CLADDING TECHNOLOGY SHANXI CO., LTDStrip Cladding of Rolling Rolls
Literature Overview
This 1999 publication by Zhao Weiyuan, Wang Hui, Zhang Huifen, and Liu Qinglin from Dalian Heavy Industry Group and Jinan No. 2 Machine Tool Group addresses the application of strip cladding technology to rolling rolls. Rolling rolls are critical components in the metal rolling industry, subjected to severe conditions including high contact stresses, thermal cycling, and abrasive wear. The application of a hardfacing or wear-resistant overlay to the roll surface can significantly extend roll life and improve rolling quality.
Background and Application Context
Rolling rolls are typically made of medium-carbon steel or low-alloy steel, with a hardness of approximately 200–250 HB. The roll surface is subjected to contact stresses of 1.0–2.0 GPa during hot rolling, and the surface temperature can reach 500–800°C. These conditions cause rapid wear of the roll surface, requiring frequent grinding and eventually roll replacement. The application of a wear-resistant overlay can extend roll life by 2–5 times, providing significant economic benefits.
Strip cladding, also known as flash butt welding or friction welding of strip to a substrate, is a process in which a strip of wear-resistant material is bonded to the roll surface by applying heat and pressure. The process produces a solid-state bond with minimal dilution of the overlay material, preserving the wear-resistant properties of the overlay.
Strip Cladding Process
The strip cladding process involves the following steps:
- Surface preparation: The roll surface is cleaned and prepared to ensure good bonding. This typically involves grinding, cleaning, and possibly preheating.
- Strip selection: The overlay strip is selected based on the required wear resistance and compatibility with the base roll material. Common overlay materials include:
- High-speed steel (HSS) for hot rolling rolls
- Cemented carbide for cold rolling rolls
- Austenitic manganese steel for abrasive wear conditions
- Nickel-based alloys for high-temperature wear conditions
- Cladding: The strip is bonded to the roll surface using flash butt welding or friction welding. The process parameters include:
- Flash current: 10–20 kA
- Flash time: 0.1–0.5 s
- Upset pressure: 100–300 MPa
- Upset speed: 5–20 mm/s
- Post-cladding treatment: The cladded roll may require machining to achieve the required surface finish and dimensional accuracy. In some cases, post-weld heat treatment may be required to relieve residual stresses.
Technical Parameters and Process Control
Key process parameters for strip cladding of rolling rolls include:
| Parameter | Typical Value |
|---|---|
| Base roll material | 45 steel, 50CrMo, or equivalent |
| Overlay strip material | HSS, cemented carbide, or equivalent |
| Strip thickness | 5–20 mm |
| Flash current | 10–20 kA |
| Flash time | 0.1–0.5 s |
| Upset pressure | 100–300 MPa |
| Upset speed | 5–20 mm/s |
| Preheat temperature | 200–400°C (if required) |
| Post-weld cooling | Controlled cooling to avoid cracking |
The process must be carefully controlled to ensure adequate bonding and to avoid defects such as incomplete bonding, cracking, or excessive dilution. Key quality control measures include:
- Visual inspection: Check for surface defects such as cracks, porosity, and incomplete bonding.
- Ultrasonic testing: Detect subsurface defects such as lack of fusion and inclusion.
- Hardness testing: Verify that the overlay hardness is within the specified range.
- Bond strength testing: Verify that the bond strength between the overlay and the base material meets the required specification.
Engineering Practice and Lessons Learned
The application of strip cladding to rolling rolls provides several advantages over traditional hardfacing welding:
- The solid-state bonding process produces a bond with minimal dilution, preserving the wear-resistant properties of the overlay material.
- The process is fast and can be automated, reducing production time and cost.
- The overlay can be applied to the entire roll surface or to specific areas, providing flexibility in roll design.
- The process produces a smooth surface finish, reducing the need for post-cladding machining.
However, the process also has limitations:
- The process requires specialized equipment, which can be expensive.
- The process is limited to flat or slightly curved surfaces, which may not be suitable for all roll geometries.
- The process may not be suitable for very thick overlays, which can cause excessive residual stresses.
Key Technical Points and Reflections
The study by Zhao and colleagues demonstrates the practical application of strip cladding technology to rolling roll manufacturing. The process provides a cost-effective solution to the problem of roll wear, extending roll life and reducing production costs. The emphasis on process control and quality assurance is consistent with modern manufacturing practices.
The work also highlights the importance of material selection in overlay design. The overlay material must be selected based on the specific wear conditions encountered during rolling, and the process parameters must be optimized to ensure adequate bonding and wear resistance.
Conclusion
The application of strip cladding to rolling rolls represents a significant advancement in roll manufacturing technology. The process provides a cost-effective solution to the problem of roll wear, extending roll life and improving rolling quality. The study by Zhao and colleagues provides valuable insights into the process parameters, quality control measures, and engineering considerations required for successful strip cladding. Engineers involved in roll manufacturing should consider strip cladding as a viable option for extending roll life and reducing production costs, provided that the process is properly qualified and the cladded rolls are thoroughly inspected.