1. Introduction

In modern continuous casting operations, the tundish nozzle plays a crucial role in regulating molten steel flow from the tundish into the Submerged Entry Nozzle (SEN) or directly into the mold. Its reliability and flow-control stability directly impact mold level fluctuation, inclusion removal, casting speed, steel cleanliness, and overall process efficiency. Among various nozzle types, the isostatic tundish nozzle—also known as the isostatically pressed tundish nozzle—has emerged as a high-performance solution due to its superior density, strength, and anti-erosion characteristics. These nozzles leverage advanced isostatic pressing technology to achieve uniform microstructure and enhanced service life, thereby supporting high-productivity and high-quality steelmaking.

This article provides a comprehensive technical overview of the isostatic tundish nozzle, including its definition, manufacturing principles, material properties, performance advantages, design features, and application recommendations for steel plants.

2. What Is an Isostatic Tundish Nozzle?

An isostatic tundish nozzle is a tundish refractory component manufactured using cold isostatic pressing (CIP) technology to achieve a highly uniform, high-density, high-strength structure. It is typically installed at the bottom of the tundish and serves as the primary outlet for molten steel flow. Its functions include:

• Controlling molten steel flow rate

• Providing stable connection with slide gate plates or stopper rod systems

• Resisting erosion and chemical attack from steel and slag

• Maintaining dimensional accuracy during long-sequence casting

Compared with conventional vibration-molded or press-formed nozzles, isostatic nozzles present:

• Significantly higher density

• Lower apparent porosity

• Better thermal shock resistance

• Longer service life

• Lower probability of cracking or chipping

• Improved flow-stability, reducing mold level fluctuation

Isostatic tundish nozzles are now widely used in billet, bloom, and slab casters, particularly industries demanding long casting sequences and high steel cleanliness, such as automotive steel, silicon steel, pipeline steel, and bearing steel.

3. Principles of Isostatic Pressing Technology

3.1 Definition of Isostatic Pressing

Isostatic pressing is a forming method in which powder materials are compacted under equal pressure from all directions. Unlike conventional pressing methods that apply pressure only from one axis, isostatic pressing ensures uniform compaction and consistent density distribution.

3.2 Manufacturing Process of Isostatic Tundish Nozzle

The typical process includes:

1. Raw material selection and batching

   • High-purity alumina (Al₂O₃)

   • Zirconia (ZrO₂) or stabilized zirconia

   • Chromia or alumina-graphite compositions for specific grades

   • High-temperature binders and antioxidants

2. Powder mixing and granulation

   • Ensures uniform distribution of fine particles and additives

3. Molding using CIP method
   The mixed material is sealed in a flexible mold and placed in a pressure vessel.
   Hydrostatic pressure of 100–400 MPa is applied uniformly.

4. Drying and cold machining

   • Ensures dimensional accuracy and smooth inner bore

5. High-temperature firing

   • Typically at 1500–1700°C depending on the composition

   • Achieves sintering, increases density and microstructural bonding

6. Final inspection and machining

   • Tolerances are tighter compared with conventional products

   • Surface quality superior, reducing erosion initiation sites

3.3 Advantages of Isostatic Pressing in Tundish Nozzle Production

• Uniform density distribution prevents structural weak points.

• Reduced porosity limits slag and steel penetration.

• Higher mechanical strength, both cold and hot.

• Improved thermal shock resistance due to dense and homogeneous microstructure.

• Better erosion resistance against molten steel turbulence and chemical attack.

4. Materials Used in Isostatic Tundish Nozzles

The material compositions vary based on the steel grade, casting time, and tundish design. Typical materials include:

4.1 Alumina–Carbon (Al₂O₃–C)

• High thermal conductivity

• Good thermal shock resistance

• Often used for billet or round caster nozzles

• Added graphite improves slag resistance

4.2 Zirconia–Graphite (ZrO₂–C)

• Very high corrosion resistance

• Suitable for high-cleanliness steel

• Excellent erosion resistance in long-sequence casting

4.3 Alumina–Zirconia–Carbon (AZC)

• Strong structural stability

• Balanced resistance to erosion and thermal stress

• Widely used in slab caster nozzles

4.4 Stabilized Zirconia (MgO-PSZ, CaO-PSZ, etc.)

• Ultra-high refractoriness

• Exceptional resistance to thermal cycling

• Premium solution for critical casting operations

The material choice significantly influences performance, and isostatic technology further enhances inherent material properties.

