Posts Tagged ‘Bellows’

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.

Cost Effective Metal Bellows Expansion Joint Solutions

Cost Effective Metal Bellows Expansion Joint Solutions

Metal expansion joints are often called by the somewhat misleading name of metal bellows, as expansion joints are completely unlike the old leather bellows that were used to pump air into a fireplace, furnace, or kiln. The resemblance shared between metal bellows and the leather variety is only slight, in that they are both sealed chambers that expand and contract along concertinaed folds in the sides. While the term “metal bellows” may be used interchangeably with metal expansion joints, bellows is usually reserved for reference to a vessel, bladder, or irregular shape that collapses when it empties, while expansion joints are used as a junction in a pipeline.
Metal expansion joints are a concertinaed in-line junction piece included in many liquid and high-pressure gas pipeline systems for a variety of reasons. When most pipelines are built, it is not uncommon for there to be sections where two pipe sections do not meet perfectly. An expansion joint allows for some shear, an imprecise gap, or a slight curve at a junction, or in other words, lateral, axial, and angular movement is allowed to occur at the join. Any significant twisting of the line at an expansion joint will cause the bellows to fail, and even slight torsion on a metal expansion joint will severely reduce its effectiveness.
Welded metal bellows have many applications in medicine, heavy industry, defense, aviation and aerospace. They are frequently used in internal medical implants, in fluid sensors, actuators, altitude sensors, pressure surge arrestors, and for waste fluid storage. Their collapsible design makes them ideal for applications where space is critical, such as on the space shuttles and International Space Station.
Expansion joints are designed to limit vibration, noise, movement from heat expansion and contraction, and pressure undulation (a common example is “water-hammer” in the pipes of an old house) in pressurized lines. Proper installation of expansion joints allows you to manage where any movement in the system occurs, preventing damage or movement to the rest of the system by forcing it to occur at the join.
Metal expansion joints can be required to operate under very extreme conditions particularly when deployed in boiler seals or aircraft, from temperatures ranging between -200 degree Celsius (less than -300 degree Fahrenheit) and 1300 degree Celsius (2500 degree Fahrenheit), and at pressures ranging between the near total vacuum of space to over 2000 pounds, and the precision required of this equipment necessitates stringent testing before deployment in many systems.
In order to prevent undue strains being placed on expansion joints, manufacturers have developed several different support structures that can be deployed on a pipeline increasing the effectiveness of a given bellows. Some bellows are fitted with internal liners or external sheaths to prevent damage to the main assembly, and external tie-rods or a universal joint called a gimbals is fitted in some applications to prevent twisting, or excessive movement in any direction beyond design limitations.
As metal expansion joins are often deployed in highly critical applications, rigorous Quality Assurance (QA) testing is often required of each individual unit after manufacture before it is deployed. Production shops may subject a finished unit to radiography, ultrasound, mass spectrometry, magnetic, hydrostatic, helium leak, and liquid penetration testing to guarantee that the unit does not contain any adverse anomalies or microscopic leaks. It is also possible to test the hardness, impact resistance, pressure limit, and positive composition of a finished product.
Only a few of the firms who manufacture metal expansion joint systems are able to deliver tailored, non-standard solutions, however, it is not unheard of to find box-shaped or toroidal metal belows deployed for some applications, as well as tailored, irregular shapes for very specific uses.
Metal bellows and metal expansion joint assemblies are manufactured with advanced techniques to precise requirements, and must frequently undergo stringent testing before deployment in the very extreme, critical applications they are used for. The skilled tradesmen who build these systems need years of experience, requiring well-honed skills and years of experience and certification. This is a field that continues to advance with science, ensuring that only cutting-edge manufacturers are able to stay competitive for the high-tech industries they serve.

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.