Types Of Refractories
In nature there is no such refractory which meets all these properties. From among the available refractories, three types meet the important properties for specific applications. These refractories are commonly used to form induction furnace linings. These are :
Silica (Acidic Lining):
The silica lining (Si02) is acidic in nature. It is produced by crushing and grading of a good quality of quartzite having very high purity (silica content above 99%). It is used in powdered condition. Correct grading is important for uniform and hard ramming. Typical size grading of silica ramming mass is given in table-2. Boric acid (or boric oxide) is the most commonly used binder. Pure silica has a melting point of 17230 C. the rammed lining is sufficiently refractory for use up to 1550 – 16500 C. Between 6000 C and 16000 C, silica expands very little, and is superior to both alumina and magnesia to resist thermal shock. Being available abundantly in nature, cost is very low in comparison to alumina and magnesia.