Vacuum pumps commonly used for vacuum coating are as follows:
I. Vacuum Coating Rotary Vacuum Pump
The selected rotary vane vacuum pump in vacuum coating is mainly composed of pump body (stator) and rotor. There are more than two rotary blades in the rotor slot, and springs are also installed between the rotary blades of some pumps. The rotor is eccentrically mounted in the pump chamber, and the gap between the outer edge and the top surface of the pump chamber is 2-3 microns. When the rotor rotates, under the action of centrifugal force, the vane slides back and forth along the groove and keeps contact with the inner wall of the pump chamber, dividing the pump chamber into two or several variable volume workshops. When the rotor rotates clockwise, the volume of the suction chamber connected with the suction port increases gradually from zero, the pressure of the gas in the chamber decreases, and the exhausted gas is continuously inhaled from the suction port. At the same time, the volume of the exhaust chamber connected with the exhaust port decreases from large to small, and the gas in the inhalation chamber is compressed. When the gas pressure is higher than the atmospheric pressure, the exhaust valve is pushed to discharge the atmosphere. When the rotor rotates continuously, the pump pumps continuously.
II. Roots Vacuum Pump with Vacuum Coating
The limit vacuum of Roots pump in vacuum coating depends not only on the structure and manufacturing accuracy of the pump itself, but also on the limit vacuum of the front pump. In order to improve the vacuum limit of the pump, Roots pump can be used in series. The working principle of Roots pump is similar to Roots blower. Because of the continuous rotation of the rotor, the exhausted gas is sucked into the space between the rotor and the pump shell from the intake port, and then discharged through the exhaust port. Since the space of V0 is completely closed after suction, there is no compression and expansion of gas in the pump chamber. But when the top of the rotor rotates around the edge of the exhaust port and the space of V0 is connected with the exhaust side, because the pressure of the exhaust side is high, some of the gas rushes back into the space of v0, which makes the pressure of the gas increase suddenly. When the rotor continues to rotate, the gas is discharged out of the pump. Roots pump in the pump chamber, there are two "8" shaped rotors installed vertically on a pair of parallel axles, driven by a pair of gears with transmission ratio of 1 to each other reverse synchronous rotation. There is a certain gap between the rotor and the inner wall of the pump housing, which can realize high speed operation.
3. Vacuum Coating Water Ring Vacuum Pump
When the impeller rotates clockwise in the direction indicated, the water is thrown around the impeller. Because of the centrifugal force, the water forms a closed ring which is approximately equal in thickness depending on the shape of the pump chamber. The inner surface of the upper part of the water ring is just tangent to the hub of the impeller, and the inner surface of the lower part of the water ring is just in contact with the top of the blade (in fact, the blade has a certain insertion depth in the water ring). At this time, a crescent-shaped space is formed between the hub and the water ring of the impeller, which is divided into several small cavities with equal number of blades by the impeller. If the starting point is 0 degrees above the impeller, the volume of the small chamber increases from small to large at 180 degrees before the impeller rotates, and is connected with the suction port on the end surface. At this time, the gas is absorbed, and at the end of the suction, the small chamber is isolated from the suction port; when the impeller continues to rotate, the small chamber becomes smaller and compresses the gas; when the small chamber is connected with the exhaust port, the gas is discharged out of the pump.
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