1. Pre-Normalization Preparation: Lay the Foundation for Uniform Cooling
Steel loading method: Arrange Q355GNH workpieces (e.g., plates, profiles) in the furnace with uniform gaps (at least 50–100mm between pieces, depending on thickness). Avoid stacking or overcrowding-this prevents blocked airflow during cooling and ensures each workpiece is exposed to the cooling medium evenly.
Thickness grouping: Process workpieces of similar thickness (maximum thickness difference ≤ 20%) in the same batch. Thicker workpieces (e.g., ≥ 50mm plates) require slower cooling to avoid internal stress, while thinner ones (e.g., ≤ 15mm) can cool slightly faster; mixing thicknesses makes uniform rate control impossible.
Surface pre-cleaning: Remove oil, rust, or oxide scale from the workpiece surface using degreasers or sandblasting. Contaminants can insulate local areas, causing uneven heat dissipation and deviations in the cooling rate.
2. Key Cooling Stage Control: Adjust Methods Based on Equipment and Workpiece Size
Method 1: Air Cooling (Most Common for Medium-Small Workpieces)
Control measures:
Place the heated workpieces on a flat, well-ventilated cooling bed (preferably made of heat-resistant steel with gaps for airflow). Avoid placing them on cold concrete or metal surfaces (which cause rapid local cooling).
Use fans for forced air circulation (if ambient temperature is high or humidity is low) to stabilize the rate. Adjust fan speed: for thin workpieces (≤ 20mm), use low-speed fans (1–2m/s airflow) to prevent overcooling; for thicker ones (20–40mm), use medium-speed fans (2–3m/s) to ensure internal heat dissipates.
Monitor ambient conditions: Avoid cooling in rainy or high-humidity environments (which accelerate surface cooling). If necessary, cool in a closed, temperature-controlled workshop (maintain ambient temp at 15–30°C).
