The dropping point of lithium grease is the temperature at which a sample of grease begins to flow in the form of a liquid. This value is important for the design of lubrication systems, as it indicates the maximum temperature at which the grease can be used without losing its lubricating ability.
The dropping point of lithium grease is determined by the nature of the thickener, which is the component that gives the grease its consistency. In lithium greases, the thickener is a lithium soap, which is composed of a lithium molecule fused to a fatty acid. The temperature at which the lithium soap begins to melt is determined by the melting point of the fatty acid.
The most commonly used fatty acids in lithium greases are stearic, oleic, and linoleic acids. Stearic acid has the highest melting point, about 177 °C, while oleic and linoleic acids have lower melting points, about 13 °C and 11 °C, respectively. Therefore, lithium greases with lithium stearate soaps have a higher dropping point than lithium greases with lithium oleate or linoleate soaps.
In addition, the dropping point of lithium grease can be influenced by the viscosity of the base oil. Greases with more viscous base oil have a higher dropping point.
In general, lithium greases have a dropping point between 180 °C and 200 °C. However, lithium greases with higher dropping points, up to 300 °C, are also available on the market.
The dropping point of lithium grease is an important parameter to consider when choosing the most suitable lubricating grease for a particular application. For applications where the grease is subject to high temperatures, it is necessary to use a grease with a high dropping point.