Precautions for the selection of vacuum pumps in vacuum coating equipment
Every vacuum coating equipment has a vacuum pump, and the choice of vacuum pump is very important. The selection of vacuum pump has the following considerations:
1. The working pressure of the vacuum pump of the vacuum coating machine should meet the ultimate vacuum and working pressure requirements of the vacuum equipment. For example, vacuum coating requires a vacuum degree of 1×10-5mmHg, and the vacuum degree of the selected vacuum pump should be at least 5×10-6mmHg. Usually, the vacuum degree of the pump is selected to be half to an order of magnitude higher than the vacuum degree of the vacuum equipment.
2. The vacuum coating machine really and correctly selects the working point of the vacuum pump. Each pump has a certain working pressure range, such as: diffusion pump is 10-3~10-7mmHg, in such a wide pressure range, the pumping speed of the pump changes with the pressure, and its stable working pressure range is 5 × 10 -4~5×10-6mmHg. Therefore, the working point of the pump should be selected within this range, and it cannot be allowed to work for a long time under 10-8mmHg. Another example is that the titanium sublimation pump can work under 10-2mmHg, but its working pressure should be less than 1×10-5mmHg.
3. Under its working pressure, the vacuum pump should be able to remove all the gas generated in the process of the vacuum equipment.
4. Correctly combine the vacuum pump. The vacuum pump is selectively pumped. Therefore, sometimes one type of pump cannot meet the pumping requirements, and several pumps need to be combined to complement each other to meet the pumping requirements. For example, the titanium sublimation pump has a high pumping speed for hydrogen, but cannot pump helium, while the three-pole sputtering ion pump (or the two-pole asymmetric cathode sputtering ion pump) has a certain pumping speed for argon. Combined, the vacuum device will get a better vacuum degree. In addition, some vacuum pumps cannot work under atmospheric pressure and require pre-vacuum; some vacuum pumps have an outlet pressure lower than atmospheric pressure and require a backing pump, so they all need to be used in combination.
5. Requirements for oil pollution of vacuum equipment. If the equipment is strictly required to be oil-free, various oil-free pumps should be selected, such as: water ring pump, molecular sieve adsorption pump, sputtering ion pump, cryogenic pump, etc. If the requirements are not strict, you can choose an oil pump, plus some anti-oil pollution measures, such as adding cold traps, baffles, oil traps, etc., can also meet the requirements of clean vacuum.
6. Understand the composition of the pumped gas, whether the gas contains condensable vapor, whether there is particle dust, whether it is corrosive, etc. When choosing a vacuum pump, you need to know the gas composition and select the corresponding pump for the gas to be pumped. If the gas contains vapor, particles, and corrosive gases, it should be considered to install auxiliary equipment such as condensers, dust collectors, etc. on the inlet pipeline of the pump.
7. How does the oil vapor discharged from the vacuum pump affect the environment? If the environment does not allow pollution, you can choose an oil-free vacuum pump, or discharge the oil vapor to the outside.
8. Whether the vibration generated by the vacuum pump has any influence on the process and the environment. If the process does not allow, choose a pump without vibration or take anti-vibration measures.
9. The price, operation and maintenance cost of the vacuum pump.
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