What Is a Flat Torsion Spring?

You need rotational force but have very little axial space. A standard, bulky round-wire torsion spring simply won't fit, forcing a complete redesign of your compact product.

A flat torsion spring is any spring made from a flat strip of material, like spring steel, that stores and releases rotational energy. Its slim profile makes it ideal for applications with tight space constraints.

When an engineer sends me a drawing for a "flat torsion spring," my first question is always, "What exactly does it need to do?" The term is a general category, not a specific part. It's like asking for a "car" when you need to specify if it's a truck, a sedan, or a sports car. Choosing the correct type of flat spring is one of the most important decisions for ensuring your mechanism works smoothly and reliably for its entire service life.

Is a Spiral Torsion Spring the Same as a Flat Torsion Spring?

You're looking for a simple return spring, but the terminology is confusing. You see different coiled flat springs and assume they all work the same, which could lead to ordering the wrong part.

A spiral torsion spring[^1] is a specific type of flat torsion spring[^2]. It's designed with open coils that do not touch and is best suited for low-rotation applications, typically less than 360 степени.

I remember working with a company that was developing a high-end control knob for audio equipment. They wanted a smooth, tactile "return-to-center" осетити. They initially tried a small power spring, but it provided too much rotation and felt inconsistent. The solution was a true spiral torsion spring. We designed one that provided just the right amount of torque over a 45-degree rotation. The gaps between the coils ensured there was no friction, giving the knob that premium, fluid motion they were looking for.

Defining Characteristics

The key to the spiral torsion spring is in its simple, open-coil design. It’s elegant and effective for specific tasks.

• Изградња: It's made from a single strip of rectangular spring steel coiled on one plane. One end is typically bent to form an inner anchor (to attach to a shaft), and the other end is formed to push against the rotating part.
• Function: As the component rotates, it winds the spring tighter, bending the material. The material's resistance to this bending creates the restoring torque. Because the coils are not designed to touch, the torque response is very linear and smooth for small deflections. It is not meant for applications requiring many turns.

When Is a Power Spring (Clock Spring) the Right Choice?

Your product needs to retract a long cord or belt, which requires many full rotations. A simple spiral spring would bind up and fail almost immediately.

A power spring, also known as a clock spring, is the correct choice for high-rotation retraction. This type of flat torsion spring[^2] is pre-stressed and contained in a housing, allowing it to deliver consistent torque over many turns.

One of our biggest clients manufactures industrial equipment, including retractable air hoses for workshops. The springs inside these reels are serious components. They have to pull back 50 feet of heavy hose smoothly and reliably thousands of times. This is the classic application for a power spring[^3]. The spring is tightly wound inside a drum. As you pull the hose, the spring gets tighter. When you release it, the stored energy pulls the hose back in. A simple spiral spring couldn't store enough energy or provide enough turns to do that job.

The Importance of the Housing

Unlike a simple spiral spring, a power spring[^3] is a complete system that relies on its housing to function correctly.

• Складиштење енергије: A power spring[^3] is made from a long strip of material that is pre-formed into a tight coil. It is then installed into a housing or case that is slightly larger than its free diameter. This process "pre-loads" the spring with energy.
• Friction and Control: As the spring works, the coils press against each other and the inside of the housing. This controlled friction is part of the design and helps create a flatter, more consistent torque curve compared to a spiral spring. This is why you get a steady pull from a tape measure instead of a force that drops off quickly.

Can You Use a Simple Flat Bar as a Torsion Spring?

You need a very simple, low-cost spring for a basic hinge or latch mechanism. A coiled spring seems like overkill, and you're wondering if there's a simpler way.

Yes, a flat torsion bar is the simplest form of a flat torsion spring. It's a straight strip of spring material that provides a restoring torque when twisted, making it perfect for simple, low-rotation applications.

I once worked on a project for an agricultural equipment manufacturer. They needed a spring for the closing mechanism on a seed hopper lid. It was a harsh, dirty environment, and the mechanism had to be foolproof and cheap. We didn't use a coiled spring at all. We designed a short, straight piece of hardened flat spring steel. One end was welded to the hinge, and the other rested against the lid. When you opened the lid, it twisted the bar. When you let go, the bar untwisted and snapped the lid shut. It was incredibly simple, cost almost nothing to make, and it will probably outlast the rest of the machine.

Simplicity in Design

Sometimes the most effective solution is the one with the fewest parts. The flat torsion bar is a perfect example of this principle.

• How It Works: A torsion bar works by resisting torsional (увијање) forces along its length. Unlike coiled springs that store energy by bending the material, a torsion bar[^4] stores energy through twisting. The amount of torque it provides is determined by its length, thickness, width, and the material it's made from.
• Applications: This design is best for low-angle, high-reliability applications where space for a coil does not exist. It's often found in vehicle suspensions, durable latches, tool battery clips, and simple hinge counterbalances. Its main advantage is its extreme durability and low cost.

Закључак

"Flat torsion spring" describes a family of solutions. Choosing the right one—whether a spiral spring, a power spring[^3], or a simple torsion bar[^4]—is critical for your design's performance and success.

[^1]: Learn about spiral torsion springs and their unique design features that make them suitable for specific applications.
[^2]: Explore this resource to understand the versatility and applications of flat torsion springs in various designs.
[^3]: Discover the functionality of power springs and their importance in high-rotation applications.
[^4]: Find out how torsion bars work and their applications in various mechanical systems.