Turbo molecular pump suction principle is to use the high-speed rotation of the rotor to transfer momentum to the gas molecules, and thus obtain the orientation speed, so as to be compressed, is driven towards the exhaust port for the first stage is drawn away after a vacuum pump.
Molecular pumping gas two necessary conditions should be met:
1)Turbomolecular pumps must operate in molecular flow state. Because when a certain volume of the pressure of the gas contained in the vessel is reduced, the mean free path of the gas molecules which are increased. In the mean free path of air molecules at atmospheric pressure is only 0.06 μm, an average of just looking at a gas molecule in space motion 0.06 μm, it may collide with gas molecules in the second. And when 1.3Pa, the mean free path between molecules of up to 4.4mm. If the mean free path increases to greater than the distance between the walls of the container, the chance of collision of gas molecules with the wall will be greater than the chance of collision between gas molecules. In the molecular flow range, the mean free path length of the gas molecules is much larger than the spacing between the blades molecular pump. When the wall by not moving the stator blades and the moving rotor blades consisting of gas molecules will be directed more to the rotor and stator blades for directional movement of gas molecules to form the foundation.
2) molecular pump rotor blade speed with the gas molecules must have a similar line speed. Has such a high speed in order to make the gas molecules collide with the rotor blades after changing the characteristics of the random scattering for directional movement. The higher molecular pump speed, to improve the molecular pumping speed, the better. Practice shows that the gas molecules with different molecular weights of its greater speed, pumping in addition to the more difficult. Molecular pump is the use of high-speed rotation of the rotor to transfer momentum to the gas molecules, and thus obtain the orientation speed, so as to be compressed, is driven towards the exhaust port of the preceding stage is drawn away after a vacuum pump.
This pump concrete can be divided into:
1) traction molecular pump and high-speed movement of gas molecules collide and get momentum rotor is driven to the pump outlet.
2) turbo molecular pump by high-speed rotation of the rotor blades and the stationary blade with each other to achieve a given pumping. Such pumps are typically operate at the molecular flow state.
3) It is composed of complex molecular pump turbo molecular pump and traction type two series combination of a complex type of molecular pump.
Turbo molecular pump composition and performance characteristics
Turbo-molecular pumps by the pump rotor with blades (ie moving impeller), static impeller and drive system components.
Discharge pressure of the pump and the intake pressure ratio is called the compression ratio. In addition to the pump compression ratio and speed-related series, but also with the type of gas related. Molecular weight of the gas has a high compression ratio. Nitrogen (or air) compression ratio of 108 to 109; 102 to 104 hydrogen; gases of a large molecular weight is greater than 1010, such as oil vapors.
Pump pressure limits 10-9Pa, working pressure range of 10-1 ~ 10-8Pa, pumping rate for tens to thousands liters per second (1L = 10-3m3).
Turbo molecular pump must be (much larger than the maximum size of the flow duct section states the mean free path of the gas molecules) in the molecular flow state work to show its superiority, thus requiring the former with a working pressure of Class 1 ~ 10-2Pa vacuum pumps.
Molecular pump itself by the rotation speed of 10000 to 60000 rev / min IF direct drive motor.