Design and Selection of Metal Bellows
Release date:
2018-10-23
Basis for the Design and Selection of Metal Bellows
In bellows applications, the specified operating conditions of the system (the complete machine) or the subsystem (the component) serve as the primary basis for bellows design and selection. Typically, the following design parameters are provided:
(1) Maximum spatial dimension or nominal diameter
(2) Nature and magnitude of the working load
(3) Working displacement amount
(4) Operating Temperature Range
(5) Properties of the working medium
(6) Accuracy Requirements
(7) Service Life
Content and Principles for the Design and Selection of Metal Bellows
The primary tasks of bellows design and selection are to choose the bellows material, structural configuration, geometric dimensions, and performance parameters based on the system’s specified operating conditions. During the selection process, it is essential to meet the system’s functional requirements while striving for an advanced and rational structural design, and, where feasible, to implement optimized design solutions. Experience has shown that proper bellows design and selection are critical; even if the manufactured bellows exhibit superior quality, inadequate design and selection will still fail to satisfy the intended service requirements.
1. Material Selection
Based on the known conditions—such as the bellows’ intended application, the type and magnitude of the applied load, precision requirements, service medium, operating temperature, and service life—and taking into account the material’s formability and weldability, select an appropriate material. Material selection should also consider its market availability.
2. Determine the structural configuration
(1) Select the corrugation shape
The appropriate corrugation profile should be selected based on factors such as the bellows’ intended application, performance requirements, operating conditions, and the characteristics and manufacturing considerations of various waveforms. In most cases, U‑shaped corrugations are the preferred choice.
(2) Determine the number of corrugated layers
The number of layers in a bellows is determined based on factors such as its intended application, operating pressure, stiffness, and the working medium. When subjected to high operating pressures, multi‑layer bellows are typically selected; for such bellows, it is essential to appropriately specify both the number of layers and the wall thickness of each individual layer.
(3) Preliminary assessment of whether to use in conjunction with other elastic components.
In some cases, bellows are used in parallel with helical springs; these situations include: improving measurement accuracy, operating under relatively high pressures, and encountering impact loads.
(4) Select the structural configuration of the end fittings at both ends of the bellows.
When selecting the structural configuration of the two ends of a bellows, it is necessary to consider the forming and welding processes for each end, as well as the structural constraints imposed on the entire system.
(5) Consider whether a guiding device is required.
When the bellows has a relatively long effective length, to prevent column buckling during operation, it is advisable to incorporate guiding devices. For example, bellows used in valves are typically equipped with such guiding mechanisms.
(6) Consider whether a reinforcing ring is required.
To meet the demands of higher operating pressures, bellows can be reinforced with stiffening rings, constructed as a multi‑layer structure, or employ a combination of both approaches. Stiffening rings provide localized reinforcement, while multi‑layer structures offer integral reinforcement.
3. Design Calculations and Selection of Structural Parameters for Bellows
The performance of a bellows depends on its structural design. The primary structural parameters of a bellows include the inner diameter, outer diameter, wall thickness, corrugation pitch, corrugation height, number of corrugations, number of layers, dimensions of the end‑fitting sections, as well as the effective length and overall length. In most cases, users should select bellows from relevant standards or product catalogs provided by manufacturers, rather than designing new products. This approach helps minimize development‑related issues while reducing manufacturing costs and shortening the production cycle.
4. Design and Calculation of Performance Parameters for Bellows
After the principal geometric dimensions of the bellows have been determined through design calculations or preliminary selection, the performance parameters of the bellows are then designed and calculated. If the bellows’ performance parameters fail to meet the technical requirements, its geometric dimensions should be appropriately adjusted. Since bellows serve different purposes, their technical requirements vary; accordingly, the design process must adopt tailored methods based on these specific demands. For bellows used in measurement applications, the primary requirements typically include stiffness, strength, and elastic characteristics. Although various bellows with different geometries and dimensional parameters may all satisfy the same stiffness requirement, the stress levels they experience can differ significantly. A design that not only meets the stiffness criterion but also minimizes operating stresses is considered optimal. Reducing stress not only enhances the safety factor but also diminishes the influence of material elasticity on hysteresis, creep, fatigue, and other phenomena, thereby improving the bellows’ accuracy and operational reliability.
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