The consumption of Eaf graphite electrode depends on the quality of electrode itself and the condition of arc furnace, So let DanCarbon talk about Eaf electrode wear mechanism, Global graphite electrode capacity & Continuous consumption processes of eaf electrode.
1. Global graphite electrode capacity
In 2017, China had an effective Graphite Electrode capacity of 900,000 tonne and a production capacity of 630,000 tonne. It produced almost 700,000 tonne of Graphite Electrode.Statistics maintained by the China Carbon Industry Association (CCIA) reveal that by December 2018, the newly-added Graphite Electrode capacity in China was 600,000 tonne. From Jan to Aug’18, Graphite Electrode output in China was 416,392 tonne, up 14.18% on a Y-o-Y basis. By 2020, production and sales of Graphite Electrodes in the country will not exceed 800,000 tonne which will be less than the total capacity of 1.5 MnT, thus resulting in overcapacity.
2. Eaf electrode wear mechanism
The consumption of graphite electrode in Eaf steelmaking is mainly related to the quality management of working electrode materials and the condition of Eaf, such as old and new furnace, whether there is mechanical equipment failure, whether continuous production can be carried out, etc. And steelmaking operations, such as smelting steel, oxygen blowing time, loading conditions, etc. As well as the consumption of graphite electrode itself, its consumption mechanism has the following aspects:
a. The ultimate target consumption mainly includes the sublimation of graphite materials caused by the high temperature of the electric arc, and the loss of the extremely important part of the electricity which reacts with the chemical substances between the molten steel and the slag. The final temperature passing through the sublimation rate depends primarily on the current density of the electrode and on the diameter of the rear side of the oxidizing electrode.
b. The chemical composition of the side oxidation electrode is carbon. Under certain economic conditions, oxidation technology will occur with the ambient air, water vapor and carbon dioxide. The amount of oxidation at the electrode side is related to the unit oxidation rate and exposed area. Typically, the oxidizing electrode side should account for about 50% of the total electrode consumption. In recent years, in order to improve the melting speed of electric arc furnace, the frequency of oxygen blowing operation is increased, which leads to the increase of oxidation technology loss of working electrode. Redness is often observed and the taper of the lower electrode harness in the steelmaking process.
c. Joint loss When the electrode is used for continuous time to connect the upper and lower two electrodes in the enterprise, a pupil part of the electrode or the joint (i.e. the residual object) will be broken due to the oxidation thinning of the working electrode or the penetration of cracks. The residual loss is related to the shape of the joint, the internal structure of the electrode and the vibration and impact of the electrode column.
d. surface peeling in the smelting process, the electrode itself has poor resistance to heat shock.
e. Electrode fracture includes electrode trunk fracture and joint fracture. The electrode fracture is related to the quality and processing of graphite electrodes and joints as well as steelmaking operations.
3. Continuous consumption processes of eaf electrode
Graphite will be oxidized at a temperature of approximately 4000℃ and sublimated at 36500℃. It is a kind of brittle non-metal material. During operating in electric furnace, the top of graphite column which located in air is cooled by spraying water; In the bottom of graphite column, the temperature at the arc discharging point reaches 4000~200000℃. Affecting heat and phase transition, the electrode will be consumed continuously during oxidation, melt and sublimation processes; on the other hand, under the independent or combined effect of different external factors such as process, equipment and operation (for example, gravity, pressure, pulling force, fracturing force, vibration, power, looseness electromagnetic force, thermal stress, thermal shock etc), the electrode will be consumed discontinuously due to looseness, breakage or cracks.