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Unshaped Materials For Heating Furnaces

Unshaped Materials For Heating Furnaces

One of the common thermal equipment is the heating furnace. Currently, the prevalent usage in heating furnaces involves the application of unshaped refractory materials. Several types of unshaped refractory materials are commonly used in heating furnaces, with refractory bricks, castables, and prefabricated blocks being frequently chosen for the furnace lining. For the refractory layer, refractory castables, refractory bricks, and prefabricated blocks are commonly employed, while lightweight clay bricks or diatomaceous earth bricks are used for the insulating layer. When discussing unshaped refractory materials used in heating furnaces, it is necessary to mention refractory castables, which have replaced refractory bricks in many high-temperature equipment locations and have demonstrated favorable performance.

Unshaped refractory materials are innovative refractory materials developed in recent years. They feature a simplified production process without the need for firing procedures, uncomplicated production equipment, and the ability to be formed into various shapes and sizes as prefabricated blocks. They can also be cast entirely onto thermal equipment to enhance the overall integrity of the furnace. These materials can be manufactured into various prefabricated blocks, expediting furnace construction and repair processes, thus saving labor costs. Additionally, they can adapt to local conditions and make use of recycled materials such as old refractory bricks, providing a comprehensive utilization of resources and reducing costs.

What Kind of Unshaped Materials For Heating Furnaces?

TypesUnshaped refractory materialsIntroduction
Type 1Plastic CastablePlastic refractory is a type of unshaped refractory material, consisting of aggregates, powders, and binders mixed in a certain proportion to form a mud-like refractory material.
Type 2Light-Weight High Strength Mullite CastableLightweight mullite castable is a novel material characterized by the use of porous mullite as its aggregate.
Type 3Special Low Cement Castablea special inorganic non-metallic material characterized by a reduced cement content and enhanced refractoriness.
Type 4Mullite Self-Flow MaterialsSelf-flow castable is a high-tech product developed based on the principles of solid-state fluid mechanics and tailored to the application characteristics of refractory materials.
Type 5Magnesite Chrome Castableservice temperature of 1500~1700°C. They are primarily employed in thermal equipment like ladles and have proven to be economically beneficial
Type 6Quick-Dry High Strength CastableThe adoption of rapid-drying technology in the abrasion-resistant castable has significantly decreased the drying time from approximately 7 days to around 30 hours, achieving satisfactory results in shortening the drying time for the abrasion-resistant castable.
Type 7Explosion-Proof Plastic CastableThe rapid-drying explosion-proof castable for heating furnaces is also known as self-flow castable, and some manufacturers refer to it as non-baking castable, with varied nomenclature. It is used in water-cooled pipes, furnace walls, and is a type of refractory castable employed at the furnace mouth.

Type 1:Plastic Castable

Plastic refractory is a novel refractory material that offers advantages such as convenient construction and extended service life. When the heating furnace has a complex arrangement of roof pipes, using plastic refractory instead of castables for constructing the furnace roof is a favorable choice. However, it is imperative to adhere to scientific construction techniques to prolong the service life of the furnace roof.

Plastic refractory is a type of unshaped refractory material, consisting of aggregates, powders, and binders mixed in a certain proportion to form a mud-like refractory material. It possesses a certain level of plasticity and can be constructed by ramming. Compared to ordinary low-cement castables, plastic refractory has advantages such as good thermal shock stability, high temperature strength, and strong resistance to spalling and erosion. Additionally, it exhibits properties like low thermal expansion, low thermal conductivity, and long service life. In recent years, it has been widely applied in furnace linings, including heating furnaces and homogenizing furnaces, as well as in areas of furnace linings where castable construction is challenging. Particularly, it has gained extensive use in the furnace roof of heating furnaces.

ITEMUNITPlastic Castable
  CT-150
Chemical ComponentsAI2O350
Bulk density110°C×24hg/cm32.4
compressive strength110°C×24hMpa4
 1350°C×3h  15
bending strength110°C×24hMpa
 1350°C×3h  
linear change on reheating1350°C×3h-1.0~+1.5
useTop

Type 2:Light-Weight High Strength Mullite Castable

Lightweight mullite castable is a novel material characterized by the use of porous mullite as its aggregate. The aggregate undergoes high-temperature artificial synthesis, with the main crystalline phase reaching 70% or more and exhibiting uniform and stable composition. The binder employed is either pure calcium aluminate cement or aluminate cement, with the addition of mullite micro powder, alumina micro powder, silica micro powder, and andalusite, among other components, in a specific ratio.

