Energy in motion - even under adverse environmental conditions

The Aluminium Oxid Stade GmbH (AOS) is one of the major alumina producers in Germany. It processes the raw material bauxite into alumina of high purity which is then sent to the processor. More than one million tonnes of alumina are produced every year in Stade. For this, one needs about double the amount of bauxite, which the deep-sea vessels bring from Africa, Australia, and South America and deliver at the AOS' own harbour. A single ship delivers up to 70,000 tonnes of raw material that is transported further via an enclosed conveyor belt system for temporary storage. The different types of bauxite are either stored in warehouses or large open spaces and fed by an impressive, highly visible paddle-wheel stockpiling unit of the production (Figure 1).

As a complete overhaul of the stockpiling unit was being undertaken, those responsible decided not only to modernise the unit itself, but also to renew the rail track and the energy supply of the conveyor system. Originally the conveyor was supplied with energy and signals over its at least 366 long track via a motor cable drum. Now a modern energy chain system from igus® undertakes this task (Figure 2). Since the push/pull forces that occur across the length of the travel shouldn't be underestimated, the project engineers recommended the use of a roller e-chain® that doesn't glide in the guide trough, but rolls via highly stable rollers with stainless steel ball bearings. Since the environmental conditions are unfavourable (outdoor use, temperature changes, humidity, dust), there is a "heavy duty" roller chain of type 5050RHD for application. Outer radius stops prevent the conveyed material from sticking (Figure 3). In addition, the guide trough is equipped with an enclosure as a protection against ascent and weather.

A floating moving end suspension provides the lateral tolerance compensation and an igus® PPDS system (Figure 4) ensures the high availability, which is essential for this application. This relatively new system - the acronym stands for Push/Pull Forces Detection System - continuously measures the tensile and shear forces. In case barriers or blockages occur during the movement of the energy chain, they are recognised by the PPDS and the system can then stop the conveyor immediately. In this way, major damage such as a cracking of cables can be avoided.
 
For Dipl.-Ing. Fabian Wilhelm, Project Manager at AOS Stade, the benefits of the e-chains® solution are obvious: "By switching from cable drum to energy chain, we can dispense with additional slip-ring drives and their brake motors. This reduces both energy consumption and maintenance costs. " In addition, fibre optic cables and media hoses can be inserted and guided safely in the e-chain®. The AOS uses these capabilities: A fibre optic cable with six fibres is also "on board" the chain, as also a heavy water hose for the sprinkling of bauxite.

igus® supplied the engineering and the e-chainsystem® with all its components including the individual console substructure. The complete installation on site in Stade was undertaken by the igus® assembly service. Its staff assembled the energy supply system that run several hundred metres long on the existing rail sleepers of the stockpiling unit. The complete assembly with steel structures was performed according to plan in two sections and a total of only twelve working days (Figure 5). The acceptance, delivery to AOS and joint test runs took place at the agreed date, and since then the energy chain runs without problems or irregularities.
 
"We attach great importance to giving reliable delivery dates and respecting them - even and especially when several trades are working in parallel on construction sites like this," says Markus Böhm, Technical Sales Consultant at igus®. "A self-developed software tailored to our products creates the conditions so that we are able to plan precisely and offer our system assemblies at fixed prices. The fact that we also agree on individual guarantees for these services, raises the reliability and availability of the entire system from a customer's perspective. “

Another reason for AOS to completely assign the energy chain system with assembly to igus®, was the effective presence and intensive consulting on site (Figure 6). There was also an in-house reference. The previous year the igus® assembly service had an e-chainsystem® installed on a 140 m travel distance on the tripper car of the AOS warehouse hall.