In the application of metal bellows, the given conditions of the system (whole machine) or subsystem (components) are the main basis for the design and selection of bellows. Generally speaking, the design conditions are as follows:
- (1) Maximum space size or path
- (2) The nature and size of work load.
- (3) Work displacement
- (4) Working temperature range
- (5) The nature of working medium
- (6) Accuracy requirements
- (7) Contents and principles of design and selection of metal bellows for service life. The main contents of design and selection of bellows are: selection of bellows materials, structural penalties, geometric dimensions and performance parameters according to known conditions given by the system.
In the process of choosing the bellows, we should fully meet the requirements of the system for bellows, and strive to achieve advanced and reasonable structure. Practice has proved that the design and selection of bellows is very important, if the design and selection is unreasonable, the quality of bellows manufacturing can not meet the use requirements.
1. Material selection according to the use of bellows, load type and size, precision requirements, working medium, working temperature and service life of known conditions, and consider the formation of materials and welding process. Choose a suitable material. Material selection should also consider its market sources.
2. determine the structure type.
- (1) Choosing the shape of the metal bellows is based on the usage, performance, use requirements, performance and manufacturing characteristics of various waveforms and other factors to choose a more reasonable shape of the bellows. In general, most of them choose U type corrugation.
- (2) Determine the number of bellows according to the use of bellows, working pressure, stiffness, working medium and other factors to determine the number of bellows. In the case of high working pressure, the multi-layer structure bellows are generally selected. For multi-layer bellows, the number of layers and the thickness of single layer should be reasonably selected.
- (3) Preliminary evaluation of whether the bellows should be used in parallel with other elastic elements in some cases, these are: in order to improve the measuring accuracy; in the case of higher working pressure; in the case of impact load. (4) Choosing the structure type of the two ends of the bellows and choosing the structure type of the two ends of the bellows, we should consider the forming process, welding process of the two ends of the bellows and the structural limitations of the whole system.
- (5) Considering whether the guide device is needed, when the effective length of bellows is relatively long, in order to avoid columnar instability in the working process, the guide device should be added. For example, bellows are usually equipped with guiding devices.
- (6) Considering whether it is necessary to use a reinforcing ring in order to meet the requirements of higher working pressure, bellows can be strengthened with reinforcing rings, or multi-layer structures, or the combination of the two structures can be applied. The strengthening ring is strengthened locally, and the multi-storey structure is strengthened as a whole.
3. The performance of the metal bellows depends on the structure of the bellows. The main structural parameters of the bellows include the inner diameter, outer diameter, wall thickness, wave distance, wave thickness, wave number, layers, the size of the two ends and the effective length and total length. In general, bellows users should select bellows from the relevant standards and manufacturing unit’s product samples, rather than designing new products. In this way, the problems in the development can be reduced to the minimum and the manufacturing cost can be reduced and the manufacturing cycle shortened.
4. The performance parameters of the bellows are designed and calculated after the main structural dimension parameters of the bellows are determined by design calculation or selection. If the performance parameters of bellows can not meet the technical requirements, the geometric parameters of bellows should be corrected appropriately. Corrugated pipes have different uses and different technical requirements. Corresponding design methods should be worked out according to different requirements.
The metal bellows usually used for measurement are stiffness, strength and elasticity. Although many kinds of bellows with different geometry and size parameters can meet the same stiffness requirements, the stress values produced in these bellows are different. Those which can meet the requirements of stiffness and the minimum stress generated during working are the most reasonable ones. The reduction of stress not only improves the safety factor, but also reduces the effect of material elasticity on hysteresis, aftereffect and fatigue, thus improving the accuracy and reliability of bellows.
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Source: China Stainless Steel Bellows Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)