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What does grease colour tell us?

Greased Bearing

Visual examination of lubricants can sometimes give users insights about products in play.

Greases are defined as lubricants in a solid or semi-solid state. They are typically composed of a base oil (mineral, synthetics) thickening agents (emulsifiers, soap, fatty acids) and other additives (Extreme Pressure, Viscosity Index improver) that give them desired attributes for specific applications.

High-viscosity lubricants, greases are produced by a wide range of manufactures like Mobil, Kluber, and Fuchs and designed to serve multiple purposes. These include lubricating the moving components of equipment so they can work freely and prevent metal-on-metal contact that cause undue wear and protecting parts from contamination and corrosive force like iron oxide (rust).

What does the colour of grease mean?

Grease is suited to applications where lower viscosity lubricants like oils and fluids won’t remain in place and to manage mechanical systems that do not require frequent lubrication. In this in-depth article, we will explore what the colour of grease can mean, assessing whether we can categorise available products by application due to their colour and whether the colour can impact lubrication. We’ll also look at whether we can tell if grease has useful active service life remaining by studying its colour.

Does the colour of grease relate to its application?

On the current lubrication market, you will encounter available greases in a full spectrum of colours, including red, blue, green, purple and yellow, but also in tones like black, grey and white. However, what these colours mean and the perceptions and opinions surrounding them can differ widely between various manufacturers and users operating in the industry.

Typically, lubricant manufacturers use colour to identify grease by type. Additionally, more vibrant colours are selected to create greater appeal in manufacturing, rather than a basic brown.

While colour coding systems for grease differ from manufacturer to manufacturer and there aren’t any specific rules, some commonalities exist. For instance, white grease is associated with food-grade grease suited for use when lubricating machinery where contact with edible products is likely in applications like bottling, food processing and packaging. H1 lubricants must be used if potential exists for incidental contact with foodstuffs.

Typically, black or grey coloured greases denote the inclusion of graphite which is added to support extreme operating conditions. Many users mistakenly belief that certain colours indicate usage related to common associations like blue for cold temperature use or red for high, However, this is not so. Today, you can buy greases designed to withstand higher operating temperatures in green, blue and red across multiple brands.

In brief, although in some cases colour can help identify grease by type (like white grease being food safe), never use just colour to select a product, as there are far more important factors to consider that should determine your purchase.

Does grease colour affect lubrication?

It is critical to remember that while users have always judged case-fresh lubricating greases by their visual appearance, this has no significant impact on the products quality or service. However, the grease’s mechanical and oxygen stability, temperature life, water resistance and load-carrying capacity are important.

Can I tell if a grease has gone bad its colour?

During its active service life, a grease can change in colour, and this can indicate issues that require attention. Depending on the lubricant’s design and composition, the grease might become darker or even turn black, however it might also lose colour becoming paler. Such colour changes can be caused by a variety of unwanted processes including contamination, thermal degradation or oxidation.

Higher operating temperatures can see the dyes used in greases to differentiate them lose colour intensity however, greases that become heavily oxidised can blacken over time. When a grease starts to look milky it is often a sign of water contamination. Grease can also alter colour when two different greases introduced to a system and become mixed with the resulting hue a blend of both.

As a rule of thumb, if a grease experiences a colour change during active service, it can be a strong indication that it has outlived its usefulness and will no longer possess the properties you employ it for.

Selecting the right grease

As with every other kind of lubricant, the aim when deploying grease is to decrease friction. This occurs when a grease produces a film in between two moving metal surfaces. Picking the correct grease is crucial to reduce friction, wear and damage, resist corrosion, defend seal bearings against contamination, and prevent leakage. Instead of selecting grease by colour purchase products for the beneficial properties they provide and adhere to your original equipment manufacturer (OEM) recommendation.

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