In order to test the application effect of the nitrogen protection device, the power frequency induction furnace is selected as the test equipment. The smelting furnace with horizontal structure can effectively control the tilting process of the converter and discharge slag without side. Combined with the closed chute with heating device and furnace cover, the molten copper in the furnace can be completely emptied in case of an accident, and W-type jet inductor is set. It has the advantages of easy disassembly, reasonable structure, good rigidity, reliable insulation and long service life. Adopting the holding furnace with box heating chamber and front chamber structure, cooperating with sealed furnace cover and selecting hydraulic or mechanical tilting furnace, the front chamber can be flexibly disassembled and replaced. The plug rod can be used to control the opening or closing of the casting port and adjust the flow rate. The maximum copper liquid can be discharged more than 10t at a time.
One is the sealing condition. When nitrogen filling replacement method is adopted, the sealing condition will directly affect the replacement effect of nitrogen on oxygen, and then determine the oxygen content in the furnace and the use effect of nitrogen protection device. In order to achieve the expected effect of nitrogen protection and reduce the requirement of sealing accuracy, the device uses the outer wall and inner wall to form a sealing system, forming a cavity between the inner and outer walls. By feeding nitrogen with a certain pressure from the air inlet hole above the cavity, the oxygen is pressed out from the upper part by the gas pressure during the downward movement of nitrogen, gradually filling the protective cover with nitrogen To achieve good sealing effect.
The other is the purity of nitrogen, which is usually inversely proportional to the oxygen content in the furnace. However, considering that the preparation of high purity nitrogen will increase the cost of equipment, and nitrogen with purity of 99.99% and 99.999% respectively has no obvious effect on the oxygen content of the slab, it is recommended to select nitrogen with purity of 99.99% as the protective gas, so as to play the role of gas protection and save the cost to the greatest extent.
The third is nitrogen flow rate, which is usually inversely proportional to the oxygen content in the cavity. Because the protective cover is located above the mold, nitrogen will accumulate on the surface of molten copper in the process of filling nitrogen into the cavity. With the increase of nitrogen content, the cooling capacity will also increase, which will easily lead to the formation of crystallization on the surface of molten copper, which will affect the casting effect and cause the slab surface cracking Crack phenomenon.
In the design of the test method, first fill nitrogen into the nitrogen protection device, keep it for 5min after the nitrogen pressure reaches 0.1pA, select the sealing cover to cover the mold, so that the nitrogen can protect the molten copper in the mold during the downward movement of the protective cover, and make the gas overflow from the reserved holes on both sides of the mold; repeat this process until the nitrogen pressure reaches 1.4pa The equipment can be operated to start the casting production of copper strip by keeping the inflation amount unchanged.