ITEMUNITLight-Weight High Strength Mullite Castable
  MQ-3
Chemical ComponentsAI2O350
Bulk density110°C×24hg/cm31.65
compressive strength110°C×24hMpa7
 1350°C×3h  20
bending strength110°C×24hMpa
 1350°C×3h  
linear change on reheating1350°C×3h0~+1.5
Lightweight mullite castable possesses the following characteristics:
  1. Suitable for Various Industrial Kiln Linings: Lightweight mullite castable can be used as a working lining or insulation lining for various industrial kilns, achieving high-temperature energy-saving effects.
  2. High Strength with Low Bulk Density: In comparison to regular low-cement castables, lightweight mullite castable can reduce structural weight by over 30% during use, thereby avoiding safety hazards such as structural brick breakage or collapse.
  3. Excellent Insulation Performance: Lightweight mullite castable utilizes high-quality porous mullite aggregates, combined with various micro powders and dispersants, resulting in a low thermal conductivity and excellent insulation properties. Compared to conventional castables, lightweight mullite castable can reduce kiln heat loss by 25% to 35%, leading to approximately 10% fuel savings.
  4. Convenient Construction: Lightweight mullite castable can be either cast in place on-site or fabricated into prefabricated shapes for easy and straightforward installation.

Type 3:Special Low Cement Castable

Low Cement Castable (LCC), also known as Low Cement Refractory Castable (LCRC), is a special inorganic non-metallic material characterized by a reduced cement content and enhanced refractoriness. Since the 1980s, LCC has found widespread application in various industrial sectors, particularly in high-temperature, high-pressure, and highly abrasive environments. Due to its outstanding performance, LCC has gradually replaced traditional High Cement Castables (HCC) in many applications.

ITEMUNITSpecial Low Cement Castable
  TDJ-1
Chemical ComponentsAI2O360
Bulk density110°C×24hg/cm32.45
compressive strength110°C×24hMpa40
 1350°C×3h  80
bending strength110°C×24hMpa7
 1350°C×3h  10
linear change on reheating1350°C×3h0~+1.0
useTop,water pipe wrap
Characteristics of Low Cement Castable (LCC):
  1. Low Cement Content: The cement content in LCC is typically between 3-8%, significantly lower than the 15-30% found in High Cement Castables (HCC).
  2. High Density: The reduced cement content in LCC decreases the porosity, leading to higher density. This, in turn, enhances the compressive and flexural strength of the material.
  3. Refractory Performance: LCC exhibits high refractory performance, capable of withstanding temperatures ranging from 1500-1800°C.
  4. Excellent Thermal Stability: LCC has a low coefficient of thermal expansion, ensuring stable dimensions and structure even in high-temperature environments.
  5. Slag Resistance: LCC demonstrates superior slag resistance compared to HCC, effectively reducing chemical erosion and physical wear.

Type 4:Mullite Self-Flow Materials

Self-flow castable is a high-tech product developed based on the principles of solid-state fluid mechanics and tailored to the application characteristics of refractory materials. It is the first of its kind domestically. The self-flowing material can utilize its own gravity to degas and level without the need for vibration, thereby achieving densification.

ITEMUNITMullite Self-Flow Materials
  SF-3
Chemical ComponentsAI2O360
Bulk density110°C×24hg/cm32.4
compressive strength110°C×24hMpa30
 1350°C×3h  60
bending strength110°C×24hMpa6
 1350°C×3h  8
linear change on reheating1350°C×3h0~+1.0
UseTop,water pipe wrap

Type 5:Magnesite Chrome Castable

Refractory castables made of magnesia-chrome materials typically utilize refractory aggregates and powders such as recycled magnesia-chrome bricks, magnesia-chrome spinel, magnesia sand, and chromite ore. These materials undergo processing and blending. As for additives, aluminum acid salt cement or covering materials are used as coagulants, and the binder employs a solution of sodium hexametaphosphate with a density of 1.3~1.35g/cm³. For instance, using waste magnesia-chrome bricks with MgO 81% and CrO3 7.3% as refractory aggregates, with particle size < 15mm, accounts for 50% of the total mix. The powder component comprises MgO 91.6% and fine-grained magnesia sand with a fineness of <0.06mm, constituting 30%. Additionally, 20% is made up of CrO3 53.2% and fine-grained chromite ore with a fineness of <1mm. Lime powder serves as a coagulant at a quantity of 1%~2%, and the sodium hexametaphosphate solution is used at a quantity of 15%~18%.

