Tundish Stopper Rod: Definition, Design, Function, and Performance in Continuous Casting

1. Introduction

In modern steelmaking, continuous casting has become the dominant technology for transforming molten steel into semi-finished products such as slabs, blooms, and billets. Within this process, the tundish plays a critical role as an intermediate vessel between the ladle and the mold. Beyond its function as a distributor of liquid steel, the tundish is also a metallurgical reactor where temperature control, inclusion flotation, and flow optimization occur. One of the most important flow-control devices installed in the tundish is the tundish stopper rod.

The tundish stopper rod is a refractory-based mechanical control system used to regulate the flow of molten steel from the tundish to the mold through the tundish nozzle. Its performance directly affects casting stability, steel cleanliness, inclusion control, nozzle clogging behavior, and surface quality of the final product. Because of these critical responsibilities, the design, material selection, and operation of tundish stopper rods are subjects of continuous development in the steel and refractory industries.

This article provides a detailed and technical explanation of what a tundish stopper rod is, how it works, its structural components, materials, operating principles, advantages, limitations, and current trends in stopper rod technology. The discussion is intended for metallurgists, refractory engineers, casting operators, and technical decision-makers in continuous casting operations.

flow control refractory
flow control refractory

2. What Is a Tundish Stopper Rod?

A tundish stopper rodis a vertically operated refractory rod assembly installed above the tundish nozzle. Its primary function is to control or completely shut off the flow of molten steel from the tundish into the mold during continuous casting. By moving the stopper rod up or down relative to the nozzle orifice, the opening area through which steel flows can be precisely adjusted.

In simple terms, the stopper rod acts as a valve. When the rod tip is pressed against the nozzle seating area, steel flow is stopped. When the rod is lifted, molten steel flows through the annular gap between the stopper tip and the nozzle, with the flow rate determined by the gap size and ferrostatic pressure.

Stopper rods are widely used in slab, bloom, and billet casting machines, particularly where accurate flow control, rapid response, and clean steel production are required.

3. Role of the Stopper Rod in the Continuous Casting Process

3.1 Flow Control and Casting Speed Regulation

The most fundamental role of the tundish stopper rod is to regulate steel flow rate into the mold. Casting speed must be carefully controlled to avoid defects such as:

  • Surface cracks

  • Mold level fluctuations

  • Breakouts

  • Internal segregation

By finely adjusting the stopper rod position, operators can maintain a stable mold level and consistent casting speed, even as tundish steel level decreases during casting.

3.2 Emergency Shut-Off

In abnormal situations such as mold breakouts, nozzle failure, or sudden equipment malfunction, the stopper rod provides an immediate shut-off mechanism. Lowering the stopper rod to fully seal the nozzle can stop the steel flow rapidly, minimizing safety risks and equipment damage.

3.3 Steel Cleanliness Control

The stopper rod system contributes indirectly to steel cleanliness. A stable and controlled flow reduces turbulence at the tundish nozzle and mold entry, limiting reoxidation and minimizing the entrainment of slag or non-metallic inclusions.

Additionally, advanced stopper rod designs help stabilize the flow pattern in the tundish, which promotes inclusion flotation and separation before steel enters the mold.

4. Structural Components of a Tundish Stopper Rod Assembly

A tundish stopper rod is not a single component but an integrated system consisting of refractory and mechanical elements.

4.1 Stopper Rod Body

The stopper rod body is typically a long refractory shaft extending from above the tundish cover down to the nozzle area. It must withstand high temperatures, thermal shock, and mechanical stresses during operation.

4.2 Stopper Head (Stopper Tip)

The stopper head is the critical working end of the rod. It interfaces directly with the tundish nozzle or seating block. The geometry of the stopper head—often conical, spherical, or mushroom-shaped—strongly influences flow characteristics, sealing performance, and wear behavior.

4.3 Seating Block or Nozzle Interface

The stopper rod tip seals against a seating block or the upper surface of the tundish nozzle. This interface must be precisely machined and well-aligned to prevent leakage, uneven wear, or unstable flow.

4.4 Steel Core and Reinforcement

Many modern stopper rods include a steel or composite internal core to improve mechanical strength and resistance to bending or breakage during handling and operation.

4.5 Actuation System

The stopper rod is connected to a mechanical or hydraulic actuator located above the tundish. This system allows precise vertical movement of the rod and can be manually or automatically controlled, often integrated with mold level control systems.

5. Materials Used in Tundish Stopper Rods

Material selection is one of the most critical factors determining stopper rod performance and service life.

ladle shroud reference
ladle shroud referenc

5.1 Alumina-Based Materials

High-purity alumina (Al₂O₃) is commonly used due to its excellent refractoriness, corrosion resistance, and mechanical strength at high temperatures. Alumina-based stopper rods are widely applied in carbon steel casting.

5.2 Alumina-Carbon (Al₂O₃–C) Composites

Alumina-carbon materials combine high corrosion resistance with improved thermal shock resistance. The presence of carbon reduces wetting by molten steel and slag, which helps minimize erosion and clogging.

However, carbon-containing materials require careful oxidation protection, often through antioxidants or protective coatings.

5.3 Zirconia and Zirconia-Containing Materials

Zirconia (ZrO₂) offers exceptional resistance to erosion and thermal shock, particularly at the stopper head. Many high-end stopper rods use zirconia inserts or zirconia-rich compositions at the working tip to extend service life.

5.4 Spinel and Advanced Composites

Magnesia-alumina spinel and other engineered composites are increasingly used to balance corrosion resistance, thermal stability, and cost. These materials are particularly effective in steels with aggressive slags or high calcium treatment levels.

6. Operating Principle of the Tundish Stopper Rod

The stopper rod operates based on hydrostatic pressure and controlled mechanical movement.

When the stopper rod tip is fully seated against the nozzle, the flow path is blocked. As the rod is lifted, an annular opening forms between the rod tip and the nozzle. Molten steel flows through this opening under the ferrostatic pressure of the steel column in the tundish.

The flow rate depends on:

  • Stopper rod lift height

  • Nozzle geometry

  • Steel temperature and viscosity

  • Tundish steel level

Modern casting operations often use automatic stopper rod control systems linked to mold level sensors. These systems continuously adjust the stopper rod position to maintain a stable mold level.

7. Advantages of Tundish Stopper Rod Systems

7.1 Precise Flow Control

Compared to slide gate systems, stopper rods provide finer and more responsive flow regulation, especially at low flow rates.

7.2 Rapid Response

The vertical movement of the stopper rod allows quick adjustment, which is critical for stabilizing mold level during transient conditions.

7.3 Improved Steel Cleanliness

Reduced turbulence and stable flow conditions help limit reoxidation and inclusion entrainment.

7.4 Compact and Simple Design

Stopper rod systems are mechanically simpler than multi-plate slide gate systems, with fewer moving parts in direct contact with molten steel.

8. Common Problems and Failure Mechanisms

Despite their advantages, tundish stopper rods face several operational challenges.

8.1 Erosion and Corrosion

Continuous exposure to high-temperature molten steel and aggressive slags leads to gradual erosion of the stopper head and seating area. This erosion can cause unstable flow or leakage.

8.2 Thermal Shock Cracking

Rapid heating during start-up or sudden temperature fluctuations can cause cracking, especially in poorly designed or low-quality refractory materials.

8.3 Misalignment and Leakage

Improper alignment between the stopper rod and nozzle can result in incomplete sealing, steel leakage, or asymmetric flow.

8.4 Nozzle Clogging Interaction

Inclusion buildup or alumina deposition in the nozzle can interact with the stopper rod, causing erratic flow control or excessive wear at the rod tip.

9. Comparison with Slide Gate Systems

Both stopper rods and slide gate systems are used for tundish flow control, and the choice depends on casting conditions.

  • Stopper rods offer better fine control and faster response.

  • Slide gates provide robust shut-off and are often preferred for long casting sequences or high-throughput operations.

In many modern steel plants, stopper rods are favored for high-quality steel grades requiring tight mold level control and superior cleanliness.

10. Recent Developments and Future Trends

Advances in tundish stopper rod technology focus on:

  • Optimized tip geometry using computational fluid dynamics (CFD)

  • Improved refractory compositions with longer service life

  • Anti-clogging coatings and surface treatments

  • Integration with fully automated casting control systems

Future stopper rod designs are expected to further enhance steel cleanliness, reduce refractory consumption, and improve overall casting reliability.

11. Conclusion

The tundish stopper rod is a critical component in the continuous casting process, serving as the primary flow-control and shut-off device between the tundish and the mold. Its performance directly influences casting stability, product quality, safety, and operational efficiency.

Through careful design, advanced refractory materials, precise mechanical control, and proper operational practices, tundish stopper rods can deliver reliable, precise, and long-lasting performance. As steelmakers continue to demand higher cleanliness levels and more stable casting conditions, the importance of optimized tundish stopper rod systems will only increase.More information please visitHenan Yangyu Refractories Co.,Ltd

Influenza dell’Offset della Submerged Entry shroud (SES) sul Campo di Flusso nella Colata Continua

1. Introduzione

Nella moderna colata continua dell’acciaio, la Submerged Entry Nozzle (SEN) svolge un ruolo fondamentale nel controllo del trasferimento dell’acciaio liquido dal tundish alla lingottiera. Oltre alla composizione dei materiali e alla geometria dei fori, la precisione di posizionamento della SEN rispetto all’asse della lingottiera ha un’influenza determinante sul campo di flusso in lingottiera, sul trasferimento di calore, sul comportamento delle inclusioni e sulla qualità superficiale del prodotto colato.

Uno dei parametri più spesso sottovalutati, ma altamente influente, è l’offset della SEN, definito come la deviazione laterale o angolare dell’ugello rispetto all’allineamento centrale ideale. Anche piccoli offset, dell’ordine di pochi millimetri, possono modificare in modo significativo il campo di flusso all’interno della lingottiera. Questo articolo analizza in modo approfondito l’influenza dell’offset della SEN sul campo di flusso, discutendo i meccanismi fluidodinamici, le conseguenze metallurgiche, le cause operative e le strategie di mitigazione.

sub entry shroud
sub entry shroud

2. Definizione e Tipologie di Offset della SEN

2.1 Cos’è l’Offset della SEN?

Per offset della SEN si intende la deviazione dell’asse del foro o dei porti di uscita dell’ugello rispetto all’asse geometrico della lingottiera. In condizioni ideali, la SEN è perfettamente allineata in senso verticale e orizzontale, garantendo un flusso simmetrico dell’acciaio liquido.

