1. Introduction

In modern continuous casting operations, precise control of molten steel flow is essential to ensure stable casting, high steel cleanliness, and consistent product quality. One of the most important refractory components responsible for this control is the metering nozzle. Although relatively small in size, the metering nozzle plays a decisive role in regulating steel flow rate, stabilizing mold level, and protecting molten steel from secondary oxidation.

The term metering nozzle is most commonly used to describe the refractory nozzle installed at the bottom of the tundish, directly above the submerged entry nozzle (SEN). Its primary purpose is to “meter,” or accurately regulate, the quantity of molten steel flowing from the tundish into the mold. Because of its position and function, the metering nozzle operates under extremely severe thermal, chemical, and mechanical conditions.

This article provides a detailed explanation of what a metering nozzle is, including its definition, structure, working principle, materials, operating environment, common designs, and its critical role in continuous casting.

2. Definition of a Metering Nozzle

A metering nozzle is a precision-engineered refractory component used in continuous casting to control and stabilize the flow of molten steel from the tundish to the submerged entry nozzle. It works in conjunction with a stopper rod system or, in some cases, a slide gate system.

In simple terms, the metering nozzle:

• Defines the flow passage for molten steel

• Determines the basic flow rate through its bore diameter

• Provides a sealing and contact surface for the stopper rod

• Protects the steel stream from air aspiration and reoxidation

Because of these functions, the metering nozzle is not merely a passive channel, but an active flow-control element in the casting system.

3. Position of the Metering Nozzle in the Casting System

3.1 Location in the Tundish

The metering nozzle is installed at the bottom of the tundish, directly aligned with the submerged entry nozzle. It is typically embedded in the tundish bottom refractory lining and forms the final outlet through which steel exits the tundish.

The typical flow sequence is:

Ladle → Tundish → Metering Nozzle → SEN → Mold

3.2 Interaction with Other Components

The metering nozzle works closely with several key components:

• Stopper rod: regulates flow by opening or closing the nozzle bore

• Submerged entry nozzle (SEN): delivers steel into the mold

• Tundish bottom blocks: provide structural support and sealing

• Argon supply system (in some designs): assists anti-clogging

The compatibility and alignment of these components are critical to metering nozzle performance.

4. Basic Structure of a Metering Nozzle

4.1 Overall Geometry

A typical metering nozzle has:

• A cylindrical or slightly conical outer shape

• A precisely machined central bore

• A flat or profiled upper surface for stopper rod contact

• A lower interface designed to connect with the SEN

The bore diameter usually ranges from 10 mm to 30 mm, depending on casting speed, strand size, and steel grade.

4.2 Bore Design

The internal bore is the most critical functional area. It is designed to:

• Provide smooth steel flow

• Minimize turbulence

• Reduce inclusion adhesion

• Maintain dimensional stability during casting

Some designs include a straight bore, while others use slightly tapered or profiled bores to optimize flow characteristics.

4.3 Composite and Insert Structures

Modern metering nozzles often adopt a composite design, such as:

• Zirconia or high-purity alumina insert at the bore

• Alumina-carbon or alumina-magnesia body

• Transition layers to reduce thermal stress

This design allows different materials to perform specific functions within the same nozzle.

5. Materials Used in Metering Nozzles

5.1 Alumina-Based Materials

High-alumina refractories are widely used due to their:

• High refractoriness

• Good mechanical strength

• Reasonable corrosion resistance

However, alumina alone can be prone to clogging when casting aluminum-killed steels.

5.2 Alumina-Carbon (Al₂O₃–C)

 

Alumina-carbon materials are the most common choice for metering nozzles because carbon:

• Improves thermal shock resistance

• Reduces wettability by molten steel

• Helps prevent inclusion adhesion

To protect carbon from oxidation, antioxidants such as aluminum, silicon, or boron carbide are added.

5.3 Zirconia-Based Materials

Zirconia (ZrO₂) inserts or full zirconia nozzles are used for high-performance applications. Their advantages include:

• Extremely low wettability

• Excellent corrosion resistance

• Superior anti-clogging behavior

These nozzles are often used for clean steels and long casting sequences.

6. Working Principle of a Metering Nozzle

6.1 Flow Regulation Mechanism

The metering nozzle itself defines the maximum flow capacity through its bore diameter. Fine flow adjustment is achieved by the stopper rod:

• When the stopper rod lowers, the bore is closed

• When the stopper rod lifts, steel flows through the annular gap

• The opening degree controls the flow rate

The metering nozzle provides a stable, repeatable geometry against which the stopper rod operates.

6.2 Gravity-Driven Steel Flow

Molten steel flows through the metering nozzle under hydrostatic pressure created by the steel head in the tundish. The nozzle must maintain structural integrity and dimensional stability under this pressure throughout casting.

6.3 Flow Stabilization Function

By smoothing the steel stream before it enters the SEN, the metering nozzle:

• Reduces turbulence

• Minimizes slag entrainment

• Improves mold level stability

This stabilization is essential for surface quality and internal cleanliness of the cast product.

7. Operating Conditions and Challenges

7.1 High Thermal Load

The metering nozzle is exposed to:

• Molten steel temperatures above 1550 °C

• Severe thermal gradients during startup and shutdown

• Repeated thermal cycling

Materials must therefore have excellent thermal shock resistance.

7.2 Chemical Attack

The nozzle is in constant contact with:

• Molten steel containing reactive elements

• Tundish slag with varying oxidation potential

Chemical reactions can degrade the bore surface and promote clogging.

7.3 Mechanical Stress

Mechanical stresses arise from:

• Stopper rod movement

• Contact pressure at the sealing surface

• Vibration during casting

These stresses can lead to wear, cracking, or deformation if not properly managed.

8. Common Types of Metering Nozzles

8.1 Conventional Metering Nozzles

These use alumina or alumina-carbon materials and rely on proper steel and slag control to prevent clogging.

8.2 Anti-Clogging Metering Nozzles

Designed with:

• Zirconia inserts

• Optimized bore geometry

• Reduced surface roughness

They are widely used for aluminum-killed steels.

8.3 Argon-Purged Metering Nozzles

These nozzles incorporate gas channels that allow argon injection along the bore wall to:

• Prevent inclusion adhesion

• Reduce reoxidation

• Improve casting stability

9. Importance of the Metering Nozzle in Steel Quality

The performance of the metering nozzle directly affects:

• Mold level stability

• Inclusion distribution

• Surface and internal defects

• Casting speed consistency

Poor nozzle performance can negate the benefits of upstream refining and tundish metallurgy.

10. Installation and Operational Considerations

Proper installation is essential:

• Accurate alignment with the stopper rod and SEN

• Secure sealing to prevent air aspiration

• Controlled preheating to avoid thermal shock

Operational discipline is equally important to ensure stable nozzle performance.

11. Future Development Trends

Metering nozzle technology continues to evolve toward:

• Functionally graded materials

• Improved anti-clogging designs

• Better integration with argon systems

• Enhanced dimensional accuracy

These developments aim to support higher casting speeds, longer sequences, and stricter steel cleanliness requirements.

12. Conclusion

A metering nozzle is a critical flow-control refractory component in continuous casting, responsible for accurately regulating molten steel flow from the tundish to the mold. Its performance depends on careful design, advanced materials, precise manufacturing, and proper operation.

Although small in size, the metering nozzle has a disproportionate impact on casting stability, steel cleanliness, and operational safety. A thorough understanding of what a metering nozzle is and how it functions is therefore essential for anyone involved in modern steelmaking and continuous casting operations.