5. Structural Design Features

Isostatic tundish nozzles are designed with special geometries to maintain stable flow and reduce stress concentration:

5.1 Bore Shape and Flow Control

Common bore shapes include:

• Straight bore

• Venturi bore

• Non-circular (oval or slot-type) depending on flow requirements

• Converging–diverging designs to optimize velocity profile

Venturi and converging designs help stabilize flow and minimize turbulence entering the SEN.

5.2 Outer-body Structure

• Multi-layer composite structures: inner erosion-resistant layer + outer insulating layer

• Reinforced shoulders to accommodate mechanical stress

• Anti-crack chamfers and optimized transition radii

5.3 Dimensional Tolerances

Isostatic nozzles maintain very tight tolerances:

• Bore dimensional tolerance ≤ ±0.2 mm

• Ovality minimized

• External surface roundness improved

This precision contributes to more predictable flow and better compatibility with slide gate or stopper mechanisms.

6. Performance Advantages

Isostatic tundish nozzles outperform conventional nozzles in several critical areas:

6.1 Enhanced Mechanical Strength

• High cold crushing strength

• High hot modulus of rupture

• Minimal deformation under thermal load

This significantly reduces fracture and chipping incidence.

6.2 Superior Thermal Shock Resistance

Dense microstructure minimizes thermal gradient damage, making the nozzle more resistant to:

• Rapid heating during tundish preheating

• Sudden temperature changes during casting

• Flame impingement and steel penetration

6.3 Excellent Erosion and Corrosion Resistance

Especially important when casting:

• High-alloy steels

• Ultra-low sulfur steels

• High-oxygen or aggressive slag systems

Zirconia-based isostatic nozzles can easily handle long sequences exceeding 16–20 hours.

6.4 Longer Service Life and Stability

The lifetime of an isostatic tundish nozzle is typically:

• 2–3× that of conventional pressed nozzles

• More stable flow rate throughout casting

• Less risk of bore enlargement or clogging

6.5 Reduced Casting Risks

• Lower risk of cracking

• Lower probability of nozzle blockage

• Reduced casting interruptions and breakouts

• More stable mold level, improving slab quality

These benefits directly contribute to higher productivity and quality consistency.

7. Applications in Continuous Casting

Isostatic tundish nozzles are used in:

7.1 Slab Casters

• Automotive steel

• Silicon steel

• High-strength low-alloy (HSLA) steel

• Pipeline grades

7.2 Billet and Bloom Casters

• Long-sequence mass production

• High-temperature operations

• High wear-resistance requirements

7.3 Special Steel Casting

• Bearing steel

• Stainless steel

• Casting requiring ultra-clean conditions

Their durability and stability reduce maintenance and downtime across all these areas.

8. Factors to Consider When Selecting an Isostatic Tundish Nozzle

8.1 Casting Time and Steel Grade

Long casting sequences require high zirconia content.

8.2 Tundish Operation Parameters

• Preheating method

• Slide gate configuration

• Stopper rod control system

8.3 Slag Composition & Erosion Conditions

Aggressive slags demand improved corrosion resistance materials.

8.4 Budget and Lifecycle Cost

While isostatic nozzles have higher initial cost, lifecycle savings are substantial.

9. Conclusion

The isostatic tundish nozzle represents a significant advancement in tundish refractories for continuous casting. By combining high-purity materials with isostatic pressing technology, these nozzles achieve unmatched uniformity, strength, erosion resistance, and thermal shock stability. Their precise dimensions and microstructural consistency ensure smooth molten steel flow, reduced turbulence, and improved casting stability.

For steel plants seeking improved process reliability, longer nozzle life, and higher product quality—particularly in demanding steel grades and long-sequence casting—the isostatic tundish nozzle is an essential and highly effective solution. As steelmaking continues to evolve toward cleaner, more efficient, and more automated operations, isostatically pressed nozzles will remain a core technology supporting the next generation of continuous casting performance.More information please visit Henan Yangyu Refractories Co.,Ltd