Tundish Turbostop Design: What CFD and Microstructure Tell Us About Oxygen Control and Service Life
By Jack Xing, Technical Sales Director, YK Chanshine · Published November 1, 2026 · 15 min read
The Engineering Problem: Where Oxygen Enters Between Ladle and Mould
Clean steel is made in the furnace and refined in the ladle. The tundish can protect that steel or it can reoxidize it. Every mill that casts special bar quality (SBQ), tyre cord, bearing steel, high-carbon wire rod or sour-service linepipe tracks total oxygen (T.O.) down to single-digit parts per million (ppm). A ladle heat that arrives at 12 ppm total oxygen can leave the tundish at 25 ppm if the stream opens the slag, if the shroud draws air, or if the steel washes against an unstable refractory.
Total oxygen is the sum of dissolved oxygen and oxygen tied up in oxide inclusions: Total O = [O]dissolved + Oin inclusions. Dissolved oxygen is set by the deoxidation equilibrium (with aluminium, silicon or manganese). Oxygen in inclusions is the number that follows the steel into the slab.
Four entry points for oxygen in the tundish
| Entry point | Mechanism | Typical ppm pickup | Furniture that helps |
|---|---|---|---|
| 1. Ladle-to-tundish stream aspiration | Air drawn into joint between collector nozzle and shroud; cracked shroud; poor argon sealing | 5 to 20 ppm | Argon-sealed ladle shroud, tight joint gasket |
| 2. Open eye in the tundish slag | Rising stream pushes covering slag away, exposing liquid steel directly to air | 8 to 25 ppm | Turbostop / turbulence inhibitor cup |
| 3. Slag and refractory reaction | Dissolved [Al] reduces FeO and MnO in slag or silica in furniture / working lining | 2 to 8 ppm | Low-silica furniture, basic flux, MgO dry mix |
| 4. Vortexing and slag carry-over at drain | Funnel vortex draws covering slag into the mould nozzle during ladle changes or drain | 10 to 40 ppm (spike) | Anti-vortex nozzle well block, minimum level rule |
Notice that entry points 2 and 4 are directly linked to fluid flow inside the tundish. A well-designed furniture set addresses both. If you only look at brick chemistry and ignore how the steel moves, you miss the largest oxygen source during steady casting.
What CFD Tells You (and What It Hides)
Computational Fluid Dynamics (CFD) is the standard tool for tundish design. Every supplier uses it to show pretty colour contours. But a buyer or plant engineer needs to know which numbers matter and which assumptions are weak.
Three numbers to demand from any CFD report
- Minimum residence time (t_min): The time from when steel enters the tundish until the very first tracer reaches any mould nozzle. In a bare tundish, t_min can be as low as 15 to 30 seconds (short-circuiting). A properly designed turbostop + weir + dam should push t_min above 60 seconds, and in many large tundishes above 120 seconds. If steel reaches the mould in 20 seconds, large inclusions (50 to 100 μm) do not have time to rise to the slag.
- Dead volume fraction (V_d): The percentage of tundish volume where steel moves slower than a critical velocity (typically < 0.005 m/s). Dead volume cools, forms crusts, and reduces the effective volume of your tundish. A good furniture set drops dead volume from 30–40% (bare) down to 10–18%.
- Maximum surface velocity at the slag line: If surface velocity near the ladle shroud exceeds roughly 0.15 to 0.20 m/s, the steel shear stress overcomes the slag layer and opens a "slag eye". Once an open eye appears, steel absorbs nitrogen and oxygen from the atmosphere at rates up to 1 ppm [N] per minute. A turbostop keeps surface velocity near the stream below 0.10 m/s.
| Configuration | Minimum residence time (t_min) | Peak residence time (t_peak) | Dead volume fraction (V_d) | Slag eye risk near shroud |
|---|---|---|---|---|
| Bare tundish (flat impact pad only) | 18 to 35 seconds | 80 to 140 seconds | 32 to 45% | High (frequent open eye) |
| Turbostop alone (no weir or dam) | 40 to 65 seconds | 150 to 220 seconds | 20 to 28% | Low (contained energy) |
| Full set: Turbostop + Weir + Dam | 70 to 130 seconds | 240 to 360 seconds | 10 to 18% | Very low (calm surface across bath) |
Flow Control Geometry: Turbostop, Dam, Weir and Seat Block
Tundish flow modifiers are not separate items bought from different catalogues; they are an integrated hydraulic system. Changing one piece without adjusting the others alters the flow pattern.
