In the cold rolling process of steel strip, stable mill operation and plate flatness directly affect the yield rate of final products and overall plant efficiency. Based on extensive field experience, CYKC Group has systematically summarized typical operational anomalies and troubleshooting methods for flatness defects in rolling mills, providing valuable reference for industry professionals.
Mill Vibration and Slippage
Vibration or slippage during high-speed rolling not only degrades strip surface quality but may also damage equipment. Common causes and countermeasures are as follows:
Causes:
- Mechanical failures in the roll system or drive motor (e.g., excessive bearing clearance, gear wear);
- Abnormal changes in friction during rolling (e.g., fluctuating emulsion lubricity);
- Excessive emulsion lubrication leading to abnormally low friction coefficient.
Troubleshooting Measures:
- Conduct a comprehensive inspection of roll assembly accuracy, transmission systems, and motor condition; perform dynamic balancing tests if necessary;
- Analyze emulsion concentration, saponification value, and oil contamination levels to ensure lubricity remains within specified process ranges;
- Inspect roll surface roughness; replace or regrind severely worn rolls promptly;
- Adjust pass reduction rates appropriately to avoid excessive deformation in single passes;
- Check incoming material surface conditions to eliminate interference from oxide scale, inclusions, or other defects affecting rolling stability.
Surface Oil Stains, Scratches, Adhesion, Roll Adhesion, and Roll Breakage
These surface defects directly increase scrap rates and typically reflect combined issues related to lubrication, roll surface condition, or temperature control.
Causes:
- Insufficient emulsion lubrication causing metal-to-metal adhesion;
- Localized scratches or burrs on rolls, or foreign matter (such as iron filings or sand) entering the roll gap;
- Inadequate preheating of rolls or rolls nearing fatigue life, resulting in unstable surface microstructure;
- Excessively high emulsion temperature or clogged nozzles causing localized roll heating;
- Poor flatness leading to stress concentration, which increases abnormal loading on rolls.
Troubleshooting Measures:
- Regularly monitor emulsion concentration, saponification value, pH, iron content, ash content, and liquid temperature;
- Stop the mill to inspect and replace damaged rolls, thoroughly cleaning the roll gap and surrounding areas of debris;
- Strictly follow roll preheating procedures and replace rolls according to their service life;
- Clear and inspect all emulsion spray nozzles for pressure and spray angle to ensure uniform cooling;
- Promptly adjust bending roll, shifting roll, and rolling force settings to improve flatness and prevent stress concentration.
Special Handling of Common Plate Shape Defects
Plate shape defects are one of the most challenging quality problems in cold rolling production. Typical defects include middle waves, bilateral waves, unilateral waves, and rib waves (periodic stripes). The causes and countermeasures vary.
Regarding middle waves, the main reasons are as follows: first, insufficient cooling during the rolling process leads to excessive extension in the middle section of the strip; second, the roller design is unreasonable or the deviation of the roller position does not match the actual roller gap; third, the rolling force is set too low, unable to effectively hold the middle section. To address middle waves, one should first check the temperature of the emulsified liquid and the overall cooling effect, and appropriately increase the cooling volume; at the same time, re-evaluate the roller design, appropriately reduce the pull-out amount of the roller deviation, to improve the roller gap shape; finally, appropriately increase the rolling force to enhance the restraint on the middle section.