Cement Manufacturers Association (CMA)

37 whereas basic refractories can be best used in alkaline environment. Actually, for various reasons, these rules are often violated. Classification Based on Method of Manufacture The refractories can be manufactured in either of the following methods: 1. Dry Press Process 2. Fused Cast 3. Hand Molded 4. Formed (Normal, Fired or chemical bonded) 5. Unformed (Monolithic – Plastics, Ramming mass, Gunning, Castable, Spraying Classification Based on Physical Form Refractories are classified according to their physical form. These are the shaped and unshaped refractories. The former is commonly known as refractory bricks and the latter as “monolithic” refractories. Types of refractories Refractories are classified as dense or insulating types. Most high-temperature refractories, such as firebricks, are of high-density type (>120 lb/ft3 ). They offer excellent resistance in challenging operating environments, such as slags with different chemical compositions, fumes, dust, and gases. Insulating refractories have lower densities (4 to 70 lb/ft3 ) and provide insulating properties, while offering resistance to corrosion and chemical reactions with the operating environment. The following brief discussion of the outstanding characteristics of the various types of refractories is an attempt to be more specific. Fire-clay brick Refractories: Fire-clay brick comprise about 75% of the production of refractories on a volume basis and are essentially hydrated aluminum silicates with minor proportions of other minerals. Typical composition consists of SiO 2 < 44%. As a type they are extremely versatile; are the most cost efficient of all refractory bricks and are extensively used in the iron and steel industry, non ferrous metallurgy, glass industry, pottery kilns, cement industry and by many others. High Alumina Refractories: Alumina refractory, which consists of aluminum oxide and traces of other materials, is the most mature of the engineering ceramics. Alumina is one of the most chemically stable oxides known, which offers excellent hardness, strength and spalling resistance. It is insoluble in water and super heated steam, and in most inorganic acids and alkalis. Alumina refractories carry the all purpose characteristics of fire-clay brick into higher temperature ranges that makes it suitable for lining furnace operating up to 3350°F. It has a high resistance in oxidizing and reducing atmosphere and is extensively used in heat processing industries. High-alumina brick are classified by their alumina content according to the following ASTM convention. These are: • Mullite refractory • Corundum refractories Silica Brick: Silica Brick is a refractory material containing at least 93% SiO 2 . From a volume standpoint, silica bricks are second only to fire clay brick. The outstanding property of silica brick is its excellent mechanical strength at Shaped Refractories & Unshaped Refractories Shaped Unshaped 1. Alumino Silicates • High Alumina • Low Alumina 2. Silica 3. Basic • Maganesite • Mag-Chrome • Mag-Carbon • Forsterite • Dolomite 4. Carbon 5. Zirconia • Zircon (Acidic) • Zirconia (Neutral) 6. Carbides/Nitride • Silicon Carbide • Silicon Nitride • Boron Carbide • Boron Nitride 7. Pure Oxides • Ferrites • Hofnium Oxides 1. Mortars 2. Castables • LCC • ULCC • NCC • SFC 3. Gunning Mass 4. Ramming Mass 5. Filling Mass 6. Felting Mass 7. Spraying Com- pound 8. Patching/Coat- ing