Spring End Types: Compression, Extension & Torsion
A mechanical spring is a rigid wire drawn into a helical coil configuration. It is designed to deform elastically under a mechanical load, storing energy and then releasing it upon unloading to achieve an intended mechanical
functionality. The spring is a simple yet clever design that can store mechanical energy in engineering and industrial applications of all sizes.
The spring type determines the spring’s end type configuration, as each of the three major spring types - compression, extension, and torsion- are designed to absorb different mechanical loads.
Understanding the importance of spring end types is crucial for design engineers because the spring end serves as the primary interface between the spring and the applied loads. As such, the spring end significantly influences the mechanical system's performance, reliability, and overall stability. Before diving deeper into spring end types, it’s essential to understand the difference between the three main spring types.
Overview of Spring Types and Their End Configurations
At a high level, each end type must be configured to absorb the mechanical loads they are designed to resist.
Compression Springs are designed to resist compressive forces, meaning the coils are designed to be pressed together. They store compressive mechanical energy when compressed.
Extension Springs are designed to resist tension forces. These springs are similar to compression springs, except their coils are wound tighter because they are designed to be extended during operation. Extension springs absorb energy as the coils separate.
Torsion Springs are designed to resist twisting forces, as the name suggests. They are tightly wound helical coils with straight ends. When these ends are displaced by an applied force, the spring stores energy by resisting forces that twist the spring coil into a tighter helical wind.
Each spring type has its own set of specially designed spring ends for various applications. For instance, the compression spring end type determines whether the spring can stand freely or must be mounted over a rod or shaft for stability. The specific end-type geometries available for each spring type are detailed below, providing practical information for your design considerations.
Compression Spring End Types: An In-Depth Look
Compression spring end types can be categorized into a few high-level types. The first differentiator is whether or not the spring ends are Open or Closed-ended. Closed-end springs are stable when standing vertically, and the manner in which this flat surface differs between standard Closed-End and Closed-ground end springs.
Open End: Open-end springs are denoted by a uniform helical coil design with equal pitch throughout the entire compression spring. Every coil in the spring is active and open, meaning there is no contact between adjacent coils at the spring ends. Open-end springs do not stand flat on their ends and are usually designed to fit over a rod or shaft. Open ends are the least commonly specified compression spring end type. Because open-end springs are inherently unstable and do not stand flat, accurately measuring the spring rate can be difficult.
Closed-End: In simplest terms, closed-end springs feature ends that are closed or squared off to create a flat mating surface on each of the spring ends. This allows the spring to stand vertically in a stable position. Squared-end springs are closed-end springs with flat ends created by the coil wind touching the previous coil.
Closed and Ground End: Instead of squaring the spring ends using a partial helical wire coil, Closed and Ground springs have the helical coils at the spring ends ground into a flat surface. At the compression spring ends, the bearing flatness surface standard is typically 270 degrees, meaning the flat surface is 270 degrees in helical arc length out of the 360-degree total circumference. Custom grind angles can be configured for applications that require additional bearing surface contact. You can also specify the surface roughness of the end grind and the end squareness when shopping for custom compression spring end types.
You can shop our compression spring selection by spring end type to find thousands of in-stock compression springs. If you need a customized compression spring end-type configuration, you can request a custom quote today!
Extension Spring End Types: Characteristics and Uses
Extension spring end types fall into two main geometric categories- the hook and loop configurations.
Loops: Several different loop configurations are available, such as the full loop, the side loop, the double loop, and the double side loop. The full loop end type is centered in the middle of the extension spring helical coil, while the side loop features an offset loop at the outer diameters of the extension spring ends. The double loop configuration strengthens the interface because the loop end wires touch, reinforcing the circular loop end type.
Hooks: The most common end type is the machine hook, while crossover, side, and extended hooks are the other common end types. The wire at the coil ends is formed into a hook across the last coils. The extended hook end type is an elongated hook shape for applications requiring additional hook space to fit the spring. The hook radius is the most vulnerable part of the spring, where stress is the highest. Extended hook end types can be susceptible to premature failure if the spring is undersized for the application. The hook length and gap are two properties that can be customized to fit any design application.
No-Hook/No-Loop: Extension springs can be custom-configured with end types without hooks or loops. Extension springs with this end type are sometimes called extension cables. The ends of the spring are most commonly affixed directly to bolt heads at the spring end wire locations. The absence of a hook or loop end eliminates stress concerns at these locations, allowing the spring to achieve long useful lifetimes because the hook and loop ends are the most vulnerable to wear.
Using our practical spring catalog, you can shop extension springs by end type to find thousands of in-stock extension springs. If you need a custom extension spring end type, you can request a custom quote today!
Torsion Spring End Types and Selection Guide
Torsion spring ends consist of a segment of wire that protrudes beyond the spring body to form what is commonly called the leg configuration. The legs serve as the point of load application on the torsion spring. When the spring legs are displaced, the torsion spring stores energy by resisting the untwisting of the helical spring coils.
Typical torsion spring end types are either straight-leg or angled-leg configurations. A zero-degree torsion spring end type has legs that protrude from each end in the same direction, while a 180-degree spring has ends that protrude in opposite directions.
You can measure the leg angle by measuring the spring directly or counting the number of torsion spring coils. For example, a spring with five coils has a zero-degree leg configuration, while a spring with 5.25 coils has a 90-degree leg configuration.
Several torsion spring angle configurations are available and in stock today, in angles of 0, 45, 60, 90, 135, 180, 225, 270, and 315-degree configurations.
Using our interactive catalog, you can shop torsion springs by leg configuration to find thousands of in-stock torsion springs. We also offer engineering experience and state-of-the-art manufacturing equipment to mass-produce custom torsion springs, including customized double torsion spring leg configurations. If you need a torsion spring with a custom leg configuration, you can request a custom quote today!
Century Spring’s Custom Solutions for Every Spring End Type Need
Century Spring is a quality-first manufacturer that specializes in stock and custom springs. We have over 40,000+ high-quality springs in stock and available to ship today.
Don’t see the spring you need in stock? We also offer custom design and fabrication services to design an end type that meets your application’s unique challenges.
We always work quickly to minimize total development time so you can move on to tackling the next design challenge. Don’t waste any more of your valuable design time; let our spring experts take the lead.
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