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:

• 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.