The Impact of Furnace Temperature Control Systems on Second-Hand Hot Rolling Mills​

Furnace temperature control systems are critical pre-rolling components in second-hand hot rolling mills, responsible for heating steel slabs to the optimal rolling temperature (1100-1250°C for carbon steel) and ensuring uniform temperature distribution. Their precision directly influences the plasticity of the slabs, the quality of the hot-rolled products, and the energy efficiency of the mill.​

Temperature Uniformity Assurance​

In second-hand hot rolling mills, advanced furnace temperature control systems use multi-zone heating (typically 6-8 zones) and infrared temperature sensors to achieve a slab temperature uniformity of ±15°C across the thickness and width. This uniform heating ensures consistent plasticity of the slab during rolling, reducing thickness variation of the intermediate slab by 30-40% (from ±0.8mm to ±0.48-0.56mm). For example, when rolling Q355B steel slabs, a 10°C temperature difference can cause a 0.3mm thickness deviation in the intermediate slab, leading to a 8-10% increase in scrap rate during subsequent finishing rolling. Outdated control systems in unrefurbished second-hand mills may have a temperature uniformity of ±40°C, significantly compromising product quality.​

Energy Efficiency Optimization​

Modernized furnace temperature control systems in second-hand hot rolling mills feature adaptive heating algorithms that adjust fuel supply based on slab thickness, material type, and incoming temperature. This reduces fuel consumption by 12-18% (from 1.2 GJ/ton to 0.98-1.06 GJ/ton of steel) compared to traditional fixed-temperature heating. For a mill processing 1,000 tons of steel daily, this translates to annual fuel savings of ​

150,000−220,000. Additionally, the system’s waste heat recovery function (recycling flue gas heat to preheat combustion air) further improves energy efficiency by 5-8%.​

Slab Quality Preservation​

Proper temperature control prevents overheating or underheating of slabs in second-hand hot rolling mills. Overheating (temperature ≥1300°C) causes grain coarsening in the slab, reducing the tensile strength of the final hot-rolled strip by 15-20% (e.g., from 510 MPa to 410-430 MPa for Q690 steel). Underheating (temperature ≤1050°C) increases the rolling force required, leading to excessive wear of the rolling rolls and a 20-25% reduction in roll life. The control system’s real-time temperature monitoring (sampling frequency: 1Hz) ensures that slabs are heated within the optimal range, maintaining the mechanical properties of the final product.​

Maintenance and Optimization Strategies​

To ensure the reliability of furnace temperature control systems in second-hand hot rolling mills:​

• Calibrate infrared temperature sensors weekly using a standard temperature source (1100-1250°C) to ensure measurement accuracy (±5°C).​

• Inspect the fuel nozzles of each heating zone monthly for clogging or wear; clean or replace nozzles if fuel flow deviation exceeds 10%.​

• Check the control system’s software parameters quarterly (e.g., heating rate, temperature setpoints) to ensure alignment with the material being processed.​

• Clean the flue gas heat exchanger quarterly to remove soot, which can reduce heat recovery efficiency by 15-20% if accumulated.​

For second-hand hot rolling mills processing low-alloy steel slabs (e.g., API 5L X70), upgrading to a model predictive control (MPC) system can further improve temperature control accuracy by 25-30%, ensuring consistent product quality even with variations in incoming slab parameters.​

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