Preventing damage and downtime in case of unexpected machine jams, collisions, and other overloads can mean the difference between profit and loss in many industrial processes. This makes an overload safety disconnect essential for drive lines with the potential for damaging torque levels to be reached.

Safety coupling STN


The R+W TORQSET series STN uses spring loaded drive ball modules which disengage within milliseconds of reaching a predetermined overload torque value, preventing damaging torques from being transmitted down the drive line.  This protects gearboxes, belts, chains, and drive shafts from failure, and instead offers a fast and simple re-engagement without the need for any special tools.  Once an overload disengagement occurs, re-engagement simply requires that the two rotating coupling halves be re-aligned, and the drive ball plungers be pushed back into engagement with the force of a pry bar, dead blow hammer, or screw tool.  Compared with other types of mechanical overload disconnect devices, this concept provides for a highly accurate and consistent disengagement setting, and an extremely rapid recovery from overload events. 


Each coupling size can be fitted with 3, 6 or 9 safety elements, which means that users benefit from the ability to make coarse adjustments to the disengagement torque by adding or removing modules.  Fine adjustment is achieved by rotating the end cap adjustment nuts on the safety elements to change the pressure applied to the drive balls.  The combination of these two features means both a very wide overall torque adjustment range, and an infinite number of individual settings possible within that range.  This makes the coupling suitable for retrofit into existing equipment and for use in high end machines with sensitive torque requirements. 


The model STN uses a high strength frictional shaft locking system, which is designed to be keyless, but can also be supplied with keyways or splines on request.  Regardless of shaft profile, this clamping style prevents wear and galling by removing backlash between the shaft and the hub during operation.  The standard version has a bolt circle on the disengaging output flange for attachment of sprockets, pulleys, and universal drive shafts.  Other versions are supplied with flexible jaw, disc, and gear couplings pre-mounted to the output for inline shaft to shaft applications.  Customized versions can be fitted with special bearings for just about any loading condition or for high rotational speeds. 


With any configuration an optional switch plate can be included, which connects all the drive ball plungers together, and moves along the length of the coupling at overload release.  This allows for a limit switch or proximity sensor to be used to detect the overload and react accordingly with a motor cutoff, alarm, or other emergency stop function.  In the near future R+W will be offering these ST style torque limiters with onboard torque measurement and wireless signal output.  Since torque overloads and torque limiters often exist downstream from motors, this feature will bring an unprecedented level of visibility to driveline behavior and provide operators with real knowledge of process torques.  Margins between operating torque and overload disengagement torque setting can also be reduced with the additional information this new optional sensor system will provide.


The STN torque limiter is available in 7 basic sizes, with customer-specified bore diameters ranging from 1.75” to 290mm, and disengagement torques ranging from 2,000 to 1.5million inch pounds.  Custom larger sizes can be made with virtually unlimited capacity – including the world’s largest ball detent torque limiter, made in 2017. 


Typical industries and application areas include:

– Steel mills

– Dynamometers and test stands

– Sawmill equipment

– Extrusion systems

– Grinding mills

– Industrial shredders

– Anywhere with the potential for a heavy rotating mass to be stopped too abruptly


To get the best torque overload protection for your application, check out the product page or contact one of or our coupling experts!

February 16, 2021|Tags: , , , |