Metal inclusions are particles of solid metals and metallic compounds which are inadvertently entrained in the production process of lubricants from base stocks or additive concentrates. Inclusion of metal particles in the lubricant or in a related industrial fluid is an undesirable occurrence. The chief source of any metallic contamination is the base stocks, but it is caused solely by contamination of contaminated additives, metallic wear from equipment and environmental sources. Metal particles entrained in the lubricant can result in poor lubricant performance, abrasive wear, and fouling of fuel injectors.
The most common metals associated with lubricants are iron, aluminum, copper and zinc. These metals are usually present in the base stocks, and can form various metallic inclusions such as oxides, sulfides and silicates. In some cases, metal particles may also be introduced during the additive blending process and can form various metal alloys or compacts present in the lubricants.
Metal inclusions can be observed in the form of flakes, powders, particles, or agglomerates. Depending upon the size and composition of the metal inclusions, they tend to interact with the lubricant and lead to metal-to-lubricant interactions that can negatively impact lubricant performance. Metal inclusions are also referred to as “stray particles” or “dowel bars”, and can cause accelerated wear of machinery and increase the risk of fires in machinery.
The detrimental effect of metal inclusions is not limited to just machinery, but also extend to fuel injectors. The presence of metallic inclusions in fuel injectors can lead to poor performance, fouling and clogging of the injectors, and increased risk of fires due to increased temperatures. In addition, the presence of metallic inclusions in fuel systems can lead to corrosion of metals within the system, resulting in further loss of fuel performance.
To prevent or reduce the risk of contamination from metallic particles, manufacturers must frequently perform quality checks and adhering to proper lubricant specification. The physical properties of the synthetic base stock and the quantity and types of additive packages used must be carefully monitored for any potential sources of contamination. Metal free, or non-metallic, synthetics should be considered. In addition, it is important to ensure the presence of appropriate filtration systems to sieve out any metallic inclusions prior to release of the finished lubricant.
The detection and removal of metallic inclusions can be accomplished in a number of ways. Physical inspection, optical inspection, and magnetic particle inspection are some of the most commonly used methods. Additionally, electronics, atomic force microscopy (AFM), and X-ray diffraction (XRD) are other methods to detect the presence of metallic inclusions. It is important to use the appropriate technique based on the size and composition of the metallic particles that may be present in the lubricant.
In conclusion, metal inclusions are an issue which must be addressed when producing lubricants, fuels and other related industrial fluids. Metal particles present in lubricants can cause poor lubricant performance, abrasive wear and other issues which can lead to increased wear on machinery and increased risk of fires. To reduce or eliminate the risk of contamination from metallic particles, manufacturers must make sure that the proper base stocks and additives are used and that proper filtration is in place to remove any metallic inclusions. Additionally, it is important to use the appropriate technique to detect the presence of any metallic particles present in the lubricant.
