How Work Roll Crown Grinding Enhances Strip Flatness in Second-Hand Hot Rolling Mills

Work roll crown grinding is a precision maintenance process for second-hand hot rolling mills, optimizing the convex curvature (crown) of work rolls to compensate for roll deflection during high-temperature rolling. Second-hand mills often use worn rolls with uneven crowns (deviation ≥0.1mm from the target), leading to strip flatness defects (e.g., edge waves, center buckles) and 7-10% scrap rates. Implementing a dedicated crown grinding system resolves these issues, improving strip flatness to ≤0.8mm/m (per GB/T 709-2019) and extending roll life by 35-45%.

1. Crown Optimization for Uniform Roll PressureDuring hot rolling, work rolls deflect under high pressure (200-300 MPa), causing the roll gap to widen at the edges—resulting in thicker strip edges (edge waves). The crown grinding system grinds a convex profile (crown height 0.05-0.2mm, depending on roll diameter) into the work rolls, counteracting deflection. For a 1200mm-wide work roll processing 10mm-thick Q355B steel, this ensures uniform roll pressure across the strip width, reducing edge wave height from 2mm to ≤0.5mm. The system uses CNC grinding (accuracy ±0.005mm) to match the crown to strip thickness: thicker strips require larger crowns (0.2mm) to offset higher deflection.

2. Roll Wear Compensation for Consistent PerformanceWork rolls in second-hand hot rolling mills wear unevenly—edge wear (0.15mm) is often more severe than center wear (0.08mm) due to higher heat at the strip edges. The crown grinding system measures wear via a laser profilometer (sampling 100 points per roll) and grinds a tapered crown that accounts for this unevenness. For example, if a roll has 0.12mm edge wear and 0.06mm center wear, the system increases crown height at the edges by 0.06mm to restore uniform pressure. This compensation extends the number of rolling passes per roll from 800 to 1,200, cutting roll replacement costs by $8,000-$12,000 annually for a medium-sized mill.

3. Integration with Roll Change SchedulesTraditional crown grinding requires off-site processing (taking 24-48 hours per roll). The on-site crown grinding system integrates with the mill’s roll change schedule: rolls are ground during scheduled downtime (e.g., between shifts), cutting processing time to 4-6 hours per roll. The system also stores crown profiles for common strip specifications (e.g., 5mm-thick automotive steel, 15mm-thick structural steel) in its PLC, allowing quick recall when switching products. For a mill changing rolls every 3 days, this reduces unplanned downtime by 50-60%, increasing annual production by 2,000-3,000 tons.

Practical Maintenance Strategies

• Inspect grinding wheel wear daily; replace wheels when diameter decreases by >5% (e.g., from 300mm to 285mm) to maintain crown accuracy.
• Calibrate the laser profilometer weekly using a standard curved surface (known crown height) to ensure measurement precision.
• Lubricate the grinding machine’s linear rails monthly with high-viscosity oil (ISO VG 320) to prevent vibration-induced crown errors.

For second-hand hot rolling mills supplying industries like construction (structural steel) or automotive (hot-rolled coils), work roll crown grinding is a critical maintenance upgrade that ensures consistent strip quality and reduces operational costs—essential for long-term profitability.

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