Stability and reliability of bellows

The maximum displacement that can be obtained without plastic deformation of the bellows is called the allowable displacement of the bellows.

The bellows will produce residual deformation in the actual working process. The residual deformation is also called permanent deformation or plastic deformation. The bellows is deformed under the action of force or pressure. When the force or pressure is removed, the bellows does not return to its original state. Residual deformation, the residual deformation is usually expressed by the amount that the bellows does not return to the original position, also known as the zero offset.

The relationship between the displacement of the bellows and the zero offset, regardless of the tensile or compressive displacement, at the initial stage of the bellows displacement, its residual deformation is very small, generally less than the allowable zero position specified in the bellows standard offset value. However, when the tensile (or compressive) displacement gradually increases beyond a certain displacement value, it will cause a sudden increase in the zero offset value, which means that the bellows produces relatively large residual deformation. If the displacement is increased a little more, the residual deformation will increase significantly. Therefore, the bellows should generally not exceed this displacement, otherwise its accuracy, stability, reliability and service life will be seriously reduced.

The allowable compression displacement of the bellows when working in compression is larger than the allowable tensile displacement when working in tension, so when designing the bellows, the bellows should work in compression as much as possible. Through experiments, it is found that in general, the allowable compression displacement of the bellows of the same material and the same specification is 1.5 times the allowable tensile displacement.

The allowable displacement is related to the geometric parameters and material properties of the bellows. In general, the allowable displacement of the bellows is proportional to the yield strength of the material and the square of the outer diameter, and inversely proportional to the elastic modulus of the material and the wall thickness of the bellows. At the same time, the relative wave depth and wave thickness also have a certain influence on it.