Why tundish board quality decides your casting sequence length
In continuous casting, sequence length is treated as a caster KPI — the number of consecutive heats a tundish sustains before change-over. A longer sequence means fewer transitions, less scrap at strand start, more billets from the same crew, and better yield. Most sequence discussions focus on the SEN, slide gate and steel chemistry. The tundish working lining — the board itself — quietly shapes the ceiling of what is possible.
What the board actually has to do
The board is the insulating and disposable working face inside the permanent tundish lining. It has three simultaneous jobs: hold liquid steel without erosion, insulate to preserve superheat, and detach cleanly at end of cast. Every failure mode of a tundish over a long sequence traces back to one of these three.
Thickness variation is a superheat problem
A board specified at 20 mm that arrives at 18–22 mm across a pack does not just make installation awkward. It changes the local thermal conductivity of the tundish wall — meaning superheat loss varies from long wall to short wall to base. Caster operators compensate with tundish preheat and ladle superheat, but that compensation is a running cost. Boards produced under controlled vacuum forming with per-batch thickness checks eliminate this hidden variability.
Density drives service temperature margin
Vacuum-formed silica board density typically sits between 0.5 and 0.6 g/cc. Too low and the board slumps under prolonged 1550°C+ exposure — the classic 'saddle' at the tundish long wall by heat 8 or 9. Too high and thermal conductivity rises, superheat drops, and the caster runs colder. The right density is a narrow band and requires binder control most local suppliers do not maintain.
The moisture question
Boards absorb moisture in humid storage. A wet board fired straight into the tundish will spall — sometimes visibly at heat 1, sometimes as microstructural weakness that only shows at heat 6. Sequenced controlled drying at manufacture, moisture-barrier packaging, and a fixed 12-hour pre-installation acclimatisation are the three interventions that cost nothing and eliminate a category of failure.
What to specify
When you buy tundish boards, insist on: batch-level SiO₂ certification, bulk density (measured, not stated), thickness tolerance ± 1 mm, moisture at despatch, and a lot number cross-referenced to production date. If your supplier cannot provide these, sequence length is not their real bottleneck — traceability is.
The takeaway
Chasing a longer sequence is worthwhile. But before you push tundish life from 8 to 12 heats, check that your working lining is doing what its datasheet claims. Consistent boards buy you a full heat of sequence length in most plants — without any change to steelmaking practice.