The marathon crane |
Demag cement crane works round the clock, every day
The Spenner cement manufacturer uses an automatic crane from Demag Cranes & Components to store cement clinker, granulated blast-furnace slag and various additives and to feed the material into mill bunkers. In its daily round-the-clock marathon, the double-girder overhead travelling crane has to perform precise positioning operations right down to the last millimetre and withstand constant change between a hot, dusty building and weather conditions outdoors without suffering any damage. In addition, the customer requested exact and transparent stock management and wanted the specified process priorities to be met.
The automatic crane from Demag Cranes & Components in Wetter/Ruhr takes the place of its predecessor, which was more than 30 years old, in the Nordstern plant of Spenner Gmbh & Co. KG. The double-girder overhead travelling crane from Demag has a load capacity of 13 tons and a span dimension of 22 metres. Since its electro-hydraulic grab weighs some five tons, it can transport loads of approximately eight tons. The old crane that was previously used was still equipped with a simple rope grab and a cabin which had to be occupied 24 hours a day.
When making the new investment, the decision fell in favour of an automatic crane, because Spenner wanted to reduce costs by using state-of-the-art technology. The initial scepticism regarding an automatic solution that was based on the crane having to handle four different types of clinker, granulated blast-furnace slag, gypsum and other materials, soon passed as the crane operated with outstanding availability from the very beginning.
The crane stores cement clinker, granulated blast-furnace slag and other materials in corresponding separate compartments when they have been delivered by truck. The operator signals the type of material to the crane control system in advance, which knows the storage location of each type. The control system also knows how much of each type has been transported, thanks to a weighing device that is integrated in the grab. The height of the material is also known. Outstanding stock transparency is guaranteed thanks to the proven control concept.
As soon as the crane control system receives the data via ultrasound sensors indicating that the defined minimum filling quantity of one of the eight mill bunkers has not been reached, the crane supplies the relevant bunker with the corresponding material. The drives that are equipped with frequency inverters provide for precise positioning right down to two to three millimetres.
The crane was also to carry out processes according to priority. The process of supplying the cement mills in good time and with sufficient quantities of material is top priority, thus retrieval operations are also of significant importance. The next priority is to empty the bunkers into which the material is unloaded by truck. The fact that the automatic crane had to reach the specified handling rate of some 200 tons per hour was also a decisive factor. If all three cement mills are being used at the same time, 100 tons of material have to be retrieved and replenished per hour in each case.
Since the crane works around the clock, seven days a week during the season, it has to offer high availability. For this reason, Spenner requested that maintenance-free bearings be installed, which help reduce service to a minimum. Furthermore, the large amount of clinker dust meant that the crane had to be especially equipped for such conditions. The control system, which Demag installed in a container situated outside the building, had to meet the same requirements. In addition to a dusty environment, the crane is also confronted with extremely high temperatures, since the clinker still has a temperature of approx 100 °C on delivery. Due to the highly abrasive nature of the clinker and granulated blast-furnace sand, the crane’s grab system has to be extremely wear-resistant.
Spenner selected Demag Cranes & Components as the supplier based on the wealth of experience Demag employees already have with cranes in the cement industry. Another important factor was the close vicinity to the Demag plant in Wetter, which guarantees prompt service. To ensure smooth operation, a survey of the crane runway using the LMS laser measuring system was also carried out by Demag before the crane was delivered. The runway was then re-aligned and partially refurbished in agreement with Demag.
The double-girder overhead travelling crane was put into service at the end of 2002 without interrupting production, as requested by the customer. The special challenge was to keep the old crane operating while the new one was being installed.
