The Role of 7-Roll Leveling Unit in Ensuring Forming Precision of 22-Pass C/U Steel Cold Forming Equipment​

The 7-roll leveling unit is a critical pre-forming component in the 22-pass one-click changeover C/U steel cold bending automatic forming equipment. It addresses the issue of residual stress and flatness defects in raw steel coils, laying a solid foundation for the subsequent 22-pass precise forming of C/U steel. Its performance directly determines the dimensional stability and surface quality of the final product, especially for high-strength or thin-gauge steel materials.​

Residual Stress Elimination​

Raw steel coils (typically 1.5-6mm thick for C/U steel) often have residual stress from the rolling and coiling process, which causes "springback" after forming—e.g., a C-steel flange designed to be 90° may 回弹 to 87°-88°. The 7-roll leveling unit uses a progressive bending process: the top 3 rolls and bottom 4 rolls apply alternating pressure (adjustable from 5-25 MPa) to stretch the steel strip plastically, eliminating 80-90% of residual stress. For high-strength Q550 steel (yield strength ≥550 MPa), this reduces springback to ≤0.5°, ensuring the final C/U steel’s angle tolerance meets GB/T 6725-2016 (≤±1°). Without effective leveling, springback can reach 2-3°, requiring secondary correction and increasing production time by 30%.​

Flatness Improvement​

Uneven flatness of raw steel strips (e.g., edge waves with a height of 2-3mm/m or center buckles) leads to uneven force distribution in the 22-pass forming process, resulting in dimensional deviations (e.g., flange thickness variation of 0.3-0.5mm). The 7-roll unit’s adjustable roll gaps (range: 0.1-5mm) target specific flatness defects: for edge waves, it increases pressure on the edge rolls (18-22 MPa) to stretch the edge; for center buckles, it boosts pressure on the middle rolls (15-18 MPa). This improves the strip’s flatness to ≤0.5mm/m, ensuring uniform contact between the strip and each forming pass. For example, when processing a 3mm-thick, 120mm-wide steel strip, the unit reduces flatness errors from 2.5mm/m to 0.4mm/m, reducing the subsequent forming’s thickness variation to ≤0.1mm.​

Material Adaptability Enhancement​

The 7-roll leveling unit in the 22-pass equipment supports a wide range of steel materials, from low-carbon Q235 steel to high-strength Q690 steel and even galvanized steel coils. For galvanized strips, the unit uses a lower initial pressure (5-8 MPa) to avoid zinc layer peeling, then gradually increases pressure to 12-15 MPa for stress elimination—this reduces zinc layer damage rate to <0.5%, compared to 3-5% with traditional 5-roll leveling units. Additionally, the rolls are coated with tungsten carbide (WC) to resist wear from galvanized layers, extending roll life by 2-3 times (from 8,000 tons to 16,000-24,000 tons of steel processed).​

Maintenance and Optimization Guidelines​

To maintain the 7-roll leveling unit’s performance:​

• Inspect roll surface condition weekly; replace rolls if WC coating wear exceeds 0.2mm or if scratches deeper than 0.1mm appear.​

• Adjust roll pressure monthly based on material type and thickness (e.g., 8-12 MPa for Q235 steel, 15-20 MPa for Q690 steel).​

• Lubricate the roll bearings monthly with high-temperature grease (resistant to 120°C) to prevent seizure during continuous operation.​

• Calibrate the pressure sensors quarterly using a hydraulic test bench to ensure pressure accuracy (±0.5 MPa).​

For manufacturers producing C/U steel for solar support structures (where dimensional precision directly affects installation stability), the 7-roll leveling unit is indispensable—it ensures the steel’s linearity and flatness meet the strict requirements of solar panel mounting systems, reducing on-site installation errors by 40-50%.​

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