Operation of industrial plants always entails friction and wear. Oil lubrication, frequently used in the form of minimum quantity lubrication , is of particular importance for industrial lubrication. Oil lubrication is mainly used for industrial plants (manufacturing industry, such as punching and folding machines, or any kind of conveyor systems, ...). Minimum quantity lubrication or minimum quantity cooling lubrication ensures a clean and economical solution for that purpose. The most commonly used lubrication medium is lubrication oil.
The characteristic features of oil lubrication systems are low consumption of lubricants with optimum lubrication of the lubrication points and very low lubricant residues from lubrication oil.
Lubrication oil that is not categorised as vehicle engine or gear oil is classified by the same system as lubrication grease . The "International Organisation for Standardization" - ISO has developed a classification system of viscosity grades (VG) for lubrication oil. A total of 18 viscosity grades are defined by standards. With oils, the concept of viscosity is generally used for differentiating whether an oil is thick or thin. Precisely speaking, the viscosity of lubrication oils represents their kinematic viscosity (i.e. their resistance to gradual deformation). It is also a measure for the natural internal friction of a fluid. With lubrication oil, this is one of the most important properties and in most cases is highly dependent on temperature. High degrees of viscosity represent higher load-bearing capacities of the lubrication film. The viscosity change behaviour of lubrication oils due to change in temperatures may differ from one type of oil to another. Therefore, the viscosity index (VI) is preferably used to define the characteristics of the VT behaviour (viscosity-temperature behaviour) of lubricants within a specified temperature range. The VI is calculated from the kinematic viscosity of a substance at 40 °C and at 100 °C, respectively. A high viscosity index stands for relatively low changes in viscosity at rising temperatures and vice versa.
The viscosity of industrial lubricants is standardised as per DIN 51519.
The ISO VG figures refer to kinematic viscosity at a test temperature of 40 °C. The previously used test temperature was 50 °C.
In case additional viscosity grades are required, only the ISO VG figures specified in DIN 51519 must be used. For conversion of kinematic viscosity to dynamic viscosity, the mean density values of the various lubrication oils were taken as a basis.
Every viscosity grade is specified by an integer, which is obtained by rounding the numeric value of midpoint viscosity obtained at 40 °C and expressed in mm²/s.