Discussion on oil circuit characteristics of the h

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Discussion on oil circuit characteristics of oil injected screw air compressor

Abstract: the basic principle and performance characteristics of oil circuit system of oil injected screw air compressor are discussed, the functions of main parts are explained, and the problems and common faults in the use of oil circuit system are discussed. 6. Check that the exchange input voltage of frequency converter of frequency conversion single column tensile testing machine is greater than the maximum value. If the main circuit and input voltage exceed the limit, Or the inverter does not operate and the corresponding countermeasures are put forward

key words: oil injected screw air compressor; Oil circuit system; characteristic; Common faults

0 preface

in recent years, with the extensive application of air-jet looms and the improvement of the automation of textile production, air compressors as the driving force of textile production have been widely used. Among them, oil injected screw compressors are widely used because of their reliable operation, long service life, air volume is not affected by exhaust pressure, smooth operation and no surge

5.1 frequency resolution calculation formula:

1 working principle and characteristics

practical oil circuit of oil injection screw air compressor without oil pump, as shown in Figure 1. When the compressor is running, the high-temperature and high-pressure air mixed with a large number of oil droplets is discharged into the oil separator by the compressor. Due to the rotation, collision and direction change of the air flow in the separator, most of the oil droplets in the air settle at the bottom of the container. Under the action of high pressure in the separator, the lubricating oil flows to the temperature control valve along the oil return pipe; According to the temperature of the lubricating oil, the temperature control valve makes some or all of the oil flow through the oil cooler, and the temperature controlled lubricating oil flows through the oil filter and the oil cut-off solenoid valve under constant pressure and then injects into the compressor screw rotor cavity and all bearings. p>

2 structure and function of parts

2.1 oil separator

is shown in Figure 2 and figure 3. In practice, there are two kinds of oil-gas separators: horizontal and vertical. The horizontal separator turns the direction of the impact of air on the arc surface after it is injected, and the flow rate is greatly reduced, so the oil droplets settle by relying on inertial force. In the vertical separator, the oil-gas mixture rotates after being sprayed into the cylinder along the tangent line. The oil droplets are thrown onto the inner wall of the cylinder under the action of centrifugal force, and the oil droplets gather and fall into the bottom of the container. Baffles can be set in the cylinder to maintain the continuous rotation of the air flow, so that the separation process continues. After the initial separation, the air still contains some very small oil droplets, which enter the filter element at the upper part of the separator with the air. The oil-gas separation filter element can be composed of one or two fiber cylinders, and the common form is shown in Figure 4; However, the ultra-fine glass wool can also be made into filter paper with a special positioning of domestic leading and world-class technology, and a layer of synthetic fiber protection is added inside and outside. The three layers of filter materials are made into composite filter materials to make filter elements. In practice, the filter materials are made into folds to increase the filtering area. Oil return pipes shall be set in the filter elements at all levels to connect back to the inlet of the compressor; There are filters, oil sight glasses and orifices on the oil return pipe to ensure the stability of oil return; The pressure drop of compressed air through the filter element is 0.02mpa-0.04mpa. The oil content of the filtered air should be less than

Figure 3 vertical oil-gas separator

Figure 4 oil-gas separation filter

2.2 temperature control valve

the dew point temperature of the compressed air increases after compression, while the exhaust temperature of the compressed air is low in the cold season or compression start-up stage. When it is lower than the dew point temperature after air compression, the moisture in the compressed air will condense in the oil-gas separator and deteriorate the lubricating oil. According to relevant data, the fuel injection will take away 82% of the total power of the compressor, so the exhaust temperature of compressed air is related to the fuel injection temperature. In the cold season or compression start-up stage, the temperature control valve is closed, and the lubricating oil is not cooled by the oil cooler, but directly flows through the oil filter from the inlet bypass pipe to each working point. Due to the absorption of heat generated in the compression process, the oil temperature gradually rises. When the oil temperature is higher than C, the temperature control valve is opened, and some or all of the lubricating oil flows into the cooler

