1. Pre-Flattening Preparation: Lay the Foundation for Quality
Reject plates with severe warping (warpage > 5 mm/m), surface cracks, or deep scratches.
Remove surface contaminants (oil, rust, dust) using a soft brush or degreasing agent-residues can cause roller slippage or indentations during flattening.
For plates with a mature patina layer: Ensure the patina is dense and adherent (no loose rust). If the patina is loose, remove it first (via mechanical brushing) to avoid flaking during flattening.
Match the leveler to the plate thickness:
Use a precision cold leveler for thin plates (0.8–20 mm) - it has small-diameter, hard chrome-plated rollers to avoid surface damage.
Use a heavy-duty hot leveler for thick plates (≥20 mm) or severely warped plates - ensure the heating furnace can control temperature accurately (900–1050°C, the austenitization range of SPA-H steel).
Check roller condition: Ensure rollers are smooth, free of wear or indentations, and aligned parallel to each other. Misaligned rollers will cause uneven flattening.
2. Flattening Process Control: Core Quality Assurance
Roller Pressure: Adjust pressure based on plate thickness and warpage degree. For 3–10 mm plates, use moderate pressure (avoid over-pressing, which causes residual stress). For warped plates, increase pressure gradually in 2–3 passes instead of one-time over-pressing.
Pass Times: 2–4 passes are sufficient for normal warpage. More passes will not improve flatness but will increase residual stress.
Roller Speed: Keep speed stable (1–3 m/min for precision flattening) - variable speed can cause uneven stress distribution.
Heating Temperature: Strictly control the furnace temperature at 900–1050°C. Overheating (>1100°C) will coarsen the steel's microstructure and reduce its corrosion resistance; underheating will lower ductility and make flattening ineffective.
Cooling Process: After hot flattening, cool the plate slowly in air (avoid water quenching or rapid cooling). Rapid cooling will cause thermal stress and re-warping, and may damage the steel's patina-forming properties.
For pre-patinated plates: Use rollers with a smooth, non-abrasive surface (hard chrome plating is best) to prevent scratching the patina.
Avoid excessive roller pressure, which can crack the patina layer and expose the bare steel substrate.
3. Post-Flattening Inspection: Verify Quality Against Standards
For decorative applications (signs, partitions): Flatness tolerance ≤ 0.5 mm/m.
For structural applications (fountain panels, partitions): Flatness tolerance ≤ 1.0 mm/m.
Reject plates with local warpage or waves that exceed the tolerance.
Check for surface defects caused by flattening: No indentations, scratches, or patina peeling.
For patinated plates: Ensure the patina remains uniform in color and texture (no obvious color differences between flattened and non-flattened areas).
4. Post-Flattening Handling & Storage: Maintain Quality Stability
Handling: Use soft slings (nylon instead of steel cables) to lift plates, avoiding edge collisions or surface scratches.
Storage: Stack plates on a flat, dry pallet with wooden separators between layers. Avoid stacking too high (≤ 10 layers) to prevent re-warping. Store in a ventilated area to avoid moisture accumulation and re-rusting.
Patina Restoration (If Needed): If the patina is slightly damaged during flattening, apply a SPA-H-specific patina accelerator to the affected area to restore a uniform rusty appearanc
