What exactly is grease, other than a Hollywood blockbuster? The National Lubricating Grease Institute along with countless manufacturers all have their own take on the substance.
Yet it can basically be described as a lubricating medium which stays in place rather than obeying the call of gravity, as straight oil does.
To achieve the lubrication of surfaces in situations where it is impossible or impractical to use liquid oil, a method had to be developed to encourage it to stay in place.
That method involved the addition of a thickener to radically alter the oil’s properties.
Animal fat had been used as a lubricant in some situations, but they suffer a low melting point and would soon disappear as the surfaces warm.
The addition of lime as a thickener overcame this to a certain extent by altering the chemistry of organic fats and oils to produce a paste.
A somewhat more reliable method came about in 1835 with the invention of the first calcium grease.
This was a mixture of oil and a calcium soap which thickened the liquid to produce a fluid, a fluid being a substance that flows, but may not actually be a liquid.
Various other metal-derived soap-type greases happened along with the popular lithium thickened grease being invented in 1938. It immediately gained favour and is perhaps the most widely used of the soap-based greases today.
Greases that did not depend on mineral soaps arrived in 1952 with the first urea-based grease and since then, the development of synthetic oils and thickeners has resulted in a huge range of greases to meet an equally huge range of uses.
Performance boosters
Besides the thickening agent there may be other chemicals added to improve the performance or add desirable qualities to the substance.
Overall oil will be the major ingredient by far with thickeners accounting for between 3% and 30% of the material.
Performance enhancing additives, which may include pigments and dyes, rarely constitute more than 5%.
Within the agricultural environment, the main requirement of grease is to lubricate bearings and joints at temperatures that are reasonably consistent and not too extreme, hence the universal cartridge that is found at every machinery dealer or co-op.
The product will be formulated to reduce friction and wear, prevent corrosion, reduce water ingress and maintain mobility while minimising any change in its structure or to properties.
It will also act as a seal and develop a durable protective barrier preventing both fluid and solid contaminants from entering the sensitive parts while minimising the risk of lubricant damage.
Grease types
The general purpose grease will suffice for a good number of jobs around the farm, but there are other greases widely available which have properties dependent upon the base oil type, thickener used and additives included.
Types are usefully categorised by the thickener used and those that may be of use around farm machinery include the following.
Calcium soap – these have excellent resistance to water and moisture ingress, however they separate at temperatures above 80°C and are only recommended for applications where the operating environment is unlikely to rise above 70°C.
Lithium soap – these have excellent thermal stability, mechanical stability, and good water resistance and are therefore the most commonly used for general purpose greasing.
Aluminium complex soap – this type has a fine fibre structure, a high dropping point, as well as excellent heat and mechanical stability and water resistance.
It is frequently used in the allied food production industries, or in paint plants, due to its resistance to dripping.
Molybdenum – these greases contain molybdenum disulphide as an additive which acts to fill the microscopic cracks in metal surfaces, reducing micro-welding and helping to resist shock loads. But they tend to have a high solids content.
The non-soap greases may be thickened with clay, polyurea and other chemicals. But these tend to be specialist products for specific purposes, especially where high temperatures are encountered in industrial situations.
Automatic lubrication systems
Of particular importance in farm situations is the use of the right product in automatic greasing systems.
Generally speaking these are of great advantage on machines with lots of lubrication points that need regular attention; not only do they make life easier, ensuring that the job gets done, but regular dosing pushes dirt out and away from bearing surfaces.
It is recommended by manufacturers that a low solid grease, typically less than 5%, is used in their systems, the reason being that the pumping components are finely honed and solids will tend to clog them over time.
Classification of greases
The NLGI classifies greases according to their consistency. This property is defined as the level of softness or hardness of every grease.
Every grease is assigned a specific NLGI number that goes from 000 to 6.
These grades are then used to express the level of consistency each grease has with grade 000 being completely fluid, while grade 0 is described as very soft; NLGI 1 grease is soft; 2 is considered normal; 3 is firm and so on until 6, which is considered as being very hard.
The test for this property is by placing an inverted cone on a sample and measuring how far it sinks in a given time.
Companies will also grade their products on water resistance, however, these tests tend to be subjective although there is a proposal for something more scientifically rigid in the form of measuring the beading of water droplets when placed on a sample.
