High alumina castables are dry refractory mixes that are combined with water on site, cast into formwork and vibrated into place, then dried and sintered in service. The body is built from a graded high-alumina aggregate held in a calcium aluminate cement bond, with Al2O3 from roughly 60% in...
High alumina castables are dry refractory mixes that are combined with water on site, cast into formwork and vibrated into place, then dried and sintered in service. The body is built from a graded high-alumina aggregate held in a calcium aluminate cement bond, with Al2O3 from roughly 60% in general-purpose grades to 85% and above where tabular or fused alumina is used. They exist to line the positions a brick cannot follow: throat openings, burner block surrounds and other contoured geometry.
XZK Group supplies high alumina castables as bagged dry mixes that need only clean water at the mixer, which keeps site work simple and the lining continuous across a whole section.
The material is a particle-size distribution rather than a single grain. Coarse high-alumina aggregate forms a load-bearing skeleton, a fines fraction fills the voids between the coarse particles, and a calcium aluminate cement bonds the two together. General-purpose grades are based on calcined bauxite and carry around 60–70% Al2O3; high-duty grades use tabular or fused alumina and reach 80–85% and above with Fe2O3 held below 1%. Cement content is the other design lever: conventional castables contain 15–20% cement, low-cement castables 5–8%, and ultra-low-cement castables 2–4% with silica fume and dispersants replacing part of the cement. Less cement means higher refractoriness and hot strength, but tighter control of mixing water and a slower heat-up.
Placement follows a fixed sequence: mix with a measured water addition, cast into formwork, consolidate with a poker vibrator until entrapped air stops rising, cure, then dry and fire on a controlled schedule. The dry-out schedule is the single largest determinant of service life. Free water in a castable turns to steam faster than a dense matrix can vent it, and heating too quickly causes explosive spalling that the material never recovers from. Vent holes and a staged ramp below 600°C are normal practice.
Performance in service depends on what happens after firing. The cement phases react with the fines to form a ceramic bond, and in high-alumina bodies mullite grows in the matrix; that in-situ bonding is what gives the lining its hot strength and volume stability. A well-graded aggregate built for packing rather than cement content reaches higher density at the same water addition, which lowers porosity and slows penetration by alkali vapour and glass. Grade selection is therefore about the aggregate system first and the cement level second.
| Item/Grade | GLJ-50 | GLJ-60 | GLJ-65 | GLJ-70 | GLJ-80 | |
| ω (Al2O3) ≥/% | 50 | 60 | 65 | 70 | 80 | |
| Refractoriness ≥/℃ | 1700 | 1720 | 1720 | 1720 | 1780 | |
| Bulk Density ≥/ (g/cm³) | 110℃*24h | 2.15 | 2.30 | 2.40 | 2.45 | 2.65 |
| Cold Modulus of Rupture ≥/MPa | 4.0 | 5.0 | 6.0 | 6.0 | 7.0 | |
| Cold Crushing Strength ≥/Mpa | 25 | 30 | 35 | 35 | 40 | |
| Permanent Linear Change (T/℃*3h)/% | ±0.8 (1350℃) | ±0.8 (1400℃) | ±0.8 (1500℃) | |||
The range divides by aggregate quality and cement level rather than by a single number. A conventional cement-bonded bauxite castable covers general lining, backing and levelling work where temperature stays below roughly 1400°C and the mechanical load is modest. A low-cement bauxite or tabular alumina castable moves the ceiling toward 1500°C with better hot strength, and is the usual choice for burner block surrounds and other load-bearing hot faces. An ultra-low-cement tabular alumina castable is reserved for the most demanding positions and for castings that must hold volume across repeated thermal cycles.
Choose by the duty, not by the highest figure available. Match the alumina level and cement content to the working temperature, the chemical exposure and the mechanical load, and specify the water addition and dry-out schedule with the order. Over-specifying a high-purity castable where a bauxite grade would do adds cost without extending life, while under-specifying in a load-bearing hot face shortens the campaign.
Where a castable is used only as backing insulation it shares the lining with insulating castable; where abrasion dominates it gives way to silicon carbide castable; and where insulation is needed at higher temperature than an insulating castable can take, lightweight mullite castable is the better match.
In a glass furnace, high alumina castable is specified where the lining must be continuous, shaped to a contour, or reinstated quickly:
Manufacturing is controlled from raw material through to finished brick. Four automatic batching lines feed 20 CNC presses ranging from 630 to 2000 tonnes, so density is set by press force rather than operator judgement, and firing runs through four 108-metre fully automatic tunnel kilns and five ultra-high-temperature shuttle kilns for a uniform soak.
Every batch is tested for bulk density, apparent porosity, cold crushing strength and refractoriness under load, and ships with a certificate of analysis. XZK Group holds ISO 9001, ISO 14001, ISO 45001 and ISO 50001 certification and operates the Henan Provincial Engineering Technology Research Center for Sintered Refractories for Glass Furnaces.
High alumina castables are supplied as part of a complete monolithic refractory package alongside insulating castable, silicon carbide castable, lightweight mullite castable, ZKM series refractory mortar and refractory cement. Browse all refractory products for the full range.
Al₂O₃:46%-60%;
Fe₂O₃: 0.7%-1.0%;
Operating Temp:1300-1500℃;
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