20th International Forgemasters Meeting - IFM 2017

Electroslag Remelting (ESR) furnaces with electrode exchange techniques offer the possibility to produce large-sized ingots with homogenous, dense structures, high cleanliness levels and desired mechanical properties for high quality materials. ESR units that form one large ingot from multiple electrodes require electrode exchange techniques and typically utilize an ingot withdrawal system. Compared with electrode exchange in stationary molds, the short-collar molds feature short electrode exchange times and provide more flexibility of electrode length. Modern, advanced control systems perform ingot withdrawal as well as electrode exchange in a fully automatic mode. A crucial requirement for automated ingot withdrawal is a reliable level control of the slag pool within the mold. In short-collar molds, a slag pool is established and the initial ingot section will be remelted under static mold conditions. When the slag pool reaches the desired level within the mold, the withdrawal system will start to pull the ingot out of the mold in order to keep the slag pool at a constant level within the mold. Various systems for determination of the slag level have been realised, including contact rods, radar, etc. ALD developed a modern ingot withdrawal control system utilizing temperature readings from the mold wall. This paper describes how temperature measurement of the mold can be useful to control withdrawal rates of the ingot, thereby maintaining constant heat transfer rates in an industrial ESR furnace. In addition to the level control function, this new technology allows an insight into the thermal process of the forming ingot. Results from several ingot dimensions and process settings will be presented.