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How Does a Tension Spring Work?

Tension Spring | KB Delta

Springs provide a mechanism for storing energy. Most springs are based on a wound coil, which takes the form of a spiral. When force is applied to the spring, its shape can either be extended or compressed. Once released, the spring generally returns to its original shape unless the amount of force exerted exceeds the spring’s capabilities.

Tension springs are a specific class of spring that operates in a particular way. This function is going to be explored throughout this article.


Tension Spring Design

A tension spring features a very tightly wound coil. On each end, there is often a hook or loop that provides a connection to another item. When a tension spring is at rest, it is generally in its most compressed form. Energy is created within the spring by stretching it, or by increasing the distance between the two ends.


How Tension Springs Create Energy

As a tension spring is stretched, the amount of stored energy begins to build. The reason the stored energy increases is due to the fact that the spring wants to return to a more compressed state. After pulling the two ends apart, if the ends are released, they will automatically come closer together. The ends can only be further apart than in the springs resting state by maintaining the extra distance through physical means.


What a Tension Spring Does

Tension springs are used to help keep two items within a particular distance while at rest, when the alternate state is for the items to be further apart. For example, a door that shuts automatically can be designed with a surface mounted tension spring door closer. When the door opens, the two ends of the spring are pulled further apart. Then, once the pressure associated with opening the door is released, such as by a person letting go of the open door, the spring automatically pulls the end that is attached to the door back towards the end of the spring that is attached to the frame. Ultimately, when the spring returns to its resting state, the door will be in the shut position.


Common Tension Spring Materials

Most tension springs are made of metal. The exact type of metal depends on the amount of stress to which it will be exposed, as well as certain environmental conditions. Some common metals for tension springs include, but are not limited to:

Each type of metal provides different benefits and is associated with a different cost.


Lifespan of a Tension Spring

Tension springs can have different life spans depending on the following:

  • their application
  • frequency of use
  • material
  • environment
  • amount of stress used

Each time a spring is stressed, the material loses some integrity. This can include micro-fractures as well as bends or warps. When fracturing occurs, springs can fail due to metal fatigue, a condition where the metal cracks in response to physical stress. Bending and warping can occur when the spring is stressed beyond its physical limits, causing the original coiled shape to be compromised.

Environmental factors are also relevant to their lifespan. Exposure to water, certain chemicals, and weather changes can affect the integrity of the metal. If a spring starts to rust or corrode, the material will not have the same amount of strength as it did previously. Over time, the can cause the metal to give way near the damaged area.


Risks Associated with Tension Spring Failure

A tension spring can fail in a few ways. First, if the metal is compromised, and causes the spring to break into two pieces, the coils will automatically attempt to return to a resting state. This can cause the metal to spring back quickly. If the end of the spring does not remain secure, the force associated with the store energy can launch the spring into motion. If this happens in a machine, the spring could damage components on impact. When it occurs in an open space, the spring may launch throw the air until it impacts a nearby item or it falls to the ground. Tension springs with enough energy can injure a person when they fail.

If a tension spring loses its form, such as through warping or bending, it will not perform its primary function as well as it did in its original condition. Expanding on the door example, a warped or bent tension spring may mean that once the door is opened, and the tension is released when a person releases the door, there might not be enough energy to pull the door back into its closed position. Essentially, the change in the coil of the spring affects its resting position, fundamentally changing its performance.


Managing Tension Spring Failure

Often, when a tension spring fails, the best course of action is to replace it. Once the original coiled shape becomes bent or warped, it is challenging to get it back into its original shape, even if the tension spring has not been subjected to significant use. If the tension spring breaks, it can be difficult to repair the break sufficiently. This means the spring could break again in the same location since it represents a weak point in the overall structure.

By getting a suitable replacement springs, you ensure that the proper amount of energy can be stored to perform the necessary function. Since most tension springs are connected to other components at each end, simply removing the old spring and attaching a new one is often all it takes to regain function.


Choosing Replacement Tension Springs

As with any replacement part, it is important the right tension spring is selected when replacements are necessary. This includes choosing options that are the same size as the original, has the same capacity for resisting stress, and that have the same amount of energy storing potential. Failing to do so will affect the overall function of any mechanisms connected to the spring, and could even produce dangerous situations that could cause harm to the items to which it is connected, as well as anyone nearby, depending on the change in performance and capacity and the exact conditions in which the tension spring is used.

When replacing tension springs in mechanical devices and equipment, refer to the owner’s manual for details regarding appropriate replacements.


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