CLADDING TECHNOLOGY SHANXI CO., LTDExperience Discussion on Roll Surface Overlay Maintenance of Roller Presses
Literature Overview
This technical paper, authored by Wang Mingwan from Baoshan Kunsteel Jiahua Cement Building Materials Co., Ltd., published in 2015 in the journal "Cement," discusses practical experience in the overlay maintenance of roller surfaces in roller presses used in the cement industry. Roller presses are critical equipment in cement production, used for the grinding of raw materials and clinker. The roller surfaces are subjected to extreme abrasive wear, impact loading, and thermal cycling, resulting in frequent and costly maintenance requirements. This paper provides a valuable account of field experience in overlay welding repair and maintenance, offering practical insights that complement theoretical welding knowledge with real-world operational data.
Technical Background of Roller Press Overlay
Roller presses in cement plants typically consist of two large cylindrical rollers (diameter 1.0–1.5 m, length 1.5–2.5 m) that rotate against each other under high compressive forces (typically 80–150 kN/cm of roller length). The rollers are made of high-chromium white iron or cast steel, with surface hardness ranging from 500–700 HV. During operation, the roller surfaces are subjected to:
- Abrasive wear: From hard particles in the cement raw material or clinker.
- Impact loading: From sudden changes in feed material composition or roller misalignment.
- Thermal cycling: From the frictional heat generated during grinding, which can raise the roller surface temperature to 150–250°C.
- Corrosive attack: From moisture and chemical compounds in the grinding material.
The combination of these loading conditions results in roller surface wear rates of 0.5–2.0 mm per month, depending on the material being ground and the operating conditions. Overlay welding is used to restore the roller surface geometry and provide a wear-resistant surface layer.
Overlay Materials and Process Selection
The paper discusses the selection of overlay materials and welding processes based on practical experience. The following table summarizes the commonly used combinations:
| Overlay Material | Hardness (HV) | Welding Process | Typical Application |
|---|---|---|---|
| High-carbon martensitic steel (e.g., D2 equivalent) | 550–650 | SAW / FCAW | General wear-resistant overlay |
| High-chromium white iron | 700–850 | Oxy-fuel / SAW | High abrasion resistance |
| Nickel-based alloy (e.g., Stellite 6) | 350–450 | PTA / Laser cladding | High-temperature and corrosive environments |
| Tungsten carbide composite | 1200–1500 | Laser cladding / SAW with carbide powder | Extreme abrasion resistance |
The paper emphasizes that the selection of overlay material and process must consider not only wear resistance but also toughness, fatigue resistance, and compatibility with the base metal. For example, high-chromium white iron overlays provide excellent abrasion resistance but are brittle and susceptible to cracking under impact loading. In contrast, nickel-based alloy overlays offer better toughness and fatigue resistance but at lower hardness and higher cost.
Practical Experience and Lessons Learned
The author shares several key lessons from years of roller press overlay maintenance:
- Surface preparation is critical: The roller surface must be thoroughly cleaned and prepared before overlay welding. Residual material, rust, and old overlay layers must be completely removed by grinding or shot blasting. Poor surface preparation is the leading cause of overlay failure due to lack of fusion and delamination.
- Preheating is essential: The roller base metal must be preheated to 150–250°C before overlay welding to reduce the risk of cracking, particularly when using high-carbon or high-chromium overlay materials. The preheat temperature must be maintained throughout the welding process to prevent thermal shock.
- Layer thickness control: The overlay layer thickness should be limited to 2–5 mm per pass, with a total overlay thickness of 5–15 mm depending on the expected service life. Excessive overlay thickness increases the risk of cracking and reduces the fatigue life of the overlay layer.
- Post-weld treatment: The overlay layer must be stress-relieved by heating to 500–600°C for 2–4 hours to relieve residual stresses and prevent delayed cracking. For high-carbon martensitic overlays, a tempering treatment at 550–650°C is recommended to reduce hardness and improve toughness.
- Inspection and quality control: Each overlay pass must be inspected by magnetic particle testing (MT) to detect surface cracks and lack of fusion. The final overlay surface must be ground to the specified geometry and finish, with dimensional tolerances of ±0.1 mm.
Common Defects and Countermeasures
The paper identifies several common defects encountered in roller press overlay maintenance and provides countermeasures:
| Defect | Cause | Countermeasure |
|---|---|---|
| Cracking | High restraint stress, inadequate preheat | Increase preheat temperature, reduce heat input, apply post-weld stress relief |
| Lack of fusion | Poor surface preparation, low current | Improve surface cleaning, increase current, use multiple passes with proper overlap |
| Delamination | Residual stress, thermal mismatch | Apply post-weld stress relief, use compatible overlay materials |
| Excessive dilution | High heat input, thick base metal | Reduce heat input, use multiple thin passes, control interpass temperature |
| Surface porosity | Flux contamination, inadequate shielding | Use clean flux, ensure proper gas shielding, maintain dry welding environment |
Engineering Practice Insights
This paper provides a valuable bridge between theoretical welding knowledge and practical field experience. The author's emphasis on surface preparation, preheating, and post-weld treatment highlights the importance of process discipline in overlay welding maintenance. The paper also underscores the economic importance of overlay maintenance in cement production, where downtime costs can exceed $10,000 per hour. A well-executed overlay maintenance program can extend roller life by 2–3 times compared to uncontrolled or poorly executed repairs.
The paper also notes the importance of operator training and qualification. Overlay welding on roller presses requires skilled operators who understand the metallurgical and mechanical requirements of the application. The author recommends that all overlay welding operations be performed by certified welders who have undergone specific training in roller press overlay techniques.
Study Reflections
This paper is a practical contribution to the body of knowledge on overlay welding maintenance in the cement industry. While it does not provide the depth of metallurgical analysis found in academic research, it offers invaluable insights from field experience that are often absent from theoretical literature. The emphasis on process discipline, quality control, and operator training is particularly relevant for engineers responsible for maintenance planning and quality assurance in cement production facilities. The paper also highlights the economic importance of overlay maintenance, demonstrating that a well-executed overlay program can significantly reduce downtime and extend equipment life, resulting in substantial cost savings.