Nelle condizioni industriali reali, tuttavia, possono verificarsi offset a causa di:

  • tolleranze meccaniche dei sistemi di montaggio;

  • dilatazioni termiche dei refrattari;

  • usura o deformazione della SEN;

  • installazione o centraggio non corretti;

  • vibrazioni durante la colata e oscillazione della lingottiera.

2.2 Tipologie di Offset

L’offset della SEN può essere classificato in diverse categorie:

  1. Offset Laterale
    Spostamento orizzontale della SEN rispetto all’asse della lingottiera.

  2. Offset Angolare (Inclinazione)
    Deviazione dell’asse della SEN rispetto alla verticale.

  3. Asimmetria dei Porti
    Erosione o parziale intasamento che altera la direzione effettiva dei getti.

  4. Offset Dinamico
    Spostamento variabile nel tempo dovuto a vibrazioni, usura o deformazioni termiche.

Ciascun tipo di offset influisce sul campo di flusso in modo specifico.

3. Caratteristiche del Campo di Flusso nella Lingottiera

flow control refractory
flow control refractory

3.1 Campo di Flusso Ideale e Simmetrico

In presenza di una SEN perfettamente allineata, il campo di flusso è caratterizzato da:

  • strutture di ricircolo simmetriche a doppio o singolo vortice;

  • impatto bilanciato dei getti sulle pareti della lingottiera;

  • distribuzione uniforme delle velocità in prossimità del menisco;

  • stabilità dello strato di scoria in superficie.

Questo tipo di flusso riduce l’intrappolamento delle inclusioni e favorisce una solidificazione uniforme.

3.2 Parametri del Campo di Flusso Influenzati dall’Offset

  • angolo e profondità di penetrazione del getto;

  • intensità della turbolenza;

  • distribuzione delle velocità al menisco;

  • simmetria delle zone di ricircolo;

  • sforzi di taglio al fronte di solidificazione.

Anche piccoli disallineamenti possono alterare significativamente questi parametri.

4. Influenza dell’Offset Laterale sul Campo di Flusso

4.1 Deviazione del Getto e Flusso Asimmetrico

Un offset laterale provoca distanze diverse tra i porti della SEN e le pareti della lingottiera, determinando:

  • impatto del getto più vicino a una faccia stretta;

  • maggiore quantità di moto su un lato;

  • flusso indebolito sul lato opposto.

Ne deriva una struttura di flusso a doppio vortice sbilanciata, con un circuito di ricircolo dominante.

4.2 Squilibrio delle Velocità al Menisco

L’aumento della velocità del flusso sul lato più vicino comporta:

  • assottigliamento locale dello strato di scoria;

  • maggiore rischio di trascinamento della scoria;

  • incremento della turbolenza superficiale.

Sul lato opposto possono invece formarsi zone stagnanti, aumentando il rischio di congelamento superficiale e formazione di difetti a gancio (hook).

4.3 Trasporto e Intrappolamento delle Inclusioni

Il flusso asimmetrico influenza il moto delle inclusioni:

  • concentrazione delle inclusioni su un lato della lingottiera;

  • maggiore cattura delle inclusioni vicino al getto ad alta velocità;

  • ridotta efficienza di flottazione sul lato a bassa velocità.

Ciò porta a una distribuzione non uniforme della pulizia metallurgica nella sezione colata.

5. Influenza dell’Offset Angolare (Inclinazione)

5.1 Effetti dell’Inclinazione Verso il Basso o l’Alto

Un offset angolare modifica l’angolo effettivo del getto:

  • inclinazione verso il basso: maggiore profondità di penetrazione e rafforzamento del ricircolo inferiore;

  • inclinazione verso l’alto: aumento della turbolenza al menisco e dell’interazione scoria-metallo.

Entrambe le condizioni possono compromettere la stabilità del flusso.

5.2 Scarico Asimmetrico dai Porti

Quando la SEN è inclinata, anche porti geometricamente simmetrici generano getti con angoli effettivi diversi, causando:

  • punti di impatto non uniformi;

  • distorsione delle zone di ricircolo;

  • incremento degli sforzi di taglio su un lato del guscio solidificato.

Questo fenomeno favorisce la formazione di cricche longitudinali e difetti interni.

6. Turbolenza e Dissipazione di Energia

6.1 Incremento Locale della Turbolenza

Le condizioni di offset aumentano generalmente l’intensità della turbolenza:

  • numeri di Reynolds più elevati vicino a un getto;

  • forti gradienti di velocità;

  • maggiore dissipazione di energia cinetica.

Una turbolenza eccessiva vicino al menisco favorisce il trascinamento della scoria e l’emulsione della polvere di colata.

6.2 Impatto sulla Stabilità del Flusso

Un campo di flusso instabile può manifestarsi con:

  • oscillazioni del menisco;

  • transizioni tra flusso a singolo e doppio vortice;

  • asimmetrie periodiche nella crescita del guscio.

Questa instabilità rende più complesso il controllo del processo e la costanza qualitativa.

7. Conseguenze Termiche e di Solidificazione

7.1 Trasferimento di Calore Non Uniforme

L’offset della SEN porta a una distribuzione non uniforme del flusso termico:

  • maggiore convezione e raffreddamento vicino al getto dominante;

  • minore estrazione di calore sul lato opposto.

Il risultato è uno spessore del guscio solidificato asimmetrico, con aumento del rischio di breakout.

7.2 Crescita del Guscio e Formazione di Cricche

Flusso e raffreddamento non uniformi causano:

  • fronti di solidificazione irregolari;

  • elevati sforzi di trazione nel guscio;

  • maggiore suscettibilità a cricche longitudinali e trasversali.

8. Cause Operative dell’Offset della SEN

8.1 Errori di Installazione e Allineamento

Le cause più comuni includono:

  • montaggio impreciso del tundish o della lingottiera;

  • disallineamento dello stopper rod o dei sistemi a saracinesca;

  • dispositivi di centraggio usurati.

8.2 Usura e Deformazione dei Refrattari

Durante la colata:

  • l’erosione della SEN modifica la geometria dei porti;

  • l’intasamento asimmetrico riduce l’area effettiva di flusso;

  • la dilatazione termica provoca spostamenti progressivi.

Questi fenomeni portano a un offset crescente nel corso della sequenza di colata.

9. Rilevamento e Diagnosi dell’Offset della SEN

9.1 Tecniche di Monitoraggio Online

  • analisi delle fluttuazioni del livello in lingottiera;

  • mappatura del flusso termico con termocoppie;

  • sensori elettromagnetici di flusso.

9.2 Modellazione CFD e Modelli Fisici

La Computational Fluid Dynamics (CFD) e i modelli ad acqua sono ampiamente utilizzati per:

  • quantificare l’asimmetria del flusso;

  • valutare la sensibilità all’offset;

  • ottimizzare il posizionamento della SEN.

10. Strategie di Mitigazione e Migliori Pratiche

10.1 Controllo dell’Allineamento Meccanico

  • strumenti di allineamento di precisione durante l’installazione;

  • ispezione periodica dei sistemi di centraggio;

  • tolleranze dimensionali rigorose per i refrattari.

10.2 Ottimizzazione del Design della SEN

  • geometria dei porti bilanciata;

  • design del foro anti-clogging;

  • materiali resistenti all’usura per mantenere la simmetria.

10.3 Misure di Controllo di Processo

  • ottimizzazione della velocità di colata;

  • controllo della portata di argon;

  • sistemi adattivi di controllo del livello in lingottiera.

11. Implicazioni Industriali e Casi Applicativi

Studi industriali dimostrano che la riduzione dell’offset della SEN da 5 mm a meno di 1 mm può:

  • ridurre i difetti superficiali di oltre il 30%;

  • migliorare l’uniformità della distribuzione delle inclusioni;

  • aumentare la stabilità della colata e la durata delle sequenze.

Questi risultati evidenziano l’impatto economico e qualitativo del corretto allineamento della SEN.

12. Conclusione

L’offset della Submerged Entry Nozzle è un parametro critico ma spesso sottovalutato nella colata continua. Anche piccole deviazioni dall’allineamento ideale possono alterare in modo significativo il campo di flusso in lingottiera, generando asimmetrie di ricircolo, aumento della turbolenza, trasferimento di calore non uniforme e incremento dei difetti.

Attraverso un corretto allineamento meccanico, un design robusto della SEN, sistemi di monitoraggio avanzati e ottimizzazione basata su CFD, è possibile controllare efficacemente l’offset e ottenere condizioni di flusso stabili, qualità superiore del prodotto e maggiore sicurezza operativa.

Composizione dell’Ugello di Dosaggio del Tundish: Materiali, Struttura e Prestazioni nella Colata Continua

Introduzione

Nella moderna colata continua dell’acciaio, il tundish svolge un ruolo metallurgico fondamentale come vasca tampone, distributore e reattore di raffinazione tra la siviera e la lingottiera. Tra tutti i refrattari funzionali del tundish, l’ugello di dosaggio del tundish (tundish metering nozzle) è uno dei componenti più critici per il controllo del flusso.

La composizione dei materiali, la progettazione interna e la microstruttura dell’ugello di dosaggio influenzano direttamente la stabilità del flusso di acciaio liquido, la pulizia metallurgica, il fenomeno di intasamento (clogging) e la sicurezza operativa. Comprendere in dettaglio la composizione di questo componente è essenziale per ottimizzare le prestazioni di colata e ridurre le interruzioni operative.

Questo articolo fornisce una spiegazione tecnica e dettagliata della composizione dell’ugello di dosaggio del tundish, includendo materie prime, fasi costitutive, additivi, leganti e zone funzionali, con un approccio adatto a professionisti del settore e contenuti ottimizzati per la visibilità SEO.

tundish metering nozzle series
tundish metering nozzle series

Cos’è un Ugello di Dosaggio del Tundish?

