Choosing Spring Steel

First the question: where will the spring work?

Material choice is not settled by asking which is stronger. Three conditions govern: the size of the load and how often it repeats, the corrosion risk of the environment, and the working temperature.

On agricultural machinery the first two dominate. A seed drill spring in constant contact with soil and moisture does not call for the same material as a contact spring inside a sealed mechanism.

Spring steel — general use

The great majority of items in our catalogue are made from spring steel. It offers high strength and good fatigue behaviour, and it is the standard choice for compression, extension and torsion springs on agricultural machinery.

Its weak point is corrosion: bare spring steel rusts in damp conditions, and rust both removes cross-section and creates crack initiation sites. Surface protection is therefore part of the choice rather than a separate decision.

Stainless — where corrosion governs

Where chemical exposure is high — sprayer arm and wing springs, for example — stainless material is considered. What it buys is life: once corrosion stops, fatigue life approaches its design value.

In return, stainless works at a different strength level from spring steel of the same size, so changing the material usually means the geometry has to be reviewed as well. The two decisions are taken together.

Chrome silicon — heavy and impact loading

For springs working at high stress and under impact, alloyed spring steels such as chrome silicon are preferred. They offer higher fatigue strength and better behaviour at temperature.

In thick-wire, impact-loaded groups such as heavy cultivator springs, heat treatment matters as much as material: a thick-wire spring coiled without stress relief takes a permanent set on the first heavy impact whatever it is made of.

Coating is not a substitute for material

Galvanised coating protects the surface against corrosion and is standard in our production. Hay rake and tine springs are also produced with silver, gold and black finishes.

But coating is not a change of material: the mechanical properties of the spring are set by the wire material and the heat treatment, while the coating provides surface protection and appearance. Choosing a coating colour does not change strength.

Strength values and the calculator

The calculator on our home page shows the permissible stress and safety factor for the selected material. The material strength values there are typical figures, intended for preliminary assessment.

Final production is verified against the real values on the supplier certificate for the wire to be used. In critical applications that verification is not skipped — the safety factor depends directly on it.