Characteristics and classification of ultra high vacuum units
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The ultra-high vacuum units working at more than 10-5pa have diffusion pump, molecular pump ultra-high vacuum units and oil-free ultra-high vacuum units. The units have the following characteristics:
1. High ultimate vacuum degree of the main pump, 10-7~10-8pa above;
2. Can withstand the high temperature of 200 ~ 450 ℃ baking;
3. The partial pressure of the backflow gas in the main pump is very low;
4. For the pumped gas selectivity of the main pump, to be equipped with a large enough auxiliary pump;
5. Requirements of vacuum chamber, pipe, valve and other components of the material output rate is very low, leakage rate is very small.
(1) Diffusion pump ultra-high vacuum unit
The diffusion pump as a priority pump in the ultimate vacuum unit, the ultra high vacuum degree is 10-7 ~ 10-8 pa.
To reduce from diffusion pump before the level of gas diffusion and block mechanical pump oil anti diffusion effect on the ultimate vacuum, but in front of the diffusion pump level type a small pumping speed of diffusion pump, in order to reduce the compression ratio, reduce the diffusion As in the diffusion pump inlet, adding titanium sublimation well above can further reduce the nitrogen partial pressure from the diffusion pump, can get 10 to 11 pa ultra high vacuum.
(2) Molecular pump ultra high vacuum unit
The ultra high vacuum unit with molecular pump as the main pump has a maximum vacuum degree of 10-8pa, which is characterized by fast start-up and small oil pollution. In addition, a liquid nitrogen cold well can be added to the unit to increase the pumping speed. A water cold well can be set at the outlet of the mechanical pump to prevent oil vapor from entering the system.
(3) Oil free ultra high vacuum unit
Vacuum units that do not use oil as working fluid and are not sealed with organic materials are known as the main pumps commonly used in oil-free ultra-high vacuum units, such as cryogenic pumps, titanium pumps, sputtering ion pumps, etc., which can obtain the ultimate vacuum degree of 10-7~ 10-8pa. Compared with oil-containing vacuum units, it has the following advantages:
1) clean vacuum without pollution sources can be obtained;
2)When the oil-free vacuum pump is started, the pre-pumping pump can be isolated;
3)If the pumping stops suddenly, the system will not be polluted;
4)No oil, no vibration, improve the working environment;
5)High limit vacuum, high pumping speed, short pumping time.