Permanent lining or back up lining.
The permanent lining is exposed to chemical corrosion (resulting from the penetration of steel and slag), mechanical wear, thermal stress (due to thermal cycling). To tackle those challenges, the permanent lining is designed to withstand such demands to allow for the optimal thermal profile to reduce heat loss, strong durability for longer life. Permanent Lining can be installed by vibration or by free-flowing techniques.
All the activities connected to the tundish back up lining such as fresh tundish back up lining or lining after removal of old lining or repair of lining is practiced in the following manner:
1. Tundish cleaning for leftover debris (manually).
2. Fixing of insulation boards after anchor position marking (200mm*200mm or 300*250 mm).
3. Welding the anchor on the sidewall of the tundish shell and using plastic caps on the anchor heads. In tundish bottom, anchor welding is not required.
4. Coating of the anchor with bituminous paints.
5. At first, tundish bottom casting is done and then sidewall casting is undertaken. Before casting, appropriate size of forma, as per the drawing of the tundish, will be placed at indicated position for well-block fixing.
6. 60% to 70% alumina base low cement castables are mixed with 5% to 6 % water into the pan mixer for 15 to 20 minutes. The mixer machine has 1.5 MT to 2 MT capacity. After properly mixing, and attaining proper consistency of castables, these are applied on the tundish bottom by manual application or by using a conveyor channel and a vibrator for enhancing flow property of castable. The use of vibrator also improves flexibility, increase compactness, releases internal stress, etc. When we achieve 160 mm to 180 mm of bottom thickness, the forma is lifted by overhead crane for placement into the tundish. The forma is basically fixed for casting of the side walls. After completion of the casting of sidewall, forma is being removed by overhead crane. The recommended wall thickness is 140 mm to 150 mm.
Preheating of back up lining
Drying of the lining commences after 24 hrs(minimum) of completion of wet curing. The drying and heat up schedules vary depending on the thickness of the lining and the mass used. The tentative heat up schedule for the low cement castable which has a thickness less than 300 mm will be:
1. Slow heating from room temperature to up to 100 deg C temperature for 2 hrs.
2. Holding for 6 hrs at 100 deg C temperatures.
3. Then increasing the temperature at the rate of 25 deg C / hr upto 300 deg C temperatures.
4. Holding for 12 hrs at 300 deg C temperatures.
5. Then increasing the temperature at the rate of 25-30 deg C / hr up to 600 deg C temperatures.
6. Holding for 4 hrs at 600 deg C temperatures.
7. Then increasing the temperature at the rate of 25 -30 deg C / hr up to 800 deg C temperatures.
8. Holding for 4 hrs minimum at 800 deg C temperatures.
9. Cooling up to room temperature for taking preparation.
Back up cleaning, patching and launder checking
1. After newly backup lining or after deskulling, tundish is taken for further preparation in the tundish preparation stand.
2. Ensure the temperature of the working lining temperature is below 100 oC by using a temperature gun.
3. Placing a ladder for getting into tundish with recommended PPE.
4. Cleaning of scales and residual spray mass, bricks, slag, etc.
5. Cleaning of tundish is done using crowbar and shovel.
6. Dropping the debris through tundish well hole into a bin to maintain the cleanliness of the floor.
7. Checking for eroded wall and open cracks on the back up lining of the tundish, if noticed patching is to be done with patching mass (containing approx. 60% alumina). Patching mass is mixed with 4-5 % water and applied on the worn areas. Checking the condition of the impact pad for any damage and is to be changed if required.
8. After patching complete drying is done by pre-heater. Preheating is done for 45 minutes to 2 hours depending on the amount of patching that is being done.
9. Cleaning of slag or metal jams on the launder area is done with the help of crowbar and shovel and finally checking the height of the launder with measurement tape.
Tundish well block fixing/ bricks lining / turbo inhibitor fixing.
1. Cleaning the tundish well block area with a wire brush and placing the well block gently and ensuring centering by lowering it down slowly.
2. Checking the horizontality of well block by using sprit level gauge.
3. Mixing the ramming mass with 2% water and ramming around tundish well block manually by iron rammer rod.
4. Split bricks (300*115*30 mm) is fixed by using mortars on the sidewall of the pouring area. Cleaning the turbulence inhibitor box placement area and leveling is done by bricks and dry spray powder.
5. Inserting the turbo handling tackle inside the turbulence inhibitor box for lifting with a crane.
6. Placing the turbulence inhibitor box inside the tundish at its predefined place gently. Then centering of the turbulence inhibitor box is done with the help of crowbar and measuring tape.
7. Checking the horizontality of turbulence inhibitor by sprit level.
8. The turbulence inhibitor box is locked by using patching mass.
9. Tundish is now ready for drying after bricks lining, well-block ramming, turbulence inhibitor box fixing and is to be placed on to the dryer for heating for about 45 minutes in low flame.
© Metal world insight
