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Compression Spring: Types, Usage and Design
Their uses vary as much as the shapes and forms they come in- from engine valve springs to ball point pens. 
Round wire is the most common material used to make this type of spring. Square, rectangular, or special shaped or sectioned wire is used in some cases. Most of this type have the same diameter throughout the whole spring. These are known as straight coil springs.
There are also the kind where the diameter of the spring varies throughout its length. These type are tapered or cone-shaped springs. Concave or convex forms are also used as well as a combination of both straight and tapered. These are specialized varieties of the standard compression spring. The conical or tapered spring can be designed so that each coil nests wholly or partially into the adjacent larger coil. This gives the spring the ability to have its solid height no larger than one wire diameter. Conical or tapered springs can be designed with a controlled increasing rate as each turn successively becomes inactive during deflection. The larger diameter coils collapse and become inactive first thus causing the pattern of an increasing rate. A conical spring can be made to have a constant rate by creating the spring with a variable pitch. Putting a larger pitch in the larger OD coils and a smaller pitch in the smaller OD coils will force the spring to collapse all the coils at the same rate when compressed. When designing a tapered spring of uniformly changing diameter you can use conventional formulas as found on the web page Design of Compression Springs, Extension Springs, Torsion Springs, and Flat Springs and use the average diameter of the spring as the mean diameter. These calculations would apply only until the first active coil becomes inactive. After that, to be accurate, the spring must be calculated turn-by-turn. Calculations for barrel and hourglass springs are performed by treating these springs as two conical springs in series. 
Standard straight springs are often made with variable pitch when used in dynamic applications such as engine valve springs. In these cases the cyclic rate of the load application is near the fundamental frequency or the harmonic of the natural frequency of the spring. (See our web page on Special Design Considerations for more on this.) When the coils of smaller pitch become inactive during deflection, the natural frequency of the spring changes, and throughout the cycle the spring has a spectrum of frequency response and not a single resonant frequency. In the above case of variable pitch surging and spring resonance are minimized. Barrel and Hourglasss springs also serve this purpose. Studies show that the variable diameters act in the same way as variable pitch to promote consecutive coiling closing. Check back, we will be adding lot's more information. Everything from material usage to spring design. Our team is constantly searching for the latest technical information. For help in designing compression springs check out this web page- Design of Compression Springs, Extension Springs, Torsion Springs, and Flat Springs Got some info you want to share? Go to our contact page and send it our way. This page on types of wire that springmakers use will help in picking out the correct type of wire to use. Don't miss any updated information! Stay in touch by subscribing to Spring Makers Resource e-zine. Return to Spring-Makers-Resource
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