What Is a Spiral Torsion Spring?

You need a rotational return force, but a standard torsion spring is too bulky. This forces design compromises, creating an oversized product or a mechanism that simply will not fit.

A spiral torsion spring is a compact solution made from a flat strip of metal wound into a spiral. It stores and releases rotational energy, providing torque in a very small axial space.

Over my years in spring manufacturing, I've seen many engineers focus on the main components of their design, leaving the spring as an afterthought. Then, at the last minute, they realize there's no space for the bulky helical spring they planned on. This is the exact moment when the unique, flat profile of a spiral torsion spring becomes a project-saver. It’s a specialized component, but for the right application, it’s the only one that will work.

How Does a Spiral Torsion Spring Actually Work?

You see this flat, clock-like coil, but it's unclear how it generates force. You're not sure how it differs from a regular torsion spring made of round wire.

A spiral torsion spring[^1] works by storing energy in its flat material as it is wound tighter or unwound from its natural state. One end is fixed to a stationary post, and the other is attached to a rotating component, delivering torque as it tries to return to its original shape.

I remember working on a prototype for a medical device that needed a knob with a very specific "return-to-center" осетити. The designers first tried using two small helical torsion springs, but the mechanism felt clunky and unbalanced. We switched to a single spiral torsion spring[^1]. By fixing the outer end and attaching the inner end to the knob's shaft, we gave it a perfectly smooth, consistent rotational force that brought it back to the zero position every time. The spring wasn't just a component; it was critical to the product's user experience.

The Principle of Flat-Plane Energy Storage

The magic of this spring is in its geometry. It stores energy in a completely different way than a standard helical spring.

• Flat Material, Not Round Wire: The spring is made from a rectangular or flat strip of material. This allows the coils to nest inside each other on a single plane, which is why its axial profile is so slim.
• Bending Stress is Key: When you rotate the spring, you are essentially bending the entire length of the flat strip. The material's resistance to this bending is what creates the restoring torque.
• Mounting for Motion: To work correctly, one end must be anchored while the other is free to rotate with your component. The inner end is typically fixed to a shaft (arbor), and the outer end pushes against a pin or slot on a rotating housing[^2].

What Are the Main Applications for a Spiral Torsion Spring?

You understand the mechanics, but you're not sure if this specialized spring is the right choice for your product. You need to know where it performs best.

Spiral torsion springs are ideal for applications that need a rotational return or retracting force over a set number of turns. They are common in tape measures, small engine rewind starters, mechanical timers[^3], and seatbelt retractors.

One of my clients designs and manufactures high-end office equipment. They were developing a new cable management system for conference tables where a user could pull out a power cord, and it would lock in place. When finished, a button press would cause the cord to retract smoothly back into the table. The heart of that entire smooth-retraction feature was a spiral torsion spring. It provided the consistent, reliable pulling force needed to wind the cord back onto its spool every time without jamming, all within a housing that had to be incredibly compact to fit under the table.

Where This Spring Excels

This design is not a general-purpose spring; it is a specialist chosen for its unique capabilities.

• Retracting Mechanisms: This is its number one job. The spring provides the pulling force to automatically rewind cables, црева, tapes, or straps onto a spool.
• Counterbalancing: In devices with hinged components, like a small lid or door, a spiral torsion spring can be used to offset the weight, making it easy to open and preventing it from slamming shut.
• "Return-to-Zero" Functions: For knobs, dials, or switches that need to return to a default position after being turned, a spiral spring provides a simple and reliable rotational return force[^4].

What Is the Difference Between a Spiral Spring and a Power Spring?

You hear the terms "power spring[^5]," "clock spring," and "spiral torsion spring[^1]" used for similar-looking parts. You're confused about the actual difference and which one you really need.

While they look alike, a spiral torsion spring's coils remain separated during operation. A power spring[^5] (or "clock spring") is designed so its coils are pressed tightly together inside a housing[^2], allowing for many more rotations and a flatter torque output.

This is a very important distinction that can cause major confusion. I once had a customer send us a drawing for what they called a "spiral spring." But their application required 15 full rotations to retract a long strap. A true spiral torsion spring can't do that; its coils would bind up. What they actually needed was a power spring, which is specifically designed for high-rotation applications by allowing the coils to slip against each other within a housing[^2]. We had to clarify the design with them to ensure we manufactured the right part for the job.

The Key Distinctions

The difference comes down to the housing[^2] and how the coils interact.

• Coil Interaction: A spiral torsion spring[^1]'s coils are designed with a gap between them. They should not touch during operation. A power spring's coils are in constant contact, sliding against each other as the spring winds and unwinds.
• Housing: A power spring[^5] must be contained in a housing[^2] or case. Ово housing[^2] keeps the coils compressed and allows them to function correctly. A spiral torsion spring is often mounted more openly, only needing an arbor for its center and a pin for its outer leg.
• Rotational Capacity: Spiral torsion springs are typically used for applications needing less than 360 degrees of rotation, though some designs allow for a few turns. Power springs are designed for many full rotations.

Закључак

Тхе spiral torsion spring[^1] is a specialized component that provides rotational force in a compact, flat package, making it the perfect solution for retracting, returning, and balancing applications where space is limited.

[^1]: Explore this link to understand the unique mechanics and applications of spiral torsion springs.
[^2]: Understand the importance of housing in ensuring the proper function of springs.
[^3]: Explore the functionality of mechanical timers and their reliance on springs.
[^4]: Learn about rotational return forces and their importance in various mechanical applications.
[^5]: Clarify the distinctions between power springs and spiral torsion springs for better design choices.