Posts Tagged ‘Applications’

Metal Bellows for Industrial Applications

Metal Bellows for Industrial Applications

When you think of the word “bellows” you probably have a picture in your mind of the leather bellow historically used to blow air into their fireplace. However, there is another kind of bellow, a metal bellows, which is a high-technology product used in machinery, medical and industrial applications. Metal bellows are manufactured and sold by companies specializing in metal expansion joints and other piping systems. Some bellows are microscopically small while others are very large.

Simply stated, metal bellows are thin-walled flexible elements which allow for expansion in a system of pipes, while at the same time containing gasses and liquids in a pressure-filled environment. A metal bellow is also commonly referred to by the names: flexible metal element, element, corrugations, and compensator.

Each metal bellow is made by taking into account its pitch, convolution height, thickness, number of plies, convoluted length, skirt length, and inside diameter. Every metal bellows has a unique working pressure, life cycle, and spring rate which are entirely dependent on their shape and the material in which they are made of. These considerations, and some specific mathematical formulas, insure that a metal bellow meets the standards set by the Expansion Joint Manufacturers Association. The EJMA specifications exist to make sure that a metal bellow is able to perform under the specifications it claims to. This is for both productivity and safety.

There are generally two different types of metal bellow available on the market today. These two types of bellows are formed and welded. Let’s look a bit at each of them:

Formed Bellows – A formed metal bellows is manufactured by one of two processes.

These processes are mechanical forming, and hydroforming. Formed bellows are generally more expensive for a custom bellows than if it were welded. The higher cost is due to the tooling required to produce the original form. However, once the original form has been created then the subsequent bellow can be produced at a lower cost than individually welded bellow.

Formed bellow must be made of metals which have high elongation characteristics. For this reason, most formed bellow are made of brass. Formed bellows generally are used in applications where a lower performance is acceptable. Formed metal bellows are also generally larger than those which are individually welded.

Welded Bellows – A welded metal bellows is manufactured by welding individual formed diaphragms to each other. A welded bellows can be fabricated in many shapes and sizes and is generally a higher performance option than a formed bellows.

Welded bellow can be made of any metal or alloy which can be welded. Generally, materials such as stainless steel, titanium, and other non-corrosive materials are used to fabricate welded bellows.

Formed metal bellow generally are used in larger applications such as HVAC, and large piping systems. Welded bellows are generally very small and have to be manufactured in laboratories using high levels of magnification. Welded bellows are generally used in medical and aerospace applications.

As you can see there are many metal bellows available to fit many needs. Bellows are available from companies who fabricate metal expansion joints.

Metal Bellows for Critical Industrial Applications

Metal Bellows for Critical Industrial Applications

I built my first bellows 35 years ago from leather and wood. My father was a union sheet-metal man and enjoyed building small projects. Metal bellows for industry generally serve a different purpose than that one, even though they function the same. Still….there are metal bellows pumps that work in some very critical applications in industry.
Bellows, in general, enclose and seal the interior of the space yet allow for movement. They provide a hermetic, all-metal, pressure barrier and seal that flexes various directions.
In air ducting for buildings, often the air handling system will vibrate, and in order to avoid transmitting the vibrations to the rest of the system, bellows are used to reduce the vibrations. Metal bellows will often allow for alignment of one end of a plenum or air duct after the system is built. They are highly resistant to cocking as compared to mechanical seals with o-rings.
Sometimes expansion is expected due to changing temperatures, so a bellows is installed to allow for expansion without stressing the joints or connections. That is the most common use; allowing one section of a material handling system to move without causing stress to the mounting brackets. Over time, movement will tear at any strongly fastened joints and holes can develop.
Stress at joints is a major problem with highly engineered structures. Recently a vehicle bridge collapsed in Minnesota, and the cause might just be stress that built up over time and eventually the joints failed. Metal bellows serve to eliminate or reduce stress in various structures in your liquid or air handling systems.
Bellows are considered an expansion joint, and their design is often covered by standards set forth by the Expansion Joint Manufacturers Association. EJMA specifications are standards used to design a proper part that will perform to the specifications called for. This is both for safety and performance reasons. The amount of pressure that the system will contain is part of the system of specs.
There are generally two different methods of producing metal bellows. Some smaller bellows are formed on a machine that mass produces the parts on a large scale.
If you have any gas appliances in your home there is likely a section of formed bellows where the gas attaches to your appliances. This flexible piping contains the gas inside, allows for easy alignment, and most importantly, reduces stress at the connection points.
When containing flammable gasses in your home, reducing long term stress is a critical safety measure. Formed metal bellows are also used in larger applications such as HVAC, and large piping systems.
On the other end there are welded bellows that may need a custom fabrication for each situation. With this method, each piece, called a diaphragm, of the bellows is custom cut and welded into the bellows needed for a particular situation. This can be made from any metal able to be welded, but generally, non-corroding materials are used.
Obviously, this is a much more expensive process and has many applications in medicine, heavy industry, defense, aviation and aerospace.
Metal bellows are manufactured and sold by companies specializing in metal expansion joints and other piping systems. These couplings have proven to be versatile and to satisfy a variety of applications. They allow you to control fluid movement and containment in your system under a wide variety of pressures, thermal expansion and contraction, pulsations, vibration, equipment movement and convoluted routing requirements.