L’ugello di dosaggio del tundish è un componente refrattario di precisione installato sul fondo del tundish, progettato per regolare in modo controllato la portata dell’acciaio liquido verso i componenti a valle, come:

  • Sub-Entry Shroud (SES)

  • Submerged Entry Nozzle (SEN)

  • Sistemi di alimentazione diretta della lingottiera

A differenza di altri refrattari del tundish (come well block o impact pad), l’ugello di dosaggio svolge una funzione attiva di controllo del flusso, richiedendo elevata precisione dimensionale, resistenza all’erosione e stabilità chimica.

Requisiti Funzionali che Determinano la Composizione

La composizione dell’ugello di dosaggio del tundish è progettata per resistere a condizioni operative estremamente severe:

  • Contatto continuo con acciaio liquido a 1550–1600 °C

  • Forti gradienti termici e shock termici

  • Sollecitazioni meccaniche dovute a stopper rod o sistemi a saracinesca

  • Attacco chimico da parte di acciaio, scorie e inclusioni

  • Resistenza all’intasamento da allumina

  • Controllo della permeabilità ai gas (nei sistemi con insufflazione di argon)

Questi requisiti guidano la selezione delle materie prime, del contenuto di carbonio, del sistema di legante e degli additivi funzionali.

Principali Sistemi di Materiali Utilizzati

1. Sistema Allumina-Carbonio (Al₂O₃-C)

Il sistema allumina-carbonio è il più utilizzato per gli ugelli di dosaggio del tundish.

Composizione Tipica

  • Al₂O₃: 70–90%

  • Carbonio (grafite): 5–20%

  • Additivi metallici: 2–6%

  • Legante (resina o pece): 2–4%

Funzione dell’Allumina (Al₂O₃)

  • Elevata refrattarietà (>2050 °C)

  • Ottima resistenza all’erosione da acciaio

  • Bassa solubilità nel metallo liquido

  • Struttura portante del refrattario

Funzione del Carbonio

  • Migliora la resistenza allo shock termico

  • Riduce la bagnabilità da parte dell’acciaio

  • Limita l’adesione delle inclusioni

  • Riduce il fenomeno di clogging

Le composizioni Al₂O₃-C sono particolarmente adatte per acciai calmati all’alluminio e colate di lunga durata.

2. Inserti in Zirconia (ZrO₂) e Strutture Ibride

Per applicazioni ad alte prestazioni, molti ugelli di dosaggio includono inserti in zirconia, soprattutto nella zona del foro.

flow control refractory
flow control refractory

Caratteristiche della Zirconia

  • Purezza ZrO₂: 94–99%

  • Stabilizzazione con CaO, MgO o Y₂O₃

Vantaggi Principali

  • Bassissima bagnabilità all’acciaio

  • Eccellente resistenza alla corrosione

  • Ridotta formazione di depositi di allumina

  • Elevata resistenza all’intasamento

A causa del costo elevato, la zirconia viene normalmente utilizzata come inserto localizzato e non come materiale dell’intero corpo.

3. Composizioni a Base Magnesia (MgO)

In alcune applicazioni specifiche vengono utilizzate composizioni magnesia-carbonio (MgO-C).

Caratteristiche

  • Elevata resistenza alle scorie basiche

  • Buone prestazioni in ambienti ad alto contenuto di CaO

  • Resistenza allo shock termico inferiore rispetto all’Al₂O₃-C

L’uso della magnesia è meno comune negli ugelli di dosaggio, ma può essere vantaggioso in condizioni operative particolari.

Fonti di Carbonio Utilizzate

Il carbonio è un componente chiave nella composizione dell’ugello di dosaggio.

Tipologie di Carbonio

  • Grafite naturale a scaglie

  • Grafite espansa

  • Grafite sintetica

  • Nero di carbonio (in quantità minori)

Funzioni del Carbonio

  • Riduzione dell’adesione dell’acciaio

  • Miglioramento della resistenza allo shock termico

  • Riduzione dell’attrito con lo stopper rod

  • Limitazione della propagazione delle cricche

Il contenuto di carbonio deve essere attentamente bilanciato per evitare ossidazioni eccessive durante il preriscaldo.

Additivi Metallici e Antiossidanti

Per proteggere il carbonio e migliorare le prestazioni ad alta temperatura, vengono utilizzati additivi metallici.

Additivi Comuni

  • Alluminio (Al)

  • Silicio (Si)

  • Magnesio (Mg)

  • Carburo di boro (B₄C)

  • Carburo di silicio (SiC)

Funzioni Principali

  • Formazione di strati protettivi di ossidi

  • Riduzione dell’ossidazione del carbonio

  • Incremento della resistenza a caldo

  • Migliore resistenza alla penetrazione delle scorie

Sistemi di Legante

Leganti a Base di Resina

I più diffusi sono i leganti fenolici, che garantiscono:

  • Elevata resistenza meccanica a freddo

  • Controllo del residuo carbonioso

  • Stabilità dimensionale durante la polimerizzazione

Leganti a Base di Pece

Oggi meno utilizzati per motivi ambientali e di sicurezza.

Durante il trattamento termico, il legante si trasforma in una struttura a legame carbonioso.

Zone Strutturali e Composizione Multistrato

Gli ugelli di dosaggio moderni presentano una struttura a zone funzionali.

Zona del Foro

  • Al₂O₃-C ad alta purezza o zirconia

  • Bassa porosità

  • Ottimizzazione anti-clogging

Zona di Lavoro

  • Elevata resistenza all’erosione

  • Buon equilibrio tra shock termico e resistenza meccanica

Zona di Supporto

  • Refrattari ottimizzati in termini di costo

  • Funzione strutturale

Metodi di Produzione e Influenza sulla Composizione

Pressatura Isostatica

  • Elevata densità

  • Microstruttura uniforme

  • Precisione dimensionale

  • Migliore resistenza alla corrosione

Pressatura Convenzionale

  • Costo inferiore

  • Adatta a colate di breve durata

Relazione tra Composizione e Prestazioni

Caratteristica della composizione Effetto sulle prestazioni
Elevata purezza Al₂O₃ Maggiore resistenza all’erosione
Contenuto ottimizzato di carbonio Riduzione del clogging
Inserto in ZrO₂ Maggiore durata di colata
Additivi metallici Vita utile prolungata
Struttura a zone Riduzione del rischio di rottura

Conclusione

La composizione dell’ugello di dosaggio del tundish è il risultato di una progettazione avanzata che combina allumina, carbonio, zirconia, additivi metallici e sistemi di legante, al fine di soddisfare le severe condizioni della colata continua dell’acciaio.

Una selezione corretta dei materiali consente di ridurre l’intasamento, stabilizzare il flusso di acciaio, aumentare la durata del componente e migliorare la qualità metallurgica finale. La comprensione approfondita della composizione è quindi fondamentale per decisioni efficaci in ambito tecnico, operativo e di approvvigionamento.More information please visit Henan Yangyu Refractories Co.,Ltd

Come installare e fissare correttamente la Sub-Entry Shroud (SES) nella colata continua dell’acciaio

1. Introduzione

La Sub-Entry Shroud (SES), spesso chiamata anche tubo di protezione di ingresso o tubo di collegamento tra siviera e tundish, è un componente refrattario fondamentale nel processo di colata continua dell’acciaio. Essa viene installata tra l’ugello di uscita della siviera e il sistema di ingresso del tundish o, in alcune configurazioni, tra il tundish e l’ugello di ingresso sommerso (SEN).

sub entry shroud
sub entry shroud

La funzione principale della Sub-Entry Shroud è proteggere l’acciaio liquido dal contatto con l’atmosfera, prevenendo l’ossidazione secondaria, l’assorbimento di azoto e l’ingresso di inclusioni non metalliche. Una corretta installazione e fissaggio della SES è quindi essenziale per garantire qualità metallurgica, stabilità del processo e sicurezza operativa.

Un montaggio non corretto può causare aspirazione d’aria, perdite di acciaio, rottura del tubo refrattario e, nei casi più gravi, incidenti durante la colata. Questo articolo descrive in modo dettagliato come fissare correttamente una Sub-Entry Shroud, analizzando preparazione, metodi di installazione, sistemi di tenuta, controlli e buone pratiche.

2. Struttura e componenti della Sub-Entry Shroud

Prima di analizzare la procedura di installazione, è importante comprendere i principali elementi del sistema SES:

  • Corpo della Sub-Entry Shroud, generalmente prodotto per pressatura isostatica

  • Materiale refrattario, tipicamente Al₂O₃-C o ZrO₂-C

  • Superficie di accoppiamento superiore, verso l’ugello della siviera

  • Superficie di accoppiamento inferiore, verso il tundish o il SEN

  • Guarnizioni di tenuta (in fibra ceramica, grafite o materiali compositi)

  • Sistema di fissaggio meccanico (morsetti, anelli di bloccaggio, sistema a baionetta)

  • Canale per insufflaggio di argon (opzionale)

L’intero sistema deve garantire tenuta ai gas, stabilità meccanica e resistenza agli shock termici.

3. Preparazione prima dell’installazione

3.1 Ispezione della Sub-Entry Shroud

Prima del montaggio, ogni SES deve essere accuratamente controllata:

  • assenza di crepe, scheggiature o difetti superficiali;

  • verifica della concentricità e della rettilineità;

  • controllo delle superfici di contatto;

  • conferma della qualità del materiale refrattario in funzione del tipo di acciaio.

Anche difetti minimi possono propagarsi rapidamente durante il riscaldamento e portare alla rottura del tubo.

3.2 Controllo dei componenti di accoppiamento

È essenziale verificare anche:

  • ugello della siviera;

  • superfici di appoggio;

  • presenza di residui di scoria o acciaio solidificato;

  • stato di usura dei componenti refrattari adiacenti.

Superfici non pulite o danneggiate compromettono la tenuta e la stabilità dell’insieme.

