| Successful new generation |
Demag cranes for greater efficiency
With its investment in four cranes supplied by Demag Cranes & Components for its press facility in Bremen, DaimlerChrysler has entered a new generation of efficiency. The conversion was necessary in order to achieve faster and more efficient production sequences.
Body shell components for the C-Class and for roadsters are primarily manufactured at the press facility in Bremen. When DaimlerChrysler had a new press line built for heavy parts in Shop 6 at the facility, the load capacity of the existing cranes was no longer sufficient, for which in any case unacceptably high maintenance costs were to be expected. For this reason, the company invested in three double-girder overhead travelling cranes and a semi-portal crane. Demag Cranes & Components supplied the new cranes in 2002 and 2003.
Two of the double-girder overhead travelling cranes mainly serve coils to the cutting machine installed in front of the press. The third double-girder overhead travelling crane, which is also fitted with a cab, transports the tools that are needed for the next series of workpieces to the press changing stations. It later retrieves the replaced tools and buffers them at one end of the press shop. The semi-portal crane provides support for maintenance in the tool-making shop at the press facility.
The two hoists on each double-girder overhead travelling crane have load capacities of 63 and 32 tonnes and 55 and 33.5 tonnes, respectively. Using tandem hoist units, which can move in opposite directions, they are able safely turn the tools, which weigh 40 to 50 tonnes, when this is necessary for repair work. In addition, DaimlerChrysler operates the hoists on the cranes either separately, or controls both of them in synchronised operation by means of frequency inverters, which ensures that the lifting and lowering motions are performed absolutely in parallel. For safety reasons and due to the height differences in the workshops, coil handling operations are always controlled from the cab position, which affords the crane operator the best view. The cranes are also fitted with radio control systems for less critical tasks.
The cranes travel at speeds of up to 80 metres per minute to ensure that the production line is always replenished. The hoist speeds are also high, at twelve metres per minute for the main lifting speed and twenty metres per minute for the auxiliary lifting motion. A highlight provided by the hoists is their load-dependent speed control, which enables heavy loads to be moved at reduced speed and, therefore, very carefully.
Demag fitted all of the double-girder overhead travelling cranes with load-sway damping systems in order to avoid any waiting times. In this way, loads can be quickly positioned. A disengaging coupling ensures that heavy workpieces can also be turned with ease. The electric-motor driven turning motion can also be controlled very carefully by means of frequency inverters. An ultra-sonic distance-maintaining system ensures that the cranes do not collide.
Above all, DaimlerChrysler required Demag to provide high speeds and load capacities. In addition, the cranes also have meet the maintenance concept requirements. This goal is achieved by virtue of the fact that Demag has supplied DaimlerChrysler with components of the same sizes for many years. Therefore, this means that the owner only needs to stock a relatively small range of spare parts despite having many cranes in operation; this benefit significantly reduces the maintenance costs.
The required crane availability of 98 per cent is also ensured by redundancy, since DaimlerChrysler operates at least two cranes on every press line. Furthermore, the in-house maintenance team is able to rectify certain malfunctions. In addition, the Demag employees who are almost permanently present at the Bremen facility can also intervene. To supplement this, the automotive manufacturer has concluded a maintenance agreement with Demag, provided for bi-annual maintenance of the cranes.
Since the production line operates 24 hours per day, it was only possible to install the new cranes over several consecutive public holidays. The work to be done was precisely co-ordinated and the schedule maintained within this tight timeframe. The crane runway already installed in Shop 6 was kept and surveyed by the LMS laser measuring system before the new cranes entered service. The wear that this revealed, which resulted from many years of operation, was compensated by more strongly dimensioned crane end carriages.
When the contract was awarded, the decision was also made in favour of Demag since DaimlerChrysler was highly satisfied with the previous project. Furthermore, the solution also represented good value for money and was therefore cost-efficient. Besides this, DaimlerChrysler’s spare parts concept also spoke in favour of focussing on one supplier and therefore for Demag.
