CF flanges and gaskets were originally developed by the Varian corporation. CF flanges use a metallic gasket, usually copper, and a knife-edge flange to achieve an ultra-high vacuum seal.
Each face of the two mating CF flanges has a knife edge which cuts into the softer metal gasket, providing an extremely leak-tight, metal-to-metal seal.
Deformation of the metal gasket fills small defects in the flange, allowing CF flanges to operate as low as 10-13 torr (10-11 Pa) pressure, which has made CF gaskets a standard for semiconductor and UHV applications. The gasket is partially recessed in a groove in each flange. The groove helps hold the gasket in place, which aligns the two flanges and reduces gasket expansion during bake-out.
One drawback of the Conflat design is that the knife edge is an asymmetrical profile with one side that has a shallow slope. This results in high compression forces and a bolt circle of tightly spaced fasteners. Note: if your situation requires lower compression forces or fewer fasteners, consider using H-Seals.
For stainless steel CF flanges baking temperatures of 450°C can be achieved; the temperature is limited by the choice of gasket material. CF flanges are sexless and interchangeable. North American flange sizes are given by flange outer diameter in inches while in Europe and Asia, sizes are given by tube inner diameter in millimeters.
©1991-2017 Bostec Engineering, Inc. H-Seals® and H-Seal® products are covered under U.S. Patent numbers 5,433,454, 5,445,393 and other patents that are pending.
H-Seal® is a trademark of Bostec Engineering, Inc. All rights reserved.
Artwork by Dan Nelson (www.dnelsonart.com)