The following article will take you through an in-depth analysis of the structure of the screw air compressor. After that, when you see the screw air compressor, you will be an expert!
1. Motor
Generally, 380V motors are used when the motor output power is below 250KW , and 6KV and 10KV motors are generally used when the motor output power exceeds 250KW .
The explosion-proof air compressor is 380V/660v. The connection method of the same motor is different. It can realize the selection of two types of working voltages: 380v and 660V . The highest working pressure calibrated on the factory nameplate of the explosion-proof air compressor is 0.7MPa . China There is no standard of 0.8MPa . The production license granted by our country indicates 0.7MPa, but in actual applications it can reach 0.8MPa .
The air compressor is equipped with only two types of asynchronous motors, 2- pole and 4 -pole, and its speed can be regarded as a constant ( 1480 r/min , 2960 r/min ) in accordance with the national industry standards.
Service factor: Motors in the air compressor industry are all non-standard motors, generally 1.1 to 1.2 . For example, if the motor service index of a 200kw air compressor is 1.1 , then the maximum power of the air compressor motor can reach 200 × 1.1 = 220kw. When told to consumers, it has an output power reserve of 10 %, which is a comparison. Good standard.
However, some motors will have false standards. It is very good if a 100kw motor can export 80% of the output power. Generally speaking, the power factor cos ∮ =0.8 means it is inferior.
Waterproof level: refers to the moisture-proof and anti-fouling level of the motor. Generally, IP23 is enough, but in the air compressor industry, most 380V motors use IP55 and IP54 , and most 6KV and 10KV motors use IP23, which is also required by customers. Available in IP55 or IP54 . The first and second numbers after the IP represent different waterproof and dustproof levels respectively. You can search online for details.
Flame retardant grade: refers to the motor’s ability to withstand heat and damage. Generally, F level is used , and B level temperature assessment refers to a standard assessment that is one level higher than F level.
Control method: control method of star-delta transformation.
2. The core component of the screw air compressor – the machine head
Screw compressor: It is a machine that increases air pressure. The key component of the screw compressor is the machine head, which is the component that compresses air. The core of the host technology is actually the male and female rotors. The thicker one is the male rotor and the thinner one is the female rotor. rotor.
Machine head: The key structure is composed of the rotor, casing (cylinder), bearings and shaft seal. To be precise, two rotors (a pair of female and male rotors) are mounted with bearings on both sides in the casing, and the air is sucked in from one end. With the help of the relative rotation of the male and female rotors, the meshing angle meshes with the tooth grooves. Reduce the volume inside the cavity, thereby increasing the gas pressure, and then discharge it from the other end.
Due to the particularity of compressed gas, the machine head must be cooled, sealed and lubricated when compressing gas to ensure that the machine head can work normally.
Screw air compressors are often high-tech products because the host often involves cutting-edge R&D design and high-precision processing technology.
There are two main reasons why the machine head is often called a high-tech product: ① The dimensional accuracy is very high and cannot be processed by ordinary machinery and equipment; ② The rotor is a three-dimensional inclined plane, and its profile is only in the hands of a very few foreign companies. , a good profile is the key to determining gas production and service life.
From the structural point of view of the main machine, there is no contact between the male and female rotors, there is a 2-3 wire gap, and there is a 2-3 wire gap between the rotor and the shell, both of which do not touch or rub. There is a gap of 2-3 wires between the rotor port and the shell , and there is no contact or friction. Therefore, the service life of the main engine also depends on the service life of the bearings and shaft seals.
The service life of bearings and shaft seals, that is, the replacement cycle, is related to the bearing capacity and speed. Therefore, the service life of the directly connected main engine is the longest with low rotation speed and no additional bearing capacity. On the other hand, the belt-driven air compressor has a high head speed and high bearing capacity, so its service life is short.
The installation of machine head bearings must be carried out with special installation tools in a production workshop with constant temperature and humidity, which is a highly professional task. Once the bearing is broken, especially the high-power machine head, it must be returned to the manufacturer’s maintenance factory for repair. Coupled with the round-trip transportation time and maintenance time, it will cause a lot of trouble for consumers. At this time, customers There is no time to delay. Once the air compressor stops, the entire production line will stop, and workers will have to take a vacation, affecting the total industrial output value of more than 10,000 yuan every day. Therefore, with a responsible attitude towards consumers, the maintenance and upkeep of the machine head must be explained clearly.
3. Structure and separation principle of oil and gas barrels
An oil and gas barrel is also called an oil separator tank, which is a tank that can separate cooling oil and compressed air. It is generally a cylindrical can made of steel welded into an iron sheet. One of its functions is to store cooling oil. There is an oil and gas separation filter element in the oil separation tank, commonly known as an oil and fine separator. It is usually made of about 23 layers of imported glass fiber wound layer by layer. A few are shoddy and have only about 18 layers.
