The metal bellows forming process also affects the spring rate. The wall thickness of the metal bellows after forming is uneven, thinner at the crest and thicker at the root, which causes the spring rate of the metal bellows to drop sharply at the crest. As the temperature increases, the spring rate of the metal bellows will decrease, but this decrease is not linear.
Spring rate is the ratio of the force applied to the metal bellows to the displacement it produces. Metal bellows will deform under external forces such as pressure or temperature changes. Depending on the direction of the applied force, bellows spring rates can be axial, lateral, or bending. In the current application of metal bellows, axial displacement is the main one, so axial spring rate is the most common. The spring rate of metal bellows is affected by the elastic modulus of the raw material, convolution shape, convolution height, convolution pitch, wall thickness, number of plies, etc. Appropriate metal bellows spring rate design is related to the operational stability and lifetime of the equipment.
The unit of metal bellows spring rate is N/mm. It means the force required for the metal bellows to deform by 1 mm.
The smaller the spring rate value, the softer the metal bellows. The larger the spring rate value, the harder the metal bellows. Some metal bellows applications require a low spring rate to provide flexibility, and some applications require a high spring rate to resist deformation.