3.3 Preparazione delle guarnizioni

Le guarnizioni svolgono un ruolo chiave nella prevenzione dell’aspirazione d’aria:

  • utilizzare solo guarnizioni approvate dal fornitore;

  • evitare guarnizioni umide o deformate;

  • conservarle in ambiente asciutto;

  • in alcuni casi è ammesso l’uso di una sottile pasta refrattaria, se previsto dalla procedura.

4. Procedura di installazione e fissaggio

flow control refractory
flow control refractory

4.1 Movimentazione e posizionamento

La Sub-Entry Shroud è un componente fragile e deve essere movimentata con estrema cura:

  • utilizzare pinze o manipolatori dedicati;

  • evitare urti e carichi laterali;

  • mantenere sempre l’asse verticale;

  • non forzare mai il posizionamento.

Una movimentazione impropria è una delle principali cause di micro-fessurazioni.

4.2 Fissaggio alla siviera (connessione superiore)

Il primo passo consiste nel collegamento al lato siviera:

  1. Posizionare la guarnizione sull’ugello della siviera

  2. Abbassare lentamente la SES fino al contatto

  3. Verificare il contatto uniforme su tutta la circonferenza

  4. Attivare il sistema di fissaggio meccanico

Il serraggio deve essere sufficiente a garantire la tenuta, ma non eccessivo per evitare tensioni nel refrattario.

4.3 Fissaggio alla parte inferiore (tundish o SEN)

La connessione inferiore richiede particolare attenzione:

  • perfetto allineamento assiale;

  • corretto posizionamento della guarnizione;

  • bloccaggio secondo la procedura prevista.

Un disallineamento può causare turbolenze nel flusso dell’acciaio e inclusioni.

5. Tenuta ai gas e prevenzione dell’ossidazione

5.1 Importanza della tenuta

Un sistema SES correttamente fissato deve impedire:

  • aspirazione di aria;

  • ossidazione secondaria;

  • aumento delle inclusioni non metalliche.

La tenuta ai gas è uno dei principali fattori che influenzano la qualità dell’acciaio colato.

5.2 Insufflaggio di argon

Molte Sub-Entry Shroud sono dotate di insufflaggio di argon:

  • collegare correttamente le linee gas;

  • controllare portata e pressione;

  • verificare l’assenza di perdite.

L’argon contribuisce anche a ridurre l’intasamento dell’ugello.

6. Aspetti termici e meccanici

6.1 Preriscaldo

In alcuni impianti è previsto il preriscaldo della SES:

  • seguire rigorosamente le curve di riscaldamento;

  • evitare gradienti termici elevati;

  • non superare le temperature raccomandate.

Un riscaldamento non uniforme può causare shock termici.

6.2 Compensazione dell’espansione termica

Il sistema di fissaggio deve consentire:

  • espansione assiale;

  • dilatazione radiale;

  • assorbimento delle vibrazioni.

Un fissaggio troppo rigido aumenta il rischio di rottura durante la colata.

7. Controlli finali prima della colata

Prima di aprire il sistema di colata:

  • verificare il corretto bloccaggio della SES;

  • controllare l’allineamento con il cristallizzatore;

  • confermare il flusso di argon;

  • assicurarsi che l’area sia libera da personale.

Questi controlli riducono significativamente il rischio operativo.

8. Problemi comuni e soluzioni

Aspirazione d’aria

Causa: guarnizione danneggiata
Soluzione: sostituzione della guarnizione

Rottura della SES

Causa: disallineamento o shock termico
Soluzione: migliorare installazione e preriscaldo

Perdite di acciaio

Causa: superfici di accoppiamento usurate
Soluzione: sostituire i refrattari danneggiati

9. Buone pratiche operative

  • standardizzare le procedure di montaggio;

  • formare regolarmente il personale;

  • utilizzare solo componenti compatibili;

  • documentare ogni installazione;

  • analizzare la SES dopo l’uso.

10. Conclusione

La corretta installazione e fissaggio della Sub-Entry Shroud è un elemento essenziale per il successo del processo di colata continua. Un approccio sistematico, che integri controllo dei materiali, precisione meccanica, tenuta ai gas e gestione termica, consente di migliorare la qualità dell’acciaio, ridurre i fermi impianto e aumentare la sicurezza operativa. In un contesto industriale sempre più orientato all’efficienza e alla qualità, la SES rappresenta un componente strategico che merita particolare attenzione.More information,please visit Henan Yangyu Refractories Co.,Ltd

How to Fix a Sub-Entry Shroud in Continuous Casting Operations

1. Introduction

The sub-entry shroud (SES) is a critical refractory component in the continuous casting process, positioned between the ladle nozzle and the tundish or directly above the mold entry, depending on caster design. Its primary function is to protect molten steel from atmospheric re-oxidation, stabilize steel flow, and prevent slag entrainment during steel transfer. Proper installation—or “fixing”—of the sub-entry shroud is essential to ensure metallurgical quality, casting stability, and operational safety.

Improper fixing of a sub-entry shroud can result in air aspiration, steel leakage, premature shroud failure, or catastrophic breakage during casting. This article provides a step-by-step technical explanation of how to fix a sub-entry shroud correctly, covering preparation, installation methods, sealing practices, alignment, and post-installation checks.

2. Understanding the Sub-Entry Shroud Assembly

Before discussing installation procedures, it is important to understand the typical SES assembly system, which usually consists of:

  • Sub-entry shroud body (isostatically pressed alumina-carbon or zirconia-based)
  • Upper connection interface (to ladle nozzle or collector nozzle)
  • Lower connection interface (to tundish nozzle or SEN)
  • Gaskets or sealing rings (fiber, ceramic, or graphite-based)
  • Fixing mechanism (clamp, bayonet, locking ring, or bolted holder)
  • Argon purging channel (optional)

Each of these components must work together to form a gas-tight and mechanically stable connection during casting.

3. Pre-Installation Preparation

3.1 Inspection of the Sub-Entry Shroud

Before fixing the shroud, a thorough inspection is mandatory:

  • Check for visible cracks, chips, or surface defects
  • Verify dimensional accuracy (length, bore diameter, joint tolerances)
  • Inspect connection ends for roundness and flatness
  • Confirm material grade matches casting requirements (e.g., Al₂O₃-C, ZrO₂-C)

Any damaged or non-conforming shroud must be rejected, as even small defects can propagate under thermal shock.

3.2 Inspection of Mating Components

The ladle nozzle, tundish nozzle, or SEN interface must also be checked:

  • Remove residual slag, steel, or refractory debris
  • Ensure seating surfaces are clean, flat, and dry
  • Check for excessive wear or erosion
  • Confirm alignment of the nozzle axis

Poor mating surface conditions are a common cause of air leakage and shroud failure.

3.3 Gasket and Seal Preparation

Gaskets play a crucial role in ensuring gas-tightness:

  • Use the correct gasket type and thickness specified by the shroud supplier
  • Avoid damaged or compressed gaskets
  • Store gaskets in a dry environment to prevent moisture absorption
  • In some plants, a thin layer of refractory paste may be applied to improve sealing (only if approved by the supplier)

4. Installation and Fixing Methods

4.1 Vertical Alignment and Handling

The sub-entry shroud must be handled with care:

  • Use dedicated lifting tools or manipulators
  • Avoid point loading or impact on the shroud body
  • Keep the shroud in a vertical position during installation

Misalignment during handling is a frequent cause of micro-cracks that later lead to in-service failure.

4.2 Fixing to the Upper Nozzle (Ladle Side)

The first fixing step usually involves connecting the shroud to the ladle nozzle or collector nozzle:

  1. Position the gasket evenly on the nozzle seating surface
  2. Lower the shroud slowly until it contacts the gasket
  3. Ensure full circumferential contact
  4. Engage the fixing mechanism:
    • Clamp system
    • Bayonet-type locking
    • Threaded or bolted holder

The connection must be tight enough to ensure sealing but not overly stressed, which can induce cracks.

4.3 Fixing to the Lower Nozzle or SEN

Depending on the caster configuration, the lower end of the sub-entry shroud may connect to:

flow control refractory
flow control refractory
  • A tundish nozzle
  • A submerged entry nozzle (SEN)
  • A transition shroud

Key steps include:

  • Confirm concentric alignment between shroud and lower nozzle
  • Insert the gasket carefully without distortion
  • Lock the connection using the specified fixing device
  • Verify axial alignment to avoid eccentric steel flow

Incorrect lower fixing often results in turbulence, slag entrainment, or nozzle clogging.

5. Sealing and Gas-Tightness Assurance

5.1 Importance of Gas-Tight Fixing

A properly fixed sub-entry shroud must form a closed system, preventing:

  • Air aspiration
  • Nitrogen pickup
  • Re-oxidation of molten steel

Even small leaks can significantly degrade steel cleanliness.

5.2 Argon Purging Integration

Many modern sub-entry shrouds are equipped with argon purging systems:

  • Connect argon lines securely to the shroud inlet
  • Check flow rate according to process requirements
  • Ensure no leakage at connection points

Argon purging not only improves sealing but also helps prevent alumina buildup and nozzle clogging.

6. Thermal and Mechanical Considerations

6.1 Preheating Practices

In some plants, sub-entry shrouds are preheated to reduce thermal shock:

  • Follow supplier-recommended heating rates
  • Avoid uneven heating
  • Do not exceed maximum allowable temperatures

Improper preheating can cause internal cracking that is not visible during installation.

6.2 Thermal Expansion Allowance

Fixing systems must accommodate:

  • Axial thermal expansion
  • Radial expansion at high temperatures

Rigid fixing without expansion allowance increases the risk of spalling or fracture during casting.

7. Safety and Operational Checks Before Casting

Before opening the ladle slide gate:

  • Verify all fixing mechanisms are fully engaged
  • Confirm shroud alignment with mold centerline
  • Check argon flow and pressure
  • Ensure no personnel are in the danger zone

A final visual and mechanical check can prevent severe safety incidents.