The principle is that when the oil and gas mixture crosses the glass fiber layer at a certain flow speed, the droplets are blocked by physical machinery and gradually condense. The larger oil droplets then fall into the bottom of the oil separation core, and then a secondary oil return pipe guides this part of the oil into the internal structure of the machine head for the next cycle.
In fact, before the oil and gas mixture passes through the oil separator, 99% of the oil in the mixture has been separated and fell to the bottom of the oil separation tank by gravity.
The high-pressure, high-temperature oil and gas mixture generated from the equipment enters the oil separation tank along the tangential direction inside the oil separation tank. Under the influence of centrifugal force, most of the oil in the oil and gas mixture is separated into the inner cavity of the oil separation tank, and then It flows down the inner cavity into the bottom of the oil separator tank and enters the next cycle.
The compressed air filtered by the oil separator flows into the rear-end cooling cooler through the minimum pressure valve and then is discharged from the equipment.
The opening pressure of the minimum pressure valve is generally set to about 0.45MPa. The minimum pressure valve mainly has the following functions:
(1) During operation, priority is given to establishing the circulation pressure required for cooling lubricating oil to ensure lubrication of the equipment.
(2) The compressed air pressure inside the oil and gas barrel cannot be opened until it exceeds 0.45MPa, which can reduce the air flow speed through the oil and gas separation. In addition to ensuring the effect of oil and gas separation, it can also protect the oil and gas separation from being damaged due to too large a pressure difference.
(3) Non-return function: When the pressure in the oil and gas barrel drops after the air compressor is turned off, it prevents the compressed air in the pipeline from flowing back into the oil and gas barrel.
There is a valve on the bearing end cover of the oil and gas barrel, called a safety valve. Generally, when the pressure of the compressed air stored in the oil separator tank reaches 1.1 times the preset value, the valve will automatically open to discharge part of the air and reduce the pressure in the oil separator tank. Standard air pressure to ensure equipment safety.
There is a pressure gauge on the oil and gas barrel. The air pressure displayed is the air pressure before filtration. The bottom of the oil separation tank is equipped with a filter valve. The filter valve should be opened frequently to drain away the water and waste deposited at the bottom of the oil separation tank.
There is a transparent object called an oil sight glass near the oil and gas barrel, which indicates the amount of oil in the oil separation tank. The correct amount of oil should be at the center of the oil sight glass when the air compressor is working normally. If it is too high, the oil content in the air will be too high, and if it is too low, it will affect the lubrication and cooling effects of the machine head.
Oil and gas barrels are high-pressure containers and require professional manufacturers with manufacturing qualifications. Each oil separation tank has a unique serial number and certificate of conformity.
4. Rear cooler
The oil radiator and aftercooler of an air-cooled screw air compressor are integrated into one body. They are generally made of aluminum plate-fin structures and are fiber-welded. Once oil leaks, it is almost impossible to repair and can only be replaced. The principle is that cooling oil and compressed air flow in their respective pipes, and the motor drives the fan to rotate, dissipating heat through the fan to cool down, so we can feel the hot wind blowing from the top of the air compressor.
Water-cooled screw air compressors generally use tubular radiators. After heat exchange in the heat exchanger, the cold water becomes hot water, and the cooling oil is naturally cooled. Many manufacturers often use steel pipes instead of copper pipes to control costs, and the cooling effect will be poor. Water-cooled air compressors need to build a cooling tower to cool the hot water after heat exchange so that it can participate in the next cycle. There are also requirements for the quality of the cooling water. The cost of building a cooling tower is also high, so there are relatively few water-cooled air compressors. . However, in places with large smoke and dust, such as chemical plants, production workshops with fusible dust, and spray painting workshops, water-cooled air compressors should be used as much as possible. Because the radiator of air-cooled air compressors is prone to fouling in this environment.
Air-cooled air compressors must use an air guide cover to discharge hot air under normal circumstances. Otherwise, in summer, air compressors will generally generate high temperature alarms.
The cooling effect of the water-cooled air compressor will be better than that of the air-cooled type. The temperature of the compressed air discharged by the water-cooled type will be 10 degrees higher than the ambient temperature, while the air-cooled type will be about 15 degrees higher.
5. Temperature control valve
Mainly by controlling the temperature of the cooling oil injected into the main engine, the exhaust temperature of the main engine is controlled. If the exhaust temperature of the machine head is too low, water will precipitate into the oil and gas barrel, causing the engine oil to emulsify. When the temperature is ≤70℃, the temperature control valve will control the cooling oil and prohibit it from entering the cooling tower. When the temperature is >70℃, the temperature control valve will only allow a part of the high-temperature lubricating oil to be cooled through the water cooler, and the cooled oil will be mixed with the uncooled oil. When the temperature is ≥76°C, the temperature control valve opens all channels to the water cooler. At this time, the hot cooling oil must be cooled before it can re-enter the circulation of the machine head.
