The Delicate CF Flange Knife Edge
The CF flange was developed in the early 1960s in response to the demand for a gas-impermeable vacuum connector. The CF flange has identical flanges where the seal mechanism is a knife-edge that is machined below the flange’s flat surface. As the bolts are tightened, the knife-edges make annular grooves on each side of the metal gasket. It is important to protect the knife edge as it is used to cut into the soft metal gasket, which in return provides that leak-tight metal-to-metal seal. You want to make sure you are very cautious and careful as one small scratch on the knife can result in a leaky seal in your vacuum chamber. Think of the most delicate object you own and remember how you have to handle it with so much care and caution. This indeed applies to the knife-edge as one mishap can have a huge consequence on accomplishing a project.
When removing the gasket specialized tools are available, but far too often most labs do not have them. One of the tools include a gasket scraper as it is specifically designed to remove gaskets. It is designed with a sharp edge giving the ability to get under, lift, and shear away old gaskets from metal surfaces. So, what if you are not in reach of these specialized tools? You will want to find a clean regular channel lock or grip pliers to remove used copper gaskets. Please be advised that due to spacing pliers may not work as this could risk potential damage to a ceramic or optic part. When spacing is found to be an issue, using the flat screwdriver is your best option.
Remember, you want to be mindful of the fragile knife edge. If you end up using pliers, position the mouth of the pliers on the inner and outer diameter of the gasket, and tilt the pliers back. The leverage will then pop the gasket out. Make sure you are applying enough pressure and have a good handle as it is not abnormal for the gasket to be tight, making it difficult to remove. It also can be the case where the gasket slides out smoothly.
When using a screwdriver keep in mind the delicate part. If the screwdriver were to slip off the gasket and damage the knife-edge the whole part could be ruined. Using a screwdriver with a flat tip can reduce the chances of damage. Place downward pressure on the tip of the screwdriver as you attempt to pull the gasket up. Remember, sometimes the gaskets can be good and tight and difficult to remove. You must take your time and pay close attention to avoid any complications or delays. Once a knife-edge gets scraped or gouged the flange may no longer seal properly. If this occurs use a small piece of soft vacuum-compatible metal such as gold or platinum to fill the void on the gouge. Store flanges by wrapping in UHV aluminum foil to ensure your flanges are well taken care of.