Lubricant: is a substance (liquid or solid) capable of reducing friction, heat and wear when introduced as a film between solid surfaces.
In consequence, lubricants makes possible movement in terms of mobility and operational purposes in a sustainable (machinery life) and safety way. Lubricants are the technology with the highest contribution on energy savings and CO2 emission reductions. A lubricant formulation is commonly composed by base oils, co-base stocks and additives.
Base oil: represent the highest percentage in a formula from 85 to 100 %.
Co-base stocks: substances used to improve properties of the base oil such as viscosity index or solubility as examples, and can be from 5% to 20% in formula.
Additives: are chemical compounds with a low percentage in a formula used to improve stability or mechanical properties.
Tribology: is the science of wear, friction and lubrication, and includes how interacting surfaces and other tribo-elements behave in relative motion in natural and artificial systems. This includes bearing design and lubrication.
Viscosity: is the most important property of a lubricating oil. This property is a measure of an oil resistance to flow. Oil with a high viscosity would be thick, heavy bodied, and slow flowing. It has a high resistance to motion within itself. Kinematic viscosity (ASTM D445) is the viscosity measured while fluid is flowing under the force of gravity.
Viscosity Index: (ASTM D2270) is the measure of the change in viscosity with temperature. The higher the viscosity index, the less the viscosity of the fluid changes with the temperature. For lubricants, a high viscosity index is usually desirable.
Volatility: evaluates the total evaporation loss of a substance under a certain conditions. There are several standardized methodologies to measure it. Most common used methodologies are ASTM D5800, DIN 51581 and ASTM D6375.
Flash Point: the lowest temperature at which a liquid will form a vapor in the air near its surface that will “flash,” or briefly ignite, on exposure to an open flame. The flash point is a general indication of the flammability or combustibility of a liquid. Its standard methodology is the ASTM D92.
Iodine value: measure of the degree of unsaturation of an oil, fat, or wax; the amount of iodine, in grams, that is taken up by 100 grams of the oil, fat, or wax. Unsaturated compounds contain molecules with double or triple bonds, which are very reactive toward iodine. The more iodine is attached, the higher is the iodine value, and the more reactive, less stable, softer, and more susceptible to oxidation and rancidification is the oil, fat, or wax.
RapidOxy: accurate oxidative stability test, where a sample is introduced into a chamber under oxygen Pressure and Temperature control, isolating the study of the oxygen degradation effect onto the chemical structure. The given value in minutes takes place when the initial Pressure drops 10%. Standardized methodology is the ASTM D8206.
Fire Point: the lowest temperature at which the vapor of a liquid will continue to burn for at least 6 seconds after ignition by an open flame of regular dimension. Standardized methodology is ASTM D92.
Pour Point: is the temperature at which a liquid becomes semisolid and loses its flowing characteristics. Standardized methodology is ASTM D97 which sometimes has lack of reproducibility when checking products with very low pour points or with high viscosities. Another feasible methodology is to measure viscosities at low temperature ASTM D445 or ASTM D7042, ASTM D7346 and ASTM D5949.
Cloud Point: is the temperature at which a liquid becomes cloudy. Standardized methodology is ASTM D2500 and ASTM D5773.
Coefficient of friction: is a measure of the amount of resistance that a surface exerts on or substances moving over it, equal to the ratio between the maximal frictional force that the surface exerts and the force pushing the object toward the surface.
Lubricity: is a measure of the effect of a lubricant on the coefficient of friction of a contacting part over a sliding surface. Lubricity can be modified by the type of base/co-base oil or additives used.
Wear: the removal of material from one or more solid surfaces in solid-state contact. When relative motion occurs between two objects in contact (i.e., sliding or rolling contact), wear products will always be produced. The type and amount of wear that results in operational systems depends on proper lubrication. Understanding the wear behavior of various materials is a very complicated process. Many factors need to be understood to determine the mechanism that caused the wear to occur.
Abrasive Wear: occurs when two materials contact each other and one is harder than the other. This type of wear is sometimes called scratching, scoring, or gouging, depending on the severity of damage to the equipment. Two-body abrasion occurs when two surfaces of different hardness are in contact with each other. The harder of the two materials will wear away the softer material when there is relative motion between the two objects in contact. Three-body abrasion occurs when two surfaces of the same hardness are in contact with each other and a piece of foreign material (i.e., grit, metal, rust) becomes lodged between the two surfaces. The foreign material (third body) is typically harder than the two surfaces in contact.
Adhesive Wear: these types of wear result when microscopic projections at the sliding interface between two mating parts weld together under high local pressures and temperature. After welding together, sliding forces tear the metal from one surface. The result is a minute cavity on one surface and a projection on the other, which will cause further damage. Adhesive wear initiates on a microscopic level but progresses steadily once it starts.
Surface fatigue: all machines are subjected to stresses during operation. The stresses subjected to operating machinery are not constant, they periodically increase and decrease. All these repeating stresses in a rolling or sliding contact can give rise to fatigue failure. The effects of fatigue wear are based on the stresses in or below the surface without a need for direct physical contact of the surfaces under consideration.
Fretting: is the accelerated surface damage occurring at the interface of contacting materials that are subjected to small amounts of periodically occurring displacement. Fretting corrosion is found in all kinds of press fits, spline connections, bearings, and riveted and bolted joints, among other places. Fretting corrosion is also called friction oxidation, bleeding, red mud, and fit corrosion. One important effect of fretting wear is its contribution to fatigue failures. Examinations of surface fractures have shown that fatigue cracks originate in or at the edge of a fretted area.
Tribofilm: is the protective layer formed between two lubricated surfaces. It is mostly used to describe strongly bound films that are formed on tribologically stressed surfaces, such as tribochemical reaction films (for example with additives containing S, Zn, P, etc.) or polymeric and non-sacrificial reaction films (such as high performance additives Docadit TM series).
Stribeck curve: is an overall view of friction variation in the entire range of lubrication, including the hydrodynamic, mixed, and boundary lubrication. It is represented by a graph where on the vertical axis corresponds to the coefficient of friction and the horizontal axis corresponds to Hersey number (dynamic viscosity of the fluid multiplied by speed of the fluid and divided by normal load per length of the tribological contact).
Boundary lubrication: lubrication regime where the solid surfaces are so close together that appreciable contact between opposing asperities is possible. The friction and wear in boundary lubrication are determined predominantly by interaction between the solids and between the solids and the liquid.
Mixed lubrication: at lower velocities or higher loads, the hydrodynamic pressure is not sufficient to completely separate the sliding parts. In this situation, a mixed lubrication regime exists where part of the load is supported directly by the contact points of the surfaces.
Hydrodynamic lubrication: at high velocities and not too high loads, the hydrodynamic pressure completely separates the sliding parts, allowing the formation of full-fluid-film lubrication. The increase of fluid film turns into a higher coefficient of friction due to the effect of the fluid friction.
Sliding friction: occurs when the surface of one solid body is moved across the surface of another solid body.
Rolling friction: occurs when a curved body, such as a cylinder or a sphere, rolls upon a flat or curved surface.
Fluid friction: is the resistance to motion exhibited by a fluid. Fluid friction exists because of the cohesion between particles of the fluid and the adhesion of fluid particles to the object or medium that is tending to move the fluid.
OEM: Original Equipment Manufacturer. It is the original designer of a machine who often defines the performance and characteristics parameters a lubricant must reach.