Electric arc furnace steelmaking is a steelmaking method with electric energy as the heat source. It is a steelmaking method that heats and melts metal charge and slag by the electric arc generated by the discharge between the EAF electrode arm and charge. Water leakage between the conductive cross arm and the electrode clamp seriously restricts the development of production.
1. Hazards of Water Leakage at the Junction of EAF Electrode Arm and Clamp Head
1.1 It Is Easy to Explode in Case of Serious Water Leakage
During steel-making, molten steel, molten iron, steel slag and slag at the bottom of the steel-making furnace are high-temperature melts. When the water leakage is serious, if the shaking furnace or oxygen supply operation is carried out, the sudden fierce reaction between water and molten iron or molten steel will cause an explosion or blowout, resulting in man-machine accidents.
1.2 Water Leakage Has Adverse Effects on Ingot Quality
The initial content of hydrogen in molten steel must be controlled. The hydrogen content in molten steel mainly depends on the partial pressure of water vapor in furnace gas, and hydrogen is very harmful to steel. In general, the influence of hydrogen on ingots is caused by hydrogen embrittlement and a large number of fine cracks - white spots - in the steel.
The solubility of oxygen in steel is very low, and almost all of it exists in steel in the form of oxide inclusions, such as FeO, Al2O3, etc., which destroys the continuity of the steel matrix and often becomes the starting point of cracks under static or dynamic loads.
1.3 Water Leakage Maintenance Is Difficult
If there is water leakage between the clamp head and the end face of the boom when the furnace is shut down, the temperature in the furnace is room temperature at this time, so it does not need to be cooled. Remove the bolts, remove the clamp head, polish the contact conductive surface to be flat, replace the seal, and then install the clamp head. It takes three hours to repair one (a total of three), but most of the time, there is serious water leakage when the furnace is opened for steelmaking, so it is urgent to deal with the clamp head water leakage. At this time, the furnace temperature is about 1500 ° and the upper temperature of the furnace cover is about 1000 °. Before treatment, the furnace cover can only be turned out and turned back after the furnace temperature is cooled for about two hours because at this time, the three-electrode holes are facing the molten steel below. The maintenance personnel need to block the three electrode holes with colored steel plate first, and then spend more than three hours under a high temperature of more than 200 degrees. It takes more than three hours to remove the bolts - Polish the end face of the card head - upper seal - Installation - water test. The whole process must be time-consuming because the molten steel will harden in the furnace and need to be reheated and melted if the treatment is not timely, The maintenance time is tight, the maintenance time is long, and the maintenance is difficult, and the maintenance temperature is high. Various reasons are constantly overdrawing the physical fitness of maintenance personnel.
1.4 Water Leakage Shortens the Service Life of the Equipment
The small amount of water leakage is quickly vaporized and extracted with the flue gas, which has little impact on the small furnace cover. However, when the water leakage is serious, the whole electric furnace stops running and continues to be used after the water leakage treatment is completed. At this time, the working face of the small furnace cover is extremely cold and hot, which will greatly reduce the service life of the small furnace cover.
2. Why Is There Water Leakage between the Conductive Clamp Head and the End Face of the Boom
2.1 The electrode clamp head and the conductive cross arm are connected by four bolts, so that the two conductive contact surfaces are firmly connected. During steel-making, a large current flows through the EAF electrode arm and the electrode clamp head to the carbon rod electrode connected with the clamp head, and arcing steel-making is carried out. At the initial stage of construction, it is well used. Later, there is water leakage on the connecting surface between the clamp head and the EAF electrode arm. After disassembling the clamp head, it is found that the bolt near the cooling water inlet has been broken, and the nearby contact surface has arc ablation, There are traces of melting on the bolt rod. Because the bolt rod is not exposed to the flame rising from steelmaking, it is inferred that it is burned by a large current. On the one hand, the cause of arc ablation on the contact surface is that the two bonding surfaces are not closely connected, and poor contact leads to ignition and discharge. At the same time, large current flows through the bonding bolt, causing the bolt to burn due to large current. On the other hand, the bolt fracture leads to the loose connection of the two bonding surfaces, the circulating water seal does not work, and there is no compression, resulting in water leakage from the gap.
2.2 Electric arc furnace steelmaking relies on the discharge between the electrode and the charge. Under the direct action of the generated arc radiation and arc, the metal charge and slag are heated and melted (the temperature of the arc zone is above 4000 ° C). Most of the flue gas and flame generated by scrap melting overflow from the gap between the electrode and the electrode hole. First of all, due to high-temperature baking and thermal radiation, the temperature at the joint of the electrode clamp head and the front end of the conductive cross arm is as high as 900 ° ~ 1300 °. Because the electrode clamp head is made of red copper and has good thermal conductivity, the four O-rings between the two produce plastic deformation under high-temperature baking, so that the cooling water path at the end of the clamp head and the conductive cross arm is not tightly sealed and leaks. Secondly, due to the arc ablation on the contact surface, the arc generated in the ablation process will instantly scorch the O-ring clamped between the contact surfaces, making the O-ring lose its sealing effect and leading to water leakage.
3. Diagram of the Transformation Process
In the early stage, the problem of water leakage between the EAF electrode arm and the electrode chuck was solved by deepening the original sealing groove on the chuck, machining a sealing groove outside the original sealing groove of the electrode chuck, or changing the sealing material, but the effect was not ideal. Finally, it was decided to completely remove the seal. Therefore, after research, it was decided to cancel the four through holes for water supply and return between the conductive cross arm and the electrode clamp head, and the original holes were repaired and welded. Then the holes are opened from the front side of the conductive cross arm and the side of the conductive card head, and the water circulation is realized through the external pipeline, which cancels the original circulation through the internal water hole, and avoids damage and water leakage caused by the high-temperature burning caused by the sealing failure to withstand high temperature and ignition. Through half a year's statistics, it is found that the effect is excellent; Finally, the transformation plan was finalized, because the four water supply and return holes at the front end of the conductive cross arm had been blocked by repair welding last time. By redesigning and entrusting the manufacturing and processing of the electrode clamp head, the water supply and return pipeline of the conductive clamp head were changed to the upper part of the electrode clamp head. On the one hand, the water supply and return pipeline was located on the upper part, which could be effectively away from high-temperature baking, making it easier to repair and replace.
4. Application Effect after Transformation
1) It avoids equipment damage and casualties caused by the fierce reactions between water and molten steel.
2) The time for dealing with a leaking chuck is shortened from 5 hours to 0.5 ~ 1 hour.
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