1.How can we control it at the source?
Hot-rolled incoming material quality:
Monitoring points: Ensure the iron oxide scale on the surface of the hot-rolled coil is uniform and can be thoroughly removed by pickling; strictly control edge quality to prevent the inheritance of defects such as cracks and flash.
Preventive actions: Establish quality feedback standards with upstream processes, and block or compromise on non-conforming incoming materials.
Roll and roll system management (of paramount importance):
Grinding accuracy: Ensure the grinding quality of work rolls, intermediate rolls, and support rolls, eliminate excessive cylindricity and runout, and prevent periodic vibration marks.
Roughness matching: Scientifically design and strictly control the initial roughness and attenuation curve of the rolls according to product surface requirements (e.g., smooth surface, rough surface).
Usage and maintenance: Strictly adhere to the roll service life (tonnage or mileage) to avoid excessive fatigue use leading to roll surface peeling or uneven wear; establish a comprehensive roll inspection (ultrasonic, eddy current) system.
2.How is the process controlled?
Rolling Process:
Emulsion System: This is the main source of streak-like color differences.
Concentration and Cleanliness: Strictly control concentration, temperature, pH, and conductivity. Regularly skim and filter to remove impurities and iron powder.
Spray Beam: Ensure nozzles are unclogging, and that the spray angle and flow rate are uniform to guarantee a uniform oil film on the rolls and strip surface.
Vibration Control: Optimize rolling procedures (reduction, tension) to avoid working in the mill resonance zone; regularly check roll gap lubrication and bearing condition.
Annealing Process:
Furnace Cleaning: Preventing roll nodules (carbide and oxide buildup) is crucial to avoiding periodic indentation streaks after annealing. Regularly polish or clean the rolls online.
Protective Gas: Ensure high purity and strictly control the dew point (moisture content) to prevent oxidation and nitriding on the inner wall or strip surface, which can cause color differences.
Stable Strip Operation: Optimize furnace tension to prevent strip vibration and friction with the rolls from causing scratches.
3.How to control the terminal?
Cleaning and Drying Section:
Ensure the concentration, temperature, and spray pressure of the cleaning solution (alkaline solution or hot water) meet the standards.
Key Equipment: Ensure the surface condition and pressure of the squeeze rolls are uniform to prevent water stains caused by incomplete dehydration; check that the dryers (such as hot air dryers and IR dryers) are functioning properly and thoroughly remove residual moisture.
Finishing and Leveling:
Process Matching: Properly set the elongation rate of the finishing machine and the bending roll parameters of the leveling machine to eliminate yield plateaus while avoiding new strain streaks (Lüders bands) caused by uneven elongation.
Roll Surface Management: Both finishing rolls and leveling rolls require meticulous grinding and cycle management.
4.How to establish a quality monitoring and feedback system?
Online Inspection System: Fully utilizes surface inspection instruments to automatically identify, classify, and record stripe defects, enabling real-time alarms and precise defect location.
Offline Analysis and Traceability:
Laboratory analysis (e.g., scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS)) is performed on typical defect samples to determine defect composition (iron powder, oxides, or residual grease), allowing for precise source tracing.
A full-process quality data traceability system is established, correlating defects with corresponding process parameters (e.g., mill vibration spectrum, emulsion indicators, furnace temperature profiles).
Standardized Operations and Training: Detailed job operation standards are developed, and employee training on defect identification and the impact of process parameters is strengthened.
5.What is the core concept of prevention?
Precision: Accurately identifying defect types is the first step.
Stabilization: Maintaining long-term stability of all process media (emulsions, cleaning fluids, protective gases) and process parameters (tension, speed, temperature).
Cleanliness: Ensuring "clean production" throughout the entire process from raw materials to finished products, controlling the introduction of foreign matter.
Preventative Maintenance: Implementing a strict periodic inspection and replacement system for all components in contact with strip steel, such as rolls, furnace rolls, and nozzles.