Lightweight insulating refractory bricks are key materials in the field of thermal equipment. They combine low thermal conductivity and high-temp resistance, which can effectively reduce heat loss and lower equipment energy consumption.
I. Lightweight Fire Clay Insulating Refractory Bricks
Core Composition: Manufactured by using refractory fire clay as the main raw material, adding an appropriate amount of combustibles (sawdust, coal powder) or foaming agents, followed by forming and firing processes. Lightweight fire clay insulating refractory brick contains 30%-46% Al2O3 and ≤3.5% Fe2O3.
Performance Characteristics:
- Lightweight fire clay insulating refractory bricks have low bulk density (0.6-1.2g/cm3), with a thermal conductivity of only 0.2-0.6W/(m·K) (at 300℃). Their refractoriness ranges from 1580℃ to 1670℃, enabling long-term service at temps below 1200℃.
- They exhibit good thermal shock resistance (≥10 cycles of water cooling at 1100℃) and are less prone to cracking due to sudden temp changes.
- Lightweight fire clay insulating bricks feature strong processability and can be cut into special-shaped sizes as needed. Additionally, the raw materials are easily accessible, and the cost is only about 30% of that of high-alumina bricks, offering outstanding cost-effectiveness.
Main Applications: Lightweight fire clay insulating refractory bricks are suitable for the insulation layer of medium-low temp thermal equipment, such as the outer insulation layer of kiln walls in ceramic roller kilns and brick tunnel kilns, as well as the inner linings of flues and chimneys. They are also used in the outer insulation structure of industrial boilers and hot blast stoves, and as the wall insulation layer in high-temp workshops of the construction industry, preventing excessive ambient temp from affecting operational safety.
II. Lightweight High-Alumina Insulating Refractory Bricks
Core Composition: Lightweight high-alumina insulating refractory bricks are prepared using high-alumina bauxite (with Al2O3 content ≥60%) as the raw material, combined with ingredients such as kaolin and silica, through foam method or compression molding process. Their Al2O3 content is classified into three grades: 48%-55%, 55%-65%, and 65%-75%.
Performance Characteristics:
- The bulk density ranges from 0.8 to 1.5g/cm3, which increases slightly as the Al2O3 content rises.
- They have a refractoriness of 1580-1670℃ and a long-term service temp of 1200-1500℃, with good resistance to softening and deformation at high temps.
- The thermal conductivity is 0.3-0.8W/(m·K) (at 600℃), so their thermal insulation effect is better than that of ordinary high-alumina bricks. They also have strong resistance to acid corrosion (good tolerance to sulfuric acid and hydrochloric acid vapors), but their thermal shock resistance is slightly inferior to that of clay bricks (≥5 cycles of water cooling at 1100℃).
Main Applications: Lightweight high-alumina insulating refractory bricks are used for the insulation layer or transition layer of medium-high temp kilns, such as the top insulation layer of steel rolling heating furnaces and soaking pits in the metallurgical industry, the checkerwork of regenerators in glass kilns, and the inner linings of cracking furnaces and reformers in the chemical industry. In the aerospace field, they are also applied in the medium-temp insulation structure of satellite ground simulation equipment to balance the requirements for thermal insulation performance and high-temp resistance.
III. Lightweight silica Insulating Refractory Bricks
Core Composition: Lightweight silica insulating refractory bricks are made from quartz sand and flint (with SiO2 content ≥95%) as raw materials, with a small amount of lime and dolomite added as mineralizers, followed by high-temp sintering (1350-1450℃). Their SiO2 content is ≥93%, and the total content of impurities (Al2O3, Fe2O3) is ≤5%.
Performance Characteristics:
- lightweight silica insulating bricks have a bulk density of 0.9-1.3g/cm3 and a room-temp thermal conductivity of 0.25-0.7W/(m·K) (at 400℃), with thermal insulation efficiency close to that of clay bricks.
- Their refractoriness ranges from 1690℃ to 1730℃, and the long-term service temp is 1400-1550℃. They exhibit excellent dimensional stability at high temps (linear change rate ≤±0.5% after holding at 1500℃ for 2 hours) and are not prone to shrinkage or expansion.
- The material is highly brittle and has poor thermal shock resistance (only 2-3 cycles of water cooling at 1100℃). Additionally, it easily reacts with alkaline substances (Na2O, K2O) to form low-melting sodium silicate, which causes structural damage.
Main Applications: Lightweight silica insulating refractory bricks are suitable for high-temp equipment in acidic atmospheres or without alkaline erosion, such as the insulation layer of coke oven carbonization chamber walls in the coking industry and the outer insulation layer of glass tank furnace walls. They are also used as the inner lining of reverberatory furnaces in non-ferrous metal smelting (contact with alkaline slag should be avoided) and the insulation layer of high-temp laboratory electric furnaces, where their high-temp stability is utilized to ensure the accuracy of experimental temps.
IV. Lightweight Corundum Insulating Refractory Bricks
Core Composition: Lightweight corundum insulating refractory bricks are prepared using fused corundum and sintered corundum (with Al2O3 content ≥90%) as raw materials, via the sol-gel method or foaming method. Some products are added with Cr2O3 and ZrO2 to enhance performance, and their Al2O3 content is classified into three grades: 90%, 95%, and 99%.
Performance Characteristics:
- Lightweight corundum insulating refractory bricks have a bulk density of 1.0-1.8g/cm3, making them a type with relatively high density among lightweight bricks, but it is still only about 50% of that of ordinary corundum bricks.
- Their refractoriness is ≥1800℃, and the long-term service temp ranges from 1600℃ to 1800℃, enabling them to withstand ultra-high-temp scouring.
- The thermal conductivity is 0.4-1.0W/(m·K) (at 800℃), and they maintain good thermal insulation performance even in the ultra-high-temp range.
- Meanwhile, they possess extremely strong corrosion resistance (resistant to erosion by molten metals and glass melts) and high hardness (Mohs hardness ≥9). However, their production cost is high—5-8 times that of clay bricks—and they are difficult to process.
Main Applications: Lightweight corundum insulating refractory bricks are used in ultra-high-temp precision equipment, such as the working layer or insulation layer of induction furnaces and vacuum melting furnaces in the metallurgical industry, the inner lining of semiconductor silicon wafer sintering furnaces in the electronics industry, and the insulation structure of rocket engine exhaust deflector devices in the military industry. In laboratories, they are also used as the insulation layer of ultra-high-temp reaction kettles to meet the extreme temp requirements for the synthesis of special materials.
