Blast Furnace Ceramic Cup — Corundum Barrier for the Hearth

The ceramic cup is a high-purity corundum barrier installed inside the carbon hearth of a blast furnace. Its job is specific and time-critical: protect the carbon during start-up and through the early campaign, when the carbon is most vulnerable.

Why Start-Up Is the Danger Window

Before a hearth has established its thermal profile and built a frozen lining, the carbon is directly exposed to alkali, zinc and molten iron. Once the campaign is running and the isotherm has moved inward, the carbon is largely protected by the solidified iron layer and by its own thermal behaviour. The window before that happens is where most early hearth damage occurs — and it is exactly the window the ceramic cup covers.

Two Materials, Two Jobs

It is worth being precise about this, because the two materials are frequently confused as alternatives:

• Ceramic cup — a chemical and start-up barrier. High-purity corundum, resistant to alkali and zinc, load-bearing at temperature.
• Microporous carbon — the thermal conductor. Moves heat to the cooling system so the 1150 °C isotherm stays inside the lining.

Neither does the other’s job. A hearth with a cup but poor carbon will overheat; a hearth with good carbon but no cup will take avoidable damage in its first months. Modern long-campaign designs specify both.

Composition and Properties

XZK ceramic cup material is specified at Al₂O₃ ≥88% with SiO₂ ≤10% and Fe₂O₃ held to 0.5%. The low iron matters: iron oxide combines with alkali and slag components to form low-melting phases at the hot face, and a barrier that forms those phases stops being a barrier. Bulk density ≥3.00 g/cm³ with porosity ≤18% and crushing strength ≥80 MPa gives the density and mechanical reserve to resist penetration, and RUL ≥1700 °C keeps it load-bearing at hearth temperature.

Joints Are Where Barriers Fail

A ceramic cup is a barrier only if it is continuous. Open or inconsistent joints let alkali and iron travel straight through, which is why block machining and installation sequence matter as much as the material itself. Blocks are individually machined to the furnace drawing and numbered, so that joint gaps are controlled and the ring closes as designed.

Supply

Quoted as part of a complete hearth package, typically 35–60 days including machining, numbering and dry trial-fitting. Density, porosity, crushing strength, RUL and chemistry are tested per batch with a Certificate of Analysis on every shipment. Send your furnace drawing, cooling configuration and campaign history for a complete zonal hearth proposal.

Where This Grade Sits in the Lining System

Silicon carbide and carbon grades are selected for what they do with heat rather than for what they resist. Thermal conductivity decides whether the cooling system ever sees the load, and the bonding system decides how long the material survives alkali attack and oxidation once it does.

XZK supplies ceramic cup as one zone of a zoned package rather than as a standalone item: the grades normally zoned alongside it — among them microporous carbon brick — are documented on the silicon carbide and carbon 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 page.

The MMK Magnitogorsk No.10 BF and 375 t ladle programme reference documents how this class of material performed in full service, with the measured campaign figures rather than datasheet values.