The bath line: why the boundary between melt and air is the most critical zone

When an aluminium furnace fails, it almost always starts at the same narrow line: where the melt meets the air. The bath line is rarely more than a hand's breadth high — and is nevertheless the most demanding zone in the entire furnace.

The reason lies in the chemistry. At the bath line, liquid aluminium, oxygen and refractory material all come together. At this three-phase boundary, oxidation and corundum growth attack most aggressively — this is where the corundum noses form that narrow the furnace cross-section.

Three points that determine service life

• Non-wetting, corundum-resistant materials — placed specifically in the band that is actually loaded. The highest material quality where it makes the difference.
• The bath line is not a fixed line: the metal level moves with every charge and every tap. That is why we deliberately extend the high-grade zone 20 to 30 cm above and below the nominal level.
• A dense, monolithic surface with joints kept to a minimum. Every joint at the bath line is a starting point for infiltration and growing corundum.