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 100OC 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 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. |