A torque limiter is a mechanical device that controls how much torque a machine’s drive shaft is subjected to at a given time. It is a protective mechanism and the goal is to prevent the machine from suffering damage due to what is known as mechanical overload. This is a situation where too much torque is imposed on the drive. For this reason, the limiter is alternately referred to as an overload connection. It can be found on everything from a ship’s propeller to a bottling conveyor to a fishing reel.
There are several different ways a torque limiter can work. Some disconnect cargo completely when an overload is detected. These types are known as separating types. Others just let the cargo slip under overload, similar to how a clutch in a car’s manual transmission works. These are known as torque limiting types.
A disconnect torque limiter can come in several different designs. These include shear bolts, synchronous magnetic, sloping latches and pawls. Generally, a disconnect type must be reset in some way after it intervenes during an overload. Depending on the type, this can be done automatically or manually.
The shaft pin limits work by inserting a small metal stick into the drive when there is overload, forcing it to disconnect. In the process, the pin is damaged and must be replaced before it can be used again. The cutting bolts are often compared to fuses, in the sense that they are sacrificed to protect more expensive parts.
A synchronous magnetic system, as the name implies, uses a pair of strong magnets to quickly connect the shaft with a magnetic impulse. Again, much like its name, a ball blocking system works by having a number of spring-loaded metal balls installed in the drive, which pop up to unplug the drive when needed. A pal-and-spring torque limiter, which initially uses the movable arm portion of a ratchet mechanism, is activated as needed, with the catch dropping down and catching a notch in the drive, forcing it to disconnect.
Torque limiting types, which act as clutches, include friction plate, magnetic particles, and magnetic hysteresis designs. Unlike coupler types, clutch-based torque limiters are not so irreversible in their use and can be modulated while the machines are running. They are also less catastrophic in the sense that a system reset is not necessary after each use. Any type of slurry design can be switched on and off in time, usually without damage to mechanical parts.