Metal Bellows Information

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DescriptionHow to Select Metal Bellows


Metal bellows perform the function of sealing environments, carrying gases, liquids and slurry, mechanical coupling, and performing electrical contact amongst other things. They are durable and flexible when used within design specifications.  Metal bellows are cylindrical vessels readily compressible and extensible as a result of numerous annular convolutions. Suppliers of metal bellows can often provide assembly services.


Applications for metal bellows include:


  • Aerospace
  • Automotive
  • Chemical
  • Motion coupling
  • Fluid coupling
  • Electrical contacts
  • HVAC
  • High purity
  • Marine
  • Petrochemical
  • Semiconductor 


The most important specifications to consider when searching for metal bellows include:   


  • Inside diameter - Specifies the minimum inner diameter of the bellows.
  • Outside diameter - Specifies the minimum outer diameter of the bellows.
  • Free length - The unloaded length of the bellows along the convolutions.
  • Spring rate - The spring force that the bellows applies.
  • Profile or shape - Common profiles or shapes for metal bellows include round and square or rectangular.

Materials of Construction


Common materials of construction for metal bellows include:


  • Aluminum
  • Beryllium copper
  • Brass
  • Copper
  • Hastelloy
  • Inconel
  • Monel
  • Nickel
  • Phosphor bronze
  • Stainless steel
  • Steel
  • Tantalum
  • Titanium

Methods of Construction


Methods of construction for metal bellows can include:How to Select Metal Bellows


  • Electroforming - Electroformed bellows are made by depositing layers of metal, usually nickel based, on a mandrel of aluminum. When the desired thickness is reached the mandrel is melted away leaving behind the bellows.
  • Chemical deposition - Chemical deposition is a method of forming bellows by electro-depositing metal on a mandrel.
  • Mechanical forming - Mechanically formed bellows include both roll-formed and hydroformed types.
  • Welding - Welded bellows are a series of convoluted rings or washers, which are stacked on top of each other and welded on the inside and outside circumference.



Common features of metal bellows include:


  • Cryogenic rated - Cryogenic rated bellows are used in cryogenic systems to hand very low temperature gases.
  • Flange - A flange is a fitting used to attach the bellows to equipment or piping.
  • Hermetic sealing - Hermetic sealing on bellows is used in high and low pressure applications in either liquid or gaseous media.
  • Medically rated - Medically rated bellows are used in applications to insure a high degree of sanitation.
  • Necks - Necks are rigid tube-like lengths running from the end of the bellows.
  • Vacuum rated - Vacuum rated includes any vacuum application to very high vacuum. 


BS EN 14917 - Metal bellows expansion joints for pressure applications




Image Credits:


Senior Aerospace Metal Bellows | Technetics Group