Consumption and use of graphite electrodes in electric arc furnace smelting (1)

Consumption Mechanism of Graphite Electrodes

As a conductive material in EAF smelting, the consumption of graphite electrode is proportional to the consumption of electric power. Modern electric arc furnace steelmaking uses electrical energy and chemical energy as thermal energy to achieve the purpose of four desorption (P, C, O, S), two removal (gas, impurities), and two adjustment (temperature, composition) in the steelmaking process. The performance of the graphite electrode is mainly reflected in the user's suitability and consumption, and the consumption of the electrode is directly related to its own quality. The consumption of graphite electrodes in electric arc furnace smelting mainly consists of the following parts.

1. Consumption of graphite electrode end and outer surface in electric furnace

The arc generated by the graphite electrode in the electric arc furnace is divided into long, medium and short arcs, and the melting of the charge and the temperature rise depend on the arc power. The arc length is proportional to the secondary voltage and inversely proportional to the secondary current and heating rate. In order to increase the smelting speed and greatly shorten the smelting time, the high chemical energy operation of forced oxygen blowing is adopted, which puts forward higher requirements on the oxidation resistance and thermal shock resistance of the graphite electrode. The end consumption of graphite electrodes in smelting includes - sublimation generated in the high temperature of the arc, chemical reactions generated in contact with molten steel and steel slag. The oxidation loss of the graphite electrode accounts for about 2/3 of the total consumption. The oxidation loss is the product of the unit oxidation rate and the area and is proportional to the time. The longer the heating time in smelting, the greater the consumption, so it is installed on the electric arc furnace electrode. A water-cooled spray system is necessary. In normal smelting, the carbon content of the graphite electrode entering the molten steel is generally about 0.01%, and it is normal for the end consumption switch to be non-conical.

2. Residual consumption of graphite electrodes produced in smelting

Residual consumption refers to the non-productive consumption of the lowest branch electrode in smelting which falls into the furnace and becomes the final waste product and is separated from the production process. The generation of residual is not only related to the internal quality of joints and electrodes, but also directly related to the magnetic card distribution, atmosphere and electric operation in the furnace. The main appearance phenomena are: the bottom part of the residual body has a "herringbone" shaped crack and a large longitudinal crack or splitting; The joint is not tight and the joint is oxidized and falls off or breaks; The connection is not in place or with bad fall off or broken; The electrode is broken at the bottom of the joint or hole by external force. When the electrode is subjected to external force, the joint or hole part is broken. The electrode can be seriously broken due to the large area of material collapse or the unreasonable operation of power transmission curve. The quality of the electrode itself is poor. This part of the loss under the premise of ensuring the quality of the electrode, the normal production of a small amount, but direct users pay attention to this.

3. The electrode surface is oxidized and spalling, accompanied by cracking and falling consumption

In normal smelting production, if the surface of graphite electrode is uneven or accompanied by peeling and falling, then there is a problem of carburization in molten steel. On the one hand, this phenomenon reflects the poor oxidation resistance and thermal shock resistance of the electrode. On the other hand, the time of horizontal oxygen blowing is too long or oxygen blowing is too large, which results in serious oxygen enrichment in the furnace and on the furnace, resulting in increased electrode peroxide loss; The second is that if there is a serious shedding phenomenon, the electrode must also be considered. This kind of abnormal consumption is a test of the internal quality and technical service level of the product.

4. Direct loss caused by broken graphite electrode in smelting

Breaking of graphite electrode is a common phenomenon in all electric furnace smelting, which is also the main factor affecting consumption. In complex environment, continuous consumption and use of occasional broken is normal, but continuous broken is not normal. The reasons are related to many factors. Generally, it can be divided into: artificial fracture and mechanical fracture. Artificial fracture mainly includes: bump and scratch in lifting, improper connection or method, improper sliding in leveling device, hard collision or poor sensitivity of transmission control, etc. Besides mechanical failure, electrode quality problem and operation problem often exist simultaneously and are difficult to distinguish.

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