Rotary Dampers | How Does It Work?

Rotary dampers work by rotating their shaft and generating the viscous resistance of oil. Therefore, when a lid is equipped with a rotary damper, it can be closed slowly with smooth, controlled motion. Rotary dampers are recommended for preventing problems such as loud noises and finger pinching that may occur when lids close suddenly with excessive force. While many people know that rotary dampers slow the movement of lids, they may be less familiar with where they should be installed, how they operate, or the types of applications they are best suited for. In this article, we will introduce how to install rotary dampers, how they work, and their main usage.

Basically, rotary dampers are mounted at the center of rotation of the object being moved. The housing, which is the main body of the rotary damper, is mounted on the fixed side, while the shaft is mounted on the moveable side, such as a lid. When using a lid equipped with a rotary damper, you must pay attention to the angle limit. If the lid is moved beyond this limit, the rotary damper may be damaged, the lid may close without the damping effect, or oil leakage may occur.

Rotary dampers exert their damping effect in either the CW or CCW directions, as viewed from the shaft. Therefore, the correct rotary damper should be installed and used according to the direction in which the lid closes. In the case of the lid shown in the picture here, an A type rotary damper operating in the CW direction is installed on the front side, and a B type rotary damper operating in the CCW direction is installed on the back side. If a rotary damper of 0.10 N⋅m is installed in the CW direction and a rotary damper of 0.10 N⋅m in the CCW direction as well, the torque value applied to the lid will be 0.20 N⋅m. If a rotary damper of 0.05 N⋅m in the CW direction and a rotary damper of 0.10 N⋅m in the CCW direction are installed, the torque applied to the lid will be 0.15 N⋅m. If rotary dampers of different torque values are installed on both sides, the lid will be twisted. Therefore, the left and right rotary dampers must have the same torque value.

Also, if rotary dampers are used beyond their range of motion, they may be damaged and will no longer function as rotary dampers. When a rotary damper fails, damage often occurs inside the shaft. The failure becomes immediately apparent when the lid is operated because the damper no longer provides its damping effect. Rotary dampers should be used within their specified range of motion and according to the operating angle of the lid.

As seen in the GIF animation on the left, a lid without a rotary damper closes forcefully, making it noisy and potentially dangerous for users. In contrast, the lid in the GIF animation on the right is equipped with a rotary damper, allowing it to slow down at the end of its closing motion and close safely. For example, if children close a piano fallboard that is not equipped with a rotary damper, they could pinch their fingers. However, if the fallboard is equipped with a rotary damper, it helps protect their fingers from being pinched. In addition, a piano without a rotary damper closes with a loud slamming noise, which may startle users or, over time, contribute to damage or malfunction.

In this GIF animation, the lid slowly at the end, but it is also possible to provide slow motion at the beginning of the closing motion or to adjust the closing speed. In addition, slow motion can be applied not only horizontally closing lids, as shown here, but also to vertically closing lids or lids that are lifted and closed at an angle. Click here to see other motions.

Finally, here are some examples of the main usages of rotary dampers.

Toilet seats and lids
By installing rotary dampers on toilet seats and lids, noise can be reduced and damage can be prevented. TOK has been supplying rotary dampers for toilet seats and lids since 1991 and has a proven track record of providing solutions to many customers with a wide range of requirements. Most of our rotary dampers are customized products, allowing us to manufacture dampers that meet the specific requirements of your application. One standard product with a proven track record in the toilet industry is the TD99 series, which is resistant to toilet detergents.

Piano fallboards
Piano fallboards are extremely heavy, so there is a risk that a player’s hand could slip and their fingers could become pinched, resulting in an injury that may prevent them from playing the piano. The use of a rotary damper not only helps prevent this danger but also gives the piano a more luxurious feel with its smooth, slow closing motion.
TOK has been producing rotary dampers for pianos since 1994, and in recent years, our rotary dampers have been used in many newly manufactured pianos. TOK also offers rotary dampers that can be retrofitted to existing pianos.

Trash cans
When the lid of a step trash can is closed, it may generate a loud noise, scatter odors, or flap when the pedal is pressed. However, the use of a rotary damper can help prevent these problems. The TD73 series is a proven solution for step trash cans. Its compact diameter allows it to be incorporated into the hinge section of the trash can without compromising the product’s design.

This article can also be viewed in this video.

To summarize the contents of this article,

・A lid with a rotary damper closes slowly at the end and allows the lid to close safely.
・Rotary dampers are mounted at the center of the rotation of an object to be moved.
・You should use rotary dampers in accordance with the movable range determined for each rotary damper and the operation angle of lids.

You can use our torque calculation page when designing your application. Our website displays only our standard products, but we also offer customized products. If you are considering a customized product or have any questions, please feel free to contact us using the inquiry form below. We recommend creating a custom mold for high-volume production. For low-volume production, we recommend selecting a standard product from our catalog.

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