Design method of corrugated pipe produced by Krah machine

With the wide application of the bellows produced by the Krah machine, people have carried out a lot of analysis, research, and experimental verification on the stress of the bellows of the Krah machine, and put forward many calculation formulas, calculation procedures, and diagrams for engineering design. However, some methods are inconvenient to use due to the Krah machine's bellows diagrams or procedures, and in some methods, the Krah machine's bellows assumptions are either too simplified or too ideal. It is difficult to ensure safe and reliable use. Many methods fail to work. Therefore, few methods truly meet the practical requirements of the Krah machine's bellows. The commonly used Krah machine bellows methods are as follows.

Here is the content list:

l A numerical method to calculate the stress of bellows

l US EJMA stress calculation method

A numerical method to calculate the stress of bellows

Assuming that all corrugations of the Krah machine's bellows are under the same conditions, only a single half-wave of the Krah machine's bellows is studied in the calculation. In this way, the Krah machine's corrugated pipe end corrugation is not considered in the study, although the boundary conditions of the Krah machine's corrugated pipe end corrugation are different from the middle corrugation. The numerical method is based on E. Lesnell solved the non-linear equations listed when the Krah machine's bellows with variable wall thickness revolving thin shell produced axially symmetric deformation.In the Lesnell equation, the general assumptions of the thin shell theory are applied, including the assumption that the thickness is small compared with the principal radius of curvature of the toroidal shell; the assumption that the material is uniform, and isotropic. Using the above assumptions will also bring certain errors to the calculations. Because when manufacturing Krah machine's bellows, the rolling and deep drawing of Krah machine's bellows tube blank and subsequent Krah machine's corrugated plastic forming will cause anisotropy and non-uniformity in the mechanical properties of materials.

US EJMA stress calculation method

Calculation of the effective area of the Krah machine's bellows

Effective area is one of the basic performance parameters of the Krah machine's bellows. It represents the ability of the Krah machine's bellows to convert pressure into concentrated force. When the Krah machine's bellows are used to convert pressure into concentrated force output, the effective area is an important parameter.

When the Krah machine's bellows are used in force-balanced instruments, the stability of its effective area will directly affect the accuracy of the instruments. Therefore, on this occasion, not only is the Krah machine's corrugated pipe required to have a reasonably effective area but also the effective area is required not to change with the working conditions during the working process.

1. The concept of effective area and the change of effective area

The effective area of the Krah machine's bellows is equivalent, and the Krah machine's bellows pressure will produce an equal axial force on this area. Under normal circumstances, with the increase of internal pressure, the effective area of the Krah machine's bellows becomes smaller, and with the increase of external pressure, the effective area becomes larger.

2. The volume effective area of the Krah machine's bellows

Under the action of external force or pressure difference of the Krah machine's bellows, the ratio of the volume change of the Krah machine's bellows to the corresponding effective length change is called the effective volume area.

3. Calculation of the effective area of the Krah machine's bellows

The requirements for the effective area of the Krah machine's bellows and its calculation method depend on the use of the Krah machine's bellows. If the Krah machine's bellows are used as elastic seals or pipeline thermal compensation, the effective area is only used to calculate the axial force when the Krah machine's bellows are formed and the thrust in the use system. There is a sharp difference between the calculated effective area of the Krah machine's bellows and the actual measured value. Under normal circumstances, a special formula is used to calculate the effective area of the Krah machine's bellows, which can meet the needs.

When the Krah machine's bellows are used in force balance instruments and field platforms that need to convert pressure to force, their effective area should be accurately determined, and measurements should be made one by one.

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