Customized additives for modern lubricants
Modern machines and engines place ever higher demands on lubricants, which they have long been unable to meet in their natural form as pure mineral oil. However, chemical agents can be used to specifically modify the properties of lubricants. Today, a carefully formulated combination of active ingredients is added as an "additive" to almost every oil and grease.
According to the set requirements:
- additives improve the positive properties of the base oil, such as wear protection.
- additives reduce or eliminate undesirable properties, such as aging
- additives give the base oil properties that go far beyond its original performance, such as an extended temperature application range.
type, quantity and individual combination of additives depend on the specific application. With their help, customized solutions are created for modern machine and engine technology. The quantity of active ingredients added can be only a few mg/kg (1mg / kg = 0.0001%), as in turbine oils, or high concentrations of up to 20%, as in high-performance engine oils.
Selected additives can only improve some properties of a lubricant, such as EP behavior. However, not all characteristics of a base oil can be positively influenced.
Optimization of low-temperature behavior
The low-temperature behavior of the lubricant is improved with pour point depressants. The pour point is the temperature at which the oil just flows at sub-zero temperatures. The thickening of the base oil at cold temperatures is caused by the crystallization of the paraffins contained in the mineral oil. Pour point depressants prevent the build-up of these paraffin crystal lattices and thus improve flowability at low temperatures.
Improvement of aging stability
Oxidation inhibitors (antioxidants) delay oil oxidation (oil aging) and the formation of aging products. Oils oxidize when exposed to heat and oxygen. Acids and oil-insoluble components may be produced, forming varnish-like deposits such as resins and sludge. The viscosity of the oil often increases. The aging of an oil usually starts very slowly when oxidation inhibitors slow down this process. The active ingredients intercept the reactive molecules (radicals) and neutralize oxygen-containing compounds. Thus, they protect the lubricating oil from the rapidly increasing attack. However, once these additives have been used up, the aging of the oil proceeds unchecked, just as with unadditivated oil. This process is further accelerated by traces of contaminants, such as metallic abrasion, water or dust.
Viscosity index improvers (VI-Improvers) increase the viscosity index of the oil. Especially at high temperatures, they prevent the oil from becoming very thin. The mineral oil becomes less sensitive to temperature. It is only through the use of these additives that modern multigrade engine oils, hydraulic oils and gear oils achieve a viscosity-temperature behavior that meets the requirements of the engines and machine elements.
Corrosion inhibitors create a protective film on metallic surfaces. They prevent the access of water or oxygen to the surface of the material and neutralize acidic reaction products from additive degradation or oxidation. In this way, they prevent the formation of a corrosive attack on non-ferrous metals. If their protection relates specifically to ferrous metals or steel, they are also referred to as rust inhibitors.
Dirt dissolving properties
Detergents dissolve contaminants, which are caused by the aging process of the oil due to combustion in the engine or by impurities, into fine particles. They are particularly effective against sludge and varnish-like deposits that have developed on the basis of soot, acid compounds, nitrogen oxides, unburned fuel residues and water, thus keeping piston rings or the oil pan clean by their "washing" action.
Dispersants are the indispensable counterpart to detergents. They keep the detached contaminants in suspension and ensure that they cannot form new deposits. In doing so, they literally envelop the dirt particles and enable them to be transported to the filter.
EP and AW (anti-wear) additives build up extremely thin protective layers on the sliding surfaces of the materials. They can influence the roughness of the surfaces by forming reaction layers. The mechanical load-bearing capacity in the contact zone is then improved by the larger load-bearing component of the surfaces. EP and AW additives reduce wear and galling (localized welding) under severe operating conditions, shock loading, vibration and frequent start-stop operation.
Antifoaming additives, usually based on silicone, are added during production, especially to oils with a high additive content. Foam can nevertheless be caused by false air from the oil pump, contamination or incompatibility with other oils. Surface foam can also be destroyed subsequently with silicone-containing solutions. However, there is a risk that it will be stabilized as air bubbles in the oil. This eliminates surface foam, but this dissolved air can cause cavitation and corrosion.