2. Refractory Bricks
The term “Refractories" embraces all
materials used in the arts for the
construction of heat resisting
containers.
Refractory bricks are made from
refractory clay, which can withstand
very high temperature without being
soften or Melting.
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4. Principles
The two principal functions involved in the use of refactory
materials are those of thermal insulation and conduction.
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5. A good refractory material should have
the following properties:
1. It should be able to withstand high temperatures generated in the furnace.
2. It should be able to withstand sudden alternating, heating and cooling, i.e.
thermal shocks.
3. It should be able to withstand abrasion and rough usage.
4. Its contraction and expansion due to the inevitable temperature variation
should be minimum possible.
5. It should be able to withstand fluxing action of the slags and the corrosive
action of gases.
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6. A good refractory material should have
the following properties:
6. It should have good heat insulating properties.
7. It should be chemically inactive at elevated temperatures.
8. It should be impermeable to gases and liquids as far as possible.
9. If used in electric furnaces, it must have low electrical conductivity.
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7. Fire resistance capacities
Grade of Refractory bricks Temperature resistance range ( o
C)
High 1482 – 1648
Medium 1315 – 1482
Low Up to 870
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8. Properties
They are yellowish white or white in color.
One general refractory brick weighs about 30 to 35 N.
The compressive strength ranges from 20 to 22 N/mm2.
The percentage of water absorption varies from 5 to 10%.
They have good chemical resistance.
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10. Acid Bricks
These bricks are used for acidic lining. Following are the
types of acidic bricks:
(i) Ordinary fire-bricks
(ii) Silica bricks
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11. Acid Bricks
These bricks are prepared from natural fire-clay and they provide
a good material for acidic refractory lining.
Not attacked by acidic environments.
The composition are
Silica - 50 to 75%
Alumina - 20 to 40%. &
Fluxes - less than 10%.
These bricks are prepared from natural fire clay mixed with small
percentage of sand.
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12. Acid Bricks - Properties
Low coefficient of thermal expansion.
Sufficient strength at high temperature.
The compressive strength of such bricks is about 15 N/mm2.
Low porosity and free from air pockets.
Good thermal expansion and conductivity.
Remarkable load bearing capacity especially at high temperatures.
Not susceptible to thermal spalling at temperatures above 400 °C.
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13. Acid Bricks - Uses
Lining of blast furnace for melting of iron, copper, lead, ect.
Lining of fuels and stocks.
Heat treatment furnaces.
Glass furnaces.
Electrical furnace.
Copper smelting.
Lining for acid storage containers.
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15. Basic Bricks
Bricks are used for Basic lining and prepared from basic refractory
materials.
This bricks are hand moulded Partially dried and repressed.
After further drying the bricks are burnt.
Not attacked by basic environments.
The composition are,
Magnesia -85%
Calcium oxide - 25%.
Silica - 5.5%.
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16. Basic Bricks - Properties
These are good at corrosion resistance and chemical resistance.
Thermal conductivity greater than acidic bricks
They contain high amount of magnesia.
High resistance to action of basic slag and iron oxide.
Starts losing strength at temperature of 1500o c.
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17. Basic Bricks - Uses
Used for open hearth furnace
Copper refractory furnace
Used in electrical and induction furnaces
Lining of steel manufacturing crucibles
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19. Neutral Bricks
Neutral brick is otherwise known as inert bricks.
This bricks are used for neutral lining are more inert to slag.
They are used to separate the acid and basic linings of a furnace so
that they cannot react with each other.
Two types – Chrome bricks and chrome magnesite bricks
Composition: Chrome oxide, Oxides of magnesia, aluminum and
little amount of silica
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20. Neutral Bricks - Properties
Low porosity
High resistance to acid and basic slag
High thermal conductivity
Low resistance to spalling
Less shrinkage
Good mechanical properties
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21. Neutral Bricks - Uses
Used in steel industry for lining of open hearth and bottom
of soaking pits
Used in electrical furnaces
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