Difference Between Close Coiled Helical Spring and Open Coiled Helical Spring

Helical springs are made by bending wires of constant diameter in the form of helix. Such springs are commonly used for storing and releasing energy as well as for absorbing shock and vibration. Based on the purpose, helical springs can be classified into two groups—extension spring and compression spring. As the name suggests, compression spring is employed when the spring is subjected to compressive loading and is required to shorten its length. Contrary to this, an extension spring is applied where it is subjected to tensile forces. Thus extension springs can substantially elongate under tensile load. Extension springs can again be of two types—close coiled and open coiled.

In a close coiled helical spring, spring wire is bent in such a way that there exists almost no gap between two adjacent coils. Thus two adjacent coils touch each other. Helix angle is usually very small (below 10º) in such springs. However, it requires minimum longitudinal space for same stiffness requirement. Thus close coiled helical springs provide a compact design. On the other hand, in an open coil helical spring, sufficient gap is maintained between two adjacent coils. Thus they offer small amount of compression without failure. Various similarities and differences between close coiled helical spring and open coiled helical spring are given below in table form.

Similarities between close coiled and open coiled helical spring

  • Both of them are extension type spring thus are used when springs are subjected to tensile loading.

Differences between close coiled and open coiled helical spring

Close Coiled Helical Spring Open Coiled Helical Spring
Helix angle of close coiled helical spring is below 10º. Helix angle of open coiled helical spring is more than 10º.
Here the spring coils are wounded in such a way that there exists almost no gap between two adjacent coils. So adjacent coils touch each other. Here sufficient gap is maintained between two adjacent coils as coils are not wound tightly.
Pitch of the spring coil is smaller as the helix angle is small. It has longer pitch because of high helix angle.
A close coiled helical spring does not deflect in axial direction under axial torsion. An open coil helical spring can deflect in axial direction under axial torsion.
Under normal state, it requires minimum longitudinal space for a given stiffness requirement. Open coiled spring requires comparatively longer space for same stiffness requirement.

 

References

  • Book: Strength of Materials by S. S. Rattan (Tata McGraw-Hill Publishing Company Limited).
  • Book: Strength of Materials: A Practical Approach by D. S. P. Rao (Universities Press).
  • Book: Introduction to Machine Design by V. B. Bhandari (McGraw Hill Education India Private Limited).