Introduction
A spring is a mechanical component in your garage doors, watches, and even electronics like switch relays. Even the car suspensions that keep you safe from bumps and disturbances are made of springs. With such wide applications, there are many types of springs each with a unique form and shape making it suitable for a specific task.
Essentially all springs are used to store mechanical energy when under compression or tension and this energy is released when the compressive or tensile force is removed bringing the spring back to its original shape.
Mechanical springs have various shapes, sizes, and purposes. This comprehensive guide explores the different types of sprint, specialized spring types, and the principles behind mechanical springs. There’s also a small tip at the end to help you decide which type of spring is suitable for your unique project.
Hooke’s Law and Spring Mechanics
Almost all springs obey Hooke’s law which simply states the force exerted on the spring is directly proportional to the displacement caused in the spring. This relationship is mathematically given by
F= -kx
Where F is the force,
x is the displacement from the spring’s natural equilibrium
and k is the spring constant
The displacement is sometimes also referred to as the ‘extension’ of spring. The spring constant is the stiffness of the spring. In simpler terms a higher k value corresponds to a stiffer spring and in turn requires a larger force to produce a displacement.
The spring constant is affected by material, wire diameter, number of turns, and length of spring.
Common Types of Springs
When it comes to the classification of metal springs, they are sorted into different categories each with a similar general identifying factor like the shape or form of the spring. This also means different types of springs can perform various functions and bear different types of loading.
The next section covers the springs’ categories and subcategories, showing how each spring type is better suited for a different function.
Category One: Helical Springs
Helical springs get their name from the helix spiral shape. These springs will always have a helix structure but a different cross-section. Listed below are the types of helical springs
1. Compression Springs
Compression springs are the most common types of springs. Compression springs are made from steel wire wound into a helix coil and cut to size.
These coil springs are built to resist compressive force along the axis where they are wound. Compression springs can resist linear compression but are ineffective if the force comes from an angle.
Car or motorbike suspension is an example of a compression spring. A ball-point pen also uses a compression spring.
The table below shows some common compression springs.
Conical
Hourglass
Barrel
Reduced Ends
2. Extension Springs
Extension springs have a small pitch (distance between centers of two successive coil turns). Extension springs are designed to resist a pulling force.
They usually have hooks on both ends that attach to two components and when the spacing between the two components increases, the stretched spring tries to return to its original position.
3. Torsion Springs
A torsion spring provides resistance to rotational motion. These springs are generally close wound meaning there’s no practical pitch. This is important to provide torque and adding pitch can make the spring less stiff.
Torsion springs have extended legs that bend when there is a force. This stores energy and the torsion spring legs try to deflect this force keeping the object in place.
4. Spiral Springs
A spiral spring stores energy just like a torsion spring. Spiral springs are usually used to store and release energy unlike torsion springs designed to hold components in place. Spiral springs are made from metal stripes cut to size and rolled into a spiral.
Generally, they are used in clocks and watches and seat belt systems in cars.
Category Two: Leaf Springs
Leaf springs are made of metal sheets of different sizes stacked on top of each other. These rectangular metal sheets are bolted and clamped together and are commonly used in car and heavy vehicle suspension systems.
5. Elliptical Leaf Spring
The elliptical leaf spring is the most common type of leaf spring. This spring contains stacked metal sheets shaped like an ellipse. It comprises two semi-elliptical springs bolted together to form a concave elliptical spring.
6. Semi Elliptical Leaf Spring
Semi-elliptical leaf spring is made from rectangular stacked sheets of the same or different sizes. This is widely used in car suspension as it can distribute the weight of the entire car on a wider area and support it.
The leaves below the top metal strip are called graduated leaves and the entire spring is connected using a central clamp. These springs are mostly used in heavy trucks as they do not provide excellent driving performance and agility.
7. Quarter Elliptical Leaf Spring
This spring has the length of half of the semi-elliptical leaf spring. It generally has a hook end connected to the chassis and a round end that can be bolted at another point. Quarter elliptical leaves provide rigid support to off-road vehicles and are used for high-ground clearance.
8. Three-Quarter Elliptical Leaf Spring
Three-Quarter elliptical leaf spring is shorter than the standard elliptical leaf spring. It exists due to old carriage systems which needed a semi-elliptical leaf spring connected to the rear and front axle and a quarter of the spring to support the carriage.
