PRODUCTS DIVISION 3

APPLICATIONS AND USE

 

Graphite electrodes are the most environmentally friendly elements for steel production today, specially when compared to blast furnaces. Its high conductivity at high temperatures makes it the ideal medium to transmit electrical energy and convert it into thermal energy. Graphite electrodes are mainly used in the production of steel, aluminium, lithium, magnesium and potassium, among other elements. 

The use in the steel industry is given as follows:

a)  The electric arc furnace can have one or three electrodes depending on whether it uses DC (Direct Current) or AC (Alternate Current). For this reason, the furnace roof has one or three symmetrical holes; in each hole fits the column of an electrode with enough clearance so it does not allow heat leakage. Moreover, the roof has a hole for the gas outlet and in many cases other holes for lime injection and sampling of the melt material and slags.

 
 
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c) Electric power controls the furnace operation during much of the metal charge melting. First, this high electric charge produces a long, high-temperature electric arc that pierces the batch of metallic charge. Second, when it reaches the limit the arc increases melting the charge around it. Third, the electrodes melt the metal charge from bottom to top at constant power. Fourth, when the load is almost molten and the ferroalloys are added, oxygen and carbon are injected. The electrodes operation delivering energy is regulated in order to keep the load in liquid state and raise the temperature to homogenize the steel.

d) The diameter of the electrode depends on the size of the furnace (diameter and weight of the melt steel) and its transformer power (limit due to maximum current density allowed) 

b) Each column of electrodes of the AC furnace represents an alternating current phase, which in contact with the metallic charge will generate an electric arc that will melt and/or keep the metallic charge in liquid state while the steel is being refined.

 
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e) Electrode types and grades are selected according to the furnace and its transformer’s technical specifications, and also by the type of steel that is produced. 

f) The production objectives are to reach the lowest cost per ton of steel and this is achieved based on the lower consumption of energy, electrodes, oxygen, carbon and operating time, in addition to metal load, quality of ferro-alloys, etc. 

g) The most common parameter used to measure the consumption of electrodes is the weight per ton of liquid melt metal normally measured after each day or cycle of operations. The consumption of electrodes includes the part burnt in the furnace (related to the time of when the arc is on) and the part lost due to mechanical breakages (mainly in the first stages of melting). Therefore, a higher quality and efficiency of an electrode will have a longer operating time.

h) The electrical power withstood by the electrodes is a function of their diameter, ash content and the use of high quality coke.

ELECTRODE SELECTION