A bolted flange with a circular knife edge machined into each face; tightening the bolts drives both edges into a flat oxygen-free copper gasket, making a metal seal good to below 10⁻¹² mbar and bakeable to about 450 °C. Sizes are usually named by outside diameter in inches (1.33, 2.75, 4.5, 6 and 8) or by DN, with 2.75 inch matching DN40CF. Bolts are tightened in a star pattern in small steps until the gap between the flanges is even all the way round.
Fresh copper on the 2-3/4 CF, tighten in a star in quarter turns till the gap's even all round.
Use silver-plated nuts or anti-seize on stainless bolts; bare stainless threads gall and seize after a bake.
Also heard as
- ConFlat
- CF
- knife-edge flange
Related terms
Knife edge
Sharp circular ridge machined into a CF flange face that cuts into the copper gasket to make the seal.
Copper gasket
Flat ring of soft oxygen-free copper crushed between two CF knife edges to make a metal vacuum seal.
UHV
Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.
Bake-out
Heating a vacuum system while pumping to drive off water and other adsorbed gas and lower the base pressure.
KF flange
Quick-release clamp flange with a centring ring and O-ring, the standard small fitting for rough and high vacuum.