How Do You Size an Extension Spring?
Because they are mechanically wound in a helical shape, extension springs offer a reliable force returning to their initial no-load resting position where the coils are compressed together. Their mechanism of work requires extension springs to be used with the right load, not too heavy, which can stretch the coils out of position permanently, or if it is light, it may not offer sufficient force to stretch the coil.
Either way, the wrong sizing of an extension spring affects the optimal functioning of the whole system.
The consistency of extension springs and the power they can generate makes them ideal for a diverse range of applications, including garage doors, storm doors, trampolines, screen doors, and even farm machinery. Here is a look at some of the aspects when sizing an extension spring:
General Extension Spring Sizing
When looking for extension springs, they are more likely to fall under these four sizes.
Micro Extension Springs
These have the following dimensions;
Outer Diameter: 0.063” to 0.100”
Wire Diameter: 0.004” to 0.012”
Small Extension Springs
These have the following dimension Outer Diameter: 0.101” to 0.500”
Wire Diameter: 0.013” to 0.035”
Medium Extension Springs
These have the following dimensions:
Outer Diameter: 0.501” to 1.000”
Wire Diameter: 0.036” 0.098”
Large Extension Springs
These have the following dimensions:
Outer Diameter: 1.001” to 1.500”
Wire Diameter: 0.099” to 0.148”
Heavy Duty Springs
These have the following dimensions:
Outer Diameter: 1.501” to 2.500”
Wire Diameter: 0.156” to 0.375”
Extension Springs Color Codes
On top of the common sizes, you can use extension spring charts to determine the appropriate spring size for the load. Unlike the color code for torsion springs, the extension spring color code relies on the load’s weight, not the wire diameter.
The color repeats itself after every 100 pounds, so you should check the weight and color respectively. The extension spring color chart is as illustrated below;
Color Load in pounds
White 10lbs, 110lbs, 310lbs, 410lbs
Green 20lbs, 120lbs, 220lbs, 320lbs, 420lbs
Yellow 30lbs, 130lbs, 230lbs, 330lbs, 430lbs
Blue 40lbs, 140lbs, 240lbs, 340lbs, 440lbs
Red 50lbs, 150lbs, 250lbs, 350lbs, 450lbs
Brown 60lbs, 160lbs, 260lbs, 360lbs, 460lbs
Orange 70lbs, 170lbs, 270lbs, 370lbs, 470lbs
Gold 80lbs, 180lbs, 280lbs, 380lbs, 480lbs
Light Blue 90lbs, 190lbs, 290lbs, 390lbs, 490lbs
Tan 100lbs, 200lbs, 300lbs, 400lbs
Spring Performance Measurements
On top of the physical attributes of a spring, several actors also matter when sizing a spring to determine if it will serve your purpose. These performance attributes include;
Spring rate: It refers to the force, usually measured in pounds, that is needed to stretch the spring by one inch. Things that affect the spring rate include the material of the spring and the wire diameter.
Maximum extended length: It is the furthest length a spring can extend before warping or failing.
Maximum load: The weight the spring can support at full extension.
Spring pitch: It’s the distance between two wire centers in coils next to each other. If the coils are closely wound, it is the same as the wire diameter.
Initial tension: It refers to the force needed to overcome the spring pitch when the spring is at rest.
Spring index: This is the result of the coil diameter divided by the wire diameter and matches the initial tension, which is the force you need to start extending the spring.
Conclusion
Finding the right size is vital when choosing your extension spring. There are many considerations and factors that can be overwhelming. As your trusted spring partner, Foshan Gonglian Metal makes the whole process easier. We guide you every step of the way and, even crucially, can custom-make any spring to your preferences and needs.