Why do new steelmaking electric arc furnaces need ovens?

The new furnace body is usually baked to sinter the furnace body and remove moisture. The basic electric arc furnace is composed of magnesia, dolomite, asphalt, tar and other materials. After the volatiles in the asphalt and tar are removed at high temperature, the remaining solid carbon becomes the skeleton of the furnace lining refractory material, which has a high resistance to high temperature. It combines with magnesia and dolomite to make the furnace lining have sufficient strength and refractoriness; at the same time, due to the removal of water, the quality of steel during smelting is guaranteed.

How to bake the new electric arc furnace?

Before the oven, lay a layer of broken electrode blocks or coke on the bottom of the furnace. The quantity is determined by the size of the furnace capacity. The electric furnace with a nominal capacity of 10~20t is generally placed 200~400kg. The waste electrode used in the oven is placed on the coke in a "T-shape" or "triangle" accurately and smoothly under the three-phase electrode.

The length of the waste electrode should be appropriate, and the two ends should not be placed directly on the furnace slope, so as to avoid burning the furnace slope during the oven. The diameter of the waste electrode should not be too thin, so as not to be blown in the middle of the oven. If there are not enough waste electrode blocks, large pieces of coke can also be used instead.

In order to make the tapping groove also bake well, do not block the tapping port during baking, and use wood and other materials to bake in the groove. The power supply system for baking varies with the lining material. When baking the asphalt furnace, high voltage and high current are required to quickly heat up and quickly pass through the softening temperature zone of asphalt and tar below 200 °C. If the temperature rises slowly, the asphalt-tar-magnesia lining will be in a softened state for a long time, and the collapse of the furnace wall will easily occur.

Brine furnace (carbon-free lining) oven must be heated slowly with low voltage and small current. If the temperature rises rapidly, the brine will be violently vaporized, which will cause the bottom of the furnace to crack and the furnace wall to crack.

During the drying process, it is necessary to arrange power outages at intervals, check the electrode position of the furnace, the sintering condition of the furnace lining, the equipment, and the water cooling system.

At present, many electric arc furnace steel mills also adopt the method of direct steelmaking without oven. According to the requirements of the smelted types of the electric arc furnace and the use of water-cooled furnace walls, the traditional furnace steelmaking method and the non-drying furnace direct steelmaking method can be used for the newly built electric arc furnace. However, if the direct steelmaking method without oven is adopted, it is still necessary to take corresponding measures according to the characteristics of the new furnace to complete the task of the oven.

Since the DC electric arc furnace has a bottom electrode, and most of it adopts a water-cooled furnace wall, it is generally not specially baked, but the direct steel-making baking technology without oven is used. The requirements are similar to those of an AC arc furnace, and the arc operation is the same as a conventional DC arc furnace. The direct steelmaking method without baking furnace is a method of directly charging steelmaking without pre-baking the new furnace before using the new asphalt magnesia lining, and using the high temperature during smelting to achieve the purpose of sintering the furnace lining. Because there is no pre-baking, it can save electricity, save coke, save time and increase steel output, and it has been widely used.

Direct steelmaking without baking, because the water is brought into the furnace when building the furnace, it decomposes into hydrogen and oxygen at high temperature and dissolves in the molten steel, which is easy to cause the ingot to rise or subcutaneous bubbles. Therefore, the direct steelmaking method without furnace requires a slow melting period to facilitate furnace bottom sintering, appropriately increase the decarburization amount in the oxidation period, and combine ore in batches with oxygen blowing for oxidation, so that a large amount of gas dissolved in molten steel can fully escape. The reduction period should not be too long to reduce the further suction of molten steel from the atmosphere.

The first furnace should smelt 35~60 steel, preferably 35 steel. When building the furnace, dry magnesia and solid asphalt powder should be used as fillers for dry building. The ingredients should be clean, dry, high-quality scrap steel of medium and small size, and the carbon content is more than 0.2% higher than the conventional one, so as to ensure that the decarburization amount during the oxygen flowering period is not less than 0.4%. Before charging, the furnace bottom should be properly added with more lime and smoothed (the DC electric arc furnace has furnace bottom electrodes, and lime is not allowed to be added to the furnace bottom, but can be added gradually after the molten pool is formed).

After the electrode is penetrated to the bottom, the current should be appropriately reduced to prevent the furnace bottom from being heated too violently and turning the furnace bottom. It is not advisable to blow oxygen to boost the melting process too early (the charge is melted by 80% to 90% or even without oxygen blowing). After the charge is melted, it can stay for a period of time (20~30min) to facilitate the escape of the lining gas, and it is best to change the slag. During the oxidation period, it is necessary to strengthen boiling and degassing, and there must be good uniform boiling, but large boiling must be avoided. Mineral addition should be carried out in small quantities and multiple batches (the amount of ore added should not be less than 3% to 5% of the material weight), the oxygen pressure should not be too large when blowing oxygen, and the insertion depth should not be too deep.

Before all the slag is pulled, the round cup sample (inserted with aluminum or added with ferrosilicon powder for deoxidation) should shrink well and not rise, otherwise it should be degassed again. The reduction period should be shortened as much as possible to reduce the suction of molten steel. It is best to use the return slag method or the quick white slag method. The tapping temperature should be controlled at the middle and lower limit, to prevent the high temperature and low temperature release of the steel. The first furnace does not block the tapping hole, and it should be opened frequently in the later stage of oxidation, so that the flame can escape and sinter this part of the furnace lining. The tapping slot should be baked with wood or gas as soon as the power is turned on.