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SILICA RAMMING MASS |
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Lining is the imported part of induction furnace, Furnace performance is directly related to the lining performance. Well-stabilized lining results in smooth working of furnace, optimum output and better metallurgical control. The lining practice best suited to particular foundry will depend upon the furnace capacity and design, metal being melted and output etc. For successful and consistent lining practice monitoring the following parameters is essential.1.Use of proper grade of lining material. 2.Careful and systematic lining practice. 3.Consistency in working conditions. REQUIREMENTS OF A LINING
An imported aspects about refractory lining for satisfactory lining life are listed as.-Thermal characteristics it should withstand the stresses developed by thermal cycles in operation -chemically inert to metal being melted. |
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| TYPES OF RAMMING MASS | |
| 1.ACIDIC/SILICA RAMMING MASS | |
| 2.BASIC RAMMING MASS | |
| 3.NEUTRAL RAMMING MASS | |
| ACIDIC/SILICA RAMMING MASS | |
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The silica(SIO2) used as lining is acidic in nature.Silica (Silica ramming mass) is used in powdered condition.It is produced by crushing and grading of good quality Quartz and Quartzite having very high purity. The impurities present will produce, Unpredictable and more amount of liquid phase at high temperature thereby lowering chemical and mechanical resistance of lining. High purity silica yields more lining life. It is also results in considerable uniformity in physical properties. The compact lining results in greater strength and life. The compactness (packing density) depends upon granulometric composition of ramming mass. It should be such that it forms the least open space between particles. The typical granulometric composition of commercial silica ramming mass is given below, |
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| Size | PERCENTAGE |
| -4 mm to 1 mm | 33% |
| -1 mm to 0.20 mm | 30% |
| 0.20 mm to 0.06 mm | 17% |
| 0.06 mm & below | 20% |
| Particular attention should be paid towards the proportion of fines within a certain tolerance. It has adverse influence on the service behavior of lining if present in more amounts than required. Since the finest particles mainly take part in the sintering reaction. | |
| BINDING/SINTERING AGENT | |
| The binding agent is added so as the refractory lining of crucible, which is formed, with silica ramming mass, must sinter during heating up and develop strength before molten metal is charged. BORIC ACID is mixed as binder. The boric oxide reacts with silica particles to produce a low melting point glassy phase, which fills the interstitial holes between the quartz grains. The selection of correct amount of boric acid is very important for optimum life of lining. It depends upon | |
| -Temperature of molten metal bath. -Chemical composition of quartzite mass. -Thickness of crucible wall |
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| RAMMING PROCESS. | |
| MIXING OF THE MASS: -Work out the quantity of ramming mass required, the exact amount will depend upon the furnace ling -work out the quantity of boric acid required -preheat the mass in a tray of sheet to 120*C in batch of 50 kgs.so as to remove traces of moisture. -Transfer it to cooling trays and cool down to 50*C -Add exactly weighed quantity of boric acid by sieving through 0.20 screen. -Mix it through by hand. -Check the mixed batch for ensuring uniform mixing of boric acid. |
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| TEST: By hand picking a small amount of mass make a thick water slurry and dip PH paper in it. The presence of boric acid will report PH less than 7. Make such test by picking 3 samples from each batch from different location in tray (used distilled Water) | |
| COIL LINING | |
| -The water cooled copper coil is coated with refractory mortar and dried well before start lining -A thick asbestos sheet is laid in around, the coil lining. |
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| RAMMING THE CRUSIBLE | |
| RAMMING BY HAND -Using flat head tools for first two layers of 60-20 mm while subsequent layers are alternately rammed with spiked and flat head tools rams the furnace bottom. -The bottom is built about 10 mm above the required height and extra mass is scrapped uniformly. Check the level. -The metallic former duly cleaned from outside is than places perfectly concentric with the coils and held in position by wooden spacers. Keep a heavy weight in side the former to resist its coming up during further ramming. -The angular space between the asbestos sheet and former is rammed in 50-60 mm layers using spiked and flat head tools from the top. HINT:DO NOT USED BLUNT AND WORN TOOLS. It can result in poor composition. -Continue the ramming till 100 mm gap from the top. -Apply thin layer of sodium silicate solution over top of silica rammed crucible before topping mix ramming. For topping mix add dilute sodium silicate solution to the silica ramming mass. -From the spout by same topping mix. -Pneumatic rammers/electric vibrators can be used in large furnaces for crucible formation. |
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| SINTERING OF FURNACE CRUCIBLE | |
| INDUCTIVE SINTERING -The furnace is filled up to the coil upper edge with starting block carefully centered for mains frequency furnace while heavy scrapes for medium frequency furnace. -The power supply must be regulated through switching on the lowest transformer tap, keep switching the power ON and OFF at few minutes intervals so that temp. rise of 100*c hour is achieved for furnaces up to 6 tones capacity and 50*c /hour for big furnaces with thick lining. -This rise in temperature is monitored up to 800*C. -After 800*C the power is raised and with about 150*C/hour the heating is continued up to tha melting of sintering charge. -For measurement of temperature chromal/alumal thermocouples is used. -As soon as the furnace is filled with liquid metal the powder is increased in order to reach the sinter temperature. |
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| SILICA RAMMING MASS ( Products) | |
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1. Super snow white (with or without boric acid) 2. semi snow white (with or without boric acid) 3. general grade (with or without boric acid) 4. quartzite ramming mass 5. Calcined ramming mass 6. Coupla ramming mass 7. Rotary ramming mass 8. Ramming for channel furnace |
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