Lightweight insulating castable refractory is a type of monolithic refractory material that integrates lightweight, thermal insulation, and refractory properties. By adjusting the proportion of aggregates, powders, binders, and admixtures, it can meet the industrial requirements of different temperatures and environments. It is widely used as an insulation layer for high-temp industrial kilns and furnaces.
I. The core differences between lightweight insulating castable refractories stem from the selection of lightweight aggregates and their maximum service temperature.
| Type | Core Lightweight Aggregates | Maximum Service temp | Key Characteristics |
| Lightweight Clay based Castable | Lightweight clay clinker, cenospheres, ceramsite | 800 – 1200 (℃) | Low cost, good thermal shock resistance preferred for basic thermal insulation |
| Lightweight High-Alumina Castable | Lightweight high-alumina clinker, high-alumina cenospheres | 1200 – 1500 (℃) | High high-temp strength better erosion resistance than clay-based castables |
| Lightweight Siliceous Castable | Lightweight silica brick clinker, siliceous microbeads | 1400 – 1600 (℃) | Good high-temp volume stability resistant to acidic erosion |
| Lightweight Corundum Castable | Lightweight corundum aggregates, corundum hollow spheres | 1600 – 1800 (℃) | High temp resistance, high strength suitable for harsh high-temp environments |
| Lightweight Mullite Castable | Lightweight mullite aggregates, mullite micro-powder | 1500 – 1700 (℃) | Excellent thermal shock stability minimal high-temp strength degradation |
| Ultra-Lightweight Insulating Castable | Perlite, vermiculite, hollow microbeads | 600 – 1000 (℃) | Extremely low bulk density (≤0.8g/cm³) extremely strong thermal insulation performance |
II. The core value of lightweight insulating castable refractories lies in balancing “thermal insulation performance” and “structural strength”, while also featuring the construction flexibility of unshaped refractories.
Low Density and Low Thermal Conductivity: Core Advantages in Thermal Insulation
Small bulk density: The bulk density of conventional products ranges from 0.8 to 1.8g/cm³ (ultra-lightweight ones can be as low as 0.4g/cm³), only 1/3 to 1/2 of that of ordinary heavy refractory castables. This significantly reduces the overall weight of kilns and lowers the load on steel structures.
Low thermal conductivity: At operating temperatures (800-1400℃), the thermal conductivity is typically 0.2-0.8W/(m·K), much lower than that of heavy refractory materials (1.5-3.0W/(m·K)). It can effectively block heat transfer, reduce kiln heat loss (by 20%-40%), and save energy consumption.
Excellent Constructability and Adaptability
Good fluidity: After mixing with water, lightweight insulating castable refractory exhibits excellent fluidity and can fill every corner of complex kiln structures (such as irregular flues, pipe interlayers, and irregular furnaces) without the need for intense vibration. The formed structure is dense and free of gaps.
Strong customizability: By adjusting aggregate types, particle gradation, and admixtures (e.g., retarders, water reducers), products with different strengths, densities, and temperature resistances can be customized. They are suitable for various scenarios, from low-temperature insulation (e.g., thermal pipelines) to high-temperature light-load working layers (e.g., preheating zones of ceramic kilns).
Moderate Mechanical Properties and Thermal Shock Resistance
Moderate room/high-temperature strength: The room-temperature compressive strength is usually 3-15MPa, and the high-temperature (1200℃) compressive strength is 2-10MPa, which can meet the needs of the insulation layer for self-bearing and resistance to slight external impacts (e.g., mild collisions during kiln maintenance).
Good thermal shock stability: Due to its low density and uniform internal pore distribution, it has a small volume expansion coefficient when heated, which can effectively release thermal stress. It is not prone to cracking or spalling after repeated thermal cycles (e.g., kiln start-up and shutdown), with a service life typically ranging from 3 to 8 years (depending on the operating environment).
Environmental Friendliness and Economic Efficiency
Low construction pollution: Compared with traditional block insulation bricks (which require cutting and masonry, generating dust and waste), lightweight insulating castable refractories are mixed and poured on-site, resulting in less waste during construction. Additionally, the formed structure has no brick joints, reducing energy waste caused by heat leakage through joints.
Low long-term cost: Although the unit price is higher than that of ordinary insulation bricks, it offers higher overall cost-effectiveness due to better insulation performance (reducing energy consumption), higher construction efficiency (shortening the construction period), and longer service life (reducing maintenance frequency).
III. The core application of lightweight insulating castable refractories lies in scenarios that require “thermal insulation + complex structure / light load”, covering multiple industrial fields.
Metallurgical Industry
Application Positions: Insulation layers of blast furnace hot stoves (inner side of the furnace shell, combustion chamber interlayer), insulation layers of converter flues, permanent layers of continuous casting tundishes, and insulation layers of the furnace roof/furnace wall of steel rolling heating furnaces.
Core Requirements: Reduce heat loss of hot stoves (to increase hot air temperature), minimize heat dissipation of flues (to avoid flue condensation and corrosion), and at the same time reduce the weight of the heating furnace body.
Building Materials Industry
Application Positions: Insulation layers of preheaters (C1-C3 grades) and calciner of cement rotary kilns, insulation layers of the preheating zone and cooling zone (furnace wall and furnace roof) of ceramic roller kilns/tunnel kilns, and insulation layers of regenerators of glass kilns.
Core Requirements: Cement kilns need to withstand high temperatures of 1000-1200℃ and reduce heat consumption; ceramic kilns need to avoid green body cracking caused by excessive temperature differences in the preheating zone, and the insulation layer must also have good stability.
Power and Thermal Energy Industry
Application Positions: Insulation layers of the furnace roof of boilers in thermal power plants, insulation layers of flue/chimney liners, insulation layers outside refractory bricks of industrial boilers, and high-temperature insulation sections of urban thermal pipelines (e.g., steam pipelines).
Core Requirements: Boilers need to block heat loss from high-temperature flue gas (to improve power generation efficiency); thermal pipelines need to reduce steam heat dissipation (to ensure transportation temperature); ultra-lightweight castables can be adapted to the arc structure of pipelines.
Chemical Industry and Other Fields
Application Positions: Insulation linings of chemical cracking furnaces, side insulation layers of non-ferrous metal smelting furnaces (e.g., aluminum electrolytic cells), and insulation layers of secondary combustion chambers of waste incinerators.
Core Requirements: Chemical furnaces need to withstand high temperatures of 1200-1400℃ and resist slight chemical erosion; waste incinerators need to prevent high-temperature flue gas from penetrating the furnace body and reduce the furnace weight at the same time.
Lightweight insulating castable refractories take “lightweight & energy-saving, flexible construction, and adaptability to complex scenarios” as their core advantages. Through the combination of different types of products (e.g., lightweight corundum-based castables for high-temperature zones and ultra-lightweight perlite-based castables for low-temperature zones), they can meet the insulation and light-load working needs in the temperature range from 800℃ to 1800℃. They are one of the key materials for modern high-temperature industries to achieve “weight reduction, energy conservation, and extension of equipment service life”. When selecting, three factors—service temperature, environmental erosion, and structural load—should be focused on to ensure that the material performance matches the application scenario accurately.
