When a blast furnace is blown out while still containing pig iron and slag, the effect of the stoppage has on the furnace's subsequent blow-in and lighting depends on the length of time it is idled and the technical measures taken to influence the outcome. According to data from the Institute of Ferrous Metallurgy, the temperature in the working space of an idled blast furnace decreases at a rate of 50 deg C/day. This cooling is accompanied by gradual thickening and hardening of the soft and semi-solid materials in the furnace and the formation of a solid monolithic slag crust over the height of the furnace. The stoppage of a blast furnace for 1-2 days does not make it necessary to resort to additional measures in order to have the furnace resume normal operation. A method of idling a furnace for 3-4 days without blowing it out has been developed and successfully introduced for class-Ill overhauls. However, to idle a furnace for more than 4 days without blowing it out, extra steps must be taken to prevent complications after smelting is restarted.
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