Temperature control of medium frequency furnace smelting gray iron



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Temperature control of smelting gray iron in medium frequency furnace

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Intermediate frequency furnace smelting gray iron temperature control!

The melting temperature of gray iron should not be too high, generally controlled below 1400 ℃. If the melting temperature is too high, the burning loss or reduction of the alloy will affect the composition adjustment at the later stage of melting. After the furnace temperature of the charge is 1460 ℃, the samples are taken for quick inspection, and then the slag is removed, and the remaining charge such as ferroalloy is added. The slagging temperature has a great influence on the quality of molten iron, which is closely related to the stable chemical composition and inoculation effect, and directly affects the control of the tapping temperature. If the slagging temperature is too high, it will aggravate the burning loss of hot metal graphite nucleus and the reduction and high silicon (in acid furnace lining), and produce carbon emission effect, which will affect the crystallization of stable system; if the slagging temperature is too low, the molten iron will be exposed for a long time, and C and Si will be burnt out It is necessary to adjust the composition again, prolong the smelting time, overheat the hot metal and increase the undercooling degree, which is easy to make the composition out of control and destroy the normal crystallization.

The temperature control of the furnace must ensure the temperature of inoculation and pouring. Generally, according to the actual situation, the outlet temperature should be controlled at 1460 ~ 1500 ℃, and the superheat temperature can be controlled at 1510 ~ 1530 ℃, and it should be kept for 5 ~ 8min. In the range of 1500-1550 ℃, increasing the superheating temperature and prolonging the standing time at high temperature will refine the graphite and matrix structure, improve the strength of cast iron, and be conducive to inoculation treatment, and eliminate the adverse effects of blowholes, inclusion defects and burden heredity on the microstructure and properties of cast iron. If the standing temperature is too low and the time is too short, the carburizing agent can not be completely dissolved into the molten iron, and the impurities in the molten iron will not float up and be removed by the slag. However, if the superheating temperature is too high or the high temperature standing time is too long, the graphite morphology will be deteriorated, the matrix will be coarsened, the undercooling degree will be increased, and the white cast tendency will be increased, the existing heterogeneous core in molten iron will be disappeared, the properties of cast iron will be seriously oxidized, and the control of discharge temperature will be affected. If the discharge temperature is too high, even if the content of C and Si is moderate, the white hole depth of pouring triangle block will be too large or there will be pockmarks in the center. If this happens, it is necessary to reduce the medium frequency power and add pig iron to the furnace to cool down and increase carbon.

The pouring temperature should not be too high, otherwise the casting will produce serious sand sticking defects, and some of them are even difficult to clean and scrap. Moreover, high pouring temperature and large undercooling are not conducive to the formation of A-type graphite. If the pouring temperature is too low, it is not conducive to degassing, but also causes the casting hard, cold shut, unclear contour and other problems. The results show that the liquid shrinkage of molten iron is small at a lower pouring temperature, which is helpful to reduce shrinkage cavity and obtain dense casting. In general, there are different pouring temperature between 1380 ℃ and 1450 ℃. For heavy castings, it is necessary to ensure "high temperature out of furnace, low temperature quick casting". In order to shorten the waiting time for the temperature of molten iron to drop to the pouring temperature and prevent inoculation and recession, the method of pouring and standing can be used to make the hot metal cool down quickly, so as to prevent shrinkage porosity and improve production efficiency.

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