Due to its dependability and variety of applications, edge-welded metal bellows mechanical seals have cemented a reputation in the fluid sealing industry today.

Bellows seals offer solutions to frequent problems like significant applications or serious problems with pump alignment in a variety of sectors. This article discusses the Things to Know before Selecting Welded Metal Bellows Seals for Your Application. So, let's get started.

Things to Know Before Selecting Welded Metal Bellows Seals for Your Application

The following are seven Things to Know before Selecting Welded Metal Bellows Seals for Your Application:

Plate shape

Flexing, stroke, and operating length are all impacted by plate shape. The bellows' plates are all similar and shaped to allow nesting when compressed in a nesting-ripple arrangement.

Additionally, contouring increases resistance to intense pressure. Additionally, more efficient at attaining maximum flexing, long (axial motion) stroke with small operating lengths, and a low spring rate is the nesting-ripple plate design. 

The sweep radius is set to 20–25% of the span to prevent the phenomena known as oil canning, which causes the plate to bulge inward and outward as it is compressed, much like the bottom of an oil can. The male and female plates that make up each convolution allow for the design of the seal to have a small axial gap.

Also Read: SECRETS OF SELECTING THE RIGHT METAL BELLOWS EXPANSION JOINT

Angle

Less reliable weld joints are caused by the heterogeneity of the micro-structure in the heat-affected zones for bellows with straight flat segments. It has been demonstrated through theoretical analysis utilizing the linear, thin-shell theory that tilting the bellows axis significantly lowers stress at the welds and heat-affected zones. 

According to the research, bending stresses predominate near the welds. Still, these bending stresses are reduced as the tilt angle increases. This design idea has also been carefully examined in theoretical and empirical investigations carried out by a non-government organization and empirically validated. 

Bending loads are diverted away from the weld heat-affected zone by a 45° tilt angle. Plate stiffness is the outcome, and this raises dependability and lowers fatigue.

Weld integrity

The bellows must be made using cutting-edge manufacturing techniques to assure weld integrity by minimizing excessive root gaps with bead geometry, bead thickness, and roll-over control. 

Make sure the bellows units are vacuum-tested to 10-6 Torr and examined with helium mass spectrometry for leak-tight performance. Helium mass spectrometry evacuates the seal inside and covers it with helium. The seal is instantly rejected if any traces of gas are detected after they have entered through a weld crack or a material fault.

Plate width

Thin plates offer lower spring rates, and as a result, face loads, unit loading, heat production, and seal life are all reduced. Bellows plates that are thicker have greater spring rates and are more prone to metal fatigue. Repeated plastic deformation of the plates during deflection can cause fatigue and significantly shorten seal life. 

Although it is simpler to weld thicker plates, doing so greatly increases the bellows' spring rate and toughness. Due to the significant differences in sealing face loading with only minor changes in seal operating duration, a high spring rate is not acceptable. Due to the increased closing force caused by this, the lubricating film that covers the sealing faces is lost, the sealing faces get overheated, and finally, the seal fails. 

This is particularly important in hot and poorly lubricated conditions. High spring rates further reduce the ability of the bellows to compensate for installation issues, shaft movements, impeller adjustments, pump end play, shaft expansion from heat, and progressive abrasion of the sealing faces. Many producers are compelled to employ bigger plates because thinner plates are more challenging to produce.

Controlling vibrations

Not all bellows used in the industry are equipped with vibration dampeners, which assist in guarding against injury from harmonic vibration brought on by dry-running episodes. A vibration dampener, however, is perfect. The vibration dampener pad is a built-in design element in some seal designs that enables protection against potentially harmful vibrations when necessary.

Also Read: How does an externally pressurized expansion joint work?

Double-Ply Bellows

Bellows with two plies add strength and flexibility without adding thickness. Double-ply bellows are frequently employed in higher-pressure applications and in situations where extra start-up torque strength may be needed, such as when the fluid is thermo sensitive or has a tendency to build up and solidify on the seal faces. 

The leaf springs used in light automobile vehicles and trailers are similar to the double-ply design basis. A spring that was made of a single, sturdy metal piece with the strength required to hold the weight would be far too stiff. 

However, the spring rate is well within the required bounds when the strength is produced by utilizing a "stack" of discrete, independently flexing thin leaf parts. Comparatively to single-ply bellows with twice the plate thickness, two-ply bellows' spring rates turned out to be much lower.

Seal and pressure balance

Prior to specifying a metal bellows seal, you must ascertain the appropriate pressure rating needed by your application in relation to temperature, speed, and sealed fluid lubricity. You should also ascertain whether the seal can withstand reverse pressure, particularly in dual-pressurized seal arrangements. The majority of common bellows seals are normally balanced at about a 70/30 ratio. 

The effective diameter is exceeded by 70% of the facial contact area, according to this. Bellows seals that are 50% balanced have recently been developed to withstand pressure in both the inner and outer diameters (ID and OD). Reverse pressure, a problem that might upset dual seal operation, can be handled using fifty-fifty balanced seals.

Conclusion

As the usage of several cutting-edge sealing technologies, including high-temperature-, non-contacting gas-lubricated-, and corrosion-resistant seals, grows, the installation of welded metal bellow seals, a core sealing technology, has increased significantly. This is crucial for the chemical and oil sectors because significant temperature swings make it difficult to move liquid from one location to another. 

The wide range of operating temperatures offered by edge-welded metal bellow seals is a key benefit and a characteristic that makes them useful in several sectors. 

If you are also thinking of buying welded metal bellow seals for your application, it is best to try metal bellows from Flexpert bellows. They are one of the leading expansion bellows manufacturers in India.

As a reliable metal bellows manufacturer In India, they deal in high-quality Metal Bellows, expansion bellows, flexible bellows, Multiply metal bellows, stainless steel metal bellows, Engine exhaust bellows, High-temperature stainless steel bellows, and Flexible metal bellows. Do check out their official website to know more.