Sealing mechanisms in bakeable vacuum seals Available to Purchase

Bakeable seals have to maintain their leak tightness during and despite repeated heating/cooling cycles. An analysis of the mechanisms by which the leak rate of demountable bakeable seals is maintained (or lost) is presented. The mechanisms are studied by following the evolution of the strain in the gasket and/or flange during heating/cooling, as related to the strain developed during the processes of mechanical ‘‘tightening’’ and releasing. It is proposed to describe these processes by the relevant strain versus load curves, where the ‘‘operating position’’ of the seal is expressed by the intersection between the strain/load curve of the gasket and that of the flange. Typical curves and operating positions of commonly used seals are presented on a comparative ‘‘map’’. Heating modifies the strain by a combination of the effects of ‘‘softening’’ of the materials and variation of the load caused by the differential expansion of the parts. The mechanisms by which these effects may lead to the loss of the (elastic) strain and/or may increase the plastic deformation are discussed. The acceptable limits of the variation of the strain (expansion, yield point) for various bakeable seals are established. A method of recording the process, by measuring (on line) the strain at appropriate points on the surface of the gasket and/or the flange, is proposed.