The Structure and kinds of metal bellows
The previous posts as below:
4, The structure and varieties of metal bellows( Updated 9th, April, 2020）
5, The Application of Metal Bellows ( to be Updated 15th, April, 2020）
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The structure and kinds of metal bellows
The performance of the metal bellows depends on its structure. Different structures have different performances, and different structures are reflected in the waveform. So What is metal bellows’ waveform? The waveforms of bellows are the form and shape after being axial cut. Generally, there are 3 kinds of waveforms, there are U-shaped C-shaped, Ω-shaped and S-shaped. In order to improve the pressure-bearing capacity and reduce the rigidity, there upgrade the multi-layer bellows and bellows with reinforced rings. The waveforms and characteristics of various bellows are shown in the table below.
In a word, the ability to withstand the high pressure of the circular cross-section is superior, but the allowable displacement is small. The U-shaped cross-section allows a large displacement but a relatively low-pressure capacity. General, the common application of waveforms in China is U-shaped. Under the conditions of withstanding high working pressure and large displacement, then choose multi-layer U-shaped structure. C-shaped metal bellows have high stiffness, poor sensitivity, and large non-linear errors. They are generally used as sealed isolation components or flexible couplings. Ω-shape and S-shape metal bellows are mainly used in applications where the working pressure is high and the working displacement is small, for example, it is used as a sealing and isolating component on high-pressure valves.
There are 5 basic structural forms of the connection parts of the two ends of the bellows:
（1） N-Inner match
（2） W-Out match
（3） D-Closed bottom
（4） QD-Straight wall section is not cut off at the crest
（5）Qd- No straight wall segment cut off at the trough expressed by Qd
The structure of the two ends of the bellows is arbitrarily combined by the above five structures, and the same kind of bellows can be combined into 14 structures as picture show:
The connected parts need to be welded with both ends of bellows. Brass, tin bronze and beryllium bronze need to be brazed or silver brazed; Stainless steel and Inconel 718 and other materials need to be argon arc welded, roll welded and EBW( Electron Beam Welding）. The connected parts’ structure of the bellows affects the forming process of the bellows. Among them, the W-shaped structure has the best manufacturability, and it is highly recommended. The N-shape structure has poor manufacturability, and its diameter D1 and L1 length are best selected according to relevant standards and current samples. If D1 and L1 sizes are too large, the bellows will be broken here when forming process.