Study Note on Cladding of Rolling Mills and Value Analysis

Literature Overview

The 2001 paper by Yu Bin, Li Conghua, and Shen Feiping, published in Sichuan Metallurgy, explores the application of weld overlay cladding to rolling mill components at Pangang Steel Co. The authors, representing the Equipment Management Department and Steelmaking Plant of Pangang, present a practical engineering study on extending the service life of critical rolling mill components through hardfacing and cladding technologies.

Core Technical Points

Rolling mill components, particularly backup rolls, work rolls, and housing components, are subjected to extreme combinations of compressive stress, abrasive wear, thermal cycling, and chemical attack from scale and lubricants. Conventional replacement of worn rolls is costly and time-consuming. Weld overlay cladding offers a proven method to restore or enhance the surface properties of these components.

Typical Cladding Applications in Rolling Mills

Component	Service Condition	Cladding Material	Method	Expected Life Extension
Work roll (hot strip)	1100–1200°C, abrasive scale	High-Cr cast iron, Co-Cr alloy	SAW, FCAW	2–3×
Backup roll	High compressive load	Maraging steel, 4340 overlay	SAW, ESW	1.5–2×
Roll housing	Impact, abrasion	Hardfacing alloy (Cr-C)	GMAW, FCAW	3–5×
Guide rolls	Abrasive, corrosive	High-speed steel, Stellite	GTAW, PTA	4–6×
Mill stands	General wear	Medium-Cr alloy	SAW, FCAW	2–3×

Process Selection Criteria

The selection of cladding process for rolling mill components depends on several factors:

Component geometry: Large, thick sections (backup rolls) are suitable for ESW or SAW, while thin-walled components (guide rolls) require lower-heat-input processes such as GTAW or PTA.
Required overlay thickness: SAW and ESW can deposit 10–20 mm per pass, while GTAW and PTA are limited to 0.5–2 mm per pass.
Dilution sensitivity: For applications requiring specific overlay composition (e.g., high-carbon cast iron for work rolls), low-dilution processes such as PTA or hot-wire TIG are preferred.
Production schedule: High-deposition-rate processes (ESW, SAW) are suitable for off-line repair, while lower-rate processes may be used for on-line maintenance.

Defect Prevention in Rolling Mill Cladding

Defect	Cause	Countermeasure
Cracking in overlay	High carbon equivalent of hardfacing alloy	Preheat 200–300°C, post-weld stress relief
Delamination	Poor surface preparation, contamination	Ultrasonic cleaning, grit blasting to Sa 2.5
Excessive dilution	High heat input, thin first pass	Multi-pass technique, low-current first pass
Porosity	Flux contamination, excessive travel speed	Flux drying at 300°C for 2 hours, speed optimization
Hardness variation	Inconsistent cooling rate	Controlled interpass temperature, uniform deposition

Economic Value Analysis

The economic justification for cladding rolling mill components is compelling. A typical backup roll replacement costs 300,000–500,000 RMB, while cladding repair costs 50,000–80,000 RMB. The life extension achieved through cladding (typically 2–3 times the original service life) results in significant cost savings. Additionally, the downtime associated with roll replacement (typically 48–72 hours) is reduced to 8–16 hours for cladding repair, translating to substantial production savings.

The 5W2H analysis applied to rolling mill cladding:

What: Weld overlay cladding of worn mill components
Why: Cost reduction and production continuity
Where: On-line or off-line at mill maintenance shops
When: Scheduled maintenance windows or emergency repair
Who: Certified welders with hardfacing qualification
How: SAW, FCAW, or GTAW with appropriate filler metals
How much: 60–80% cost reduction versus new component procurement

Study Insights and Practical Implications

This early-2000s research from Pangang reflects the mature application of cladding technology in Chinese steel mills. The value analysis approach is particularly instructive, as it demonstrates the business case for cladding beyond mere technical feasibility. In contemporary practice, the integration of cladding with surface engineering technologies such as thermal spray and laser cladding has expanded the options available for rolling mill component restoration. However, the fundamental principles established in this paper—process selection based on component geometry, defect prevention through proper parameter control, and economic justification through life-cycle analysis—remain equally valid today.