The Basics of Spring Rate
Spring rate is a measurement of how much force is required to change the length of a spring by a given amount. It's typically measured in pounds per inch (lb/in), or in some cases, newtons per millimeter (N/mm).
Some springs have a spring rate of just 0.67 lbs/in, whereas others have a spring rate of 2.83 lbs/in. In the former example, for every 0.67 pounds of force you apply to the spring, you'll change its length by 1 inch. If you apply 1.34 pounds of force, for instance, the spring will become longer or shorter by 2 inches.
Compression vs Extension Spring Rate
Spring rate affects all types of mechanical springs, including compression springs and extension springs. Compression springs are characterized by their ability to become shorter when exposed to a load. As their name suggests, they "compress" under a load. Extension springs, on the other hand, are characterized by their ability to become longer or "extend" under a load.
For compression springs, spring rate typically represents the amount of force needed to shorten the spring by 1 inch. For extension springs, it typically represents the amount of force needed to elongate the spring by 1 inch.
Why Spring Rate Matters
You should consider the spring rate when choosing a mechanical spring. It provides insight into how stiff or rigid the spring is. Generally speaking, the higher the spring rate, the more stiff it will be. A high spring rate means you'll have to apply more force to change the spring's length. If it's a compression spring, you'll have to apply more force to make it shorter. If it's an extension spring, you'll have to apply more force to make it longer.
Springs must be strong enough to support the load or loads to which they are exposed. If a spring is too weak, it may sustain damage, such as permanent deformation. By choosing a spring with the right spring rate, you can avoid problems such as this.
