A torque limiter is a device that automatically shields mechanical equipment and its work from being damaged because of mechanical overload. It is possible for the torque limiter either uncouple the load completely (shear pin) or simply limit torque by slippage. A torque limiter is particularly useful to reduce damage caused by crash jams and stops. Torque limiters could either be packaged as a hub for sheave or a shaft coupling. Another name for a torque limiter is an overload clutch. Disconnect drives are able to reset both manually or automatically and uncouple the drive with minimal residual torque on the load. A shear pin sacrifices the mechanical component i.e. the pin to disconnect the shaft. A magnetic torque limiter that is synchronous deploys permanent magnets on every shaft with separation through an air gap.
Magnetic torque limiters are fast acting but potentially have greater backlash when compared to mechanical torque limiters. As the mechanical contact between shafts is non-existent, magnetic torque limiters transmit the torque through physical barriers such as a thin plastic wall. In the case of some models, it is even possible to adjust the torque limit by adjusting the gap between magnets.
The two main types of torque limiters available in the torque limiter market are mechanical and electrical torque limiters. A few people believe that mechanical torque limiters are unnecessary and old-fashioned today. They opine that electronic torque limiters are perfectly suited to operator safety and machine protection. What is actually required though, is a device that prevents accidental collision damage that could cause potentially lead to expensive downtime. There is also a greater focus on operator safety that demands a higher level of protection than was tolerated before. In all these situations, the simple mechanical torque limiter is the perfect solution as it disconnects the drive from driven parts in the shortest amount of time.
In case there is a slow load increase on account of dirt contamination or damaged bearings, electric sensing serves its purpose; there is sufficient time to stop the drive and the signal could even function as a preventive alarm. When the load increase is sudden as a result of mechanical breakage or misfeed though, only mechanical torque limiters provide the required protection. By way of disconnect between the driven load and the motor, the torque limiter is able to take out most of the inertial energy from the drive train. Where the torque limiter is positioned near to the output at a low speed, almost the entire kinetic energy can be disconnected. This helps a great deal in substantially reducing the chance of damage or injury.
The disconnection is not immediate and depends primarily on the size and design of the torque limiter. It is difficult for electronic torque limiters to equal this performance as they need to sense overload and only then apply a brake torque to stop the drive train. That is why mechanical torque limiters are the best option when it comes to safety and required protection. As the years have gone by, torque limiters have been tweaked to suit a variety of market niches. Every torque limiter market niche has specific requirements for sensitivity and protection. Where operator safety is the primary concern, higher standards are vital and experienced suppliers’ sound advice is recommended.
Some of the major manufacturers actively involved in the torque limiter market are ComInTec, x4 Tool, Sytcobrakes, Rotolinear Systems and Cross & Morse.