Safety Couplings – A Sound Investment


Safety couplings generally play a protective role in machinery or equipment, i.e. they ensure that the other components in the drive train are protected and kept safe from overload caused by unintended defects or disruptions.  In doing so they provide the further benefit of reduced downtime. 

The main expectation of a safety coupling is almost always the same: it must operate reliably and effectively in releasing excessive torque. R+W Antriebselemente GmbH offers users from an extremely broad range of industry sectors the solutions to match their specific application requirements. Consultation with an R+W employee will ensure the correct safety coupling is selected for each individual situation. Once the application data is collected a possible initial selection is made. The user is provided with a technical overview of the coupling types in question and presented with information on the specific features and benefits of the couplings. This step in the process is often supported by physical demonstrations or samples. The suitable safety coupling is then chosen together with the R+W designers – if the requirements cannot be met by a standard component, a special solution is prepared. 

Shear pin couplings are no longer the optimal solution 

A maintenance employee working in the open pit mining sector contacted R+W for advice on this type of coupling, and presented the machine, of which there were three in operation. These were mobile crushing units, which remove coarse stones and gravel from mined soil for further processing into the required product – in this instance clay. Until now, elastic coupling elements had been used to damp vibration and shock, with a shear pin coupling to protect the drive train from catastrophic overload (Figure_1). In the event of an overload, the shear pins are stressed to the point that they shear and break free. This solution is certainly an economical design and had been completely satisfactory up to this point. However, the manufacturer of the shear pin had since changed the pin material so that it now fractures in a way which makes removal more difficult. This means that it can take from 1 hour to a whole day to put the machine back into operation, depending on how complicated the fracture of the pin was. This was a perfect case for the R+W industrial safety coupling ST2 (Figure_2) which is characterised by rapid shut down and recovery times.  

Why use a safety coupling at all? And how do they work exactly? 

Safety couplings protect machinery from damage which can be caused by overloading, usually from blockages, which cause a torque spike to occur in the drive train. If overloading occurs (i.e. the transmitted torque exceeds an acceptable limit) the safety coupling reliably separates the drive train. No special tools are required to put the machine back into operation. Unlike the shear pin couplings which were used in the past, stocks of special replacement parts are also not required. The coupling is based on the backlash free ball-detent principle, which has been a proven solution for many years. Unlike other couplings, it consists of a two-component safety module: the detent segment, and the adjustable disengagement safety element. Inside each safety element is a drive ball which is axially preloaded by a disc spring package. One half of the ball protrudes from the element and is loaded into the second half of the coupling, in the mating conical detent segment. Torque is transmitted backlash free and accurately via this positive drive connection. As soon as the torque acting on the ball creates a tangential force such that the spring package can no longer preload the drive ball, the drive ball slips back into the housing of the safety element. The ball is guided into the safety element housing by a pin which moves in a corresponding axial direction during the disengagement process. To re-engage the coupling, both halves of the coupling must simply be returned to their original positions and the drive ball can be pressed back into its detent segment by striking it gently with a mallet or by using a lever on the pin on the back side of the element to reload the coupling system. Incalculable costs from down time can be reduced or avoided by investing in the R+W safety coupling. While the up-front cost compared to the shear pin used in the application described above is somewhat greater, it is quickly absorbed by the cost savings from reduced down time.  

Protection to a torque limit of 250,000 Nm and beyond 

ST series industrial couplings are available as a standard product for torques up to 250,000Nm, and significantly higher values can be accommodated by special designs, depending on the machine specification. The robust and powerful safety couplings in this series are also available with a wide range of shaft/hub connectionsns (keyway mounting, conical clamping ring etc.) and sizes for an extremely diverse range of demands.  Customer-specific special solutions are possible even for quantities of one after consultation. 

Backlash free safety couplings 

The classic series (SK/ES) covers disengagement torques between 0.1 and 2,800 Nm. The different models in this series are also available for direct or indirect drive connections, with radial clamping screws, conical clamping rings, and keyway connections, as well as in torsionally rigid metal bellows or vibration damping elastomer insert coupling versions. To suit different requirements, this series is also available with different operating principles:  single position with automatic re-engagement, multi-position with automatic re-engagement, full disengagement with manual re-engagement, and a special load blocking version, which releases for just a few degrees of free rotation before locking-up again. In order to meet constantly changing market requirements, such as lower moments of inertia, greater operating speeds or more efficient processes, R+W also has a lightweight safety coupling (series SL) which is characterised by its particularly high power density. The SL series is also available in a range of designs and different versions for use in direct or indirect drives (Figure_3). 

ATEX certification required – no problem 

R+W models are also available in ATEX designs for use in explosive atmospheres, in both the industrial and precision safety coupling categories. A special ATEX certified limit switch, which meets the European Union ATEX guidelines, is available to sense the safety coupling disengagement and signal an emergency stop condition. ATEX certification is available on request, and with short lead times. 


R+W offers a wide range of practical accessories for use with safety couplings. Engagement and disengagement devices are available for quick and easy maintenance of industrial safety couplings. Face and hook spanner wrenches can be used for easy adjustment of the disengagement torque of industrial safety couplings and precision safety couplings respectively. Proximity switches and mechanical limit switches are also available to detect disengagement and signal for emergency stop.  

Benefits recognized, danger averted 

When it comes to protecting valuable equipment and avoiding downtime, fractions of a second are decisive. Mechanical safety couplings not only provide users with a significant technical advantage that’s easy to implement and use, but they also make an important contribution to increasing process safety.  

Precision Servo Gear Heads, Precision Right Angle Gearboxes, Precision and Industrial Couplings, Keyless Locking Assemblies, and Shrink Discs are among the most recent technological innovations. of Power Ace India. One of the top gearbox manufacturers in India, Power Ace India, helps businesses choose the best drives to maximise machine production and efficiency. 

× How can I help you?