Three common pollutants and detection methods of air compressor lubricants

Three common pollutants and detection methods of air compressor lubricants

Lubricating oil is known as the blood of the equipment, flowing inside the equipment, and has the functions of lubricating, reducing wear, cooling, cleaning and preventing rust. If the lubricating oil is contaminated, it will cause lubrication failure and increase equipment wear, which will cause equipment failure and shorten equipment life.

Contamination of lubricating oil is a complicated problem. Sometimes it can be found by daily inspection, but not in some cases, and some contamination cannot be observed by naked eyes. Moreover, for all the pollution, when the naked eye can detect it, it means that it is already serious. In short, the pollution of lubricating oil should be detected and treated early, especially for the more sensitive and critical equipment. Oil detection can accurately analyze the contaminants in lubricating oil by detecting oil, just like finding abnormalities in the human body through blood testing

1. Particulate matter:

Particulate matter is one of the most harmful pollutants. They enter the lubrication system and cause abrasive wear, metal crushing and scratching, and metal fatigue. Particles generally have a certain degree of hardness. Many particles are very small in size and can pass through the gaps between parts and circulate inside the equipment, causing wear. Common particles include dust, grit, fine metal particles generated during equipment operation, rust slag, etc.

　Particulate pollution not only harms the equipment itself, but also shortens the life of the lubricant. Abrasive wear will increase the metal powder content in the oil. These fine metal particles will not only further wear the equipment, but also accelerate the oxidation and deterioration of the lubricant, because the metal powder will catalyze the oxidation rate of the oil. Given that the hazards of these particulate matter are chained, early monitoring and early treatment are very important.

Oil testing can find fine particles in the oil, as well as early wear and tear of equipment. By detecting the particle count in the oil, we can understand the cleanliness of the oil and whether it has entered particulate contaminants. In addition, through metal analysis, we can find the early wear of the equipment. When the particulate matter and the metal of the equipment are abrasively worn, the scraped metal can be monitored. Through the analysis of the composition of the metal, the wear source can also be found. For example, the material of the gear is mostly iron with a small amount of other alloy components (chromium, nickel, manganese, etc.).

