Abstract: A furnace valve suitable for use in an electric furnace in the manufacture of mineral fibre comprising a water cooled sleeve provided with a carbonaceous member which is formed with a flow passage extending therethrough and a shutter plate movable across the face of the carbonaceous member to control the effective discharge area of the flow passage.

Abstract: An electric furnace for fusing of fusible metal/non-metal oxide compounds, for example slag, having a side wall of steel, a plurality of electrodes depending into the furnace, a coolant distributing conduit surrounding the furnace near its upper end, and a tapping valve located in the side wall of the furnace between its upper and lower ends, the furnace being operated by melting the slag to form a melt, the outer layer of which is in contact with the inner surface of the furnace side wall which is frozen by the chilled coolant flowing over the outer surface thereof, to thereby form a frozen slag lining on the side wall inner surface which is continuously replenished as it is depleted.