All About Compression Springs
As simple as they may seem, springs play a vital role in modern life. You can find them just about everywhere, including in nature. A wide range of everyday items depend on springs to function: retractable pens, shock absorbers, clocks, keyboards, window blinds, mattresses (and box springs, of course), door knobs, HVAC systems, trampolines, garage doors, and just about anything with a button.
In its most basic form, a spring is an elastic object, meaning that when someone, or something, pulls or pushes or hammers or otherwise manipulates it, it returns back to its original shape. Beyond that, springs can take on many forms, and not all springs look like springs.
In this blog series, we explore the many types of springs, along with their history, uses and manufacturing techniques. This installment focuses on one of the most common spring types: compression springs.
When you think of what a spring looks like, you’re probably imagining a compression spring. These simple coiled springs come in the shape of open-wound helixes, but beyond that they can be conical, elliptical, circular or even rectangular in cross section (magazine springs, for example). Appropriately, compression is the main function of compression springs. When compressed, they exert force in the opposite direction as they try to return to their resting lengths.
Compression springs officially date back to 1763, when British inventor R. Tradwell filed the first patent for a coiled spring. Replacing the leaf spring in an automotive suspension system, Tradwell’s first spring was a compression spring. Springmakers innovated in a variety of ways in Tradwell’s time, but it wasn’t until 1865 that the most logical use of a compression spring was patented. That is, of course, the mattress coil. After all, what’s an invention worth if it doesn’t contribute to the comfort of its user?
Today, compression springs are just about everywhere, and there are a wide variety of sub types.
- Conical compression springs (also known as tapered springs) are used in applications where the fully compressed height of the spring needs to be minimized. Real-world uses for conical springs are everywhere, but you’ll most often find springs of this shape in buttons and electrical contacts (look inside the battery compartment of your remote control for an example).
- Magazine springs, with an elliptical or rectangular cross section, are generally used in firearm magazines to push bullets toward the firing chamber. Their shape allows them to fit snugly into the rectangular magazines of most firearms. Surprisingly, magazine springs have another common use: when woven together, they create the basis for durable, flexible steel conveyor belts used in many industries.
Manufacturing compression springs
As with all springs, compression spring manufacturers must take into account several parameters. Product designers need to know the basics of the spring they want to produce before deciding on the production method. For example:
- Spring diameter: the size of a circular spring’s cross section
- Spring index: a measure of the tightness of the spring coil
- Spring rate: a measure of the stiffness of the spring
- Ends: different ways to treat the ends of the wire after a spring is formed: closed, plain or ground, for example
- Wire diameter: along with material, wire diameter does a lot to determine the spring rate
Most CNC spring coilers can coil springs with a variety of wire diameters, but none can coil any size wire. For example, Automated Industrial Motion offers a line of seven spring coilers that, together, can manufacture springs from wire as thin as .006” in diameter, all the way up to wire as thick as .787” in diameter.
Programmable spring coilers, like AIM’s line of CNC coilers, can be configured to produce compression springs with a wide variety of cross sections. For example, designers can program convex or concave springs with varying cross sections, or even magazine springs with rectangular cross sections. AIM also offers a pneumatic control option for the AIM 100, allowing manufacturers to produce springs on demand. The pneumatic coiler is programmed to produce one type of spring, and to fit seamlessly into an automation workflow.
Take a look at these resources for more information on the springs and spring coilers discussed in this blog. Be sure to subscribe so you don’t miss any updates.