Magnesia-Alumina-Carbon Spinel Brick (MAC) for Ladle Transition Zones

Magnesia-alumina-carbon brick (MAC) exists to solve a problem that most lining drawings ignore: the boundary between two different materials. Put a MgO-C slag line directly against an AMC barrel and you create a discontinuity in thermal expansion, slag behaviour and wear rate. In service that boundary becomes a groove, and the groove — not the slag line — decides when the ladle comes down.

What Actually Happens at a Grade Boundary

Three mechanisms combine. First, the two materials expand by different amounts, so the joint between them opens and closes more than joints within a single grade. Second, they dissolve into slag at different rates, so a physical step forms. Third, once a step exists, it changes the local flow of steel and slag, which accelerates wear right at that point. The result is a self-reinforcing groove.

MAC interrupts this. With 52–54% MgO it stays close enough to the slag line in slag behaviour, while its 25% alumina keeps it spinel-forming and expansive like the barrel below. The property gradient becomes gradual instead of abrupt, and the groove does not establish itself.

Specification Guidance

• Course count — one to three courses is typical; we usually start with two and refine after reviewing your wear profile.
• Porosity control — MAC is held to 4.0–4.5% apparent porosity, lower than the adjacent AMC grades, because the boundary is where penetration starts once a step forms.
• Mortar consistency — use the same mortar and joint thickness across the transition; a change in joint behaviour reintroduces the discontinuity you are trying to remove.
• Where it is not needed — if your slag line and barrel already reach end of life together, or if a carbon-free castable working lining runs the full height, MAC adds little.

MAC, AMC and MgO-C at a Glance

• MgO-C — 72–89% MgO, 4–19% C. Maximum slag corrosion resistance. Slag line and metal zone.
• MAC — 52–54% MgO, ~25% Al₂O₃, 11% C. Spinel-forming, magnesia-dominant. Transition courses and upper barrel.
• AMC — ~25% MgO, 50–55% Al₂O₃, 11% C. Spinel-forming, alumina-dominant, maximum expansion. Barrel and bottom.

Read as a gradient, the three grades let you step smoothly from a corrosion-resistant slag line to an expansive, joint-sealing barrel — which is the whole point of zonal lining design.

Quality and Supply

XZK MAC bricks are pressed on 2,000-ton class CNC hydraulic presses and tempered under controlled atmosphere, with apparent porosity and crushing strength verified per batch per ASTM C830 and C133. Every shipment carries a Certificate of Analysis, and transition courses can be pre-sorted and labelled by course to speed installation. Send your ladle drawing for a zone-by-zone grade map within 48 hours.

Where This Grade Sits in the Lining System

Carbon-bonded basic grades are never specified in isolation. Carbon level, antioxidant package and bulk density are all set by the zone, and the zone map is set by the vessel — which is why a grade that performs well in one position can fail early in the next.

XZK supplies magnesia-alumina spinel brick as one zone of a zoned package rather than as a standalone item: the grades normally zoned alongside it — among them magnesia carbon brick — are documented on the magnesia-carbon and basic 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 steel ladle and RH/VD page.

Campaign data measured on this class of lining — including the wear profile that drove grade selection — is published in the JFE Steel RH degasser snorkel and ladle flow control programme project reference.