Thermal cycling and torque analysis of an ultrahigh vacuum flange

Abstract

A major design objective of a vacuum assembly in a specialized ultrahigh vacuum exhaust/leak detection processing system was to incorporate replaceable vacuum sealing flange ports. The vacuum processing operation with which the system was to be used required that these ports be capable of repeatable thermal cycling, from ambient to 525±25 °C and be torqued between the range of 17 to 50 ft lb prior to each thermal cycle while guaranteeing a leak-free seal to less than 1×10−12 std cm3/s. This design concept was proven to be feasible through computer analysis and documented experiments. One of the major breakthroughs was the employment of nickel metal gaskets for sealing as opposed to OFHC copper (standard high vacuum gasket material). This nickel gasket was proven to be vastly superior to copper in its sealing reliability with respect to thermal cycling at elevated temperatures. Torque analysis results have shown that these ports could be torqued to as high as 50 ft lb, both at ambient and elevated temperatures, and still be leak free.