By Jack Xing, Technical Sales Director, YK Chanshine · Continuous Casting Refractories · Updated
A tundish lining decides three things at once. It decides how clean your steel stays between ladle and mold. It decides how long your sequence can run before the tundish has to come off the car. And it decides how much gas, labor and turnaround time your prep bay spends between casts.
Most continuous casting shops use one of three working-lining systems: insulation boards, spray / trowel coatings, or a dry vibration mix. This guide compares their chemistry, operating trade-offs, binder choices and installation discipline, with typical TDS ranges and a checklist for quoting.
Key points from this guide:
- Dry vibration mix delivers the longest sequence life (20 to 60+ hours) and cleanest steel because it brings zero free water and forms a dense hot face with an insulating backing.
- Insulation boards require no pre-heat equipment and deskull easily, but silica boards can react with Al-killed steel, causing inclusion defects.
- Spray coatings sit between the two on material cost, but require long, high-temperature gas baking (800–1000 °C) to drive out water.
- Ultra-low-carbon and hydrogen-sensitive grades require inorganic binders (polyphosphate, sodium silicate, or boric acid) to eliminate carbon and hydrogen pickup.
At a glance: board vs. coating vs. dry vibration mix
| Question | Board | Spray / trowel coating | Dry vibration mix |
|---|---|---|---|
| Water in the system | None | High | None |
| Pre-heat | Cold start possible | 800–1000 °C, 2–6 h | 200–300 °C, 45–90 min (or quick-heat) |
| Strongest point | Fast, easy tear-out | Low cost to apply, good insulation | Long life, dense hot face, clean steel |
| Main risk | Si, H or strength problems, depending on type | Water attack, H and O pick-up, spalling | Needs former and discipline |
| Typical life | Short sequences | Longer than board | 20 h+, 60–70 h reported |
The tundish lining: zones and layers
A continuous casting tundish has several refractory zones, each with its own role:
- Insulating layer: sits against the steel shell (calcium silicate board or ceramic fiber) to protect the shell from overheating.
- Permanent (safety) lining: high-alumina bricks or low-cement castable that remains in place for months.
- Working lining: the replaceable layer (board, spray or dry mix) in direct contact with molten steel and tundish slag.
- Flow control furniture: impact pad, weirs, dams and turbulence inhibitors that govern residence time and inclusion flotation.
Insulation boards
Tundish boards are pre-formed panels wedged or mortared against the permanent lining. They allow cold starts and very fast deskulling, making them popular for small billet casters running short sequences.
| Board | Best for | How it performs | Watch-out |
|---|---|---|---|
| Silica board | Plain carbon & rebar | Low cost, easy install | SiO₂ reduces in Al-killed steel, causing inclusions |
| Magnesia board | Clean & alloy steel | High basicity, low reaction | Needs careful storage to avoid hydration |
| Forsterite board | Intermediate grades | Balanced thermal expansion | Lower refractoriness than pure MgO |
Spray and trowel coatings
Coating mixes are applied with robotic spray arms or trowels. While cheaper per ton than dry mix, they introduce 15% to 25% water that must be completely removed by gas baking:
| Parameter | Typical range | Impact on caster |
|---|---|---|
| Water addition | 18–25% (spray) / 14–18% (trowel) | High hydrogen risk if pre-heat is shortened |
| Bake-out cycle | 800–1000 °C for 2–6 hours | Consumes significant fuel gas in prep bay |
| Rebound loss | 5–12% during application | Material waste during spraying |
Dry vibration mix
Dry vibration mixes (MgO 80% to 92%) represent the current standard for clean steel and high-productivity sequence casting. Because they are installed completely dry around a heated former, there is no water to drive off.
