CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Plasma Arc Powder Cladding Equipment for Rolling Mill Rolls
Literature Overview
This study, published in 2011 by Yang Haibo, Pan Houhong, Zhang Daxiang, and Yang Jian from the School of Materials Science and Engineering at Southwest Jiaotong University, focuses on the development of plasma transferred arc (PTA) powder cladding equipment specifically designed for rolling mill rolls. Rolling mill rolls are critical consumable components in steel production, and their surface performance directly determines product quality, roll life, and production efficiency. The research addresses the need for a robust, field-deployable PTA cladding system capable of depositing wear-resistant and friction-reducing coatings on large cylindrical roll surfaces.
Core Technical Content
The fundamental challenge in PTA cladding of rolling mill rolls lies in the geometric configuration and the demanding operating conditions. Unlike flat plate cladding, cylindrical rolls require the plasma torch to maintain a consistent standoff distance and traverse speed while following a helical or circular path. The equipment described in this study integrates a specialized torch holder, powder feeder, cooling system, and motion control system into a unified platform.
Key Process Parameters
| Parameter | Typical Range | Rationale |
|---|---|---|
| Plasma current | 100–250 A | Balances dilution rate with deposition efficiency |
| Powder feed rate | 100–300 g/min | Controls layer thickness per pass |
| Travel speed | 100–400 mm/min | Affects heat input and microstructure |
| Shielding gas flow (Ar) | 15–25 L/min | Prevents oxidation of the molten pool |
| Powder particle size | 38–75 μm (ASTM E11) | Ensures stable plasma transfer |
| Standoff distance | 3–8 mm | Critical for arc stability and dilution control |
Equipment Design Considerations
The study emphasizes several design elements that distinguish a production-grade PTA system from a laboratory prototype:
- Powder delivery system: A pneumatic powder feeder with a hopper capable of handling 25–50 kg of powder continuously, equipped with a gas flow regulator to maintain consistent powder concentration in the plasma jet.
- Cooling system: A water-cooled torch body and nozzle assembly capable of handling continuous operation for 4–8 hours without thermal degradation of the torch components.
- Motion control: A servo-driven traverse mechanism with positioning accuracy of ±0.1 mm, enabling overlap control between adjacent passes.
- Polarity configuration: Transferred arc with cathode-negative polarity (DCEN) for stable arc and deep penetration with controlled dilution.
Process-Material Interactions
The choice of cladding powder for rolling mill rolls depends on the specific service condition. For finishing rolls, low-friction coatings such as copper-based or PTFE-filled composites are preferred, while work rolls in hot strip mills typically require wear-resistant Ni-Cr or Co-Cr alloys. The PTA process offers the advantage of minimal dilution (typically 5–15% with optimized parameters), which preserves the alloying elements in the coating and ensures the desired surface properties.
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking | High carbon equivalent, rapid cooling | Reduce travel speed, increase preheat to 150–200°C |
| Porosity | Moist powder, insufficient shielding | Dry powder at 200°C for 2 h, verify gas flow rate |
| Poor bond strength | High dilution, substrate oxidation | Clean substrate, reduce current, increase powder feed rate |
| Surface roughness | Unstable arc, powder feed fluctuation | Stabilize gas pressure, calibrate feeder |
| Arc blow | Magnetic field distortion from residual magnetism | Demagnetize roll before cladding |
Engineering Practice Insights
From a practical standpoint, the integration of PTA cladding into a rolling mill maintenance schedule requires careful planning. The equipment must be transportable to the mill floor, where ambient temperatures may range from 25°C to 45°C, and where dust and metal fines are prevalent. The study's approach of designing a self-contained system with integrated powder handling, gas supply, and motion control represents a pragmatic engineering solution that reduces setup time and operator dependency.
One critical insight is that the dilution rate in cylindrical cladding is not uniform around the roll circumference. At the top of the roll, gravity assists the molten pool flow, potentially increasing dilution on the trailing side. The traverse mechanism must compensate for this by adjusting travel speed or applying a slight tilt to the torch axis. This geometric effect is often overlooked in flat-plate studies but becomes significant for rolls with diameters exceeding 500 mm.
Study Insights and Implications
The research from Southwest Jiaotong University demonstrates that PTA cladding equipment for rolling mill rolls is not merely a scaled-up version of laboratory systems. The transition from lab to production demands attention to continuous operation capability, powder supply logistics, and operator ergonomics. The equipment described here reflects a mature understanding of the plasma arc physics, powder metallurgy, and the practical constraints of heavy industry environments. For engineers evaluating PTA systems for roll cladding, the key selection criteria should include: powder feeder capacity and consistency, torch cooling adequacy for continuous operation, traverse precision for overlap control, and the ability to handle multiple powder types without extensive reconfiguration. The study's emphasis on system integration rather than isolated component optimization is a hathe writing systemark of production-ready engineering design.