Graphite electrode is used as a conductive material in electric arc furnace smelting, and its consumption is proportional to the consumption of electric work. Modern electric arc furnace steelmaking uses electric energy and chemical energy as thermal energy sources to achieve the purpose of four removal (P, C, O, S), two removal (gas, impurities), and two adjustments (temperature, composition) in the steelmaking process. The performance of the graphite electrode is mainly reflected in its applicability 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 is mainly composed of the following parts.
1. Consumption of the end of the graphite electrode and the outer surface in the 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 heating depends on the arc power. The arc length is directly proportional to the secondary voltage, and inversely proportional to the secondary current and the 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 for the oxidation resistance and thermal shock resistance of the graphite electrode. The end consumption of graphite electrodes in smelting includes the sublimation generated in the high temperature of the arc, and the chemical reaction generated in contact with molten steel and steel slag. The oxidation loss of graphite electrode accounts for about 2/3 of the total consumption. The oxidation loss is the product of unit oxidation rate and area and is proportional to time. The longer the heating time in smelting, the greater the consumption, so install it on the arc furnace electrode Water-cooled sprinkler system is very 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-cone-shaped.
2. Consumption of residual graphite electrodes produced in smelting
Residual body consumption refers to the non-productive consumption part of the smelting process where the bottom electrode falls into the furnace and becomes the final waste product, which is separated from the production process. The generation of the residue is not only related to the internal quality of the joints and electrodes, but also the distribution of the cloth in the furnace, the atmosphere in the furnace, and the power transmission operation are directly related to the magnetic card. The main appearance phenomena are: "Herring"-shaped cracks at the bottom of the residual body and large longitudinal cracks or splits; the joints are not tight enough to cause the joints to oxidize and fall off or break; the connections are not in place or the fit is not good, and they fall off. Or break; the electrode is subjected to external force to break the joint or the bottom of the hole; the electrode is subjected to external force to break the joint or the hole part; the unreasonable fabric in the furnace causes a large collapse area after the well or the unreasonable operation of the power transmission curve can cause the electrode Severely broken; the electrode itself is of poor quality, etc. Under the premise of ensuring the quality of the electrode, this part of the loss is not large in normal production, but the direct user pays much attention to it.
3. The electrode surface is oxidized and peeled off with the consumption of opening and falling off
In normal smelting production, if the surface of the graphite electrode is uneven or accompanied by peeling and lumps, then there will be a problem of carbon increase in the 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 horizontal oxygen blowing time in the smelting is too long or the amount of oxygen blowing is too large, which causes serious oxygen enrichment in and on the furnace. As a result, the electrode peroxide loss is increased; secondly, if there is a serious shedding phenomenon, the problem of the electrode must also be considered. This abnormal consumption is a test of the inherent quality of the product and the level of technical service.
4. Direct loss caused by broken graphite electrode during smelting
Graphite electrode breaking is a common phenomenon in all electric furnace smelting, and it is also the most important factor affecting consumption. In a complex environment, continuous consumption and occasional breakage is normal, but continuous breakage is abnormal. The reason is related to many factors. Generally speaking, it can be divided into: artificial breakage and mechanical breakage. Man-made breaking mainly includes: bumps and scratches during lifting, improper connection or improper method, improper sliding in the flat holder, hard collision or poor transmission control sensitivity, etc. In addition to mechanical failures in mechanical breaking, electrode quality problems and operational problems often coexist and are difficult to distinguish. The following phenomena mainly exist:
(1) The electrode body is broken
One is that the electrode may have structural defects and may be of low strength; the second is that the short arc operation is still in the smelting process and there is a large side impact force of the collapse; the third is that the three-phase electrode on the furnace is seriously not vertical and there is slag hanging in the furnace Or the phenomenon of scraping the furnace cover and so on. The sound is very crisp and loud when broken
(2) The bottom of the electrode body is broken
The first is that the structure of the electrode end is loose or has dark lines, the joint and the hole are not matched properly, or the material difference does not match the linear expansion coefficient; the second is the phase electrode is not concentric, the electrode stroke is too long or the lifting is not sensitive; the third is the fabric in the furnace , There are non-conductive objects under the electrode. The sound is not loud when it is broken, but the tilt is heavier.
(3) The joint is broken and is irregular
One is that the taper of the joint is different or the ellipse of the joint hole is too large; the second is that the dust in the hole during the connection causes excessive contact resistance, and the joint thread is locally oxidized and too fast; the third is that the electrode is not connected in place and the torque requirement is not met, resulting in loosening ; Fourth, the holder is tilted, the electrode is not concentric with the furnace lid hole, etc. The sound is crisp and small when broken.
(4) The joint breaks are regular phenomenon
The first is that the quality of the joint itself varies greatly, and the strength of the joint cannot meet the requirements of the smelting furnace; the second is that the electrode hole and the joint tolerance are not properly matched or the connection torque does not meet the requirements, and the return is caused; There is a sudden increase phenomenon, and the maximum instantaneous current far exceeds the rated value by more than 1.2 times; fourth, the thermal shock generated when the output power is too large is also too large, and the electrode connection is red and the resistance is too large. The sound becomes muffled when broken.
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