Protection and safety for the tough guys 04 Apr 2019

In the field of heavy-duty TBMs and mining machines, Mayr® power transmission stands for high performance as well as high torque and speed. The recently introduced EAS®-HT torque limiters by Mayr are actuated reliably and traceably to sustainably protect the drive components. They cannot be manipulated and the factory-set torque is accessible again even after disengagement. Recommissioning takes place quickly and easily, and without requiring additional tools.

Disengaging EAS®-HT torque limiters operate with precision and are immediately ready for operation once cuase of an overload stoppage is rectified

“As TBMs advance they may not be halted daily by overload cases but whenever they do, the Mayr EAS®-HT torque limiters disengage the operation to protect the motor, gears and drive line against damage,” explains Ralf Epple, Product Manager at Mayr® in Mauerstetten, Germany. “This avoids long downtimes and machines can be operated sustainably.”

“To operate correctly, the safety concept must not be susceptible to manipulation,” emphasized Epple. “This means that the torque on our clutches is factory-set and is immediately accessible again after disengagement. In other words, the safety aspect is not dependent on recommissioning.”

Protection at extremely high torques

“The disengaging EAS®-HT clutches are element clutches which represent the ideal solution for extremely high torque and speed or large mass moments of inertia”, said Epple. These clutches are based on individual overload elements, which are integrated into the flanges. The achievable torque results from the pretension force of the elements multiplied by the number of elements and the radius at which the individual elements are arranged. Using this modular concept, not only can clutches be built which are tailored to the respective application, but also far higher torques can be controlled than with a central disengagement mechanism.

Mayr offers the torque limiters from the EAS®-HT construction series in a standard version with a torque of up to 440,000Nm. However, the limits of what is possible have not yet been reached. “Thanks to the modular construction, the possibilities are endless,” said Epple.

EAS®-HT torque limiters (in blue) withstand the extreme stresses involved in TBM operation

Function during overload

On the EAS®-HT element clutches, the individual overload elements transmit the torque through positive locking during functional operation. In case of overload, they disconnect input and output almost residual torque-free within a fraction of a second, with high switch-off and repetitive accuracies. Only the friction of the high-quality pressure flange bearing takes effect. The kinetic energy of the rotating mass stored in the system can slow down freely. The element clutches remain disengaged until they are re-engaged manually or using pneumatic, hydraulic, mechanical or electromechanical devices or more simply and quickly using only a hammer. Additional tools are not required. Overload clutches can cope with long slow-down times for the drive following disengagement. Only the robust clutch bearing is to be considered when defining the permissible slow-down times. “Our clutches are designed so that the bore stroke can, if necessary, be traversed to the end with the clutch disengaged,” explained Ralf Epple.

Non-destructive overload protection

In contrast to other overload systems, which work for example with pressurized hydraulic oil or shear pins, the EAS®-HT torque limiters are immediately ready for operation after the overload cause has been resolved. They are not damaged and can withstand several hundred overload protection cases. In addition, it is possible to trace at which torque the EAS®-HT clutches disengaged. “On other systems, the proof, so to speak, is destroyed after the overload cases, and uncertainty prevails regarding the disengagement torque,” said Epple. “Moreover, the destroyed components have to be replaced. This generates costs and system downtime. The required components have to be available, and in addition, specialist knowledge is required for recommissioning. There is also a risk of the torque being incorrectly adjusted and an incorrectly adjusted clutch does not make sense; the consequences, particularly in the field of TBM tunnelling are simply too high.”

Two TBMs on the Semmering project in Austria are fitted with Mayr torque limiters

With regard to size and weight, the EAS®-HT clutches by Mayr are compact designs developed especially for tunnelling have largely the same weight and the same outer diameter as other overload systems.

Prior to each clutch leaving the Mayr works in Mauerstetten, it is extensively tested and set exactly to the required value. For this purpose, the company has diverse, modern testing equipment. It also calls on extensive experience in the development and design of these components. “We have put several thousand clutches into use and have gathered the appropriate experience with regard to the adjustment values,” added Epple. “From the feedback we receive from operators, it is possible to decisively increase performance using our clutches, in particular if existing systems have to be retrofitted.”

Mayr is a family-run company founded in 1897 and is a leading manufacturer also of safety brakes and shaft couplings. These products are primarily designed for application in electrically driven machines and systems. The company is active through more than 60 branches worldwide and currently, employs about 700 at the headquarters in Mauerstetten. Worldwide, Mayr employs about 1,200 employees with production plants in Poland and China, sales subsidiaries in the USA, France, UK, Italy, Singapore and Switzerland, and with representatives in an additional 36 countries.

For more details, visit the Mayr power transmission technicians and engineers at the WTC World Tunnel Congress, from 3 to 9 May 2019 in Naples, Pavilion 10, Stand 40.