The range of vacuum degree of high vacuum equipment is 10-2 power and 10-5 power PA. High vacuum acquisition equipment is generally composed of multiple vacuum units working in series in different pressure ranges, plus pipes, vacuum measuring instruments and valves. It is widely used in electronics, automobile, biotechnology, metallurgy, aerospace and other industrial fields because of its low extraction rate, low pressure and low emission. The commonly used high vacuum equipment includes the vacuum unit with diffusion pump as the main pump (such as diffusion pump mechanical pump unit, diffusion pump Roots pump mechanical pump unit), and the vacuum unit with molecular pump as the main pump (such as turbine molecular pump Roots pump mechanical pump).
Oil diffusion pump vacuum unit is an early vacuum pump unit used in the field of high vacuum. The oil diffusion pump uses the oil steam with low-pressure and high-speed directional movement to inject into the extracted gas, driving the gas to move downward, and bringing the extracted gas to the exhaust port, so as to reach the exhaust port. The pumping speed range of oil diffusion pump is very large, from dozens to hundreds of thousands of liters per second. The ultimate vacuum is 10-4 ~ 10-8 power PA, and it has a stable pumping rate in the vacuum range of 10-2 ~ 10-4 power PA. Oil diffusion pump is an important pumping device for high vacuum, which is widely used in vacuum coating, metallurgy and other industries.
Oil diffusion pump is widely used because of its simple structure, low price, no selectivity to the pumped gas, high limit vacuum, no mechanical transmission and friction, easy maintenance. The disadvantage is that it is easy to produce oil vapor back flow, which causes oil pollution in the vacuum chamber; the start-up time is long; the power is large and the power consumption is relatively high. The return oil of diffusion pump makes it limited in the use of vacuum system which requires high vacuum cleanliness. In order to solve this problem, a cold trap and baffle are usually installed in the pipeline between the vacuum chamber and the main pump inlet of the vacuum unit, which can effectively remove the condensed steam from the vacuum chamber and the reflux oil steam from the steam flow pump.
The vacuum unit with molecular pump as the main pump is also called oil-free vacuum unit. It was invented by guy of Germany. Super high real air turbine molecular pump. Although molecular pump is a kind of mechanical pump, it is different from mechanical pump. Mechanical pump is a positive displacement pump by changing the volume of the pump cavity, and molecular pump is a rigid body in high-speed rotation, its momentum is transferred to the gas molecules, so that the gas molecules have a directional speed, and then compressed, and then discharged through the exhaust port. Turbomolecular pump uses fixed blades and high-speed rotating blades to cooperate with each other to achieve air extraction.
In the past 20 years, molecular pump has been widely used in various industries, especially in the film industry, semiconductor microelectronics industry and high-tech industry, because it can obtain clean high vacuum. Not only that, the molecular pump produced in foreign countries can be directly pumped from the atmosphere to high vacuum, without the need for pre pump matching. The starting speed of the molecular pump is also very fast, which can effectively improve the working efficiency. However, as the molecular pump is pumped by mechanical movement, the wear between the rotating blades which have been used for a long time is also intensified, greatly reducing the service life of the molecular pump. In addition, the molecular pump has some restrictions on the extracted gas, which is not suitable for pumping heavy gas such as steam