Understanding Spring Load and Its Relation to Spring Rate
You may know spring rate, but do you understand the calculation of spring load? This is crucial as it pertains to the proper creation of springs for your applications and products. Read the details below.
Having a good understanding of spring load and its relation to spring rate will ensure you design the right spring for your application. The reason lies in your ability to measure the proper dimensions of the spring and also calculate the spring load and rate.
Accordingly, let’s guide you on these measurements and calculations.
What is Spring Load?
The spring load describes a certain amount of force or pressure at the desired loaded height. Here’s an example depicting how spring load works and how it can be derived from spring rate.
If a spring has a 5-inch free length, a spring rate of 7.5 pounds of force per inch (lbf/in) and will travel 2 inches. How much load should be applied for the spring to travel down to a loaded height of 3 inches?
The following considerations will help you solve the problem above:
Imagine you have a spring whose free length is 5 inches and the spring rate is 7.5 pounds of force per inch (lbf/in). The spring needs to attain a solid height of 3 inches, which requires it to travel 2 inches.
Accordingly, you’ll multiply the distance covered by the spring rate using the spring load formula to determine the working load of the amount of force needed to reach a solid height of 3 inches.
The formula to use in this case is:
- Spring Load Formula
- Rate (Travel) = Load
Inputting your data into the formula, you get:
15 = L
What is Spring Rate?
The spring rate, on the other hand, is the constant amount of force required to move an inch or millimeter of distance. Compared to spring load that measures a specific amount of force at a specific loaded height, spring rate determines the rate of force needed to travel a unit of measurement.
It’s possible to use either spring load or spring rate to calculate the other i.e the rate to calculate working loads and working loads to calculate the rate.
Here’s a more detailed outline of the spring rate calculation:
Spring rate is a complex calculation that can be made easy with the use of a formula.
The formula is:
- Spring Rate Formula
- Rate = Load ÷ Travel
- k= L ÷ T
Using the values in the first example, (If a spring has a 5-inch length, the spring rate of and will travel 2 inches), you can calculate the amount of spring rate needed to travel down to a loaded height of 3 inches using the formula above.
Therefore, you’ll have:
- k = 15 ÷ 2
- k = 7.5 lb/in
You’ll be able to calculate the needed spring rate based on the spring’s working loads.
Other formula variables you may come to appreciate are:
- Formula Variables
- Spring Wire Diameter = d
- Spring Outside of Spring = D outer
- Mean Diameter Of Spring = D
- Young’s Modulus of material = E
- Shear modulus of material = G
- Spring Constant = K
- Active Coils = na
- Poisson ratio off Material = V
How to Theoretically Determine Spring Load
Although you now have the formula to work with to determine spring load, there’s another easy way to go about this calculation. It’s being able to theoretically determine spring load.
In your manufacturing process, it is essential to know how to theoretically determine spring load to ensure you design the right spring for your specific application. A wide range of springs are used in different products and these springs have different considerations to pay attention to while determining the load.
With that in mind, hold the following in high esteem.
1. Helical Compression Springs
The theoretical load of helical compression springs can be determined by knowing the outer diameter, free length, wire diameter, and the number of coils.
Other details to pay attention to are end type for e.g closed and squared, where the last coils are in contact with the previous coil. Another end type is open ends, where the ends have space between them.
Further, there’s the closed and grounded, where the last coil is flat. There’s also the double closed ends and in this case, the last two coils on the ends are closed to stabilize it or assist in minimizing tangling.
2. Tension and Extension Springs
The theoretical load of tension and extension springs can be determined by considering the outer diameter, wire diameter, length of the body, length inside the hook, and the type of hook used.
The types of hook are machine hooks and this hook is made out of the coils at the end. Also consider cross-over center hook and in this case, the ends are bent straight down the center and then loops around. There are side hooks and these are bent outwards from the spring’s side. No hooks depict when the ends serve as threading when you want to insert a bolt in the middle.
3. Torsion Springs
When it comes to torsion springs, you need to measure the number of coils, wire diameter, length of legs 1 and 2, outer diameter, and any bends or shapes on the legs.
Measuring the Dimensions
Now that you know the dimensions to measure for each spring, it’s also important to get the accurate dimensions to determine spring load. In accordance, use calipers to measure the spring.
The calipers can be held in one hand while the base of the spring is held with the other hand.
The outside diameter can then be calculated by measuring the largest dimension on the outside of the last coil. The inside diameter can be calculated by placing the teeth of the caliper on the inside diameter.
The free length is measured by placing the calipers on the entire length of an uncompressed spring. What’s more, put the calipers in the center of the spring to find the wire size.
Start counting all the coils from one end beside where the wire has been cut while ensuring that all portions of the coil are counted.
All the dimensions having been determined means you can proceed to calculate the spring load using a spring calculator or employing the services of an expert. It’s often advised that you allow a spring expert to carry out the calculation on your behalf to ensure you get an accurate gauge.
These are the important details to understand when it comes to spring load and its relation to spring rate.
The formula to calculate each has been provided and even how to theoretically determine spring load for a torsion spring, helical spring, and other spring types.
We’ll re-emphasize how important it is to get the right dimensions for each spring in a bid to ensure the spring is the best for its application.
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