Springs are mechanical devices that are capable of storing mechanical energy because of their elasticity. Springs are often made of coiled, hardened steel, although non-ferrous metals such as bronze and titanium and even plastic are also used. There are various types of springs, the designs of which take advantage of different energy storage management.
Types of Springs
One of the most common types of springs is the compression spring. This is the type of spring found in a pen or an automobile engine. It is typically used because it compresses when loaded with weight, and decompresses when the load is removed. They don’t need to be attached to anything, unlike other types of springs.
An extension spring is attached to an application on both ends. For instance, a screen door hinge might employ an extension spring to force the door closed when not being held open. These springs are made of coiled steel and feature loops on either end for attachment. When it is holding a load, it stretches apart.
A torsion spring is also attached on two ends, but it works at a 90 degree angle from other springs. When it takes a load, the torsion spring rotates on its axis. A good example of a torsion spring is a mouse snap trap: when the trap is set, the trap is held back on a torsion spring. When the trap is sprung, the force of the torsion spring causes the trap to snap closed.
Clocks feature clock springs, or constant force springs. Constant force springs are tightly wound bands of steel that resemble a roll of tape. A load forces the spring to contract, and when it is removed, the spring rebounds with a constant force. Constant force springs are also found in wind-up toys and devices.
Belleville springs, or washers, resemble a slightly tapered disc. They are used in conjunction with fasteners like bolts for pretensioning purposes. Typically, a bolt is inserted in a Belleville spring, and then attached to a substrate.
Leaf springs are used in vehicle suspensions. They do not resemble helical springs, but rather several flat bands of steel piled on top of each other cut to sequentially shorter lengths. The benefit of a leaf spring is that it can be used to direct loads along a specific path.
Spring Materials and Manufacturing
Springs are often made of hardened steel, which can either be pre-hardened before spring formation or hardened following formation. For helical springs, such as compression springs, long stock wire is used and fed into an auto-coiler. The wire stock can also be coiled on a lathe if a smaller run is being prepared, but there are many safety concerns to consider. Spring wire will uncoil dramatically if it is not tied down or if a machinist loses control of it. This uncoiling behavior can be extremely dangerous to those nearby, especially if it is a heavy gauge wire.
An auto-coiler is a machine that can force spring wire into a coiled shape. Although it has a similar name to an automotive autocoil transmission, it is a different device. They are typically adjustable machines that can alter the coil tension, length and number. Auto-coilers use rollers to feed spring wire through headers and then quickly spin the wire around a cylinder. The quick spinning action forces the spring to adapt a coiled helical shape. The auto-coiler then ejects the spring and coils the next piece of wire.
Leaf springs are formed differently from helical springs. First, a flat bar is sheared into shape and then a collection of bars are punched together. Several machines trim the resulting bars to remove extra metal and taper ends. The spring is then heat treated to harden the steel, while other treatments such as painting finishes are performed to match the spring to predetermined visual specifications.