Between 2014 and 2016, several spills of molten liquid iron occurred during unloading operations in a steel plant. The molten cast iron produced by the blast furnaces is discharged through a pouring hole in the lower part of the crucible. It is then collected in a refractory lined casting channel, where the separation of pig iron and slag occurs owing to their specific weight. After the slag is separated, the molten cast iron is dumped by means of a rocker loading arm into “torpedo” cars. These elongated cars are lined with refractory materials.
In one accident, the spillage of the molten cast iron on the ground was due to a failure of the control system of the articulated rocker arm that transports the molten cast iron to the torpedo car. The transfer of molten cast iron via the tilting system generates considerable stress on the rocker arm. This eventually caused the arm to break, resulting in a spill of molten iron from the overflowing torpedo car. Another cause has been identified: cooled aggregates falling from the tilting system into the torpedo car, causing the melt to overflow.
The following measures were taken:
- stamped identification of the loading arms of each blast furnace in order to guarantee a unique combination of arms associated with a blast furnace,
- weekly monitoring and adjustment for each loading arm,
- semi-annual replacement of the loading arms.
In the other accident, the spillage of molten cast iron onto the ground occurred because the cooled aggregates, initially formed by molten cast iron splashing onto the vertical surfaces of the structure, caused deflections in the melt flow. In addition, the structure at the end of the discharge channel separated due to mechanical and thermal wear generated by the melt flow.
To prevent the spillage of molten cast iron, the following measures were taken:
- the empty area of the vertical discharge channel was filled with refractory cement to transport the melt over a longer forced path, thus reducing the distance between the discharge hole and the entrance of the torpedo car,
- employee training.
In both accidents, a massive reddish emission of iron oxide dust and a fire occurred with no other direct consequences for the plants or employees.