Power Springs: Principles, Applications, and Design Points

Power springs, as a device for storing and releasing torque, work by precisely winding strip material around a mandrel and then embedding it in a specific housing or fixed ring. This design allows power springs to effectively store energy and release it in the form of torque when needed.

1. Wide Application of Power Springs

Power springs play a key role in many applications that require torque output. From common watches and toys to seat belt pretensioners, canister vacuum cleaners, and even dog leashes and badge reels, power springs provide these products with long-lasting power through their unique performance.

2. Design Points: Inner Diameter of Housing and Spring Material

When designing a power spring, the inner diameter of the housing is an important consideration. It determines the amount of space the spring material can occupy, which in turn affects the number of coils and performance of the spring. Typically, the spring material should occupy 40% to 50% of the housing space to maximize space utilization. This ensures that the spring has enough room to move during winding and unwinding, while avoiding excessive compression that causes performance degradation.

3. Box Width and Spring Design

When designing a power spring, box width is a critical parameter. This value is directly related to the maximum width of the spring steel, which affects the overall performance of the spring. Knowing the box width helps us to accurately calculate the space that the spring can occupy, ensuring that the effectiveness of the spring is maximized within the limited space.

4. Spring Box Height and Material Utilization

When considering the width of the box, we also need to pay attention to the height of the spring box. Although the spring box does not usually need to occupy all of the available space, knowing the overall size of the box can help us determine how to use the spring material most effectively. Once the design has been determined, we can recommend the most appropriate spring size and type based on the size of the shell to achieve the best performance.

5. The Importance of Mandrel Size

As the core component of the power spring, the size of the mandrel has a significant impact on the performance of the spring. The mandrel is located in the center of the housing, and the inner part of the spring is connected to it. The diameter of the mandrel not only determines the spatial arrangement inside the case, but also affects the number of available coils and the overall size of the spring.

6.Maximum Torque and Hysteresis

When discussing the performance of power springs, maximum torque is a key parameter. Torque is not the tension on the cable as we usually think of it, but the rotational force generated by the spring when it is uncoiled. The size of this force directly affects the size of the load the spring can drive or operate.

It should be noted, however, that power springs experience hysteresis due to the presence of friction. This means that the torque required to wind the spring is often greater than the torque required to unwind the spring. Therefore, this hysteresis effect must be taken into account in the design to ensure that the spring is stable and reliable in practical applications.

7.Torque variation characteristics

The torque of power springs is not uniform. The torque increases rapidly in the first few turns and the last few turns of the spring. In order to fully utilize the performance of the spring and avoid excessive stress, it is usually recommended to keep the first 20% of the turns available and the last 20% inactive when designing the spring. This means that in practical applications, we will only use the middle 60% of the turns of the spring to drive the load, thus ensuring the stability and reliability of the spring.

8.Life Cycle Considerations

The service life of a power spring refers to the number of complete winding and unwinding cycles that it can withstand. In general, the life of a power spring rarely exceeds 200,000 cycles, and in some applications where space and torque are optimized, it may be less than 100,000 cycles. However, it should be noted that this life is not absolute and is affected by many factors such as frequency of use, load size, environmental conditions, etc.

Therefore, when designing a power spring, we must set reasonable service life targets based on the requirements of the actual application. At the same time, by selecting suitable materials, optimizing design parameters and taking appropriate maintenance measures, the service life of the power spring can be extended and its reliability improved.