Application of the hottest water-cooled furnace co

Application of water-cooled furnace cover core in 5T electric arc furnace

Abstract: This paper briefly introduces the main problems existing in the production of traditional electric arc furnace cover, summarizes the experience that the displacement measurement accuracy must be improved to meet the requirements of users in the application and improvement of local water-cooled furnace cover in 5T electric arc furnace, and explains the obvious effect achieved by the application of this technology

our factory is one of the designated professional production plants of high manganese steel frog castings, with an annual output of more than 5000 tons. A 5T electric arc furnace is used for one shift production, with a total of about 800 furnaces of steel making throughout the year. Due to its location in the northeast and limited by climatic conditions, the production of all castings must usually be completed from March to November every year, which requires that the furnace shall not be shut down within the effective working hours. One of the conditions to ensure the normal operation of the electric furnace is to keep the furnace lining in good condition. Furnace cover is an important part of furnace lining, and its working conditions are very bad. Ensuring the normal working state of furnace cover is one of the keys to ensure the normal operation of electric furnace. Therefore, we have carried out continuous tests on the application and improvement of the furnace cover, with the focus on the application of water-cooled furnace cover core, and found out more successful experience, and achieved good results in production practice

I. application status before improvement

the furnace cover is in a high temperature state for a long time in the smelting process, especially in the reduction period. Due to the reflection of slag, the temperature of the furnace cover can reach 1800 ℃. The furnace cover is often subjected to rapid cooling and heating. After tapping, the temperature of the furnace cover drops sharply below 1000 ℃. Sometimes, the waiting and loading time is longer, and the temperature drops more, which is easy to cause cracking and spalling of the furnace cover. In addition, the furnace cover is also eroded and washed by high-temperature furnace gas, slag and smoke during the smelting process. In addition, the lifting and lowering of the furnace cover and the tilting of the furnace, as well as the mechanical vibration during the boiling of the molten pool, are easy to cause the failure of the furnace cover, reduce its service life, and affect the normal operation of the electric furnace

in order to prolong the service life of the furnace cover, we have taken measures such as improving the refractory used for building the furnace cover, improving the masonry quality, reducing the gap between bricks, and improving the camber of the furnace cover (i.e. increasing the distance from the center of the furnace cover to the molten pool), but the effect is not too great. Problems such as falling bricks of the furnace cover and frequent replacement of the furnace cover still occur. The slag forming operation will be seriously affected after the furnace cover brick falls into the molten pool; Replacing the furnace cover not only increases the heating loss, but also reduces the production efficiency and increases the maintenance cost. According to statistics, before the improvement, the average annual shutdown time was about 45h, affecting 15 steelmaking furnaces, resulting in an annual economic loss of more than 300000 yuan. However, it is more difficult to estimate the further harm to the molten steel smelting quality due to the slag formation caused by the falling bricks of the furnace cover

II. Preliminary improvement

1 Application attempt of local water-cooled furnace cover technology

in the absence of better refractory materials and measures, how to make 400000 change fatigue tests according to the sampling of parts in each furnace batch of materials in production, improve the service life and production efficiency of furnace cover, reduce the consumption of refractory materials and power consumption, and improve the quality of molten steel has become an urgent problem to be solved by the factory. According to the actual production situation, we boldly tried the local water-cooled furnace cover technology, that is, in addition to the water-cooled furnace cover ring, a water-cooled furnace cover core is set in the center of the furnace cover, and three electrode holes are set in the middle to make the three electrodes rise and fall in it. The furnace cover core and the furnace cover ring are still built with high aluminum refractory products. Compared with the traditional refractory masonry, the service life of the furnace cover is improved, but the effect is not particularly obvious

2. Existing problems and cause analysis

after the initial improved water-cooled furnace cover was put into use for a period of time, we found that water leakage occurred several times a month, and deformation occurred, resulting in furnace shutdown for repair welding or replacement (severe), which still affected production to a certain extent. In particular, once the cooling water enters the molten pool, it will increase the gas content in the steel, and the gas in the casting will destroy the continuity of metal structure, which will directly affect the mechanical properties and service life of high manganese steel frog products. Therefore, further improvement must be made on this basis

after repeated observation and research, the author found that the main reasons for water leakage and deformation are as follows:

