There is a convex sharp edge at the inside of the CF flange, which is sealed by squeezing an oxygen-free copper gasket (or other soft metal) to ensure vacuum sealing. It is an all-metal sealing method that is widely used in ultra-high vacuum system. CF flanges are also commonly referred to as ICF flanges. The number behind the CF is the standard inner diameter of the catheter, and the number behind the ICF is the outer diameter of the flange. Table 1 is the types and dimensions of commonly-used CF flanges.
CF flange is divided into fixed type and loose type. The fixed flange has integrated structure. The loose-type flange consists of the knife-edge part of the extruded copper washer and the fixed part that through the bolt. Through-hole or threaded hole can be tapped in the flange. The flange with the through hole needs to be fixed by the bolt and the nut, while the flange with the threaded hole should be directly fixed with the bolt. The material of the flange is mainly SUS304 (or SUS304L) because SUS304 emits less gas and it is easy to process and weld.
Table 1 Models and sizes of commonly-used CF flange
Note: For n×d, n refers to the number of holes and d means the aperture (mm).
CF flanges are characterized by it is both male and female, and all the parts include oxygen-free copper gaskets are made of metal, so it can withstand high temperatures (above 250°C). The disadvantage is that the price is high and the oxygen-free copper gasket cannot be used repeatedly.
Installation of CF flange
Mounting requirements of CF flange are rather high. Since the oxygen-free copper gasket deforms after being squeezed, it is very important to tighten the bolt with equal force. If the bolts are not evenly pressed, the flanges in the opposite corners will be tilted so that the system will leak. The tightening torque of the bolt is approximately as follows: M4 bolt 20kgf·cm, M6 bolt 70kgf·cm, M8 bolt 100kgf·cm.
Caution of CF flange
When using the CF flange, there are several points to note: The bolt must be coated with MoS2 to prevent the bolt and nut from snapping. The flange should be aligned on the outer circumference. The flange surface should be kept at a distance to allow room for further tightening the bolt after baking.
For CF flange, blade should cut into the metal seal to ensure vacuum sealing. For long-term use, the blade will gradually become blunt. In addition, the blade is susceptible to injury after being hit by a hardener. One of the remedies is to use an IPD metal seal. IPD metal seals do not rely on the edge of the flange, but rely on the incline of the knife edge to seal.