As a qualified vacuum system has strict requirements on its leakage rate, air release is the main factor affecting the pressure reduction of the system, and air release is a slow process, even if baking and other measures are adopted, it often takes a long time to reach a predetermined pressure.
As the change of outgassing depends on temperature and time, but has little relation with the pressure of gas phase space, as long as the pressure is lower than the equilibrium pressure corresponding to the existing adsorption capacity, this condition is generally met in the process of air extraction. Therefore, even if the space pressure is reduced to a very low level in a very short period of time with a strong pumping speed, the amount of air release in the vacuum chamber cannot be significantly reduced. Instead, a proper pumping speed must be configured to make the amount of air release reach the water standard required by the process in a reasonable time under a reasonable baking temperature, which generally takes tens of minutes. The typical applications are sputtering coating and ion coating in titanium industry, smelting of rare earth permanent magnet materials, etc. Among them, excessive active gas will affect the quality of the film and the quality of the material, so there is a long period of fine extraction process in the process.
Large displacement vacuum system can remove water and gas from oil in a deep level. A two-stage vacuum unit composed of a vacuum pump with five times the evaporation rate and a large displacement and roots is selected to vacuum the equipment respectively, which can quickly remove the water vapor and other gases separated from the oil in the vacuum separator. The optimized fluid design can reduce the loss and uneven distribution of air extraction, resulting in the influence of secondary pollution caused by local air extraction (steam), so as to effectively control the oil from secondary pollution, and ensure that the equipment can meet the requirements once processed.
The roots vacuum pump needed by roots vacuum unit can’t directly discharge the atmosphere. If the air is directly discharged, the pressure difference between the suction port and the exhaust port of Roots vacuum pump will be too large, which will overload the roots vacuum pump. If the motor power of Roots vacuum pump is simply increased, the overheating of Roots vacuum pump will result in the small gap between the rotors of Roots vacuum pump being blocked due to thermal contraction. In order to ensure that the roots vacuum pump can reach a higher vacuum and ensure the clearance between the rotors of Roots vacuum pump. Therefore, the roots vacuum pump is equipped with a front-end pump when it is used. When the pressure in the system is pumped to a certain range by the front-end pump, the roots vacuum pump can be started again, so as to prevent the overload of Roots vacuum pump. The front stage pump can select water (liquid) ring vacuum pump, rotary vane vacuum pump, slide valve vacuum pump, vacuum pump and other vacuum pumps that can directly exhaust the atmosphere.
In general, water ring pump is more advantageous than other vacuum pumps in Roots vacuum unit. This is mainly because it can pump a lot of condensable steam, especially when the mechanical vacuum pump with air ballast oil seal can not clean the condensable steam enough, or the solvent used can make the pump oil deteriorate and affect the performance, or when the vacuum system does not allow oil pollution, it is more obvious Obvious.