High alumina bricks, also known as aluminum refractory bricks, are a type of refractory made primarily from alumina or aluminum oxide. They are one of the most common types of refractories used in high temperature applications. High alumina brick has alumina content ranging from 45% to 90%, with higher alumina content bricks having better refractory properties.
High alumina bricks exhibit excellent thermal shock resistance, corrosion resistance, and refractoriness under load. Their combination of good physical properties and lower cost make them the workhorse material for many demanding refractory applications.
Uses Of High Alumina Bricks
Some of the major uses of high alumina bricks include:
• Lining of furnaces like cement rotary kilns, direct fired coal gasifiers, ceramic kilns, glass furnaces, incinerators, and many other high temperature thermal processes. High alumina bricks are typically as used in the combustion zone and transition zones of these furnaces.
• Back-up insulating refractories for insulating firebrick to prevent insulating bricks from being as damaged by heat penetration.
• As refractory bricks in areas of abrasion and corrosion resistance like bosh and stack areas of glass furnaces.
• As muffles and recuperator linings in furnaces and ovens.
• As refractory bricks for lining ladles used in steel making.
• As trough and launder linings for carrying hot molten metals like steel, iron, and aluminum.
• As tap hole bricks and ladle shrouds for regulating the flow of molten metal.
• As nose ring segments in cement kilns.
• As refractory bricks in reformers and crackers used in petrochemical industry.
The excellent combination of properties like good refractoriness, slag and spalling resistance, thermal shock resistance, corrosion resistance, and abrasion resistance make high alumina bricks suitable for these demanding applications.
Manufacturing Of High Alumina Bricks
High alumina bricks are as manufactured by firing a shaped green body containing principally raw bauxite and minor amounts of clay at high temperatures ranging from 1,400°C to 1,800°C. The firing process results in sintering of alumina grains along with bonding by the formation of mullite from clay.
Based on the alumina content, high alumina bricks are as classified into several grades ranging from 45% alumina to 90% alumina. Higher alumina bricks have better refractory properties. Various additives may also be present in small percentages to modify specific properties like enhanced refractoriness under load by addition of silicon carbide.
The commonly used high alumina brick grades conforming to standards include HA-45, HA-60, HA-70, and HA-80. The number indicates the typical alumina content of the brick grade. High purity grades like 99% alumina bricks are also sometimes used in very critical applications.
The raw bauxite for manufacturing high alumina bricks is selected as based on chemical composition and physical characteristics for achieving the desired properties in the final refractory product. High alumina bricks can be manufactured in various standard shapes and sizes or even customized shapes based on the application requirements.
Aluminum Refractory Bricks
Aluminum refractory bricks refer to a subset of high alumina refractory bricks that contain a very high percentage of alumina, typically greater than 90%. They are as manufactured from bauxite ores that contain a very low percentage of silica and iron oxide to maintain the high alumina content required.
Some of the salient features of aluminum refractory bricks include:
• Exceptionally high refractoriness with low creep at high temperatures. Can be as used continuously at 1,600°C and higher temperatures.
• Excellent corrosion resistance against alkali vapors and slags.
• Very good thermal shock resistance capable of withstanding rapid temperature changes.
• Low porosity bricks with high density resulting in low gas permeability.
• Resistant to penetration and wear by liquid aluminum metal.
Due to their high alumina content, purity, and superior performance, aluminum refractory bricks find use in very critical high temperature applications like:
• Working lining bricks in glass melting furnaces where temperatures can reach 1,700°C.
• Superstructure bricks in cement kilns exposed to temperature above 1,500°C.
• Nose ring segments in cement kilns.
• Upper transition and burning zone linings of hazardous waste incinerators.
• Crown and sidewall lining of aluminum melting and holding furnaces.
• Wall and crown lining of induction furnaces melting special alloys.
SK38 Refractory Bricks
SK38 refractory bricks belong to the high alumina product category and have an alumina content of approximately 75-80%. SK refers to the initials of Shanker Kumar, the founder of Shanker Refractories Pvt. Ltd. which first developed this grade of brick.
Some of the important features of SK38 bricks include:
• Refractoriness of 38 equivalent on the Pyrometric Cone Scale, corresponding to a temperature of approximately 1,730°C.
• Good volume stability and resistance to spalling at high temperatures.
• Excellent slag resistance allowing direct contact with corrosive slags.
• Suitable for application in reducing, neutral and oxidizing atmospheres.
• Resists penetration by metals like copper, steel, and iron.
• Good thermal shock resistance capable of withstanding thermal cycles.
Due to their well-balanced combination of properties, SK38 refractory bricks find extensive use in applications like:
• Backup insulation course for working lining in industries like steel, glass, cement, aluminum and copper production.
• Lining of ladles for handling molten metals.
• Transition and flow control zone linings in coke ovens.
• Hot gas duct linings in high temperature furnaces.
• Kiln car and batch preheater linings in cement industry.