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Bellows technology of the twentieth and twenty-first century is centered on metal bellows. These high-technology products bear little resemblance to the original leather bellows used traditionally in fireplaces and forges.
There are two types of metal bellows - formed and welded. Formed bellows are produced by a variety of processes, including mechanical forming and hydroforming. The welded bellows is manufactured by welding individual formed diaphragms. The pro and con comparison between the two (formed and welded) bellows generally centers around cost and performance. Formed bellows generally have a high tooling cost, but may have a lower piece price. However, the formed metal bellows has significantly lower performance characteristics. Welded metal bellows are produced with a lower tooling cost and maintain significantly higher performance characteristics. Another area of comparison is in metals of construction. The formed bellows is limited to metals with high elongation characteristics, whereas metal bellows may be fabricated from a wide variety of standard and exotic alloys, such as stainless steel and titanium, as well as other high-strength, corrosion-resistant materials. Welded bellows can be fabricated from a greater variety of exotic metals and alloys, whereas formed bellows are limited to alloys with good elongation – brass being a prime example. Welded bellows are not fabricated from brass because of its fundamentally poor weldability. Other advantages to welded bellows include compactness (higher performance in a smaller package), ability to be compressed to solid height with no damage, resistance to nicks and dents, and dramatically greater flexibility. The welding of metal bellows is a microscopic welding process, typically performed under laboratory conditions at high magnification. Welded metal bellows are used in a wide variety of products and marketplaces, including medical applications like implantable drug pumps, to industrial seals, sensors and actuators, to aerospace applications such as altitude sensors and fluid management devices (accumulators, surge arresters, volume compensators, and fluid storage). Welded metal bellows are also found in space applications, providing reservoirs with potable water as well as accumulators to collect wastewater.
