GREASE LUBRICATION
A grease is a lubricant and contains base oil, additives and thickener.
In the early days animal fat was used to lubricate bearings of animal-driven cats. However, this could not resist high temperature and technology discovered that if a base oil plus an alkaline with animal fat are cooked together, they form a grease. The animal fat reacts with an alkaline to form a thickener, sometime referred to as soap, as it uses the same process of soap manufacture i.e. saponification.
In grease lubrication, the material that separates the two moving parts is the oil and its performance is enhanced with the additives just like in lubricating oils. The thickener normally determines the melting (dropping point) of the grease.
The original thickener was Calcium based and the grease used to melt at 100˚C and could only use up to 60˚C. This required more frequent greasing and many bearings were fitted with grease cups to facilitate frequent lubrication.
In the mid 1950s, a lithium grease was discovered and was found to have a higher dropping point of 180˚C and could be used up to 120˚C. This was a major achievement as the grease could be used on all parts of the vehicles. It was referred to as a multi or all purpose grease.
As the demand has progressed, so has the ability of the grease been put to test under high temperature, high pressures, increased water presence e.t.c… It was found if a complex grease is used instead of the normal lithium, the grease will have higher dropping point (260˚C) and temperature usage (160˚C) which is better than lithium grease.
Other features that play an important role is the base oil viscosity of the oil. For vehicle wheel bearing it is preferred an SAE 40 or SAE 50 base oil is used. If the grease is used on wheel bearings which are subject to shock loading, then the grease must have EP properties.
The application of grease varies and therefore the stiffness of the grease is important. The National Lubricating Grease Institute (NLGI) came up with a classification that showed the very soft grease was given 000, followed by 00, 0, 1, 2, 3, 4, 5, 6. The measure of stiffness is when a cone is placed is on the flat surface of the grease and because of its weight it will sink in the grease. The depth to which the cone goes is measured and this is referred to as the penetration.
For wheel bearings, it is preferable you use an NLGI 3 and for all other application you use NLGI 2.
Our recommendations are as follows;
- Heavy duty/ high temperature/ wheelbearing grease – Delstar Lithium Complex Grease EP3.
- Chassis lubrication – Slusol Nu-tec Grease EP2.