Springs are mechanical devices that pull, push, support, lift, or protect, and some of the most commonly used mechanical assemblies incorporate springs in their design. This article will cover different types of springs, their use, and how each type operates in specific applications.
Springs are mechanical devices used to exert force; compressive, tensile, or torsion, for things like lifting engine valves, opening die sets, and something more simple, like holding batteries in place.
Springs are typically wound from wire, but they can also be machined from solid steel stock, shaped into cylinders, stamped, as assembled from other springs. They're mostly custom built to order, with dedicated wire-winding machines that can wound a wire through a certain number of turns over a specific length to create the required force constant.
They're also used to store energy, and the force exerted by the spring grows linearly as the spring is pushed, tugged, or twisted (the technical term is "loaded"). Hooke's law describes the deforming force, or load, as equal to the displacement, size, or small deformations of an elastic object, such as a spring.
The springs store mechanical energy when a force is applied and then release it when the load is removed. Regardless of the type of spring used in specific applications, they're designed to return to their original shape when the load is removed, provided that the actuation is performed under normal conditions.
We're going to cover three basic types of springs in this guide: mechanical, gas, and air springs. We're going to start with the most common type found in almost all consumer devices and industrial equipment — the mechanical springs.
Mechanical springs are further divided into three subcategories: helical springs, leaf springs, and disc springs. Let's start with helical springs
Helical springs are the most common type of springs used in product manufacturing. They're made from wire wrapped into helix form (thus the name) with variable cross-sections. The types of springs that fall into the category of helical springs are listed below.
Compression springs are open-coiled helical springs that provide an opposite force when compressed. During actuation, the spacing between the coils closes as the load increases until the spring's compressed length is reached, at which point the coils touch.
Compression springs are most typically used in manufacturing applications requiring a varied and opposing force between components. The ends of the spring can be left open or closed — the latter of which includes flattening the last coil against the adjacent one. Additionally, the last coil can be ground to square the ends.
Coil springs are typically made from wire, although more demanding, heavy-duty purposes may require machined springs or die springs. They're frequently found to order, but they're also available in stock sizes and selection kits. They're incredibly versatile, and you can find them almost everywhere, from shock absorbers to mattresses and retractable pens.
Extension springs, also known as tension springs, are helical springs designed to provide an opposing force when tugged or stretched. Just like compression springs, these are also available in many sizes, spring rates, and spring materials, depending on the force required by a specific application.
The ends of extension springs are most commonly shaped like hooks or loops; however, they can be made to order. Many different types of spring ends are used in specific applications.
They're not self-limiting, and since they can be stretched beyond their breaking point, their use is limited to non-critical applications where failure isn't a major concern. Trampolines and garage doors are typical applications for extension springs, though you can find them in numerous other devices and mechanisms.
Torsion springs are helical or spiral springs that are used to exert or resist torque loads. In addition to standard metrics, such as spring rates, spring end types, diameters, and materials, torque rating at a known position is also a crucial factor during selection.
Torsion springs are generally used as motion control components in manufacturing applications, though you can typically find them in door hinges and mousetraps. They're divided into two basic categories: helical and spiral torsion springs. The former is very similar to compression and extension springs by exerting force in a radial direction rather than axial.
Spiral torsion springs, on the other hand, are wound as concentric spirals from flat or rectangular stock and can be found mostly in numerous mechanisms, such as car seatbelts, clocks and watches, clothespins, seat recliners, and motion controls in industrial machinery.
Constant force springs, also known as clock springs, are basically spiral torsion springs that are used in clocks and wind-up toys. They're tightly wound steel bands that resemble a roll of tape. When the load is applied, the tape is extended, and the inherent stress resists the loading force at a constant rate.
Leaf springs are made of rectangular metal plates, known as flat springs or leaves, which are usually fastened together and are most commonly found in large vehicles, ranging from bigger cars to trucks and train carts. Different types of leaf springs and their applications are listed below:
Semi-elliptical leaf springs are the most common leaf springs in the automotive industry. Steel leaves of various lengths (but the same thickness and width) are stacked on one another to form a semi-elliptical leaf spring. The longest, uppermost leaf on both ends is called a master leaf. These springs got their name from the semi-elliptical shape created by arranging the steel leaves.
One end of semi-elliptical leaf springs is permanently attached to the vehicle frame, while the other is attached to the shackle. Their main purpose is to help vary the lengths and absorb the shocks of traveling through rough terrains. They're very low maintenance, easy to repair, and long-lasting.
The elliptical leaf spring is made by connecting two semi-elliptical springs in opposite directions, forming an elliptical shape. Both the axle of a vehicle and its frame are attached to the individual semi-elliptical springs composing the full-leaf spring.
