Lubricating oil is the "blood" flowing in the compressor. The normal operation of the compressor can not be separated from the role of lubricating oil. If the coking of lubricating oil will seriously affect the working efficiency of the compressor. This not only reduces the quality of compressor operation and insufficient gas volume, but also causes nose lock, increases maintenance costs, affects the normal production order of enterprises, and brings immeasurable losses to users.
Generally speaking, coking is caused by a series of chemical changes in screw compressor oil. Lubricating oil belongs to organic compounds. Taking mineral oil as an example, its main components are various hydrocarbons (including alkanes, aromatics, naphthenes, etc.). Hydrocarbon compounds can be oxidized by heating, oxygen and light. The higher the contact heat and oxygen intensity, the stronger the oxidation reaction speed. Oxidation can break or cross-link molecular chains, which will change the properties of hydrocarbons. In practical application, oil viscosity increases, acid value increases, color changes, insoluble matter increases, etc. When deep oxidation occurs, oil viscosity increases significantly beyond a certain range, resulting in oil coking phenomenon.
Of course, the properties of compressor oils with different properties change differently when they are oxidized. In practical application, most coking accidents of screw compressor oils are caused by the use of low-grade mineral oils.
1. Metal ions: The wear debris inside the compressor will not only block the oil system, but also be a catalyst for oil oxidation. The presence of iron and other metal ions acts as initiators for the polymerization of some hydrocarbons. The more water content in oil, the higher the temperature, the higher the tendency of metal catalysis. Therefore, metal debris in oil products should be removed in time.
2. Oxidation: Compressor oil reacts with oxygen, sulfur and other substances in the air under high temperature and metal catalysis to produce alcohols, aldehydes, ketones, acids and oxides. Under the long-term action of oxygen and high temperature, some hydrocarbons are polymerized to form insoluble substances. The higher the pressure of the compressor, the higher the oxygen concentration, the more intense the oxidation degree of the oil and the shorter the service life of the oil.
3. Water effect: Because air compressor oil often contacts with compression medium, water in air will condense and enter into oil after compression, coupled with severe agitation during the operation of the unit, so that two liquids, oil and water, which could not be mixed together, are mixed together. When oil is used for a long time without replacing, one phase of the liquid is dispersed into many particles and molecules. In another phase, it becomes an emulsion. The emulsified oil not only reduces the lubrication effect, but also causes the hydrolysis of additives or base oil, which causes equipment corrosion. Rust deposits gradually and forms a part of sludge or coke.
4. Old oil effect: Most of the compressors now use mineral oil or semi-synthetic oil based on mineral oil. Their service life is generally between 2000 and 4000 hours. This kind of oil usually cokes when it runs for about two years. Even a normal oil change can occur. Because it is impossible to discharge 100% of sunken oil cleanly every time, the remaining old oil is deposited at the low point of the oil pipeline, and with the new oil, it will participate in a new round of oil pipeline cycle, which will cause oil deterioration and coking after a certain period of operation. How much pressure do YOU need?
It can be seen from the above that coking of lubricating oil does not necessarily occur, and the fundamental reason lies in "people" rather than "things". The factor of "human" can be considered from two aspects: production and use.
1. Lubricating oil manufacturers are not professional enough, the quality of compressor oil can not be guaranteed. In view of the current market situation, many professional compressor manufacturers do not produce matching compressor oil products, mostly rely on professional supply and cooperation of petroleum enterprises. Individual manufacturers, in order to reduce costs, look for small factory supply. In this way, the quality of oil will not be guaranteed, and supervision will not be in place, which is a major source of problems in the quality of oil.
2. When some users use compressors, in order to reduce costs, they do not use the required label oil. The main manifestations are as follows: (1) The mixture of old and new oil products causes the failure of new oil. When the production enterprises use the equipment, they do not change oil for a long time. As long as the compressor can rotate, if the lubricant is insufficient, it will be added, resulting in mixed pollution of old and new oils, thus losing the proper role of new oils; (2) the oil of various compressor brands is mixed, resulting in the reduction of compressor oil. It is unknown that the formulation of additives for compressor oil from different manufacturers is different, and their compatibility with similar products is very poor, so the original efficacy is reduced or invalid; (3) blind use of various alternative oils. Use gear oil, hydraulic oil, base oil and other non-compressor (screw type) professional oil products to replace. This not only wastes resources but also raises costs. More importantly, it has not played the due role of professional oil products.
