What are the Reheating Furnaces ? | Refractory Industry | Iron and Steel | Industry Guru

09-Oct-2022

Reheating Furnaces are used for heating the intermediate products of steel like- ingots, blooms or billets at temperatures around 1000 - 12000C before rolling to give them different shapes of angles, channels, bars, slabs, rods & wires etc. The furnace is a chamber having inside refractory lining to conserve heat and generally includes a mechanism for transporting products continuously from one end to the other end. Heat for the furnace is provided by natural gas or fuel oil.

Reheat Furnace which is considered an accessory to the rolling mill is a critical factor in the quality of end-product. There are various types of reheating furnaces which can be differentiated on the bases of - (1) the method of heating, (2) method of charging the reheating furnace, (3) the movement of steel stock in the reheating furnace, and (4) the heat recovery methods.

Based on the method of heating, a reheating furnace can be Combustion Heating type or Electrical Heating type. The combustion heating type furnace can use solid, liquid, or gaseous fuel. Based on the method of charging, the reheating furnace can be classified as Batch type or Continuous type. In batch type reheating furnaces the charged material remains in a fixed position on the hearth until heated to rolling / forging temperature while in continuous type reheating furnaces the charged material moves in the reheating furnace and is heated to rolling temperature as it progresses in the furnace. Based on the movement of steel stock inside the furnace, continuous type reheating furnaces can be further classified as Pusher Furnace, Rotary Hearth Furnace, Walking Beam Furnace, Walking Hearth Furnace, and Roller Hearth Furnace.

Based on heat recovery method a reheating furnace can be either Regenerative type or Recuperative type. Regenerating type reheating furnace uses regenerative burners while Recuperative type reheating furnace uses recuperators for heat recovery from the exhaust gases.

(If you want to know in details about any of the above mentioned types of reheating furnaces then please let us know in the comment section below as we will bring separate post for the same).

In view of saving energy, requirement of Refractories with low thermal conductivity are required particularly for Door, Heaters, Flue-stack and further, for Hearths these criteria are corrosion, abrasion & spalling resistances with good strength. For these purposes, dense low-iron, high-alumina or chrome-magnesia bricks are best suited for Hearth. The side-wall and roof are lined with high-grog alumino-silicate bricks. Precast / Prefired (PCPF) blocks can be used for Burner-block, Seating Well Block, Well Block as well as for Furnace Bottom, made of low-iron high-alumina dense refractories having excellent spalling & abrasion resistances. The advantage of using PCPF blocks is that they can save time for both installation & for drying/preheating inducing more availability of the furnace. In the event of choosing Precast / Pre-fired (PCPF) blocks one has to take care of the design of these blocks which should be such that one person can handle them.

For more details refer to our post: Area wise Refractory specifications and lining procedure for reheating Furnaces