1.What is the working principle of an online surface quality inspection system?
Technology: Employs machine vision technology, using a high-resolution linear scan camera and special light sources (such as LED linear light sources and laser scanning) to continuously photograph the surface of high-speed running steel strips.
Principle: Dents alter light reflection, forming characteristic dark spots or ring shadows on the image. The system identifies and classifies these defects using image processing algorithms, and displays alarms, marks locations, and assigns ratings in real time on the HMI in the control room.
Advantages: Full coverage, uninterrupted operation, high speed, and the ability to create a quality "map".
Limitations: High investment cost; may miss very shallow and tiny dents; requires regular maintenance and algorithm optimization.
2.What are the advantages and disadvantages of manual inspection versus stroboscope-assisted testing methods?
Method: Production line operators or quality inspectors conduct visual inspections at the exit section (e.g., before coiling). A stroboscope is used; by adjusting the flash frequency to synchronize with the strip speed, the high-speed moving strip is "frozen," facilitating clear visual observation of its surface condition.
Advantages: Flexible, low cost, and can be combined with experience-based judgment.
Disadvantages: Relies on personal experience, prone to fatigue, cannot provide full coverage, and cannot record quantitative data.
3.How to analyze macroscopic features and morphology?
Visual and Tactile Examination: On a stationary steel coil, observe the distribution of pits (random or periodic?), color (shiny, dark, or oxidized?), and touch the edges (sharp or tactile?).
3D Surface Profilometer/Roughness Meter:
Function: Accurately measures the depth, width, volume, and edge morphology of pits. This is crucial for quantitative analysis.
Output: Generates 2D profile curves and 3D morphology images, determining whether pits are "pointed-bottomed" or "flat-bottomed," and whether they are "isolated" or "patterned."
Coating Method:
For large coils or situations where on-site measurement is inconvenient, special tape or polymer material can be used to imprint the defect. After removal, a negative mold is formed and brought back to the laboratory for observation using a microscope or profilometer.
4.How to analyze a metallographic cross-section?
Samples were cut perpendicular to the pit, mounted, polished, and etched to create metallographic samples.
Observations:
Whether there are non-metallic inclusions or foreign particles at the bottom of the pit.
Whether the grain deformation flow lines of the metal below the pit are disrupted or interrupted.
Whether the matrix structure is abnormal.
5.What are the procedures for handling problems after they occur?
Step 1: Macroscopic Location – Determine the location of the pits on the steel coil (distance from the edge, position along the length), and their distribution pattern (random/periodic). Measure the dimensions using a 3D profilometer.
Step 2: Microscopic Source Tracing – Perform compositional analysis on typical pits using SEM/EDS. This is the lowest-cost and fastest method for root cause diagnosis.
Step 3: Metallographic Verification – If there is controversy or further analysis is needed (e.g., observing the influence of microstructure), perform metallographic cross-sectional analysis.
Step 4: Process Inspection – Based on the analysis results, provide feedback to the relevant processes (e.g., if EDS finds iron oxide scale, focus on investigating the hot rolling descaling and pickling processes; if periodicity is found, check the corresponding circumference roll system).