The production of aluminum oxide and hydroxide requires bauxite, a reddish sedimentary rock mined mainly in Australia, China and South America. Aluminum Oxide Stade GmbH (AOS), one of the major alumina producers in Germany, processes around 2 million tonnes of bauxite every year, from which around 1 million tonnes of alumina is extracted.
A single ship delivers up to 70,000 tonnes of raw material to the AOS port. After it is unloaded by ship-to-shore crane, it is transported via an enclosed conveyor belt system for intermediate storage before it is taken for processing. Both when loading and unloading ships as well as during storage, AOS relies on reliable energy supply systems from igus for the conveyor units. Heavy dust arising during the movement of bauxite and abrasive salt dust in the seaport cause enormous stress on moving machine components.
“In the past, we used motor cable drums for the energy supply,” says Fabian Wilhelm, Head of Electrical Engineering at AOS. “Here we had the problem time and again that the cables were not properly wound on the drum, which ultimately caused machine failure due to cable damage.”
Wilhelm decided to use an energy chain system from igus for the first time in 2012. “At that time, Mr Böhm from igus introduced me to the principle of energy chains,” he says. “At first I was sceptical about the operation of the chains in this environment. However, after looking at a seaport and an aerated concrete plant as reference applications and having the opportunity to talk to other customers and users, we decided in favour of igus.”
The first joint project was the so-called ‘loop car’. Very dusty bauxite is stored in a large hall to reduce the dust released into the environment. In this hall, the loop car moves back and forth under the roof a distance of almost 140m to different points to discharge the bauxite. Temperatures reach 60°C in summer, while in winter transporting warmer bauxite to the cold heap causes condensation, which rises and becomes liquid, causing rain inside the hall. Moisture coupled with the bauxite dust results in a tough material that sticks everywhere and affects the path of the energy supply.
This is where the igus e-chain system brought another benefit, as all applications at AOS also have built-in electronic push/pull force monitoring systems. “If the run of the chain is hampered too much by dust and dirt, the push/pull monitoring system will shut down the system before any damage occurs,” explains Wilhelm. “The fact that igus was the only provider to offer such an electronic surveillance system then was one of the main reasons in favour of igus. If the monitoring shuts down the system today, we know that it is time again to clean the travel of the chain. Then the system will run again without any problems.” The potential to carry compressed air was another point in its favour.
A short time later, AOS again opted for an e-chain system from igus in the course of a major overhaul of the open dumping unit, where the bauxite that does not have to be stored in the hall lands. In this project as well, AOS relied on the support of the igus assembly service, which undertook the complete installation of the chain and trough system. The dumping unit is now supplied by the longest e-chain in use at AOS, a roller energy chain moving along a travel of 330m. “The rolling in the chain links causes the push/pull forces to drop enormously over long travel distances when the upper run of the chain lies on the lower run,” explains Markus Böhm, Technical Sales Consultant in charge at igus. “Because of the lower coefficients of friction, up to 57 per cent of the energy required to drive the energy chain system can be saved.”
In addition to various energy and data supply cables, a water hose with a diameter of 48mm for sprinkling the bauxite is also located in the chain on the dumping equipment. As with the other applications, a floating moving end ensures lateral tolerance compensation and undisturbed movement. This is necessary especially on long travels in order to save drive energy, and to compensate for possible parallelism errors between running rail and guide trough.
In the most recent project, in 2017, two energy chains move on a travel of 218m reverse in a common trough. They supply the two cranes that deliver the bauxite and then remove the produced alumina. Here, medium-voltage motor cables and fibre optic cables are routed. “This is a real advantage for us,” says Wilhelm. “Earlier, in the event of crane failures or maintenance, we always had to first climb 40 metres onto the crane with a laptop to read the data. Today, thanks to the fibre optic cable connection, this is done directly from the desk. This enormously improves the maintenance effort.”
In the past, motorised cable drums were used in these two applications. However, these always caused problems because torque motors had to be operated, which always kept the cables of the motorised drum under tension. “The starting resistors on the motors rusted time and again and had to be replaced,” recalls Wilhelm. “This meant a ten-day shutdown. And we only had one unloading crane that can handle around 50 ships a year. Therefore, a failure naturally weighs very heavily and must be avoided at all costs. Today, of course, the energy chain systems from igus give us a longer service life and significantly less maintenance.”
Wilhelm sums up: “Less maintenance effort, higher availability, the possibility of running all different cables and hoses in one system, electronic push/pull force monitoring ... all these advantages have completely convinced us of the igus products. I would always use igus energy chains!”
1300 65 75 64