According to the different ways of compressing gas, Air Compressors are divided into two categories: volume type and speed type. The displacement type Air Compressor changes the working volume through the reciprocating piston or the rotary motion rotor in the cylinder, so that the gas is compressed, and the speed type Air Compressor uses the high-speed rotating impeller to make the gas get high Then the speed drops sharply in the diffuser, so that the kinetic energy of the gas is converted into pressure energy. The Air Compressors used in the spraying process are mostly volumetric. The type and structural diagram of the Air Compressor are shown in Figure 4-30.
(1) Diaphragm Air Compressor (oil-free type)
As shown in Figure 4-31, it is a portable Air Compressor. Due to its light weight, convenient movement and low cost, it is suitable for small-scale spraying construction. The compressor shell is a die-casting part, and there is a metal or A flexible diaphragm made of synthetic rubber, which is driven by a piston rod driven by a small electric motor, reciprocates up and down in the cylinder, and sends the incoming air into the compression chamber above the flexible diaphragm during the downward stroke and closes the compression chamber , During the upward stroke, the air in the compression chamber is compressed to a certain extent and then discharged, and the outside air is allowed to enter the cylinder at the same time, which can generate compressed air with a pressure range of 206.8~241.8kPa. Since the machinery does not use lubricating oil, the compressed air does not contain oil, but contains moisture.
It should be noted during use that it can only be used for a short time and the wearing parts such as diaphragms and valves should be replaced in time according to work needs. This kind of pump generally needs to run continuously when it is started (some can also be designed as automatic opening/closing type), and it cannot be started under load. Before starting, the air in the compressor should be emptied, and the excess compressed air can pass through the top of the compressor. Pressure relief valve discharge.
(2) Rotary Air Compressor
It uses the rotating rotor or screw to change the volume of the intake air during the movement to achieve the purpose of compression. The rolling rotor type uses the sliding plate to press the eccentric wheel under the action of the spring and rotate with the eccentric wheel, so that the eccentric wheel is slid The volume of the crescent-shaped space separated by the sheets continuously expands and shrinks, so as to realize functions such as air intake, compression, and exhaust.
This kind of compressor has the advantages of compact structure, small size, light weight, less moving parts, less wearing parts, high operation reliability, small vibration, stable operation, low noise, easy installation and low price. Since lubricating oil is used for cooling and sealing during use, an isolator is installed on the machine to prevent lubricating oil from entering the air circuit system, but it still cannot guarantee that the compressed air does not contain oil, so an absorption filter should be installed behind the compressor outlet Further degreasing.
(3) Reciprocating Air Compressor
The reciprocating Air Compressor is a type of compressor commonly used in the spraying process, and its working principle is shown in Figure 4-32. Its main components include a piston with a piston ring, a cylinder, and intake and exhaust valves. The piston can be pressurized at one end or at both ends, which are called single-acting and double-acting respectively. It uses the piston to reciprocate in the cylinder to complete the steps of expansion, suction, compression and exhaust. Figure 4-32 is a working schematic diagram of two stroke reciprocating Air Compressors. In the down stroke, the outlet valve is closed, and the intake valve is opened to complete the two steps of intake and expansion. In the up stroke, the intake valve is closed to complete the compression step. a gas words gas b compressed air step. When the compressed air pressure reaches a certain level, open the outlet valve to complete the exhaust step. It is a mature production technology, but its disadvantages are complex structure, many wearing parts, and the pressure will pulsate because it cannot transmit gas continuously. Since lubricating oil needs to be added to lubricate the piston to reduce friction, take away heat, and strengthen the seal between the piston and the cylinder, the compressed air contains oil and needs to be degreased. Use one stroke cycle of the compressor to inhale air and compress it to a downward stroke: air enters an upward stroke: the process of compressing air to a constant pressure is called a single-stage compressor, and the compressed air pressure diagram generated by a single-stage compressor The working principle of 4_32 reciprocating Air Compressor can reach 689.5kPa. When the pressure exceeds 689.5kPa, the efficiency of single-stage compressor is quite low. In order to obtain higher pressure, two-stage compression can be used, that is, two reciprocating The compressed air cylinder performs two compressions. In the low-pressure cylinder, the inhaled air is first compressed to a medium pressure of about 275.8kPa, and then cooled by the cooler before entering the high-pressure cylinder for further compression. The difference between the two cylinders is that the cylinder bores are different, and the diameter of the high-pressure cylinder is only about half of that of the low-pressure cylinder. When it is necessary to obtain compressed air with a pressure in the range of 689.5~1379kPa, a two-stage compressor can be used. The pressure in this range can meet the needs of most spraying constructions. If you need to get compressed air with higher pressure, you can use a multi-stage compressor, which can produce compressed air higher than 1379kPa. The highest pressure can reach 82746kPa.
