A torque-limiting coupling is key in protecting capital equipment investments in high- energy applications, such as crushing and milling in steel production, high-speed rotating equipment and high-speed gearboxes, states fluid couplings manufacturer Voith.

“The Voith SafeSet torque-limiting coupling is designed to release the drive unit from the driven equipment at a very specific torque, in case of an overload situation,” says Voith Europe, Middle East and Africa division, mining and metals, Africa south VP Grant Robinson.

According to Voith, the torque-limiting couplings protect all components in the driveline, allowing equipment to work at a maximum reliable, efficient and high availability level. Therefore, production can be maximised without risk to equipment.

“In the event of a catastrophically high torque occurrence, the couplings interrupt the power flow in the driveline, which means that consequential damage and production downtime remain at a minimum. Special designs provide additional advantages to the production process.”

Robinson explains that the SafeSet has a twin-walled pressure sleeve, which creates a pressure cavity in the coupling. “By pressurising oil, the inner bore coupling will compress around the shaft and a perfect defined friction grip is created,” he says.

During an overload situation, when the set torque is exceeded, the SafeSet instantly releases, owing to the shear tube being sheared off to release the hydraulic fluid, allowing the coupling to freely rotate to a standstill, without damaging the drive equipment.

The shear tube can easily and quickly be replaced and the coupling pressurised to the required pressure, which is dependent on the application – a repeatable process, to ensure that the drive system continues operating, Robinson emphasises.

Voith is currently involved in the installations of five SafeSet torque-limiting couplings, complete with connecting couplings, outside Africa.

“Companies that need to protect high-end expensive capital equipment, do not want to take the risk or gamble with protection,” Robinson says, adding that this is not normally the case. While some end-users, particularly in the high-energy industries, are aware of the benefits of the SafeSet couplings, this offering is often disregarded.

TP-XL Coupling
In addition to its SafeSet couplings, Voith also offers fluid couplings mainly used in mining and power generation materials handling equipment. Voith EMEA division, Mining and Metals, Africa South regional manager Hans Voshol highlights Voith’s new 780 TP-XL fill-controlled fluid coupling for six or eight-pole asynchronous motors used in belt conveyor drives, which has been developed in the past four years. The coupling, which features a new internal design, has a smaller diameter, but a higher range of power. It is designed for 750 rpm to 1 000 rpm applications.
Since the coupling has been tested at an iron-ore port, on a driveline for a high-inertia belt application in Brazil for just over a year, the local Voith EMEA, Mining and Metals, Africa South team is in the process of negotiating the retrofit of a drive with two of these couplings on an inclined belt system at a mine in the Northern Cape within the next year.
Key features of the coupling include its compact design, resulting in a smaller footprint, full controllability of the startup, torque limitation, speed variability options, self-alignment, as well as damping of torsional vibration. Further, it prevents damage resulting from dynamics, such as resonant dynamic oscillations. Voshol adds that the coupling can provide a cost saving of 20% to 30%, while it also reduces maintenance and repair work.
“Moreover, there are no wearing components on the coupling, apart from the bearings and oil seals,” Robinson says.
To support its product offering, Voith also provides a modelling and simulation solutions software, called TurboSim, Robinson highlights.
“Voith can model any coupling within the application with the requirements of the drive, including the inertia, torque, power and speed. The software enables the company to show the performance of the coupling, and its potential success in a required application or system, prior to installation,” he concludes.