Two types of the reverberatory furnace are used in smelting. Fig. 9 shows a roasting furnace in which ores are roasted to simplify them before they are placed in the melting furnace shown in Fig. 10. The melting furnace is much used for smelting copper and tin ores, for refining copper and tin, and for melting copper and brass in large quantities in the foundry for castings.
Both furnaces have several similar parts, as follows:
G. Grate for fuel. D. Fuel door.
A. Ash pit.
W. Bridge wall to separate the fuel from the ore or metal in the furnace.
B. Furnace arch, which reflects heat down upon the furnace charge.
F. Hearth, on which the charge rests.
C. Chimney opening, controlled by a damper.
These furnace roofs are arched from side to side, and the sides are braced by iron plates connected with long rods over and under the brickwork of the furnace. The melting furnace must generate a more intense heat than the other, hence its fire box is larger. These furnaces have no air blast, and their draft is produced by a tall chimney. The fuel is usually oil, gas, or soft coal which produces a long flame. .. ..
Fig. 9. - Reverberatory Furnace for Roasting.
Fig. 10. - Reverberatory Furnace for Melting.
The roasting furnace has a flat hearth over which the ore, introduced through covered hoppers H, is evenly spread. The hearth is so shaped that every part of it can be reached by a rake or rabble through one of the doors M (two on each side) and when roasting has reached the proper degree, a plate in the hearth at the edge of each door is lifted and the charge raked into the arched space L. From there it is taken to the melting furnace.
In the regular process of smelting, the slope of the bottom leads the metal to the breast K (Fig. 10) from which it is tapped. This opening is stopped with a clay plng which is dug out by a pointed iron bar when the metal is to be drawn off. The slag is removed through an opening at the back of the furnace, higher than the breast opening.
After charging the furnace with ore and flux, the door H is plastered around the edges with clay to exclude air. The progress of the operation is watched and any stirring needed is done through the small covered opening P.
Unlike the blast furnace, the melting reverberatory furnace can be placed in operation and cooled down in a short time. Usually only a single charge is smelted and drawn off, after which the furnace is opened, recharged, and again put in operation without much lessening of temperature. Feeding hoppers may be placed on top and the furnace made to operate continuously.