| Binder type | Common materials | Advantages | Limitations |
|---|---|---|---|
| Organic | Phenolic resin, novolac, pitch | High green strength after bake at 200–250 °C | Emits smoke/fumes during cure; adds C and H |
| Inorganic | Polyphosphate, solid sodium silicate, boric acid | Zero smoke, zero carbon/hydrogen pick-up | Requires strict former temperature control |
Typical TDS specifications for dry vibration mix
| Parameter | Standard grade (billet) | High-purity grade (slab / clean steel) |
|---|---|---|
| MgO content (%) | 82.0–85.0% | 88.0–92.0% |
| SiO₂ content (%) | ≤ 5.5% | ≤ 3.0% |
| CaO content (%) | ≤ 3.0% | ≤ 2.2% |
| Bulk density (g/cm³) | 2.10–2.25 | 2.25–2.40 |
| Cold crushing strength (after cure 250 °C) | ≥ 4.0 MPa | ≥ 5.0 MPa |
| Cold crushing strength (after firing 1500 °C) | ≥ 18.0 MPa | ≥ 25.0 MPa |
Tundish furniture & flow modifiers
Precast dams, weirs, and turbostops work in tandem with the dry vibration mix to optimize fluid flow, extend residence time, and prevent short-circuiting to the metering nozzle.
| Shape | Location | Main function |
|---|---|---|
| Turbostop / impact pad | Directly below ladle shroud | Dissipates kinetic stream energy, prevents slag vortexing |
| Weir | Between pouring & casting zones | Forces steel flow downward, retains top slag |
| Dam | Ahead of strand nozzle | Forces steel flow upward to promote inclusion float-out |
Decision guide: choosing the right lining for your caster
| Caster type | Steel grades | Recommended working lining |
|---|---|---|
| Small billet caster (short sequences < 4 heats) | Rebar, merchant bar | Silica or low-MgO insulation board |
| Medium billet / bloom caster (4–12 heats) | Structural, SBQ carbon | MgO spray coating or 82% MgO dry mix |
| High-production slab caster (10–30+ heats) | Deep drawing, IF steel, API linepipe | High-purity MgO dry vibration mix (88–92% MgO) |
| Ultra-low-carbon / bearing steel caster | 100Cr6, tyre cord, ULC | Inorganic-bonded high-purity MgO dry mix |
Frequently Asked Questions (FAQ): Tundish Working Lining Systems
What is the difference between a tundish dry vibration mix and a coating?
A coating is mixed with water and applied wet, so it needs a long bake at 800–1000 °C. A dry vibration mix is placed dry, vibrated around a former and cured at only 200–300 °C, so it brings no free water into the lining.
How long does a tundish dry vibration mix last?
Typically 20 casting hours or more. High-end results of 60–70 h are reported. Actual life depends on steel grade, slag, temperature and installation quality.
Can I use silica board for Al-killed steel?
It is not recommended. Al and Mn in the steel reduce the SiO₂ in the board, forming Al₂O₃ and 2MnO·SiO₂ that add oxide inclusions.
Which binder is best for ultra-low-carbon steel?
An inorganic binder such as polyphosphate, solid sodium silicate or boric acid. It adds no carbon or hydrogen and gives off no irritating fumes during cure.
What temperature do I cure a tundish dry mix at?
Heat the former to 200–300 °C for 1–2 h, strip it, then fire for about 1 h to above 1000 °C before use. Always follow the supplier’s own guide.
Why do tundish dams and weirs use magnesia?
Magnesia keeps its strength in steel, costs less than alumina-magnesia, and absorbs Al₂O₃ inclusions to form a spinel skin. It is also reported to carry about 80% less oxygen into the steel than high-alumina furniture.
Why add α-Al₂O₃ and silica microfines to a dam castable?
Alumina microfines react with MgO to form spinel with about 8% expansion, which densifies the matrix. Silica microfines reduce hydration and cracking but create low-melting phases, so they are kept at about 2% or below.
What should I send to get a tundish lining quotation?
Capacity, strand count, steel grades, sequence length, slag data, current lining and failure mode, binder restrictions, quantity and port. We reply with a grade recommendation and the TDS.
Send Us Your Continuous Caster Parameters & Sequence Targets
Looking to extend sequence casting hours, reduce turnaround downtime, or eliminate hydrogen/oxygen pick-up in clean steel? Send us your caster format (billet/bloom/slab), steel grades, sequence length, and current lining life. We provide custom dry mix / board recommendations, TDS, and cost comparisons within 24 to 48 hours.