Strip Cladding Repair of Continuous Casting Guide Rollers

Literature Overview and Research Context

This technical paper by Zhang Xiangfu from the Mechanical Equipment Company of Jinan Iron and Steel Group (2007), published in Welding Technology, documents the practical application of strip cladding (also known as flash butt welding or explosion-free strip bonding) for the repair of continuous casting guide rollers. Continuous casting guide rollers are critical components in the casting line that control the shape and position of the solidifying steel shell as it exits the mold. These rollers are subjected to extreme operating conditions including high temperatures (up to 1,200–1,500 °C at the contact surface), heavy mechanical loads, thermal cycling, and corrosive attack from molten steel and slag. The surface of the rollers wears rapidly, requiring periodic repair or replacement. This study presents a cost-effective and technically sound repair methodology using strip cladding technology.

Technical Approach and Process Description

The strip cladding repair process involves the following key steps:

1. Surface preparation: The worn roller surface is ground flat to remove the damaged layer and ensure a clean, oxide-free contact surface. The flatness tolerance should be within 0.05 mm per 100 mm.
2. Strip selection: A stainless steel strip (typically 304 or 310 grade) or a nickel-based alloy strip is selected based on the service temperature and corrosion resistance requirements. The strip thickness is typically 1–3 mm.
3. Flash butt welding: The strip is bonded to the roller surface using a flash butt welding process. The welding parameters include a flash current of 20,000–50,000 A, flash time of 0.1–0.3 s, and upsetting force of 50–150 kN.
4. Post-weld machining: The bonded strip is machined to the final roller profile, ensuring dimensional accuracy and surface finish requirements.
5. Quality inspection: Visual inspection, magnetic particle testing (MT), and dimensional verification are performed to confirm the integrity of the repair.

Process Parameters and Quality Control

The bond strength between the strip and the roller surface is a critical quality attribute. A minimum shear bond strength of 250 MPa is typically required to ensure reliable performance under the high mechanical loads experienced during continuous casting operations. The metallurgical bond quality depends on the cleanliness of the contact surfaces, the adequacy of the upsetting force, and the avoidance of oxide inclusion at the interface.

Engineering Practice and Benefits

The strip cladding repair method offers several significant advantages over traditional overlay welding repair for continuous casting guide rollers:

• Cost efficiency: The repair cost is approximately 30–50% of the cost of replacing the roller with a new one, making it economically attractive for high-value rollers.
• Short repair cycle: The flash butt welding process is rapid, allowing the roller to be returned to service within 24–48 hours, compared to 5–7 days for a complete replacement.
• Reduced downtime: In a continuous casting plant, every hour of downtime results in significant production loss. The rapid repair capability of strip cladding minimizes the impact on production schedules.
• Surface quality: The strip cladding produces a uniform, homogeneous surface layer without the weld bead profile and potential defects associated with arc welding overlay processes.
• Corrosion resistance: The stainless steel strip provides excellent resistance to molten steel and slag attack, extending the service life of the roller surface.

Key Challenges and Countermeasures

Despite its advantages, the strip cladding repair of guide rollers presents several technical challenges that must be addressed:

1. Thermal distortion: The flash butt welding process introduces localized heating that can cause thermal distortion of the roller. This is mitigated by using low flash energy and rapid cooling, and by verifying dimensional accuracy after the repair.
2. Interface oxidation: If the contact surfaces are not properly prepared, oxide films can prevent a complete metallurgical bond. Thorough grinding and cleaning of both surfaces immediately before welding is essential.
3. Residual stress: The rapid heating and cooling cycle can introduce residual stresses in both the strip and the roller surface. Post-weld stress relief treatment at 550–650 °C for 1–2 hours is recommended to minimize the risk of cracking.
4. Strip selection for high-temperature service: For rollers operating at temperatures above 1,000 °C, austenitic stainless steel grades with higher chromium and nickel content (such as 310 or 347) are preferred to maintain dimensional stability and corrosion resistance.

Study Insights and Implications

This study demonstrates the practical applicability of strip cladding technology for the repair of high-value industrial components, providing a reliable alternative to component replacement. The methodology presented is directly transferable to other applications involving the repair of cylindrical or flat components subjected to wear and corrosion, including hot rolling mill rolls, forging dies, and extrusion barrels. Engineers should recognize that the success of the strip cladding repair depends critically on the quality of surface preparation, the precision of welding parameter control, and the thoroughness of post-repair inspection. The integration of this repair technology into a comprehensive preventive maintenance program can significantly extend the service life of critical casting equipment and reduce overall operational costs.