Transcript Dias nummer 1

Refractories
Definition & Classification
Tina Stendal Svendsen
Product Manager
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Definition of Refractory
“non-metallic
ceramic material or product whose
chemical and physical properties allow it to be
used in a high temperature environment”
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Application of Refractory
Lining of plants for thermal processing (melting, firing and heattreatment furnaces) e.g.:
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Iron and steel
Cement and lime
Glass and ceramics
Chemical and petrochemical
Heat- and power (waste and biomass)
Heat-insulation
Functional products: shaped products with an additional function during
service
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Classification due to product type
Refractory
Monolithics
(unshaped)
Castables
Dense
Heatinsulating
Bricks
(shaped)
Functional
products
Mortars
Insulating
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Classification due to bond type
and cement content
Dense
castable
Hydraulic
bond
‘high
technology’
Conventional
Traditional
castables
Gunning
Chemical
bond
Low cement
1.0-2,5%
CaO
Ultra low
cement
< 1.0% CaO
No cement
< 0.2% CaO
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Classification according to type of chemical composition
Focus on Alumina-Silicate refractory products based on:
• Al2O3 (alumina)
• SiO2 (sillica)
The variants of alumina-silica castables are formulated by:
• Different amounts of Al2O3 and SiO2 in raw materials
• Different crystal structures of raw materials
• Different properties of raw materials
• Grain size distribution and matrix products
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Composition of dense refractory castables
Aggregates (> 45 μm) 65-75%
• Croase; build the foundation of the castable
• Fine; fill the voids between the croase aggregates
Matrix products (< 45 μm) 25-35%
• Fill the micron size voids, affects workability and strength
• Binders; hold castable together until thermal sintering occurs
• Additives; reduces water or control setting time
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Raw materials characterization
• Chamotte (calcined fireclay): 30-45% Al2O3
• Andalusite: 50-60% Al2O3
• Bauxite: 80-90% Al2O3
Alkali resistance
Shock resistance
Abrasion resistance
• Corrundum (alumina): 99% Al2O3
High refractoriness
• Syntetic mullite (calcined bauxitic clay): 60-80% Al2O3
• Silicon carbide: SiC
Strength
High thermal conductivity
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High quality refractory raw materials:
Are subjected to Calcination (minerals fired at 1400-2000°C)
• Reduces the amount of impurities
• Low porosity
• High density
• Chemically stable
• Increased refractoriness
Low iron (Fe2O3) content (minimize the risk of CO-attack)
Low alkali content (minimize the formation of low-melting-temp. glasses)
Be aware of recycled materials!
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Summary
• Refractory materials can be classified according to e.g. type, cement
content, application/installation technique and the main raw material
• We will focus on Alumina-Silicate castables
• Dense castables contains approx. 70% aggregates and 30% matrix
products
• The variants of alumina-silicate castables are achieved by a diversity
of different raw materials with different properties
• Both natural minerals and calcined minerals are used
• Fractions (and optimal particle distribution) are obtained by crushing,
sieving and grinding/milling
• High quality raw materials performs better!
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