The best thing about the new ST torque limiters from R+W is not only do they offer distinct benefits over shear pin and hydraulic alternatives they are also smaller than other mechanical torque limiters rated for up to 160,000 Nm. And their merits don’t stop there. These torque limiters are also lighter in weight making assembly easier and quicker. They are easily adjustable and can be serviced in situ. Yet even with all these attributes these newcomers have been introduced at a highly economical price.
Now available from sole UK distributor Tandler, the ST torque limiter is up to 23% more compact, with respect to outer diameter at a given torque, by comparison with its mechanical competitors. The difference in overall coupling weight in the most extreme case is one ton. As a result, considerably greater circumferential speed is possible. So in terms of physical size, weight and maximum operating speed the ST is a star performer.
The size factor in particular makes the ST torque limiter very much easier to install. A lighter weight drive line that can be pre-assembled is another clear benefit. Lower overall weight also reduces mass moment of inertia as a consequence of lower flywheel mass. In addition to shortening the acceleration and braking processes, the system therefore achieves greater dynamics. This in turn translates into higher productivity.
A shear pin coupling by comparison may cost less but it requires considerably more time to install, adjust and put into operation. It also demands heavy duty and specialist maintenance, a factor that is especially pronounced in the event of a stoppage. And whilst a hydraulic overload coupling has the advantage of being extremely compact this is counterbalanced by the need for complicated procedures following overload and the significant potential of oil contamination to nearby components.
In designing its ST torque limiters, R+W examined and addressed all these disadvantages. The R+W operating principle utilises disc springs, allowing the ST’s immediate re-engagement following a stoppage. There is no need to replace any expendable parts like pins or valves. Furthermore its disengagement does not result in hydraulic oil being sprayed onto adjacent components.
The most important factor of all is that the ST torque limiter is 100% reliable. Thanks to R+W’s patented spring-loaded ball detent design, the coupling will disengage at exactly the same torque, again and again. The disengagement value is easily set via the torque adjustment range that is engraved on the body of the coupling.
Dependent on the disengagement torque required, 3, 6 or 9 actuation elements are distributed around the given radius but additional elements can be retrofitted at any time. If minimal space and high torque are the pre-requisites for an application, up to 12 actuation elements can be fitted or the number of disc springs increased to produce greater force. Such measures can increase performance by as much as 25%.
The ST torque limiters are available for torques from 1,000 to 160,000 Nm in four different body sizes and shaft diameters from 40 – 290mm. They are absolutely backlash and maintenance-free and supplied in a comprehensive product package that includes the torque limiter, torque adjustment wrench and a special tool for manual disengagement and re-setting.
The ST product programme also comprises three application specific classes. The ST1 is for indirect drives and ideal for power transfer in heavy machine construction. For direct drives the ST2 includes in its design an elastomer compensation element that accommodates axial, lateral and angular misalignment. This feature also has the effect of filtering torque fluctuations. Model ST3 is configured as a torsion resistant coupling. It is characterised by exact torque transmission, exceptional durability and compensation for all three types of misalignment with very small restoring forces.
Where the ST torque limiter is to be used in aggressive, corrosive environments, a stainless steel version can be supplied. ATEX certification for hazardous areas Zone 1/21 and Zone 2/22 is also available.