8. Common Installation Problems and Solutions

8.1 Air Aspiration

Cause: Poor gasket seating or damaged sealing surface
Solution: Replace gasket, clean seating surface, re-fix shroud

8.2 Shroud Breakage During Casting

Cause: Misalignment, excessive mechanical stress, or thermal shock
Solution: Improve handling, adjust fixing force, review preheating practices

8.3 Steel Leakage at Joints

Cause: Incorrect fixing or worn mating components
Solution: Replace worn nozzles, verify compatibility of components

9. Best Practices for Reliable Sub-Entry Shroud Fixing

  • Use supplier-approved fixing systems only
  • Standardize installation procedures and training
  • Maintain installation tools in good condition
  • Record installation parameters for traceability
  • Conduct post-cast inspections to identify improvement areas

10. Conclusion

Fixing a sub-entry shroud correctly is a critical operation in continuous casting that directly influences steel quality, casting stability, and plant safety. A systematic approach—covering inspection, alignment, sealing, and mechanical fixing—ensures reliable performance of the shroud throughout the casting sequence. By following best practices and understanding the interaction between refractory materials, mechanical systems, and thermal conditions, steel plants can significantly reduce failure rates and improve overall casting efficiency.

European Sub-Entry Shroud Market: Trends, Drivers, and Future Outlook

IntroductionThe sub-entry shroud (SES) is a specialized refractory component used in the continuous casting of steel, acting as a protective tube between the ladle nozzle and the tundish entry to shield molten steel from atmospheric oxidation, stabilize flow, and improve steel quality. Sub-entry shrouds play a critical role in modern steelmaking by helping to prevent re-oxidation, reduce inclusion formation, and support stable casting operations. With Europe’s advanced industrial base—especially in steel, automotive, and heavy manufacturing—the market for sub-entry shrouds is an important niche within the broader refractories market.This article analyzes the current market dynamics, growth drivers, challenges, competitive landscape, and future prospects for sub-entry shrouds in Europe, positioning the segment within broader industrial and refractory trends.The Role of Sub-Entry Shrouds in Continuous CastingIn the continuous casting process, molten steel flows from the ladle through a ladle shroud or nozzle into the tundish and then through either a submerged entry nozzle (SEN) or a sub-entry shroud into the mold. Sub-entry shrouds are refractory tubes, typically isostatically pressed and tailored to specific casting configurations, designed to:

  • Protect the molten steel from air exposure
  • Eliminate oxygen absorption during transfer
  • Minimize nitrogen pickup
  • Stabilize flow patterns into the mold
  • Reduce slag entrainment during ladle changes
flow control refractory
flow control refractory

Their design and material composition (e.g., alumina-carbon or zirconia-based) influence both steel quality and operational efficiency.Europe’s advanced continuous casting operations—especially in high-quality steel production—depend on reliable sub-entry shrouds for consistent output and compliance with stringent quality standards.European Refractories Market Overview (Including Sub-Entry Shrouds)Sub-entry shrouds are part of the broader refractories market, which in Europe is both mature and technologically sophisticated. Recent market research indicates that:

  • The Europe refractories market was valued at around USD 6.4–6.7 billion in 2024 and is projected to reach USD 9.6–13.7 billion by 2032–2033 at a compound annual growth rate (CAGR) ranging from 5% to 10% depending on the report and segment focus.
  • Europe accounts for approximately 14–19% of the global refractory market, reflecting its significant industrial base.
  • The iron and steel sector dominates refractory consumption, driving much of the demand for components like sub-entry shrouds.

Within this market, sub-entry shrouds are a high-performance category, often aligned with premium refractory products due to their importance in continuous casting quality and reliability.Drivers of the European Sub-Entry Shroud Market1. Steel Production and Continuous Casting TrendsEurope remains a key region for steel production, with countries like Germany, Italy, France, and Poland among the largest producers. Steelmakers are increasingly adopting continuous casting for slabs, blooms, billets and specialty steels. This trend drives demand for sub-entry shrouds as essential components in the casting train.The modernization and automation of older steel plants to improve environmental performance and operational efficiency also support investments in advanced refractory consumables, including sub-entry shrouds.2. Focus on Steel Quality and CleanlinessEuropean steelmakers face stringent end-user quality expectations—particularly in the automotive, appliance, and construction sectors—where enhanced mechanical properties and surface quality are critical. Sub-entry shrouds directly contribute to improving steel cleanliness by reducing oxidation and minimizing inclusions, prompting procurement of higher-performance SES products adapted to specific grades and casting conditions.3. Environmental and Regulatory PressuresEuropean Union (EU) regulations covering emissions, energy efficiency and worker safety increasingly influence refractory design and adoption. For example:

  • The REACH regulation drives manufacturers away from harmful materials (e.g., chromium VI) toward chrome-free alternatives.
  • The Industrial Emissions Directive pressures high-temperature manufacturers to reduce kiln emissions and adopt cleaner refractory formulations.

Although these regulations are not specific to sub-entry shrouds, they indirectly shape the design, production, and selection of refractory components across steelmaking—including SES linings—by promoting more sustainable materials and manufacturing methods.4. Technological Advancements and CustomizationEuropean refractory suppliers are increasingly integrating advanced materials science and simulation tools into SES design. Customized sub-entry shrouds may be engineered with:

  • Optimized internal flow geometries
  • Anti-clogging or low-wetting refractory mixes
  • Zirconia-enhanced borer surfaces
  • Argon or flow-control enhancements

These advanced designs help mitigate casting defects and extend service life, which European steelmakers have prioritized given high labor costs and quality expectations.Market Challenges1. High Energy and Production CostsEuropean refractory manufacturing must contend with high energy prices and stringent investment requirements to comply with environmental controls. These factors increase production costs for refractory producers and translate into higher prices for sub-entry shrouds compared to products manufactured in lower-cost regions.2. Skilled Labor ShortagesA shortage of skilled refractory installers and technicians impacts refractory performance in the field, particularly for advanced components like sub-entry shrouds that demand precise installation and handling. Europe’s refractory workforce is aging, and training pipelines are limited, making installation quality a potential constraint on market growth.3. Replacement Cycles and Operational DisruptionsSub-entry shrouds are consumables requiring scheduled replacement. However, casting plant availability pressures—short turnaround windows and the need to avoid unplanned shutdowns—can delay shroud changes, potentially impacting production continuity and customer purchasing patterns.Competitive Landscape and Major PlayersThe sub-entry shroud market in Europe is served by a mix of global refractory manufacturers and specialist producers, typically as part of larger continuous casting refractory portfolios. Key providers include multinational refractories companies with European manufacturing or distribution, such as:

  • RHI Magnesita – Europe’s largest refractory supplier with advanced refractories optimized for casting consumables.
  • Vesuvius – Offers engineered tundish mechanisms including shrouds with flow modeling support.
  • Saint-Gobain Performance Ceramics & Refractories – Provides high-quality refractories for steel applications including shrouding solutions.
  • Shinagawa Refractories – Japanese manufacturer with European distribution capable of servicing SES demand.
  • IFGL Refractories – Global supplier with European operations offering SEN and SES components.

These companies leverage local technical support, customization capabilities, and industry partnerships with steelmakers across Europe to compete on both performance and reliability.Future OutlookGrowth ProjectionsAlthough specific market reports for sub-entry shrouds alone are limited, the broader European refractory market is poised for steady growth. Market projections suggest growth toward USD 9.6–13.7 billion by 2030, supported by modernization investments and demand for advanced refractory solutions.This underlying growth in refractories, particularly in steel and continuous casting applications, implies ongoing demand for sub-entry shrouds as integral elements of casting consumables.Innovation and SustainabilityFuture opportunities for sub-entry shroud manufacturers in Europe will likely center on:

  • Green refractory materials aligned with EU environmental compliance
  • Digital integration including predictive maintenance sensors
  • Customization via CFD and modeling tools for optimized flow control
  • Refractory recycling and circular economy initiatives

sen reference.

As steelmakers pursue sustainability and cost efficiency, suppliers that offer longer life, lower emissions, and performance data integration will gain a competitive advantage.ConclusionThe sub-entry shroud market in Europe is an important, technically advanced segment of the broader refractory industry. Driven by sustained steelmaking and casting modernization, this market benefits from Europe’s strong industrial base and demand for high-quality steel. Although challenges such as production costs and skilled labor shortages persist, long-term trends favor growth and innovation, particularly in high-performance refractory materials and integrated solutions. With key multinational players and strong regional demand, Europe continues to be a strategic and influential market for sub-entry shrouds within the global refractory landscape

Global Importance of the Refractories Industry

The refractory industry is a foundational segment of global heavy industry, providing essential high-temperature materials used in steelmaking, cement production, glass manufacturing, non-ferrous metals processing, petrochemicals, and energy sectors. Refractory materials—such as shaped bricks, monolithics, insulating products, and advanced engineered components—must withstand extreme thermal, chemical, and mechanical stress. A small group of multinational companies dominates this market, combining deep technical expertise, broad geographic footprint, and extensive product portfolios.

flow control refractory
flow control refractory

According to market analyses of the global refractories sector, the largest players by revenue and market influence include RHI Magnesita, Vesuvius plc, Saint-Gobain High-Performance Refractories, Shinagawa Refractories Co., Ltd., and IFGL Refractories Ltd. These organizations not only supply refractory products but also offer advanced solutions, engineering support, and technical services worldwide.

The following sections present a detailed overview of each company, highlighting their history, core competencies, strategic focus, product range, and contribution to the refractory industry.

1. RHI Magnesita

RHI Magnesita is widely regarded as the largest refractory manufacturer in the world in terms of global revenue and market share. It holds a commanding position in basic refractories, particularly magnesia-based products, which are critical for high-temperature industrial applications.

Company Background

Founded in 1908 in Austria, RHI Magnesita has a long heritage as a supplier of refractory materials and systems. The company resulted from the 2017 merger of RHI AG with Brazilian refractory producer Magnesita, creating a combined entity that spans mining, raw material processing, and refractory production. It is publicly traded and included in the FTSE 250 Index.

Market Position

RHI Magnesita generates multi-billion-dollar annual revenue and maintains a significant share of the global refractory market. Its vertically integrated business includes raw material extraction (such as magnesite and dolomite), refractory manufacturing, technical services, and aftermarket support.

