How Roll Cooling Water Temperature Control Systems Optimize Second-Hand Hot Rolling Mills’ Performance

Roll cooling water temperature control systems are critical thermal management components in second-hand hot rolling mills, addressing the issue of inconsistent cooling water temperature—caused by outdated cooling towers or fluctuating ambient temperatures. Second-hand mills often use unregulated cooling water (temperature variation ±8°C), leading to work roll thermal fatigue (cracks after 800-1000 tons of rolling) and strip shape defects (e.g., edge waves, center buckles). Upgrading to a closed-loop temperature control system resolves these issues, extending work roll life by 40-50% and improving strip flatness to ≤0.7mm/m (per GB/T 709-2019).

1. Precise Temperature Control for Roll Thermal StabilityHot rolling work rolls operate at 300-400°C, and even a 5°C change in cooling water temperature can alter roll thermal expansion by 0.05mm—disrupting the roll gap and causing strip thickness variation. The temperature control system uses a combination of:

• Chillers (cooling capacity 50-100 kW) to lower water temperature to the target range (25-30°C).
• Heaters (backup, 10-20 kW) to prevent water from dropping below 25°C in cold ambient conditions.
• Temperature sensors (sampling frequency 10 Hz, accuracy ±0.5°C) to monitor water temperature in real time.For a second-hand mill processing 500 tons of Q355B steel daily, this maintains cooling water temperature variation within ±1°C, reducing roll thermal expansion variation to ±0.01mm. This stability eliminates thermal stress cracks (a major cause of roll failure) and extends work roll life from 1,200 tons to 1,800-2,000 tons per set—saving $8,000-$12,000 annually in roll replacement costs.

2. Strip Shape Improvement via Zone-Specific CoolingThe system integrates with the mill’s segmented roll cooling zones (8-12 zones per roll), allowing independent temperature control for edge and center zones. For example, if the strip develops edge waves (caused by overcooled roll edges), the system increases water temperature in the edge zones by 2-3°C to reduce cooling intensity—softening the roll edges and correcting the wave defect. For 12mm-thick hot-rolled strips used in bridge construction, this reduces shape defects from 10% to <2%, meeting the flatness requirements of EN 10025-2. The system also adjusts cooling based on strip thickness: thicker strips (≥10mm) require cooler water (25°C) to handle higher heat loads, while thinner strips (≤5mm) use slightly warmer water (28°C) to avoid overcooling.

3. Energy Efficiency & Water ConservationTraditional cooling systems in second-hand mills waste energy by running chillers and cooling towers continuously—even when water temperature is within range. The closed-loop system uses variable-frequency drives (VFDs) for chillers and pumps, adjusting power based on cooling demand: if water temperature is 27°C (close to the 28°C target), the chiller runs at 30% capacity instead of 100%. For a mill with a 75kW chiller, this reduces annual energy consumption by 30,000-40,000 kWh—saving $3,000-$4,000 (based on $0.1/kWh). The system also recycles 95% of cooling water (via filtration and disinfection), reducing fresh water consumption from 15m³/ton to 0.75m³/ton—cutting annual water costs by $22,500-$30,000 for a 1,000-ton/month mill.

Practical Maintenance Strategies

• Clean temperature sensors weekly to remove scale; replace sensors if measurement accuracy drops below ±0.5°C.
• Inspect chiller coils monthly for fouling; clean coils if heat exchange efficiency decreases by >10% (tested via temperature difference).
• Calibrate the system quarterly using a standard temperature source (25-30°C) to ensure control accuracy within ±1°C.

For second-hand hot rolling mills supplying industries like construction (structural steel) or automotive (hot-rolled coils), the roll cooling water temperature control system is a high-impact upgrade that ensures consistent strip quality, reduces maintenance costs, and aligns with sustainability goals—essential for long-term competitiveness in the steel industry.

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