Factors affecting graphite electrode consumption in eaf smelting

The electric arc furnace smelting in the steelmaking process can be divided into rough smelting and refining, but the electric energy is transferred into the electric furnace by the graphite electrode and converted into heat energy to heat up and melt the solid furnace charge. Coarse smelting is an oxidation process aimed at melting scrap and discharging harmful gases and impurities. 

Refining is also a reduction process aimed at adjusting steel elements and degassing impurities by raising temperature. It can be seen that electric arc furnace smelting uses graphite electrode to adjust furnace temperature to achieve oxidation and reduction reaction and meet the requirements of steelmaking process. The generalized consumption of graphite electrode in smelting can be divided into active consumption, natural consumption or technical consumption. Reactive power consumption refers to the tangible consumption that has not participated in the heating process or has not fully participated in the heating process, which is also non-technical consumption.

Main factors affecting consumption of graphite electrode in EAF

The consumption of graphite electrode in electric furnace steelmaking runs through the whole smelting process, and its consumption is affected by many factors. Here, it is only for the operation of smelting process to analyze.

1. Poor quality or improper proportion of scrap steel results in poor slagging effect and prolongs smelting time

The increase of feeding times and penetration data increases the probability of electrode bottom damage and fracture; The extension of smelting time is a direct factor leading to the rise of power consumption and electrode consumption and loss.

2. The electric furnace power supply equipment does not match the electrode specifications and varieties

Electric arc furnace is operated with high current and low voltage. If the capacity of the power supply equipment is too large to exceed the limit load of the electrode, the electrode will turn red from bottom to top within 5~10min of arcing, and the boundary at the connection is very obvious, and most of the broken accidents occur; If the current is too high or the fluctuation is too large, the breaking frequency of the joint at the connection will increase and the bottom consumption will be tapered. If the power supply capacity is low, the furnace temperature cannot meet the process requirements within the effective intermediate heating time, and the operation will be delayed. Overload and overtime operation have the greatest loss and consumption to the graphite electrode.

3. Forced increase of chemical energy and smelting intensity during oxidation period

Forced increase of oxygen blowing volume during smelting (generally less than 45m ³/ t) In order to achieve rapid melting and improve furnace temperature, it is easy to make the furnace condition worse and the furnace and furnace are in oxygen rich state, so that each phase of electrode is in a high temperature flame. When the electrode is in this furnace environment, there are serious phenomena of delamination and surface oxidation.

4. Configuration and operation technicality of electric furnace

The modern electric arc furnace is essentially different from the traditional electric furnace. The appearance of super high power large-scale electric arc furnace and hot charging steelmaking process has improved the smelting intensity and productivity, thus putting forward higher technical requirements for the quality of graphite electrode. The selection of power transmission curve and gear during operation, the control of arc starting and arc stabilizing voltage and current, the combined use of long, medium and short arcs, and the configuration and application of water cooling system all play a key role in the service life and consumption of electrodes.

5. Quality of graphite electrode

At present, the smelting and process of electric arc furnace have increasingly strong requirements on the oxidation resistance and thermal shock resistance of graphite electrode, and the high consumption caused by quality fluctuation is greatly concerned by direct users. Therefore, the quality balance and stability of graphite electrode are the most important factors to determine the consumption.

Comparative analysis of arc furnace graphite electrode consumption

When the process and operating conditions of smelting electric arc furnace change little in a certain period, the consumption level of graphite electrode is basically balanced. It is normal that the electrode consumption fluctuates with the prolongation of furnace life or the change of process. Then, when there is a product from the same company on the same electric arc furnace, its consumption fluctuation is highly regarded by users. It is a common phenomenon to raise an objection to this. The quality of any product fluctuates, but the extent of fluctuation reflects the technical equipment level and comprehensive management level of the manufacturer.

Further analysis of the broken graphite electrode in electric furnace smelting

The accidental electrode breakage in electric arc furnace smelting is a normal phenomenon and can not be absolutely avoided, while the electrodes of large DC, AC and LF electric furnaces are regarded as accidents. Treatment of electrode broken residue is the hardest work in operation, which inevitably results in high consumption, longer smelting cycle, lower output and higher cost. The reasons for electrode breakage in electric furnace smelting operation are relatively complex:

1. Smelting process

(1) The proportion of raw materials shall be such that there shall be no bulk materials and non-conductive materials under the electrode;

(2) When the phenomenon of "bridging" occurs after the well is penetrated, the long arc operation shall be used to avoid the impact of large collapse materials;

(3) The electrode lifting and the small furnace cover must be concentric to avoid breaking due to scratching during thermal shock.

2. Power transmission system

(1) Determine the initial arcing gear and raise it in sequence (each furnace shall have at least 3 power transmission curves) to avoid excessive thermal shock caused by excessive current fluctuation and frequent changes of long and short arcs in the furnace;

(2) With the increase of furnace temperature, certain internal stress shall be released at the electrode connection, and the current passing through the electrode unit area after arc striking shall have a gradual rising process, which is the adaptation process of electrode and furnace conditions.

(3) Overload operation: the overload capacity of the new electric furnace is generally not more than 20%. If the arcing current exceeds the rated value, the connector is most likely to break. When the electrode adapts to the furnace conditions, even if it is overloaded, it will operate normally, but the connector is red.

3. Smelting furnace condition

(1) The operation of feeding and power transmission is related to the change of furnace conditions, but oxygen blowing, burner steam and fuel oil are the keys to worsen the furnace conditions. The utilization of chemical energy reduces the power consumption, but increases the oxidation degree of electrode surface and upper end face. Especially when the negative pressure is too large, the oxidation speed of the electrode surface is accelerated, and the electrode body surface is tapered.

(2) The steelmaking process is the slag making process. The use of chemical energy increases the stirring force of molten steel and is more conducive to the production of foam slag. The boiling of molten steel, the thickness of slag layer, the fluidity of slag liquid and the submerged arc effect are not only related to the smelting effect, but also to the consumption of carbon addition at the bottom of the electrode and the consumption of U-turn and circumferential surface.

(3) The operation during furnace deterioration is frequently changed, and the electrode vibrates with left and right swing. The frequent change of current increases the thermal shock, which not only accelerates the surface consumption of graphite electrode in oxygen rich environment, but also tests the connection part (joint strength).

4. Electrode storage and transportation

(1) The on-site storage electrode shall not contact with the liquid medium, otherwise fish scale will appear after being heated.

(2) The joints stored on site shall not be close to the high temperature heat source, otherwise the joint bolt is easy to melt and flow out after being heated.

5. Electrode quality

For large UHP and HP upper limit electric furnaces, the quality of graphite electrodes provided must be improved.

(1) The structural defects or insufficient strength problems must be eliminated, otherwise the joint breaking accident will occur within 1~3min after the power transmission of the first ladle of smelting.

(2) The machining accuracy of the electrode end face is also crucial. If there is a gap, it will produce air permeability and local redness. The junction is obviously red after about 10min of power transmission, and the inner buckle is easy to be oxidized after 2~3 heats of continuous smelting, resulting in fracture or falling off accident.

(3) The tolerance and fit problems must be paid attention to at all times. Whether they are loose or not in place, they will break or fall off as long as there are gaps. From the perspective of use, most of the problems at the position are caused by tolerance fit.