Refractory Bricks, Mortar and Castable for Reheating Furnace Lining

17-Jun-2023

Reheating Furnaces serve the purpose of heating various intermediate products of Steel like- ingots, blooms or billets before rolling to give them different shapes of angles, channels, bars, slabs, rods & wires etc 

Read: What are Reheating Furnaces Area wise specifications of Refractory Bricks and Castables or Blocks which can be used for lining of reheating furnaces and the quality of Refractory Mortar which can be used for laying the bricks are given hereunder -

Reheating Furnace Hearth

1. Dense high alumina bricks with low iron content. Alumina (Al₂O₃) 88-90%, Iron (Fe₂O₃) 1.8% (max), Bulk Density (BD) 3-3.2 gm/cc, Apparent Porosity (AP) 16-18%, CCS(kg/cm²) 800 (min), RUL(ta^OC) around 1550-1600, PLC at 1600^OC/2hrs (+/-) 0.2% (max).

2. Basic Magnesia, Mag-chrome bricks. MgO around 55-60%, Chrome (Cr₂O₃) around 12-15%, Silica (SiO₂) 8% (max), AP 18-20%, CCS (kg/cm²) around 450-500, RUL (ta^OC) 1600 (min), PLC at 1600^OC/2hrs (+/-) 0.5% (max).

Furnace Roof

Alumina (Al₂O₃) around 70%, Iron (Fe₂O₃) around 2.5-2.8%, BD 2.6-2.7 gm/cc, AP 21-23%, CCS (kg/cm²) 500 (min), RUL (ta^OC) around 1450-1500, PLC at 1500^OC/2hrs (+/-) 2.5% (max).

Furnace Side-Wall and for General purpose

1. Low porosity dense bricks. Alumina (Al₂O₃) 45%, Iron (Fe₂O₃) 1.6-1.8%, BD around 2.2 gm/cc, AP around 16%, CCS (kg/cm²) around 500, RUL (ta^OC) 1500 (min).
2. Alumina (Al₂O₃) 40%, Iron (Fe₂O₃) 2.0-2.2%, BD 2.1 gm/cc (min), AP 22% (max), CCS (kg/cm²) around 350, RUL (ta^OC) 1400 (min).

Furnace Bottom, Blocks (Burner Block, Well Block, Seating Block, Seating Well Block) and Castables

1. Medium purity Low Cement Castable (LCC). Alumina (Al₂O₃) around 90%, Iron (Fe₂O₃) 1.0-1.5%, BD 2.7-2.9 gm/cc, PCE 37 Orton (min), CCS (kg/cm²) at 110^OC/24hrs 600 (min), at 1500^OC/3hrs 550 (min), PLC at 1500^OC/2hrs (+/-) 1.0% (max).
2. Medium purity Castable conventional type. Alumina (Al₂O₃) around 60%, Iron (Fe₂O₃) 1.8% (max), BD 2.1 gm/cc (min), PCE 36 Orton (min), CCS (kg/cm²) at 110^OC/24hrs 350 (min), at 1500^OC/3hrs 450 (min), PLC at 1500^OC/3hrs (+/-) 1.5% (max).

Furnace Door, Flue Stack, Heaters

Insulating Castables. Iron 1% (max), BD 1.0-1.2 gm/cc, CCS (kg/cm²) at 110^OC/24hrs around 12-15.

Mortars

Have to be compatible with the laying brick quality (chemical spec).

All the data given above are tentative and should not be considered as ‘Typical Specification Data’. 

Methods of installation (Read: Refractory Installation Procedure and Heating Schedule to be followed after starting a Furnace) may be provided by the refractory supplier.

Refractory Installation Procedure and Heating Schedule to be followed after starting an Induction Furnace | Furnace Operation

Installation of refractories in any furnace is a tricky process and after the lining is done the most important thing is the heating schedule. That means how the furnace after repairing or with new refractory lining should be started, what should be the rate of heating (rising temperature) and holding time at any particular temperature. You cannot start the furnace by raising its temperature to peak at one go, as otherwise the refractories will be damaged or even the refractory lining may fall apart. The furnace starting heating schedule depends on various aspects including, thermal conductivity of the refractories used.

Here is a step-by-step guide for installation of Refractories (Ramming Masses, etc.) in Induction Furnace also the heating schedule that should be followed after starting the furnace:

 Read: 

• Refractories with their Specifications for Lining for different types of Induction Furnaces
• Refractory Lining Installation of Pipes and Chutes in a Furnace

1. Scrub all loose materials and clean the furnace.

2. Before using heat the refractory material (Ramming mass) at about 100^OC to make it free from moisture. Spread the material at the furnace bottom to about 50 - 60 mm thick layer at each time. Then ram the layer uniformly using a suitable rammer. The material has to be rammed layer by layer to get maximum compaction. Before ramming, little bit poking with a rod help to drive away the air-pockets trapped within the loose refractory material spread.

3. Place the steel former on the rammed bottom. Then fix the steel iron block at the center of the steel former to get uniform thickness throughout the furnace wall.

4. For ramming the upper portion of the side-wall just above the induction coil, mix the dry refractory material with 1-1.5% Sodium Silicate solution and 3-4% water.

5. Best results can be achieved by following the heating schedule for the furnace as mentioned hereunder -

Furnace Heating Schedule | Furnace Operation

Furnace Temperature	Rate of Heating with Holding Time
Ambient temp to 100OC	@ 30OC / hr.
Hold at 100OC.	4-6 hr depending upon the lining thickness.
100O - 800OC.	@ 50OC / hr.
Hold at 800OC.	2 - 3 hr.
800O - 1400OC.	@ 100OC / hr.
Hold at 1400OC.	4 - 6 hr.
1400OC to furnace operating temperature.	@ 100OC / hr.

Related Article

• Induction Furnaces | Channel Type and Coreless Induction Furnaces - Design, Advantages and Disadvantages