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                      A furnace is essentially a thermal enclosure and is employed to process raw materials at high temperatures both in solid state and liquid state. Several industries like iron and steel making, non ferrous metals production, glass making, manufacturing, ceramic processing, calcination in cement production etc. employ furnace. The principle objectives are a) To utilize heat efficiently so that losses are minimum, and b) To handle the different phases (solid, liquid or gaseous) moving at different velocities for different times and temperatures such that erosion and corrosion of the refractory are minimum. 

Types and Classification of Different Furnaces

Forging Furnaces

The forging furnace is used for preheating billets and ingots to attain a ‘forge’ temperature. The furnace temperature is maintained at around 1200 to 1250o C. Forging furnaces, use an open fireplace system and most of the heat is transmitted by radiation. The typical loading in a forging furnace is 5 to 6 tonnes with the furnace operating for 16 to 18 hours daily. The total operating cycle can be divided into (i) heat-up time (ii) soaking time and (iii) forging time. Specific fuel consumption depends upon the type of material and number of ‘reheats’ required.

ii) Re rolling Mill Furnace       



  • Batch type
  • A box type furnace is employed for batch type rerolling mill. The furnace is basically used for heating up scrap, small ingots and billets weighing 2 to 20 kg. for rerolling. The charging and discharging of the ‘material’ is done manually and the final product is in the form of rods, strips etc. The operating temperature is about 1200 oC. The total cycle time can be further categorized into heat-up time and rerolling time. During heat-up time the material gets heated upto the required temperature and is removed manually for rerolling. The average output from these furnaces varies from 10 to 15 tonnes / day and the specific fuel consumption varies from 180 to 280 kg. of coal / tonne of heated material.
  • Continuous Pusher Type:
  • The process flow and operating cycles of a continuous pusher type is the same as that of the batch furnace. The operating temperature is about 1250 oC. Generally, these furnaces operate 8 to 10 hours with an output of 20 to 25 tonnes per day. The material or stock recovers a part of the heat in flue gases as it moves down the length of the furnace. Heat absorption by the material in the furnace is slow, steady and uniform throughout the cross-section compared with batch type.

    • iii) Continuous Steel Reheating Furnaces
    • The main function of a reheating furnace is to raise the temperature of a piece of steel, typically to between 900°C and 1250o C, until it is plastic enough to be pressed or rolled to the desired section, size or shape, The furnace must also meet specific requirements and objectives in terms of stock heating rates for metallurgical and productivity reasons. In continuous reheating, the steel stock forms a continuous flow of material and is heated to the desired temperature as it travels through the furnace.


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