Analyzing wear and contaminants in lubricant is crucial to prevent industrial machinery breakdowns
21 September 2022Article by Beatriz Graça and Pedro Marques, INEGI specialists in Tribology and Industrial Maintenance
Most equipment used in industry includes components in motion, and in contact with each other, which require lubrication to ensure their proper functioning. However, while in contact, no matter how good the lubrication conditions are, wear will always occur, which could lead to a failure and eventual unscheduled stop.
The analysis of the particles resulting from this wear contains crucial information to identify not only the type and severity of wear, but also the component that is wearing out. Extremely useful information, as it helps to identify prematurely if there is a risk of an unexpected failure of a machine.
Today, there are several techniques associated with industrial maintenance, aiming to prevent malfunctions. In the case of equipment being lubricated, ferrography stands out - a technique that allows a detailed analysis of the type, shape, color and material of wear particles and contaminants.
Carrying out this technique involves collecting a representative lubricant sample, which is subsequently analyzed and processed in a specialized manner suited to its characteristics. A sample of lubricating oil will necessarily have to be treated differently from a sample of lubricating grease, for example.
To deposit the wear particles and contaminants contained in the lubricant sample, a lamella, called ferrogram, is used, which accommodates a controlled deposition process, in such a way that the ferromagnetic particles contained in the sample are strategically organized from the largest to the smallest. In turn, the non-ferromagnetic particles are evenly distributed throughout the sample deposited on the ferrogram.
This is followed by a microscopic analysis, sometimes using a polarized light source, which makes it possible to check morphology and size, as well as the type of alloy after a heat treatment. Different types of wear arise from different types of particles. Thus, by the shape, size and type of surface of these particles it is possible to assess the type of wear that is occurring, and thus understand if a process is developing that could lead to the failure of the lubricated machinery. By knowing the mechanics of the machine and by analyzing the type of metal alloy of the particles, it is possible, in many situations, to understand which component is in a wear process that will lead to failure.
As an example, Figure 1 shows wear particles resulting from a sample of lubricant that was tested in an experimental bearing test. In Figure 1 a) superimposed particles of large dimensions are observed with typical characteristics of having been generated by fatigue processes. Some friction polymers (transparent particles) also appear, which reveal the degradation of additive compounds in the lubricant. Also noteworthy in Figure 1 a), a bluish-looking particle that reveals high temperatures in the contact areas, highlighting the severity of operating conditions and a potential accelerated degradation process.
After heat treatment, Figure 1 b), it is possible to verify that the particles acquired different colors, some more bluish and others more brownish. For the temperature at which the heat treatment was carried out, bluish colored particles indicate low-alloy carbon steel, while brownish particles are alloyed steel. In this way, it is possible to indicate with some degree of certainty that the blue particles, present in large quantities, come from the cage, while the brown particles will come from the rolling elements or the bearing races. Due to its size and quantity, in this analysis it was possible to perceive that the bearing was in an abnormal degradation process, with high wear on the cage.
Figure 2 shows external contaminants, two fibers, dust and silica crystals (sand). The presence of external contaminants such as dust and sand of very high firmness and in significant quantities potentiate the appearance of failures, in addition they can also indicate the poor functioning of the filtering and sealing systems of the lubricant.
Figure 2: External contaminants, polarized light
Thus, ferrography presents itself as a technique with great potential for application, not only in diagnosis, but also in the prevention of malfunctions in high-value lubricated machines, or in situations where an unscheduled stop due to failure translates into very high costs.
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Pre heat treatment / Post heat treatment at 330ºC.
Figure 1: Wear particle and respective treatment for material identification
Figure 2 shows external contaminants, two fibers, dust and silica crystals (sand). The presence of external contaminants such as dust and sand of very high firmness and in significant quantities potentiate the appearance of failures, in addition they can also indicate the poor functioning of the filtering and sealing systems of the lubricant.
Figure 2: External contaminants, polarized light
Thus, ferrography presents itself as a technique with great potential for application, not only in diagnosis, but also in the prevention of malfunctions in high-value lubricated machines, or in situations where an unscheduled stop due to failure translates into very high costs.
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