Transworld Engineering Ltd. supplies manufacturing solutions through the sale of high quality machinery and engineering support for spring makers and end users in the UK and European market.
To assist our clients, we are providing a database of information related to springs and spring manufacturing solutions. This article represents part one of this database.
Our first part looks at the different types of spring. Each has its set of applications and performs a different basic function. There are fundamental differences between Spring types, how they are made, the materials they may be manufactured from and their application.
“A compression spring resists a load pushed against or onto it”
Compression springs are perhaps the type of spring you are most likely to see in everyday life. They are found in household objects, engines, manufacturing control and have many domestic and commercial uses.
Compression springs provide some flexibility of movement white the force they provide attempts to return the object or objects the spring is attached to back to its original position.
Compressions springs are used in most forms of automation, cars, trains, aeroplanes. They provide such mundane functionality as door-stops. They can provide basic shock absorption functionality. Providing a load with just enough freedom of movement to prevent fixed stress under vibration, while always looking to return the load to its ideal position.
Hole and Rod. Typically, a compression spring is anchored with a rod which runs through its centre, inside the diameter. This rod prevents the spring from distorting, bulging, or fouling under load.
The free length of a spring refers to the length of the spring material unwound
Compression springs can be manufactured in different shapes. Conical, convex, concave and pipe.
“An extension spring is used to bring things together or place 2 objects attached to the spring under a fixed diametrically opposing load”
Extension springs are most commonly used in situations where some degree of movement should be allowed between 2 objects or one object and its anchor point where the force of the spring encourages the objects to return to their original proximity
For example. In a traditional “up and over” garage door, closing the door extends the spring. Someone closing the door will feel the tension despite having gravity on their side. The door wants to return to its open position. Only when vertical does the mechanism lock, leaving the spring extended and the locking mechanism preventing the door from opening.
It is the initial tension that determines how tightly together the spring is coiled. This initial tension can be manipulated to achieve the load requirements of a particular application. Designs normally have hooks, eyes, or other interface geometry at the ends which attach to the opposing components. They are frequently used to provide a return force to components that extend in an actuated position.
The reverse is true when opening the door. Once started, with the momentum of the first lift, the door easily returns to its up and over position.
“Torsion springs provide a rotary (tangential) force are most typically anchored at both ends and providing radial resistance (torque) to movement.”
These anchors, sometimes known as legs provide radial resistance. Unlike the lateral forces that other spring types provide or resist, torsion springs provide or resist bending stress.
A good example in everyday use that might visualise this is the common office clip board. The clip at the side or top of the board uses a torsion spring, one leg attached to the board itself, the other to the clip. When the clip is lifted it provides pressure which ensures that, once paper is placed between it and the board the pressure ensure the paper remains fixed.
Torsion springs provide an angular torque around their circumference. This force is measured ion kilograms per degree around this circumference.
Torsion springs have a maximum deflection. This is the amount of force needed to overstress the spring. The point at which it will fail in terms of providing too much movement or material stress within the spring itself will occur which usually permanently damages the spring
Maximum Load is the amount of force that can be placed on a spring before maximum deflection is reached
Principles of Spring Design
There are three core principles in spring design.
- Heavier gauge spring wire provides a stronger spring
- The more tightly wound a coil is, the strong the spring will resist
- More active coils mean less force is required to move the spring a specific distance from its resting point.
There are some caveats to these rules.
Firstly, they apply to springs made from the same material. Depending on the spring type there are materials suitable for different applications that provide different properties. The rules above apply to springs made with the same material.
The same is true for the age and lifetimes uses of any spring. Due to the stresses of use, the material in any spring will degrade in relation to its ability to perform over time. Different materials provide different projected lifetimes depending on their use case.
The endurance limit is defined for ferrous (steel and iron) material as the stress level below which the material can be cycled infinitely without failure. (Shigley et al., 2003)
Extended lifetimes can be expected if the spring is made with the correct material for its application. For example, a stainless-steel spring can provide both corrosion resistance and an expected lifespan that can be longer than the application or device it is used in.
However, the correct material for any spring in any given application can vary. There is usually a best material for the job.
Based in Birmingham with a small but highly skilled team, we work to ensure the machines we supply are of top quality, without charging over the odds. Once a machine is sold, we continue to provide manufacturers with expert engineering support and after-sales care.
If you have any queries, please contact us on 0121 772 9796 or using the contact button at the top of any page of this website.