Fig. 123. Ludlum Six-Ton Electric Furnace.

bulged boiler head ends. The furnace doors are at the ends, and the spout is located in the front or pouring side of the furnace. The cylindrical shell has an open top on which is located the roof, which

Volta

This furnace is made in standard sizes of 1-3-610-15 ton capacity and is of the Heroult type but embodies a number of modifications. The furnace is provided with charging doors and pouring spout. Each of the three electrodes is controlled independently by a motor driven winch. The furnace is tilted by means of the motor operated tilting mechanism.

The general construction as regards the shape of the hearth, roof, electrodes, holders, etc., are very similar to the Heroult Furnace as previously described. See Fig. 127.

Girod

In the Girod furnace an arc is formed between one or more electrodes and the charge. The two and three ton furnaces are operated preferably with single phase. The low tension voltage is approximately seventy-five volts. The single phase furnace re

tension and two phase low tension. The bottom electrode is embedded under the lining of the hearth. Electrical Equipment Usually Required for Steel Furnaces

The success of any furnace installation depends to a large degree on the electrical equipment. In common with steel mill practice electric apparatus is required, which is rugged, thoroughly reliable and dependable. The furnace transformers are one of the most important items.

The electrical equipment for steel furnaces comprises:

(a) Furnace Transformers.

(b) Switch Board and Protective Equipment.
(c) Automatic Electrode Regulator.
(d) Electrode (Winch) Motors.
(e) Tilting Motor.

are required which are obtained by means of taps on the high tension. See Fig. 128.

(b) The Switchboard contains the metering equipment, circuit-breakers, etc. While the general lay-out of the switchboard is substantially the same for the various types of furnaces, it usually differs in the amount or arrangement of the equipment.

(c) Arc Furnace Regulator is used for automatically controlling the movable electrodes, thus. maintaining any pre-determined value of current at the furnace. It is actuated by the current flowing in the line and the voltage drop across the arc, and in turn controls the motors which raise and lower the electrodes.

matic control of the electrodes requires a winch (d) Every electric furnace equipped for automechanism for raising and lowering the electrodes. The winch is generally connected to the electrode by a steel cable. For driving the winch, an electrode

or winch motor, as it is often called, is required. In steel furnaces which are of the tilting type the electrode motors are mounted on the furnace and are tilted with it. For this reason, oil ring lubrication can not be used, and instead the bearings are provided with grease cups or self lubricated bearings. Direct current motors are used. They are totally

Fig. 127. Volta, Six-Ton, Three-Phase Electric Furnace.

enclosed to protect them from dust and foreign matter. One electrode motor is required for each movable electrode. Where direct current is not available a small motor generator unit must be provided.

(e) A tilting motor is used for tilting the furnace except where the furnaces are tilted by hand. Either alternating or direct current motors with breaks and controller with resistance for heavy duty are suitable.

While the electrical apparatus is substantially the same for various types of steel melting and refining furnaces, the size, voltage, and other characteristics. are usually different. There are a number of other important points to be considered in furnace installation, such as the arrangement of the heavy conductings, connecting the furnace to the transformers. Such problems as skin effect, reactance, inter-lacing of leads, etc., require careful study in connection with any proposed furnace installation. The amount of power which can be fed into the furnace and the power factor are seriously affected by these factors. Fortunately, these problems have been very carefully investigated by both the electrical manufacturers and also furnace representatives, with the result that these points are usually given the consideration they deserve.

Most of the electric steel furnaces installed are charged cold and both melting and refining are car