Article updated on 13 May 2020.
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Lubricants are used throughout the automotive and manufacturing industries and play a key role. However, because they are used in energy-intensive environments, they are susceptible to both wear and contamination. Therefore, it is important for any company that uses lubricants to monitor the purity and effectiveness of their lubricants and change them where necessary. In this article, we look at some of the different ways in which lubricants can be studied to ensure that they are performing their function efficiently.
Why Lubricants Need to Be Studied and Monitored
There are many different problems that can occur when lubricants are used. Because they are used in movable mechanical environments, such as in an engine or industrial machinery, they can wear and become contaminated over time. As most mechanical environments involve moving metallic parts, one of the most common issues is the deposition of metallic particles into the lubricant after long periods of use. Once these particles become a part of the lubricant, then the effectiveness of the lubricant is reduced; where the lubricating properties of the lubricant is reduced, and the unwanted particles interact with the mechanical system, both of which cause wear to the system.
Aside from particle debris, lubricant systems can become oxidized or contaminated with other types of lubricant and/or water, and these impurities also reduce the effectiveness of the lubricant. Therefore, it is important to study how the lubricant is performing, and in doing so, you can check the purity of the lubricant and decide whether it needs replacing before irreversible damage is done to the mechanical system.
Infrared (IR) Spectroscopy Methods
Infrared (IR) spectroscopy techniques, both standard IR and Fourier-transform infrared (FTIR), are used for determining if there has been a mix-up with lubricants—i.e. in cases where a specific lubricant is required, and a different type of lubricant is mixed in. However, it is not a technique that can measure lubricants in real-time and is often used when a mix-up is known (or is suspected).
IR spectroscopy has become a widely used technique for lubricant mix-ups because it enables an unknown sample to be compared against a known reference. So, by analyzing the lubricant from a designated system, it can be compared against a pure form of the lubricant and this enables any differences between the pure lubricant and the lubricant currently in use to be determined. FTIR takes the analysis one step further by detecting and identifying functional groups within the oil, as well as any additive packages in the lubricant.
Elemental Analysis Methods
Elemental analysis techniques have become a widely used method for determining if a lubricant possesses any contaminants. There are many techniques used to study lubricants which fall under the elemental analysis banner, including inductively coupled plasma (ICP), rotating disc electrode (RDE) spectroscopy and X-ray fluorescence (XRF).
There are many different types of contaminants that can be picked up using these techniques, but given the environment that lubricants are used in, elemental analysis methods are often used to identify ‘wear metal’ contaminants—metal particles which have broken off from the machinery under wear. The key advantages of using elemental analysis methods in the study of lubricants is that they can easily identify ash-type additives and can deduce the elemental ratios of contaminants within the lubricant.
Wear Debris Analysis Methods
Wear debris analysis is not a single technique, rather, it is a collection of techniques that help to determine the extent of particulate matter within a lubricant and the amount of wear within a mechanical system. A series of techniques is required because wear particles in the lubricant can enter at different times of the lubricant’s life cycle, which sometimes makes it difficult to understand the root cause of the wear.
Particle Size and Shape Analysis
The size and shape of particles within a lubricant are important parameters for determining the amount of wear/damage a system is likely to undergo using the lubricant in its current state. Overall, three different parameters are measured as standard: the average particle size, the particle size distribution, and the largest particle size. Taking these parameters into account, the amount of potential wear to machinery is proportional to the size of the particles within the lubricant—and there are different classifications on damage around the different size range, but any particles greater than 20 microns in size pose a threat to a mechanical system.
Aside from the size, the shape of the particles can help to identify the wear mechanism by which the particle contaminants were created. In general, those of a 2D or platelet-like geometry are more likely to have been released from the components by metal-to-metal sliding, whereas 3D spherical particles are often attributed to fatigue or lubrication failure. By studying the particles from a shape and size perspective, it enables a picture to be built up about how the contaminant particles came to be in the lubricant and the threat they possess to the mechanical system.
Color Analysis
Color analysis is needed when studying the wear particles within a lubricant as it can often help to distinguish between different types of metallic particle. Some of the most distinguishable particles are those composed of iron, not only for its color (red or black depending on the type of oxide) but also because it is a common contaminant as many mechanical components have iron in their compositional makeup. By comparison, aluminum and chromium-based particles are a bright white color, copper particles are bright yellow in nature, and lead-based particles are grey. The colors are all very distinguishable from each other and this helps to determine what type of metallic particle is contaminating the lubricant.
Sources and Further Reading
- “Infrared Spectroscopic Methods for the Study of Lubricant Oxidation Products”- Coates J. P. and Setti L. C., Tribology Transactions, 2008, DOI: 10.1080/05698198608981701
- Plant Services: https://www.plantservices.com/articles/2014/oil-analysis-methods-lubrication-monitoring/?start=1
- Spectro Scientific: https://www.spectrosci.com/
- Intertek: http://www.intertek.com/petroleum/testing/lubricants/
- Mobil: https://mobilserv.mobil.com/en/lubricant-oil-analysis/
- Machinery Lubrication: http://www.machinerylubrication.com/Read/30443/oil-analysis-reports
- FA-ST: https://www.fa-st.co.uk/oil-analysis/lube-oil-analysis
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