Tension Springs: Engineering Selection Guide 2026
What Are the Core Technical Characteristics of Tension Springs?
Tension springs store energy via wire torsion, resisting pull forces. Key metrics include wire diameter, mean coil diameter, and initial tension force.
Tension springs function by storing energy through the torsion of their coils when a load is applied. Unlike compression springs that push back, these components are designed to pull two connected parts together. In industrial applications, they are rarely used to their absolute extension limit to prevent permanent set.
Standard materials include music wire (ASTM A228) for high-stress applications or 316 stainless steel for environments requiring corrosion resistance. Always verify the wire grade before installation in load-bearing machinery.
| Material | Typical Tensile Strength (MPa) | Corrosion Resistance | Max Operating Temp (°C) | Typical Applications |
|---|---|---|---|---|
| Music Wire (ASTM A228) | 1800–2200 | Low (requires coating/plating) | 120 | High‑stress industrial, automotive, garage doors |
| 316 Stainless Steel | 860–1000 | Excellent (marine, chemical) | 400 | Food processing, medical devices, marine hardware |
| Phosphor Bronze | 600–800 | Good (atmospheric, seawater) | 200 | Electrical contacts, springs requiring conductivity |
| Beryllium Copper | 1200–1400 | Good (non‑sparking) | 300 | Aerospace, oil & gas, precision instruments |
| Inconel X‑750 | 1100–1300 | Outstanding (high‑temp, oxidizing) | 700 | Turbochargers, nuclear, high‑temperature valves |
How is Initial Tension Calculated?
Initial tension is the internal force holding coils together, measured in Newtons (N). It must be overcome before any coils will separate.
Initial tension is a defining characteristic created during the winding process. It serves to keep the coils tightly closed when no external load is applied. When specifying, remember that this force is not linear; it is a fixed value that exists before spring extension begins.
- Initial tension equals roughly 5-15% of the spring’s maximum load capacity.
- Calculations must account for the wire diameter to coil diameter ratio.
- High initial tension is required to prevent gap formation in high-vibration systems.
- Use our Force Calculator to ensure your tension spring load profile meets application specs.
What Roles Do End Fittings Play?
End fittings transfer the pulling force to the coils. Common types include machine loops, cross-over loops, and extended swivel hooks.
The hook design is the most frequent point of failure in tension spring assemblies. Stress concentration occurs at the bend radius where the loop transitions into the body of the spring. I have seen hundreds of premature failures caused by using standard machine loops in high-cycle fatigue environments where a full-loop or swivel fitting would have doubled the service life.
How Do I Determine the Correct Spring Rate?
The spring rate is the force increase per millimeter of extension, determined by wire diameter, coil diameter, and the number of active coils.
Spring rate is constant for most standard helical tension springs. To increase the stiffness of an assembly, you must either increase the wire gauge or decrease the mean coil diameter. Simply stretching a spring further will not change its fundamental rate, but it will increase the risk of plastic deformation.
How Do I Diagnose Tension Spring Failure Modes?
Common failures include hook breakage from stress concentration, loss of initial tension, and permanent deformation from over-extension.
Why Do Hooks Break at the Bend?
Hooks break because the bending radius is too tight for the wire gauge. High stress concentration leads to fatigue cracking under cyclic load.
When specifying custom springs for industrial machinery, always request an increased bend radius. Sharp transitions at the hook base create high-stress risers that initiate fractures. In 2026, many manufacturers offer computer-aided stress relief at these points to mitigate failure.
How Does Plastic Deformation Occur?
Plastic deformation occurs when the spring is extended beyond its elastic limit, causing the coils to remain gapped after unloading.
Operating a spring beyond its yield strength permanently alters the coil geometry. Once the spring is “set,” it loses its initial tension and requires lower force to extend. If your mechanism relies on precise tension, discard any springs that show permanent length changes.
Can Tension Springs Be Reused?
Reusable springs must show no evidence of permanent set or corrosion. If the spring was overstretched during removal, it is effectively scrap.
In high-reliability assemblies, tension springs should be treated as single-use components during maintenance. Given the low cost of the component relative to the potential damage of a spring failure, I consistently recommend full replacement during overhaul.
Frequently Asked Questions About Tension Springs
What is the difference between open and closed coils?
Closed coils maintain initial tension, while open coils have gaps between them, meaning they offer no initial tension until stretched.
How do I account for temperature drift?
Springs lose approximately 1% force per 50 degrees Celsius of heat increase. Use stainless alloys for high-temperature stability.
Does mounting orientation matter?
Tension springs operate at any angle, but vibration damping is more effective when the spring is mounted parallel to the force vector.
For further guidance on selecting components for specific equipment, refer to our compatibility resources. Accurate specification prevents costly downtime in your production environment.
