Back To CF-GASKETS

Bostec CF-Gaskets are engineered for ultra-pure applications.

Ultra-pure manufacturing standards specify that machined components in the wetted zone have extremely fine surface finishes, on the order of Ra of 5 μin. (0.13 μm), smooth transitions and fully swept flow paths to minimize entrapped or generated particles.

Stamped CF gaskets deviate significantly from this standard in four ways.

1. The inside edges of a stamped CF gasket are rough and jagged due to shear-tear, leaving a large ID surface area for particle sloughing or entrapment.


2. The flat sealing surfaces of the gasket are micro-pitted from the rolling process that produces the raw sheet stock the gaskets are made from, which is a secondary surface for potential particle entrapment.


3. Stamped CF gaskets are often tumble de-burred in an attempt to smooth over jagged edges. This process does more harm than good by not removing burrs but rolling them over, thus trapping contaminants.


4. Stamped CF gaskets are not usually annealed, which means the gaskets may be nearly as hard as the knife edge itself. This increases compression force and reduces the life of your gland.

Stamped CF gaskets are sometimes nickel-plated over a copper base to provide a degree of corrosion resistance. Field experience shows that the plating often flakes away, exposing the underlying copper to your corrosive gas or liquid causing rapid deterioration and contamination.


While low grade gaskets are plentiful and inexpensive, they are not suitable for high precision processes found in the manufacture of semiconductors, or many applications in aerospace, outer space, nuclear or high-pressure oilfield situation


The Origin of CF (Conflat) Flanges and Gaskets

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.