Baking and degassing in ultra-high vacuum system (4)

    Ultra-high vacuum systems vary in size and internal structure, and it is difficult to use a unified baking program to meet the requirements of various users. When the user conducts the operation and debugging of the ultra-high vacuum system for the first time, the system’s baking program should be specially tested, including different baking temperature, baking time, heating rate, cooling rate, temperature of each part, and vacuum degree of each stage. , Formulate reasonable baking process parameters. What needs to be pointed out here is that during the heating and baking of the system, the heating rate should be controlled to prevent the pressure in the container from being too high, so as to exceed the maximum working pressure of the vacuum pump and destroy the normal pumping function of the pump.

    The sealing material of the ultra-high vacuum system is an important factor that affects the baking parameters. Special attention must be paid. The low outgassing rate of the metal seal can allow a higher baking temperature, but the difference of different thermal expansion coefficients may cause it when cooled to room temperature. Cold leakage. For disposable sealing rings, they need to be replaced each time they are exposed to the atmosphere. Reusable metal seals can easily cause air leakage due to knife edge misalignment or improper sealing pressure. The rubber sealing gasket is easy to replace, but the air out rate is high and high temperature baking is not allowed. Even if fluoroelastomer is used, the rubber ring needs to be baked in a reasonable temperature range.

    In order to obtain a pressure of 10^-6Pa or lower with a rubber sealing ring, a fluorine rubber sealed ultra-high vacuum flange with a small area of the sealing material exposed to the vacuum and welded with a water-cooled tube and a freon refrigeration tube, or a freon refrigeration Ultra-high vacuum flange with tube and double-channel fluorine rubber sealing ring. After the baking is completed, the flange is cooled to room temperature and then freon is used to cool the flange to reduce the temperature of the flange to -20~-30℃. At the same time, the middle of the double-channel sealing ring is drawn Vacuum can reduce the leakage and deflation rate of the sealing ring.

(Huiputech)