6. PLC and display
PLC can be interpreted as the host computer of a computer, and the air compressor LCD display can be regarded as the monitor of the computer. PLC has the functions of input, export (to the display), calculation, and storage.
Through the PLC, the screw air compressor becomes a relatively highly intelligent fool-proof machine. If any component of the air compressor is abnormal, the PLC will detect the corresponding electrical signal feedback, which will be reflected on the display and fed back to the equipment administrator.
When the air filter element, oil filter element, oil separator and cooling oil of the air compressor are used, the PLC will alarm and prompt for easy replacement.
7. Air filter device
The air filter element is a paper filter device and is the key to air filtration. The filter paper on the surface is folded to expand the air penetration area.
The tiny pores of the air filter element are about 3 μm. Its basic function is to filter out dust exceeding 3 μm in the air to prevent the shortening of the life of the screw rotor and the clogging of the oil filter and oil separator. Generally, every 500 hours or a shorter time (depending on the actual situation), take out and blow air from the inside out with ≤0.3MPa to clear the tiny pores that are blocked. Excessive pressure may cause the tiny pores to burst and enlarge, but it will not meet the required filtration accuracy requirements, so in most cases, you will choose to replace the air filter element. Because once the air filter element is damaged, it will cause the machine head to seize.
8. Intake valve
Also called the air inlet pressure regulating valve, it controls the proportion of air entering the machine head according to the degree of its opening, thereby achieving the purpose of controlling the air displacement of the air compressor.
The capacity-adjustable intake control valve controls the servo cylinder through an inverse proportional solenoid valve. There is a push rod inside the servo cylinder, which can regulate the opening and closing of the intake valve plate and the degree of opening and closing, thereby achieving 0-100% air intake control.
9. Inverse proportional solenoid valve and servo cylinder
The ratio refers to the cyclone ratio between the two air supplies A and B. On the contrary, it means the opposite. That is, the lower the air supply volume entering the servo cylinder through the inverse proportional solenoid valve, the more the diaphragm of the intake valve opens, and vice versa.
10. Uninstall the solenoid valve
Installed next to the air inlet valve, when the air compressor is shut down, the air in the oil and gas barrel and the machine head is evacuated through the air filter to prevent the air compressor from being damaged due to oil in the machine head when the air compressor is re-operated. Starting with load will cause the starting current to be too large and burn out the motor.
11. Temperature sensor
It is installed on the exhaust side of the machine head to detect the temperature of the discharged compressed air. The other side is connected to the PLC and displayed on the touch screen. Once the temperature is too high, usually 105 degrees, the machine will trip. Keep your equipment safe.
12. Pressure sensor
It is installed at the air outlet of the air compressor and can be found on the rear cooler. It is used to accurately measure the pressure of the air discharged and filtered by the oil and fine separator. The pressure of compressed air that has not been filtered by the oil and fine separator is called pre-filter pressure. , when the difference between the pre-filtration pressure and the post-filtration pressure is ≥0.1MPa, a large oil partial pressure difference will be reported, which means that the oil fine separator needs to be replaced. The other end of the sensor is connected to the PLC, and the pressure is indicated on the display. There is a pressure gauge outside the oil separation tank. The test is the pre-filtration pressure, and the post-filtration pressure can be seen on the electronic display.
13. Oil filter element
Oil filter is the abbreviation of oil filter. The oil filter is a paper filter device with a filtration precision between 10 mm and 15 μm. Its function is to remove metal particles, dust, metal oxides, collagen fibers, etc. in the oil to protect the bearings and machine head. Blockage of the oil filter will also lead to too little oil supply to the machine head. Lack of lubrication in the machine head will cause abnormal noise and wear, cause continuous high temperature of the exhaust gas, and even lead to carbon deposits.
14. Oil return check valve
The filtered oil in the oil-gas separation filter is concentrated in the circular concave groove at the bottom of the oil separation core, and is led to the machine head through the secondary oil return pipe to prevent the separated cooling oil from being discharged with the air again, so that the oil content in the compressed air will be very high. At the same time, in order to prevent the cooling oil inside the machine head from flowing back, a throttle valve is installed behind the oil return pipe. If the oil consumption suddenly increases during the operation of the equipment, check whether the small round throttling hole of the one-way valve is blocked.
15. Various types of oil pipes in the air compressor
It is the pipe through which the air compressor oil flows. The metal braided pipe will be used for the high-temperature and high-pressure oil and gas mixture discharged from the machine head to prevent explosion. The oil inlet pipe connecting the oil separator tank to the machine head is usually made of iron.
16. Fan for rear cooler cooling
Generally, axial flow fans are used, which are driven by a small motor to blow cold air vertically through the heat pipe radiator. Some models do not have a temperature control valve, but use the rotation and stop of the electric fan motor to adjust the temperature. When the exhaust pipe temperature rises to 85°C, the fan starts running; when the exhaust pipe temperature is less than 75°C, the fan automatically stops to maintain the temperature within a certain range.
Post time: Nov-08-2023