If particulate matter is found to enter the lubricating oil, general remedial measures include: finding where the particulate matter came in, then blocking the source, and filtering to remove the particulate matter. However, this approach is not always effective. Sometimes it is difficult to filter the oil to completely remove the particles, and the oil has to be replaced. If the wear is obvious, it is recommended to perform a ferrography analysis to determine the degree of wear and guide equipment maintenance. Moisture is a common pollutant. Although the hazard is not as serious as particulate matter, moisture can destroy the lubrication effect, deteriorate the oil, and cause equipment wear. Moisture can also cause metal corrosion. There are three forms of water in lubricating oil: dissolved water, emulsified water, and free water. Among them, emulsified water is the most harmful.　Dissolved water is the water that has been dissolved in the lubricating oil. Lubricating oil is hygroscopic and will absorb moisture in the air, so it contains a small amount of moisture. Generally speaking, a small amount of dissolved water will not cause any harm, unless certain circumstances require particularly strict requirements for the water content of the lubricant. The maximum allowable dissolved water content of lubricating oil is the water absorption saturation point. Before reaching the water absorption saturation point, although the lubricating oil contains water, it will not show signs of water, such as emulsification, turbidity, and reduced transparency. After the lubricating oil enters the water, if it is not separated from the oil, the tiny water droplets are suspended in the oil and become a suspension, which becomes emulsified water. Emulsified water is the most harmful. When the lubricating oil is emulsified, the water content has exceeded the saturation point. When the oil contains emulsified water, the transparency of the lubricating oil will be reduced, turbid, white in color or even milky white. Emulsified water is very harmful because it can flow freely and contaminate the oil in the entire lubrication system. In addition, moisture will destroy the lubricity of the oil. After the emulsified water reaches the pressure-bearing area where the equipment is running, these areas will be poorly lubricated, increased friction and wear. When water and lubricating oil are completely separated, it becomes free water. Free water is relatively less harmful, but it can also cause problems. First, free water may also circulate with the lubricating oil, causing oil to emulsify. In addition, the water in the oil will weaken the demulsibility of the lubricating oil, resulting in increased foam, consumption of additives in the lubricating oil, shortening the life of the lubricating oil, and easy to breed bacteria. In addition to poor lubrication, the damage to equipment caused by moisture includes hydrogen embrittlement and rust. Lubricating oil can prevent metal corrosion. If water enters the oil, it will easily cause metal corrosion. Hydrogen embrittlement is also called hydrogen damage, which can cause bearing damage. Water will decompose into hydrogen and oxygen. Electrolysis and corrosion will also produce hydrogen. Water will promote electrolysis and corrosion. High-strength steel is particularly vulnerable to this problem. In addition, the additives added to lubricating oil and grease contain sulfur (extreme pressure additives, anti-wear agents, etc.). Mineral oil itself also contains certain sulfur impurities, which will promote metal corrosion and cracking. Both humid atmosphere and free moisture may cause hydrogen embrittlement of metals 2. Moisture: 3. 　Moisture will destroy the strength of the oil film and the integrity of the oil film. Lubrication relies on the oil to form an oil film between the metal contact surfaces. The oil film separates the direct friction between metals and prevents direct metal contact. If moisture enters the bearing metal contact area, it will destroy the integrity of the oil film, reduce the strength of the oil film, cause poor lubrication or direct friction between metals, and cause metal fatigue damage, metal scratches, and chipping. Water will shorten the life of lubricating oil. In addition, water will also cause the loss and consumption of antioxidants in lubricating oil, leading to oxidative deterioration of lubricating oil. The oxidation of lubricating oil will form acidic substances, sludge and paint film, increase the viscosity of the oil, and affect the effect of splash lubrication. On the spot, you can observe the appearance of the lubricant. If the transparency of the lubricant decreases, becomes white, turbid or emulsified, it means that water has entered the oil. In addition, the heating method is also a simple and easy method. This method can make the most basic judgment. The operation is simple. Use a piece of iron and heat it to about 130°C on a fire. Put a drop of lubricating oil on the iron. If there is moisture, bubbles will be observed because the moisture in the oil is heated. Bubbles caused by evaporation. The larger the bubbles and the larger the number, the greater the water content. If you see the bubbles and you can hear the crackling sound, it means that the water content is relatively high, which may have reached more than 2000ppm. However, the heating method is only suitable for measuring emulsified water and free water. Karl Fischer moisture detection is the most accurate moisture detection method. Free water, emulsified water, and dissolved water can be detected. With proper operation, the detection of moisture can be quantified to the level of 10ppm (0.001%). General industrial monitoring And precise industrial monitoring can be used. When it is found that the lubricating oil has entered water, the correct way to deal with it is to find the source of water first, cut off the source, and then take measures to remove water. In severe cases, it is best to change the oil, which is best determined by oil testing. When using lubricating oil, avoid contact with other oils. But some situations, such as leakage, using the wrong lubricant when refueling (the wrong lubricant viscosity or the wrong additive type), etc., will cause different lubricants to mix. 4. Mixed with other lubricants: For example, mineral oil is not compatible with conventional PAG synthetic oil (non-oil-soluble PAG). If these two oils are mixed, the viscosity of the mixed oil will increase and sludge will be formed. Other phenomena include increased acid value and blockage of the filter element. At the same time, due to poor lubrication due to mixing, equipment wear will also occur. When other oils are mixed into the lubricating oil, the solution is to change the oil and flush the lubrication system, and it cannot be removed by filtering. Using the wrong type of lubricant is also a common problem. It may be caused by accidentally adding the wrong oil when changing the oil, or simply selecting the wrong oil. For example, if the equipment requires extreme pressure lubricating oil (EP) or anti-wear lubricating oil (AW), and the user mistakenly adds general anti-oxidant and anti-rust oil, it will cause the equipment to wear during operation. If the equipment with higher requirements for the demulsibility of lubricating oil is mixed with oil with detergent and dispersant, the demulsibility/oil-water separation of the oil will be weakened. For example, if the steam turbine oil is mixed with engine oil, and 1 liter of engine oil is mixed with 7000 liters of turbine oil, the demulsibility of the steam turbine oil can be destroyed. Therefore, it is important to avoid mixing the lubricating oil. In this case, you need to replace all the oil and flush the lubrication system. For another example, if the equipment has yellow metal (such as copper), but extreme pressure lubricants are required, then it is necessary to understand the corrosiveness of the lubricant to yellow metals, because some extreme pressure lubricants contain active sulfur, which will corrode yellow metal. Through infrared spectrum detection, it can be found that the lubricant is misused or mixed. In addition, it is best to use ferrograph analysis together to find out whether equipment wear has occurred. Misuse or mixing of lubricating oil is likely to cause equipment wear. Misuse of lubricating oil may also be caused by the wrong viscosity, the wrong viscosity selection, or the oil of other viscosity mixed into the oil. If the viscosity of the oil is too high, or if high-viscosity oil is mixed in, abrasion will be observed in the gear system, as well as abnormal splash lubrication. For hydraulic systems, the equipment will respond slowly and the oil filtration rate will decrease. 　In the case of low oil viscosity, equipment wear almost always occurs. If you suspect that the viscosity of the lubricating oil is incorrect, you can perform a viscosity test. In addition, metal element detection can also be performed, because lubricating oils with different viscosities, even in the same product series, will have different additives (the additives contain some metal elements). 　If the viscosity of the lubricating oil is wrong, the recommended treatment is to replace the oil. For systems with a large amount of oil, it is necessary to partially replace the new oil and gradually replace it with lubricating oil with suitable viscosity.