The life of the bellows

The life of the bellows is the shortest working period or number of cycles that can guarantee normal operation when used under working conditions. The elastic sealing system composed of bellows often works under the conditions of variable load and large displacement with more cycles, so it is of great significance to determine the service life of the bellows. Because the function of the bellows is different, the requirements for its service life are also different.

(1) When the bellows is used to compensate for the positional deviation caused by installation in the pipeline system, only a few times are required for its life.

(2) The bellows is used in thermostatic controllers with high switching frequency, and its lifespan must reach 10,000 times to meet the use requirements.

(3) When the bellows is used as a vacuum seal for a vacuum switch, its lifespan must reach 30,000 times to ensure normal operation.

It can be seen from the above three use cases that due to different use conditions, the required service life of the bellows varies greatly. The life of the bellows is related to the fatigue characteristics of the selected material, and also depends on the residual stress of the formed bellows, the stress concentration 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.

During the working process of the bellows, its life span mainly depends on the maximum stress generated during the working process. In order to reduce the stress, it is generally achieved by reducing the working displacement of the bellows and reducing the working pressure. In the general design, it is stipulated that 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.

The test of the produced corrugated pipe proves that if the corrugated pipe works according to the above specifications, its service life can basically reach about 50,000 times.

According to the nature of the working pressure, the allowable displacement of the bellows is also different. Generally, when the bellows only bears axial load (tension or pressure), its allowable displacement can be selected between 10% and 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.

The application of multi-layer bellows can reduce the stress caused by stiffness and deformation, and thus can greatly improve the life of the bellows.

The service life of bellows will be different when working under the same conditions but different working pressure properties (constant or alternating load). Obviously, the life of the bellows is shorter when working under alternating load than when working under constant load.