真空密封技术.pdf

Chapter 3 Vacuum seal 1 2 3 2. virtual leak A virtual leak is a source of gas that’s physically trapped within the chamber with only a small, very low conductance, path from the trapped pocket of gas into the chamber. 4 5 6 Common Solutions to Trapped Volumes 7 Seal Methods 1. Welding 2. Elastomer seal 3. Metal Seal 4. Standard vacuum feed through 8 Welding 1. Methods TIG welding MIG welding EBW Brazing 2. Maximum leak rate: -7 3 10 Pa m /s.m 9 Elastomer seal 1. low vapor pressure at the service temperature 2. reliable, reusable and long life sealsmost common type of seal used 3. no components or materials which will vaporize at the pressures and temperatures to which the joint will be subject. 4. seal vacuum as low as 10 -8 Torr 10 11 Typical seal method Bolt and clamp 12