In a continuous casting line, the casting ladle and the casting ladle are not interchangeable: the ladle is a batch vessel (typically 50–300 t steel capacity) that carries molten metal from secondary metallurgy to the caster turret, while the tundish is a smaller, continuously-fed buffer/distributor (commonly 10–60 t working capacity) that sits between the ladle and the casting mold and decouples the two rhythms [S1][S3].
The split exists because steelmaking is a batch process and continuous casting is a steady-state process: the ladle empties in 30–60 minutes per heat, whereas the strand must run for hours. The tundish absorbs that mismatch, and the industry now runs more than 90% of the world's steel through this ladle-tundish-mold chain [S4].
Position in the Line and Primary Purpose
The casting ladle sits on a rotating turret at the top of the caster, with one position "on-cast" and the other "off-cast" so a fresh ladle can be swung in without stopping the strand [S3]. Its job is transfer, alloy trim, and temperature/top-slag conditioning at the ladle furnace station, then controlled teeming into the tundish through a refractory shroud and a stopper or slide-gate nozzle [S3].
The tundish sits one stage below the ladle, receives the ladle stream, and feeds one or more molds through submerged entry nozzles (SEN) or metering nozzles [S1][S3]. It is the last metallurgical vessel before solidification begins, and on multi-strand slab or billet casters it physically splits one ladle stream into 2, 4, 6, or 8 mold streams [S5].
Function-by-Function Comparison
On the criterion "rhythm role," the ladle runs batch mode (one heat per ladle, drained in 30–60 minutes), while the tundish runs semi-continuous and must hold enough heel to keep the SEN fed during the full ladle-swap window, typically 3–8 minutes per change [S1][S4].
On "metallurgical role," the ladle handles bulk secondary metallurgy (alloying, desulfurization, vacuum degassing, inclusion modification, temperature trim) before the strand starts, while the tundish handles only final-stage cleanup: floating out re-oxidized inclusions, homogenizing temperature (target spread typically held to within 5°C above the liquidus), and absorbing ladle-slag carryover [S1][S5].
On "flow-control role," the ladle regulates only its own discharge (stopper rod, slide gate, or porous plug), while the tundish regulates mold-level stability through a constant liquid-steel head maintained above the nozzles, plus flow modifiers (baffles, weirs, dams, impact pads, turbulence inhibitors, dams-and-strainers) that extend residence time and force inclusions upward [S1][S3].
On "refractory regime," the ladle is a permanent-lined vessel relined on a campaign cycle of hundreds of heats with magnesia-carbon or doloma working linings, while the tundish usually uses a disposable "tundish board" working lining (MgO or MgO-based boards plus dry-vibratable or sprayable back-up) that is stripped after each sequence [S1][S3].
On "sequence length," the ladle governs the heat-to-heat interval, while the tundish governs the cast-sequence length (typically 6–12 ladles per sequence on a slab caster, limited by tundish refractory wear and steel cleanliness drift) [S1][S4].
Operational Limits and Failure Modes
The ladle-side failure mode is mainly ladle-nozzle clogging (alumina build-up after aluminum trim) and slag entrainment on ladle change, both of which can spike SEN clogging on the tundish side downstream [S1]. The ladle also has strict dry-out and preheat rules, since cold-ladle teeming drops tundish superheat and risks skulling the impact pad [S6].
The tundish-side failure modes are tundish-skeleton (skull) growth, slag-eye opening during ladle change, and SEN alumina clogging; skulls are removed mechanically (scraping, cutting) and the recovered metal is recycled back to steelmaking [S1]. A multi-strand caster that loses one tundish nozzle effectively halves productivity, which is why tundish flow control (dams, weirs, baffles, argon bubbling, ceramic filters) is treated as a process-critical design variable rather than a refractory detail [S1][S5].
Typical operating ceilings: ladle superheat at tap is held 20–40°C above liquidus at the tundish, and the tundish itself is normally kept within 5°C top-to-bottom to keep centerline segregation in check on the strand [S5].
Standards, Equipment, and Engineering Reference
There is no single ISO or API standard that hard-specs "ladle" versus "tundish" geometries; the engineering reference sits in equipment-supplier datasheets (ladle turret, tundish car, tundish preheater, ladle preheater), OEM process manuals, and refractory-supplier application notes, e.g. magnesia-based tundish boards and MgO-C ladle bricks for clean-steel grades [S1][S2].
On "thermal prep," the two vessels use different preheaters sized to their mass: a ladle preheater runs higher duty and longer cycles (gas-fired or regenerative, often reaching 1000–1200°C or higher in the working lining zone) to drive bound moisture out of the thick MgO-C working lining, while a tundish preheater runs lower hood preheat (typically 600–1000°C over 60–120 minutes) because tundish boards are thinner and the sequence starts from a colder state [S6]. Cross-using the two preheaters risks either ladle explosion from trapped moisture or tundish thermal-shock spalling of the disposable board.
For a deeper dive into how a related ladle variant (teapot vs bottom-pour) changes the upstream interface feeding the tundish, see Teapot Ladle vs Bottom-Pour Ladle in Steel Casting.
Selection Rules: Who the Ladle Is For, Who the Tundish Is For
The casting ladle is the right vessel for batch transport from EAF/BOF to caster, for ladle-furnace metallurgical trim, and for storage of one heat (50–300 t) at the caster top; it is the wrong vessel for steady-state flow distribution or for holding metal across a ladle swap [S3].
The tundish is the right vessel for flow smoothing, multi-strand splitting, sequence-level metallurgy (final inclusion float-out, temperature trim ±5°C), and ladle-swap continuity; it is the wrong vessel for bulk alloy trim or vacuum degassing, both of which belong upstream in the ladle furnace or RH/VD station [S1][S3][S5].
Trackable signals to watch on the next casting sequence: tundish SEN clogging rate (target typically below 1–2 clog events per sequence on clean-steel grades) and tundish superheat at first ladle versus last ladle (drift should stay within the 5°C band cited above) [S1][S5].