Important terms and definitions in the field of grease
Oil component – the basic oil for grease; it can be petroleum oil, synthetic or vegetable oil. The basic oil represents 80-90 % of the grease composition.
Hardener – most often it is soap of a metal, such as aluminium, lithium etc. It can also be a non-soap hardener of organic origin – polyurea or of inorganic origin – earth (bentonit)
Additives – compounds to improve some specific grease properties, like protection from corrosion, oxidation, to improve the abrasion stability to increase the EP properties etc.
All these compounds together form the characteristic grease properties that are described by certain measurable parameters. Among the basic properties belong:
Consistence – penetration is measured and expressed by the depth of penetration of a metal cone into surface of grease in tenths of a millimeter. According to this value, the grease products are classified to particular consistence categories (NLGI) that are mentioned on the package.
The pour point – is a temperature at that the first drop separates at the bottom from the container. The pour point after deduction of app. 80 °C may be informatively considered the upper temperature limit for the usability of the grease.
Colloidal stability – characterizes the strength of grease structure, i.e. the attractive forces between the oil particles and the hardener.
Oil separability – gives the quantity of separated oil flowing through the bottom of the container and the sieve of the cone during a certain time. This value talks more or less about the behavior of lubricants during storage.
Besides these most common properties, further other properties of the grease are determined that are required depending of the way of use of a particular product. It is e.g. the oxidizing stability, water elutriation from the bed, determination of anti-abrasion properties (4-GP), determination of mechanical dynamic properties (SKF R2F test), anti-corrosion properties and others.
Specifications – as already mentioned, each grease is characterized by a group of properties to be met based on its purpose. Such information take a relatively big space and that is why it is impossible to indicate them at length at the package. In order that the customer can quickly navigate through the offers of various companies, a code labeling system of the grease characteristics (type of grease, consistence, and the temperature of use). On the European market, the products are labeled in line with the German standard DIN 51 502, or ISO 6743-9. Such a label has every grease.
As an example for the specification DIN 51 502 and ISO 6743-9, for the most common automotive lithium grease – MADIT LTA the following classification may be mentioned:
DIN 51 502 KP 3K-30
The meaning of the individual symbols:K – grease for rolling and sliding surfaces – use
P – grease with high pressure additives (EP) – additive
3 – degree of consistence NLGI “3”
K – maximum (upper) operation temperature 120 °C and water resistance
-30 – minimum (lower) operation temperature
IS0 6743-9 L-X-CCHB-3
Meaning of individual symbols:
L – general grease types
X – symbol for grease
C – lower operation temperature (-30 °C)
C – upper operation temperature (+120 °C)
H – behavior towards water and anti-corrosion grease
B – contains the EP additives (properties)
3 – consistence degree NLGI