most of the original domestic products are electromagnetic temperature control valves. In recent years, through the digestion and absorption of imported compressor technology, wax temperature control valves are also widely used. The temperature control valve is composed of a valve and a temperature control element; The temperature control elements include special expansion temperature sensing paraffin and red copper shell. Under the specific phase change temperature, the expansion stress of the expanded paraffin is a fixed value, which is far greater than the thrust required by the thermostatic valve. The expanded paraffin is sealed in the shell. When the temperature rises to the melting point of paraffin, the volume expands and pushes the ejector rod, causing the slide valve driving the temperature control valve to move; When the temperature drops, the paraffin shrinks when it is cold, and the valve resets under the action of spring rebound. The characteristics of this temperature valve: large thrust, the paraffin inside the element can reach more than 200 atmospheres when expanding, and the linearity of the travel temperature curve is good, so the temperature control ability is strong; The components have high rigidity, high strength and long service life

2.3 oil cooler

oil cooler has two types: air cooling and water cooling. Most of the water coolers are shell and tube heat exchangers. In foreign products, mm copper tubes are used as heat exchange tubes. The product volume is very compact when the oil goes outside the tube and the water goes inside the tube. Air cooled type can adopt round core tube heat sink, (including large heat sink inserted with tube bundle), elliptical core tube heat sink, etc. In recent years, aluminum plate fin radiators are also widely used in air-cooled coolers

2.4 oil cut-off valve

the oil cut-off valve is closed when the compressor stops, otherwise a large amount of high-pressure lubricating oil in the oil separator and oil cooler will flow back to the inlet of the compressor host, emerging from the suction filter and polluting the suction filter element. When starting up, the oil cut-off valve is opened under the control of the exhaust pressure of the compressor host to ensure that the oil circuit is unblocked

2.5 lubricating oil

the lubricating conditions and working environment of screw compressor are relatively harsh, and the lubricating oil is about 0 It should be recycled once within minutes; At high temperature and in the presence of steel, copper and other catalysts, oil products are very easy to oxidize and deteriorate, so there are certain requirements for oxidation, which is measured by the oxidation stability index. In addition, due to the fast circulation speed and the intense mixing of oil, it is very easy to form foam, especially when the operation temperature is low at startup, and the oil foam is not easy to be destroyed. A large amount of oil foam is poured into the oil-gas separator, which increases the resistance and oil consumption, resulting in serious overload and overtemperature. Anti foam and defoaming measures must be taken. This performance is measured by the foam resistance, foam tendency and foam stability of the oil. As the pipes and some parts of the compressor cooler are copper or copper alloy, they are easy to be corroded and cause early oxidation and deterioration of the oil products, forming oil sludge. Water vapor and dust in the air will inevitably be mixed into the oil, which will rust and wear the surface of other parts in contact with the gas. These two properties are measured by oil corrosion index and rust prevention test index. During the operation of the compressor, the oil constantly meets with the condensed water in the air and is violently stirred, which is easy to produce emulsification, resulting in poor oil-gas separation and increased oil consumption. The emulsification of the oil will damage the oil film and aggravate the wear. Therefore, anti emulsification is also an important performance of the oil. Other performance indicators of compressor lubricating oil include: kinematic viscosity, viscosity index, pour point, flash point, mechanical impurities, water, water-soluble acid or alkali, carbon residue, etc

the oil injected screw air compressors of Sullair and Ingersoll Rand adopt synthetic special lubricating oil to ensure the service life of screw rotors

at present, domestic lubricating oil can not completely replace foreign products or joint venture products, so synthetic special lubricating oil is expensive. When the m3/h unit works normally, oil barrels are used every year

