How to Avoid Problems of Sub-Entry Nozzle in the Steel Industry

In modern continuous casting operations, the Sub-Entry Nozzle (SEN) is one of the most critical components ensuring the smooth transfer of molten steel from the tundish into the mold. SEN performance directly affects casting stability, flow control, tundish metallurgy, and final steel quality. Any failure or malfunction of the SEN can lead to production interruptions, quality defects, and serious safety incidents such as breakout events.

To guarantee safe, stable, and efficient steel casting, it is essential for steel plants to understand the common SEN problems and implement robust preventive measures. This article provides a comprehensive technical overview of SEN issues and presents effective ways to avoid them in industrial practice.

The SEN performs several key functions:

The SEN prevents molten steel from being exposed to the surrounding atmosphere as it flows into the mold. This minimizes:

• Oxygen pickup
• Nitrogen absorption
• Formation of non-metallic inclusions

The SEN determines:

• Jet speed
• Jet angle
• Meniscus conditions
• Turbulence level
• Mold heat transfer

These factors are essential for preventing surface defects, breakout, or unstable solidification.

A stable steel flow through a properly designed SEN reduces slag entrapment and prevents inclusion defects.

The SEN must withstand:

• High-temperature thermal shock
• Erosion from molten steel
• Chemical attack from slag
• Pressure variations

Any deterioration compromises casting stability.

Before addressing prevention, understanding common SEN failures is crucial.

Clogging is the most significant issue encountered during casting.

• Alumina buildup from deoxidized steel
• Reaction between steel and refractory
• Turbulence causing inclusion deposition
• Slag entrapment and infiltration
• Temperature drop leading to partial solidification

• Reduced steel flow rate
• Meniscus instability
• Shell thickness variations
• Casting speed reduction
• Risk of breakout

Gradual material loss from the inner bore or outer surface is common.

• High jet velocity
• Chemical reaction with mold flux
• Steel flow containing inclusions or slag
• High tundish metal head pressure

• Enlargement of bore diameter
• Uncontrolled steel flow
• Vibration and hydrodynamic instability

Thermal shock during preheating or steel contact can cause cracks.

• Improper preheating procedure
• Rapid temperature fluctuation
• Uneven temperature distribution

• Sudden nozzle failure
• Ladle gate blockage
• Casting interruption

Leakage at the SEN-tundish joint is dangerous.

• Improper mounting
• Seal deterioration
• Misalignment
• Poor refractory seating quality

• Steel leakage
• Tundish breakout
• Safety hazards

If immersion depth is incorrect:

• Too shallow → air aspiration and oxidation
• Too deep → excessive turbulence and mold flux disturbance

This section outlines practical, effective methods used by leading steel plants to avoid SEN issues.

Modern SENs use materials such as:

• Zirconia-based refractories (ZrO₂ > 70%) for alumina build-up resistance
• MgO-C composites for reducing reaction with steel
• ZrO₂ coatings on internal bore surfaces

These materials significantly reduce chemical interaction and deposition.

Steel plants should:

• Limit excess aluminum in Al-killed steels
• Consider partial Si-deoxidation
• Use calcium treatment to modify alumina inclusions into liquid Ca-aluminates
• Control dissolved oxygen levels

Calcium treatment is particularly effective for preventing alumina nozzle clogging.

Uniform casting temperature reduces:

• Partial freezing
• Viscosity increase
• Inclusion deposition

Ideal superheat control ±5°C improves SEN stability.

EMS can:

• Reduce inclusion deposition
• Improve flow uniformity
• Minimize clogging tendency

Features that improve resistance:

• Thickened slag line area
• High-density zirconia structural reinforcements
• Optimized port geometry

Aggressive mold flux can severely erode SEN walls. Plants should:

• Use flux with proper viscosity and melting point
• Control CaO/SiO₂ ratio
• Reduce fluoride-based fluxes for corrosion-sensitive refractories

Very high casting speeds increase:

• Jet velocity
• SEN inner wall erosion

A controlled, steady casting speed prevents unnecessary erosion.

SEN should be heated uniformly to 800–1100°C depending on material.

Key precautions:

• Use slow, steady heating curves
• Ensure even flame distribution
• Avoid direct flame impingement

Materials such as:

• MgO-C
• Zirconia-spinel
• Alumina-graphite

provide excellent resistance to sudden temperature changes.

Any moisture on SEN surface can cause explosive spalling.

Achievable by:

• Using high-density, low-porosity seating blocks
• Ensuring proper machining tolerance
• Avoiding cracks or surface roughness

Operators must ensure:

• Correct placement
• Proper alignment
• Uniform tightening force

Specialized gaskets and sealant powders help prevent tundish–SEN leaks.

Proper SEN immersion depth depends on:

• Casting speed
• Mold dimensions
• Steel grade

• Normal carbon steel: 50–90 mm
• Stainless steel: 70–100 mm
• High-speed thin slab casting: 100–130 mm

Correct depth prevents air aspiration and excessive mold turbulence.

Leading steel plants adopt improved SEN designs:

• Swirling flow ports
• Enlarged upper bore
• Internal coatings
• Controlled surface roughness

• Multiport SEN
• Biased port SEN
• Bottom-entry SEN

These help stabilize flow patterns and minimize inclusion entrapment.

CFD allows engineers to:

• Predict flow patterns
• Analyze erosion risk zones
• Optimize port design
• Reduce turbulence

Modern CFD-based design reduces SEN problems by up to 40%.

Beyond design and materials, operational discipline is critical.

• Clean steel practice
• Proper slag management
• Inclusion flotation via gas bubbling

Any residual oxide can cause SEN buildup.

Strict cleaning schedule is essential.

A small argon flow:

• Reduces clogging
• Maintains bore temperature
• Improves flow stability

Flow rate must be optimized to avoid:

• Blow holes
• Mold level fluctuations

Use of sensors and live process data helps detect early signs of:

• Clogging
• Temperature drop
• Flow instability

The Sub-Entry Nozzle is a vital component in modern steel continuous casting. Problems such as clogging, erosion, cracking, and leakage can severely impact production efficiency and product quality. However, by applying a comprehensive strategy that covers material technology, SEN design, casting practices, tundish metallurgy, and operational control, steel plants can significantly minimize SEN-related issues.

Key takeaways include:

• Use advanced zirconia-based materials and anti-clogging coatings
• Optimize steel deoxidation and ensure proper calcium treatment
• Implement strict preheating and installation procedures
• Control casting speed, temperature, and mold flux properties
• Use argon purging and real-time monitoring systems
• Apply CFD-guided SEN design improvements

A well-maintained and properly operated SEN system enhances casting stability, reduces defects, increases productivity, and improves overall steel plant performance

More information please visit Henan Yangyu Refractories Co.,Ltd