Graphite electrode is used as a conductive material in electric arc furnace smelting, and its consumption is proportional to the consumption of electric arc power.
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 furnace burden and the temperature rise depend 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 on 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 its contact with molten steel and steel slag. The oxidation loss of graphite electrodes accounts for about 2/3 of the total consumption. The oxidation loss is proportional to the unit oxidation rate and area, and is proportional to time. The longer the heating time in smelting, the greater the consumption. Therefore, it is very necessary to install a water-cooled spray system on the electric arc furnace electrodes. 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.
Residual consumption refers to the non-productive consumption part of the lowest branch electrode that falls into the furnace, becomes the final waste and is finally phased out of the production process in the smelting process. The generation of residues is not only related to the internal quality of the joints and electrodes, but also directly related to factors such as the distribution of the cloth in the furnace, the atmosphere in the furnace, and the power transmission operation.
The main appearance phenomena are: the bottom end of the residual body has a "人"-shaped crack and a large longitudinal crack or split; the connection is not tight, which causes the joint to oxidize and fall off or break; the connection is not in place or the fit is not good, and the fall or breakage occurs; the electrode is exposed to external force and the joint or the bottom of the hole is broken; the unreasonable distribution of the furnace causes the large collapse area after the well is dug or the unreasonable operation of the power transmission curve can cause the electrode to be severely broken; the graphite electrode itself is of poor quality. Under the premise of ensuring the quality of graphite electrodes, this part of the loss is not large in normal production, but direct users pay much attention to it.
In normal smelting and 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 molten steel. First of all, this phenomenon reflects the poor oxidation resistance and thermal shock resistance of the graphite electrode; secondly, the horizontal oxygen blowing time is too long or the amount of oxygen blowing in the smelting is too large, which causes serious oxygen enrichment in and on the furnace, resulting in increased over-oxidation loss of the electrode; 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.
Graphite electrode breaking is a common phenomenon in all electric furnace smelting, and it is also the most important factor affecting consumption. It is normal for it occasionally to break once in a complex environment during continuous consumption and use, but it is abnormal for continuous breaks. The reason is related to many factors. Generally speaking, it can be divided into: artificial breakage and mechanical breakage. Man-made breakages mainly include: bumps and scratches during lifting, improper connection or improper method, improper sliding in the flat holder, hard collision or poor drive control sensitivity, etc. In addition to mechanical failures in mechanical breaking, the problem of electrode quality and operational problems often coexist and are difficult to distinguish.