CF flange fastening installation operation

CF flange is a common type of flange standard in the ultra-high vacuum industry. After years of development, although the naming methods in different regions are different (such as NWCF, ICF, etc.), an industry standard has been formed worldwide. Its advantages are all-metal sealing, high temperature resistance, corrosion resistance, and extremely high vacuum (10-12 mbar) under appropriate operating conditions. However, its disadvantage is that it is relatively complicated to install compared to ISO and KF standards. If it is not installed properly, it will greatly affect the vacuum degree. In this issue of the official account, we will introduce the CF flange fastening installation operation steps and precautions.

CF flange

CF flange is called Conflat Flange in English. It is a flange connection used in ultra-high vacuum, a metal static seal that can withstand high temperature baking.

CF flange can be opened with through holes or threaded holes. Flanges with through holes should be fixed with bolts and nuts, and flanges with threaded holes can be fixed directly with bolts. Common specifications: CF16, 35, 63, 100, 150, 200, 250, 300, 350 CF flange sealing materials are usually oxygen-free copper washers. According to different segmentation requirements, oxygen-free copper washers can be thickened, gold-plated, silver-plated, high-temperature annealed, etc.

CF flange materials are usually 3 series stainless steel (304~316LN) stainless steel, etc. The common forms of CF flanges are shown in the figure below:

CF flange installation method

Take the flange fastening installation operation of CF35 through hole as an example, the operation method and steps are as follows:

Step 1: Prepare the following materials and tools:

Materials:

① CF35 plate nuts, 2 pcs (M6 nuts can be used instead if there are no plate nuts)

② 304 stainless steel hexagon socket bolts M6*35, 6 pcs (external hexagon screws can also be selected)

③ Ø6mm flat washers, 6 pcs

④ CF35 copper washer, 1 pc

⑤ CF35 blind plate, 1 pc

Tools:

① Dust-free gloves

② Alcohol

③ Super clean cloth

④ 5mm hexagon wrench (if external hexagon screws are used, a No. 10 wrench is required)

Step 2: Wear dust-free gloves, use a super clean cloth dipped in alcohol to wipe the copper washer and CF35 blind plate, and carefully place the copper washer on the edge of the blind plate after wiping.

Step 3: Use a clean cloth dipped in alcohol to wipe the cavity flange edge, and cover the cavity flange edge with the blind plate (with a copper gasket on the edge) wiped in the second step to align the upper and lower flange leak detection ports.

*In the second and third steps, it is necessary to check whether the sealing blade and copper gasket are intact and without scratches. If there are any abnormalities, the installation must be stopped. Defects in the copper gasket or flange will not only cause the vacuum to fail to meet the standard, but may even damage the matching flange.

Step 4: Insert the 304 stainless steel hexagon socket bolt M6*35 with a gasket into the through hole, and fix the other side with a plate nut (or M6 nut), screw the bolt into the plate nut (or M6 nut), and tighten the bolts crosswise; tighten each bolt clockwise 1/4 or 1/2 turn at a time with appropriate tightness.

Step 5: Tighten all bolts evenly clockwise with a 5mm hexagon wrench.

If possible, we strongly recommend the use of a torque wrench to complete the installation of the CF flange. According to the recommendations of some manufacturers, the tightening torque can be referred to as follows (www.lesker.com)

Flange outer diameter O.D.		Bolt torque (ft-lbs.)
inch	mm
1-1/3	34	7
2-3/4	70	12
4-1/2	114	15
6	152	15
8	203	15
10	254	15

< 1. When setting up the vacuum system, you must wear clean clothes, clean hats, and gloves, because slight fingerprints or other stains can greatly affect Vacuum degree; 2. Before installation, carefully check the surface finish or roughness of the blind plate, flange edge and copper gasket. No bumps, scratches, marks or other defects that affect the vacuum sealing performance are allowed. Make sure that the blade and copper gasket are free of defects before installation;

3. Choose different flanges according to different flange sizes The type of screws should be selected so that the length of the screws protrudes 1~2mm from the nut;

4. When bolts, nuts and washers are assembled with flanges, molybdenum disulfide lubricant should generally be added between bolts and nuts;

5. When tightening flange screws, force must be applied evenly. For small flanges For example, for flanges of size CF16-63, the screws can be tightened step by step in sequence. However, for larger flanges, such as flanges of size CF150 and above, diagonal tightening is required to avoid uneven force on one side. Uniform, affecting the sealing effect;

6. For parts with ceramic or glass seals, such as feedthrough or windows, it is recommended to use annealed copper washers, which can reduce the compressive stress inside the seal and reduce the chance of damage; < If you need to purchase copper washers and plate nuts, please send an email to info@fermi.com for consultation.

The following is the table of bolt/screw lengths corresponding to the CF flange sizes commonly used by Feminian Instruments (for reference only)