3 common problems and Countermeasures of oil circuit system

3.1 poor cooling effect

in the air-cooled oil cooler, whether it is in the form of aluminum plate fin, single fin or integral fin of various core tubes, the gap between the fins or fins is small. If the surrounding environment of the air compressor room is not clean, there is much dust, or there is no filter in the air inlet duct, and the screen window, the gap between the fins or fins is very easy to be blocked, which will lead to insufficient cooling of the lubricating oil, The circulating lubricating oil brings part of the heat back to the cylinder body. Such circulation causes the heat accumulation of the cylinder body, the exhaust temperature increases, and the exhaust volume decreases. In addition, when the lubricating oil temperature is high, the oil viscosity decreases, and the oil film becomes thinner, which makes it difficult to form air tight resistance between the screw and the cylinder body, resulting in cross leakage between the rotor and the cylinder body, which is also the reason for the reduction of the exhaust volume. According to the actual experience of the factory, the outer surface of the cooler, fan blades and unit dust should be cleaned every 3 months, and the fins and fins of the air cooler can be purged with compressed air or steam to make them clean and smooth; After cleaning in a factory, the exhaust temperature fell from C to C

in the water-cooled oil cooler, the main reason affecting the cooling effect is the water quality of the cooling water. The water quality in northern China is hard. When some factories use tap water or deep well water for recycling, the scale deposition in the oil cooler is more serious within 3 months, and chemical cleaning must be carried out regularly according to the local water quality; Therefore, some factories use demineralized water as cooling water for recycling, but algae are still easy to grow on the inner wall surface of pipes and heat exchangers during operation, affecting heat exchange, and they should also be cleaned regularly

3.2 the oil filter is blocked

the pressure difference before and after the oil filter is 0 140MPa, when it is greater than the specified value, it should be replaced in time. The specific replacement time is the accumulated h of initial use and operation, and it will need to be replaced every h in the future. If the compressor operates for less than the rated time every year, the filter element should also be replaced at the time of oil change. When replacing, drain the dirty oil in the oil filter. When cleaning the inside of the filter and installing the filter element, pay attention to check the sealing ring or gasket in the filter, and strictly prevent the oil bypass caused by lax sealing, which will make the filter ineffective

3.3 deterioration of oil quality

generally speaking, the factors affecting the service life of oil include: 1. Inhaling impure air, such as iron oxide and carbon dioxide, accelerates the deterioration of oil; 2. The used oil is not discharged cleanly, and mixing with the newly charged oil will significantly reduce the service life of the newly charged oil (there is a certain oil capacity in the oil cooler, and the oil cooler position of some compressors is low, so it is not easy to discharge the old oil through the oil separator); 3. The operating temperature of the compressor is too high, which accelerates the oxidation and deterioration of the oil; 4 when the operating temperature is lower than the dew point temperature, condensed water will enter the oil and emulsify during use

all compressor manufacturers have strict regulations on the replacement period of lubricating oil. The replacement period of Shanghai Ingersoll Rand lubricating oil is 3500h, and that of American Sullair lubricating oil is 8000h. If conditions permit, users use regular sampling inspection to determine whether the oil needs to be replaced; See Table 1 for the main contents of sampling inspection. Table 1 quantitative inspection items of lubricating oil deterioration

when conditions permit, metal particles in insoluble substances should also be analyzed. See Table 2 for specific values. Table 2 the metal content in the oil sample comes from the place and the maximum allowable content

lubricants of different brands cannot be mixed. When lubricating oils with different quality and brand are mixed, the performance of the oil will be reduced, and viscous deposits and lacquer deposits will be produced, which will block the oil system and affect the oil delivery

for economic reasons, at present, some user units do not regularly replace the lubricating oil as required, but only regularly add oil, resulting in excessive oil viscosity, poor heat dissipation, high compressor exhaust temperature, and more than 100C in summer

in addition, according to the experience of the user unit, the air humidity is high after the rain in summer, and there will be moisture deposition at the bottom of the oil separator. Open the drain pipe valve at the bottom of the separator to drain the moisture in time


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