KF Or CF — Which Should I Use?

Vacuum pumps require the right type of flange connections for proper sealing and reliable operations. Take a moment to review the differences between KF and CF flange connections to determine which one is best for your environment and applications.

KF Flanges

A KF (Klein Flansche) flange connects with a vacuum pump using the following components:

• Clamp
• Centering bracket
• O-Ring
• Seal ring

KF Seal Material

There are many KF seal materials from which to choose.

• Aluminum – Non-magnetic metal
• Buna – Nitrile rubber
• Elastomeric – A rubber, cellular urethane, silicone foam, or fluorosilicone material
• EPDM – A synthetic rubber
• Silicone – A polymer made of siloxane
• Viton – A synthetic rubber and fluoropolymer elastomer blend

KF Flange Vacuum Pressure

• 10-8 mbar

KF Flange Calibers

• DN10
• DN16
• DN20
• DN25
• DN32
• DN40
• DN50

Advantages of KF Flanges

• Because KF flanges are held together with clamps, they are easy to remove. This makes them a great choice for applications that call for frequent port changing.
• In general, KF flanges are also less expensive than CF flanges. Consider that if your budget is a concern.

KF flanges are excellent for:

• Vacuum manifolds

CF Flanges

A CF (ConFlat flange) is a seal that remains stationary, much like a gasket. Because of that, CF flanges are referred to as static metal seals.

CF Seal Material

The available materials vary for CF seals.

• Copper – Oxygen-free copper enables the seals to run cooler.
• Polytetrafluoroethylene (PTFE)
• Viton – A synthetic rubber and fluoropolymer elastomer blend.

CF Flange Vacuum Pressure

• 10-12 mbar

CF Flange Calibers

• DN10
• DN16
• DN25
• DN35
• DN40
• DN50
• DN63
• DN75
• DN100
• DN150
• DN160
• DN200
• DN250

Advantages of CF Flanges

• CF flanges work well with surplus feedthroughs for fusers and large hemispheres on standard chambers.
• Higher vacuum temperatures are another benefit of CF flanges. As noted earlier, CF flanges can withstand vacuum pressures up to 10-12 mbar.
• CF flanges are excellent for long-term sealing due to the construction of the metal gaskets

Suggested uses for CF flanges include:

• Filling flange surface defects
• High-voltage feedthroughs
• Gauge heads

Commonalities: KF and CF Flange High-Grade Steel

Both KF and CF flanges are made of quality steel material.

• SS304 or 304L – This grade of steel is best for formability. It is also a lower-cost option than 316. Grade 304 steel contains a weight of up to 10.5 percent nickel and up to 20 percent chromium. This makes it corrosion resistant and appropriate for environments where standard carbon steel would corrode.

• SS316 or 316L – This grade of steel is suitable for environments that are located under water, contain corrosive elements, or where hardness or strength is required. Chromium, silicon, manganese, carbon, molybdenum, and iron are this grade of steel’s composition. Up to 3 percent of molybdenum makes the 316 grade more corrosive resistant than the 304 grade of steel.

Considerations

Seal materials make a difference too. For example, Viton has a higher heat threshold (up to 230 degrees Celsius) than some other rubber seals.

Overall, CF flanges are best used for vacuum applications where the connection is meant to stay sealed. KF flanges may be appropriate in vacuums where the continual removal of the flange is a regular practice.

Because CF flanges can handle more heat than KF flanges, consider if your application must withstand the highest vacuum pressure. But realize that although CF flanges are resistant to heat, KF flanges may be more sufficient and more appropriate for certain environments. This is partly because a KF flange’s heat capacity depends on how much heat its o-ring can withstand. In addition, the clamps that hold KF flanges in place are easily removable, and this is convenient for maintenance.

Gasket choice matters too. For example, silver-plated copper gaskets tend to take the heat in bakeouts of high-temperatures. The silver plating is needed to avoid flaking into the chamber when removing the gasket. If you are using aluminum gaskets, it is advisable to match them with aluminum CF flanges for quality consistency.

Once installed, CF flanges are meant to remain in place for a while. The increased cost of CF flanges may be due to their longevity potential. This could explain why there is often a noticeable price difference between CF and KF flanges.

Overall, it is a good idea to review every component of the flange and its connecting parts before deciding on which style is best for you.

Which should you choose?

CF flanges and KF flanges are both excellent choices for providing quality connections for vacuum pumps. Each flange style has unique advantages that benefit industrial, laboratory, and production environments. Whichever flange you choose, it is always a good idea to keep extra parts on hand so that production is never delayed due to handling a flange replacement maintenance task.

High Vac Depot is your go-to source for all of your vacuum pump needs. Like many industry professionals, you may require a combination of CF and KF flanges. Our trained specialists can help you select the appropriate flange style for your vacuum chamber. Call High Vac Depot toll-free at 1-800-289-6945 or message us online today.