the body of the oil (e.g., anti-oxidants) while others do their work on the surface of the metal (e.g., anti-wear additives and rust inhibitors).
These chemicals usually metal-organic based are designed to control deposits and keep engine components clean, they can clean up existing deposits in the engine, as well as disperse insoluble matter into the oil, detergents control contamination resulting from high temperature operation, over-based detergents also neutralize acidic contaminants from fuel sulfur, engine exhaust, oil oxidation and/or nitration.
Primarily detergents used in engine oils are alkaline or basic in nature, since these metal compounds leave an ash deposit when the oil is burned, they may cause unwanted residue to form in high temperature applications, due to this ash concern, many OEMs are specifying low-ash oils for equipment operating at high temperatures, detergent additive is normally used in conjunction with a dispersant additive.
Dispersants are mainly found in engine oil with detergents to help keep engines clean and free of deposits, these are usually ashless organic chemicals, which control contamination from low temperature operation, both detergents and dispersants attach themselves to contaminant particles, such as soot or varnish and hold them in suspension, preventing sludge and deposit formation, the suspended particles together with their additive carrier are so small that they can pass harmlessly between moving surfaces and through oil filters, this contamination is removed from the engine when the oil is changed.
Substance added in small quantities to a petroleum product to increase its oxidation resistance and thereby lengthening its service or storage life, oxidation is the general attack of the weakest components of the base oil by oxygen in the air, it occurs at all temperatures all of the time but is accelerated at higher temperatures and by the presence of water, they are present in almost every lubricating oil and grease.
CORROSION AND RUST INHIBITORS
Acids are produced by the combustion process and when an engine oil degrades with use, these acids can cause rapid deterioration of engine components, corrosion inhibitors protect non-ferrous metals by coating them and forming a barrier between the parts, rust inhibitors protect metal surfaces from oxygen attack, by forming a chemical protective barrier, these inhibitors are specific to protecting certain metals, therefore, an oil may contain several corrosion inhibitors, they are common in almost every oil and grease.
Antiwear additives (AW additives) are lubricant components that chemically react with the metal surface to be protected, forming a lubricious sacrificial coating that protects the metal from wear under boundary lubrication conditions, they are activated by the heat contact to form a film that minimizes wear, they also help protect the base oil from oxidation and the metal from damage by corrosive acids.
Foam dispersant additives can facilitate aeration of an oil, which leads to foaming, this can reduce the lubricating ability of an oil and even interfere with oil pumping, they have an indirect effect on oxidation by reducing the amount of air oil contact, some of these additives are oil insoluble silicone materials that are not dissolved but rather dispersed finely in the lubricating oil, low concentrations are usually required, if too much anti-foaming additive is added, it can have a reverse effect and promote further foaming and air entrainment.
VISCOSITY INDEX (Vl) IMPROVERS
Viscosity index improvers are large polymer additives that partially prevent the oil from changes in viscosity as the temperature increases, to visualize how a VI-improver additive functions, these additives are polymeric molecules that are sensitive to temperature, as the temperature increases, these molecules tend to stretch out, as the molecules stretch out, the fluid's internal friction will increase, causing the fluid to flow at a slower rate, therefore, it will have a higher viscosity.
These additives are used extensively when blending multi-grade engine oils, they are also responsible for better oil flow at low temperatures, resulting in reduction in wear and improved fuel economy, VI improvers resist breakdown due to shear and high temperatures to ensure a long-lasting effect, there are several different types of VI improvers olefin copolymers.
EXTREME PRESSURE (EP) ADDITIVES
Extreme pressure additives are more chemically aggressive than AW additives, they react chemically with metal surfaces to form a sacrificial surface film that lower wear of metal surfaces exposed to high pressures, they are activated at high loads and by the high contact temperatures that are created, extreme pressure additives are usually used in applications such as gearboxes, greases and other lubricants that need to work under extreme load and pressure, EP additives are molybdenum disulfide, graphite, sulfurized olefin and dialkyldithiocarbamate complexes.
POUR POINT DEPRESSANT ADDITIVES
Pour point depressants are polymers that allow oil and lubricants to flow at very low temperatures without heavy wax formation at cold temperatures and enable the oil to remain fluid, wax crystals forms in paraffinic mineral oils crystallize at low temperatures, the solid crystals form a lattice network that inhibits the liquid oil from flowing, the additives in this group modifies the interface between the crystallized wax and the oil, allowing the oil to continue to flow at low temperatures, PPD additives are alkylated wax naphthalene, polymethacrylates, alkylated wax phenol.
Friction modifiers agents are polar molecules added to lubricants to minimizing light surface contacts that may occur in machine components, these are also called boundary lubrication additives, typically used to emphasis on lowering friction to improve fuel economy, these chemicals form a chemical or physically bonded film that reduces the friction between the lubricated engine parts, friction modifiers are typically used in engine oils and automatic transmission fluids to alter the friction between engine and transmission components.