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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
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
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