3. Under the condition of long-term high temperature, the oil evaporates naturally and forms coking. Compressor working environment is not good, cooling water supply is insufficient, air-cooled radiator blockage, resulting in reduced cooling effect, making the equipment work in high or high temperature critical state for a long time, forming natural oxidation of compressor oil, accelerating the overall aging of oil, forming coking.
4. Compressor fittings are of poor quality and the technical parameters of products can not meet the requirements. The poor quality of compressor parts purchased by individual enterprises can not meet the technical requirements of the unit itself, which leads to the failure of compressor oil and coking. The main reasons are as follows: 1) poor quality of air filters and poor dust filtering effect make dust directly inhaled into the oil products of compressors, directly polluting oil products, leading to ageing of oil products in compressors, resulting in poor oil pipeline, causing high temperature shutdown of compressors and coking of compressor oil products; 2) poor oil filtering quality of compressors, preventing impurities from entering oil products; 3) oil content; The effect can not meet the requirements of technical specifications. The main manifestation is unclear oil separation, so that compressor grease with the evaporation of compressed gas loss, so that the compressor body lack of oil, forming a high temperature phenomenon.
1. Be sure to use oil in accordance with the requirements of compressor equipment, and shorten the use time of oil products appropriately. Before each oil change, the oil pipeline of the compressor should be cleaned first to prevent impurities and coke from blocking the oil pipeline. If coking is found (even rarely), professional cleaning is also necessary. After cleaning, air filter, oil filter and oil should be replaced in time. According to the coking situation and economy, carbon deposit cleaning agent, acetone cleaning, Tina water, caustic soda and so on can be selected for cleaning.
2. Guarantee the quality of compressor accessories and spare parts. In particular, we should strictly control the procurement and ensure the use of authentic compressor accessories. For example, for air filtration, attention should be paid to the waterproof, filtration accuracy and air permeability of the product. Following is a brief description of the detection methods:
1) Water detection method, which is also the most critical and simplest method of identification. For the inexperienced, water is the best way to detect the quality of air filters. Place the air filter flat on the floor or on the table and sprinkle some water on the filter paper.
If the filter paper seeps into the water in less than 5 minutes, it is air filtration made of cotton pulp paper, absolutely not used, this kind of goods in the screw compressor industry is only used by a few greedy and cheap people; B. If the filter paper seeps into the water in 2-5 hours, it is made of low-grade wood pulp paper, which can be used, but it will affect the efficiency of screw compressor air pumping (more electricity consumption, less air pumping), because of the air filtration price phase made of the filter paper. For lower, installed on the screw compressor can also be used, so now the compressor industry this filter paper air filtration dominates the mainstream; C. If the filter paper only 12-15 hours into the water, belongs to the passable filter paper (medium-grade filter paper), usually the quality of domestic screw compressor plant using this kind of filter paper as raw material; D. If 24 hours does not infiltrate into the filter paper, then absolute. For high-grade products (high-grade filter paper), usually the high-grade machine factory only chooses this kind of filter paper as raw material.
2) Light detection. Look at the light to see whether the filter paper is uniform, whether the transmittance is good, to see whether the filter paper surface finish is good. The filter paper has uniform and meticulous observation to the light, good transmittance and good surface finish, which indicates that the filter paper has good filtering accuracy and air permeability.
3) Look at the depth and fold of the filter paper. If the filter paper is deep and folded more, it means that the air filtration area is large, the air filtration area is large, and the air permeability will be better.
3. Keep the cooling system unobstructed and ensure the supply of cooling water. Every six months or a year, the coolers must be opened for inspection, and the scale must be cleaned up for scale removal and maintenance treatment. All air-cooled equipment should be cleaned regularly to ensure that the heat sink window is smooth. Especially in the northern region, many cooling water quality is hard, easy to form scale, affecting cooling efficiency, so special attention should be paid to scale removal and maintenance or cooling water softening treatment.
4. Adhere to the use of special lubricants. No hydraulic oil, gear oil, base oil or other compressor oil is used to replace screw compressor oil. In terms of oil function, hydraulic oil has good hydraulic transmission, good wear resistance and poor oxidation resistance at high temperature; gear oil has good shearing performance, but high viscosity and poor high temperature resistance; base oil is based on additives to help complete the functional development of oil products, and can not be directly used without additives.