9. Transverse Leaf Spring
A transverse leaf spring is a semi-elliptical leaf spring that is mounted upside down (concave down) across the width of the frame. In previous examples of leaf springs, almost all of them ran on the longitudinal axis or from front to the rear. A transverse leaf spring is mounted side to side.
Category Three: Disk Springs
Disc springs can be ideally thought of as washers. They are a class of circular discs which have a small rise to make it look like a shallow cone. This shape makes them relevant for those engaging in conical spring finder shopping. Disc springs take less space than other springs and are designed to provide large stiffness in small spaces.
Most disk springs are used to remove any axial play and gaps between components for vibration control.
10. Belleville Disk Spring
Belleville disk spring is the most common disk spring and it has a conical shape with an elevated center. The conical shape allows them to compress under load.
The loading can be thought of as similar to a stack of coin under a load but when the force is removed, the flat discs rise back to their conical shape.
11. Curved Disk Spring
Curved disk springs are round cylindrical springs with a curved perimeter. They are not flat and are often called crescent washers designed to provide a small amount of axial deflection and radial stability.
12. Slotted Disk Spring
Slots are rectangular cut outs and having slots on a disk spring serves a unique purpose. Slots can be made on the inner or outer diameter of the disk spring. Having slots increases the flexibility of the spring and reduces the stiffness allowing the spring to deflect more easily.
There are many reasons slotted disk springs are designed and one of them is to reduce hysteresis for more accurate and consistent load cycles.
13. Wave Disk Springs
Wave disk springs are similar to compression springs and in most applications serve as a replacement for coil springs. They have a flattened wave feature with multiple turns on each level unlike wound coil springs that have a single turn.
The load is immediately supported by multi-turn waves and this provides a more stiffer spring for the same height as other compression springs.
Functions of Springs
Mechanical springs are classified into three main types of springs according to the application of force.
Compression Springs
Compression springs are helical wound springs designed to resist push force and maintain force between two components. While typically cylindrical, they can also be conical or hourglass-shaped. Deflection varies based on spring parameters.
Spring rate: Stiffness of the spring
Outside diameter: Diameter of the spring from its external ends. This is specified if the spring needs to be fitted inside a hole
Inside diameter: The internal diameter of the spring is specified when the spring goes over a rod or shaft.
Free length: Length of the spring under no load
Free position: The highest point of the spring under no load
Solid height: This is the length or height of the spring when it is under complete compression.
Wind direction: Compression spring can be wound left or right. Choosing the direction of winding is important if the application involves threading the spring into a component.
Torsion Springs
Torsion springs are also helical springs designed to resist rotational motion. They have a very small pitch and high stiffness with spring legs attached to another component or fixed at one end. Stock torsion springs come in many varying lengths and turns of coil.
A stock torsion spring is able to twist around an axis instead of a linear applied force. Many mouse traps use such a spring.
When a torsion spring deflects the inside diameter of the coil decreases, this is because the force is applied to the spring leg. In other types of spring, there is minimal change in coil diameter.
Extension Springs
Metal springs designed to resist ‘pull’ force are extension springs. Stock extension springs work by stretching along the axis on which they are wound. This type of spring resists tensile forces and is sometimes referred to as tension spring or stock tension spring. Extension springs can either have loops or hooks at the end as attachment style.
Materials used for Springs
Spring types used in different applications require different types of properties. Mainly they require a different stiffness which can be adjusted using spring parameters like wire diameter and length. However, spring material can drastically change the stiffness and also provide other benefits like corrosion resistance, cost effectiveness and weight benefits.
The most common spring materials used are listed as:
Beryllium Copper Alloy
Alloy springs are very common and desirable for their long life. Beryllium copper has a high tensile strength meaning it can withstand intense loading and resist fatigue failure. This alloy is also non-magnetic and ideal for components with electromagnets.
Copper also offers high corrosion resistance and excellent machinability meaning these springs are easy to shape on a winding machine.
Their applications include specialized aerospace equipment because it doesn’t spark and musical instruments because it can be shaped easily.