Product Portfolio

RHI Magnesita’s extensive product range includes:

  • Basic refractories (magnesia bricks, dolomite bricks)
  • Corundum and high-alumina refractories
  • Monolithic refractories (castables, gunning mixes)
  • Specialized flow-control solutions
  • Refractory systems for glass, cement, and petrochemical industries

The company also develops advanced formulations to improve oxidation resistance, thermal shock performance, and service life in harsh environments.

Strategic Focus

RHI Magnesita emphasizes:

  • Global supply chain integration
  • Expansion into emerging markets (especially Asia and India)
  • Energy-efficient and sustainability-oriented products
  • Digital monitoring and performance analytics for refractories

Recent actions include commissioning a low-carbon magnesia production facility and enhancing digital furnace performance services to reduce total cost of ownership for customers.

2. Vesuvius plc

Vesuvius plc is a major UK-based refractory and engineered ceramics company, renowned for its specialization in flow control and continuous casting refractory systems. It plays a central role in high-precision refractory applications within the steel and foundry industries.

Company Background

Established in 1704, Vesuvius has evolved into a global provider of engineered refractory solutions. The company is listed on the London Stock Exchange and is part of the FTSE 250 Index.

Core Competencies

Unlike some competitors that focus heavily on raw refractory bricks, Vesuvius’s strength lies in high-value, industry-specific refractory and flow control products, particularly for continuous casting and steelmaking.

Product and Solution Portfolio

Vesuvius offers refractory materials and systems for:

  • Steel flow control components (slide gate plates, nozzles, stopper rods)
  • Foundry technologies (molds, filters, gating systems)
  • Advanced refractories for extreme conditions
  • Process diagnostics and services

The company has cultivated deep expertise in metallurgy and refractory science, with solutions engineered to improve casting quality and reduce inclusion defects.

Innovation and Services

Vesuvius invests a notable portion of revenue in research and development, enhancing product performance and digital tools for refractory life prediction. Its strategic initiatives include acquisitions that broaden manufacturing capabilities and the introduction of AI-based tracking systems for refractory assets.

3. Saint-Gobain High-Performance Refractories

Saint-Gobain is a historic French materials conglomerate with a significant presence in refractories through its High-Performance Refractories division. The company’s refractory operations serve multiple industries, with a strong emphasis on engineered products and thermal insulation solutions.

Corporate Context

Saint-Gobain, founded in 1665, is one of the oldest industrial enterprises in the world. Its refractory business encompasses a network of production facilities, research centers, and sales offices across continents.

Refractory Specializations

The company’s refractory activities include:

  • Fused cast refractories for glass and industrial furnaces
  • High-alumina and zirconia materials
  • Sintered and unshaped refractories
  • Insulating products and next-generation ceramic fibers

A specialized arm of the business, Saint-Gobain SEFPRO, focuses on refractory solutions for the glass industry with products such as AZS (alumina-zirconia-silica) and high zirconia refractories.

Global Footprint and Capabilities

Saint-Gobain’s refractory segment operates globally, with manufacturing and R&D spread across Europe, Asia, and the Americas. Its industrial ceramics expertise spans thermal barriers, insulation, and advanced refractory composites that meet stringent performance and sustainability requirements.

4. Shinagawa Refractories Co., Ltd.

Shinagawa Refractories Co., Ltd. (now Shinagawa Refra) is one of Japan’s oldest and most respected refractory manufacturers, with more than a century of experience in advanced refractory solutions for steel, glass, cement, and other high-temperature industries.

Company Profile

Founded in 1875, Shinagawa is recognized for its commitment to technical quality and innovation. The company produces shaped and unshaped refractories, ceramic fibers, and advanced materials tailored to demanding industrial applications.

Product Offerings

Shinagawa’s product portfolio includes:

  • Shaped refractories (high-alumina, basic, carbon-bearing bricks)
  • Monolithic refractories (castables, gunning mixes)
  • Continuous casting consumables (slide gate plates, nozzles, stoppers)
  • Ceramic fibers and insulation materials
  • Fine and advanced ceramics for diversified industrial use

The company’s offerings are engineered for thermal shock resistance, corrosion resistance, and long service life in extreme environments.

Global Presence and Capabilities

With revenue in the tens of billions of Japanese yen and a workforce of several thousand employees, Shinagawa maintains production facilities and sales networks across Asia, Australia, North America, and beyond. Its manufacturing expertise combines precision machining, quality control, and material science to meet global customer needs.

Innovation and Quality

Shinagawa emphasizes technology development and quality assurance as cornerstones of its business. Research partnerships and internal R&D initiatives focus on developing advanced refractory materials, including zirconia-based and specialty refractories for tailored applications.

5. IFGL Refractories Ltd.

IFGL Refractories Ltd. is an Indian refractory manufacturer that has grown into a global player, particularly in steel and non-ferrous industry applications. Its focus on engineered systems and global integration has differentiated IFGL in the competitive refractory market.

Company Evolution

Founded in 1979 as Indo Flogates, IFGL has expanded through strategic acquisitions and partnerships. Over the decades, it has broadened its product portfolio and geographic reach, now operating multiple manufacturing units across Asia, Europe, and North America.

Product and Service Portfolio

IFGL supplies a wide range of refractory products, including:

  • ISO-certified shaped refractories
  • Monolithic and precast products
  • Flow control systems and slide gate solutions
  • Continuous casting consumables
  • Tailored refractory systems for ferrous and non-ferrous industries

The company’s diverse offering supports customers across the steel, cement, glass, aluminum, and chemical sectors.

Strategic Expansion

IFGL has pursued growth through acquisitions such as Monocon International Refractories and Hofmann Ceramic GmbH, enhancing its product capabilities and access to European and U.S. markets. It also established a research center in India to drive next-generation refractory solutions.

Strategic Trends Shaping the Refractory Industry

Across all five top manufacturers, a few common themes emerge:

  • Innovation and R&D: Refractories must meet evolving demands for longer service life, lower lifecycle costs, and greater sustainability. Companies are investing in advanced materials and digital technologies.
  • Global Footprint and Local Support: The ability to serve steel mills, glass plants, and cement kilns globally while providing local technical support is a key competitive advantage.
  • Sustainability and Energy Efficiency: Environmental regulations and decarbonization goals are driving development of low-carbon refractory products and energy-efficient manufacturing.
  • Value-Added Services: Beyond products, companies offer furnace diagnostics, performance monitoring, installation services, and custom engineering.

Conclusion

The global refractory industry is dominated by a handful of companies with deep technological expertise and broad industrial reach. RHI Magnesita, Vesuvius, Saint-Gobain, Shinagawa Refractories, and IFGL Refractories represent the pinnacle of refractory manufacturing, each with distinct strengths:

  • RHI Magnesita: World leader with integrated supply and extensive product range.
  • Vesuvius: Specialist in engineered flow control and steelmaking refractories.
  • Saint-Gobain: Historic materials innovator with diverse refractory offerings.
  • Shinagawa Refractories: Japanese quality and precision across advanced refractory products.
  • IFGL Refractories: Growing global competitor with engineered refractory systems.

Together, these companies shape the development, performance standards, and technological direction of the refractory industry, enabling high-temperature processes that underpin major segments of the global economy.

More information please visit Henan Yangyu Refractories Co.,Ltd

Types of Sub-Entry Shrouds You Should Know in Continuous Casting

1. Introduction

In continuous casting, maintaining the cleanliness and stability of molten steel as it flows from the ladle to the tundish is a critical requirement. One of the most important components responsible for protecting the steel stream during this transfer is the Sub-Entry Shroud (SES), sometimes also referred to as a ladle-to-tundish shroud or ladle shroud.

The sub-entry shroud is a tubular refractory component installed between the ladle nozzle and the tundish entry zone. Its primary function is to prevent contact between molten steel and atmospheric air, thereby minimizing reoxidation, nitrogen pickup, and inclusion formation. As steel grades become cleaner and casting sequences longer, the design and selection of the appropriate type of sub-entry shroud have become increasingly important.

This article provides a detailed overview of the main types of sub-entry shrouds you should know, including their structures, materials, operating principles, advantages, limitations, and typical applications.

flow control refractory
flow control refractory

2. Basic Function of a Sub-Entry Shroud

Before discussing the types, it is essential to understand the fundamental role of a sub-entry shroud in the casting process.

The sub-entry shroud performs the following key functions:

  • Protects molten steel from air aspiration and secondary oxidation
  • Reduces nitrogen and hydrogen pickup
  • Stabilizes the steel stream entering the tundish
  • Minimizes slag entrainment during ladle change
  • Improves steel cleanliness and casting stability

Without a properly designed and installed shroud, the benefits of ladle refining and tundish metallurgy can be significantly reduced.

3. Classification of Sub-Entry Shrouds

Sub-entry shrouds can be classified based on several criteria:

  • Material composition
  • Structural design
  • Functional features
  • Casting application

In industrial practice, the most common classification is based on material and functional design, which directly influence performance and service life.

4. Conventional Alumina-Based Sub-Entry Shrouds

4.1 Description and Structure

Conventional alumina-based sub-entry shrouds are among the earliest and most widely used designs. They are typically manufactured from:

  • High-alumina refractories (Al₂O₃ ≥ 70–90%)
  • Low-carbon or carbon-free matrices

The shroud consists of a straight or slightly tapered tubular body with coupling ends designed to connect to the ladle nozzle and the tundish cover or well.

4.2 Advantages

  • Good refractoriness and thermal stability
  • Relatively low manufacturing cost
  • Adequate performance for conventional carbon steels

4.3 Limitations

  • Higher wettability by molten steel
  • Susceptibility to chemical corrosion
  • Limited resistance to thermal shock
  • Higher tendency for steel adhesion and clogging

As a result, conventional alumina shrouds are increasingly being replaced in demanding applications.

5. Alumina-Carbon Sub-Entry Shrouds

5.1 Description and Material System

Alumina-carbon (Al₂O₃–C) sub-entry shrouds are currently the most widely used type in modern steel plants. They incorporate controlled amounts of carbon into the alumina matrix.

