When the induction melting furnace using a quartz crucible is used to melt pig iron, the quartz crucible is subject to factors such as direct scouring of high-temperature metals and repeated heating and cooling. It is easier to generate cracks and the furnace needs to be rebuilt, which greatly increases the production cost and thus has been Since then, all factories have attached great importance to extending the service life of crucibles. The furnace sintering quality after the quartz crucible is built is the key to the service life of the quartz crucible. Oven for sintering the quartz crucible, commonly used prior art "sintering temperature" process, the high temperature sintering process characteristics of the ingredients is added to the molten iron in an oven heated to a high temperature stage 1450 after ℃, the temperature will continue to rise the molten iron 155 0 deg.] C and Insulate for 2 hours to make the crucible sinter quickly and fully. The "high temperature sintering" process oven curve is shown in Table 1. This process is more suitable for continuous operation of crucibles, and for crucibles with intermittent operation that have surplus production capacity, the application results have proved that the use effect is poor and cannot be well. start and stop frequently bring solve thermal shock cracking furnace, the crucible life is low, generally run less than 80 furnace will need to re-Zhulu table 1 "high temperature sintering" process ovens
The crucible is under-sintered during the oven, that is, when the oven is operated after the crucible is built, after adding the ingredient iron in the high-temperature stage of the oven and melting it, the temperature of the molten iron is increased to 1450 ℃, and the heating of the "furnace temperature to 1550 ℃ is not performed . And heat preservation 2 hours "high-temperature sintering step, but directly out of molten iron. Since the high temperature sintering step is not adopted, the ratio of scale quartz to cristobalite (1470 ℃ ) can be effectively reduced , the thickness of the sintered layer can be reduced , the thickness of the semi-sintered layer and the unsintered layer can be increased, and the frequent start-stop furnace zone can be effectively dispersed The stress and barrier to the leakage of molten iron extend the service life of the crucible. The curve of the crucible under-sintering process oven is as follows. Table 2 "Unsintered" oven process After the induction melting furnace lining is built, the thermocouple is buried in the furnace (without contacting the furnace lining) for temperature measurement, the furnace opening is covered with asbestos board, the furnace is started, and the low power is used. Continuous or intermittent power transmission to ensure that the temperature is raised according to the oven system. When the temperature of the furnace reaches about 115 0 ℃, load the clean and dry charge, that is, the batching iron, and use the high power to enter the charge according to the heating curve, and the charge is added. The amount should be able to ensure that the molten iron in the furnace is full to the furnace mouth to facilitate the sintering of the furnace mouth. When the molten iron in the furnace is completely melted, add 0. 05% (mass percentage) of broken glass to control the temperature of the molten iron in the furnace at 1. Hot metal is produced at around 450 ℃.
The problem of short service life due to frequent start and stop of crucibles that are operated intermittently and the crucibles are subject to rapid cooling and heat to produce thermal stress impact is well solved. For crucibles operating intermittently, the under-sintering oven process can extend the furnace life by more than 40 furnaces.