(1) the cooling mode of the furnace cover core is unreasonable. Although the furnace cover core is divided into three cooling areas according to the position of the electrode hole, the three areas are connected in series by rigid or soft connection to form a one in one out cooling mode. On the one hand, the cooling effect is not ideal, which is easy to deform the furnace cover; On the other hand, the joints and pipelines are entangled in the high-temperature area near the electrode, which is prone to ignition, cracking and even water leakage, as shown in Figure 1

(2) the welding quality is poor, the weld has defects such as bubbles, inclusions, incomplete penetration, etc., and the pressure is too small (0.7MPa), the pressure holding time is short (5min), and sometimes there is a hidden danger of leakage without hydrostatic test

(3) when the furnace cover is built, the parallelism between the furnace cover core and the ring mouth of the water-cooled furnace cover and the electrode and the hole of the furnace cover core is poor, and the electrode contacts with the water-cooled furnace cover core during the descending process, causing water leakage

(4) the cover core of the water-cooled furnace is unclean, with more dust and iron oxide scale (powder), which not only affects the heat dissipation, but also easily causes ignition and water leakage

(5) the thickness of the steel plate for making the furnace cover core is 10mm, and the rigidity and strength are insufficient, resulting in deformation

III. improvement measures

1 Improve the cooling water circulation mode

in view of the disadvantages of the original cooling water one in one out circulation mode, each cooling area is changed into an independent cooling circulation system, that is, the highest temperature is set as the cooling water inlet, which is discharged separately after circulating in the area for a week. The improved cooling method prevents the deformation of the furnace cover, and the joint is far away from the conductive transverse, which is widely used in the high-temperature area of the arms and electrodes of parts such as automobiles, electrical appliances, sporting goods, etc., avoiding the occurrence of ignition and water leakage. This method has two more inlet pipes and two more outlet pipes than the original structure. See Figure 2 for details

2. Supporting measures

(1) weld the furnace cover core with 14mm thick boiler steel plate, construct in strict accordance with the technical requirements of the drawing, strengthen the welding quality and follow-up inspection to ensure that the welding quality meets the standard

(2) before laying the furnace cover, the water-cooled furnace cover core shall be subject to hydraulic test strictly, with pressure ≥ 1MPa and time ≥ 60min

(3) use a level gauge to calibrate the mold used to build the furnace cover to ensure the parallelism between the water-cooled furnace cover core and the water-cooled ring mouth of the furnace cover

(4) adjust the electrode holder cross arm and collet to ensure that the electrode rises and falls vertically

(5) when loading, the upper part must be loaded with some small materials in order to pass through the well, so that the arc can be buried in the material as soon as possible, so as to avoid local overheating and damage of the furnace cover caused by the arc light

(6) regularly purge the dust and iron oxide scale (powder) on the furnace cover

(7) remove the sundries in the circulating water tank in time, keep the water clean, and add a filter at the circulating water inlet. 1. The direction of the friction of the main part of the hydraulic material testing machine of Jinan experimental machine factory on the indication is to produce positive and negative filtration

(8) limit the use times of the furnace cover core and replace it regularly, that is, replace it every 280 heats

IV. application effect

through the installation and use of water-cooled furnace cover core on 5T electric arc furnace, and through continuous improvement and improvement, good application effect has been achieved, which has played an important role in the production of high manganese steel frog castings and brought good economic benefits to the enterprise

(1) the times of furnace shutdown, maintenance and replacement caused by various faults of the original furnace cover are greatly reduced. 15 more furnaces of steel can be made every year, creating more than 300000 yuan in benefits, and creating better conditions for expanding production

(2) the maintenance cost of the equipment is significantly reduced, more than 30 tons of furnace cover refractory bricks are saved every year, and the labor intensity of workers is greatly reduced

(3) long arc operation can be adopted. The smelting time of each heat of steel can be shortened by 35min, and the electricity of each heat can be saved by 200kW · h and 160000 kW · h per year

(4) because there is almost no water leakage, the external gas in the steel is greatly reduced, and various slags can be easily produced in the operation to meet the process requirements, effectively improving the product quality. (end)