Constant Force Spring

Ⅰ. Definition

As the name suggests, a constant force spring is a spring that can maintain a constant elastic force within the corresponding stroke. It is also called a constant force spring. It is used for linear motion and generally uses its rebound force.

Advantages: Compared with ordinary compression or tension springs, its elastic force is very constant and can output a nearly straight-line elastic force, ensuring that the product will not change due to changes in elastic force during use. In a narrow space, the space can be reduced as much as possible , increasing the possibility of beautiful design of products. The graph is as follows:

Disadvantages: Since it is used in a straight line, its space must be of a certain length to exert its effect. Compared with the power spring, its lifespan is obviously shorter, generally only about 2000 to 5000 times.

Ⅱ. Application of constant force spring

1. Lift fan

Compared with the old design that relies on screws to fix the fan head, constant force spring can be easily raised and lowered, and can be easily fixed in the middle position, making the fan more beautiful and convenient. At present, this type of design has been sold abroad for many years, and the design is quite mature.

2. LCD display

As monitors become larger and larger and the requirements become higher and higher, the old monitors that can only adjust the angle forward and backward are obviously no longer able to meet the requirements. Today's monitors can rotate 360°, tilt forward and backward, and slide up and down, almost omnipotent. The function of sliding up and down and stopping at any fixed point is achieved by using a constant force spring. Through its balanced elastic force, it can stably hold the monitor head at any position and prevent it from sliding down. At present, all the PC giants in the world adopt this new design, making it more and more perfect in function.

3. Up and down sliding doors and windows

In the European and American markets, up-and-down sliding doors and windows have always been popular, and the force of their upward sliding comes from constant force springs. Through the rebound force of a set of constant force springs on each side, the glass doors and windows can slide upward easily. Alleviating its heavy resistance.

4. Supermarket automatic vending shelves

In order for customers to see that the goods on the shelves are neat and beautiful, salespeople are often required to organize the shelves. Now in some high-end shopping malls, automatic push shelves are being used. As long as the goods in the front are taken out, the goods in the back will automatically move to the front. Pushing not only ensures beauty and tidiness, but also saves time. It is the automatic vending shelves that use constant force springs that realize this function.

5. Motor carbon brush pressing device

Since the ordinary carbon brush device uses a compression spring, the elastic force of the compression spring gradually weakens when it is used to the end, so that the carbon brush cannot press the rotating shaft with a constant force, which reduces the performance of the motor. However, the double curl design constant force spring can always provide constant elastic force to the carbon brush from beginning to end, so that the performance of the motor is always stable.

Ⅲ. Material selection of constant force spring

The preferred material for constant force springs is SUS301 series. This material has high hardness, high tensile strength, smooth surface, good rust-proof performance, and easy side processing... making this material almost the best choice for constant force springs. Its hardness can reach about Hv600 (after low-temperature heat treatment), its tensile strength can reach more than 1665Mpa, and its nickel content is between 6.0 and 8.0, ensuring its good anti-rust performance.

Of course, if the operating environment is more severe, in ultra-high temperature or ultra-low temperature environments, you can also choose the SJ101 series of wide-temperature, high-strength and constant-elastic alloys, which can still maintain high strength, constant elasticity, and low expansion coefficient at high temperatures. However, the unit price of its materials is expensive and it is generally not used.

4. Design of constant force spring

The design of constant force springs is generally considered from two aspects:

1. Performance

The two most important properties are elasticity value and lifespan. Elasticity Generally, the thicker and wider the material is, the higher its elasticity will be. Among materials of the same size, the smaller the inner diameter of the curl, the higher the elasticity. The lifespan is the opposite. Under the same manufacturing conditions, the thinner the material, the better its lifespan. Among materials of the same size, the smaller the inner diameter of the curl, the shorter the lifespan.

2. Installation space

Generally, the outer diameter of constant force spring is set according to the installation space. Sometimes when using a bottom bracket, the inner diameter must also be taken into consideration. Generally, the outer diameter of constant force spring cannot be larger than the installation space, otherwise friction will occur and affect the normal use.