Metal bellows are elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape, as long as the materials have not been pushed past their max strength. Bellows sealed valves are commonly used to reduce the leakage that creates emissions in the pipelines of chemical plants. The welded bellow and the formed bellow are the two main types of bellow sealed valves.
A welded metal bellows is a zero leakage dynamic seal with the ability of a large range of motion. The metal bellows is manufactured from sheet stock. The material of construction may be stainless steel, high nickel alloys, titanium or other alloys to suit the application requirements. The material thickness may range from 0.001” to 0.025” thick.
Formed bellows are produced by reworking tubes. This is normally done by deep drawing, with a variety of processes, including electroforming and hydroforming.
Hydroformed bellows normally have a high tooling cost. When produced in bulk they may have a lower price point. The hydroformed bellows have lower performance characteristics due to relatively thick walls and high stiffness with less room for stretch expansion.
Electroformed bellows are made by plating or electroforming, a metal layer onto a model while subsequently removing the mandrel. The electroformed bellows may be made with modest production costs and with thin walls (25 micrometers or less). This provides bellows with high sensitivity and precision in many exacting applications.
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