High Alumina Insulating Brick

Lightweight high alumina insulating bricks combine an alumina-silicate body with a high-strength bond, producing a stronger brick at a given density than a conventional fireclay insulator. XZK supplies the LI140 series at 48% Al₂O₃ minimum, in bulk densities from 0.6 to 1.2 g/cm³, with thermal conductivity from 0.25 to 0.50 W/(m·K) at 350°C and cold crushing strength from 1.5 to 8.0 MPa. The strength at a given density is what allows the brick to be used where insulation must also carry load or hang.

XZK Group manufactures grades XZK-LI140-1.2, LI140-1.0, LI140-0.8 and LI135-0.6 at our Xinmi plant in Henan. Their most important glass furnace duties are the tank bottom insulation layer, where the block carries the structure above it, and the doghouse suspended wall, where the lining hangs from anchors.

What Is a High Alumina Insulating Brick?

The body is an alumina-silicate insulating brick in which the aggregate is a mullite or high-alumina grog rather than a plain fireclay. All four LI grades carry the same 48% minimum Al₂O₃; unlike a graded family in which chemistry and density both change, the chemistry here is held constant and only the density, and therefore the strength and conductivity, vary. That simplifies selection considerably, because the question becomes simply how much load the position imposes and how much insulation it needs.

Manufacture follows the same route as other lightweight firebrick: graded lightweight aggregate, a plasticiser and a pore-forming addition are batched, formed and fired slowly enough that the aggregate does not collapse. The alumina content of the grog is what lifts refractoriness above that of a fireclay insulator, and the bond system is formulated to develop strength at the low densities involved, which is the harder technical problem. Getting 8 MPa out of a 1.2 g/cm³ brick requires the bond to bridge between aggregate particles across the pore space rather than simply fill it.

The design consequence is that this material can be specified in positions that would otherwise force a heavier, denser, poorer-insulating brick. A tank bottom insulation course sits under several metres of paving, structural and glass load; an ordinary 0.8 g/cm³ clay insulator would crush under that. The LI140 series carries the same insulation duty with enough cold crushing strength to survive the compressive stress, so the bottom can be insulated more aggressively and less heat is lost downward.

The trade-off is the familiar one, but shifted upward. LI140-1.2 delivers 8.0 MPa at a conductivity of 0.50 W/(m·K); LI135-0.6 delivers only 1.5 MPa but conducts just 0.25 W/(m·K). Positions that carry the structural load take the dense grade; positions that merely close the stack take the light one.

Key Properties

• Alumina content ≥ 48% in every grade, higher than a fireclay insulator, which raises refractoriness and flue-gas resistance without changing between grades.
• Bulk density from ≤ 0.6 to ≤ 1.2 g/cm³, so an insulation course can be matched to the load it carries rather than specified at one fixed weight.
• Cold crushing strength from ≥ 1.5 MPa (LI135-0.6) to ≥ 8.0 MPa (LI140-1.2), the highest strength-to-density ratio in the ZZK insulation family — the reason this brick is used at the tank bottom and on hanging walls.
• Thermal conductivity from ≤ 0.25 to ≤ 0.50 W/(m·K) measured at 350 ± 25°C, giving predictable shell temperatures across the whole density range.
• Volume stability under sustained compression, which a green strength figure alone does not show and which matters under a full tank bottom.
• Clean alumina-silicate chemistry with no free silica phase to react with alkali condensates in the lower regenerator and bottom structures.