Lubricants and Additives
What are lubricants?
The process of lubrication is simply the use of a material to improve the smoothness if movement of one surface over another; the material which is used in this way is called a lubricant. Lubricants are usually liquids or semi-liquids, but may be solids or gases or any combination of solids, liquids, and gases. In addition to that lubricants should be reducing or controlling friction, and also prevent overheating and corrosion.
Lubricants contain typically > 90% on one type of base oil (fractions of petroleum called mineral oils) and less than < 10% additives.
Lubricants are usually divided into four basic classes.
- Oils: Cover all liquid lubricants, whether they are mineral oils, natural oils, synthetics, emulsions, or even process fluids.
- Greases: Technically these are also oils, which contain a thickening agent to make them semi-solid. It is convenient, however, to include the anti-seize pastes and the semifluid greases under the same heading.
- Dry lubricants: These include any lubricants, which are used in solid form, and may be bulky solids, paint-like coatings, or loose powders.
- Gases: The gas usually used in gas bearings is air, but any gas can be used which will not attack the bearings, or itself 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.
- 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. by the Abel-Pensky-Method: Substances with flash point < 40 °C
Pensky-Martens-Method: Substances > 40 °C (DIN 51758):
EU-method A. 9
- Ready biodegradation
Biodegradation is one of the most important factors in assessing the environmental fate of lubricants and chemicals. Lubricants coming into the aquatic environment and get in contact with the sewage treatment microorganisms, which is the basis for the assessment of aquatic biodegradation:
Sturm Test acc. OECD 301B
- Determining Carcinogenic Potential.
Use of the modified Ames test as an indicator of the carcinogenicity of residual aromatic extracts:
ASTM E1687 - 10(2014): Standard Test Method of Virgin Base Oils in Metalworking Fluids