The electrode support arm is the key component of an electric furnace, which supports the electrode, conducts electrical energy from the transformer through the electrode to the furnace, and produces a strong arc current within the furnace material to raise the temperature of the weld pool. The electrode support arm is usually mounted on the brace, and its front end holds the electrode by the gripper to keep it in position at the electrode center circle during the lift process.
During the operation, a high-temperature arc with a large power output is formed between the extremes of electrodes and the weld pool, which can cause intense electromagnetic oscillation of the electrode support arm. Therefore, the electrode support arm should have great strength and low resistance value. In modern electric furnaces, the secondary bus on the furnace body is retrofitted from the former copper tube bus to the copper-steel conductive electrode arm and aluminum conductive arm. To manufacture the copper-steel conductive electrode arm of a 5-ton ultrahigh power (UHP) electric furnace, a copper plate is welded around the steel structure and a cooling water pipe with a rectangular cross-section is formed on its bottom surface to cool the heat generated when the high current flows through the copper plate.
So far, many studies have been published on the cooling systems in the furnace body and furnace ceiling, but no mention has been made on the cooling in the electrode support arm section. The reason lies in the fact that Joule heat generated in the conductive arm is too small and only recently has the bimetallic conductive arm been widely used. However, during the reducing operation of the electric furnace, the temperature of the furnace should be raised to the maximum, so the operation is carried out without ventilation. Therefore, the convective heat transfer by this flue gas must be considered because the gas ambient temperature around the electrode support arm increases to about 700K.
Ri Sim Hyok, a researcher at the Faculty of Metal Engineering, has analyzed the temperature distribution of the copper-steel conductive electrode arm of UHP electric furnace, determined the geometry of the cooling water pipeline to minimize the cooling water consumption, while keeping the temperature of the conductive copper plate within the acceptable range (50℃), and determined the consumption amount of cooling water.
He analyzed the current flow in the bimetallic conductive arm using Maxwell software and found that the current flows only into the copper plate. Then, he simulated the temperature distribution of the bimetallic conductive arm during the reducing stroke with ANSYS FLUENT. After that, he simulated the temperature changes of the conductive copper plate and the cooling water, and verified the results with the experimental data obtained in situ.
The results show that the cooling water flow rate of 1 to 1.5kg/s and the 6-stroke pipeline guarantee the minimum consumption of cooling water while keeping the temperature of the copper plate bus of the copper-steel conductive electrode arm within the acceptable range.
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