PLANT DESCRIPTION

Production of forged and rolled ingots is performed in three stages:

  • Smelting of scrap metal
  • Secondary metallurgic processes:   
    • Alloy, homogenisation, desulphurisation, degassing
  • Casting

Smelting of scrap metal and the secondary metallurgical process are each performed in separate plants.


Smelting of scrap metal in the electric arc furnace
In the electric arc furnace, scrap metal is smelted together with the alloying elements and additives. The scrap steel used is determined taking into account the costs and smelting output of the electric arc furnace. The electric arc furnace, itself, is a conventional three-phase AC current furnace. It is equipped with a natural gas / oxygen burner and a lime injection system.

Secondary metallurgical treatment at the combined ladle furnace and vacuum degassing system
The most important properties of steel are achieved during treatment in the ladle furnace and vacuum treatment.

Our ladle furnace is a two-phase plasma arc furnace. In contrast to conventional ladle furnaces, it operates with two electrodes. This is an advantage, particularly with our relatively small 15-ton ladle. At the same time carbonisation takes place during heating, even with a low carbon content. This facilitates treatment of molten metals after vacuum refining. The analysis at the ladle furnace can be easily configured due to the known tap weight and the options for homogenisation of the molten steel through intensive gas flushing using argon or nitrogen. For alloying of some elements, such as carbon, titanium or aluminium, the ladle furnace is equipped with a wire coiling system. The vacuum system is a DETEM system. In 1985, Dörrenberg developed this process in cooperation with former Technometal from Duisburg. The main characteristic of this process is that the vacuum ladle, itself, forms a part of the vacuum vessel. At the bottom, the ladle is positioned on a vacuum floor and from above the vacuum lid is positioned on the ladle. The advantage with regard to conventional tank degassing systems is the lower volume that needs to be evacuated, which results in lower investment and operating costs. An oxygen lance allows for refining under vacuum for removal of carbon to a small extent.

Casting
All ingots are cast by "Uphill Teeming". The casting velocity is measured and recorded. With special applications, casting is performed with a pouring stream protection. After casting, the lids are removed.

Bogie hearth furnaces
Our bogie hearth furnaces are used for keeping the ingots warm for hot delivery to the customer and for annealing of ingots. The annealing programs are specifically tailored to the material and are processed by the controls of the bogie hearth furnace.

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© Dörrenberg 2013