Carbon provides:

  • Improved thermal shock resistance
  • Reduced steel wettability
  • Enhanced resistance to erosion

Antioxidants such as aluminum, silicon, or boron carbide are added to reduce carbon oxidation.

flow control refractory
flow control refractory

5.2 Structural Characteristics

Typical features include:

  • Dense inner bore with low surface roughness
  • Multi-layer structure with wear-resistant inner zones
  • Reinforced ends for mechanical stability

5.3 Advantages

  • Excellent resistance to thermal shock
  • Reduced steel adhesion and clogging
  • Stable performance during long casting sequences
  • Suitable for aluminum-killed steels

5.4 Limitations

  • Carbon oxidation if improperly protected
  • Requires controlled preheating and storage
  • Slightly higher cost than alumina-only shrouds

6. Zirconia-Based Sub-Entry Shrouds

6.1 Description and Composition

Zirconia-based sub-entry shrouds utilize zirconium dioxide (ZrO₂), either as:

  • Full zirconia shrouds
  • Zirconia inserts in the bore region

Zirconia is selected for its exceptional chemical stability and low wettability.

6.2 Key Properties

  • Extremely low steel wettability
  • Outstanding resistance to chemical corrosion
  • High density and smooth bore surface

6.3 Advantages

  • Superior anti-clogging performance
  • Excellent steel cleanliness control
  • Long service life for clean steel grades

6.4 Limitations

  • Higher material and manufacturing cost
  • Higher thermal expansion, requiring careful design
  • More sensitive to thermal shock if not engineered properly

Zirconia shrouds are commonly used in high-end applications such as automotive or bearing steels.

7. Insulated Sub-Entry Shrouds

7.1 Design Concept

Insulated sub-entry shrouds incorporate an insulating layer between the working lining and the outer shell. This design aims to:

  • Reduce heat loss from molten steel
  • Maintain stable steel temperature
  • Minimize thermal gradients

7.2 Applications

These shrouds are particularly useful in:

  • Long transfer times
  • Small tundishes
  • Low superheat casting conditions

7.3 Advantages and Challenges

While insulation improves thermal performance, it may reduce mechanical strength. Therefore, a careful balance between insulation and structural integrity is required.

8. Argon-Protected Sub-Entry Shrouds

8.1 Functional Principle

Argon-protected sub-entry shrouds are designed with gas injection channels or porous zones that allow argon gas to flow along the inner bore or coupling area.

Argon serves to:

  • Displace air from the steel stream
  • Reduce oxygen partial pressure
  • Prevent reoxidation and inclusion formation

8.2 Structural Features

  • Integrated argon inlet ports
  • Controlled pore size or slit geometry
  • Gas-tight sealing at connection points

8.3 Advantages

  • Enhanced steel cleanliness
  • Reduced nitrogen pickup
  • Improved performance during ladle changes

8.4 Limitations

  • Requires stable and controlled argon supply
  • Risk of flow disturbance if gas rate is excessive
  • Higher system complexity

9. Split-Type and Quick-Change Sub-Entry Shrouds

9.1 Design Purpose

Split-type or quick-change sub-entry shrouds are designed to:

  • Reduce ladle turnaround time
  • Improve operational flexibility
  • Facilitate rapid replacement during casting

9.2 Structural Characteristics

  • Two-piece or modular design
  • Quick-lock or clamp systems
  • Pre-assembled coupling ends

9.3 Advantages and Trade-Offs

These designs improve productivity but require precise alignment and sealing to avoid air ingress.

10. Sub-Entry Shrouds with Anti-Splash and Anti-Turbulence Design

10.1 Flow Control Features

Advanced sub-entry shrouds may include:

  • Internal flow straighteners
  • Optimized bore profiles
  • Anti-splash collars

These features help stabilize the steel stream entering the tundish.

10.2 Benefits

  • Reduced tundish surface turbulence
  • Lower slag entrainment risk
  • Improved inclusion flotation

11. Selection Criteria for Sub-Entry Shroud Types

Choosing the correct type of sub-entry shroud depends on:

  • Steel grade and cleanliness requirements
  • Casting speed and sequence length
  • Ladle change practice
  • Argon protection strategy
  • Cost and service life expectations

No single shroud type is optimal for all conditions.

12. Common Failure Modes Across Shroud Types

Regardless of type, sub-entry shrouds may suffer from:

  • Thermal shock cracking
  • Chemical corrosion
  • Mechanical breakage at joints
  • Carbon oxidation

Understanding these risks is essential for proper selection and operation.

13. Future Trends in Sub-Entry Shroud Technology

Current development focuses on:

  • Functionally graded materials
  • Improved zirconia composites
  • Better integration with argon systems
  • Enhanced dimensional precision

These advances aim to support higher casting speeds and cleaner steels.

AG 5

14. Conclusion

The sub-entry shroud is a critical protective refractory component in continuous casting. A clear understanding of the different types of sub-entry shrouds—from conventional alumina designs to advanced zirconia and argon-protected systems—is essential for selecting the right solution for each casting condition.

As steelmaking technology evolves toward higher cleanliness, longer sequences, and stricter quality standards, the importance of choosing the appropriate type of sub-entry shroud will continue to increase.

Ugello di Dosaggio (Metering Nozzle): Definizione Tecnica, Struttura e Funzione nella Colata Continua

1. Introduzione

Nel processo di colata continua dell’acciaio, il controllo accurato e ripetibile del flusso di metallo liquido rappresenta un requisito fondamentale per garantire la stabilità operativa, l’elevata pulizia dell’acciaio e la conformità del prodotto finale alle specifiche qualitative. Tra i componenti refrattari funzionali del sistema di colata, l’ugello di dosaggio (metering nozzle) riveste un ruolo essenziale.

tundish metering nozzle series
tundish metering nozzle series

Secondo la terminologia tecnica comunemente utilizzata nell’industria siderurgica europea, l’ugello di dosaggio è un componente refrattario di precisione installato sul fondo della paniera (tundish), con funzione primaria di regolazione e stabilizzazione della portata dell’acciaio liquido verso l’ugello di colata immerso (SEN).

A causa della sua posizione e funzione, l’ugello di dosaggio opera in condizioni estremamente severe dal punto di vista termico, chimico e meccanico, e deve pertanto soddisfare rigorosi requisiti di progettazione, materiali e controllo dimensionale.

2. Definizione Tecnica di Ugello di Dosaggio

Dal punto di vista normativo e funzionale, l’ugello di dosaggio può essere definito come:

Un componente refrattario funzionale destinato al controllo della portata dell’acciaio liquido dalla paniera all’ugello di colata immerso, operante in combinazione con un sistema di regolazione meccanica (stelo tappo o valvola equivalente).

Le funzioni principali dell’ugello di dosaggio sono:

  • Definizione del canale di flusso dell’acciaio liquido
  • Determinazione della portata nominale in funzione del diametro del foro
  • Fornitura di una superficie di contatto e tenuta per lo stelo tappo
  • Riduzione dell’aspirazione d’aria e della riossidazione secondaria
  • Stabilizzazione del flusso in ingresso al SEN

Pertanto, l’ugello di dosaggio è da considerarsi un elemento attivo del sistema di regolazione del flusso, e non un semplice condotto refrattario.

3. Posizionamento nel Sistema di Colata Continua

3.1 Installazione nella Paniera

L’ugello di dosaggio è installato nella zona inferiore della paniera, integrato nel sistema refrattario di fondo e allineato assialmente con l’ugello di colata immerso. Esso rappresenta l’ultimo punto di controllo del flusso prima dell’ingresso dell’acciaio nella lingottiera.

La sequenza funzionale del flusso dell’acciaio è generalmente la seguente:

Siviera → Paniera → Ugello di dosaggio → Ugello di colata immerso (SEN) → Lingottiera

3.2 Integrazione con Altri Componenti Funzionali

Dal punto di vista impiantistico, l’ugello di dosaggio opera in sinergia con:

  • Stelo tappo (stopper rod): dispositivo di regolazione meccanica della portata
  • Ugello di colata immerso (SEN): protezione del flusso in ingresso in lingottiera
  • Blocchi refrattari di fondo paniera: supporto strutturale e tenuta
  • Sistema di protezione con gas inerte (argon), ove previsto

Un corretto allineamento geometrico e una compatibilità dimensionale tra questi elementi sono essenziali per garantire la funzionalità e la sicurezza del sistema.

4. Struttura e Geometria dell’Ugello di Dosaggio

4.1 Geometria Esterna e Interna

Dal punto di vista costruttivo, l’ugello di dosaggio presenta generalmente:

  • Corpo esterno cilindrico o leggermente troncoconico
  • Foro centrale di precisione, con tolleranze dimensionali ristrette
  • Superficie superiore piana o sagomata per il contatto con lo stelo tappo
  • Interfaccia inferiore progettata per l’accoppiamento con il SEN

Il diametro del foro è definito in funzione dei parametri di colata (velocità, sezione del prodotto, grado di acciaio) ed è tipicamente compreso tra 10 mm e 30 mm.

4.2 Progettazione del Foro di Passaggio

Il foro di passaggio rappresenta la zona funzionale più critica ed è progettato per:

  • Garantire un flusso laminare e stabile
  • Limitare fenomeni di turbolenza
  • Ridurre l’adesione di inclusioni non metalliche
  • Mantenere stabilità dimensionale alle alte temperature

Le configurazioni più comuni includono fori rettilinei, leggermente conici o profilati, in funzione delle esigenze metallurgiche.

4.3 Strutture Composite e Inserti Funzionali

In conformità alle moderne pratiche industriali europee, gli ugelli di dosaggio sono spesso realizzati con strutture composite, comprendenti:

  • Inserti in zirconia stabilizzata o allumina ad alta purezza nella zona del foro
  • Corpo strutturale in allumina-carbonio o allumina-magnesia-carbonio
  • Strati di transizione per la riduzione delle tensioni termiche

Questa progettazione consente di ottimizzare le prestazioni funzionali e la durata in esercizio.

5. Materiali Refrattari Utilizzati

5.1 Refrattari ad Alta Allumina

I materiali ad alto contenuto di Al₂O₃ sono utilizzati per la loro:

  • Elevata refrattarietà
  • Buona resistenza meccanica
  • Stabilità chimica generale

Tuttavia, in applicazioni con acciai calmati all’alluminio, possono presentare una maggiore tendenza all’intasamento.

