Jun 06 , 2025
When it comes to industrial furnace insulation, both high-density calcium silicate boards and high-density ceramic fiber boards offer unique advantages. Choosing the right material depends on your specific application needs, such as operating temperature, mechanical load, exposure to molten metals, and thermal cycling conditions.
High-density calcium silicate boards are primarily composed of calcium silicate hydrates and are often reinforced with fibers such as glass or carbon. The “high-density” designation refers to their compact, rigid structure, which is denser than that of low-density variants.
· High Compressive Strength: This is a major strong point. High-density calcium silicate boards offer excellent mechanical strength, making them suitable for load-bearing applications or areas subjected to mechanical stress, impacts, or abrasion.
· Dimensional Stability: They exhibit very low shrinkage at high temperatures, maintaining their shape and structural integrity even after prolonged exposure to heat.
· Rigidity and Structural Integrity: They provide a rigid, self-supporting structure, which can simplify furnace construction and reduce the need for extensive external support.
· Non-Wetting to Molten Aluminium: Specific grades (especially carbon-fiber reinforced ones) are engineered to be non-wetting with molten non-ferrous metals like aluminium, preventing metal adhesion and contamination. This makes them ideal for direct contact applications in aluminium holding furnaces, launders, and casting components.
· Good Thermal Insulation: While typically higher in thermal conductivity than ceramic fiber boards at equivalent thicknesses, they still provide effective insulation.
· Resistance to Chemicals: Generally resistant to various chemicals, though some formulations may react in highly acidic environments.
· Easy to Machine: High Density Calcium Silicate Board can be precisely machined into complex shapes and components, offering design flexibility.
· Non-combustible and Asbestos-Free: Safe for use in high-temperature environments.
· Lower Thermal Shock Resistance: Compared to ceramic fiber boards, they are more susceptible to cracking or spalling when subjected to rapid heating and cooling cycles.
· Brittle Nature: Can be brittle and prone to chipping or breaking if handled roughly or subjected to significant impact, particularly during transportation and installation.
· Higher Density/Weight: Generally heavier than ceramic fiber boards, which can be a consideration for certain furnace designs or installation logistics.
· Moisture Absorption: Some grades can absorb moisture, requiring careful storage and gradual drying before initial firing to prevent cracking.
· Back-up insulation behind dense refractories (bricks, castables).
· Hot-face lining in aluminium holding furnaces, launders, and distribution systems (especially carbon-fiber reinforced grades).
· Furnace door insulation and other applications requiring structural support.
· Core plates, platen press insulation.
· Electrical insulation in high-temperature settings.
Made from high-purity alumina-silica fibers, high-density ceramic fiber boards are vacuum-formed and treated with binders for rigidity. The high-density version offers improved strength and insulation.
· Excellent Thermal Shock Resistance: The ceramic fiber board can withstand rapid and repeated heating and cooling cycles without cracking or degrading, making it suitable for batch furnaces or applications with frequent temperature fluctuations.
· Very Low Thermal Conductivity: Generally offers superior insulating properties (lower thermal conductivity) compared to calcium silicate at similar thicknesses, leading to better energy efficiency and lower heat loss.
· Lightweight: Significantly lighter than calcium silicate boards, which can reduce the overall weight of the furnace structure, simplify installation, and lower transportation costs.
· Good Chemical Resistance: Resistant to most chemical attacks, with specific grades available for different chemical environments.
· Flexible (to a degree): While rigid, they have a slight degree of flexibility compared to calcium silicate, which can be beneficial in certain applications.
· Low Heat Storage: Their low thermal mass allows for faster heating and cooling cycles, improving furnace productivity.
· Good Machinability: Can be cut and machined relatively easily.
· Lower Compressive Strength: Generally have lower mechanical strength and are less suitable for load-bearing applications or areas subjected to high mechanical stress or abrasion unless specifically engineered for high strength.
· Not Non-Wetting to Molten Metals: Standard ceramic fiber boards will be wetted by and react with molten aluminium, making them unsuitable for direct contact applications with non-ferrous metals unless specially coated or protected.
· Fiber Shedding: Some ceramic fiber products can shed fibers, which may require precautions for worker safety and air quality, especially during installation or maintenance. (Bio-soluble fiber boards are an alternative to address this concern).
· Higher Cost: Often more expensive than calcium silicate boards.
· Hot-face lining in various industrial furnaces (e.g., heat treatment furnaces, kilns) where direct molten metal contact is not an issue.
· Back-up insulation behind dense refractories.
· Furnace door linings, expansion joints, and other areas requiring thermal shock resistance.
· High-temperature gaskets and seals.
· Insulation for boiler ducts, stacks, and other hot gas handling systems.
| Feature | High-Density Calcium Silicate Board | High-Density Ceramic Fiber Board |
| Primary Advantage | High compressive strength, dimensional stability, non-wetting (specific grades) | Excellent thermal shock resistance, very low thermal conductivity |
| Typical Max Temp. | 1000–1100°C (some grades up to 1200°C) | 1260–1600°C (depending on fiber composition) |
| Thermal Conductivity | Good, but generally higher than ceramic fiber | Excellent, very low |
| Mechanical Strength | High, rigid | Lower, less rigid |
| Thermal Shock Resistance | Lower | Very high |
| Molten Aluminum Contact | Suitable (carbon-fiber grades) | Not suitable unless coated |
| Weight | Heavier | Lighter |
| Brittleness | Brittle, prone to chipping | More resilient |
| Cost | Moderate | Generally higher |
Choosing between high-density calcium silicate boards and high-density ceramic fiber boards requires a thorough understanding of your operational environment. Here’s some expert advice from professional thermal insulation material manufacturers.
Use calcium silicate boards when mechanical strength, dimensional stability, or molten metal contact resistance is required.
Use ceramic fiber boards for superior thermal insulation, thermal shock resistance, and lightweight applications.
Consider the specific requirements of the application, including operating temperature, mechanical stresses, exposure to molten metals, and thermal cycling. Often, a combination of both materials is used in different layers of the furnace lining to leverage their respective strengths.
