How to Select the Right Tension Spring

Knowledge Center · 2026-10-06 09:21:19 · 3 hits

Tension Springs.jpg

1. Definition and Function

1.1 Definition

A tension spring (also called an extension spring) is a mechanical element that stores energy or generates force through elastic deformation. It is made by coiling metal wire into a helix, so it stores energy when stretched and releases it as it returns to its original shape.

1.2 Main Functions

Restoring force: When pulled by an external force, it produces a restoring force opposite to the direction of stretch.

Energy storage: It stores mechanical energy through tensile deformation and returns it on recoil.

2. Classification and Operating Principle

2.1 Classification

By material: Carbon steel, stainless steel, and other materials are selected for different working environments (e.g., corrosion resistance, temperature).

By shape: Common forms include cylindrical and conical springs.

2.2 Operating Principle

Per Hooke's law, the deflection of a spring is proportional to the applied force:

F = k · x

where F is the force, x is the extension, and k is the spring rate (stiffness). The spring rate is not a material constant alone — it is governed by the material's shear modulus and the spring geometry (wire diameter, mean coil diameter, and number of active coils). This is why two springs of the same material can have very different stiffness.

3. Key Selection Parameters

3.1 Dimensions

Free length (L₀): The natural length of the spring with no load applied.

Inner / outer diameter: Determined by the available installation space (housing bore or mandrel).

3.2 Mechanical Properties

Spring rate (k): The force required per unit of extension; it defines the spring's working characteristic.

Maximum load capacity: The greatest tensile force the spring can safely withstand.

Parameter	Sets / affects
Free length (L₀)	Installed length and initial gap
Outer / inner diameter	Fit to housing or mandrel
Spring rate (k)	Force produced per unit extension
Maximum load	Safe working limit
Wire diameter	Strength and stiffness

3.3 End Type

The end form determines how the spring anchors to mating parts and how it handles misalignment.

End type	Feature	When to use
Machine loop (standard)	Closed coil loop at both ends, in-line	General-purpose, purely axial loading
Extended hook	Loop on a short straight extension	Needs standoff / clearance from the mount
Cross-over hook	Loops on opposite sides	Compact, resists tangling
Swivel hook	Rotating hook end	Misaligned or moving anchor points

4. Selection by Application

4.1 Industrial Equipment

High precision is required, so specify springs made to tight manufacturing tolerances.

Wear resistance and corrosion resistance are important considerations for duty life.

4.2 Consumer Products

Cost control matters, while basic functional requirements must still be met.

Appearance should also suit the overall product style.

4.3 Material Selection by Duty

Material	Corrosion resistance	Strength / cost	Best for
Carbon steel	Low (needs plating)	High strength, low cost	Indoor, dry, cost-sensitive duty
Stainless 302 / 304	Good	Moderate, higher cost	Humid or mildly corrosive environments
Stainless 316	Excellent	Good, higher cost	Outdoor, chemical, marine duty
Music wire (high-carbon)	Low	Very high strength	High-fatigue, precision applications

Quick Selection Checklist

Defined the required force at the target extension (use F = k·x).

Chosen material for the environment (stainless for corrosion, carbon steel for cost).

Confirmed free length and diameters fit the installation space.

Verified max load ≥ expected peak load with a safety margin.

Specified end type (loop / hook) compatible with mounting.

For fatigue duty, confirmed cycle-life rating.

5. Installation and Maintenance

5.1 Installation Points

Ensure accurate positioning to avoid eccentric (side) loading that causes uneven stress.

Check that mating parts are smooth so they do not abrade the spring surface.

5.2 Maintenance Recommendations

Periodically inspect spring condition and address any abnormality promptly.

Keep the spring and its surroundings clean and dry.

6. Application Cases

6.1 Automotive Suspension

Effectively absorbs road shock to improve ride comfort.

Requires good fatigue resistance for long service life.

6.2 Electronic Switch Devices

Provides appropriate trigger-force feedback for buttons.

Spring parameters must be precisely controlled to ensure switch sensitivity.

7. Common Issues

ssue	Likely cause	Corrective action
Premature breakage	Overload, sharp bend at hook, fatigue	Lower load; increase wire diameter; use larger bend radius
Loss of force (set / relaxation)	Exceeded elastic limit	Keep within max load; specify pre-set manufacturing
Corrosion	Wrong material for environment	Switch to stainless or plated version
Tangling in bulk	Loose coils, hooked ends	Use sorted packaging or cross-over ends
Hook deformation	Side load / eccentric pull	Align load axis; use swivel hook