This chapter will discuss what compression springs are and the considerations when choosing compression springs.

What are Compression Springs?

Coil springs called compression springs can store mechanical energy when they are compressed. These open-coiled, helical springs provide resistance to compressive loading. When these springs are subjected to a compression load, they compress, grow shorter, and absorb a large amount of potential force.

The springs are forced back to their original lengths and forms after the load is reduced or eliminated by the stored energy. When weighted, compression springs become more compact. In contrast to extension springs, compression springs' spiral wires do not contact when they are relaxed; instead, when stressed, they are tightly compressed.

Considerations When Choosing Compression Springs

The are various considerations when choosing compression springs which include:

Compression Spring End Considerations

Compression spring end types might be normal or customized. Standard ends can be open or closed, or they can be ground or not. Given the same number of coils, wire size, and outside diameter (OD), open or closed ends will alter the spring rate.

However, when combined with closed ends, this characteristic will enhance the squareness of the loading force and lessen spring buckling tendencies. Ground ends demand additional manufacturing work.

Certain manufacturers, while not all, offer closed and ground ends in their regular catalog stock designs; this is an important distinction to understand. Examples of special ends include expanded coils to snap into ring grooves, offset legs to serve as alignment pins, and decreased coils for screw attachment.

Compression Spring Material Considerations

Carbon steel and exotic alloys are only a few possible spring materials. The most popular material is music wire, a high carbon spring steel. Stainless steel 302 improves overall corrosion resistance but is less strong than music wire.

Nickel alloys are chosen for their extreme high or low operating temperatures, specialized corrosive conditions, and non-magnetic properties. They are labeled under a variety of trademarks. In addition, copper alloys with superior electrical conductivity and corrosion resistance include phosphor bronze and beryllium copper.

Compression Spring Physical Considerations

Outer Diameter: If the compression spring is going into a hole, its outside diameter should be considered. In any case, if any internal components of the device will surround the spring, those must also be measured. A spring's outer diameter (OD) will enlarge when it is compressed, which is also important to consider if the spring will be used in a tube or a bore.

The outside diameter of springs is also subject to manufacturing limitations, which can increase the assembly's needed envelope size. Most spring manufacturers will specify a work-in-hole diameter for a spring based on projected OD expansion and manufacturing tolerance. Use this information to more effectively express the product needs when obtaining custom-made springs or to easily choose from stock spring catalogs.

Inner Diameter: If the compression spring passes over a shaft or mandrel, the spring's inner diameter needs to be considered. To prevent friction, there must be a ten-thousandth of an inch between the shaft and the spring.

Free Length: To ensure that the compression spring is in a preloaded state and stays in position, it is advised that its free length be a little bit longer than the available space.

Solid Height: The wire diameter and the total number of coils impact the solid height of the spring. Make sure the loaded height is not shorter or taller than the solid height.

The setting in which the spring will be used includes the temperature and additional components such as moisture. The more expensive the spring’s material, the higher the temperature a spring can withstand, but this will increase its cost.

Compression Spring Load Considerations

The compression spring's loading or travel needs to be considered as well. The relationship between the force needed to compress a spring by a unit of length—typically pounds per inch (lbs/in)—is known as the spring rate or spring constant. The product designer can therefore determine projected spring travel with a particular load. The spring is put under increasing strain as it is driven further. The substance of the wire may eventually give way under stress, leading to a phenomenon known as spring set. The spring won't re-expand to its initial unloaded length once it has been set. Nevertheless, depending on the assembly, this spring may be useful.