1. Common Flattening Methods for SPA-H Weathering Steel Plates
Process: Use a precision leveler (also called a flattening machine) to pass the SPA-H plate through a series of staggered upper and lower rollers at room temperature. The rollers exert controlled pressure to stretch and compress the plate's surface, eliminating warping and achieving a flat finish.
Advantages: No need for heating equipment, low energy consumption, and no impact on the steel's alloy composition or corrosion resistance. Suitable for plates with a thickness of 0.8–20 mm (the most common range for weathering steel plates used in signs, partitions, or flower beds).
Precision: Can achieve a flatness tolerance of ≤0.5 mm/m, meeting the requirements of most structural and decorative applications.
Process: First heat the SPA-H plate to a temperature of 900–1050°C (within its austenitization range), then use a heavy-duty leveler to flatten it while the steel is in a high-ductility state. After flattening, the plate is cooled slowly to avoid generating new residual stress.
Advantages: Can handle thick plates (≥20 mm) or plates with severe warping that cannot be corrected by cold flattening.
Note: Avoid overheating or rapid cooling, as this may affect the steel's microstructure and reduce its patina-forming ability. Post-heat treatment (e.g., stress relief annealing) is recommended if needed.
2. Key Considerations for Flattening SPA-H Weathering Steel
If the plate already has a mature patina layer, cold flattening will not damage the patina significantly (the roller pressure is uniform and does not cause scratching). However, avoid using rollers with rough surfaces, which may scratch the patina.
For plates with thick, loose initial rust (before patina maturation), flattening may cause rust to flake off-it is recommended to flatten the plate first, then perform artificial patina acceleration to ensure a uniform patina layer.
Over-flattening (excessive roller pressure) may introduce new residual stress, which can cause the plate to warp again during subsequent processing (e.g., cutting, welding). Adjust the leveler's roller pressure and pass times according to the plate's thickness and warpage degree.
For high-precision applications (e.g., decorative scenic signs), perform stress relief annealing after flattening to stabilize the plate's shape.
Choose a leveler with rollers made of hard chrome-plated steel to avoid leaving indentations on the SPA-H plate surface.
For thin plates (<1 mm), use a micro-leveler with fine roller adjustment to prevent bending or creasing during flattening.
3. Post-Flattening Treatments
Surface Cleaning: Wipe the flattened plate with a soft cloth to remove oil or dust residues from the processing equipment.
Patina Restoration (If Needed): If the patina is slightly damaged during flattening, apply a thin layer of patina accelerator to the affected area to restore a uniform rusty appearance.
Sealing: For plates used in harsh environments (coastal, industrial), apply a transparent breathable sealant after flattening and patina maturation to enhance corrosion resistance.
