What is the Ladle Furnace?
By:Yvonne Aug 05, 2020
First ladle furnaces were constructed in the middle of the 1960s by ASEA in Sweden. In the ASEA–SKF process, ladle was put down in a chamber which had two lids, one for vacuum treatment and the other lid with three electrodes for heating. Another method introduced in the 1960s was Finkl–Mohr process which had only one, vacuum-tight lid through which the electrodes were inserted. The construction was technically demanding with vacuum-tight electrode lead-ins. This kind of technology was generally called VAD. It has spread moderately although heating under atmospheric pressure is much more common.
ASEA introduced an extra specialty, namely, inductive stirring in ladles. To apply inductive power, the ladle wall inside the induction coil cannot be of ferromagnetic material like carbon steel, but was made of nonmagnetic austenitic stainless steel. Nowadays heating units are mostly separated from the vacuum unit, but they form a “secondary metallurgy station” where heats are easy to operate. For vacuum treatment, it can be “tank degassing,” RH degassing, or other method. The installation for heating is called ladle furnace (LF). Typically, there is argon bubbling from the ladle bottom to circulate the steel and to improve heating efficiency. Also electromagnetic stirring is possible (ASEA–SKF furnaces, nowadays ABB). The electric power in LF is quite moderate (compared with EAF for steel melting) providing a heating rate ~ 5 °C min− 1 max. The required heating energy depends not only on the desired temperature increment but also on the amount and thermal properties (specific heat) of the alloys which are added in the ladle. Except for heating, ladle furnace is an excellent place to make desulfurization with slag, Ca-treatment, and other alloying and trimming additions.