Hot terrain - cranes for molten metal |
Demag suspension monorail for transporting molten metal
When M. Busch GmbH & Co. KG, Bestwig, wanted to invest in its casting shop in order to increase its performance, the system used to transport the molten metal was also reviewed. Since the capacity of the monorail system used previously did not meet the requirements for the planned production volume of the new casting shop, Busch asked Demag Cranes & Components to modernise the system. Demag accepted this hot challenge and met a whole range of demands to ensure that the casting shop will always be supplied with sufficient material in good time. Otherwise, an important requirement to achieve the performance increase would not have been satisfied.
The modernisation of the monorail system mainly concerned much faster operating sequences. Since the manufacturer of brake discs, brake drums, flywheels and components for truck axles specified a time slot of 186 seconds for a complete working cycle, planning focussed on determining the cycle times. With the help of software, it was found that there were only time reserves to utilised in the lifting motion and along the 70 metre travel section, which is supplemented by additional sections at both sides. Therefore, the track section had to be replaced, since its tolerances were too great to allow the trolleys to be guided without any problems at the required speed. A special profile section designed for monorail trolleys was selected. In addition, Demag met the requirement to allow part of the monorail to run in a slight curve, without prejudicing travel of the monorail trolleys.
Besides the track section, Demag also replaced the trolleys. Although the basic concept was maintained, for example with reference to resistance to dust and heat, they also had to be rated for the much higher speeds. Two travelling hoists fitted with turning mechanisms and DH 2000 rope hoists now operate in the installation. They are used in three shifts, six days a week. The main hoist speed is up to 20 metres per minute. The trolleys even reach travel speeds of 120 metres per minute. Classified according to FEM 5m, the trolleys can handle transport ladles filled with molten metal weighing 6.3 tons.
The Demag scope of delivery also included a transfer bridge, the entire conductor line system as well as the latching devices used by the trolleys to transfer from the fixed to a moving track section. Demag also installed control pushbuttons which operators use to ensure that the units safely transfer from automatic operation to the 30 centimetre long manual sections at the beginning and end of the line.
The logistics sequence begins when a stacker transfers a transport ladle with some three tons of molten metal from a heat-maintaining furnace to a lifting station. This slightly raises the ladle to enable the worker to turn it by 180 degrees. Automatic operation then starts with a lifting motion of some twelve metres and transfer of the ladle to the Demag monorail system. This travels to the casting machine on the opposite side of the bay, lowers the ladle some five metres and suspends it in the machine. Since it is not possible to transfer the ladle direct from above, Busch needs the transfer bridge. The entire transport system is controlled from a central control station. All parameters can be programmed and malfunctions visualised here.
Busch selected Demag as its partner for the modernisation work because the supplier specifically satisfied all of the customer's needs. Demag also made a highly professional impression during the negotiations. Further criteria were the close vicinity to Demag, the manufacturer's good reputation and the positive experience Busch had already enjoyed with its cranes and components. At the initial stage of planning, Busch also considered implementing the horizontal transport of the molten metal exclusively using stackers and to limit the use of the crane to vertical handling. This would have resulted in too much space being needed for the long stacker travel path. Besides this, complex mechanical equipment that is potentially prone to malfunctions would have been necessary to turn the ladle 180 degrees before it is suspended in the casting machine.
Demag has also created a reference installation with the monorail system. After all deadlines had been met, the installation provided the agreed performance straight away. And this was achieved although a period of only three weeks was available and Demag had to share the shop crane with the company that converted the mould machine. After three years of operation, it has been shown that Demag has even undercut the specification limits. One reason for this is the guaranteed availability of 97 per cent, six days per week. It was also agreed that the cycle time of 186 seconds could only be exceeded by a maximum of two per cent and that the travel rail may only exhibit a maximum of two millimetres wear in 24 months. The travel rollers also have to reach a service life of twelve months.
