Compression Spring Rate Calculator

Compression Spring Rate Formula:

\[ K = \frac{G \times d^4}{8 \times D^3 \times N} \]

Shear Modulus (G):

N/mm²

Wire Diameter (d):

Mean Coil Diameter (D):

Active Coils (N):

number

Spring Rate (K):

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1. What is Compression Spring Rate?

The compression spring rate (K) is the amount of force required to compress a spring by a unit distance. It's a fundamental property that determines how stiff or soft a spring is, measured in Newtons per millimeter (N/mm).

2. How Does the Calculator Work?

The calculator uses the compression spring rate formula:

\[ K = \frac{G \times d^4}{8 \times D^3 \times N} \]

Where:

\( K \) — Spring rate (N/mm)
\( G \) — Shear modulus of material (N/mm²)
\( d \) — Wire diameter (mm)
\( D \) — Mean coil diameter (mm)
\( N \) — Number of active coils

Explanation: The formula shows that spring rate is directly proportional to the shear modulus and the fourth power of wire diameter, and inversely proportional to the cube of mean diameter and number of active coils.

3. Importance of Spring Rate Calculation

Details: Accurate spring rate calculation is crucial for designing mechanical systems, ensuring proper force deflection characteristics, and predicting spring behavior under load.

4. Using the Calculator

Tips: Enter all values in the specified units. Ensure wire diameter and mean coil diameter are measured accurately as they have significant impact on the result.

5. Frequently Asked Questions (FAQ)

Q1: What is typical shear modulus for spring steel?
A: For common spring steels, G is approximately 79,300 N/mm² (11,500 ksi).

Q2: How does wire diameter affect spring rate?
A: Spring rate increases with the fourth power of wire diameter - doubling wire diameter increases spring rate by 16 times.

Q3: What is meant by "active coils"?
A: Active coils are those that are free to deflect under load, excluding any ground or inactive end coils.

Q4: Can this formula be used for extension springs?
A: This formula is specifically for compression springs. Extension springs have slightly different calculations due to initial tension.

Q5: How does temperature affect spring rate?
A: At elevated temperatures, the shear modulus decreases, which reduces spring rate. Special high-temperature alloys may be needed for hot environments.