How do graphite electrodes work? graphite electrode manufacturing process
By:YvonneDec 14, 2020
Electricity then passes through the electrodes, forming an arc of intense heat that melts the scrap steel. So let DanCarbon talk about How do graphite electrodes work? graphite electrode manufacturing process and Why do graphite electrodes need replacing?
1. How do graphite electrodes work?
The electrodes are part of the furnace lid and are assembled into columns. Electricity then passes through the electrodes, forming an arc of intense heat that melts the scrap steel.
The electrodes are moved down onto the scrap in the meltdown period. Then the arc is produced between the electrode and metal. By considering the protection aspect, low voltage is selected for this. After the arc is shielded by electrodes, the voltage is increased for speeding up the melting process.
2. graphite electrode manufacturing process
The graphite electrode is mainly made of petroleum coke, needle coke as aggregate, coal asphalt as binder. It is includes calcination, forming, baking, impregnation, graphitization and machining. It is to discharge electric energy in the form of electric arc in the electric arc furnace. The conductor that heats and melts the charge can be divided into a common power graphite electrode, a high power graphite electrode and an ultra high power graphite electrode according to its quality index.
♦ Raw material
Graphite electrode is made of high quality calcined needle coke.
♦ Medium crushing and sieving
The needle coke is broken in the machine and sifted, then proportioned according to the recipe requirements.
After batching, the raw material is mixed with certain proportion of asphalt by heating and kneading to make a plastic paste.
After mixing and kneading, the paste is cooled to the process temperature and then pressed into the press according to the product specifications.
♦ The roasting
In the roasting furnace, the "raw embryo" electrode is roasted to the specified temperature according to the technological requirements, and the roasted product is impregnated with special impregnated asphalt according to the specific technological process to improve the product density and mechanical strength, and then the impregnated product is re-roasted to improve the product performance.
The secondary roasted products are electrified in the graphitized resistance furnace and heated to 3000℃, so that the carbon atom structure is rearranged in a specific crystal form, and the carbon is converted into graphite.
3. Why do graphite electrodes need replacing?
According to the consumption principle, there are several reasons of replacing graphite electrodes.
• The end use: These include the sublimation of graphite material caused by the high temperature of arc and the loss of chemical reaction between the electrode and the molten steel and slag. High temperature sublimation rate at the end mainly depend on the current density going through the electrode; also related with the diameter of the electrode side after oxidation; End consumption is also related to whether to insert the electrode into the steel water to increase carbon.
• Lateral oxidation: The chemical composition of the electrode is carbon, Carbon will oxidize with air, water vapor and carbon dioxide under certain conditions, and the oxidation amount of electrode side is related to unit oxidation rate and exposure area.Normally, Electrode side oxidation accounts for about 50% of the total electrode consumption. In recent years, in order to improve the smelting speed of electric furnace, the frequency of oxygen blowing operation is increased, oxidation loss of the electrode is increased.
• Residual loss: When the electrode is used continuously at the junction of the upper and lower electrodes, a small section of the electrode or joint is detached because of oxidative thinning of the body or penetration of cracks.
• Surface peeling and dropping: The result of the poor thermal shock resistance of the electrode itself during the process of smelting.Include electrode body broken and nipple broken. Electrode broken is related to the quality and machining of graphite electrode and nipple, also related to the operation of steel making.
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