Grease isn’t just a thick oil; it is made up of all different components. This article will break down what grease is about, when to use it and what happens when different grease samples are mixed together.

The Components that make up Grease
Grease is manufactured by the combination of three essential components: base oils, thickeners and additives. The base oil is the liquid and the largest component of the grease, typically making up 80 to 97% of the compound. It is a common lubricating oil and is usually mineral, synthetic or any fluid that contains lubricating properties. The viscosity may range from light (like mineral seal oil) to heavy (like heavy cylinder stock). The thickeners are any material that is combined with the base oil to produce a semi-fluid to solid substance. Lithium (being the most common), aluminium, calcium, clay and polyurea can be used alone or as a combination. Additives add special properties or enhance the existing properties of the grease. The additives or modifiers that are usually used are oxidation or rust inhibitors, pour point depressants, extreme pressure additives, anti-wear agents, lubricity-or-friction-reducing agents, molybdenum disulfide, graphite, and dyes or pigments (which only affect the colour and not the lubricating capability).

Mixing Incompatible Greases and the Consequences
An important factor to keep in mind is that mixing different grease types can result in incompatibility problems. This results from chemical interactions between the thickener or additive systems of dissimilar greases and can lead to equipment failure or damaged lubricant components. It is therefore imperative to test the compatibility of greases in a laboratory before changing from one grease to another.

When Grease is Used
Grease is often used as an alternative for a lubricant fluid when it’s required to maintain the original position in a mechanism. This alternative is especially used when frequent re-lubrication may be limited or not economically viable. The may be due to the physical configuration of the mechanism, motion and sealing type, or the need for the lubricant to perform the sealing function in the incident of lubrication loss or entrance of contaminants. The solid nature of grease represses its cooling and cleaning efficacy compared to a fluid lubricant. Other than those two elements, grease performs all other requirements a fluid lubricant fulfils.

How Grease is Graded
Consistency can be defined as the degree to which plastic material resists deformation under pressure. In grease, it’s the measure of relative softness or hardness and may indicate something of flow and dispensing properties. The consistency is measured in line with ASTM D 217 and Cone Penetration of Lubricating Grease. It is then documented with the National Lubricating Grease Institute (NLGI) grade.

The consistency is measured after the sample has been worked 60 strokes in the ASTM grease worker and is at a temperature of 77ºF. When the sample is ready, a penetrometer cone is released and sinks into the grease under its own weight and left for five seconds. The depth is then measured in millimeters and recorded. The NLGI uses a standardised numerical scale in order of increasing hardness for classifying grease consistency.The consistency is a result of the base oil and thickener ratio and not the base oil viscosity.

With this information, it will be easier to decide which fluid will be most suitable for your machinery: a grease or a lubricant.