In modern furnace design, choosing the correct insulating refractory brick is essential for achieving energy efficiency, stable operation, and long service life. Among all insulation materials, mullite insulation bricks-classified by grades such as JM23, JM26, and JM28-are among the most popular options in industrial kilns and furnaces.
But how do you decide which grade of mullite brick best suits your application? This article explains the differences between these grades and provides practical guidance for refractory buyers and engineers.
What Are Mullite Insulation Bricks?
Mullite insulation refractory bricks are lightweight refractory materials made from high-purity alumina and silica. The key crystalline phase is mullite (3Al₂O₃·2SiO₂), which gives these bricks excellent thermal stability and mechanical strength at elevated temperatures.
They are designed with controlled porosity and low bulk density to achieve low thermal conductivity while maintaining good structural integrity. Typical bulk density ranges from 0.6 to 1.2 g/cm³, making them much lighter than dense firebricks.
Understanding Mullite insulation Brick Grades: JM23, JM26, JM28
Each grade of mullite insulation refractory brick corresponds to a specific maximum service temperature, alumina content, and thermal conductivity. Choosing the right grade depends on your furnace's operating temperature and insulation requirements.
| Grade | Max Working Temp (°C) | Al₂O₃ (%) | Bulk Density (g/cm³) | Thermal Conductivity (W/m·K at 1000°C) | Typical Applications |
|---|---|---|---|---|---|
| JM23 | 1260 | 46–48 | 0.6–0.9 | 0.16–0.20 | Kiln insulation, backup lining, heat-treatment furnaces |
| JM26 | 1400 | 55–57 | 0.8–1.0 | 0.18–0.22 | Ceramic kilns, glass furnaces, petrochemical heaters |
| JM28 | 1500 | 65–68 | 1.0–1.2 | 0.20–0.25 | High-temperature industrial furnaces, rotary kilns, steel reheating furnaces |
Key Differences Between JM23, JM26, and JM28
Temperature Resistance
JM23 bricks are ideal for low to medium temperature insulation.
JM26 handles higher temperatures up to 1400°C.
JM28 is best for demanding high-temperature environments up to 1500°C.
Energy Efficiency
JM23 offers the lowest thermal conductivity, making it the best choice where insulation performance is critical.
JM28, being denser, has slightly higher heat storage but provides superior strength and durability.
Mechanical Strength and Durability
JM28 bricks have the highest crushing strength and are better suited for load-bearing areas of the furnace.
JM23 and JM26 are typically used as non-load-bearing insulation layers.
Cost Consideration
JM23 is the most economical grade.
JM28, with higher alumina content and strength, comes at a premium but offers longer service life.
Applications of Different Mullite Brick Grades
JM23 Mullite Insulation Brick
Used in low- to medium-temperature furnaces such as:
Heat treatment furnaces
Shuttle kilns and laboratory furnaces
Backup lining behind dense refractory bricks
JM26 Mullite Insulation Brick
Commonly applied in:
Ceramic and porcelain kilns
Glass melting furnace insulation
Petrochemical heaters and regenerators
JM28 Mullite Insulation Brick
Ideal for high-temperature operations such as:
Rotary kilns in cement and metallurgical industries
Steel reheating and annealing furnaces
Continuous tunnel kilns
How to Select the Right Mullite Brick for Your Furnace
When selecting a suitable grade, consider these key factors:
Operating Temperature:
Always select a brick with a maximum working temperature 10–15% higher than the furnace's regular operating range.
Insulation Efficiency:
For energy-saving furnaces, prioritize lower thermal conductivity grades like JM23 or JM26 for the backup layer.
Mechanical Load and Position:
Areas exposed to higher mechanical stress (like kiln floors or load-bearing walls) should use JM28.
Atmosphere and Fuel Type:
Furnaces with fluctuating oxidizing/reducing atmospheres benefit from the stability of JM26 or JM28.
Cost vs. Longevity:
While JM28 costs more, it provides longer life and reduces long-term maintenance costs.
Our mullite insulation bricks are trusted by customers across steel, glass, ceramic, and petrochemical industries worldwide.
Selecting the right mullite brick grade depends on balancing temperature requirements, strength, and insulation efficiency.
JM23: Best for low-temperature insulation and energy-saving applications.
JM26: Versatile mid-grade brick suitable for most industrial furnaces.
JM28: Premium high-strength brick for extreme heat and heavy-duty applications.
By partnering with Topower Refractory, you can be assured of consistent quality, reliable delivery, and expert technical support for all your refractory needs.
