The Impact of Roll Cooling Systems on Second-Hand Hot Rolling Mills’ Productivity & Roll Life

Roll cooling systems are vital thermal management components in second-hand hot rolling mills, controlling the temperature of work rolls and backup rolls during high-temperature rolling (800-1200°C). Second-hand mills often have outdated cooling systems with clogged nozzles or uneven water distribution—leading to roll overheating (surface temperature >500°C), thermal fatigue cracking, and reduced roll life. An upgraded cooling system resolves these issues, extending roll life by 40-50% and allowing the mill to operate at higher speeds (180-220m/min vs. 140-160m/min), increasing annual throughput by 25-30%.

1. Uniform Cooling Prevents Roll Thermal CrackingHot rolling generates intense heat that raises work roll surface temperature by 300-400°C per pass. Outdated cooling systems in second-hand mills create temperature gradients (±50°C across the roll width), causing thermal stress and fatigue cracks (depth 0.5-1mm) after 800-1000 tons of rolling. The upgraded system uses:

• High-pressure water nozzles (pressure 2-3 MPa, spacing 50-80mm) for uniform water distribution (flow deviation ≤5% across the roll).
• Segmented cooling zones (8-12 zones per roll) to adjust water flow based on heat load—e.g., increasing flow by 30% in high-heat edge zones.For work rolls processing Q355B structural steel, this reduces temperature gradients to ±15°C, eliminating thermal cracking and extending roll life from 1,200 tons to 1,800 tons per set. For a second-hand mill using cast iron rolls ($6,000 per set), this saves $30,000-$40,000 annually in roll costs.

2. Temperature Control for Strip Shape StabilityOverheated rolls in second-hand mills undergo thermal expansion (0.1-0.2mm for every 100°C increase), changing the roll gap and causing strip shape defects (e.g., edge waves, center buckles). The cooling system’s real-time temperature monitoring (using thermocouples embedded in rolls) adjusts water flow to maintain roll surface temperature at 300-350°C—keeping roll expansion within ±0.03mm. For 10mm-thick hot-rolled strips used in bridge construction, this reduces shape defects from 10% to <2%, meeting the flatness requirement of ≤1mm/m (GB/T 709-2019). It also eliminates the need for secondary leveling, saving 0.2-0.3 labor hours per ton of strip.

3. Energy & Water Efficiency OptimizationTraditional cooling systems in second-hand mills use excessive water (15-20 m³/ton of steel) and require high-power pumps (150-200 kW). The upgraded system features:

• A closed-loop water recycling system (with 5μm filters) that reuses 90% of cooling water, reducing fresh water consumption to 1.5-2 m³/ton.
• Variable-frequency drive (VFD) pumps that adjust power based on cooling demand—reducing pump energy use by 40% (from 180 kW to 108 kW) during low-heat rolling.For a second-hand mill processing 1,000 tons of steel daily, this translates to annual water savings of 4.5-5 million m³ and energy savings of 250,000-300,000 kWh—equivalent to $25,000-$30,000 in utility costs.

Practical Maintenance Strategies

• Clean cooling nozzles daily to remove scale and debris; replace nozzles if flow rate decreases by >10%.
• Test water quality weekly (pH 7-8, hardness <100 mg/L as CaCO₃) to prevent scale buildup in nozzles and rolls.
• Calibrate temperature sensors monthly using a portable infrared thermometer to ensure accuracy within ±10°C.

For second-hand hot rolling mills aiming to improve productivity, reduce costs, and meet strict strip quality standards, the roll cooling system is a critical upgrade that aligns with modern sustainability and efficiency goals—essential for long-term competitiveness in the steel industry.

For more information, please pay attention to the website of Jinyujie Mechanical and Electrical Used Pipe Mill Supplier：www.usedpipemill.com