Figure 1: Adding the lubricating oil to the compressor.
Maintaining the air compressor oil is critical to the compressor’s performance. And the service life of the oil is directly related to the user's equipment operation costs and economic benefits. This article focuses on the factors affecting the service life of the air compressor oil to provide ideas for the user's air compressor maintenance and oil selection. The main factors can be divided into two parts, including the oil itself, and the use conditions.
The lubricating oil, as an organic compound, is inevitable to be oxidized and life reduced. For example, the oxidation of hydrocarbon lubricants has been documented as an auto-oxidation process, namely the chain reaction mechanism of free radicals, which can be summarized as four stages, including chain initiation, chain growth, chain branching, and chain termination.
Oxidation reaction generates large molecular chain products, which will eventually lead to the growth of oil viscosity and acid value. More prominent is the possible generation of insoluble sediments and paint film, leading to lubrication failure and equipment wear. In serious cases, it will lead the head to be locked and the air compressor stopped. Therefore, oil oxidation is a major factor affecting the service life of air compressor oil.
In response to oil oxidation, manufacturers can optimize it from the formula, and choose the base oils of high saturation degree and oxidation resistance, or choose appropriate additives.
Figure 2: The oil oxidation.
In the selection of base oils, the higher saturation degree makes the structure more stable to avoid oxidation. Both Poly-Alpha-olefin (PAO) with regular chain structure and gas-made oils have the advantages of simple structure, high saturation degree, extremely stable chemical properties, no sulfur, and heterocyclic compounds, which are good base oils. In addition, synthetic esters, polyethers, and other synthetic base oils, due to their excellent high- and low-temperature performance, oxidation resistance, sediment control ability, are also favored by formulation engineers.
As for the selection of additives, antioxidants are the most direct additives for oil oxidation and interrupt further oxidation by capturing hydrocarbon and alkyl peroxide free radicals, and oxygen peroxides. There are a variety of antioxidants, including main antioxidants such as blocked phenols and aromatic amines, as well as sulfides and organophosphates that are auxiliary.
In the formulation selection of air compressor oil, two or more kinds of antioxidants are often used in combination. The synergistic effect between different antioxidants will retard oil oxidation. The antioxidant performance evaluation of the synergistic effect is a relatively complex work. In the laboratory of air compressor oil manufacturers, it is necessary to evaluate the antioxidant capacity of additive formula through several methods of comprehensive evaluation.
In addition to antioxidants, metal corrosion inhibitors and rust inhibitors can capture catalytic impurities and alleviate the catalytic reaction of metals for oxidation. It can also play a role in delaying the oxidation of the oil.
Figure 3: A type of antioxidant.
Besides, the anti-wear, anti-corrosion, anti-rust, anti-emulsification and anti-foam performance, viscosity retention performance are also important to the service life of the compressor oil. On the one hand, the anti-wear, corrosion, and rust resistance performance defects will affect the service life of the equipment. On the other hand, wear, corrosion of metal debris, particles, and impurities will also accelerate the oxidation, thus further affecting its service life.
Anti-emulsification and anti-foaming performance measure the tolerance of air compressor oil for water and air. The lack of these two performances will cause oil failure because of emulsification and foam aggravation.
Viscosity retention ability is the evaluation of the stability and continuity of the air compressor oil film. The stable oil film is helpful for the longer lubrication and reducing the corresponding wear and corrosion of the compressor, prolonging the service life of oils.
In a word, the formula of the air compressor oil is a reflection of the comprehensive performance of base oils and a variety of functional additives. The balance and stability, high-performance raw material characteristics, and scientific ratio are fundamental.
In addition to the air compressor oil itself, the use conditions will also influence oil’s life. The main factors are concluded in the following.
The management of the air compressor station mainly consists of site management and equipment management. Site management refers to the daily use of the air compressor, scientific management of oils and spare parts, cleaning, heat dissipation, and gas exchange of the air compressor station.
You should designate some specific person as equipment managers. When the compressor stops, managers should carry out a full inspection, and frequently monitor the use conditions. Besides, you should not ignore small failures. The air compressor oil and the air compressor are inseparable as a whole. Only by maintaining the air compressor can the oil products play a maximum role.
Figure 4: The air filter, oil filter, and oil separator.
The main spare parts that affect the service life of oil products include the air filter, oil filter, and oil separator, which are also significant for air compressors.
The filtration performance and quality of the air filter affect the level of cleanliness of the intake air, thus affecting the impurities in the air compressor oil. And the filtration performance and quality of the oil filter directly influence the impurities of the air compressor oil.
The performance of the oil separator affects the degree of oil-gas separation. The amount of the oil taken out of gas and the amount of the gas brought in the oil have a direct relationship with the oil separator. Therefore, the choice of spare parts has a great impact on the service life of oils.
For air compressor daily maintenance, in addition to the normal replacement of oil, filter element, oil separator and other vulnerable parts, the maintenance of the motor and cooling system is also crucial.
Motor failure will infect the start and operation of the air compressor, and cooling system failure will cause the compressor to overheat, which will infect the service life of air compressor oil.
Qualified air compressor maintenance is not only a regular oil change but also comprehensive and detailed maintenance of various parts and operation conditions of the compressor.
In a conclusion, to prolong the service life of air compressor oil, oil manufacturers, equipment maintenance providers, and equipment users all play an important role. They must cooperate perfectly to maximize the benefits of the air compressor and air compressor oil.