Title: consumption reduction analysis of graphite electrode in LF refining furnace
Keywords: graphite electrode consumption
Abstract:: The mechanism of end face consumption, side consumption and break consumption of graphite electrode in LF furnace was analyzed. Through such effective measures as processing and reuse of broken electrode, recycling of hot slag, reasonable control of temperature, selection of reasonable power supply system, optimization of bottom blowing argon control, and adoption of electrode spray device for water-cooled electrode, electrode consumption is 0. 55 kg /t goes down to 0. The 25kg /t steel ensures stable production, achieves the purpose of reducing cost and increasing efficiency, and creates conditions for the survival and development of the enterprise.
Graphite electrode consumption affects steelmaking cost:
LF is actually a special form of the electric arc furnace. In a non-oxidizing atmosphere, the electric arc heat generated between the graphite electrode and the molten steel is used as the heat source. Through arc heating, argon blowing and stirring at the bottom of the coating, the slag with high alkalinity is produced to reduce slag. Wuhu xinxing casting tube co., ltd. completed and put into production three 120t ladle refining furnaces in 2012. The equipment is mainly used for heating and plays a good connection between converter and continuous casting. During the process of LF refining furnace, the electric electrode consumption usually accounts for 15% ~ 20% of the cost of LF steelmaking, which is an important economic indicator of LF furnace and one of the important factors affecting the cost of steelmaking. Especially at present, the price of graphite electrode has skyrocketed, and the cost of electrode consumption is increasing day by day. During the process of using the graphite electrode of LF furnace, there are many problems, such as fracture, natural shedding of joint, electrode slide-wire and unlocking, etc., which greatly increase the consumption of electric electrode, increase the refining cost of LF furnace, and seriously affect the process production. In order to ensure the production of LF furnace equipment in line, improve the composition of molten steel, temperature qualification rate and product quality, increase the number of continuous pouring furnace, effective control of cost, in the process operation and use of the electrode function is necessary to further improve.
Mechanism analysis of graphite electrode consumption:
Graphite electrode is mainly composed of coal mine grinding powder and graphite tar, which can convert electrical energy into heat energy to heat up the molten steel. During the heating process of LF furnace, the electrode itself is prone to oxidation, melting loss, thermal vibration and peeling. Electrode consumption mainly includes electrode end consumption, fracture consumption and side consumption [2]. In terms of smelting technology, the total electrode consumption in smelting can be divided into side oxidation and end consumption.
- Graphite electrode is broken and consumed
The graphite electrode is usually broken at the highest joint or joint seat of the electrode. Mainly for the electrode head screw is not tight or indirect connection between the dust not clean, there is a small gap, cause have larger contact resistance between the electrode and electrode, make joint will be local hot, and due to the oxidation of the situation, in the process of heating up, due to the effect of electromagnetic force, the electrode lifting system is not stable, by this will lead to fracture appears high.
- Graphite electrode side consumption
When the electrode temperature is 400 degrees Celsius, the graphite surface will be
permeated with oxygen, oxidation occurs, when to 600 degrees Celsius, the oxidation
reaction should be more serious. This consumption on the side of the electrode is mainly
due to the oxidation reaction on the surface of the cylinder on the electrode. Since the
oxidation rate is very sensitive to the airflow velocity and oxidation concentration near
the electrode, when the oxygen pressure in LE furnace is low, the side consumption is
less [6]. In practice, compared with the oxidation reaction of carbon in the LF furnace, the
weak carbon gasification reaction is not the first cause of electrode consumption.
- Graphite electrode end face consumption
The consumption of the electrode consists of evaporation, thermal stripping, dissolution and chemical reaction. When the temperature of graphite reaches 3650℃, sublimation will occur, while in the process of arc heating, the internal temperature of the arc column will far exceed 3650℃. During electrode use, thermal stress is generated due to the temperature difference between different parts, which leads to thermal spalling phenomenon. When the arc current density increases, thermal spalling will be intensified. The unreasonable control of the air supply at the bottom of ladle in different refining stages or the poor adjustment of the electrode energy force will cause the molten steel to contact the electrode and lead to the electrode dissolution. LF furnace with low voltage, high current power supply system will lead to shorter arc length, arc by the magnetic field force will be offset to the outside, coupled with the arc column on its surrounding slag agitation, electrode by slag intense erosion, resulting in electrode erosion; The electrode reacts with highly oxidized components such as Fe O and MnO.
Measures to reduce consumption of graphite electrode in LF refining furnace
- The broken electrode is processed and reused
The LF graphite electrode with a length of more than 1 meter was cut off and then reworked. Internal threads were processed at both ends and connected with the graphite electrode joint. The LF — 84 — total phase 244 metallurgical electrode was set up for re-use in phase 4 of August 2018
- Refining hot slag recycling
LF furnace hot slag is with a certain alkalinity, temperature reduction slag refining, hot slag recovery, through the role of argon stirring, coupled with a certain amount of powder deoxidizer, can be quickly produced reducing slag. The power supply time and power consumption of single furnace can be reduced by recycling hot slag, and the purpose of reducing the consumption of electric extremes is achieved.
- Reasonable temperature control
Raise and stabilize the arrival temperature of molten steel in LF furnace, and lower the outlet temperature as far as possible to shorten the heating time.
- Optimizing power supply system
Generally, short arc and high power are used at the beginning of refining to melt slag quickly. After slag melting, choose the appropriate long arc, increase the input power, fast heating; At the later stage of refining, the appropriate arc length and input power are selected according to the requirements of the steel type, and the temperature of the steel is controlled within a narrow range (± 5℃). At the same time, the carbonization of the steel is controlled to meet the requirements of continuous casting on the composition and temperature of the steel.
- Optimized bottom blowing argon control
If the length of the arc is not well matched with the argon blowing, the electrode will be licked by the molten steel and the consumption of the electrode will increase. Therefore, the whole process of argon blowing in LF furnace is carried out and the whole process of argon blowing in LF furnace is optimized. In the actual production process, the flow control of argon gas is better, which not only reduces the slag on the furnace cover, but also avoids the electrode breaking accident caused by the strong vibration of molten steel.
- Water-cooled electrode modification
The consumption caused by side oxidation of graphite electrode accounts for about 50% of the total consumption. The main function of electrode cooling device is to prevent the oxidation reaction of graphite electrode at high temperature. Water is sprayed to the surface of the electrode through the spray tube ring. When water drops along the surface of the electrode, the surface of the electrode is isolated from the air, reducing the contact area between the air and the surface of the electrode, thus preventing its oxidation reaction. At the same time, due to the continuous evaporation of water, the surface temperature of the electrode effectively decreases, and the temperature strip of the electrode oxidation reaction cannot be established, thus eliminating the side oxidation of the graphite electrode and reducing the electrode consumption.
