Application of Overlay Welded Work Rolls on 4200 Rolling Mill

Literature Overview

This paper by Wang Zhenyu from Wuyang Steel Company, published in Special Steel in 1993 (Volume 14, Issue 4, pages 41-42), describes the application of overlay welded work rolls on a 4200 rolling mill. The paper discusses the challenges of work roll wear in hot rolling operations and the benefits of using overlay welded rolls for extending roll life and reducing costs. The classification code TG333.17 indicates the focus on rolling technology. This work is relevant to engineers in the steel industry and to those dealing with wear-resistant overlay applications in heavy industrial equipment.

Technical Background

Work Roll Function and Wear Mechanisms

Work rolls in a rolling mill are the most critical and wear-prone components in steel production. During hot rolling:

• Direct contact: Work rolls are in direct contact with hot steel slabs.
• High temperature: Roll surface temperature can reach 600-1000°C during rolling.
• High pressure: Rolling forces can exceed 1000 tons per roll.
• Thermal cycling: Repeated heating and cooling during rolling cycles.
• Abrasive wear: Contact with scale, oxide, and abrasive particles on the slab surface.
• Adhesive wear: Material transfer between the roll and the slab.
• Fatigue wear: Thermal and mechanical fatigue leading to surface cracking and spalling.

Consequences of Work Roll Wear

The consumption of work rolls significantly impacts production costs. Roll replacement requires production stoppage, roll dressing, and installation, all of which reduce productivity.

Overlay Welded Work Roll Technology

Design Principles

Overlay welded work rolls are designed to combine the toughness of a steel core with the wear resistance of a hard overlay layer:

1. Core material: Typically a high-strength steel with good toughness and machinability.
2. Overlay material: A hard, wear-resistant alloy with high hardness and thermal stability.
3. Bonding layer: A transition layer that ensures good fusion between the core and overlay.
4. Surface finish: The overlay surface must be suitable for rolling operations.

Overlay Material Selection

The selection of overlay material depends on the specific rolling application:

Manufacturing Process

The manufacturing of overlay welded work rolls involves:

1. Core preparation: Machining the core to the required dimensions.
2. Surface preparation: Cleaning and preparation of the core surface for overlay welding.
3. Overlay welding: Application of the overlay layer using appropriate welding processes.
4. Post-weld heat treatment: Stress relief and hardening as required.
5. Machining: Final machining of the overlay surface to required tolerances.
6. Quality inspection: Verification of dimensions, hardness, and surface quality.

Performance on 4200 Rolling Mill

4200 Rolling Mill Specifications

The 4200 rolling mill refers to a four-high rolling mill with a roll diameter of 4200 mm. This type of mill is used for hot rolling of steel plates or bars. The specific conditions on this mill include:

• Roll diameter: 4200 mm (large diameter for plate rolling).
• Rolling temperature: High temperature during hot rolling.
• Rolling force: High forces due to large reduction.
• Product range: Various steel grades and thicknesses.

Performance Results

The paper reports successful application of overlay welded work rolls on the 4200 rolling mill. The key performance indicators include:

Comparison with Other Steel Companies

The paper mentions that major steel companies in China, including Ansteel (Anshan Iron and Steel) and TISCO (Taiyuan Iron and Steel), have also adopted overlay welded work rolls. This indicates that the technology has been validated across multiple companies and rolling mill configurations.

Integration with Engineering Practice

Application to Other Industrial Components

The principles of overlay welded work rolls can be applied to other industrial components that experience severe wear:

1. Pipe fittings: Elbows, tees, and reducers in abrasive service can benefit from overlay welding.
2. Valve components: Valve seats and plugs in abrasive service can be overlay welded for extended life.
3. Pump components: Pump impellers and casings in abrasive slurry service can be overlay welded.
4. Conveyor components: Conveyor rollers and tracks in mining applications can be overlay welded.

Quality Control for Overlay Welded Components

Cost-Benefit Analysis

The economic justification for overlay welded work rolls depends on:

1. Initial cost: The cost of overlay welded rolls is higher than conventional rolls.
2. Service life extension: The extended service life reduces the number of roll changes.
3. Productivity improvement: Reduced roll changes improve overall productivity.
4. Quality improvement: Improved roll surface quality improves product quality.
5. Maintenance cost: Reduced maintenance and repair costs.

The break-even point is typically reached within a few roll changes, after which the overlay welded rolls provide net cost savings.

Key Questions and Reflections

1. Long-term performance data: The paper reports successful application but does not provide detailed long-term performance data. Engineers should seek additional data on the service life of overlay welded rolls under various operating conditions.
2. Overlay spalling: One of the failure modes of overlay welded rolls is spalling of the overlay layer. This can occur due to thermal fatigue, mechanical fatigue, or poor bonding between the overlay and the core. Understanding the mechanisms of overlay spalling is critical for improving roll life.
3. Roll dressing: Overlay welded rolls may require different dressing procedures than conventional rolls. The dressing process must remove wear without exposing the core material or damaging the overlay.