Metal bellows design (3)


life The life of the bellows is the shortest working pe […]

The life of the bellows is the shortest working period or the number of cycles that can ensure normal operation when used under working conditions. The elastic sealing system composed of bellows often works under the condition of withstanding a large number of cycles of variable load and large displacement, so it is of great significance to determine the service life of the bellows. Because the role of the bellows is different, the requirements on its service life are also different.
(1) When the corrugated pipe is used to compensate the position deviation caused by installation in the pipeline system, only a few times is required for its service life.
(2) Bellows are used in thermostatic controllers with high switching frequency, and their service life must reach 10,000 times to meet the requirements of use.
(3) When the bellows is used as a vacuum switch as a vacuum seal, its service life must reach 30,000 times to ensure normal operation.
It can be seen from the above three usage examples that due to the different usage conditions, the required service life of the bellows varies greatly. The life of the bellows is related to the fatigue characteristics of the selected materials, but also depends on the residual stress of the formed bellows, the concentration of stress and the surface quality of the bellows. In addition, the service life is related to the working conditions of the bellows. For example: displacement, pressure, temperature, working medium, vibration conditions, frequency range, impact conditions, etc. of the bellows during operation.
The working life of the bellows depends on the maximum stress generated during the working process. In order to reduce stress, it is generally achieved by reducing the working displacement of the bellows and lowering the working pressure. In the general design, the working displacement of the bellows should be less than half of its allowable displacement, and its working pressure should be less than half of the pressure resistance of the bellows.
Tests on the produced bellows prove that if the bellows work according to the above specifications, its basic service life can reach about 50,000 times.
Depending on the nature of the working pressure, the allowable displacement of the bellows is also different. Generally, when the bellows only bears an axial load (tension or pressure), its allowable displacement can be selected from 10% to 40% of the effective length of the bellows When the bellows is subjected to lateral concentrated force, torsional moment or comprehensive force, the allowable displacement of the bellows should be appropriately reduced.
Application of multi-layer bellows can reduce the stress caused by rigidity and deformation, and thus can greatly improve the life of bellows.
When the bellows are operated under the same conditions but with different working pressure properties (constant or alternating load), their service life will be different. Obviously, when working under alternating loads, the life of the bellows is shorter than when working under constant loads.

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