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Contents table�Refractory

�Classification

�Properties of Refractories

�General Manufacturing (flow sheet)�General Manufacturing (flow sheet)

�Selection of Refractories

�Applications

-Refractories in Cement Industry.

�Some Common Refractories

RefractoryA refractory material is one that retains its strength and do

not fuse at high temperatures.

ASTM defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F (811 K; that are exposed to environments above 1,000 °F (811 K; 538 °C)“.

Examples

Fire clay.

Silica.

Chromite magnesite.

ClassificationRefractories can be classified

-on the basis of chemical composition

-method of manufacture-method of manufacture

-according to their refractoriness.

On the basis of chemical composition

� Acidic refractories

These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis.

e.g. fire clay, silica, Quartz, Zirconia.

� Basic refractories

These are used on areas where slags and atmosphere are basic, stable to alkaline materials but reacts with acids.

e.g. Magnesia , Alumina, Dolomite.

Contd…

Contd..

� Neutral refractories

These are used in areas where the atmosphere is

either acidic or basic and are chemically stable to

both acids and bases.

e.g. Chromite, Carbide, Mullite.e.g. Chromite, Carbide, Mullite.

Based on refractoriness� Low heat duty refractories

For low temperature environment i.e. 1520 —1630 ºC

� Medium heat duty refractories

For temperature ranging from 1630—1670 ºCFor temperature ranging from 1630—1670 ºC

� High heat duty refractories

For temperature ranging from 1670—1730 ºC

� Super duty refractories

For temperature above 1730 ºC

On basis of Manufacture

� Dry pressed

� Fused Cast

� Hand molded

� Formed

� Unformed

Properties

� Porosity

Greater the porosity of the refractory great is the chance of chemical attack of material

� Refractoriness or Fusion point

The temperature at which the refractory fuses, so it The temperature at which the refractory fuses, so it must be higher than the operating temperature of the refractory.

� Strength

It is the resistance of the refractory to loads tension and shear stresses.

Contd..

Contd..� Thermal ConductivityFor a given composition, a better pressed,less permeable

product has higher thermal conductivity.

-For use in Furnace and kiln Thermal conductivity should be low.

-For use in coke oven and regenerators thermal conductivity should be high.conductivity should be high.

� Spalling

It is the fracture of refractory due to its uneven expansion on account of heat when they are subjected to rapid heating and cooling.

Contd..

Contd..

� Slag Resistance

It is the resistance to slag action which depends on

nature of the slag and refractory.

� Abrasion resistance� Abrasion resistance

It is the resistance to abrasion which can be

increased by using dense (low porosity) fine

grained and wear resistance refractory.

� Erosion resistance

Resistance to erosion due to mechanical action.

Manufacturing steps� Transportation of Raw material

� Grinding

� Pre-Treatment

Calcination

Stabilizer addition

� Mixing

Bonding material

Wet Mixing (14-20% water)

Semi plastic

Dry Mixing ( < 5% water)

� Moulding

Hand Moulding (Wet Mixed)

Machine Moulding (Dry and Semi wet Mixed)

Contd..

Contd..

� Drying

Avoids high shrinkage and gives strength.

Make refractories safe for handling.

� Firing� Firing

Removes water of Hydration,

30% Shrinkage in Volume.

Selection of Refractories

� Area of application

� Working temperatures

� Extent of abrasion and impact

� Stress due to temperature gradient

Heat transfer and fuel conservation� Heat transfer and fuel conservation

� Cost consideration

Applications

Refractories are meant to sustain at high temperature so

the very common applications are

� Used in furnaces such as blast furnace and coke oven.

� Used in boilers.

� Mostly used in cement industry in� Mostly used in cement industry in

Preheater

Rotary Kiln

Burner pipe

Clinker cooler

Some Common RefractoriesSome Common Refractories

Fire Clay refractories

� Common in industry: materials available

and inexpensive

� Consist of aluminium silicates

Decreasing melting point with increasing � Decreasing melting point with increasing

impurity and decreasing AL2O3

High Alumina Refractories

� 45 - 100% alumina

� High alumina % = high refractoriness

� Applications: hearth and shaft of blast furnaces, ceramic kilns, cement kilns, furnaces, ceramic kilns, cement kilns, glass tanks

Silica Bricks

� >93% SiO2 made from quality rocks

� Iron & steel, glass industry

� Advantages: no softening until fusion point

is reached; high refractoriness; high is reached; high refractoriness; high

resistance to spalling, flux and slag, volume

stability

Zirconia refractories

� Zirconium dioxide ZrO2

� Stabilized with calcium, magnesium, etc.

� High strength, low thermal conductivity, not

reactive, low thermal lossreactive, low thermal loss

� Used in glass furnaces, insulating refractory

Question ?Question ?

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