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What is the maximum test force of a spring?

The maximum spring test force is also known as the maximum spring test load.

The maximum test force of the spring can be obtained by the following formula.

　Maximum test force of spring = (circumference ratio x wire diameter) / (8 x coil mean diameter) x uncorrected shear stress

The units for each item are as follows.

Maximum test force of spring → N, Wire diameter → mm, Coil average diameter → mm, Uncorrected shear stress → N/mm ²

Looking at each item of this formula, we can immediately understand the pi, wire diameter, and coil average diameter.

The problem is, what is the unknown value of "shear uncorrected stress"?

How do we know this "shear uncorrected stress"?

This is the key to knowing the maximum test stress.

What is the "shear uncorrected stress" at maximum test force?

The shear uncorrected stress at maximum test force can be obtained from the following formula:

　Shear Uncorrected Stress = Tensile Strength x Factor

The unit of tensile strength is N/ ^mm2 .

This formula has two items, "tensile strength" and "coefficient".

Let's start with the "coefficient".

There are two factors that determine the coefficient.

One is the material, and the other is the push spring (compression spring) or extension spring (tension spring).

First, coefficients are pre-determined for each material category: hard steel wire/piano wire, oil tempered wire, stainless steel wire, brass wire, nickel silver/phosphor bronze/beryllium copper.

Then the modulus of the extension spring will be 80% of the modulus of the compression spring.

Putting this all together, the coefficient table looks like this:

The uncorrected shear stress is obtained by multiplying the tensile strength by the factor in this table.

Tensile strength is standardized for each wire diameter for each material.

It is important to note here that the minimum standard value is used as the tensile strength in the calculation.

For example, the "uncorrected shear stress" for a piano wire of grade B (SWP-B) with a wire diameter of 1.0 mm is

The minimum value of the standard is 2260N/mm2 ^, so it is as follows.

　2260×0.5=1130 (N/mm ² ) for compression spring

　2260×0.4=904 (N/mm ² ) for extension spring

　Or you can use 1130×0.8=904.

Knowing the "Shear Uncorrected Stress", it is easy to determine the "Maximum Spring Test Force".

For example, the "maximum test force of the spring" in the case of an extension spring with SWP-B material, wire diameter of 1.0mm, and coil average diameter of 10mm is

　Maximum test force of spring = (circumference ratio x wire diameter) / (8 x coil mean diameter) x uncorrected shear stress

Therefore,

　(3.14 x 1.0) / (8 x 10) x 904 = 35.482 (N/ ^mm2 )

See below for the standard minimum tensile strength of each spring material.

＞Standard minimum tensile strength of spring materials (Japanese Page)

＞What is the shear uncorrected stress of a spring?(Japanese Page)