An extension spring or tension spring is a length of tightly coiled metal, usually steel with hooks or loops at either end. Extension springs absorb and store energy. You can find out more in our extension springs guide.
What is an Extension Springs?
Extension springs absorb and store energy as well as create resistance to a pulling force. These springs are usually attached to other components at both ends and when those components come apart the spring tries to bring them back together again.
It is the initial tension that determines how tightly together the spring is coiled. This initial tension can be manipulated to meet the load requirements of a particular application. Designs usually have hooks, eyes, or other interface geometry on the ends that attach to the opposing components.
They are often used to provide a restoring force to components that extend in an actuated position.
How do Extension Springs work?
Extension springs generally have a hook or eye at each end to facilitate attachment. Variations on the ends include open hooks, extended hooks, side hooks, and double full loops.
Extension springs are often used to create a restoring force in mechanisms such as latches and counterbalances. Since extension springs are under tension, they do not need any support along their length. This often results in a simpler mechanism than if a compression spring were used.
The ends of an extension spring are attached between two mechanisms. The hooks and loops of the tension spring store and absorb energy. An extension spring provides the connected mechanisms with a restoring force through hooks or loops.
Tightly coiled extension springs typically sit in the idle position. More stress in the end hook in contrast to the spring body limits the performance of extension springs.
Key Features of Extension Springs
- Coiled Design: Made of tightly wound coils to provide resistance.
- End Attachments: Hooks or loops on both ends for easy installation.
- Initial Tension: A small force is required to start extending the spring.
- Elasticity: Ability to return to the original shape after stretching.
Materials Used
Extension springs are commonly made from materials that provide strength and flexibility, such as:
- High-carbon steel
- Stainless steel
- Alloy steel
The choice of material depends on the environment in which the spring will be used, such as exposure to moisture, temperature, or heavy loads.
Applications
Extension springs use a variety of hook or loop end configurations to serve specific functions. Tension spring ends include threaded inserts, extended twist loops, crossed center loops, hooks, expanded eyelets, reduced eyelets, square ends, and teardrop-shaped ends.
Change the length of the hooks and spring body spacing for custom tension spring fits and functions.
Find extension springs in a wide variety of everyday items from garage doors to tools to washing machines and toys. The variety of sizes makes extension springs versatile as they are used in small medical devices and off-road machines.
Common applications of extension springs include:
- Car interiors and exteriors
- Garage door assemblies
- Vise-grip pliers
- Carburetors
- Trampolines
- Washing devices
- Farm machinery
- Toys
Advantages
- Simple Design: Easy to manufacture and install.
- Cost-Effective: Affordable compared to more complex components.
- Versatile: Suitable for a wide range of applications.
- Reliable Performance: Durable when used within design limits.
Limitations
- Risk of Overstretching: Can lose elasticity if stretched beyond capacity.
- End Weakness: Hooks or loops may be points of failure under high stress.
- Safety Concerns: If a spring breaks under tension, it can snap back dangerously.
Maintenance and Safety Tips
- Regularly inspect springs for signs of wear or corrosion.
- Avoid exceeding the recommended load capacity.
- Replace damaged springs immediately.
- Use safety cables in high-tension applications like garage doors.