Alkaline refractory castables exhibit high strength and good slag resistance, with a service temperature of 1500~1700°C. They are primarily employed in thermal equipment like ladles and have proven to be economically beneficial. In recent years, low-cement and ultrafine powder alkaline refractory castables have been developed, offering excellent performance and ease of construction. This has led to widespread application, limiting the use of sodium hexametaphosphate alkaline refractory castables.

ITEMUNITMagnesite Chrome Castable
MGeJ-50
Chemical ComponentsAI2O350(MgO)
MgO6(Cr2O3)
Bulk density110°C×24hg/cm32.7
compressive strength110°C×24hMpa25
1500°C×3h40
bending strength110°C×24hMpa4
1500°C×3h6
linear change on reheating1350°C×3h-0.1~+1.5
UseBurden slag parts

Type 6:Quick-Dry High Strength Castable

High-strength rapid-drying abrasion-resistant castable is developed by introducing special additives into abrasion-resistant castables. The addition of these additives creates elongated gas channels within the refractory material, facilitating the discharge of water vapor. This enhances the castable’s resistance to cracking and reduces drying time in the kiln. This high-strength rapid-drying abrasion-resistant castable is an ideal material for both new construction and boiler maintenance. It has been successfully utilized in over twenty boilers. The adoption of rapid-drying technology in the abrasion-resistant castable has significantly decreased the drying time from approximately 7 days to around 30 hours, achieving satisfactory results in shortening the drying time for the abrasion-resistant castable.

ITEMUNITQuick-Dry High Strength Castable
  KHJ-1
Chemical ComponentsAI2O365
 MgO  
Bulk density110°C×24hg/cm32.5
compressive strength110°C×24hMpa30
 1500°C×3h  50(1350°C)
bending strength110°C×24hMpa5
 1500°C×3h  8(1350°C)
linear change on reheating1350°C×3h0~+1.0(1350°C)
UseRapid repairing lining

Type 7:Explosion-Proof Plastic Castable

The rapid-drying explosion-proof castable for heating furnaces is also known as self-flow castable, and some manufacturers refer to it as non-baking castable, with varied nomenclature. It is used in water-cooled pipes, furnace walls, and is a type of refractory castable employed at the furnace mouth.

Non-baking castables are also categorized based on different qualities and grades, tailored for specific locations. For use in furnace walls, a medium-grade non-baking castable is generally sufficient, offering cost savings. However, when applied at the furnace mouth or for wrapping water-cooled pipes, a self-flowing rapid-drying explosion-proof castable must be used. This is because the usage conditions for water-cooled pipes differ from furnace walls. Using high-quality castables at critical locations allows for simultaneous replacement in other areas.

In the production process of rapid-drying explosion-proof castables, it is essential to control the process ratios to prevent cracking and peeling during use. Therefore, the rational handling and incorporation of reasonable proportions of ultrafine powder and aluminum oxide powder in the process are indispensable. However, the proportion of binders must not be excessive because this type of refractory castable requires a larger water addition during construction to enhance its flowability. Excessive binder content can impact its compactness and flowability.

Each category of castable is divided into high, medium, and low grades based on its quality. The production is tailored to its intended usage temperature and erosion level. It is not a one-size-fits-all solution, and different qualities are used to meet the needs of various locations and temperatures. The lining used in heating furnaces also varies in quality. Higher quality is required for wrapping water-cooled pipes, while slightly lower-grade refractory castables may suffice for furnace walls.

For areas such as the burner nozzle at the furnace mouth, the quality should match that used for water-cooled pipes. This is crucial as, in most cases, prefabricated bricks are used at the burner nozzle, necessitating meticulous attention to quality. The rational use of rapid-drying explosion-proof castables involves distinct classifications.

ITEMUNITExplosion-Proof Plastic Castable
  FBJ-1
Chemical ComponentsAI2O360
 MgO  
Bulk density110°C×24hg/cm32.4
compressive strength110°C×24hMpa15
 1500°C×3h  30(1350°C)
bending strength110°C×24hMpa4
 1500°C×3h  6(1350°C)
linear change on reheating1350°C×3h0~+1.0(1350°C)
USERapid repairing lining
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