Often, colour is just a consequence of the base oils and additives used in the formulation. For example, Group I mineral oils colour can vary from light yellow to dark brown, and darker colours in mineral oils are an indicator of larger quantities of impurities such as sulphur or aromatics. In addition, dark colour is more noticeable in higher viscosity mineral oils, however on a finish lubricant, darker colour doesn’t necessarily mean higher viscosity. Additives, such as calcium sulfonate detergents or magnesium-based additives will darken the lubricant. If a formulation changes frequently colour does too, and end users are very sensitive to these changes, hence communicating them appropriately is vital.
Differences of darkness in the lubricant can also influence end users’ perception regarding its viscosity, as there is a natural and illusive predisposition to think that a darker fluid is more viscous.
Another known example is the addition of solid particles such as graphite or molybdenum disulphide powders to increase load carrying capacity, turning the grease black or dark grey, which can be a limiting factor for many applications, driving formulators to change to colourless additives such as polytetrafluoroethylene (PTFE). In fact, many industries such as the food, paper, and aluminium or textile industry require colourless and stainless lubricants for many applications that need the best performance whilst sustaining its stainless properties throughout time. To achieve this, a lubricant must be formulated with colourless additive chemistry and synthetic base oils with increased oxidation stability.
With its use, lubricants and greases will suffer thermal degradation, oxidation, wear particle contamination or even external contamination, leading to darkening and loss of its original colour. This observation is often used as a factor to condemn the lubricant and the rate of darkening can be an indicator of the lubricant or grease overall quality and suitability for the application4
helping to detect problems and prevent
equipment damage. There are several implemented methods to assess colour in a liquid lubricant, such as ASTM D 1500, or Saybolt colour scale, used for classifying light-coloured products, though when it comes to greases, visual methods are habitually a better tool as its colour after use is strongly influenced by the initial one.
Colour-coding is also a useful tool for end users. Specific lubricants need to be formulated with colour, in order to distinguish them from other lubricants and prevent errors that may result in equipment failure. Transmission fluids are a good example, which are typically manufactured in red or green, to reduce risk of using the wrong lubricant and additionally helping to quickly assess the condition of the transmission lubricant in use.
Another interesting example is the two-stroke engine lubricant that can be found typically in red or blue. Due to the way a two-stroke engine is built lubrication of the pistons is achieved through mixing the right quantity of lubricant with fuel. In many cases, this mixture is prepared beforehand by the petrol station or by the end user, and colour plays an important role helping to ensure that the correct amount of lubricant has been added to the fuel and that it has been well homogenised, once again, reducing equipment failure by error.
These are just some examples that demonstrate how colour plays a very important role in lubricants and greases. Whether it is achieved with a purpose or simply a consequence of the molecular chemistry in the performance additives and base oils, it is unquestionably a mesmerising multifunctional tool that continuously contributes to the shaping of the lubricant industry.
Sources: 1. [online]
https://www.theatlantic.com/health/ archive/2014/01/how-color-shapes-our- lives/283376/
2. [online]
https://www.rd.com/culture/heres-japan- blue-traffic-lights/
3. [online]
http://www.machinerylubrication.com/ Read/31032/grease-color-lubrication
4. [online]
http://www.machinerylubrication.com/ Read/29531/grease-color-quality
EMAIL
daniel.saraiva@
galp.com
LUBE MAGAZINE NO.146 AUGUST 2018
15
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