A new vacuum arc remelting furnace and electro-slag remelting furnace have been installed at Shibukawa Plant of Daido Steel in 1991.
The contorol systems of those furnaces are discussed in this report.
The furnaces are equipped with automatic melting systems which possesses distinct sub-systems each other.
For both the systems, the sub-systems to keep the melt rate constant and to keep the distance between the tip of the electrode and the molten pool surface constant are very important.
For these reasons, “Drip short control system” to keep the arc gap constant is proivided for the VAR and “Resistance swing control system” to keep the immersion depth of the electrode tip into the molten pool constant is provided for the ESR.
And the Melt rate control system by which melting rate is contorolled to the preset point by the sensitive measurement of melting rate via the load cell systems are also provided.
The conception of the contorol is remarkably improved compared to the existing systems.
Both the existing contorol systems, Arc Gap Contorol for VARs and Immersion Depth Contorol for ESRs, are based on the change of voltage. However the change of voltage by the change of distance between the electrode tip and molten pool is too small to use it for the contorol in both cases.
Drip short control is based on the phenomena that occurrence of the drip short follows to the Poisson Distribution, and Resistance Swing Control system is based on the phenomena that the resistance fluctuates very widely when the immersion depth of the electrode tip in the slag is small.
These systems give optimun heat transfer from arc heat or joule heated slag to the molten bath and then segregation free ingots of good surface can be produced.
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