Lubricants and Additives
What are lubricants?
A lubricant is a material utilized to reduce friction of movement between surfaces. Usually lubricants are liquids or semi-liquids, but may be solids or gases or any combination thereof. Besides reducing or controlling friction, they can prevent overheating, corrosion and abrasion.
Lubricants typically contain > 90% of base oil (fractions of petroleum called mineral oils) and < 10% additives.
Lubricants are usually divided into four basic classes:
- Oils: Liquid lubricants, e.g. mineral oils, natural oils, synthetics, emulsions, or even process fluids
- Greases: Oils, which contain a thickening agent to make them semi-solid, anti-seize pastes and semifluid greases
- Dry lubricants: Lubricants, which are used in solid form, bulky solids, paint-like coatings, or loose powders, e.g. graphite
- Gases: Usually air, or any gas which will not attack the bearings or decompose.
What are the main properties of lubricants?
- Viscosity and Viscosity index
Viscosity describes the flow behaviour of a fluid. The viscosity of lubricating oils diminishes as temperature rises and consequently is measured at a given temperature (e.g. 40°C) e.g. with the Pycnometer method (OECD 114).
- Pour point
The pour point refers to the minimum temperature at which a lubricant continues to flow. Below the pour point, the oil tends to thicken and to cease to flow freely.
- Flash point
The flash point is the minimum temperature at which an oil-vapour-air-mixture becomes inflammable. It is determined by progressively heating the oil-vapour-air-mixture in a standard laboratory receptacle until the mixture ignites e.g. EU-method A. 9
- Abel-Pensky-Method: Substances with flash point < 40 °C
- Pensky-Martens-Method: Substances > 40 °C (DIN 51758):
- Ready biodegradability
Biodegradability is one of the most important factors in assessing the environmental fate of lubricants. Lubricants get in contact with the aquatic environment and sewage treatment microorganisms, which is the basis for the assessment of aquatic biodegradability:
Sturm Test acc. OECD 301B
- Carcinogenic Potential.
The modified Ames test provides information about the carcinogenicity of residual aromatic extracts:
ASTM E1687 - 10(2014): Standard Test Method for Virgin Base Oils in Metalworking Fluids