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.

The most important specifications to consider when searching for metal bellows include inside diameter, outside diameter, free length, and spring rate.  The inside diameter specifies the minimum inner diameter of the bellows.  The outside diameter specifies the minimum outer diameter of the bellows.  The free length is the unloaded length of the bellows along the convolutions.  The spring rate is the spring force that the bellows applies.  Common materials of construction for metal bellows include aluminum, beryllium copper, brass, copper, Hastelloy, Inconel, Monel, nickel, phosphor bronze, stainless steel, steel, tantalum, and titanium.  Methods of construction for metal bellows can be electroforming, chemical deposition, mechanical forming, and welding.  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 is a method of forming bellows by electro-depositing metal on a mandrel.  Mechanically formed bellows include both roll-formed and hydroformed types.  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.

Other important parameters to consider include profile or shape of the bellows, applications, and features.  Common profiles or shapes for metal bellows include round and square or rectangular.  Applications include aerospace, automotive, chemical, motion coupling, fluid coupling, electrical contacts, HVAC, high purity, marine, petrochemical, and semiconductor.  Common features of metal bellows include cryogenic rated, flange, hermetic sealing, medically rated, necks, and vacuum rated.  Cryogenic rated bellows are used in cryogenic systems to handle very low temperature gases.  A flange is a fitting used to attach the bellows to equipment or piping.  Hermetic sealing on bellows is used in high and low pressure applications in either liquid or gaseous media.  Medically rated bellows are used in applications to insure a high degree of sanitation.  Necks are rigid tube-like lengths running from the end of the bellows.  Vacuum rated includes any vacuum application to very high vacuum.  Suppliers of metal bellows can often provide assembly services.

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