Since the two semi-elliptical springs are loaded by the same amount of force during compression, no spring shackles are necessary. Full-elliptical leaf springs were mostly used in older cars and horse carts; they're no longer in use, except for decorative purposes.
Just like the full-elliptical leaf spring, the quarter-elliptical spring, commonly known as the cantilever-type leaf spring, is an archaic type of spring that's no longer used, except in old vehicles. They use a U-clamp of an I-Bolt to secure one end to the frame's side member while the other is freely connected to the front axle. When a shock load is applied to the front axle beam, the leaves straighten to absorb the impact.
Think of three-quarter elliptical springs as torsion springs used in door hinges but massively oversized for use in the automotive industry. The working principle remains the same: when you open the door, the spring stores rotational energy, and when you release it, the spring uses the stored energy to return the door to its original position. The rotational force is determined by the spring's rotation.
It's basically the same with three-quarter elliptical springs, which are a combination of a semi-elliptical, and a quarter elliptical leaf spring. The vehicle frame is attached to one end of the semi-elliptical section, while the quarter elliptical spring is attached to the other. The I-bolt connects the other end of the quarter elliptical spring to the frames and head.
A semi-elliptical leaf spring is mounted transversely across the width of the vehicle to create a transverse leaf spring. The spring's longest leaf is positioned at the bottom, and the mid-portion is secured to the frame with the help of a U-bolt. Two shackles are used in transverse leaf springs. However, they can induce rolling, making them unsuitable for use in cars.
Disc springs, also known as disc washers or spring washers, are perfect for high-load applications, particularly in tight spaces. The conical disc is composed of a convex disc, with the outside edge working against the disc's center. This results in a massive spring force in a small moving region.
Disc springs can generally carry higher loads with less deflection and solid height than ordinary helical spring designs because of their disc configuration. These are incredibly useful in a variety of manufacturing and work-holding applications.
Belleville springs, also known as conical springs, feature a cupped construction and don't lie flat as typical washers do. Instead, their conical shape compresses, allowing them to exert force. They're mainly used with fasteners for pre-tensioning reasons, as the bolt is usually inserted into a Belleville spring before it's mounted to a substrate. They're mostly made of stainless steel, spring steel, or beryllium copper.
The curved disc washer, or cylindrically curved disc spring, is particularly suited for applications that require flexibility, light loads (from ounces to around 100 pounds), and repeated cycles through a range of motion. In comparison to the wave and Belleville type disc springs, the curved disc spring has the most uniform spring that is consistent over the broadest range of deflection. They're mostly made of spring steel.
Slots on either the inner or outer diameter form a lever that operates on the slotted disc spring's unslotted portion. This effect reduces the spring load while increasing the deflection, giving the spring a softer nature with larger deflection and lesser spring loads in relation to the outside diameter.
The allowed stresses in the annular region must not be exceeded while using this type of spring. To compensate, the exterior diameter of the disc must be increased. Slotted disc springs are widely used in car transmissions.
A wave spring is created out of coiled flat wire with waves added for a spring effect. In some applications, wave springs outperform coil springs by allowing for lower work heights while maintaining the same force. This not only saves space but also results in smaller assemblies that employ fewer resources, lowering production costs.
Gas springs are assemblies that employ the pressure from a cylinder and a rod that use the pre-charge of nitrogen or other inert gasses to produce a force bias on a piston or rod. They're most commonly used in the automotive industry to raise and lower hoods and trunk doors.
Exerting force on the piston pushes it into the cylinder and compresses the gas. When you remove the force, the gas pushes the piston back. Nitrogen or other inert gas can flow freely around the piston, moving from one side of the cylinder to the other as the piston moves. However, the gas is compressed by the amount equal to the volume of the piston rod.
Air springs have been an active component in heavy-duty applications for more than a century, especially in suspension systems. An air spring is essentially a column of air contained within a bellows-shaped rubber-and-fabric container. The air compresses and expands, resulting in the spring motion. Air springs can keep a vehicle at a constant standing height regardless of load when used on the road.
There are more than a dozen types of springs used in machinery, manufacturing, and engineering. They're incredibly versatile mechanical devices with broad applications across several industries. However, there are some limiting factors.
For example, compression springs are generally favored over extension springs in critical applications due to their self-limiting properties, as they can't be pushed beyond their breaking point. Extension springs, on the other hand, can be easily overloaded, leading to failure.
It's very important to consider your application, and determine the correct spring type, spring rate, spring constant, ends type, wire diameter, and material used in your application to avoid critical failure.
Besides various spring types presented in this guide, other types of springs are available on the market or made specifically to suit more specific applications. To learn more about springs and their use, visit Reid Supply — a hardware supplier with over 40,000 parts and components in stock and an extensive library of downloadable professional literature and guides.