The largest machines that are currently digging underground on the construction site of the Semmering base tunnel are two tunnel boring machines. For the overload protection of these heavyweights comes the safety clutch EAS-HT by Mayr Antriebstechnik for use. These couplings trigger reliably and understandably and protect the drive components sustainably. They cannot be manipulated and the factory-set torque is available again even after disengagement. Recommissioning is also quick and easy, without additional tools.
It is one of the most important infrastructure projects in the heart of Europe - the Semmering Base Tunnel. From 2026 it connects Lower Austria with Styria. Two tunnel bores are currently being used on the construction site. (Picture above) They are 120 m long and 2500 t heavy and together weigh about as much as 800 elephants.
Overall, the two drills work from the Fröschnitzgraben in Steinhaus am Semmering through the mountain about 9 km towards Gloggnitz. Like moving factories underground, they line the excavated tunnel with prefabricated concrete parts. The excavated material that the machines “spit out” at the rear is transported to the surface with conveyor belts. On average, a machine travels between 10 and 15 m daily. Every single meter counts. An overload case caused by irregularities in the rock, for example, must not stop the drilling machines.
Disengage the safety clutches
"If our EAS-HT safety clutches snap out on the construction site, this happens with a defined and traceable torque and only so that they protect the transmission, motor and drive train from damage caused by overload," explains Ralf Epple, Product Manager at Mayr Drive Technology in Mauerstetten. Long downtimes are avoided and the work is sustainable. "The security concept must not be susceptible to manipulation," emphasizes the product manager. “That's why we set the torque on our clutches at the factory. So it is available again immediately after it has been unlatched. The safety aspect does not depend on the restart. "
Extremely high torques and speeds
"The isolating EAS-HT safety couplings are an element coupling that are very well suited for use under high torques and speeds as well as large moments of inertia," says Ralf Epple. These overload clutches are based on individual overload elements that are integrated in the flanges. The achievable torque results from the preload force of the elements multiplied by the number of elements and the radius at which the elements are arranged. Thanks to the modular concept, it is not only possible to build couplings tailored to the application. Above all, much higher torques can be achieved with these overload clutches than with a central disengagement mechanism. Mayr has safety couplings from the EAS-HT series as standard with a torque of up to 440.000 Nm. However, this does not mean that the possibilities are exhausted: the modular structure means there are practically no limits.
Advantageous function in case of overload
In the EAS-HT clutch, the individual overload elements transmit the torque in a form-fitting manner in trouble-free operation. In the event of an overload, they separate the drive and output in fractions of a second with high switch-off and repeat accuracy with almost no residual torque. Only the friction of the high-quality pressure flange bearing works. The kinetic energy of the rotating masses stored in the system can flow freely. The element coupling remains disconnected from the drive until it can be easily and quickly re-engaged using a hammer, using hydraulic, pneumatic, mechanical or electromechanical devices or by hand. No other tools are required. After activation, release clutches can cope with long drive down times. When defining the permissible run-down time, only the robust coupling bearing must be taken into account. "Our couplings are designed so that the drilling stroke can be completed with the clutch disengaged," explains Ralf Epple.
Overload protection is non-destructive and safe
In contrast to other overload systems, which e.g. B. work with pressurized hydraulic oil or shear pins, the EAS-HT safety coupling is immediately ready for operation again after eliminating the cause of the overload. It is not damaged and can handle several hundred overload cases. In addition, it is understandable at which torque it is disengaged. "In other systems, the evidence is, so to speak, destroyed after the overload and there is uncertainty about the disengagement torque," said Mr. Epple. “In addition, the destroyed components have to be replaced after an overload.
In addition to the resulting costs and plant downtime, the necessary components must also be available. This also requires the Konw-how for the restart. There is a risk that the torque will be set incorrectly, the consequences of this will be too great, especially in the tunnel and mining sector. ”The EAS-HT from Mayr power transmission also score in terms of size and weight. “The new, compact designs were specially developed for the tunnel area. They have about the same weight and outer diameter as other overload systems, ”adds the product manager.
Tested and found good
"We now have several thousand couplings in use and have experience with setting values," says Ralf Epple. Before a coupling leaves the factory in Mauerstetten, it is thoroughly tested and set exactly to the required value. Mayr also offers a wide range of modern testing options. You can fall back on decades of experience in construction and development. Even if existing systems are converted, the performance can be increased significantly with the Mayr couplings.