HIGH VACUUM FLANGE TEST OF A BAKEABLE ALUMINUM WIRE SEAL

As a part of the development work associated with the design of vacuum components for the Thermonuclear Project, a program was initiated for the testing of high vacuum bakeable flange and gasket designs for leak-tight sealing requirements. The flange and gasket components, chosen for the initial study because of the simplicity in design and low yield point of the gasket material, consisted of the fully annealed, type 1100, aluminum alloy compressed between plane flange surfaces which had a 32 mu in.-rms finish. Leak-tight sealing of the 99% aluminum, 10-inch wire was found to be dependent on the yield point and creep properties of the alloy. It was demonstrated, (1) that sealing was accomplished when the bolt loaded flange exceeded the yield point of the strain hardened gasket, and (2) the life of the gasket was dependent on the rate of deformation during thermal cycling between room temperature and 250 deg C. It was possible to maintain a satisfactory vacuum seal STA<10/sup -9/ torr liter-sec/sup -1/-(gasket in.)/sup -1/! for more than 18 thermal cycles with four hours per bake at the elevated temperature. Initial sealing of this 0.088-in. diameter gasket was achieved with approximately 0.028-in. gasket deformation and a force of 1500 lbs (linear in.)/sup -1/ or (71/2 tons-in./sup -2/) The maximum loading force required to achieve a seal (i.e., to cause plastic flow) was approximately 81/2 tons. in./sup -2/, or 3000 lbs (linear in.)/sup -1/ of gasket. (auth