Steel springs are essential components in many devices, systems and machinery and can be defined as an elastic member that exerts a resisting force when its shape is changed.
There are four major styles of steel springs: compression springs, extension springs, torsion springs and flat springs. Each of these steel springs performs a very different function. Compression springs act as a cushion for a downward acting force; extension springs, also known as tension springs, act in reverse by giving resistance to outward acting forces, elongating when pulled by attached hooks at either side; torsion springs store mechanical energy within a twisted coil and act by exerting a twisting force, or torque; and flat springs are very simple devices, being constructed of flat strips of steel that have been tempered with a specific curvature in order to give resistance and shock absorption in simple applications.
Common applications of steel springs include outdoor power equipment, retractable safety devices, tape measures, timing devices, fitness equipment, gardening equipment and toys. Steel springs serve these applications and more in industries such as medical, automotive, oil and gas, telecommunications, textiles, hardware, electronics, military, aerospace and agriculture.
There are a few main types of steel used to make springs: blue steel, which is also sometimes called spring steel, and stainless steel. Blue steel is the traditional type of steel using in springs and is a high carbon spring steel. Aesthetically-pleasing, but inclined to rust, blue steel is hardened, tempered and polished to meet specifications.
Stainless steel offers properties that are not available in blue tempered spring steel such as high corrosion-resistance; however, it is similarly aesthetically-pleasing. Steel springs are most commonly formed through the cold rolling process. A type of roll forming, cold rolling utilizes roll forming machines, which consist of sequences of calenders, or roller die pairs, positioned both above and below the metal coil that is being formed.
As the metal moves through the machine, the rollers bend the material along the linear axis, pressing the metal into a more uniform grain flow while shaping the metal into flat coil strips. Cold rolled parts are created at temperatures below the recrystallization point of the metal. The cold rolling process increases the tensile strength of the metal.
Since blue tempered steel springs work well with heat treatment, the next step for this type of steel spring is to be annealed, or made softer through heating, so that they can be wound or coiled. Next, they are heat treated in order to reduce stresses and fractures, which further strengthens the spring.
However, stainless steel springs cannot undergo heat treatment and thus are coiled using a different process. One possible winding process for stainless steel springs is to be lathe formed, which uses a lathe machine that winds the coils through a process of rapid rotation.