When a mining operation in South Africa’s Mpumalanga province found that one of its planetary gearboxes on a high-torque conveyor was failing, it called SEW-Eurodrive for a solution. Greg Lewis, Business Development Manager Projects for SEW-Eurodrive, says the application at the mine demanded a customised and carefully-considered approach.
“The application itself was in the plant where a steel-belt transfer conveyor moves extremely slowly, with the 4 metre diameter head pulley turning just one revolution every 25 minutes,” Greg explains. “Two planetary gearboxes drive the pulley, one on each side, and the mine had been facing the pending failure of one of these, which needed to be replaced.
Not an option
“With the original installer of that gearbox unavailable, the mine came directly to us as we already have a good relationship having provided most of the power transmission items on the site. One of the key challenges was that the mine required only the one gearbox to be replaced at that stage. It is important to understand that in this application the two gearboxes must run together, at exactly the same speed and torque. Any variation in the speeds is not an option.”
SEW-Eurodrive was able to match one of its units very closely with the unit being replaced, but there was still a very slight difference in the ratios. This led to a 0,001 difference in the revolutions per minute.
Matching the torque
“While this may sound insignificant, it makes a difference when the gearbox torque is a couple of hundred thousand Nm’s,” Greg explains. “At this high torque level, any misalignment or desynchronisation can affect the foundation and potentially cause catastrophic failure.” With the expert input of one of SEW-Eurodrive’s in-house mechatronics engineers, the solution uses the company’s Movi-C technology in a way that has never been done before.
The new planetary gearbox supplied by the company will match the torque of the original gearbox – ensuring that they turn at precisely the same speed. The solution involves removing the existing base plate and providing a new, drop-in solution with an SEW-Eurodrive planetary gearbox, designed to match the current infrastructure in the plant.
Required ratio
“To prove this intelligent design, we built a small-scale working mock-up for the customer to witness. Together with its own customised base-plate, the ‘model’ arrangement was taken to site and demonstrated to the customer’s satisfaction.”
Greg explains that the project was designed and delivered as a complete solution, from the fully customisable panels to the electronics and the installation of the gearbox. The installed unit is an XP planetary gearbox with shrink disk, with a primary X-series gearbox as a further reduction unit to achieve the required ratio.
Considerable scale
“We engineered the steel base to fit onto the existing concrete foundation without any modifications required from the customer’s side,” he adds. The significance of the project is enhanced by the considerable scale of its elements. At about 1,7m in height, and measuring 2,1m wide and long, the gearbox itself is sizeable, weighing about 6t. Moving at 0,07rpm, it moves the steel belt that carries a fine cake of raw chrome material.
“There are not many companies who can produce a solution to meet these very slow revolutions.” Says Greg, “Being among those who can is a source of great pride for us. This project has been particularly rewarding as it demonstrates our capability in matching another footprint, eliminating the need for the customer to break down existing structures and build new ones.”
The unique requirements of the project meant extensive on-site engagement with the customer and detailed measurement of plant requirements. SEW-Eurodrive’s engineers in Johannesburg generated the working drawings from which global counterparts within the group could begin manufacturing the unit in Germany.
