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2. Contents table
Refractory
Classification
Properties of Refractories
General Manufacturing (flow sheet)
Selection of Refractories
Applications
-Refractories in Cement Industry.
Some Common Refractories

3. Refractory
A 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;
538 °C)“.
Examples
Fire clay.
Silica.
Chromite magnesite.

4. Classification
Refractories can be classified
-on the basis of chemical composition
-method of manufacture
-according to their refractoriness.

5. 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…

6. 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.

7. 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 ºC
High heat duty refractories
For temperature ranging from 1670—1730 ºC
Super duty refractories
For temperature above 1730 ºC

8. On basis of Manufacture
Dry pressed
Fused Cast
Hand molded
Formed
Unformed

9. 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
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..

10. Contd..
Thermal Conductivity
For 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.
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..

11. Contd..
Slag Resistance
It is the resistance to slag action which depends on
nature of the slag and refractory.
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.

12. 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..

13. Contd..
Drying
Avoids high shrinkage and gives strength.
Make refractories safe for handling.
Firing
Removes water of Hydration,
30% Shrinkage in Volume.

15. Selection of Refractories
Area of application
Working temperatures
Extent of abrasion and impact
Stress due to temperature gradient
Heat transfer and fuel conservation
Cost consideration

16. 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
Preheater
Rotary Kiln
Burner pipe
Clinker cooler

17. Some Common Refractories

18. Fire Clay refractories
Common in industry: materials available
and inexpensive
Consist of aluminium silicates
Decreasing melting point with increasing
impurity and decreasing AL2O3

19. High Alumina Refractories
45 - 100% alumina
High alumina % = high refractoriness
Applications: hearth and shaft of blast
furnaces, ceramic kilns, cement kilns,
glass tanks

20. Silica Bricks
>93% SiO2 made from quality rocks
Iron & steel, glass industry
Advantages: no softening until fusion point
is reached; high refractoriness; high
resistance to spalling, flux and slag, volume
stability

21. Zirconia refractories
Zirconium dioxide ZrO2
Stabilized with calcium, magnesium, etc.
High strength, low thermal conductivity, not
reactive, low thermal loss
Used in glass furnaces, insulating refractory

22. Question ?

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