Vacuum chamber baking
Observe the change in the degree of vacuum when the vacuum chamber is baked, and the baking is performed by winding the heating belt. When the degree of vacuum reached about 10-3 Pa, the heating belt was gradually energized and heated, and the chamber was kept baked at 150 ° C for a long time. The ion pump is turned off during the baking process, and the ion pump is also energized for heating and baking. At this time, the vacuum chamber is only exhausted by the molecular pump and the foreline pump. As the temperature of the cavity increases, a large amount of gas molecules such as water vapor adsorbed on the inner surface of the cavity are released, and the degree of vacuum rapidly deteriorates. The amount of gas released gradually decreases with the extension of the baking time, so the degree of vacuum is gradually improved. When the baking is stopped, the baking power of the heating belt and the ion pump is cut off, and then the titanium sublimation pump is degassed while the crucible body is still at a high temperature. The degassing treatment of the titanium sublimation pump refers to the operation of heating the Ti wire, but controlling the temperature below the sublimation temperature of Ti. The purpose of the degassing treatment of the titanium sublimation pump is to remove the gas molecules adsorbed on the surface of the Ti wire and other possible contaminants to ensure the normal operation of the titanium sublimation pump. After fully completing the degassing treatment of the titanium sublimation pump, the ion pump and the titanium sublimation pump are activated to increase the intensity of the vacuum exhaust. As the exhaust force increases and the gas evolution decreases due to the lowering of the chamber temperature, the vacuum of the system will rapidly improve.
When the newly completed cavity is first baked, it usually takes one week, and the individual baking time after repeated baking can be appropriately reduced. In order to accurately measure the degree of vacuum, the vacuum gauge should also be degassed after stopping the baking. If the vacuum pump is fully capable and the baking time is sufficient, the vacuum can be increased by several orders of magnitude after baking.
One atmosphere produces a pressure of about 1 kgf over an area of ??1 cm2, and for a flange of 20 cm diameter, it is a pressure of 1 t. Cylindrical or spherical cavities, due to the special structure of the structure, the pressure is dispersed, and the wall thickness of the cavity is not deformed by 2 to 4 mm. However, for a square cavity, the side plate has to withstand a pressure of ton, and it is necessary to increase the wall thickness or set the rib to prevent deformation. The square cavity is generally heavier than the cylindrical and spherical cavity, and the price is high. Several representative vacuum chambers are shown, cylindrical, spherical, and square, respectively.
