Metal bellows are versatile and a key enabling technology for a wide range of engineering applications. They play an essential role in controlling motion, vacuum, and pressure. Numerous industry sectors use metal bellows in a broad array of machine assemblies and components.
Being flexible, spring-like, and precision-engineered components, metal bellows are typically custom-designed, performing a variety of engineering functions. Metal bellows can convert temperature, mechanical, and pressure changes to linear or rotational motion. Flexible electronic applications can also use them.
Although the metal bellow is only a small part within the overall machine assembly, the role it plays is a critical one in the overall functionality of the system. While elegantly addressing a number of engineering challenges, a range of applications uses the bellow. These include—mechanical test stands, agriculture, solar power, semiconductor, ultra-high vacuum, cryogenic, military and defense, oil and gas service, aerospace, instrumentation, and industrial automation.
As part of the larger machine component or assembly, bellows generate a specifically defined dynamic response. In some cases, this provides a more precise, more reliable, and less expensive alternative to a more complex engineering solution.
With advanced manufacturing techniques, designers can engineer metal bellows with precision and manufacture them with extremely small dimension. Several engineering applications benefit from using metal bellows and different engineering scenarios demonstrate their broad functionality.
Sensitive military and aerospace applications use the highly reliable metal bellows as mechanical backups for their mission-critical electronic systems.
Form and Function
A metal bellow has the physical form of a spring-like accordion, and is flexible and lightweight. Manufacturers fabricate bellows as a part of a leak-tight sealed assembly, having appropriate ends for allowing connections within the equipment. In both vacuum and pressure applications, the bellows appears as a ribbed or corrugated tubing.
The bellows can function like a spring for many engineering applications. However, when filled with a pressurized gas or liquid, or in conditions of vacuum, the bellows displays extreme sensitivity to various forces such as temperature and pressure changes affecting the hydraulic gas or fluid sealed within or outside the bellows. Knowing the coefficient of expansion of the gas or fluid, the designer can fashion the bellows to provide a dynamic and predictable mechanical response against these forces.
Sealed metal bellows, filled with a known silicone-based fluid, will extend or compress with temperature changes. This happens as the fluid inside experiences volume changes, in response to falling or rising temperature. The change in fluid volume translates into a linear movement of the bellows, producing a predictable response. Used within a machine assembly, the bellows provides precision positioning.
The advantage with thin-walled bellows is they remain flexible even under cryogenic conditions, suffering no compromise in their stroke. Since bellows retain their integrity and do not crack even at such low temperatures, they are very reliable for coupling, offset, rotation, extension, and compression capabilities. For instance, they are used reliably for pumping liquid nitrogen, liquid helium, and liquid oxygen in space valve applications.
The thermal expansion of the concealed fluid allows metal bellows to be used as indicators of temperature and pressure. Missile technology and navigation make use of metal bellows where low-temperature operations are critical. Astronomy applications use bellows for positioning mirrors precisely.