Structure and Types of Metal Bellows
Release date:
2018-10-23
The performance of a metal bellows depends on its structure; different structures exhibit distinct characteristics, which are reflected in the wave profile—defined as the pattern and shape of the corrugations when viewed in axial cross‑section. Bellows typically feature U‑shaped, C‑shaped, Ω‑shaped, or S‑shaped waveforms. To enhance pressure‑bearing capacity and reduce stiffness, multi‑layer bellows and bellows equipped with reinforcing rings have been developed.
In general, a circular‑ring cross‑section offers superior resistance to high pressures but permits only limited allowable displacement. A U‑shaped cross‑section allows for greater displacement at the expense of relatively lower pressure‑bearing capacity. Under typical conditions, the U‑type corrugation is the most widely used configuration domestically. When subjected to elevated operating pressures and substantial displacements, a multi‑layer U‑type corrugated structure is employed. C‑type bellows exhibit high stiffness, poor sensitivity, and significant nonlinear errors; they are generally used as sealing or isolation elements or as flexible couplings. Ω‑type and S‑type bellows are primarily suited for applications involving high operating pressures and small working displacements, such as sealing and isolation components in high‑pressure valves.
End-structure types of metal bellows
The end structures of the connection sections at both ends of the bellows comprise five basic types:
(1) Internal coordination is denoted by N.
(2) External coordination is denoted by W.
(3) The closed bottom is denoted by D.
(4) No straight-wall section is cut at the wave crest using a QD gauge.
(5) The absence of a straight-wall segment at the wave trough is denoted by Qd.
The end structures of the bellows can be formed by any combination of the five aforementioned configurations, yielding 14 distinct structural variants for a given type of bellows.
The two ends of the bellows must be welded to the mating components. For brass, tin bronze, and beryllium bronze, brazing or silver soldering is recommended; for stainless steel and materials such as Inconel 718, welding methods like GTAW, roll welding, and electron beam welding may be employed. The end‑structure of the bellows significantly influences its formability; among these, the W‑type configuration offers superior processability and is therefore preferred. By contrast, the N‑type configuration exhibits poorer formability, so its diameter D1 and length L1 should be selected in accordance with relevant standards and product catalogs—random selection is not advisable. If D1 and L1 are chosen too large, the bellows is prone to cracking at these locations during the forming process.
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