How are industrial oils classified

Requirements and properties of lubricants

Requirements for lubricants

  • Essentially, lubricants must have the following properties:
  • Separation of surfaces at all loads, temperatures and speeds in order to reduce friction and wear.
  • Function as a coolant to dissipate heat generated by friction or external causes
  • Maintaining sufficient stability to ensure consistent behavior throughout the expected service life
  • Protection of surfaces from damage by aggressive substances that arise during operation
  • Cleaning and dirt-carrying capacity to remove residues and dirt that can build up during operation


Properties of lubricants
The most important lubricant properties that are usually listed in the technical data of the product are as follows:

  • viscosity
  • Viscosity index
  • Pour point
  • Flash point


The viscosity describes the flow behavior of a liquid. The viscosity of lubricating oils decreases with increasing temperature and is therefore measured at a given temperature (e.g. at 40 ° C). The viscosity of a lubricant determines the thickness of the oil layer between metallic surfaces.
The most common unit of measurement for viscosity is the centistoke (cSt).

Viscosity index
The viscosity index is a measure of the changes in viscosity of a liquid as a function of temperature changes. The higher the viscosity index, the more stable the viscosity with a change in temperature. From this it follows that with two lubricants with the same viscosity at 40 ° C, the lubricant with the higher viscosity index ensures the following:

  • better engine start at low temperatures (lower internal friction)
  • more stable lubricating film at high temperatures


Viscosity classification
The viscosity can be classified in different ways, usually by giving a number or a more or less broad viscosity range. The classification, in conjunction with the viscosity index, should enable a quick determination of the most suitable lubricant for the respective application.

ISO-VG grades are widely used to classify industrial oils. Each class denotes a kinematic viscosity range, measured at 40 ° C. SAE grades are used in the field of engine and gear oils.

Pour point
The pour point indicates the minimum temperature at which a lubricant continues to flow. Below the pour point, the oil increasingly thickens and has only limited flowability.

Flash point
The flash point indicates the minimum temperature at which a flammable oil-vapor-air mixture is created. It is determined in the laboratory by mixing a laboratory container with oil-steam-air and gradually heating it until the mixture ignites.