Views: 0 Author: Site Editor Publish Time: 2022-07-22 Origin: Site
A tapping box protruding from the furnace shell is installed on the original tapping side to replace the original tapping groove. Refractory materials are built inside the tapping box, and a small molten pool is formed. It is connected with the large molten pool at the bottom of the original furnace and has a smooth transition. The tapping hole is opened vertically at the bottom of the small molten pool of the tapping box. The upper part of the tapping box is provided with a water-cooled cover plate with operating holes on it to close the small molten pool and clean and maintain the tapping port. The steel outlet is a double-layer structure, the outer layer is a square seat brick, the inner layer is a glazed brick, and the layers are filled with magnesia refractory materials to facilitate the replacement of the glazed bricks. The opening and closing of the tapping port can be completed by opening and closing the swinging cover. The lower part of the steel outlet is the tail brick. It is cooled with water. The cover plate and tail brick are made of graphite to prevent high temperature deformation and protect the furnace. Before charging, close the tapping plate, and fill the Mqo-sic2 mixed powder containing 10% Fea0. into the tapping to block the tapping. Determine a reasonable distance (eccentricity) from the center of the tapping hole to the center of the furnace and the size of the tapping hole to ensure that all molten steel and slag are discharged within 1~2min, and the maximum inclination angle of the furnace is not greater than 12-15°.
EBT electric furnace smelting has changed from steelmaking equipment that included melting, oxidation, reduction refining, temperature, composition control and quality control in the past to chemical steel equipment that only retains melting, heating and necessary refining functions (dephosphorization, decarburization). And transfer those process operations that only require lower power to the ladle refining furnace. The ladle refining furnace can completely provide various optimal refining conditions for the initial molten steel, and can strictly control the composition, temperature, inclusions, gas content, etc. of the molten steel to meet the increasingly strict requirements of users on the quality of steel. As far as possible, dephosphorization and even partial decarburization are carried out in advance to the melting period, while the oxidation refining and heating period after melting only carry out carbon control and are not suitable for ferroalloys that are easily oxidized and added in a large amount during the feeding period. Melting is particularly beneficial for shortening the smelting cycle, reducing consumption and improving productivity.
The EBT electric furnace adopts the operation of retaining steel and slag, and there is a ready-made molten pool at the beginning of melting, supplemented by enhanced oxygen blowing and bottom blowing stirring, which provides good conditions for the metallurgical reaction in advance. In terms of improving productivity and reducing consumption, electric furnaces are required to have the shortest melting time, fastest heating rate and least auxiliary time (such as repairing furnace, feeding, replacing electrodes, tapping, etc.), in order to achieve the best economic benefits.
The formation of crusts at the bottom of the electric arc furnace is a common problem in the production of high alloy steel, especially when a high percentage of FeCr is added to the furnace, and the tapping time is short. The crust layer at the bottom of the furnace is composed of unmelted scrap steel, unmelted ferrochromium and solid slag. The thickness of the crust can sometimes reach 1000mm, depending on the age of the lower furnace shell. The formation of crusts brings a series of process problems, such as reducing furnace capacity, reducing tapping weight hit rate, reducing steel output, and reducing production efficiency.
It has been reported that the use of electromagnetic stirring (EMS) at the bottom of the furnace can reduce the formation of crusts in the stainless steel production of electric furnace long-groove tapping. The electromagnetic stirring coil installed under the bottom of the furnace has a stirring effect on the whole molten pool, which accelerates the melting of scrap steel and uniformizes the temperature of the molten pool, which is beneficial to remove the crusting phenomenon.
The electromagnetic stirrer is placed below the furnace bottom, which is made of non-magnetic (austenitic stainless steel) steel plate. Low-frequency currents through the stirrer windings generate a moving magnetic field that penetrates the furnace floor and creates a force in the molten steel. Since the magnetic field penetrates the entire depth of the molten pool, the molten steel moves in the same direction in the lower furnace shell, and this molten steel movement is through the entire diameter of the electric furnace, and is the molten steel movement of the full depth of the molten pool. After reaching the furnace wall, the molten steel must flow back along the furnace wall. When the magnetic field is reversed, the molten steel flows in the opposite direction. Since the stirrer is arranged over almost the entire diameter of the lower furnace shell, a good stirring force is obtained in the entire molten pool.
Compared with furnace bottom gas-permeable core stirring, electromagnetic stirring produces mixed agitation throughout the molten pool. This effect accelerates the homogenization of the temperature and chemical composition of the molten steel. It should be pointed out that the electromagnetic force acts not only in the horizontal direction, but also in the vertical direction, which makes the mixing and stirring effect of the whole molten pool more effective. Another advantage of electromagnetic stirring EMS is that there is no physical contact with the molten steel, so maintenance needs are very low.