Lightweight High-Alumina Insulating Brick (LI Series) for Furnace Backup

Lightweight high-alumina insulating brick is the general-duty workhorse of furnace backup linings. At 48% Al₂O₃ across four densities from 0.6 to 1.2 g/cm³, it covers the great majority of insulation duty — and it does so at a cost that mullite insulation cannot match below about 1350 °C.

Use the Cheaper Grade Where It Works

Most furnace backup never reaches the temperature at which mullite becomes necessary. Specifying mullite throughout a backup lining is one of the more common ways insulation budgets get inflated: the premium buys temperature capability that most of the lining will never use.

The correct design is usually graded by depth and temperature — high-alumina insulation through the bulk of the backup, mullite only in the hottest courses where dimensional stability genuinely matters.

Reading the Density Range

• XZK-LI140-1.2 — 1.2 g/cm³, CCS ≥8.0 MPa, conductivity ≤0.50 W/(m·K). Nearest the working lining, where incidental load is possible.
• XZK-LI140-1.0 — 1.0 g/cm³, CCS ≥3.0 MPa, ≤0.40 W/(m·K). Mid backup.
• XZK-LI140-0.8 — 0.8 g/cm³, CCS ≥2.5 MPa, ≤0.35 W/(m·K). Mid to outer backup.
• XZK-LI135-0.6 — 0.6 g/cm³, CCS ≥1.5 MPa, ≤0.25 W/(m·K). Near the shell, pure insulation.

Note how strength falls with density. That is the trade you are managing: strength where load is possible, insulation where it is not.

What It Is Not

Insulating brick is not a working lining. High porosity and low strength mean slag, abrasion and dust-laden gas destroy it quickly. It belongs behind the working lining, and its job is thermal resistance and shell protection — nothing else. Where a zone is exposed, dense refractory is the answer, not denser insulation.

Two Practical Failure Modes

First, moisture: saturated insulation loses strength and can spall on first heat-up, and that failure is routinely blamed on the product. Store dry and under cover. Second, mechanical damage: insulating brick is fragile, and damage in transit or from site traffic is the most common reason an insulation layer underperforms. Low-density grades are crated rather than palletised, and traffic over installed insulation should be avoided.

Supply

Minimum order 10 metric tons for standard shapes and 20 metric tons for cut-to-fit work, 20–35 days where cutting is involved. Density, crushing strength, thermal conductivity, permanent linear change, classification temperature and chemistry are tested per batch with a Certificate of Analysis on every shipment.

Where This Grade Sits in the Lining System

Insulating grades are specified backwards, from the shell temperature or the fuel figure you need to hit, and then checked against the mechanical load the backup lining actually carries. Picking a density out of a catalogue is the usual reason insulation underperforms its own datasheet.

XZK supplies high-alumina insulating brick as one zone of a zoned package rather than as a standalone item: the grades normally zoned alongside it — among them mullite insulating brick — are documented on the insulating refractories page, and the vessel-level architecture — where each zone starts and ends, and which mechanism actually limits the campaign — is set out on the blast furnace and hot blast stove pages.

Campaign data measured on this class of lining — including the wear profile that drove grade selection — is published in the MMK Magnitogorsk No.10 BF and 375 t ladle programme project reference.