Video decrypts the working principle of molecular pump
How molecular pumps work?
The pump mechanism of the molecular pump is different from that of a mechanical pump, which relies on the change of the pump chamber volume to extract air.
The molecular pump is driven by the motor to rotate at high speed. In the molecular flow region, the gas molecules collide with the high-speed blade surface, and the momentum is transferred to the gas molecules, so that some of the gas molecules move in the direction of the rigid body surface and are expelled from the pump, to achieve the purpose of air extraction. Usually with the high-speed movement of rigid body surface to carry gas molecules, and make it move in a certain direction of the phenomenon known as molecular traction phenomenon, using this phenomenon made of vacuum pump known as traction molecular pump (gad pump). The advantage of traction molecular pump is that the starting time is short, in the molecular flow state has a high compression ratio, can remove all kinds of gases and vapors, especially suitable for the extraction of heavier gases. However, because the traction molecular pump pumping speed is small, the seal gap is too small, the work reliability is poor, easy to mechanical failure, and manufacturing difficulties, in fact, rarely used. Later, the traction molecular pump was improved and the turbo molecular pump appeared.
The turbo-molecular pump contains multiple groups of alternating rotor blades and fixed rotor blades, and there are many slanted blades at a certain Angle on each blade, as shown in FIG. 1. The actual turbo molecular pump is composed of a multi-stage cascade, namely, the actuating blade, the fixed blade and the moving blade are arranged alternately. Moving blades act like electric fan blades when they rotate, pumping gas from one side to the other. Increasing the speed of the molecular pump is beneficial in improving the pumping speed of the molecular pump. Because of the speed limit of the blade, if the gas molecules move faster, it is more difficult to pump vacuum.
It can be seen that turbo molecular pump is also a kind of mechanical vacuum pump. The combination of high-speed rotating multi-stage turbine rotor blades and static blades is used for air extraction, which produces a high compression ratio for the extracted gas in the molecular flow area, so as to obtain the required vacuum performance. The ultimate vacuum of turbomolecular pump is higher than diffusion pump, up to 10^-8pa. In normal operation, certain vacuum degree of the front stage is required, which varies slightly depending on the pump, generally ranging from 1 to 200Pa. Mechanical pump can be used as the front stage pump. The high vacuum unit is composed of molecular pump and mechanical pump. Due to the high speed of turbo molecular pump, it is usually driven by if motor, and the if power supply frequency is between 300-400hz. Turbomolecular pumps are usually water-cooled.
The compound molecular pump is a series combination of turbo molecular pump and traction molecular pump, which combines the advantages of the two kinds of pumps into one, and can be in a wide pressure range of 10^ -6-1pa, with larger pumping speed and higher compression ratio, which greatly improves the outlet pressure of the pump.
(1) the rotor speed reaches 20000r/min, so the starting time of molecular pump is relatively long.
(2) the gas is in the state of molecular flow, so it needs to be equipped with the front stage pump. Generally, the rotary vane pump is used as the front stage pump
Molecular pump features:
Oil lubrication molecular pump: the amount of lubricating oil is small, and in the vacuum section of the former stage, the pollution of the vacuum chamber is small.
Grease lubricating molecular pump: the amount of grease is very small, the pre-stage dry pump can get a clean vacuum almost without oil.
Full magnetic suspension molecular pump: no need for lubrication, can be used with dry pump, clean vacuum environment without oil.
Other common applications:
1. Analysis (mass spectrometry, electron microscope, etc.)
2. Semiconductors (electronic components, integrated circuits, flexible solar cells, etc.)
3. Optics/glass (thermal protection, anti-reflection, reflection, optical filter)
4. Coating (surface protection, decorative paint, display, screen)
5. Vacuum metallurgy (vacuum furnace, vacuum brazing, vacuum sintering, vacuum alloy,)
6. Leakage detection (vacuum system, vehicle fuel tank, airbag)
7. Research experiments (medical magnetic resonance imaging, nuclear particle physics, fusion research, laser applications and much more)
8. Lamp production industry and related industries
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