Proper Torquing of CF Flanges

A flange is an extended ridge or a rim, either internal or external, and is used for guiding machine parts or surging strength for easy attachment to another object. It can also be a plate or a ring to create a rim at the end of the rim when fixed to the pipe. There are various types of flanges: pipe flange, steel pipe flange, weld neck flange, slip-on flange, lap joint flange, blind flange, spectacle blind flange, and others.

The CF flange, also known as ConFlat, is a sexless design where both designs are the same. It is a flanged attachment for ultra-high vacuum and is equipped with a static metal seal that can combat high-temperature baking. The standard flanges are mainly manufactured from stainless steel types and surface hardened aluminum. However, they also come in various stainless steel grades and can be customized depending on customers’ tastes and preferences. ConFlat flanges offer complete coverage for vacuum chamber systems. ConFlat flanges use an OFHC copper gasket knife-edge machined under the flange’s flat surface to enhance a tight seal. The knife-edges make circular groves on each side every time the flange-pair bolts are fastened. It penetrates into the softer copper gasket to create a leak-tight metal–to–metal seal. ConFlat flanges are available in four versions: Fixed flange, Rotatable Flange, Clearance-holes, and Tapped holes.

Proper Torquing of CF Flanges

The idea of torque is the concept of force, the amount of energy needed to rotate objects, including bolts and flywheels. Torque is needed to get a stable connection. For instance, in order to get fluid transmission with zero leakage, correct gasket installation is needed, and bolts must be tightened onto the flanges with the correct tension and balance over the whole flange face. Torque develops tension which fixes two components so that they can repel pulling or sliding apart. Proper torquing of CF flanges entails:

Making the Faces of the Flange ‘Metal to Metal’

Most people using CF flange tightens the bolts until the surfaces of the flanges come into direct contact with each other. The flange responds by offering a built-in gauge to establish when the gasket has been sufficiently deformed. However, there is a potential risk of over-tightening the bolts when you apply this method.

Tighten the Bolts to a Particular Torque

The majority of ConFlat flanges manufacturers provide the approved values of the bolt torque. While there is a good harmony for the larger sizes, there is a significant spread in the approved torque for the smaller flanges. So, what is the appropriate torque to use? As the bolt is fixed, some strength is used to the gasket, and an equal and opposite tensile stress is used to the bolt. A useful rule of thumb is that the bolt may be tightened, stretching the stress to 75 percent of the yield stress of that material. While it may be hard to compress a gasket with minimal torque, shifting the bolts to this torque will compromise the integrity of the bolt, and there is generally minimal incentive to use a smaller torque.

Effective tightening a bolt on a CF flange needs the right tools for the work. These tools are used for different applications. For instance, a torque wrench exerts tension to screws, nuts, and bolts to fasten two parts securely. They are used to avoid popular over-tightening or under-tightening, which can bring about costly fixes later on. To ensure you do the right torquing, follow the following procedure:

Modify the wrench to the recommended manufacturer listed setting. This entails; loosening the tightener at the end of the wrench’s handle, examining the dimensions on the wrench, setting the wrench in the correct setting, and locking the setting into the wrench.

Check Cleaning. Ensure the dirty or rusted threads are thoroughly cleaned before tightening the nuts.

Lubricate the Threads. For appropriate lubrication, ensure the fasteners are well lubricated, with lube present on every thread and a bead of lube oozing out of the bottom of the nut.

What is the Right Tightening Sequence?

When tightening bolts, High Vac Depot recommends you fix them in a row. This is because tightening them singly disorients the preload on other bolts in the group. However, caution should be taken to avoid over-tightening the bolts, thus causing a leak. The circular bolts are tightened in a crisscross way, while the non-circular bolts are tightened in a spiral tightening sequence. First, tighten the bolt partially, then crisscross to the next bolt while repeating the same procedure. After all, bolts are tightened partially, repeat the process to complete the tightening.

Effective Installation process

CF flanges are the perfect flange selection for Ultra-high vacuum (UHV) systems. However, for the UHV pressure to be maintained, a tight seal must be observed. For your system to operate efficiently, you must follow the correct installation guideline. High Vac Depot will offer installation services to suit all your technical needs. A successful installation process requires:

Observe Cleanliness

Check the flanges and the sealing surfaces to ensure they are free from dirt. There should be no dirt or scratches at the surface of the seal as they can interfere with the functioning of the vacuum seal.

Use Anti-Seize Lubricant

The use of anti-seize lubricant does not apply to all bolts. For instance, if you are using silver-plated bolts, avoid using this lubricant. If using other bolts, use the anti-seize lubricant to the threaded part of your bolts. Apply a small portion of coating on each bolt to safeguard the flange in corrosive environments.

Fix the Sealing Gasket

CF flanges have a sealing pair that possess a similar flange face, together with a knife-edged machine on the outside. Position a copper or Viton sealing against the knife edge of the fixed flange.

Line- Up the Bolt Holes and Place the Bolts

For complete placement of the bolts, ensure the bolt holes are properly lined-up. After that, put the bolts and include the washer to the nut on the inner side of the assembly. Use your hand to make sure all bolts are completely tightened.

Tighten the Bolts with a Wrench

Use a wrench to both the bolt head and the nut. Adjust the nuts slightly to tighten the bolts. To achieve the required torque pressure, continue with the slight tightening of the nuts.

In conclusion, as the fastening bolts are being screwed up, the flanges squeeze the gasket. The compression initiates pressure which forces the knife-edges of the two flanges into the gasket, forming a circular groove. The pressure pushes the gasket material to fill the microscopic imperfections on the sealing knife-edges, forming a vacuum-tight seal that can combat very high temperatures and low pressures. If you have any questions, please don’t hesitate to contact us!