One-Directional Glass Fiber Composite Materials
This is a typical composite material with glass fibers locked in a matrix. The springs made from fibers can have varying stiffness depending on the alignment of the fibers. They can produce isotropic or anisotropic mechanical properties.
Glass fiber springs have a high strength and stiffness but are extremely lightweight and are primarily used for their lightweight. This opens the door for application in damp conditions without rust blocking the spring coil or lightweight suspensions.
Steel Alloys
When we think of a spring, metal, specifically spring steel comes to mind. Steel is the most common material for making springs. Stainless steel offers good tensile strength, toughness and corrosion resistance making it suitable for most applications.
Stock extension spring and stock compression spring all around the world are readily made of steel. Rolls of alloy steel wire of different wire diameter are readily available and it is easy to match spring specifications according to requirement and quickly wind custom springs.
Rubber/Urethane
Rubber springs are a common sight in vibration damping applications. They are made of natural or synthetic rubber and have large deformation properties. They are excellent energy dissipaters and do not corrode. They are sought for their non-magnetic and non-conductive properties.
Common Manufacturing Process Of Types Of Springs
Since there are spring types and spring washers, multiple treatment and correction procedures turn the spring into its different types. The most common spring manufacturing process is using a wire with a pre-defined inner diameter and winding it.
Before winding starts, spring wire is loaded to the manual or cnc winding machine in rolls. The wire is straightened and fed into the winding machine automatically.
1. Winding
Winding springs involves taking the fed wire and passing it through guides to a mandrel. The wire is rolled over a mandrel at specific angles with the desired tension. The feed rate and angles is important to match the end spring’s specifications. This process is also called coiling.
Once the spring reaches its desired length, it is cut-off from the rest of the wire.
2. Heat Treating
When the spring is being coiled, it is bent, shaped and deformed. This builds up stresses inside the spring. Residual stresses stay inside the material of the spring and are concentrated at some regions leaving an inconsistent spring rate.
Heat treatment processes like tempering and annealing ensure correct spring stiffness and remove residual stresses. To do this, springs are heated to a fixed temperature and allowed to cool at different rates depending on the material.
3. Grinding
When a spring is cut off abruptly from the main wire, it does not have smooth or straight ends. In the grinding process a spring is brushed against a grinding tool which spins at moderate RPM.
For large springs, the springs are grinded on a single ended grinder and for smaller sized springs, both ends can be ground simultaneously. The abrasion surface removes layer of spring metal giving it an even size and length for precision.
This gives each batch of springs a good squareness and consistent torsion spring rate. This process is frequent to stock conical springs.
4. Coating and Finishing
Springs are coated for to improve their properties and performance. In many cases, this also affects the spring rate and mechanical properties. Spring are also electroplated with zinc or copper to improve their rust resistance or conductance. Electropolished springs also have better wear resistance and fatigue resistance.
Most commercial springs are usually finished with powder coating and anodizing.
Powder coating: This is an aesthetic option which provides resistance to moisture and UV protection. Powder coated springs can withstand unintentional abrasion and chipping.
Anodizing: Anodizing is a relatively expensive finishing method for springs. Anodized springs have increased corrosion resistance and surface hardness. It also makes the surface non-conductive for applications in electronics.
Custom Spring Manufacturing at Aria
If you’re interested to learn more about custom spring solutions for projects as large as shock absorbers in large trucks or vibrational damping springs in robotics you can contact our sales and engineering teams for a quick recommendation.
FAQ
How many different springs are there?
Springs are classified into three main types according to their general shape. These are leaf springs, disk springs and helical springs.
What is the difference between helical spring and spiral spring?
A helical spring is coiled in a helix shape and the spring wire has a constant diameter meaning the entire spring has the same cross-section. However, a spiral spring is a spring that is coiled flat. Each coil wraps around the next but in a helix spring the coil loops in a helix.
What is the strongest type of spring?
The strongest spring often depends on the stiffness of the material and the strength. More force is needed to compress a spring made of titanium than that of steel. Generally compression springs are the strongest for their purpose but this can change depending on the type of load.
Where can I get torsion spring finder shopping?
You can find torsion springs specifically made for your project by providing your spring specifications to a manufacturer. Custom manufactures can also help you get extension spring finder shopping guides and advise you on springs suitable for you.