Working Principle of Torque Limiters

Torque limiter, also known as a safety coupling or torque coupling, is a protective device commonly used to prevent machinery from damage due to excessive load. Torque limiters are typically categorized based on their structure. The two main types are friction-based and ball-based torque limiters.

1. Friction-based Torque Limiters

In this design, the torque limiter works by locking a nut, which applies force on a spring. This spring, in turn, applies pressure on the friction plates, with sprockets or other wheel-like objects placed between them. These components are used to transmit torque.

When the equipment experiences an overload, the friction plates and sprockets will slip relative to each other, but the torque will remain at the set limit. As a result, the driving end will idle while the driven end is disconnected. Once the overload is cleared, the limiter will automatically reset.

Friction-based torque limiters are simple, cost-effective, and easy to maintain. However, they may not offer the level of precision required for some high-precision applications.

2. Ball-based Torque Limiters

This type of torque limiter uses precision springs to control the critical torque value. Compared to friction-based limiters, ball-based torque limiters provide more accurate torque control. The design is more adaptable, as different internal springs can be swapped to set different slip-torque values. These are typically used in applications where the driving and driven shafts are connected via a coupling.

When an overload occurs, the torque limiter first disconnects the driven side. The driving side idles, while the ball-based mechanism displaces axially, giving an amount of movement. A proximity switch can be placed beside this displacement to detect the movement, sending a signal for either an alarm or to stop the motor, enabling full automation of the system.

After the overload is cleared, the limiter will reset either to a single position or to multiple preset positions, depending on the system’s requirements.

Key Differences

The main differences between the two types lie in their precision and reset mechanisms:

• Friction-based torque limiters are more straightforward and may not provide the high level of precision required in certain applications.
• Ball-based torque limiters offer higher precision and are typically used in more demanding, high-accuracy applications. They also provide a more automated and flexible reset process, which can be beneficial for systems requiring advanced monitoring and control.