Spring Design

Design information for engineers, such as spring calculation formulas,

which are the basis of spring design, can be found here.


(1)When Used under A Static Load

Fig1 shows the fatigue strength diagram of shear stress (JIS B 2704).

As shown in Fig1, JIS B 2704 defines the criteria of permissible bending stress for torsion coil springs that are subject to a static load.
However, when the usage environment is of a high temperature, it is necessary to consider permanent deformation, choose appropriate materials, and set a permissible stress.

(2)When Used under A Repeated Load

Fig2  shows the fatigue strength diagram of shear stress (JIS B 2704).

As a prediction of the service life, the reference method of JIS B 2704 is shown below.

When using wires with excellent fatigue resistance such as piano wire and oil-tempered wire for valve springs, the service life in a normal environment can be estimated by using the fatigue strength diagram in Fig2.

σB is the tensile strength of the material.

The diagonal line (γ)

and thick horizontal line of the upper limit stress coefficient of 0.7 moves up and down depending on the permissible degree of deterioration, and so if a slight amount of deterioration is allowed, the σmax of the coefficient’s σmax/σB may be taken up to the permissible bending stress shown in Fig2, and the thick horizontal line may be moved upward.

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