5.2 Refrattari Allumina-Carbonio (Al₂O₃–C)

Secondo la pratica industriale più diffusa in Europa, gli ugelli di dosaggio sono prevalentemente realizzati in allumina-carbonio, poiché il carbonio:

  • Migliora la resistenza agli shock termici
  • Riduce la bagnabilità dell’acciaio liquido
  • Ostacola l’adesione delle inclusioni

Per limitare l’ossidazione del carbonio, vengono impiegati sistemi antiossidanti a base di Al, Si o B₄C.

5.3 Materiali a Base di Zirconia

Gli inserti o ugelli in zirconia (ZrO₂) sono impiegati in applicazioni ad alte prestazioni per:

  • Acciai di elevata pulizia
  • Sequenze di colata prolungate
  • Elevati requisiti di stabilità del flusso

La zirconia presenta bassa bagnabilità, eccellente resistenza alla corrosione e ottime caratteristiche anti-intasamento.

6. Principio di Funzionamento

6.1 Regolazione della Portata

L’ugello di dosaggio definisce la portata massima teorica attraverso il diametro del foro. La regolazione fine è affidata allo stelo tappo:

  • Chiusura del foro mediante abbassamento dello stelo
  • Apertura controllata mediante sollevamento
  • Regolazione continua della portata in funzione della posizione

L’ugello fornisce una geometria stabile e ripetibile per il corretto funzionamento del sistema.

6.2 Flusso per Pressione Idrostatica

Il flusso dell’acciaio attraverso l’ugello avviene per effetto della pressione idrostatica generata dal livello del metallo nella paniera. L’ugello deve mantenere integrità strutturale e precisione dimensionale per tutta la durata della colata.

7. Importanza Tecnologica e Operativa

Le prestazioni dell’ugello di dosaggio influenzano direttamente:

  • Stabilità del livello in lingottiera
  • Controllo delle inclusioni
  • Qualità superficiale e interna del prodotto
  • Sicurezza e affidabilità dell’impianto

Un ugello di dosaggio non conforme o degradato può compromettere l’intero processo di colata.

8. Conclusioni

Dal punto di vista tecnico e normativo, l’ugello di dosaggio è un componente refrattario funzionale di primaria importanza nella colata continua dell’acciaio. La sua corretta progettazione, selezione dei materiali, installazione e gestione operativa sono determinanti per il raggiungimento degli obiettivi di qualità, produttività e sicurezza richiesti dall’industria siderurgica europea.

tundish nozzle
tundish nozzle

Una comprensione approfondita delle caratteristiche tecniche e del principio di funzionamento dell’ugello di dosaggio è pertanto indispensabile per ingegneri di processo, metallurgisti e responsabili di produzione.

Existing Problems of Tundish Metering Nozzles in Continuous Casting

1. Introduction

The tundish metering nozzle (TMN), also referred to as the tundish nozzle or metering nozzle, is a critical refractory component in continuous casting. Installed at the bottom of the tundish, it controls the flow rate of molten steel from the tundish into the submerged entry nozzle (SEN) and ultimately into the mold. By regulating steel flow, the tundish metering nozzle plays a key role in ensuring casting stability, steel cleanliness, and surface quality of the final product.

tundish metering nozzle insert
tundish metering nozzle insert

Despite continuous improvements in material technology and nozzle design, tundish metering nozzles still face numerous operational challenges. These problems often limit nozzle service life, disrupt casting operations, and negatively affect steel quality. Understanding the existing problems of tundish metering nozzles is essential for metallurgists, refractory engineers, and casting operators who seek to optimize performance and reliability.

This article systematically analyzes the major technical, operational, and material-related problems encountered in tundish metering nozzles, explains their root causes, and discusses their impact on continuous casting performance.

2. Severe Nozzle Clogging

2.1 Nature of the Clogging Problem

Clogging is widely recognized as the most serious and common problem affecting tundish metering nozzles. It occurs when non-metallic inclusions accumulate and adhere to the inner wall of the nozzle bore, gradually restricting molten steel flow.

flow control refractory
flow control refractory

Typical clogging products include:

  • Aluminum oxide (Al₂O₃)
  • Calcium aluminate inclusions
  • Complex oxide clusters
  • Reoxidation products

As clogging progresses, operators must increase stopper rod opening or casting speed, which destabilizes the process.

2.2 Causes of Clogging

Key factors contributing to nozzle clogging include:

  • Aluminum-killed steel grades with high Al content
  • Reoxidation due to air aspiration
  • High oxygen activity in tundish steel
  • Rough or chemically active nozzle bore surfaces
  • Insufficient argon protection

Once inclusions begin to adhere, they act as nucleation sites for further buildup, accelerating clogging.

2.3 Impact on Casting Operations

Clogging leads to:

  • Unstable steel flow
  • Mold level fluctuations
  • Reduced casting speed
  • Emergency casting interruptions
  • Increased inclusion defects in final products

3. Chemical Corrosion of Nozzle Materials

tundish metering nozzle series
tundish metering nozzle series

3.1 Slag–Refractory

Dissolution of Al₂O₃ and MgO

  • Penetration of liquid slag into pores
  • Structural weakening

3.2 Steel–Refractory Chemical Reactions

Reactions between dissolved elements in steel (such as Al, Ca, or Ti) and the nozzle material can change the chemical stability of the bore surface. These reactions often promote inclusion adhesion and accelerate wear.

3.3 Consequences of Chemical Corrosion

  • Accelerated bore enlargement
  • Increased surface roughness
  • Reduced resistance to clogging
  • Shortened nozzle service life

4. Erosion and Washout of the Nozzle Bore

4.1 High-Velocity Steel Flow

Molten steel flows through the tundish metering nozzle under significant hydrostatic pressure. High casting speeds and large tundish steel heads increase flow velocity, resulting in mechanical erosion of the bore.

4.2 Inclusion-Assisted Erosion

Hard oxide inclusions carried by the steel act as abrasive particles, intensifying material removal at:

  • Bore inlet edges
  • Flow direction changes
  • Nozzle outlet region

4.3 Effects of Erosion

series of tundish metering nozzle
series of tundish metering nozzle

Erosion causes:

  • Enlarged bore diameter
  • Increased steel flow rate
  • Loss of precise flow control
  • Higher risk of slag entrainment

5. Thermal Shock and Crack Formation

5.1 Rapid Temperature Changes

Tundish metering nozzles experience severe thermal cycling:

  • Heating during tundish preheating
  • Sudden exposure to molten steel
  • Cooling during casting interruptions

Rapid temperature changes generate thermal stress that can exceed material strength.

5.2 Crack Initiation and Propagation

Cracks often initiate at:

  • Surface defects
  • Insert–matrix interfaces
  • Regions with non-uniform microstructure

Once formed, cracks provide pathways for steel and slag penetration, accelerating failure.

6. Structural and Dimensional Instability

6.1 Manufacturing-Related Variations

Inconsistent manufacturing can result in:

  • Non-uniform density
  • Uneven bore geometry
  • Residual internal stresses

These issues reduce nozzle reliability under service conditions.

6.2 Deformation During Service

Prolonged exposure to high temperature and mechanical stress may cause:

  • Creep deformation
  • Loss of dimensional accuracy
  • Poor sealing with the stopper rod or SEN

7. Air Aspiration and Secondary Oxidation

7.1 Inadequate Sealing

Poor sealing between the tundish metering nozzle and adjacent components allows air to be sucked into the steel stream, especially at low steel levels.

7.2 Consequences of Air Ingress

Air aspiration causes:

  • Reoxidation of molten steel
  • Formation of new inclusions
  • Increased clogging tendency
  • Deterioration of steel cleanliness

8. Limited Effectiveness of Argon Protection

8.1 Non-Uniform Argon Distribution

In nozzles with argon injection capability, improper design may lead to:

  • Localized gas flow
  • Dead zones without protection
  • Turbulent steel flow

8.2 Operational Constraints

Argon flow rates must be carefully balanced. Excessive argon can:

  • Disturb mold flow
  • Entrain slag
  • Create surface defects

Insufficient argon, however, fails to prevent clogging.

9. Compatibility Issues with Stopper Rod Systems

9.1 Poor Contact and Alignment

Misalignment between the stopper rod head and tundish metering nozzle can cause:

  • Uneven wear
  • Localized erosion
  • Steel leakage

9.2 Wear at the Contact Interface

Repeated opening and closing movements create mechanical wear at the contact surface, increasing surface roughness and clogging risk.

10. Short and Unpredictable Service Life

10.1 Heat-to-Heat Variability

Service life of tundish metering nozzles often varies significantly due to:

  • Changes in steel grade
  • Slag composition variations
  • Operational instability

This unpredictability complicates maintenance planning.

10.2 Economic Impact

Frequent nozzle replacement results in:

  • Increased refractory costs
  • Higher downtime
  • Reduced productivity

11. Safety Risks

Failure of a tundish metering nozzle can lead to:

  • Molten steel leakage
  • Uncontrolled steel flow
  • Severe safety hazards

Thus, reliability is a critical concern beyond cost and quality.

12. Summary and Outlook

Despite being a relatively small component, the tundish metering nozzle faces a wide range of existing problems, including clogging, corrosion, erosion, thermal cracking, air aspiration, and compatibility issues with stopper rod systems. These problems are interconnected and often reinforce each other.

Key Challenges Identified:

  • Severe clogging in aluminum-killed steels
  • Chemical and mechanical degradation
  • Thermal shock sensitivity
  • Inconsistent service life
  • Operational and safety risks

Future improvements will depend on:

  • Advanced refractory materials (e.g., zirconia-based systems)
  • Improved argon protection design
  • Better tundish atmosphere control
  • Enhanced manufacturing quality
  • Integrated process optimization

Addressing the existing problems of tundish metering nozzles requires a system-level approach involving materials science, process control, and operational discipline. Only through coordinated optimization can steelmakers achieve stable casting, high steel cleanliness, and extended nozzle service life.