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Ensuring reliable energy supply in harsh environments

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article image The Aluminum Oxid Stade GmbH (AOS) processes around two million tonnes of bauxite every year. Before processing, the material is stored in a large heap.
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During the mining and subsequent storage of bauxite, a sedimentary rock for the production of aluminium oxide, a lot of dust is produced, which is a major challenge especially for the moving machine parts of conveyor units. For this reason, the Aluminum Oxid Stade GmbH (AOS), a major German alumina producer decided to use energy chains from motion plastics specialist igus. For several years now, they have reliably supplied conveyor units and stockpiling equipment with energy, data and media.

Aluminum oxide and hydroxide are basic materials used in the manufacture of a wide variety of aluminium products needed throughout the world. The production of these substances requires bauxite, a reddish sedimentary rock that is mined mainly in Australia, China and South America. From there, it is shipped to Germany, to the Aluminum Oxide Stade GmbH (AOS), one of the major alumina producers in Germany. The company processes around two million tonnes of bauxite every year, from which around one million tonnes of alumina can be extracted.

A single ship delivers up to 70,000 tonnes of raw material to the AOS port. After unloading by the ship-to-shore crane, it is transported via an enclosed conveyor belt system for intermediate storage before being 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. The heavy dust arising during the movement of bauxite is an enormous stress, especially for moving machine components. "In the past, we used motor cable drums for the energy supply," recalls 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."

Different applications, same challenges

Since the previously used energy supply systems were very maintenance-intensive and always caused problems, Fabian 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 explains. "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." As with AOS, the visited references were all applications with travels over 100 metres, or applications in coarse dust and dirt. In particular, the stress of the abrasive salt dust in the seaport on the systems is very high.

First joint project – extreme stress under the hall roof

The first joint project of AOS and igus was the so-called 'loop car'. When it comes to very dusty bauxite, it is not stored in a heap in the open, but in a large hall to reduce the dust released into the environment. In this hall, the loop car moves back and forth over a distance of almost 140 metres under the hall roof to different points to discharge the bauxite. While temperatures up to 60 degrees Celsius prevail in summer, the environmental conditions in winter are even more difficult. "When warmer bauxite is transported from a height of 20 metres to the cold heap, the temperature difference causes condensation," reports Fabian Wilhelm. "This rises and becomes liquid again at the roof of the hall, causing it to start to rain inside the hall. Moisture coupled with the bauxite dust results in a stubborn tough material that sticks everywhere and also affects the path of the energy supply." This is where the igus energy chain system brings 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," Fabian Wilhelm explains. "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 not only data and energy but also compressed air was another plus point in its favour.

Second joint project – general overhaul of the dumping equipment

Just a short time after the first successful conversion, AOS again opted for an energy chain system from igus in the course of a major overhaul of the dumping unit. The bauxite that does not have to be stored in the hall lands here, in the open. In this project as well, AOS relied on the support of the igus assembly service, which undertakes the complete installation of the chain and the trough system in which the chain is moved. "The special feature of all the projects in this regard has always been the good cooperation between AOS and igus," explains Markus Böhm, Technical Sales Consultant in charge at igus. "The work was very well dovetailed and it worked very well together even when mutual support was required in the assembly work."

The dumping unit will now be supplied by the longest e-chain in use at AOS. A roller energy chain of type 5050RHDAX moves along a travel of 330 metres. "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 from igus. "Because of the lower coefficients of friction, up to 57 percent of the energy required to drive the energy chain system can be saved." The 'AX' in the product name stands for 'external stop-dogs'. Since the stop-dogs are not situated inside between the chain links, as usual, the dust cannot get into the stop-dogs very much.

In addition to various energy and data supply cables, which were also produced by igus and specifically developed for use in e-chains, a water hose with a diameter of 48 millimetres for sprinkling the bauxite is also located in the chain on the dumping equipment. Furthermore, 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 on the one hand, and to compensate for possible parallelism errors between running rail and guide trough on the other hand.

Third joint project – loading and unloading of ship

In the most recent joint project of AOS and igus, which was implemented in 2017, two energy chains move on a travel of 218 metres reverse in a common trough. They supply the two cranes that deliver the bauxite and then remove the produced alumina again. Here, among others, medium-voltage motor cables of the CFCRANE series are routed, as well as fibre optic cables of the CFLG series. "This is a real advantage for us," affirms Fabian 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."

Motorised cable drums were also used in these two applications in the past. However, these always caused problems here because torque motors had to be operated, which always kept the cables of the motorised cable drum under tension. "Here in the past, the starting resistors on the motors rusted time and again and had to be replaced," recalls Fabian Wilhelm from AOS. "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."

Maintenance at AOS is also handled by igus experts. "Once a year, we check all the chains according to the igus maintenance manual and carry out visual inspections," explains Markus Böhm. "The first chain on the loop car has been in use for over five years now. Here at the last inspection we did not notice any significant signs of wear despite the very difficult conditions under the hall roof." This also applies to the other systems from igus that are in use at AOS. In addition, Fabian Wilhelm from AOS 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!"

The igus products are available from Treotham Automation in Australia. Contact Treotham today to find out how igus energy chains can improve your application.

For more information, please visit the Treotham Automation website www.treotham.com.au or call 1300 65 75 64.

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