Refractory lining for high temperature furnaces

Furnaces are used for heating steel within the temperature range  to  for heat treatment and deformation processing. Many different types of furnaces are used namely soaking pits (batch type) and continuous furnaces. Fireclay and high alumina refractories are used. Most of the continuous furnaces are lined with fireclay bricks. Plastic chrome ore ramming mixture and hard burnt chrome magnesite bricks are used to line the hearth to provide resistance to scale.

Emerging trends

Refractory has undergone many changes to meet the diversified requirements of the industry particularly steel industry. The main objective is to increase the lining life at reduced cost by developing

• High quality refractory for critical applications in steel making at e.g. slag line, impact area of molten steel stream, bottom tuyere  refractory  in hybrid blowing, immersion   nozzles in continuous casting etc. In this connection mention may be made of some   refractory like MgO-C,  Al₂O₃ – Si C – C, MgO– Ca O – C, Al,Mg and Al-Si alloy   stabilized  MgO – C brick, zircon based refractory, and Al₂O₃  – C
  
  
• Repairing methods like slag splashing, slag coating, hot patching, gunning (flame  gunning involves melting and spraying on hot surface).
  
  
• Monolithic refractory

Monolithic refractory

Monolithic linings are a relatively recent development and consist of unshaped refractory products. These are materials which are installed in some form of suspension that ultimately hardens to form a solid mass. There are two basic types of monolithic lining, namely castable refractory and plastic refractory

Castable refractory consists of mixtures of coarse and fine refractory grains together with a bonding agent which is normally based on high alumina cement. Installation of the refractory is important. Due to relatively poor strength, durability of monolithic lining depends on the design and installation of the anchors.

Monolithic linings are installed by casting the refractory in a mould or by spraying the furnace shell. Largest problem with use of monolithic refractories are:

• Long drying time
• Steam explosion.