Function and design parameters of each element
| Element | Primary hydraulic function | Key dimensions to check on drawing | Main wear mechanism |
|---|---|---|---|
| Turbostop (Turbulence Inhibitor) | Dissipates kinetic energy of ladle stream; rolls flow inward; prevents open eye | Internal cavity depth, lip overhang angle, base thickness under stream | Thermal shock at first fill, hot erosion at impingement centre, lip slag corrosion |
| Weir (Baffle with bottom gap / top wall) | Forces steel downward or keeps slag in the pour chamber; prevents short-circuiting across surface | Submersion depth, underflow clearance area, thickness for mechanical strength | Slag-line cutting at both faces, bending stress from steel level variations |
| Dam (Bottom wall with or without holes) | Forces steel upward toward the covering slag so inclusions can be absorbed; eliminates bottom dead zone | Height relative to bath depth (typically 25–40%), hole angles if castellated/perforated | Hole erosion / enlargement, thermal bending, mechanical impact during deskulling |
| Nozzle Seat Block / Well Block | Locates inner nozzle or metering nozzle; prevents vortexing during transition and drain | Inner bore profile, anti-vortex ribs/vanes, top chamfer angle | Joint erosion, oxygen lancing thermal shock during nozzle opening |
Refractory Material Selection: Microstructure and Raw Materials
Tundish furniture faces extreme operating demands: cold preheat (often only 800–1000°C), thermal shock when 1550–1620°C steel suddenly strikes, turbulent liquid steel erosion, and corrosive tundish slag containing SiO2, CaO, Al2O3, FeO, and MnO.
Precast formulation matrix for tundish furniture
| Property / Specification | Corundum-Spinel Precast (High Performance) | High Alumina Low-Cement (Standard Service) | Basic Magnesia Precast (Special Clean Steel) |
|---|---|---|---|
| Main chemical composition | Al2O3 ≥ 88%, MgO 6–10%, SiO2 ≤ 1.0% | Al2O3 ≥ 78%, SiO2 ≤ 8.0%, Fe2O3 ≤ 1.2% | MgO ≥ 85%, CaO ≤ 3.5%, SiO2 ≤ 4.0% |
| Bulk density (110°C x 24h) | ≥ 3.05 g/cm³ | ≥ 2.80 g/cm³ | ≥ 2.75 g/cm³ |
| Cold Crushing Strength (1450°C x 3h) | ≥ 90 MPa | ≥ 70 MPa | ≥ 55 MPa |
| Modulus of Rupture (1450°C x 3h) | ≥ 14 MPa | ≥ 10 MPa | ≥ 7 MPa |
| Thermal shock resistance (1100°C air cooling) | ≥ 20 cycles | 12 to 16 cycles | 8 to 12 cycles |
| Best fit application | Long sequence casting (> 12 heats), SBQ, bearing steel, high-erosion tundish | Rebar, merchant bar, standard carbon steel, short to medium sequences (< 8 heats) | Ultra-low oxygen steels, high-basicity flux practices, Ca-treated grades |
Technical Procurement Checklist: Buying on Cost-per-Tonne
Tundish furniture represents less than 2% of total caster operating costs, but a failure costs a downgraded heat or a caster breakout. Buying the cheapest precast shape is the most expensive mistake a purchasing manager can make.
Six technical verification steps before placing an order
| Step | What to check | Engineering pass criteria | Risk if ignored |
|---|---|---|---|
| 1. CFD Verification | Simulated for your actual tundish geometry, strand count and casting speed | t_min > 60s; Dead volume < 20%; Surface velocity < 0.12 m/s | Slag eye opening, high reoxidation, macro-inclusions in strand |
| 2. Pre-firing Temperature | Verify whether pieces are pre-baked at 350°C or pre-fired at > 1000°C | Pre-baked ≥ 350°C for hydration safety; Pre-fired for maximum thermal shock strength | Steam explosion or explosive spalling during rapid gas preheating |
| 3. Raw Material Origin | Tabular alumina vs fused brown corundum; synthetic fused spinel vs in-situ | WFA/Tabular alumina matrix with pre-synthesized spinel for clean steel | Variable impurities (SiO2, Fe2O3) cause premature erosion at slag line |
| 4. Steel Fibre Addition | Presence, grade, and volume fraction of stainless steel fibres | 1.5–3.0 wt% 304/310 stainless melt-extracted fibres in impact base | Through-thickness cracking under initial stream impact |
| 5. Dimensional Tolerances | Base flatness, lip angle, and wall perpendicularity | ± 2 mm on base flatness; ± 3 mm on exterior envelope | Gaps between dry vibration mix and turbostop lead to steel penetration |
| 6. Packaging & Moisture | Sealed plastic wrap, desiccant pouches, heavy-duty export palletizing | Vacuum stretch wrapped, IPPC treated heat-treated wooden crates | Hydration of cement and MgO during sea freight destroys hot strength |
Frequently Asked Questions (FAQ): Tundish Turbostops & Oxygen Control
What is a tundish turbostop?
