Cladding Repair and Utilization of a Large Hot Rolling Support Roll

Literature Overview

This paper by Zhou Min, published in 2004 by Anyang Iron and Steel Co., Ltd., documents the cladding repair and reutilization of a medium plate hot rolling support roll with dimensions Φ1800 mm × 2740 mm. This is a significant case study in the field of roll repair and cladding technology, addressing the economic and technical challenges of restoring large-diameter hot rolling rolls to serviceable condition through weld overlay techniques. The work represents a practical application of cladding technology in the metallurgical industry, where roll life extension and cost reduction are critical economic drivers.

Core Technical Context

Roll Specifications and Service Conditions

Hot rolling support rolls (also known as backup rolls) are subjected to extreme operating conditions:

• Diameter: 1800 mm (large diameter requires substantial cladding thickness)
• Length: 2740 mm (long working length requires uniform cladding over extended surface)
• Operating temperature: 800–1200 °C (contact with hot strip)
• Contact pressure: 200–500 MPa (high rolling force transmission)
• Cooling method: Typically water-cooled through internal channels
• Expected service life: Varies with material and maintenance practices

Common Roll Failure Modes

The primary failure modes that necessitate roll repair include:

Interpretation of Technical Points

Cladding Process Selection

For large-diameter hot rolling support rolls, several cladding processes are applicable:

Submerged Arc Welding (SAW) Overlay

SAW is the most commonly used process for roll cladding due to:

• High deposition rate: 5–15 kg/h, essential for economical repair of large rolls
• Deep penetration: Reduces the number of passes required
• Good weld quality: Low porosity rates with proper technique
• All-position capability: With mechanized equipment, can be applied to horizontal, vertical, and overhead positions

Typical SAW overlay parameters for roll repair:

Flux-Cored Arc Welding (FCAW) Overlay

FCAW offers advantages for roll repair:

• Higher deposition rate: Compared to solid wire GMAW
• Better all-position capability: Self-shielded flux-cored wire
• Lower equipment cost: Simpler power supply requirements

Gas Metal Arc Welding (GMAW) Overlay

GMAW is used for:

• Precise first pass: Better control of the root pass
• Thin overlay layers: When precise thickness control is required
• Repair of localized damage: Targeted cladding of specific areas

Cladding Material Selection

The selection of cladding material for hot rolling support rolls depends on the specific application requirements:

For the Φ1800 mm × 2740 mm support roll described in this paper, the cladding material was likely selected based on:

• The type of product being rolled (carbon steel, stainless steel, alloy steel)
• The operating temperature and thermal cycling conditions
• The required surface hardness and wear resistance
• The need for thermal fatigue resistance

Repair Procedure

The cladding repair of a large hot rolling support roll typically involves the following steps:

1. Inspection and assessment:

• Visual inspection of the roll surface
• Non-destructive testing (UT, MT) to identify subsurface defects
• Measurement of remaining roll diameter and out-of-roundness
• Determination of required cladding thickness

1. Surface preparation:

• Grinding to remove damaged surface material (typically 2–5 mm)
• Cleaning to remove scale, rust, and contaminants
• Machining to ensure dimensional accuracy and surface finish

1. Preheating:

• Induction or gas heating to the specified preheat temperature (150–250 °C)
• Temperature monitoring at multiple locations
• Maintaining preheat throughout the welding operation

1. Cladding application:

• Multi-pass overlay to achieve the required thickness (typically 10–30 mm total)
• Careful control of interpass temperature
• Overlap of adjacent passes to ensure complete fusion
• Periodic hardness checks to monitor weld quality

1. Post-weld heat treatment:

• Stress relief annealing (typically 600–700 °C for 2–4 hours)
• Hardening and tempering if required by the material specification
• Controlled cooling to prevent cracking

1. Final machining and inspection:

• Grinding to final dimensions and surface finish
• Hardness testing across the cladding thickness
• Non-destructive testing (UT, MT) of the cladding layer
• Dimensional verification and roundness check

Standards and Quality Requirements

The repair of hot rolling support rolls must comply with relevant standards:

Key quality requirements include:

• Hardness: 40–50 HRC for H13 cladding (tempered condition)
• Toughness: Minimum Charpy V-notch impact energy (typically 27 J at test temperature)
• Bond strength: Peel test per ASTM A263 or equivalent
• Surface finish: Ra ≤ 1.6 μm for precision rolling
• Out-of-roundness: ≤ 0.05 mm for support rolls

Engineering Practice Implications

Economic Considerations

The economic case for cladding repair versus roll replacement is significant:

• New roll cost: A Φ1800 mm × 2740 mm support roll may cost $50,000–$150,000 depending on material and specifications.
• Cladding repair cost: Typically $5,000–$20,000 including materials, labor, and heat treatment.
• Downtime savings: Repair can be completed in 1–2 weeks versus 3–6 months for new roll procurement.
• Life extension: Properly executed cladding can restore 80–100% of the original roll life.

Quality Assurance Challenges

The repair of large rolls presents specific QA challenges:

1. Thermal distortion: Large rolls are susceptible to distortion during heating and cooling, requiring careful thermal management.
2. Residual stress: Incomplete stress relief can lead to in-service cracking.
3. Microstructural uniformity: Achieving consistent hardness and toughness across the entire cladding surface.
4. Interface integrity: Ensuring complete fusion between the cladding layer and the base roll without excessive dilution.

Monitoring and Maintenance

After cladding repair, the following monitoring practices are recommended:

• Regular hardness surveys during roll changes to detect wear progression
• Non-destructive testing (UT, MT) at scheduled intervals to detect subsurface defects
• Dimensional measurement to monitor diameter reduction and out-of-roundness
• Surface inspection for signs of cracking, spalling, or excessive wear

Key Questions and Reflections

This case study raises several important questions for the cladding repair industry:

1. What is the optimal cladding thickness for a given roll diameter and service life requirement?
2. How can the thermal fatigue resistance of the cladding layer be improved through material selection and heat treatment?
3. What are the limits of repeated cladding repair, and at what point does the accumulated heat input compromise the base roll integrity?
4. How can advanced monitoring techniques (such as in-service UT or acoustic emission) be used to predict remaining roll life?

Study Insights and Implications

This research demonstrates the practical viability of cladding repair for large hot rolling support rolls, providing a technical basis for extending roll life and reducing production costs. The key insights include:

• Cladding repair is a technically mature and economically viable alternative to roll replacement for large-diameter support rolls.
• Careful process selection, material specification, and quality control are essential for achieving reliable repair outcomes.
• The economic benefits of cladding repair are substantial, with typical savings of 70–90% compared to new roll procurement.
• Long-term success depends on comprehensive quality assurance, including proper preheat, interpass temperature control, and post-weld heat treatment.

For engineering practice, this case study underscores the importance of:

• Developing standardized repair procedures for common roll sizes and materials.
• Investing in mechanized cladding equipment to improve consistency and productivity.
• Implementing comprehensive quality assurance programs that include both in-process and post-repair inspection.
• Maintaining detailed records of repair history to support life prediction and maintenance planning.

The practical value of this work lies in its direct applicability to metallurgical operations where roll availability and cost are critical production factors. By demonstrating the successful cladding repair of a large support roll, the research provides confidence and technical guidance for similar applications in the steel industry.