Metal Bellows for Industrial Applications

By: Anna Woodward

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.

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