A turbostop is a precast cup placed on the tundish floor under the ladle stream. It takes the energy of the falling steel inside the cup and sends the steel out slowly over the rim. It is also called a turbulence inhibitor.
What is the difference between a turbostop and a flat impact pad?
A flat pad is a slab. The stream spreads along it and rises at the walls. A turbostop adds a rim and sloped walls that hold the stream inside the cup first. The turbostop usually gives lower surface flow near the shroud, but cup depth and alignment must suit your stream.
How does a turbostop help control oxygen in steel?
It cuts reoxidation by keeping the surface slag layer closed around the ladle shroud (no open eye). It also gives the steel a smoother path toward the mould, which gives oxide inclusions more time to rise to the covering slag.
Can a turbostop remove inclusions by itself?
No. A turbostop manages flow. Inclusions rise only if the tundish gives them time (longer residence time) and an upward flow path, and if the covering slag can absorb them. A weir and dam are usually used with the turbostop for that reason.
Do I need both a dam and a weir?
Many plants use both. The weir stops slag and forces the steel down; the dam forces it up toward the surface again before it reaches the nozzle. Some tundishes use only a turbostop and a dam. A CFD run shows the difference for your tundish.
What should a CFD report for a turbostop include?
Look for surface velocity around the shroud, residence time distribution (minimum and peak residence time), dead-volume fraction, and a note of the stream speed and bath depth used. Ask if the design was tested against a water model or plant data.
Is CFD enough, or do I need a water model?
CFD is the usual design tool. A full-scale or 1:3 water model is still the most reliable way to check slag-eye behaviour, because slag-steel-air interfaces are difficult to compute accurately. For a new tundish shape, both help.
What is residence time distribution and why does a buyer care?
RTD shows how long steel stays in the tundish after entering. An early peak means some steel takes a short path to the outlet. A later, wider peak means more time for inclusions to rise. The minimum residence time is the first number to check.
Which material suits a turbostop: alumina, spinel or magnesia?
High-alumina low-cement castable is common. Alumina-magnesia castable, which forms spinel, is used where slag and erosion are harder. Magnesia-based castable suits basic slag and low-silica needs. The right choice depends on your steel grade and slag, so read the data sheet and ask for a cut-face report.
Why does my impact pad wear through at the centre?
The stream lands there. Common causes are an off-centre pad, a high stream, a thin floor in the cup, or a matrix that is too open. Check alignment first. Then look at cup depth, floor thickness and the density of the material.
How many heats should a turbostop last?
There is no honest single number. It depends on steel grade, heat size, stream height and practice. Set the target from your sequence length plus a margin, record heats on every set, and compare sets by cost per tonne cast.
Does silica in tundish furniture matter for aluminium-killed steel?
Yes. Silica can give oxygen to dissolved aluminium and form alumina inclusions. For aluminium-killed grades, ask for low silica in the zones that touch the steel and slag, and ask for the SiO2 value on the data sheet.
How should I dry and heat up a precast turbostop?
Follow the supplier’s written dry-out curve. Keep the slow hold at low temperature so water can leave, then ramp up. Heating too fast is a common cause of cracks and spalling at first fill. Store pieces dry and on pallets.
Can you make a turbostop or dam to my drawing?
Yes. Send the tundish drawing, ladle shroud size, stream height, casting speed, steel grades and the current set with its life in heats. Photos of used pieces help a lot.
How do I calculate cost per tonne for tundish furniture?
Add the set price, installation and a figure for stoppage risk. Divide by heats times tonnes per heat. A cheaper set that lasts fewer heats can cost more per tonne. Add the cost of a downgraded heat from your own records.
What do I send for a design check or a quote?
Send the tundish drawing and capacity, ladle shroud size and stream height, casting speed, steel grades and deoxidation route, the current set and its life, photos of worn pieces, and your oxygen or cleanliness target.
Talk to Us About Your Tundish Lining & Flow Optimization
Tell us your tundish drawing, casting parameters, steel grades, and current furniture campaign life. We provide an engineered technical CFD evaluation and quotation within 24 to 48 hours.